Scientia Marina, Vol 64, No S1 (2000)

Photosynthetic planulae and planktonic hydroids: contrasting strategies of propagule survival


https://doi.org/10.3989/scimar.2000.64s1173

Patrizia Pagliara
Dipartimento di Biologia, Stazione di Biologia Marina, Museo dell’Ambiente, Università di Lecce, Italy

Jean Bouillon
Laboratoire de Biologie Marine, Université Libre de Bruxelles, Belgium

Ferdinando Boero
Dipartimento di Biologia, Stazione di Biologia Marina, Museo dell’Ambiente, Università di Lecce, Italy

Abstract


Settlement delays can be important to prevent propagule waste when proper settling substrates are not immediately available. Under laboratory conditions, the planulae of Clytia viridicans underwent two alternative developmental patterns. Some settled on the bottom, forming a hydranth-gonotheca complex that produced up to four medusae and later either degenerated or gave rise to a hydroid colony. Other planulae settled right below the air-water interface, forming floating colonies that eventually fell to the bottom and settled. Halecium nanum released planulae with a rich population of symbiotic zooxanthellae that survived into a rearing jar for three months. After a long period of apparent quiescence (possibly fuelled by photosynthetic activities of zooxanthellae) the planulae produced new colonies. Both photosynthetic planulae and settlement at the interface air-water allow a delay in the passage from a planktonic to a fully functional benthic life.

Keywords


Hydrozoa; life cycle; planula; floating hydroid; Zooxanthellae; dispersal

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