sm82n2-4781

Free-diving underwater fish photography contests: a complementary tool for assessing littoral fish communities

Ana Gordoa 1, Jordi Boada 1, Antoni García-Rubies 1, Oscar Sagué 2

1 Department of Marine Ecology, Centro de Estudios Avanzados de Blanes, Spanish National Research Council (CSIC), Blanes, Girona, Spain.
(AG) (Corresponding author) E-mail: gordoa@ceab.csic.es. ORCID iD: http://orcid.org/0000-0003-1822-8196
(JB) E-mail: jboada@ceab.csic.es. ORCID iD: http://orcid.org/0000-0002-3815-625X
(AG-R) E-mail: tonigr@ceab.csic.es. ORCID iD: http://orcid.org/0000-0002-4824-9337
2 International Forum for Sustainable Underwater Activities (IFSUA), Carrer València 231, Bxs., Ap. correus 36003, 08007 Barcelona, Spain.
(OS) E-mail: ifsua@ifsua.net. ORCID iD: http://orcid.org/0000-0002-4053-6614

Summary: Characterizing fish communities must be a priority to safeguard resources and determine critical changes. Here, species richness and the spatial and temporal evolution in the structure of fish assemblages were analysed based on photos taken in underwater free-diving contests. A total of 29 contests held from 2008 to 2015 at four different locations along the northeastern Spanish coast, including a marine protected area were analysed. Contests reward the number of species per participant and photographic quality. Species image frequency from each tournament were standardized to catch image rate. A total of 88 taxa were recorded, including 32 cryptobenthic species, the highest number recorded in the Mediterranean littoral system so far. Cluster analyses yielded four major groups. Catch image rates in the marine protected area were significantly higher for seven species of high commercial interest and for two big labrids of recreational interest, including an endangered species (Labrus viridis). Overall, the study showed that photographic free-diving contest data are a potential tool for determining species richness in littoral systems since contest rules promote competition between participants to obtain maximum fish diversity. We believe that this type of cost-effective data can be applied worldwide as a complementary way of monitoring littoral fish assemblage.

Keywords: littoral fish assemblages; species richness; diversity; photography contests; Mediterranean Sea.

Competiciones fotográficas de peces en buceo libre: una herramienta complementaria para la valoración de las comunidades de peces litorales

Resumen: La caracterización de las comunidades de peces debe ser una prioridad para salvaguardar los recursos y para la detección de cambios críticos. La información de las competiciones fotográficas a buceo libre se utilizó para analizar la riqueza específica y las variaciones espaciales y temporales de la comunidad íctica. Se analizaron un total de 29 concursos celebrados entre el 2008 y el 2015 en cuatro puntos de la costa Noroeste de España, incluida un área marina protegida. Estas competiciones premian a los participantes por el número de especies fotografiadas y su calidad. En cada concurso se estandarizó la frecuencia de imágenes por especie, convirtiéndola a la tasa de imágenes capturadas. Se registraron 88 taxones, incluidas 32 especies criptobénticas, el mayor número registrado hasta la fecha en el litoral Mediterráneo. El análisis de conglomerados identificó cuatro grupos principales. La tasa de imágenes capturadas de siete especies comerciales fue superior en el AMP y también superior para dos especies de lábridos de interés recreativo, una de ellas considerada como especie amenazada (Labrus viridis). En suma, el estudio mostró que los datos de los concursos fotográficos a buceo libre son una herramienta potencial para determinar la riqueza específica en los sistemas litorales debido a que las competiciones fomentan la competencia entre los participantes para obtener la máxima diversidad de especies. Consideramos que estos datos, eficaces en los costes, se pueden utilizar a nivel mundial para complementar los sistemas de seguimiento de las comunidades de peces litorales.

Palabras clave: comunidades de especies litorales; riqueza específica; diversidad; concursos fotográficos, mar Mediterráneo.

Citation/Cómo citar este artículo: Gordoa A., Boada J., García-Rubies A., Sagué O. 2018. Free-diving underwater fish photography contests: a complementary tool for assessing littoral fish communities. Sci. Mar. 82(2): 95-106. https://doi.org/10.3989/scimar.04781.14A

Editor: E. Macpherson.

Received: March 20, 2018. Accepted: June 11, 2018. Published: June 20, 2018.

Copyright: © 2018 CSIC. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) License.

Contents

Summary
Resumen
Introduction
Materials and methods
Results
Discussion
Acknowledgements
References

INTRODUCTIONTop

The marine coastal environment is threatened both locally and globally in different ways. In Europe the coastal habitats have been progressively degraded over the last few decades (e.g. Benedetti-Cecchi et al. 2001Benedetti-Cecchi L., Pannacciulli F., Bulleri F., et al. 2001. Predicting the consequences of anthropogenic disturbance: large-scale effects of loss of canopy algae on rocky shores. Mar. Ecol. Prog. Ser. 214: 137-150., Lotze et al. 2006Lotze H.K., Lenihan H.S., Bourque B.J., et al. 2006. Depletion, degradation, and recovery potential of estuaries and coastal seas. Science 312: 1806-1809., Claudet and Fraschetti 2010Claudet J., Fraschetti S. 2010. Human-driven impacts on marine habitats: a regional meta-analysis in the Mediterranean Sea. Biol. Conserv. 143: 2195-2206.). Future projections are not encouraging: The Mediterranean Action Plan predicts that the urban population of the coastal Mediterranean could reach 176 million by 2015 plus 350 million tourists yearly. Furthermore, an increase in the number of introduced species (Boudouresque et al. 2005Boudouresque C., Cadiou G., Le Diréac’h L. 2005. Marine protected areas: a tool for coastal areas management. Nato Science Series IV: Earth and Environmental Sciences. Springer Netherlands, pp. 29-52.) and climate-induced stressors are contributing to changes in the Mediterranean biodiversity (Fraschetti et al. 2011Fraschetti S., Guarnieri G., Bevilacqua S., et al. 2011. Conservation of Mediterranean habitats and biodiversity countdowns: what information do we really need? Aquat. Conserv. 21: 299-306.), emphasizing the need to foster the surveillance of coastal systems.

Maintaining diversity in coastal systems is essential for the sustainability of communities, ecosystem functioning and services (Pickaver 2009Pickaver A.H. 2010. 10 Integrated coastal zone management progress and sustainability indicators. In: Telford T. (eds), Integrated Coastal Zone Management. Wiley-Blackwell, Oxford, UK. pp 226-250., Costanza et al. 2014Costanza R., de Groot R., Sutton P., et al. 2014. Changes in the global value of ecosystem services. Global Environ. Chang. 26: 152-158.). Changes in coastal ecosystems can be one-off events and have dramatic effects (i.e. artificial modifications of the coast or severe storms), or rather progressive and relatively slow (at the scale of human life), and are difficult to notice through snapshot studies. Moreover, the negative impact on them may be difficult to document (Støttrup 2009Støttrup J.G. 2009. The challenge towards sustainable utilisation of coastal fish resources. In: Moksness E., Dahl E., Støttrup J. (eds), Integrated Coastal Zone Management. John Wiley & Sons, pp. 25-34.). One of the aims of the European Marine Directive is to ensure that biodiversity is maintained, that is, kept in line with the natural state appropriate to the area in question. However, baseline shifts can affect reference sites as much as impact sites (Støttrup 2009Støttrup J.G. 2009. The challenge towards sustainable utilisation of coastal fish resources. In: Moksness E., Dahl E., Støttrup J. (eds), Integrated Coastal Zone Management. John Wiley & Sons, pp. 25-34.), masking variations and distorting perceptions.

