Ökologische Untersuchungen an Hydroiden des Felslitorals von Santa Marta (Kolumbien)

Abstract

The ecology of tropic hydroids on the rocky shore of Santa Marta, Colombia, was studied from January 1971 to April 1972. Main interests concentrated on vertical distribution, temporal succession, activity, maturity, population density, shape and growth of colonies, and on type of settlement. These aspects have been related to quantitative data and to variations in biotic and abiotic factors. The results are compared with those obtained on other types of shores, viz. artificial and sandy shores. They indicate that local abiotic differences in water quality are influenced, above all, by the sequence of dry and rainy seasons. In a rapidly changing abiotic environment, life cycles and ontogenetic stages (settlement, growth, maturity) follow each other faster than in a static environment. With increasing water depth, the density of the hydroid populations decreases, while the size of single colonies increases. In addition, with increasing depth, the length of the maturity period increases. For the same species, the time of attainment of maturity may be different in different localities. Hydroid species with short life cycles settle faster than species with long life cycles. Hydroid polyps may counteract environmental perturbations by changes in activity. Distribution and zonation of hydroid populations depend to a high degree on water movement, sun orbit, and shade-spending coastal profiles. © 1975 Biologischen Anstalt Helgoland.