Physiological ecology of Adalaria proxima (Alder et Hancock) and Onchidoris muricata (Müller) (Gastropoda: Nudibranchia). I. Freeding, growth, and respiration

Abstract

The nudibranch molluscs Adalaria proxima (Alder et Hancock) and Onchidoris muricata (Müller) are annual, semelparous, simultaneous hermaphrodites which are largely sympatric and preferentially graze the same bryozoan Electro pilosa (L.). Ecologically, morphologically, and taxonomically, these species are similar, however, they reproduce by means of contrasting larval types: O. muricata has long-term planktotrophic larvae and A. proxima has short-term pelagic lecithotrophic larvae. The present paper is the first of a series which aims to analyse these contrasting larval types within the context of detailed dynamic energy budgets. Here we present data on the rates of feeding, prespawning growth, and respiration for laboratoryheld “populations” of both species. Nudibranchs were collected from the field as juveniles and maintained at near-ambient (not constant) temperatures. For both O. muricata and A. proximo feeding rate displayed an asymptotic increase with body size. Both the observed mean and (fitted) estimates of feeding rates for A. proxima exceeded those for comparable-sized O. muricata. Correspondingly, A. proxima individuals demonstrated greater somatic growth rates, and attained greater maximum body sizes than did O. muricata. Furthermore, growth of A. proxima was approximately linear whilst that of O. muricata followed an increasing curvilinear pattern. Respiration rates were relatively constant within any given individual, however significant differences between individuals were observed for both species. O. muricata individuals displayed a more rapid increase in respiratory rate with increasing body size than did A. proxima. Respiration rates of either species were not significantly affected by (seasonal) flucuations in water temperatures, with the exception of A. proxima individuals during the spawning period.