INTRODUCTION
⌅The endobenthic deposit-feeder polychaetes belonging to the Capitella capitata (Fabricius, 1780) species complex have been reported worldwide in polluted and organically enriched marine and estuarine sediments, often being referred to as bioindicators (e.g. Pearson and Rosenberg 1978Pearson T.H., Rosenberg R. 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanogr. Mar. Biol. Ann. Rev. 16: 229-311. , Méndez et al. 1997Méndez N., Romero J., Flos J. 1997. Population dynamics and production of the polychaete Capitella capitata in the littoral zone of Barcelona (Spain, NW Mediterranean). J. Exp. Mar. Biol. Ecol. 218: 263-284. https://doi.org/10.1016/S0022-0981(97)00078-6 ,2000Méndez N., Linke-Gamenick I., Forbes V.E. 2000. Variability in reproductive mode and larval development within the Capitella capitata species-complex. Invetebr. Reprod. Dev. 38: 131-142. https://doi.org/10.1080/07924259.2000.9652448 ). The Capitella capitata complex consists of at least 50 sibling species, with about 13 being described from laboratory cultures (Grassle and Grasle 1976Grassle J.P., Grassle J.F. 1976. Sibling species in the marine pollution indicator Capitella (Polychaeta). Science 192: 567-569. https://doi.org/10.1126/science.1257794 , Blake 2009). The non-interbreeding, morphologically similar cryptic species of this complex are distinguishable mainly by protein variation and ecophysiological, developmental and reproductive features (Wu et al. 1991Wu B.L., Qian P.Y., Zhang S.L. 1991. Morphology, reproduction, ecology and allozyme electrophoresis of three Capitella sibling species in Qingdao (Polychaeta: Capitellidae). Ophelia Suppl. 5: 391-400., Linke-Gamenick et al. 2000aLinke-Gamenick I., Vismann B., Forbes V.E. 2000a. Effects of hydrocarbon contamination on survival and metabolism in different sibling species of the Capitella capitata-complex. Mar. Ecol. Prog. Ser. 194: 169-177. https://doi.org/10.3354/meps194169 , Adkins and Schulze 2011Adkins M, Schulze A. 2011. Development of Capitella sp. G from Galveston Bay, Texas. Mar. Biol. Res. 7: 202-207. https://doi.org/10.1080/17451000.2010.489612 ). However, only a few have been described in detail (Méndez 2016Méndez N. 2016. Laboratory development of Capitella sp. A (Annelida: Capitellidae) from a NW Mediterranean fish farm reared under different organic enrichment conditions. Sci. Mar. 80: 535-542. https://doi.org/10.3989/scimar.04450.08B ).
The genus Capitella mostly includes opportunistic r-selected species able to produce either free-swimming planktotrophic or benthic lecithotrophic larvae (Grassle and Grassle 1974Grassle J.F., Grassle, J.P., 1974. Opportunistic life histories and genetic systems in marine polychaetes. J. Mar. Res. 32: 253-284., Méndez 2002Méndez N. 2002. Experimental evidence of polymorphysm of sexual development in Capitella sp B (Polychaeta: Capitellidae) from Barcelona, Spain. Sci. Mar. 66: 103-110. https://doi.org/10.3989/scimar.2002.66n2103 , Adkins and Schulze 2011Adkins M, Schulze A. 2011. Development of Capitella sp. G from Galveston Bay, Texas. Mar. Biol. Res. 7: 202-207. https://doi.org/10.1080/17451000.2010.489612 ) and showing a wide geographical and interspecific variety of reproductive strategies (Méndez et al. 2000Méndez N. 2002. Experimental evidence of polymorphysm of sexual development in Capitella sp B (Polychaeta: Capitellidae) from Barcelona, Spain. Sci. Mar. 66: 103-110. https://doi.org/10.3989/scimar.2002.66n2103 ). The latter include planktotrophy, lecithotrophy and direct development, as well as hermaphroditism and poecilogony, which give rise to differences in size and duration of the life stages, number of brooded embryos, and ciliation patterns in metatrochophore larvae (Méndez et al. 2000Méndez N. 2002. Experimental evidence of polymorphysm of sexual development in Capitella sp B (Polychaeta: Capitellidae) from Barcelona, Spain. Sci. Mar. 66: 103-110. https://doi.org/10.3989/scimar.2002.66n2103 , 2019Méndez N., Hilliard J., Schulze, A. 2019. Early development of two Capitella species (Annelida: Capitellidae) from the Gulf of Mexico. J. Mar. Biol. Ass. U.K. 99: 15571568. https://doi.org/10.1017/S0025315419000687 , Méndez 2016Méndez N. 2016. Laboratory development of Capitella sp. A (Annelida: Capitellidae) from a NW Mediterranean fish farm reared under different organic enrichment conditions. Sci. Mar. 80: 535-542. https://doi.org/10.3989/scimar.04450.08B ).