In the Mediterranean, littoral fish communities are threatened by numerous stressors, including habitat loss, global warming, changes in the continental water discharges, artificialization of the coastlines, introduction of alien species and fishing pressure (e.g. Guidetti et al. 2002Guidetti P., Fanelli G., Fraschetti S., et al. 2002. Coastal fish indicate human-induced changes in the Mediterranean littoral. Mar. Environ. Res. 53: 77-94., Claudet et al. 2006Claudet J., Pelletier D., Jouvenel J.Y., et al. 2006. Assessing the effects of marine protected area (MPA) on a reef fish assemblage in a northwestern Mediterranean marine reserve: Identifying community-based indicators. Biol. Conserv. 130: 349-369.). Fish communities are a key component of the aquatic ecosystem (Holmlund and Hammer 1999Holmlund C.M., Hammer M. 1999. Ecosystem services generated by fish populations. Ecol. Econ. 29: 253-268.) as fish provide fundamental services for ecosystem functioning and resilience (Schindler et al. 1997Schindler D.E., Carpenter S.R., Cole J.J., et al. 1997. Influence of food web structure on carbon exchange between lakes and the atmosphere. Science 277: 248-251., Vanni 2002Vanni M.J. 2002. Nutrient cycling by animals in freshwater ecosystems. Annu. Rev. Ecol. Syst. 33: 341-370., Myers et al. 2007Myers R.A., Baum J.K., Shepherd T.D., et al. 2007. Cascading effects of the loss of apex predatory sharks from a coastal ocean. Science 315: 1846-1850.). Moreover, numerous studies support the use of fish assemblages as biological indicators for marine coastal waters (e.g. Sano 2000Sano M. 2000. Stability of reef fish assemblages: responses to coral recovery after catastrophic predation by Acanthaster planci. Mar. Ecol. Prog. Ser. 198: 121-130., Seytre and Francour 2008Seytre C., Francour P. 2008. Is the Cape Roux marine protected area (Saint-Raphaël, Mediterranean Sea) an efficient tool to sustain artisanal fisheries? First indications from visual censuses and trammel net sampling. Aquat. Living Resour. 21: 297-305., Azzurro et al. 2011Azzurro E., Moschella P., Maynou F. 2011. Tracking Signals of Change in Mediterranean Fish Diversity Based on Local Ecological Knowledge. PLoS ONE 6: e24885.). Nevertheless, studying and monitoring fish assemblages is as complex as the diversity of groups represented. Littoral fish assemblages include groups of different niches, so different complementary sampling methods are required to capture all the components (Elliott et al. 2002Elliott M., Hemingway K., Marshall S., et al. 2002. Data quality analysis and interpretation. In: Elliott M., Hemmingway K.L. (eds), Fishes in Estuaries. Blackwell Science, Oxford, pp. 510–554.). It is widely recognized that no single assessment technique can provide unbiased, qualitative or quantitative estimates of fish assemblages (Sale and Douglas 1981Sale P.F., Douglas W.A. 1981. Precision and accuracy of visual census technique for fish assemblages on coral patch reefs. Environ. Biol. Fish. 6: 333-339., Ackerman and Bellwood 2000Ackerman J.L., Bellwood D.R. 2000. Reef fish assemblages: a re-evaluation using enclosed rotenone stations. Mar. Ecol. Prog. Ser. 206: 227-237.). This problem was highlighted decades ago (Harmelin-Vivien et al. 1985Harmelin-Vivien M., Harmelin J., Chauvet C., et al. 1985. The underwater observation of fish communities and fish populations. Methods and problems. Rev. Ecol. Terr. Vie 40: 466-539.) but it is still an open issue and it is recommended to apply different sampling methods simultaneously to the same study site (Connell et al. 1998Connell S.D., Samoilys M.A., Lincoln Smith M.P., et al. 1998. Comparisons of abundance of coral-reef fish: Catch and effort surveys vs visual census. Aust. J. Ecol. 23: 579-586., Willis et al. 2000Willis T.J., Millar R.B., Babcock R.C. 2000. Detection of spatial variability in relative density of fishes: comparison of visual census, angling, and baited underwater video. Mar. Ecol. Prog. Ser. 198: 249-260., Cappo et al. 2004Cappo M., Speare P., De’ath G. 2004. Comparison of baited remote underwater video stations (BRUVS) and prawn (shrimp) trawls for assessments of fish biodiversity in inter-reefal areas of the Great Barrier Reef Marine Park. J. Exp. Mar. Biol. Ecol. 302: 123-152.).

Studies of fish populations in shallow littoral waters usually rely on underwater visual censuses (e.g. Harmelin-Vivien et al. 2008Harmelin-Vivien M., Le Diréach L., Bayle-Sempere J., et al. 2008. Gradients of abundance and biomass across reserve boundaries in six Mediterranean marine protected areas: Evidence of fish spillover? Biol. Conserv. 141: 1829-1839., Bussotti et al. 2015Bussotti S., Di Franco A., Francour P., et al. 2015. Fish assemblages of Mediterranean marine caves. PloS ONE 10: e0122632., Prato et al. 2017Prato G, Thiriet P., Di Franco A., et al. 2017. Enhancing fish Underwater Visual Census to move forward assessment of fish assemblages: An application in three Mediterranean Marine Protected Areas. PLoS ONE 12: e0178511.). Video techniques have been increasingly used (Mallet and Pelletier 2014Mallet D., Pelletier D. 2014. Underwater video techniques for observing coastal marine biodiversity: a review of sixty years of publications (1952-2012). Fish. Res. 154: 44-62.) and are recognized mainly as an additional technique to underwater visual censuses, with stationary (Francour 1999Francour P. 1999. A critical review of adult and juvenile fish sampling techniques in Posidonia oceanica seagrass beds. Nat. Sicil. 23: 33-57.), diver-operated (Tessier et al. 2013Tessier A., Pastor J., Francour P., et al. 2013. Video transects as a complement to underwater visual census to study reserve effect on fish assemblages. Aquat. Biol. 18: 229-241.) or roving cameras (Tessier and Chabanet 2006Tessier E., Chabanet P. 2006. Using video techniques for estimating fish post-larvae abundance after mass settlement on artificial reefs. Proc. 10th Intl. Coral Reef Symp., Okinawa, Japan.), or stationary baited underwater video (Gledhill et al. 1996Gledhill C.T., Lyczkowski-Shultz J., Rademacher K., et al. 1996. Evaluation of video and acoustic index methods for assessing reef-fish populations. ICES J. Mar. Sci. 53: 483-485., Willis and Babcock 2000Willis T.J., Babcock R.C. 2000. A baited underwater video system for the determination of relative density of carnivorous reef fish. Mar. Freshwater Res. 51: 755-763., Stobart et al. 2007Stobart B., García-Charton J.A., Espejo C., et al. 2007. A baited underwater video technique to assess shallow-water Mediterranean fish assemblages: Methodological evaluation. J. Exp. Mar. Biol. Ecol. 345: 158-174.). Fishing techniques are also used as a complementary method in littoral fish research surveys (Franco et al. 2012Franco A., Pérez-Ruzafa A., Drouineau H., et al. 2012. Assessment of fish assemblages in coastal lagoon habitats: Effect of sampling method. Estuar. Coast. Shelf Sci. 112: 115-125.). The appropriateness of a methodological approach depends on its capacity to fulfil the purposes of the study. However, accurate standardized measurements of fish species richness and community structure are essential for monitoring the progress towards biodiversity targets (Hutchings and Baum 2005Hutchings J.A., Baum J.K. 2005. Measuring marine fish biodiversity: temporal changes in abundance, life history and demography. Philos. T. Roy. Soc. B. 360: 315-338.), as well as for conservation actions (MacNeil et al. 2008MacNeil M.A., Tyler E.H., Fonnesbeck C.J., et al. 2008. Accounting for detectability in reef-fish biodiversity estimates. Mar. Ecol. Prog. Ser. 367: 249-260.). Underwater visual census methods cannot assume equal detectability across all species, and it is recognized that this methodology under-represents a large number of cryptobenthic fish species (e.g. Smith 1988Smith M.L. 1988. Effects of observer swimming speed on sample counts of temperate rocky reef fish assemblages. Mar. Ecol. Prog. Ser. 43: 223-231., Ackerman and Bellwood 2000Ackerman J.L., Bellwood D.R. 2000. Reef fish assemblages: a re-evaluation using enclosed rotenone stations. Mar. Ecol. Prog. Ser. 206: 227-237., Kovačić et al. 2012Kovačić M., Patzner R.A., Schliewen U. 2012. A first quantitative assessment of the ecology of cryptobenthic fishes in the Mediterranean Sea. Mar. Biol. 159: 2731-2742.) because more than 90% of them may go undetected by underwater visual censuses (Willis 2001Willis T.J. 2001. Visual census methods underestimate density and diversity of cryptic reef fishes. J. Fish Biol. 59: 1408-1411.). In fact, cryptic fish are particularly difficult to accurately survey. They are under-sampled components of fish communities and their ecological roles have generally been ignored (Smith-Vaniz et al. 2006Smith-Vaniz W.F., Jelks H.L., Rocha L.A. 2006. Relevance of cryptic fishes in biodiversity assessments: a case study at Buck Island Reef National Monument, St. Croix. Bull. Mar. Sci. 79: 17-48.). The use of destructive techniques such as ichthyocides and anaesthetics for cryptic species is controversial but also justified for obtaining reasonably complete inventories of reef fish (Smith-Vaniz et al. 2006Smith-Vaniz W.F., Jelks H.L., Rocha L.A. 2006. Relevance of cryptic fishes in biodiversity assessments: a case study at Buck Island Reef National Monument, St. Croix. Bull. Mar. Sci. 79: 17-48., Glavičić et al. 2016Glavičić I., Paliska D., Soldo A., et al. 2016. A quantitative assessment of the cryptobenthic fish assemblage at deep littoral cliffs in the Mediterranean. Sci. Mar. 80: 329-337., Thiriet et al. 2016Thiriet P.D., Di Franco A., Cheminée A., et al. 2016. Abundance and Diversity of Crypto-and Necto-Benthic Coastal Fish Are Higher in Marine Forests than in Structurally Less Complex Macroalgal Assemblages. PloS ONE 11: e0164121.).

