GROWTH, FECUNDITY AND MORTALITY-RATES OF 2 INTERTIDAL BRITTLESTARS (ECHINODERMATA, OPHIUROIDEA) WITH CONTRASTING MODES OF DEVELOPMENT

Theories of life history evolution hypothesize an inverse relationship between recruitment predictability and longevity. It also has been pr oposed that marine species with direct development should have more pr edictable recruitment than species with planktotrophic larvae; consequ ently, brooders should be shorter-lived than broadcasters. This hypoth esis was tested in a field study at False Point, San Diego, California , using two brittlestar species with similar sizes but with contrastin g modes of development. Ophionereis annulata (Le Conte) produces plank tonic larvae whereas Ophioplocus esmarki Lyman is a brooder. Growth ra tes, over a period of 1 yr, were determined in the field using calcein , a fluorescent marker of calcification sites in skeletons. Ossicles m arked with calcein were used to establish initial and final sizes that were used to estimate parameters of the Brody-Bertalanffy equation fo r disc diameter growth: for Ophionereis annulata, K = 0.075 . yr(-1) a nd S-infinity = 20.0 mm; for Ophioplocus esmarki, K = 0.069 . yr(-1) a nd S, = 19.4 mm. Mortality rates were estimated using growth parameter s and mean disc diameter in field samples. Annual survival rate was 90 % for Ophionereis annulata (the broadcaster) and 95% for Ophioplocus e smarki (the brooder), which is opposite of expectation. We conclude th at brooding does not necessarily confer an advantage that is evident b y shorter adult life spans and, indeed brooding may pose a liability w ith respect to fitness.