Nevertheless, the life cycle of the different species follows a similar pattern. With faecal materials, substrate and potential food, females construct brood tubes that are open at both ends to allow oxygenation. The fertilized eggs are brooded until the trochophore stage (Reish 1980Reish D.J. 1980. Use of polychaetous annelids as test organisms for marine bioassay experiments. In: Buikema A.L. Jr, Cairns J. Jr. (eds), Aquatic Invertebrate Bioassays, ASTM STP 715, American Society for Testing and Materials, pp. 140-154. https://doi.org/10.1520/STP33413S ). In species with planktotrophic development they are then directly hatched (then progressing to the metatrochophore stage in the water column), whereas in lecithotrophic species they stay inside the tube until they reach the metatrochophore stage (George 1984George J.D. 1984. The behaviour and life history of a mangrove-dwelling capitellid (Polychaeta). In: Hutchings P.A. (ed), Proceedings of the First International Polychaete Conference. Sydney Australia, Milsons Point: The Linnean Society of New South Wales, pp. 323-337.). The juvenile stage can be reached inside the tube (direct development) or in the sediment after settling of metatrochophores. Juveniles are already vermiform, with a complete segmentation, a clear distinction between thorax and abdomen and a chaetal arrangement consisting of capillaries in the first three segments and hooded hooks in the subsequent ones (Méndez 1995Méndez N. 1995. Non-pelagic development of Capitella capitata (Polychaeta) in the littoral zone of Barcelona, Spain. Sci. Mar. 59: 95-101.). Juveniles are first transparent, and then become pink and red because of haemoglobin production until they become immature adults (Méndez 2002Méndez N. 2002. Experimental evidence of polymorphysm of sexual development in Capitella sp B (Polychaeta: Capitellidae) from Barcelona, Spain. Sci. Mar. 66: 103-110. https://doi.org/10.3989/scimar.2002.66n2103 , 2006Méndez N. 2006. Life cycle of Capitella sp Y (Polychaeta: Capitellidae) from Estero del Yugo, Mazatlan, Mexico. J. Mar. Biol. Ass. U.K. 86: 263-269. https://doi.org/10.1017/S0025315406013117 ); a change from intense red to greyish red indicates that specimens are becoming old (Méndez 2006Méndez N. 2006. Life cycle of Capitella sp Y (Polychaeta: Capitellidae) from Estero del Yugo, Mazatlan, Mexico. J. Mar. Biol. Ass. U.K. 86: 263-269. https://doi.org/10.1017/S0025315406013117 ). Adult males bear genital spines between chaetigers 8 and 9 (Reish 1980Reish D.J. 1980. Use of polychaetous annelids as test organisms for marine bioassay experiments. In: Buikema A.L. Jr, Cairns J. Jr. (eds), Aquatic Invertebrate Bioassays, ASTM STP 715, American Society for Testing and Materials, pp. 140-154. https://doi.org/10.1520/STP33413S ). Immature females bear paired, yellowish, sac-like ovaries suspended by mesenteries in the ventral coelomic cavity throughout the mid-body segments (Bellan et al. 1972Bellan G, Reish D.J., Foret J.P. 1972. The sublethal effects of a detergent on the reproduction, development and settlement in the polychaetous annelid Capitella capitata. Mar. Biol. 14: 183-188. https://doi.org/10.1007/BF00348278 , Eckelbarger and Grassle 1983Eckelbarger K.J., Grassle J.P. 1983. Ultrastructural differences in the eggs and ovarian follicle cells of Capitella (Polychaeta) sibling species. Biol. Bull. 165: 379-393. https://doi.org/10.2307/1541203 ), which become visibly white when mature (Méndez 2002Méndez N. 2002. Experimental evidence of polymorphysm of sexual development in Capitella sp B (Polychaeta: Capitellidae) from Barcelona, Spain. Sci. Mar. 66: 103-110. https://doi.org/10.3989/scimar.2002.66n2103 , 2006Méndez N. 2006. Life cycle of Capitella sp Y (Polychaeta: Capitellidae) from Estero del Yugo, Mazatlan, Mexico. J. Mar. Biol. Ass. U.K. 86: 263-269. https://doi.org/10.1017/S0025315406013117 , Méndez and Barata 2015Méndez N., Barata C. 2015. Effects of the antidepressant fluoxetine in spiked-sediments on developmental and reproductive features of the polychaetes Capitella teleta and Capitella sp A. Ecotoxicology 24: 106-118. https://doi.org/10.1007/s10646-014-1362-z ).
Field and laboratory studies have demonstrated that growth depends strongly on environmental food availability (Forbes and Lopez 1990Forbes T.L., Lopez G.R. 1990. Ontogenic changes in individual growth and egestion rates in the deposit-feeding polychaete Capitella sp I. J. Exp. Mar. Biol. Ecol. 143: 209-220. https://doi.org/10.1016/0022-0981(90)90071-J , Qian and Chia 1992Qian P.Y, Chia F.S. 1992. Effects of diet type on the demographics of Capitella capitata (Annelida: Polychaeta): Lecithotrophic development vs planktotrophic development. J. Exp. Mar. Biol. Ecol. 157: 159-179. https://doi.org/10.1016/0022-0981(92)90160-C , Linton and Taghun 2000Linton D.L., Taghun G.L. 2000. Feeding, growth, and fecundity of Capitella sp. I in relation to sediment organic concentration. Mar. Ecol. Prog. Ser. 205: 229-240. https://doi.org/10.3354/meps205229 , among others) and quality (Qian and Chia 1991Qian P.Y., Chia F.S. 1991. Fecundity and egg size were mediated by quality of diet in the marine polychaete worm, Capitella sp. J. Exp. Mar. Biol. Ecol. 148: 11-25. https://doi.org/10.1016/0022-0981(91)90143-K , Hu et al. 2003Hu S.I., Horng C.Y., Cheng I.J. 2003. The use of growth and ingestion rates of Capitella sp. I as the bioassay approaches to determine the sediment quality of coastal wetlands of Taiwan. J. Exp. Mar. Biol. Ecol. 297: 179-202. https://doi.org/10.1016/j.jembe.2003.07.009 , Ramskov and Forbes 2008Ramskov T., Forbes V.E. 2008. Life history and population dynamics of the opportunistic polychaete Capitella sp. I in relation to sediment organic matter Mar. Ecol. Prog. Ser. 369: 181-192. https://doi.org/10.3354/meps07584 ). The presence of high amounts of food accelerated growth and offspring production in a species of Capitella and increased fecundity (because their generation time became shorter), while limiting food-induced growth delays (thus increasing generation time), and egg size became food-quality mediated (Qian and Chia 1992Qian P.Y, Chia F.S. 1992. Effects of diet type on the demographics of Capitella capitata (Annelida: Polychaeta): Lecithotrophic development vs planktotrophic development. J. Exp. Mar. Biol. Ecol. 157: 159-179. https://doi.org/10.1016/0022-0981(92)90160-C ). Such a key role of organic matter in the physiology of the species of Capitella allows us to focus our study on determining the effects of two different organic content conditions on mortality, growth and development of two populations of Capitella in laboratory conditions.