In addition to research surveys, fisheries-dependent data are also used for fish assemblage monitoring. For all their flaws and lack of scientific methodology, fisheries-dependent data have some advantages: they generally provide large data sets with wide temporal and spatial coverage and they are cost-effective. Furthermore, other cost-effective sources of information are providing good findings in different fields (http://www.observadoresdelmar.es, Fairclough et al. 2014Fairclough D., Brown J., Carlish B., et al. 2014. Breathing life into fisheries stock assessments with citizen science. Sci. Rep. 4: 7249.) jointly with citizen science (e.g. www.seawatchers.org, redmap.org.au), which is currently expanding worldwide. Valuable data gathered by public agencies or private entities also have informative potential that is worthy of being analysed. This is the case of recreational fishing tournaments in certain regions, which have extensive spatial coverage and/or temporal continuity, and have been shown to be valuable for characterizing and monitoring littoral fish assemblages (Lincoln Smith 1989Lincoln Smith M.P. 1989. Improving multispecies rocky reef fish censuses by counting different groups of species using different procedures. Environ. Biol. Fish. 26: 29-37., Coll et al. 2004Coll J., Linde M., García-Rubies A., et al. 2004. Spear fishing in the Balearic Islands (west central Mediterranean): species affected and catch evolution during the period 1975-2001. Fish. Res. 70: 97-111., Gordoa 2009Gordoa A. 2009. Characterization of the infralittoral system along the north-east Spanish coast based on sport shore-based fishing tournament catches. Estuar. Coast. Shelf Sci. 82: 41-49.).

Another potential source of information is underwater photo contests. The technological developments in underwater photography have led to the expansion of a new sport activity: free-diving underwater photography. A recent event in underwater fish photography contests rewards the number of species photographed. Participants are given scores according to the number of species photographed, and they therefore search in every possible habitat to obtain the largest possible number of species. Consequently, the species richness resulting from these tournaments is expected to be higher than when traditional visual survey techniques are used. In Spain, and particularly in Catalonia, these tournaments began in the 1980s and have now become regular. The objective of this study was to assess species richness and classify fish communities based on the underwater free-diving fish photography contests held in Catalonia at four different locations from 2008 to 2015, including a no-take marine protected area (Medes Islands marine reserve).

MATERIALS AND METHODSTop

Data description

This study analysed the information from the free-diving photography contests held in Catalonia, which was provided by the Catalan Underwater Activities Federation (FECDAS). The objective of these contests is to photograph only of live fish in the natural system while free-diving. The participants aim to photograph the highest number of fish species possible. Each participant can only present one photo per species so the number of photos per participant is equivalent to the number of species per participant. In Catalonia, the first official championship was held in 2005, and since then FECDAS has gathered the data from each contest, which includes the following information: date, location, number of participants, number of species and total number of photographs per species. In this study we only considered the championships held after 2007 when analogue cameras were completely replaced by digital ones.

A total of 29 tournament reports were analysed. Each tournament had on average 18 participants and lasted 5 hours. FECDAS provided us with a copy of the photographic database, which allowed us to validate the records of dubious species appearing in the contest reports.

Site features

The contests were held at four locations along the Catalan coast in northeast Spain (Fig. 1). Annual contests are held at the same locations and provide informative data for studying the spatial and annual variability of littoral fish communities. In addition to their latitudinal differences, the four locations also have different habitat features, and these differences should also be reflected in their fish assemblages.

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Fig. 1. – Study area and locations of free-diving underwater fish photography. A, Medes Islands; B, Palamós; C, Mataró; and D, Ametlla de Mar.

The Medes Islands, located in the northern area, are a group of islands ~1 km from the mainland coast. This archipelago is one of the oldest marine reserves in the western Mediterranean. It has been protected since 1983 and has become a popular scuba diving destination. The contests were located on the southern side of the main island, at depths ranging from 0 to 20 m and characterized by diverse habitats: rocks, sand, Posidonia oceanica meadow and coralligenous. The second location, also in the northern area and near to the Medes Marine Reserve, was a coastal zone of Palamós, Margarida Cove, which has a diverse habitat: rocks, breakwater blocks, sand and P. oceanica meadow, at depths ranging from 0 to 15 m. The third location was Mataró, where the contest site was located ~500 m offshore from the coast at depths ranging from 6 to 12 m. The location is restricted to a natural rock barrier that is over 150 m long, has many cracks and cavities, and is surrounded by sandy beds with some P. oceanica patches at the eastern extreme. Finally, the fourth location was L’Ametlla, a coastal area at Port d’Estany, which has brackish water of depths between 0 and 10 m with a similar bottom structure: rocks, sand and a large P. oceanica meadow.

Data analysis

Species relative abundance data from the tournament information were estimated from the catch image rate for each location, which was estimated as the total number of reported photos per species divided by the total number of participants. Taxonomic resolution was not fully attained and some species were classified at the level of genera (Atherina and Sphyraena) or family (Mugilidae).

Absolute number of species richness (S) and Margalef index, α=(S–1)/ln (N) (N total number of images) were estimated as measures of species richness and diversity for each contest. One-way ANOVAs using STATISTICA 10 (Stat-Soft Inc. 2010) were performed to assess potential differences in species richness and diversity (α) among locations. As the number of samples varies among localities the weighted mean was used in the analysis. The spatial structure and fish community was analysed using the PRIMER software package (Clarke KR and tutorial. PRIMER-E) and agglomerative hierarchical clustering was applied. A community similarity matrix based on the Pearson correlation coefficient was calculated for hierarchical group average linking. Catch rates were not transformed because participants could only present a single photo per species, regardless of the number of photos or encounters they had with the most frequent species. Consequently, the most frequent species were already down-weighted by the contest rules, but the information of species relative frequency was retained because it is equivalent to the probability of being photographed.

