Associations between hydroid species and their substrates from the intertidal zone of Mar del Plata (Argentine)

Abstract

Colonial organisms, including many species of Hydrozoa, typically have short life cycles and rapid growth. Moreover, they are often found attached to other organisms. The associations between ten hydroid species, Clytia gracilis (Sars, 1851), Obelia longissima (Pallas, 1766), Halecium beanii (Johnston, 1838), Halecium delicatulum Coughtrey, 1876, Sertularella mediterranea Hartlaub, 1901, Plumularia setacea (Linnaeus, 1758), Tubularia crocea (Agassiz, 1862). Sarsia sarsii (Loven, 1836), Bimeria vestita Wright, 1859 and Rhizogeton nudum Broch, 1909, and their substrata, from the rocky intertidal zone at Mar del Plata, Argentine, were studied between March 1990 and February 1992. Sarsia sarsii and T. crocea (Anthothecata) and P. setacea (Leptothecata) were the most frequent epibiotic species. Two principal groups of hydroids were found, those that grew on other hydropolyps and those that grew predominantly on Mollusca (bivalves). The rnost irnportant substrates were Mollusca (48.7%) and Hydrozoa (24.4%); less frequent substrates included Tunicata, rocks, algae, and sponges. In auturnn, the predominant substrate changed frorn Mollusca to hydroids.