MATERIALS AND METHODS
⌅Test organisms
⌅Capitella teleta was first identified as Capitella sp. I (Grassle and Grassle 1976Grassle J.P., Grassle J.F. 1976. Sibling species in the marine pollution indicator Capitella (Polychaeta). Science 192: 567-569. https://doi.org/10.1126/science.1257794 ) and later designated as C. teleta (Blake et al. 2009Blake J.A., Grassle J.P., Eckelbarger K.J. 2009. Capitella teleta, a new species designation for the opportunistic and experimental Capitella sp. I, with a review of the literature for confirmed records. Zoosymposia 2: 25-53. https://doi.org/10.11646/zoosymposia.2.1.6 ). It is a hermaphroditic species with lecithotrophic development originally found in organically polluted sediments in Setauket Harbour (Long Island, New York, USA) and then successfully cultured in the Department of Life Sciences and Chemistry of the Roskilde University, Denmark (DLSCRU) for many generations over more than 40 years (Ramskov et al. 2009Ramskov T., Selk H., Salvito D., Forbes V., 2009. Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I. Environ. Toxicol. Chem. 28: 2695-2705. https://doi.org/10.1897/08-522.1 ). This species has been considered the most opportunistic among the Capitella complex because of its rapid growth rate and numerical dominance in organically enriched areas (Grassle and Grassle 1974Grassle J.F., Grassle, J.P., 1974. Opportunistic life histories and genetic systems in marine polychaetes. J. Mar. Res. 32: 253-284., Tsutsumi 1987Tsutsumi H. 1987. Population dynamics of Capitella capitata (Polychaeta: Capitellidae) in an organically polluted cove. Mar. Ecol. Prog. Ser. 36: 139-149. https://doi.org/10.3354/meps036139 , Forbes et al. 1994Forbes T.L., Forbes V.E., Depledge M.H. 1994. Individual physiological responses to environmental hypoxia and organic enrichment: implications for early soft-bottom community succession. J. Mar. Res. 52: 1081-1100. https://doi.org/10.1357/0022240943076849 ). It is thus the subject of much ecological and experimental research worldwide (Méndez et al. 2000Méndez N., Linke-Gamenick I., Forbes V.E. 2000. Variability in reproductive mode and larval development within the Capitella capitata species-complex. Invetebr. Reprod. Dev. 38: 131-142. https://doi.org/10.1080/07924259.2000.9652448 ). The specimens analysed in this study came from DLSCRU.
Capitella sp. has not been morphologically described in a formal way. It was collected at the Trabucador Beach (40º63’N 0º79’E, Alfacs Bay, Tarragona, Spain) in October 2012, at about 30 cm depth on sandy sediments with 0.5±0.04% of organic matter (OM) content. OM was always estimated as loss by ignition (Dean 1974Dean W.E. Jr. 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss of ignition: comparison with other methods. J. Sed. Petrol. 44: 242-248. https://doi.org/10.1306/74D729D2-2B21-11D7-8648000102C1865D ) and expressed as average ±standard error based on three measurements. The sediment was sieved through a 0.5 mm mesh and the retained worms were sorted with forceps. The accompanying fauna was mainly composed of amphipods, isopods and gastropods, together with polychaetes of the families Capitellidae, Spionidae, Phyllodocidae, Maldanidae and Sabellidae.
Cultures
⌅All specimens were cultured in plastic aquaria (20×12×17 cm) containing 200 g (dry weight) of clean sediment from Vallcarca Beach (41°14’N 1°52’E, Sitges, Barcelona, Spain), previously washed with freshwater (to kill fauna), dried (60°C) and sieved to keep the <250 µm fraction (OM=0.089±0.007%). Each stock culture contained 1.5 L of aerated and filtered (<30 µm) seawater with 31 ppm for C. teleta (Ramskov et al. (2009)Ramskov T., Selk H., Salvito D., Forbes V., 2009. Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I. Environ. Toxicol. Chem. 28: 2695-2705. https://doi.org/10.1897/08-522.1 and 34 ppm for Capitella sp. (native water salinity) and was maintained at 20°C in the dark. Once in the aquaria, the worms were fed weekly with 0.5 g of artificial food (Méndez et al. 2013Méndez N, Lacorte S., Barata C. 2013. Effects of the pharmaceutical fluoxetine in spiked-sediments on feeding activity and growth of the polychaete Capitella teleta. Mar. Environ. Res. 89: 76-82. https://doi.org/10.1016/j.marenvres.2013.05.004 , Méndez and Barata 2015Méndez N., Barata C. 2015. Effects of the antidepressant fluoxetine in spiked-sediments on developmental and reproductive features of the polychaetes Capitella teleta and Capitella sp A. Ecotoxicology 24: 106-118. https://doi.org/10.1007/s10646-014-1362-z , Méndez 2016Méndez N. 2016. Laboratory development of Capitella sp. A (Annelida: Capitellidae) from a NW Mediterranean fish farm reared under different organic enrichment conditions. Sci. Mar. 80: 535-542. https://doi.org/10.3989/scimar.04450.08B ) consisting of a mixture of equal parts of commercial fish food (Wardley*), baby cereal (Milupa) and dried spinach (Forbes et al. 1996Forbes V.E., Forbes T.L., Holmer M. 1996. Inducible metabolism of fluoranthene by the opportunistic polychaete Capitella sp. I. Mar. Ecol. Prog. Ser. 132: 63-70. https://doi.org/10.3354/meps132063 , Ramskov and Forbes 2008), dried, ground and sieved to less than 250 µm. The worms were acclimatized for six (C. teleta) and one (Capitella sp.) months prior to the start of the experiments (OM=6.536±0.060%). The experiments were performed at the Department of Environmental Chemistry of the Institute of Environmental Assessment and Water Research (IDAEA) of the Spanish National Research Council (CSIC).
Experimental sediments
⌅Sediments from Vallcarca Beach were used to prepare two experimental conditions: (1) non-organically enriched sediments (NOES), washed with freshwater, dried (60°C), sieved to less than 250 µm (OM=0.089±0.007%); and (2) organically enriched sediments (OES), a mixture of 100 g (dry weight) of clean, dry (60°C) and <250 µm sieved sediment with 0.5 g of artificial food (OM=6.264±0.052%, similar to the acclimatizing sediments). No more artificial food was added to the OES to avoid fungi and bacteria development, as occurred in previous experiments (pers. obs.) or a decrease in oxygen concentrations. Experimental sediments were stored dry until used. Sediments and seawater (<30 µm filtered, 31 ppm for C. teleta and 34 ppm for Capitella sp.) were replaced weekly.