A silhouette analysis (Rousseeuw 1987Rousseeuw P.J. 1987. Silhouettes: A graphical aid to the interpretation and validation of cluster analysis. J. Comput. Appl. Math. 20: 53-65.) was performed to evaluate the precision of the hierarchical clustering using the R statistical software (R Development Core Team, 2013R Development Core Team. 2013. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.). Silhouette analyses were performed to evaluate consistency within the identified clusters. Differences were examined with an analysis of the similarity percentages (SIMPER). This procedure used to identify which species contributed to the resulting clusters. The analysis was complemented by multidimensional scaling (MDS).

One-way ANOVA was used to assess catch image rate differences between locations in the species of commercial interest. Unequal N HSD post hoc tests (multiple comparison test), a modification of the Tukey test for unequal sample sizes (Winer et al. 1991Winer B.J., Broan D.R., Michels K.M. 1991. Statistical Principles in Experimental Design. McGraw-Hill, New York.), were used to determine the significant differences to investigate the efficacy of free-diving photographic data to detect the already known effect of this marine protected area (MPA).

RESULTSTop

In total, 16307 photographs corresponding to 29 different contests were analysed. The mean number of participants per contest was 17 and the average number of photographs per participant was 33. The number of photographs per participant has increased over recent years at two locations, Palamós and the Medes Islands, with no effect on the total number of species recorded (Table 1).

Table 1. – Descriptors of the free-diving fish photograph contests studied.

Location Date No. photos No. species No. participants No. photos/participants
Ametlla de Mar 30/05/2009 574 61 15 38
Ametlla de Mar 16/06/2012 603 62 20 30
Ametlla de Mar 26/05/2013 355 52 13 27
Ametlla de Mar 08/06/2014 478 68 13 37
Ametlla de Mar 31/05/2015 315 67 7 45
Mataró 17/05/2009 452 46 14 32
Mataró 23/05/2010 635 47 24 26
Mataró 22/05/2011 537 47 22 24
Mataró 20/05/2012 337 42 13 26
Mataró 09/06/2013 277 48 9 31
Mataró 18/05/2014 449 53 15 30
Mataró 17/05/2015 289 47 9 32
Medes 18/03/2007 251 49 9 28
Medes 05/04/2008 560 58 20 28
Medes 04/04/2009 650 62 21 31
Medes 17/04/2010 1001 62 34 29
Medes 09/04/2011 931 63 31 30
Medes 22/04/2012 536 57 20 27
Medes 22/06/2013 917 70 22 42
Medes 21/06/2014 1147 78 24 48
Medes 20/06/2015 389 66 9 43
Palamós 27/05/2007 368 52 13 28
Palamós 18/05/2008 627 62 21 30
Palamós 22/03/2009 469 60 16 29
Palamós 07/03/2010 692 54 28 25
Palamós 03/06/2012 669 56 20 33
Palamós 12/05/2013 641 59 18 36
Palamós 04/05/2014 686 62 18 38
Palamós 03/05/2015 472 65 11 43

A total of 88 taxa belonging to 26 families were photographed (Table 2). The actual species richness was higher, as the genera Atherina, Sphyraena, Trachurus and Trachinus and the family Mugilidae were not identified to the species level. The families with the highest number of species were Sparidae with 17 species and Labridae with 15 species, followed by Blenniidae and Gobiidae with 14 and 10 species, respectively. According to the International Union for Conservation of Nature (IUCN) Red List categories and criteria, 2 of these species are not yet evaluated, 1 is data-deficient to assess its status, 80 are on the least-concern list, 3 are considered vulnerable, 1 is near threatened endangered and 1 is already endangered. It is worth mentioning that the species identified until now as Gobius bucchichi in this region, should be considered to be the recently described G. incognitus (Kovačić and Šanda 2016Kovačić M., Sanda R. 2016. A new species of Gobius (Perciformes: Gobiidae) from the Mediterranean Sea and the redescription of Gobius bucchichi. J. Fish Biol. 88: 1104-1124.). The lists of species observed at the Medes Islands are 7 species that do not appear in the previous available fish inventory in this MPA (Dufour et al. 2007Dufour F., Guidetti P., Francour P. 2007. Comparison of fish inventory in Mediterranean marine protected areas: Influence of surface area and age. Cybium 31: 19-31). Species richness and Margalef diversity indices showed significant differences among locations (Fig. 2). The multiple comparison Tukey test showed that only Mataró has a significantly lower species richness (Table 1), mainly due to the lower number of species of blenniids and gobids (Table 2).

Table 2. – Fish species average catch image rate and standard deviation by location. The letters within brackets next to the species correspond to those with a catch image rate significantly higher in the Medes Marine Reserve; each letter corresponds to the location where the significant differences were observed. Asterisks indicate a species described for the first time in the Reserve.

