Growth, fecundity and mortality rates of two intertidal brittlestars (Echinodermata: Ophiuroidea) with contrasting modes of development

Abstract

Theories of life history evolution hypothesize an inverse relationship between recruitment predictability and longevity. It also has been proposed that marine species with direct development should have more predictable recruitment than species with planktotrophic larvae; consequently, brooders should be shorter-lived than broadcasters. This hypothesis was tested in a field study at False Point, San Diego, California, using two brittlestar species with similar sizes but with contrasting modes of development. Ophionereis annulata (Le Conte) produces planktonic larvae whereas Ophioplocus esmarki Lyman is a brooder. Growth rates, over a period of 1 yr, were determined in the field using calcein, a fluorescent marker of calcification sites in skeletons. Ossicles marked with calcein were used to establish initial and final sizes that were used to estimate parameters of the Brody-Bertalanffy equation for disc diameter growth: for Ophionereis annulata, K = 0.075 · yr −1 and S ∞ = 20.0 mm; for Ophioplocus esmarki, K = 0.069 · yr −1 and S ∞ = 19.4 mm. Mortality rates were estimated using growth parameters and mean disc diameter in field samples. Annual survival rate was 90% for Ophionereis annulata (the broadcaster) and 95% for Ophioplocus esmarki (the brooder), which is opposite of expectation. We conclude that brooding does not necessarily confer an advantage that is evident by shorter adult life spans and, indeed brooding may pose a liability with respect to fitness.