Experimental design
⌅Twelve pale or transparent juveniles with a length of 1.9 to 6.5 mm (C. teleta) and 3.7 to 10.6 mm (Capitella sp.) bearing eyes and lacking sexual structures were selected, placed individually in 2 cm diameter plastic dishes containing 0.3 g (dry weight) of rehydrated experimental sediments and 3 mL of filtered seawater and kept at 20°C in the dark. Each dish contained one juvenile to record data at individual level. Measurements and qualitative observations (mortality, haemoglobin production and development of reproductive structures) were taken until all worms died, every 6 to 8 days for C. teleta, and every 3 to 4 days (days 1-51) and 6 to 8 days (day 58 until death) for Capitella sp.
Adult worms with haemoglobin (7.6-9.3 mm for C. teleta; 6.5-13.8 mm for Capitella sp.) were selected and placed individually in 3.5 cm diameter plastic dishes containing 0.5 g (dry weight) of rehydrated experimental sediment and 7 mL of filtered seawater and kept at 20°C in the dark until all worms died. Mature specimens were identified by the genital spines (males) and the yellow (immature) or white (mature) ovaries (females) (Méndez and Barata 2015Méndez N., Barata C. 2015. Effects of the antidepressant fluoxetine in spiked-sediments on developmental and reproductive features of the polychaetes Capitella teleta and Capitella sp A. Ecotoxicology 24: 106-118. https://doi.org/10.1007/s10646-014-1362-z ). Three males and three females of C. teleta and six immature females with yellow ovaries of Capitella sp. (males were absent) were selected and observed individually. Measurements, mortality and development of reproductive structures were recorded for each worm until death, every 4 to 7 days for C. teleta, and every 3 to 4 days (days 1-41) and 6 to 7 days (day 48 until death) for Capitella sp.
Juveniles and adults were photographed each census day for body volume (V) determination, as V=π A2/4L, where A is the area and L the length (Forbes et al. 1994Forbes T.L., Forbes V.E., Depledge M.H. 1994. Individual physiological responses to environmental hypoxia and organic enrichment: implications for early soft-bottom community succession. J. Mar. Res. 52: 1081-1100. https://doi.org/10.1357/0022240943076849 ). When possible, three photographs of each worm were taken to estimate an average V. Photographs were taken with a camera (Nikon Digital Sight DS-R1) connected to a dissecting microscope (Nikon SMZ1500, mod. CDSD230). Body length and area were measured using the NIS-Elements AR 3.0. S16 software (Nikon Laboratory imaging, 1991-2008). Both juveniles and adults were observed and measured one day after being placed in their respective treatments (experimental and census day 1) to avoid handling stress (i.e. animals jerking and curling), which could hinder the photographic process and thus cause mistakes in V estimates.
Calculations
⌅Juvenile and adult mortality (as percentages) for NOES and OES was calculated as the number of living individuals in each census day divided by the number of dead individuals in the subsequent census day (taking into account the number of days for each period). Due to the high number of days that elapsed until the death of all the individuals of Capitella sp., the graphic representations of mortality and body volume results were built for the two species using census days (i.e. days when observations and measurements were made) instead of real days (Table 1). Size and development data (Tables 2-4) refer to real days (hereafter termed “days”).
| Capitella teleta | Capitella sp. | ||||
|---|---|---|---|---|---|
| Census days | Days | Census days | Days | Census days | Days |
| 1 | 1 | 1 | 1 | 24 | 114 |
| 2 | 7 | 2 | 4 | 25 | 121 |
| 3 | 14 | 3 | 8 | 26 | 129 |
| 4 | 21 | 4 | 11 | 27 | 136 |
| 5 | 28 | 5 | 15 | 28 | 143 |
| 6 | 35 | 6 | 18 | 29 | 150 |
| 7 | 42 | 7 | 22 | 30 | 157 |
| 8 | 49 | 8 | 25 | 31 | 164 |
| 9 | 57 | 9 | 29 | 32 | 171 |
| 10 | 64 | 10 | 33 | 33 | 185 |
| 11 | 36 | 34 | 191 | ||
| 12 | 40 | 35 | 202 | ||
| 13 | 43 | 36 | 209 | ||
| 14 | 47 | 37 | 227 | ||
| 15 | 51 | 38 | 234 | ||
| 16 | 58 | 39 | 240 | ||
| 17 | 65 | 40 | 247 | ||
| 18 | 71 | 41 | 254 | ||
| 19 | 78 | 42 | 256 | ||
| 20 | 85 | 43 | 265 | ||
| 21 | 92 | 44 | 272 | ||
| 22 | 99 | 45 | 279 | ||
| 23 | 107 | 46 | 287 | ||
| Volume (mm3) | N | Days | ||
|---|---|---|---|---|
| Capitella teleta | ||||
| Juveniles in NOES | 0.11 ± 0.08 | (0.06-0.29) | 12 | 42 |
| Juveniles in OES | 0.47 ± 0.24 | (0.04-0.78) | 12 | 57 |
| Adults in NOES | 1.18 ± 0.60 | (0.73-1.93) | 6 | 33 |
| Adults in OES | 1.51 ± 0.55 | (0.63-2.29) | 6 | 33 |
| Capitella sp. | ||||
| Juveniles in NOES | 0.70 ± 0.31 | (0.27-1.19) | 12 | 51 |
| Juveniles in OES | 1.55 ± 0.61 | (0.77-2.83) | 12 | 164 |
| Adults in NOES | - | - | 6 | 0 |
| Adults in OES | 1.28 ± 0.51 | (0.51-2.59) | 6 | 217 |
| Developmental structures | Experimental days | Initial volume range (mm3) | Mean volume (mm3) | N |
|---|---|---|---|---|
| Capitella teleta NOES | ||||
| Pink spots of Hb | 7-42 | 0.03-0.16 | 0.1±0.1 | 12 |
| Red spots of Hb | NO | NO | NO | NO |
| YO | NO | NO | NO | NO |
| YO + GS | NO | NO | NO | NO |
| YO + WO | NO | NO | NO | NO |
| Capitella teleta OES | ||||
| Pink spots of Hb | 1-7 | 0.84-0.28 | 0.14±0.07 | 8 |
| Red spots of Hb | 1-57 | 0.48-0.85 | 0.64±0.18 | 4 |
| YO - 1st app | 7-42 | 0.53-0.63 | 0.58±0.05 | 3 |