Species Feeding (trophic levels) Feeding behaviour Commercial value IUCN status Ametlla Mataró Medes Islands Palamós
Mean Sth Mean Sth Mean Sth Mean Sth
Ammodytidae
Gymnammomytes cicerelus* ≥2.8 Filtering plankton Unknown LC 0.06 0.08 0.20 0.36 0.00 0.01 0.01 0.02
Apogonidae
Apogon imberbis ≥2.8 Hunting macrofauna NONE LC 0.47 0.34 0.54 0.28 0.41 0.38 0.68 0.17
Atherinidae
Atherina sp. ≥2.8 Hunting macrofauna Low LC 0.54 0.25 0.41 0.26 0.68 0.30
Blenniidae 0.47 0.46 0.33 0.37
Aidablennius sphynx (M) 2.2-2.79 Grazing NONE LC 0.31 0.27 0.48 0.33 0.64 0.31
Coryphoblennius galerita 2-2.19 Grazing None LC 0.03 0.06 0.05 0.06 0.11 0.15
Lipophrys trigloides 2.2-2.79 Variable NONE LC 0.46 0.17 0.26 0.30 0.29 0.27
Microlipophrys canevae 2-2.19 Variable NONE LC 0.76 0.17 0.53 0.32 0.32 0.30
Microlipophrys dalmatinus* 2.2-2.79 Variable NONE LC 0.25 0.23 0.12 0.22 0.05 0.06
Microlipophrys nigriceps 2.2-2.79 Variable NONE LC 0.29 0.17 0.15 0.18 0.19 0.22 0.02 0.06
Parablennius gattorugine 2.2-2.79 Grazing Unknown LC 0.8 0.1 0.45 0.17 0.47 0.25 0.79 0.14
Parablennius incognitus 2.2-2.79 Variable NONE LC 0.98 0.21 0.45 0.36 0.49 0.23
Parablennius pilicornis ≥2.8 NA NONE LC 0.89 0.13 0.77 0.18 0.80 0.21 0.88 0.19
Parablennius rouxi 2.2-2.79 Variable NONE LC 0.04 0.06 0.49 0.3 0.17 0.11 0.09 0.09
Parablennius sanguinolentus 2-2.19 Grazing Unknown LC 0.54 0.24 0.32 0.36 0.65 0.30
Parablennius tentacularis ≥2.8 Browsing NONE LC 0.02 0.04 0.05 0.09
Parablennius zvonimiri 2.2-2.79 Variable NONE LC 0.62 0.13 0.44 0.21 0.44 0.24 0.46 0.28
Scartella cristata 2-2.19 Grazing NONE LC 0.11 0.14
Bothidae
Bothus podas ≥2.8 Predator High LC 0.38 0.26 0.08 0.1 0.04 0.09 0.02 0.06
Callionymidae
Callionymus pusillus* ≥2.8 Predator NONE LC 0.01 0.02 0.05 0.07
Carangidae
Trachurus sp. ≥2.8 Predator Medium VU 0.02 0.03 0.08 0.13 0.04 0.07 0.02 0.06
Centracanthidae
Spicara smaris ≥2.8 Predator Low LC 0.02 0.05 0.02 0.04
Clinidae
Clinitrachus argentatus ≥2.8 Predator NONE LC 0.09 0.11 0.02 0.07 0.06 0.13
Congridae
Conger conger (P) ≥2.8 Predator Medium LC 0.19 0.18 0.33 0.18 0.43 0.24 0.14 0.14
Gadidae
Phycis phycis (A,M,P) ≥2.8 Predator High LC 0.03 0.06 0.09 0.22 0.42 0.14 0.04 0.08
Gobiesocidae
Lepadogaster candollei 2.2-2.79 NA NONE N.E. 0.20 0.4 0.26 0.22 0.34 0.27
Lepadogaster lepadogaster NA NA NONE LC 0.18 0.18 0.15 0.14 0.33 0.32
Gobiidae 0.40 0.23 0.20 0.39
Gobius bucchichi 2.2-2.79 Variable NONE LC 0.97 0.11 0.65 0.31 0.78 0.17 0.94 0.19
Gobius cobitis 2.2-2.79 Variable NONE N.E. 0.43 0.35 0.23 0.24 0.52 0.21
Gobius cruentatus ≥2.8 Browsing NONE LC 0.41 0.3 0.05 0.12 0.06 0.18 0.35 0.26
Gobius geniporus ≥2.8 NA NONE LC 0.24 0.18 0.80 0.16 0.29 0.14 0.49 0.24
Gobius niger ≥2.8 plankton feeding NONE LC 0.01 0.03 0.01 0.02 0.09 0.11
Gobius paganellus ≥2.8 Predator NONE LC 0.6 0.05 0.03 0.05 0.34 0.31 0.65 0.31
Gobius vittatus 2.2-2.79 Variable NONE LC 0.01 0.03 0.03 0.06
Pomatoschistus sp* 3.2 Hunting macrofauna NONE LC 0.55 0.34 0.16 0.24 0.11 0.19 0.13 0.14
Gobius xanthocephalus NA NA NONE LC 0.12 0.16 0.03 0.05 0.09 0.11 0.03 0.07
Zebrus zebrus* NA NA NONE LC 0.06 0.06 0.01 0.03 0.03 0.10
Haemulidae
Pomadasys incisus* ≥2.8 Predator Medium LC 0.13 0.19 0.01 0.02 0.03 0.07
Labridae 0.55 0.57 0.57 0.56
Coris julis ≥2.8 Predator Low LC 0.99 0.03 0.99 0.03 0.98 0.04 0.99 0.04
Ctenolabrus rupestris ≥2.8 Predator Low LC 0.12 0.19 0.76 0.14 0.25 0.19 0.66 0.11
Labrus merula (A,M,P) ≥2.8 Predator Low LC 0.68 0.26 0.57 0.17 0.99 0.08 0.74 0.14
Labrus mixtus ≥2.8 Predator Low LC 0.06 0.09 0.02 0.06
Labrus viridis (A,M,P) ≥2.8 Predator NONE VU 0.11 0.11 0.03 0.06 0.71 0.20 0.37 0.16
Symphodus cinereus ≥2.8 Predator Low LC 0.82 0.22 0.49 0.3 0.38 0.31 0.18 0.16
Symphodus doderleini ≥2.8 Predator NONE LC 0.06 0.11 0.03 0.06 0.09 0.07 0.19 0.08
Symphodus mediterraneus ≥2.8 Predator Low LC 0.3 0.13 0.81 0.09 0.72 0.19 0.77 0.17
Symphodus melanocercus ≥2.8 Predator NONE LC 0.04 0.06 0.33 0.19 0.62 0.27 0.59 0.21
Symphodus melops ≥2.8 Predator Low LC 0.32 0.19 0.01 0.02 0.10 0.09 0.10 0.16
Symphodus ocellatus ≥2.8 Variable NONE LC 0.98 0.06 0.69 0.2 0.62 0.26 0.84 0.15
Symphodus roissali ≥2.8 Predator Low LC 0.96 0.04 0.97 0.1 0.97 0.15 0.99 0.12
Symphodus rostratus ≥2.8 Predator NONE LC 0.66 0.14 0.29 0.11 0.58 0.20 0.37 0.16
Symphodus tinca ≥2.8 Predator Low LC 0.94 0.07 0.97 0.06 0.99 0.07 0.93 0.08
Thalassoma pavo ≥2.8 Predator Low LC 0.72 0.42 0.97 0.05 0.50 0.29 0.73 0.34
Moronidae
Dicentrarchus labrax (M,P) ≥2.8 Predator High LC 0.47 0.22 0.44 0.27 0.08 0.16
Dicentrarchus punctatus* ≥2.8 Predator Low LC 0.94 0.1 0.75 0.16 0.65 0.29 0.42 0.42
Mugilidae
2-2.19 Variable Low LC 0.79 0.14 0.02 0.04 0.85 0.14 0.81 0.21
Mullidae
Mullus surmuletus ≥2.8 Predator High LC 0.65 0.22 0.96 0.06 0.89 0.11 0.76 0.27
Muraenidae
Muraena helena ≥2.8 Predator Low LC 0.3 0.77 0.28 0.17 0.36 0.17 0.20 0.09
Pomacentridae
Chromis chromis ≥2.8 Predator Unknown LC 0.95 0.07 0.96 0.06 0.94 0.03 0.98 0.07
Sciaenidae
Sciaena umbra (M,P) ≥2.8 Predator High NT 0.3 0.28 0.03 0.04 0.29 0.22
Scorpaenidae
Scorpaena maderensis ≥2.8 Predator Low LC 0.09 0.13 0.41 0.19 0.03 0.04 0.09 0.11
Scorpaena notata ≥2.8 Predator Low LC 0.47 0.22 0.90 0.09 0.21 0.19 0.51 0.21
Scorpaena porcus ≥2.8 Predator Low LC 0.82 0.12 0.44 0.22 0.24 0.28 0.58 0.19
Scorpaena scrofa (P) ≥2.8 Predator High LC 0.3 0.32 0.63 0.26 0.61 0.33 0.03 0.04
Serranidae
Epinephelus marginatus (A,M,P) ≥2.8 Predator High EN 0.21 0.17 0.15 0.17 0.49 0.16 0.08 0.07
Serranus cabrilla ≥2.8 Predator Medium LC 0.82 0.37 0.98 0.03 0.97 0.05 0.96 0.05
Serranus scriba ≥2.8 Predator Medium LC 0.91 0.17 0.97 0.05 0.94 0.05 0.76 0.26
Sparidae 0.43 0.46 0.45 0.31
Boops boops ≥2.8 plankton feeding Low LC 0.31 0.22 0.77 0.22 0.22 0.26 0.32 0.33
Dentex dentex ≥2.8 Predator High VU 0.08 0.07 0.06 0.06 0.16 0.24 0.04 0.11
Diplodus annularis ≥2.8 Predator Low LC 0.58 0.26 0.75 0.14 0.30 0.39 0.15 0.16
Diplodus cervinus (A) ≥2.8 Predator Low LC 0.06 0.09 0.21 0.25 0.42 0.20 0.14 0.21
Diplodus puntazzo ≥2.8 Predator Low LC 0.94 0.1 0.75 0.16 0.65 0.29 0.42 0.42
Diplodus sargus (P) ≥2.8 Predator High LC 0.96 0.04 0.85 0.11 0.98 0.04 0.77 0.14
Diplodus vulgaris ≥2.8 Predator Low LC 1.00 0 0.98 0.04 0.95 0.05 0.90 0.12
Lithognathus mormyrus ≥2.8 Predator Medium LC 0.13 0.11 0.17 0.28 0.03 0.05
Oblada melanura ≥2.8 Predator Low LC. 0.96 0.04 0.83 0.1 0.82 0.14 0.66 0.22
Pagellus acarne ≥2.8 Predator Medium LC 0.1 0.17 0.01 0.03 0.10 0.12 0.06 0.11
Pagellus erythrinus ≥2.8 Predator Medium LC 0.01 0.02 0.01 0.03 0.05 0.11 0.02 0.04
Pagrus pagrus ≥2.8 Predator High LC 0.11 0.2 0.01 0.03 0.08 0.10
Sarpa salpa 2-2.19 Grazing Low LC 0.98 0.13 0.70 0.18 0.96 0.05 0.96 0.08
Spicara smaris ≥2.8 Predator Low LC 0.02 0.05 0.02 0.04
Spicara maena ≥2.8 plankton feeding Low LC 0.03 0.06 0.18 0.14 0.29 0.25 0.08 0.08
Spondyliosoma cantharus ≥2.8 Variable High LC 0.25 0.22 0.53 0.26 0.24 0.22 0.03 0.04
Sphyraenidae
Sphyraena sp. ≥2.8 Predator Medium LC 0.01 0.02 0.01 0.02 0.04 0.10
Torpedinidae
Torpedo marmorata ≥2.8 Predator NONE DD 0.06 0.13 0.05 0.07 0.06 0.11
Trachinidae
Trachinus sp. ≥2.8 Predator Low LC 0.02 0.03 0.08 0.14 0.04 0.07 0.02 0.06
Tripterygiidae
Tripterygion delaisi ≥2.8 Predator NONE LC 0.5 0.31 1.00 0.15 0.81 0.16 0.85 0.08
Tripterygion melanurus ≥2.8 Predator NONE LC 0.14 0.32 0.14 0.38 0.10 0.30 0.11 0.32
Tripterygion tripteronotus ≥2.8 Predator NONE LC 0.46 0.37 0.11 0.06 0.66 0.23 0.95 0.12

