Seasonality and reproductive periods of the hydroid Clytia gracilis in temperate littoral ecosystems. Is asexual reproduction the prime mechanism in maintaining populations?

JAUBET L.; GENZANO G. N.

MARINE BIOLOGY RESEARCH

TAYLOR & FRANCIS AS

Año: 2011 vol. 7 p. 804 - 811

1745-1000

Hydropolyps inhabiting temperate ecosystems exhibit marked seasonality, and undergo regression as a normal part of their life cycle. In the campanulariid species Clytia gracilis, both hydroids and medusae are decidedly seasonal in occurrence.Epizoic colonies of C. gracilis, growing on colonies of Ectopleura crocea, were collected monthly in the intertidal zone at Mar del Plata, Argentina (38808?S57837?W) during low tide from February 2000 to January 2001. Abundance, seasonality and reproductive periods were analysed. The hydroid reached peak abundance during the summer, yet reproductive structureswere scarce and observed in only a few colonies. A remarkable regression period was evident in the cold season. During that period, hydroids of the species had few functional polyps, and the colonies were largely reduced to dormant tissue in the coenosarc of hydrocauli and stolons. Hydranths of C. gracilis regenerated during summer and produced a profuse asexual growth by stolonization. Asexual propagation is proposed as the prime mechanism in maintaining these hydroidpopulations. In comparisons of intertidal and subtidal populations of C. gracilis, available hydroid colonies ofAmphisbetia operculata and Plumularia setacea collected from neighboring rocky outcrops (38810?S57830?W), at depthsof 1820 m, during both warm and cold seasons were analysed. As in the intertidal populations, these colonies showedmarked stolonal growth at the end of summer.