| YO - 2nd app | 14-42 | 0.53 | 0.53 | 1 |
| YO - 3rd app | 21-42 | 0.75 | 0.75 | 1 |
| YO - 4th app | 42 | 0.57 | 0.57 | 1 |
| Female + GS | 14-48 | 0.99 | 0.99 | 1 |
| WO | 21-34 | 0.72-0.81 | 0.77±0.06 | 2 |
| Capitella sp. NOES | ||||
| Pink spots of Hb | 4-58 | 0.68-1.69 | 1.15±0.33 | 8 |
| Red spots of Hb | NO | NO | NO | NO |
| YO | NO | NO | NO | NO |
| YO + GS | NO | NO | NO | NO |
| YO + WO | NO | NO | NO | NO |
| Old | NO | NO | NO | NO |
| Capitella sp. OES | ||||
| Pink spots of Hb | 4-24 | 0.45-2.59 | 1.68±0.68 | 8 |
| Red spots of Hb | 25-164 | 1.20-2.28 | 1.81±0.56 | 3 |
| YO | 25-164 | 1.20-2.28 | 1.81±0.56 | 3 |
| YO + GS | NO | NO | NO | NO |
| YO + WO | NO | NO | NO | NO |
| Old | 191-254 | - | 1 |
| New sexual structures | |||||
|---|---|---|---|---|---|
| Developmental structures | Initial volume (mm3) | Final volume (mm3) | Death day | Volume (mm3) | Appearance days |
| Capitella teleta NOES | |||||
| Male 1 with GS | 2.26 | 2.26 | 11 | - | - |
| Male 2 with GS | 2.02 | 0.94 | 25 | - | - |
| Male 3 with GS | 1.86 | 0.37 | 33 | - | |
| Female 1 with YO | 1.39 | 0.21 | 33 | - | - |
| Female 2 with YO | 0.97 | 1 | 33 | - | - |
| Female 3 with WO | 1.29 | 0.45 | 33 | - | - |
| Capitella teleta OES | |||||
| Male 1 with GS | 1.68 | 0.06 | 11 | YO (0.06) | 5 |
| Male 2 with GS | 2.34 | 0.81 | 20 | - | - |
| Male 3 with GS | 2.44 | 1.11 | 33 | YO (0.48) | 12 |
| Female 1 with YO | 1.06 | 0.54 | 33 | WO (1.78) | 5 |
| Female 2 with YO | 1.68 | 2.16 | 33 | GS (0.96) | 12 |
| Female 3 with WO | 4.53 | 0.72 | 33 | - | - |
| Capitella sp. OES | |||||
| Female 1 with YO | 1.69 | * 0.62 | 279 | - | - |
| Female 2 with YO | 1.91 | 1.91 | 4 | - | - |
| Female 3 with YO | 3.43 | 3.74 | 7 | - | - |
| Female 4 with YO | 0.95 | 1.25 | 11 | - | - |
| Female 5 with YO | 1.28 | 2.38 | 15 | - | - |
| Female 1 with YO | 6.27 | 4.03 | 7 | - | - |
Growth rates (mm3 day-1) were calculated for each worm as the difference in V between one day and the subsequent one, divided by the number of days between measurements. Global growth rates for each developmental stage and treatment were estimated as the mean for all analysed worms. Worms dying during the first and second days were not taken into account.
RESULTS
⌅Worms
⌅The stock cultures after the acclimation period contained juveniles, males, females and brooding females for C. teleta and a low number of specimens lacking males and brooding females for Capitella sp. The latter were characterized by having a conical (instead of dorsoventrally flattened) prostomium lacking eyespots, capillary chaetae from chaetiger 1 to 4-7, a ventral depression along the posterior abdominal region, and a pygidium that was a large, simple, rounded, dark lobe lacking anal cirri (Fig. 1).
Mortality
⌅Living juveniles of C. teleta were observed until days 42 (in NOES) and 57 (in OES), while adults always died on day 33 (Tables 1 and 2; Fig. 2A). Mortality in Capitella sp. was highly variable. Four juveniles died on day 1 in the two treatments. In NOES, seven juveniles (66.7%) died on day 33 (mean survivorship = 24 days), while the last juvenile died on day 58. Six juveniles (83.3%) in OES survived before day 43 (mean survivorship = 26 days), while the last two juveniles died on days 164 and 254, respectively. The six adults died on day 1 in NOES, while five adults (83.3%) in OES died before day 15 (mean survivorship = 8 days) and the last adult died on day 279 (Tables 1 and 2; Fig. 2B).
Growth
⌅Juveniles and adults of C. teleta were smaller in NOES than in OES (Table 2) and showed a general V reduction during the experiment (Table 1; Fig. 3A). Their growth rates were always negative, both for juveniles (N=12, −0.012±0.012 mm3 day-1 in NOES, 0.0006±0.01 mm3 day in OES) and for adults (N=5, −0.03±0.05 mm3 day in NOES and 0.09±0.08 mm3 day-1 in OES).
Capitella sp. also showed reductions in V at the end of the experiment. Juveniles in NOES were smaller (Table 2), and those in OES showed a general increase in the first part of the experiment and reached a maximal average V (2.83 mm3) on day 58 (two individuals), which was higher than the maximal V of the only living adult in OES (1.82 mm3 on day 51) (Table 1; Fig. 3B). Growth rates for juveniles were -0.03±0.011 mm3 day-1 (N=8) in NOES and -0.017±0.47 mm3 day-1 (N=7) in OES, and 0.034±0.38 mm3 day-1 for adults in OES (N=3, alive until day 15) (N=3) and 0.032±0.04 mm3 day-1 (N=3, from day 1 to 217, when the last survivor could be measured because it was not damaged). The growth rate of this survivor from day 1 to 217 was negative (−0.002±0.10 mm3 day-1, N=1; 31 observations). Under OES, the sporadic peaks corresponded to the two juveniles and one adult that survived longer, thus causing a high standard deviation (Fig. 3).
Development
⌅The juveniles of C. teleta in NOES remained transparent with a few pinkish haemoglobin spots, without developing reproductive structures or producing tubes during the whole experiment (Table 3). In contrast, some specimens in OES reached the adult stage, becoming initially red (because of a high haemoglobin production) and then building a high number of tubes. Yellow ovaries appeared between days 7 and 42 and white ovaries between days 21 and 34 (two individuals). One female developed genital spines on day 14, indicating hermaphroditism, and remained like that until dead.