figure2

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Fig. 2. – Weighted mean and 0.95 confidence intervals of species richness and Margalef diversity index per location. AM, Ametlla de Mar (N=5); MA, Mataró (N=7); MIB, Medes Islands (N=9); and PA, Palamós (N=8).

Cluster analysis based on the species catch rates by location and year yielded four distinctive clusters (Fig. 3) corresponding to each specific location. Regardless of the year, each location was grouped in the same cluster, with one exception, the Medes Islands in 2015. The silhouette analysis (mean silhouette width=0.46) revealed that all contests had positive silhouette widths, which is indicative of correct classification within groups. The two-dimensional ordination of the 29 contests (Fig. 4) yielded a moderate level of ordination (stress=0.14), reflecting cluster separation through a gradual continuum of change. A gradient from north to south was observed among locations near the shoreline (Medes, Palamós and L’Ametlla). Consistently, the results of the cluster analysis showed that the most dissimilar group was represented by the contests held in Mataró.

figure3

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Fig. 3. – Heatmap result of cluster analysis of locations on the basis of species images catch rates. A, B, C and D represent the four main groups identified in the analysis.

figure4

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Fig. 4. – 2-d nMDS ordination plot for the 29 contests. Superimposed symbols for the different clusters.

The first cluster, grouping all the samples from Mataró, had a low number of gobiid and bleniid species, scarcity of mugilids and the absence of Atherinidae and European seabass (Dicentrarchus labrax), which mainly marked the difference of this group. An additional difference was the high values of species such as Scorpaena notata, Thalassoma pavo, Boops boops and Gobius geniporus.

The second cluster grouped all the contests of L’Ametlla de Mar, the southernmost location (the last contest held at the Medes Islands was also part of this group). The main differences compared with other groups were the high abundance of the genera Pagellus, Symphodus cinereus and Parablennius incognitus together with the scarcity of Ctenolabrus rupestris, Microlipophrys canevae, Symphodus melanocercus and Diplodus cervinus. In this group the relative abundance of European seabass was also high, and only comparable with the values observed at the Medes Islands.

The third and fourth cluster comprised the contests held at the northernmost location corresponding to a non-protected and protected area respectively with the exception of the most recent year (see above) for the latter group. The main features of this group were the low relative abundance of gobiids, the maximum observed abundance of some species of labrids (Symphodus melanocercus, Symphodus viridis and Labrus merula) and the scarcity of S. ocellatus. This group was also characterized by high abundance of commercial species (e.g. Epinephelus marginatus, Conger conger and Phycis phycis), including the red scorpion fish (S. scrofa), but it also had the lowest abundance of the other three species of the same genus (S. notata, S. porcus and S. maderensis).

Although the clusters did not show any temporal variability within locations, except for the last contest held in Medes Islands, some shifts can be depicted. Some temporal changes were observed in the contest distances within the Medes Islands cluster, in which the 2013 and 2014 contests were clearly separated from the earlier ones. Similarly, differences were observed within the Palamós (cluster C) contests: those from 2012 onwards were distant from the previous ones, while in L’Ametlla the temporal pattern was more gradual.

The post hoc test showed significantly higher catch rates at the Medes Islands MPA with respect to the other locations (Table 2). These higher rates were mostly observed in species of commercial interest such as P. phycis and E. marginatus, but the list can be extended to Conger conger, D. labrax, S. umbra, S. scrofa, D. cervinus and D. sargus. In addition, the MPA also showed significantly higher catch rates for two species of labrids that are of negligible commercial interest but are highly targeted by spear fishers (L. merula and L. viridis). Furthermore, the relative abundance of S. cinereus decreased from southern to northern locations, while S. melanocercus displayed the opposite pattern.

DISCUSSIONTop

Overall, the obtained outcomes show that free-diving fish photography contests could be a very useful tool for analysing fish assemblages and species richness in the littoral system. In general, fish classification results grouped each location separately, as expected from their differences in latitude, depth range and habitat. In addition, the already known effect of the Medes Islands MPA (García-Rubies and Zabala 1990García-Rubies A., Zabala M. 1990. Effects of total fishing prohibition on the rocky fish assemblages of Medes Islands marine reserve (NW Mediterranean). Sci. Mar. 54: 317-328., García-Rubies et al. 2013García-Rubies A., Hereu B., Zabala M. 2013. Long-Term Recovery Patterns and Limited Spillover of Large Predatory Fish in a Mediterranean MPA. PloS ONE 8: e73922.) was evidenced by the higher abundance of species of high commercial values.

The high number of species recorded in this study exceeds by far those reported in any published study on littoral communities carried out in the Mediterranean (e.g. Consoli et al. 2016Consoli P., Esposito V., Battaglia P., et al. 2016. Fish Distribution and Habitat Complexity on Banks of the Strait of Sicily (Central Mediterranean Sea) from Remotely-Operated Vehicle (ROV) Explorations. PloS ONE 11: e0167809.), and is only comparable to but still higher than the number of species reported in the marine reserve of Ustica Island (La Mesa and Vacchi 1999La Mesa G., Vacchi M. 1999. An analysis of the coastal fish assemblage of the Ustica Island Marine Reserve (Mediterranean Sea). Mar. Ecol. 20: 147-165.). It is worth mentioning that the high number of species reported in the study of Ustica Island could be due to the combined sampling methodology used (strip transects by SCUBA, SCUBA diving tracts and snorkelling), which minimized the constraints inherent in survey methods, particularly for cryptic species (Brock 1982Brock R.E. 1982. A critique of the visual census method for assessing coral reef fish populations. Bull. Mar. Sci. 32: 269-276., Willis 2001Willis T.J. 2001. Visual census methods underestimate density and diversity of cryptic reef fishes. J. Fish Biol. 59: 1408-1411., MacNeil et al. 2008MacNeil M.A., Tyler E.H., Fonnesbeck C.J., et al. 2008. Accounting for detectability in reef-fish biodiversity estimates. Mar. Ecol. Prog. Ser. 367: 249-260.). This indicates the effectiveness of the analysed information source for measuring fish species richness with a single data source.