The eight living juveniles of Capitella sp. exposed to NOES had little haemoglobin and did not become adults during the experiment (Table 3). Only three specimens in OES produced high amounts of haemoglobin and developed yellow ovaries, but did not reach maturity. Only one individual survived for 254 days; it was greyish and moved slowly, indicating that it had became old. In both treatments, tube production was low.
None of the adults of C. teleta raised in NOES developed sexual structures (Table 4), while in OES, two males developed yellow ovaries at days 5 and 12, respectively, and a female developed genital spines at day 12, indicating hermaphroditism. Only one female developed white ovaries at day 5. None of the Capitella sp. immature females with yellow ovaries from OES reached maturity (Table 4).
DISCUSSION
⌅The two populations of Capitella studied here came from different localities and living conditions. Capitella teleta, an opportunistic species originally inhabiting very polluted environments (Blake et al. 2009Blake J.A., Grassle J.P., Eckelbarger K.J. 2009. Capitella teleta, a new species designation for the opportunistic and experimental Capitella sp. I, with a review of the literature for confirmed records. Zoosymposia 2: 25-53. https://doi.org/10.11646/zoosymposia.2.1.6 ), came from a laboratory culture held for more than 40 years (Ramskov et al. 2009Ramskov T., Selk H., Salvito D., Forbes V., 2009. Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I. Environ. Toxicol. Chem. 28: 2695-2705. https://doi.org/10.1897/08-522.1 ). Capitella sp. came from natural population inhabiting a low organically enriched environment and was acclimatized to laboratory conditions for a brief period just before the experiments started. Capitella teleta showed females, males and hermaphrodites, while all Capitella sp. were females, hindering developmental comparisons. Capitella teleta, as described by Blake et al. (2009)Blake J.A., Grassle J.P., Eckelbarger K.J. 2009. Capitella teleta, a new species designation for the opportunistic and experimental Capitella sp. I, with a review of the literature for confirmed records. Zoosymposia 2: 25-53. https://doi.org/10.11646/zoosymposia.2.1.6 , was smaller than Capitella sp., a prostomium flattened dorsoventrally (conical in Capitella sp.), eyespots in adults (absent in Capitella sp.), capillary chaetae in chaetigers 1-7 (1-4/7 in Capitella sp.) and a pygidium with two rounded lobes and a narrow dorsal slit-like notch (with a large simple rounded and dark lobe in Capitella sp.).
Capitella sp. did not produce mature males and females or brooding females, and did not develop reproductive structures in laboratory conditions, which prevented both its formal description and proper comparisons with other morphologically described sibling species from close locations, such as Capitella sp. A from Les Cases d’Alcanar, Tarragona, a town less than 20 km from the Trabucador Beach (Méndez 2016Méndez N. 2016. Laboratory development of Capitella sp. A (Annelida: Capitellidae) from a NW Mediterranean fish farm reared under different organic enrichment conditions. Sci. Mar. 80: 535-542. https://doi.org/10.3989/scimar.04450.08B ) or Capitella capitata (Méndez 1995Méndez N. 1995. Non-pelagic development of Capitella capitata (Polychaeta) in the littoral zone of Barcelona, Spain. Sci. Mar. 59: 95-101.) and Capitella sp. B (Méndez 2002Méndez N. 2002. Experimental evidence of polymorphysm of sexual development in Capitella sp B (Polychaeta: Capitellidae) from Barcelona, Spain. Sci. Mar. 66: 103-110. https://doi.org/10.3989/scimar.2002.66n2103 ), both from Barcelona. Our Capitella sp. is probably the same species as that of a field population from disturbed sands (OM <1%) from the Trabucador Beach showing females with brooding tubes and males with modified chaetae, with continuous reproduction over one year studied by Martin and Grémare (1997)Martin D., Grémare A. 1997. Secondary production of Capitella sp. (Polychaeta: Capitellidae) inhabiting different organically enriched environments. Sci. Mar. 61: 99109.. These authors used the width of the fourth thoracic setiger to infer biomass (instead of total body length), which prevented proper comparisons with our Capitella sp. However, compared with the populations from nearby (i.e. less than 3 km away) organically enriched muds, those in disturbed sands showed more stable and less productive populations, as well as much lower biomasses and densities (<0.4 vs. >15 g of dry weight m-2 and <5000 vs 170000. ind m-2, respectively) and smaller individuals (0.2 µg dry weight ind-1 vs. 0.5 µg dry weight ind-1) (Martin and Grémare 1997Martin D., Grémare A. 1997. Secondary production of Capitella sp. (Polychaeta: Capitellidae) inhabiting different organically enriched environments. Sci. Mar. 61: 99109.), which strongly supports not only the key role of OM in structuring the populations but also its influence in their responses at individual level.
During our experiments, the weekly replacement of sediments provided enough food for the two species to feed, as demonstrated during their acclimation and in previous stock cultures of C. teleta (Méndez et al. 2013Méndez N, Lacorte S., Barata C. 2013. Effects of the pharmaceutical fluoxetine in spiked-sediments on feeding activity and growth of the polychaete Capitella teleta. Mar. Environ. Res. 89: 76-82. https://doi.org/10.1016/j.marenvres.2013.05.004 ) and Capitella sp. A (Méndez 2016Méndez N. 2016. Laboratory development of Capitella sp. A (Annelida: Capitellidae) from a NW Mediterranean fish farm reared under different organic enrichment conditions. Sci. Mar. 80: 535-542. https://doi.org/10.3989/scimar.04450.08B ). Also, the sediment in the original stock culture of C. teleta had enough food to feed all worms (OM=3.00±0.21%) (Ramskov et al. 2009Ramskov T., Selk H., Salvito D., Forbes V., 2009. Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I. Environ. Toxicol. Chem. 28: 2695-2705. https://doi.org/10.1897/08-522.1 ), a similar value to that used in their experiments (maximum OM=3%) (Ramskov and Forbes 2008Ramskov T., Forbes V.E. 2008. Life history and population dynamics of the opportunistic polychaete Capitella sp. I in relation to sediment organic matter Mar. Ecol. Prog. Ser. 369: 181-192. https://doi.org/10.3354/meps07584 ).