In the Mediterranean, the littoral fish community is under various anthropogenic threats (Bianchi and Morri 2000Bianchi C.N., Morri C. 2000. Marine biodiversity of the Mediterranean Sea: situation, problems and prospects for future research. Mar. Pollut. Bull. 40: 367-376., Claudet and Fraschetti 2010Claudet J., Fraschetti S. 2010. Human-driven impacts on marine habitats: a regional meta-analysis in the Mediterranean Sea. Biol. Conserv. 143: 2195-2206., Costello et al. 2010Costello M.J., Coll M., Danovaro R., et al. 2010. A census of marine biodiversity knowledge, resources, and future challenges. PloS ONE 5: e12110.), but systematic monitoring is limited to a small number of commercial species or to protected areas (e.g. Coll et al. 2012Coll J., Garcia-Rubies A., Morey G., et al. 2012. The carrying capacity and the effects of protection level in three marine protected areas in the Balearic Islands (NW Mediterranean). Sci. Mar. 76: 809-826., García-Rubies et al. 2013García-Rubies A., Hereu B., Zabala M. 2013. Long-Term Recovery Patterns and Limited Spillover of Large Predatory Fish in a Mediterranean MPA. PloS ONE 8: e73922.). Although overall littoral fish monitoring would be unrealistic to finance, many commercial groups, such as sparids, are not subject to assessment, so they are not under any systematic monitoring programmes, and this lack of information is hard to justify. The species recorded in this study that have a known status are mainly on the least-concern list: only one is endangered (E. marginatus) and one is considered vulnerable (L. viridis).

Among the results shown in this study, of particular relevance is the capacity of free-diving photography contests to count and assess cryptic species, which can be missed by underwater visual censuses (Ackerman and Bellwood 2000Ackerman J.L., Bellwood D.R. 2000. Reef fish assemblages: a re-evaluation using enclosed rotenone stations. Mar. Ecol. Prog. Ser. 206: 227-237., Willis 2001Willis T.J. 2001. Visual census methods underestimate density and diversity of cryptic reef fishes. J. Fish Biol. 59: 1408-1411., Smith-Vaniz et al. 2006Smith-Vaniz W.F., Jelks H.L., Rocha L.A. 2006. Relevance of cryptic fishes in biodiversity assessments: a case study at Buck Island Reef National Monument, St. Croix. Bull. Mar. Sci. 79: 17-48.). A total number of 32 cryptic species were photographed during these contests, a figure that is also higher than in any previous studies targeting this group based either on visual censuses (e.g. Macpherson 1994Macpherson E. 1994. Substrate utilization in a Mediterranean littoral fish community. Mar. Ecol. Prog. Ser. 114: 211-218., La Mesa et al. 2006La Mesa G., Di Muccio S., Vacchi M. 2006. Structure of a Mediterranean cryptobenthic fish community and its relationships with habitat characteristics. Mar. Biol. 149: 149-167., Bussotti et al. 2015Bussotti S., Di Franco A., Francour P., et al. 2015. Fish assemblages of Mediterranean marine caves. PloS ONE 10: e0122632.) or destructive techniques (Patzner 1999Patzner R.A. 1999. Habitat utilization and depth distribution of small cryptobenthic fishes (Blenniidae, Gobiesocidae, Gobiidae, Tripterygiidae) in Ibiza (western Mediterranean Sea). Environ. Biol. Fish. 55: 207-214., Kovačić et al. 2012Kovačić M., Patzner R.A., Schliewen U. 2012. A first quantitative assessment of the ecology of cryptobenthic fishes in the Mediterranean Sea. Mar. Biol. 159: 2731-2742., Glavičić et al. 2016Glavičić I., Paliska D., Soldo A., et al. 2016. A quantitative assessment of the cryptobenthic fish assemblage at deep littoral cliffs in the Mediterranean. Sci. Mar. 80: 329-337.). Although they contribute greatly to the species richness of littoral systems, small cryptic species are perceived as minnows (small non-game or non-commercial fish species) due to their small size and cryptic behaviour. Consequently, they are generally overlooked or underestimated (Ackerman and Bellwood 2000Ackerman J.L., Bellwood D.R. 2000. Reef fish assemblages: a re-evaluation using enclosed rotenone stations. Mar. Ecol. Prog. Ser. 206: 227-237., Willis 2001Willis T.J. 2001. Visual census methods underestimate density and diversity of cryptic reef fishes. J. Fish Biol. 59: 1408-1411.), and it is difficult to gain support for monitoring and conserving them (Sheldon 1988Sheldon A.L. 1988. Conservation of stream fishes: patterns of diversity, rarity, and risk. Cons. Biol. 2: 149-156.). Therefore, an important part of the strictly substratum-dependent littoral fish community is usually ignored, preventing any changes from being detected both in the community and in the microhabitat of the substratum.

Overall, the most abundant species were C. julis, S. roissali, S. tinca, S. cabrilla, D. vulgaris and C. chromis. In numerous studies these species have been reported as the most common in the rocky reef habitats of the Mediterranean littoral system (Bell 1983Bell J.D. 1983. Effects of depth and marine reserve fishing restrictions on the structure of a rocky reef fish assemblage in the north-western Mediterranean Sea. J. Appl. Ecol. 20: 357-369., García-Rubies and Zabala 1990García-Rubies A., Zabala M. 1990. Effects of total fishing prohibition on the rocky fish assemblages of Medes Islands marine reserve (NW Mediterranean). Sci. Mar. 54: 317-328., Claudet et al. 2006Claudet J., Pelletier D., Jouvenel J.Y., et al. 2006. Assessing the effects of marine protected area (MPA) on a reef fish assemblage in a northwestern Mediterranean marine reserve: Identifying community-based indicators. Biol. Conserv. 130: 349-369.). However, the most abundant species differed between locations. The most abundant species in Mataró was T. delaissi. The preferred habitat of this species, flat, rocky and sheltered from wave action of the open sea (La Mesa et al. 2004La Mesa G., Micalizzi M., Giaccone G., et al. 2004. Cryptobenthic fishes of the Ciclopi Islands marine reserve (central Mediterranean Sea): assemblage composition, structure and relations with habitat features. Mar. Biol. 145: 233-242.), match the Mataró habitat location, a small, relatively flat, natural rock over 150 m in length. Further characteristics of this location, offshore at a minimum depth of 6 m that minimizes wave action and light, are also considered to be preferred by T. delaisi (Zander and Heymer 1970Zander C., Heymer A. 1970. Tripterygion tripteronotus (Risso, 1810) and Tripterygion xanthosoma n sp., an ecological speciation (Pisces, Teleostei). Vie Milieu 21: 363-394.). Mataró’s minimum depth also explained the absence of species typical of shallow waters, such as many species of blenniids (e.g. A. sphynx, L. trigloides and M. canevae), whose highest diversity (Kotrschal 1988Kotrschal K. 1988. Blennies and endolithic bivalves: differential utilization of shelter in Adriatic Blenniidae (Pisces: Teleostei). Mar. Ecol. 9: 253-269., Macpherson 1994Macpherson E. 1994. Substrate utilization in a Mediterranean littoral fish community. Mar. Ecol. Prog. Ser. 114: 211-218.) is restricted to the narrow depth zone from 0 to 1 m (Illich and Kotrschal 1990Illich I.P., Kotrschal K. 1990. Depth distribution and abundance of Northern Adriatic littoral rocky reef blennioid fishes (Blennidae and Trypterygion). Mar. Ecol. 11: 277-289.) and the negative correlation between depth and blenniid diversity was recently proved (Tiralongo et al. 2016Tiralongo F., Tibullo D., Brundo M.V., et al. 2016. Habitat preference of combtooth blennies (Actinopterygii: Perciformes: Blenniidae) in very shallow waters of the Ionian Sea, South-Eastern Sicily, Italy. Acta Ichthyol. Piscat. 46: 65-75.). This absence was also detected for some other species characteristic of shallow waters (C. argentatus and Z. zebrus). Another interesting observation in Mataró was the coexistence with high relative abundances of the four species of scorpenids (S. maderensis, S. notata, S. porcus and S. scrofa). On this basis, we could reject the mutual species displacements by interspecific competition for habitat or food resources that have been hypothesized for this group (La Mesa et al. 2004La Mesa G., Micalizzi M., Giaccone G., et al. 2004. Cryptobenthic fishes of the Ciclopi Islands marine reserve (central Mediterranean Sea): assemblage composition, structure and relations with habitat features. Mar. Biol. 145: 233-242.). However, based on the findings in the MPA, we cannot entirely reject this hypothesis. In the MPA, while S. scrofa was highly abundant, the other species of scorpaenids showed values generally below those observed in the non-protected locations. S. scrofa is bigger than the other species (Petrakis and Stergiou 1995Petrakis G., Stergiou K. 1995. Weight-length relationships for 33 fish species in Greek waters. Fish. Res. 21: 465-469., Ordines and Massuti 2009Ordines F., Massuti E. 2009. Relationships between macro-epibenthic communities and fish on the shelf grounds of the western Mediterranean. Aquat. Conserv. 19: 370-383., La Mesa et al. 2010La Mesa G., Molinari A., Tunesi L. 2010. Coastal fish assemblage characterisation to support the zoning of a new Marine Protected Area in north-western Mediterranean. Ital. J. Zool. 77: 197-210.) and under the protection effect the species can get older and bigger (e.g. Halpern and Warner 2003Halpern B.S., Warner R.R. 2003. Review paper. Matching marine reserve design to reserve objectives. Proc. R. Soc. Lond. B Biol. Sci. 270: 1871-1878.) and easier to see.