Capitella teleta and Capitella sp. showed physiological differences in our two treatments, which were reflected in different mortality, growth and development. The species of the C. capitata complex have high physiological and morphological variability, with even sibling offspring from a single female having different responses to identical environment conditions (Qian and Chia 1991Qian P.Y., Chia F.S. 1991. Fecundity and egg size were mediated by quality of diet in the marine polychaete worm, Capitella sp. J. Exp. Mar. Biol. Ecol. 148: 11-25. https://doi.org/10.1016/0022-0981(91)90143-K ). However, in general terms, juveniles and adults of C. teleta survived longer than those of Capitella sp., which agrees with previous observations leading C. teleta to be considered the most tolerant species among the C. capitata complex (Grassle and Grassle 1974Grassle J.F., Grassle, J.P., 1974. Opportunistic life histories and genetic systems in marine polychaetes. J. Mar. Res. 32: 253-284., Tsutsumi 1987Tsutsumi H. 1987. Population dynamics of Capitella capitata (Polychaeta: Capitellidae) in an organically polluted cove. Mar. Ecol. Prog. Ser. 36: 139-149. https://doi.org/10.3354/meps036139 , Forbes et al. 1994Forbes T.L., Forbes V.E., Depledge M.H. 1994. Individual physiological responses to environmental hypoxia and organic enrichment: implications for early soft-bottom community succession. J. Mar. Res. 52: 1081-1100. https://doi.org/10.1357/0022240943076849 ). Its high tolerance to adverse conditions may explain its higher survivorship under NOES than under OES. Its generation time in cultures has been reported to vary, depending on food abundance and temperature, from 20 days (Tenore and Chesney 1985Tenore K.R., Chesney E.J. Jr. 1985. The effects of interaction of rate of food supply and population density on the bioenergetics of the opportunistic polychaete Capitella capitata. Limnol. Oceanogr. 30: 118-1195. https://doi.org/10.4319/lo.1985.30.6.1188 ) to 30 to 40 days (Grassle 1984Grassle J.P. 1984. Speciation in the genus Capitella (Polychaeta, Capitellidae). Fortschr. Zool. 29: 293-298., Whitlatch and Zajac 1985Whitlatch R.B., Zajac R.N. 1985. Biotic interactions among estuarine infaunal opportunistic species. Mar. Ecol. Prog. Ser. 21: 299-311. https://doi.org/10.3354/meps021299 , Tsutsumi et al. 1990Tsutsumi H., Fukunaga S., Fujita N., Sumida M. 1990. Relationship between growth of Capitella sp. and organic enrichment of the sediment. Mar. Ecol. Prog. Ser. 63: 157-162. https://doi.org/10.3354/meps063157 ), and can reach up to 147 days (Linke-Gamenick et al. 2000bLinke-Gamenick I., Forbes V.E., Méndez N. 2000b. Effects of chronic fluoranthene exposure on sibling species of Capitella with different development modes. Mar. Ecol. Prog. Ser. 203: 191-203. https://doi.org/10.3354/meps203191 ), which agrees with the high juvenile and adult survivorship in our treatments.
Capitella teleta (like Capitella sp. I) may be found at low densities in organic-poor sediments, where they only produce small numbers of larvae (Grassle and Grassle 1974Grassle J.F., Grassle, J.P., 1974. Opportunistic life histories and genetic systems in marine polychaetes. J. Mar. Res. 32: 253-284., 1976Grassle J.P., Grassle J.F. 1976. Sibling species in the marine pollution indicator Capitella (Polychaeta). Science 192: 567-569. https://doi.org/10.1126/science.1257794 , Tsutsumi et al. 1990Tsutsumi H., Fukunaga S., Fujita N., Sumida M. 1990. Relationship between growth of Capitella sp. and organic enrichment of the sediment. Mar. Ecol. Prog. Ser. 63: 157-162. https://doi.org/10.3354/meps063157 ); this is in agreement with the scarcity of specimens in the studied field population of Capitella sp., with only 0.51% of OM. The high variability in mortality and growth of Capitella sp. could be attributed to a failure in acclimatizing to laboratory conditions, which may also explain why some worms survived long under NOES, where the organic content was similar to that of their natural habitat. However, the extremely high survivorship shown by two juveniles (164 and 254 days) and one adult (279 days) under OES suggests a higher longevity, comparable to C. capitata (one year lifespan; Warren 1976Warren L.M. 1976. A population study of the polychaete Capitella capitata in Plymouth. Mar. Biol. 38: 209-216. https://doi.org/10.1007/BF00388934 ), C. capitata (nine months lifespan; Lardicci and Ceccherelli 1994Lardicci C., Ceccherelli G. 1994. Dinamica di popolazione di una specie del complesso Capitella capitata in un piccolo bacino salmastro dell’isola d’Elba. Biol. Mar. Medit. 1: 355-356.), Capitella sp. L (one year lifespan; Gamenick and Giere 1994Gamenick I., Giere O. 1994. Population dynamics and ecophysiology of Capitella capitata from North Sea intertidal flats: evidence for two sibling species. Polychaete Res. 16: 44-47.) and Capitella sp. Y, (six months on average, two years and a half of maximum survivorship; Méndez 2006Méndez N. 2006. Life cycle of Capitella sp Y (Polychaeta: Capitellidae) from Estero del Yugo, Mazatlan, Mexico. J. Mar. Biol. Ass. U.K. 86: 263-269. https://doi.org/10.1017/S0025315406013117 ).
Although juvenile and adult growth was highly variable and negative for both species, all juveniles showed higher shrinkage in NOES than in OES, as expected owing to relationships between growth and environmental food availability (Tenore 1977Tenore K.R. 1977. Growth of Capitella capitata cultured in various levels of detritus from different sources. Limnol. Oceanogr. 22: 936-941. https://doi.org/10.4319/lo.1977.22.5.0936 , Tsutsumi et al. 1990Tsutsumi H., Fukunaga S., Fujita N., Sumida M. 1990. Relationship between growth of Capitella sp. and organic enrichment of the sediment. Mar. Ecol. Prog. Ser. 63: 157-162. https://doi.org/10.3354/meps063157 , Linton and Taghun 2000Linton D.L., Taghun G.L. 2000. Feeding, growth, and fecundity of Capitella sp. I in relation to sediment organic concentration. Mar. Ecol. Prog. Ser. 205: 229-240. https://doi.org/10.3354/meps205229 ). Though food content in the experiments proved to be enough to feed adults, the higher size reduction of adults of C. teleta in OES could be attributed either to food quality (Quian and Chia 1991Qian P.Y., Chia F.S. 1991. Fecundity and egg size were mediated by quality of diet in the marine polychaete worm, Capitella sp. J. Exp. Mar. Biol. Ecol. 148: 11-25. https://doi.org/10.1016/0022-0981(91)90143-K , Hu et al. 2003Hu S.I., Horng C.Y., Cheng I.J. 2003. The use of growth and ingestion rates of Capitella sp. I as the bioassay approaches to determine the sediment quality of coastal wetlands of Taiwan. J. Exp. Mar. Biol. Ecol. 297: 179-202. https://doi.org/10.1016/j.jembe.2003.07.009 ) or to investing energy in developing sexual structures rather than growing (Ramskov and Forbes 2008Ramskov T., Forbes V.E. 2008. Life history and population dynamics of the opportunistic polychaete Capitella sp. I in relation to sediment organic matter Mar. Ecol. Prog. Ser. 369: 181-192. https://doi.org/10.3354/meps07584 ).
Our observations confirm the importance of organic enrichment for development and reproduction in the species of the Capitella complex (Grémare et al. 1988Grémare A., Marsh A.G. Tenore K.R. 1988. Short-term reproductive responses of Capitella sp. I (Annelida: Polychaeta) fed on different diets. J. Exp. Mar. Biol. col. 123: 147-162. https://doi.org/10.1016/0022-0981(88)90166-9 , 1989Grémare A., Marsh A.G. Tenore K.R. 1989. Fecundity and energy partitioning in Capitella capitata type I (Annelida: Polychaeta). Mar. Biol. 100: 365-371. https://doi.org/10.1007/BF00391152 , Marsh et al. 1990Marsh A.G., Harvey H. R., Grémare A., Tenore K. R. 1990. Dietary effects on oocyte yolk-composition in Capitella sp. I (Annelida: Polychaeta): fatty acids and sterols. Mar. Biol. 106: 369-374. https://doi.org/10.1007/BF01344314 ), with juveniles of Capitella sp. under NOES not reaching the adult stage, and no adults under NOES developing new sexual structures, while juveniles of Capitella sp. under OES reached the immature adult stage and juveniles and immature adults of C. teleta under OES reached maturity.
The presence of ovaries and genital spines in an individual of C. teleta under OES confirmed its hermaphroditism (Petraitis 1990Petraitis P.S. 1990. Dynamics of sex change in a capitellid polychaete. Lect. Math. Life Sci. 22: 127-154., Blake et al. 2009Blake J.A., Grassle J.P., Eckelbarger K.J. 2009. Capitella teleta, a new species designation for the opportunistic and experimental Capitella sp. I, with a review of the literature for confirmed records. Zoosymposia 2: 25-53. https://doi.org/10.11646/zoosymposia.2.1.6 , Ramskov et al. 2009Ramskov T., Selk H., Salvito D., Forbes V., 2009. Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I. Environ. Toxicol. Chem. 28: 2695-2705. https://doi.org/10.1897/08-522.1 ). Most species of the Capitella complex appear to be only protandrous (having genital spines first and then also white ovaries), while protogyny (having ovaries first and then also genital spines) seems to be rarer (Grassle and Grassle 1977Grassle J.F., Grassle J.P. 1977. Temporal adaptations in sibling species of Capitella. In: Coull B.C. (ed), Ecology of Marine Benthos, University of South Carolina Press, South Carolina, pp. 177-189., Petraitis 1990Petraitis P.S. 1990. Dynamics of sex change in a capitellid polychaete. Lect. Math. Life Sci. 22: 127-154., Ramskov et al. 2009Ramskov T., Selk H., Salvito D., Forbes V., 2009. Individual- and population-level effects of the synthetic musk, HHCB, on the deposit-feeding polychaete, Capitella sp. I. Environ. Toxicol. Chem. 28: 2695-2705. https://doi.org/10.1897/08-522.1 ). However, protogynous specimens appeared when the species was exposed to fluoxetine, a beneficial result as protogyny could be an excellent strategy for ensuring the population survivorship in natural conditions (Méndez et al. 2013Méndez N, Lacorte S., Barata C. 2013. Effects of the pharmaceutical fluoxetine in spiked-sediments on feeding activity and growth of the polychaete Capitella teleta. Mar. Environ. Res. 89: 76-82. https://doi.org/10.1016/j.marenvres.2013.05.004 , Méndez and Barata 2015Méndez N., Barata C. 2015. Effects of the antidepressant fluoxetine in spiked-sediments on developmental and reproductive features of the polychaetes Capitella teleta and Capitella sp A. Ecotoxicology 24: 106-118. https://doi.org/10.1007/s10646-014-1362-z ). However, the fact that one immature female developed genital spines during our experiments suggests that other factors (e.g. type of sediment or artificial food) could also trigger protogyny.
The scarcity of mature males and females and brooding females in the field population of Capitella sp. prevented progeny production and made it impossible to follow the development of the species in the laboratory. Although some juveniles under OES showed yellow ovaries (immature stage), none of them developed white ovaries (mature stage). In some species of the complex, the period of storage of coelomic oocytes in females is minimal when there are mature males in the culture (Eckelbarger and Grassle 1983Eckelbarger K.J., Grassle J.P. 1983. Ultrastructural differences in the eggs and ovarian follicle cells of Capitella (Polychaeta) sibling species. Biol. Bull. 165: 379-393. https://doi.org/10.2307/1541203 ), which could explain the females’ delay in or lack of maturity during our experiments. Knowing the life cycle of Capitella sp. could improve the design and interpretation of experiments testing environmental stress effects at individual and population levels, which would require further future laboratory studies.
Our results confirm the role of sediment organic content in the physiological responses of benthic detritivores, with juvenile and adult survival, growth and development of both C. teleta and Capitella sp. being impaired under NOES. Moreover, juveniles and adults of C. teleta under OES developed sexual structures, including two protandrous and one protogynous individuals. Finally, we suggest that the negative growth rates in worms under OES could be better attributed to food quality or to investing energy in developing sexual structures rather than in growing.