The results on species richness and diversity index showed no positive effects on the MPA, as has been proposed in other studies (Guilhaumon et al. 2015Guilhaumon F., Albouy C., Claudet J., et al. 2015. Representing taxonomic, phylogenetic and functional diversity: new challenges for Mediterranean marine protected areas. Divers. Distrib. 21: 175-187.). The results are indicative of the positive effect of the MPA on species of commercial interest, but not on all species, because responses to protection can be highly variable among fish taxa (Claudet et al. 2006Claudet J., Pelletier D., Jouvenel J.Y., et al. 2006. Assessing the effects of marine protected area (MPA) on a reef fish assemblage in a northwestern Mediterranean marine reserve: Identifying community-based indicators. Biol. Conserv. 130: 349-369.). The positive effect of the MPA in contrast with the abundance observed in the closest comparable non-protected location (Palamós) was unquestionable for species of high commercial value. A total of eight species showed higher and significant values within the MPA: C. conger, P. phycis, D. labrax, S. umbra, S. scrofa, E. marginatus and D. sargus. The recovery of the dusky grouper in MPAs has been reported in numerous studies (e.g. Bell 1983Bell J.D. 1983. Effects of depth and marine reserve fishing restrictions on the structure of a rocky reef fish assemblage in the north-western Mediterranean Sea. J. Appl. Ecol. 20: 357-369., García-Rubies and Zabala 1990García-Rubies A., Zabala M. 1990. Effects of total fishing prohibition on the rocky fish assemblages of Medes Islands marine reserve (NW Mediterranean). Sci. Mar. 54: 317-328., Sahyoun et al. 2013Sahyoun R., Bussotti S., Di Franco A., et al. 2013. Protection effects on Mediterranean fish assemblages associated with different rocky habitats. J. Mar. Biol. Assoc. UK. 93: 425-435.) as has that of white seabream (Sahyoun et al. 2013Sahyoun R., Bussotti S., Di Franco A., et al. 2013. Protection effects on Mediterranean fish assemblages associated with different rocky habitats. J. Mar. Biol. Assoc. UK. 93: 425-435.). The positive effect in this particular MPA, the Medes Islands, has already been observed for most of the above-mentioned species (i.e. D. labrax, E. marginatus, D. cervinus, S. aurata and S. umbra) (García-Rubies et al. 2013García-Rubies A., Hereu B., Zabala M. 2013. Long-Term Recovery Patterns and Limited Spillover of Large Predatory Fish in a Mediterranean MPA. PloS ONE 8: e73922.). In addition, two species of labrids (L. merula and L. viridis) of no commercial interest but of recreational spear fishing interest were also favoured by the protection. L. viridis is considered vulnerable and its protection is recommended. The lack of information on fish sizes prevents us from analysing the well-known positive effect of MPA on this key indicator (Lester et al. 2009Lester S.E., Halpern B.S., Grorud-Colvert K., et al. 2009. Biological effects within no-take marine reserves: a global synthesis. Mar. Ecol. Prog. Ser. 384: 33-46.).

A different argument is that the response to protection can also be negative for certain taxa, and changes in fish assemblages in MPAs could occur because predation pressure is expected to be higher (Francour 1994Francour P. 1994. Pluriannual analysis of the reserve effect on ichthyofauna in the Scandola natural reserve (Corsica, Northwestern Mediterranean). Oceanol. Acta 17: 309-317., Ashworth and Ormond 2005Ashworth J., Ormond R. 2005. Effects of fishing pressure and trophic group on abundance and spillover across boundaries of a no-take zone. Biol. Conserv. 12: 333-344.). A potential negative effect on small cryptic species has been suggested (Willis and Anderson 2003Willis T.J., Anderson M.J. 2003. Structure of cryptic reef fish assemblages: relationships with habitat characteristics and predator density. Mar. Ecol. Prog. Ser. 257: 209-221., Claudet et al. 2006Claudet J., Pelletier D., Jouvenel J.Y., et al. 2006. Assessing the effects of marine protected area (MPA) on a reef fish assemblage in a northwestern Mediterranean marine reserve: Identifying community-based indicators. Biol. Conserv. 130: 349-369.), but our results confirm that only two species were significantly higher at the unprotected site (P. gattorugine and T. tripteronotus). However, not all the differences in species abundance can be attributed to protection measures or to the type of data, because we also found a latitudinal gradient of variability that was unrelated to these factors. S. melanocercus, which prefers rocky areas and seagrass beds, decreases from north to south, while S. cinereus and S. ocellatus, which generally inhabits seagrass beds and sometimes soft bottoms and estuarine lagoons, increases from north to south. This partitioning is consistent with the previous categorization in the Catalan littoral system based on shore-based fishing tournament reports (Gordoa 2009Gordoa A. 2009. Characterization of the infralittoral system along the north-east Spanish coast based on sport shore-based fishing tournament catches. Estuar. Coast. Shelf Sci. 82: 41-49., Boada et al 2017Boada J., Sagué O., Gordoa A. 2017. Spearfishing data reveals the littoral fish communities’ association to coastal configuration. Estuar. Coast. Shelf Sci. 199: 152-160.).

The type of information used in this study has several weaknesses, such as a potential underestimation of the most frequent species because the number of photographs per species and participant is limited to one, and the possibility that the same fish could be photographed by different participants. However, despite the potential weaknesses of photographic free-diving contest data, the results of this study show their effectiveness for evaluating species richness, in particular of cryptobenthic species, and for analysing littoral fish communities. Furthermore, it has also proved its worth as a tool for updating fish inventories. We can summarize that this type of contest enhances competition between participants to obtain maximum fish diversity. Additional positive aspects of this information source are that it is cost-effective, non-destructive, a potential observatory, an platform for interaction between scientists and free divers, and an alternative for spear fishers in MPAs. We conclude that the monitoring of photographic free-diving contests could be a complementary information source to scientific monitoring.

ACKNOWLEDGEMENTSTop

The authors are very grateful to the Catalan Federation of Underwater Activities (FECDAS) for providing all the information analysed in this study and in particular to Carles Font, delegate of apnoea photo-hunting and responsible for compiling the database of these contests and to Catherine Stonehouse for revising and improving the original English manuscript. We also thank the anonymous referees for their useful comments.

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