Molecular and Morphological Characterization of Two Species of Sea Cucumber, Parastichopus parvimensis and Parastichopus californicus, in Monterey, CA

Parastichopus parvimensis and P. californicus, two ecologicallysimilar species of sea cucumber, are the only sea cucumber fisheries in California.1 Aside from the economic importance that this distinction affords them, the two also play an important ecological role as subtidal, benthic detritivores.1, 2 Though some ecological distinctions between the two species exist – P. californicus, notably, can be found at greater depths (to 150 m) than P. parvimensis (to 20 m) (A. Haupt personal communication) – the ostensible similarities between them raise questions concerning the dual management of their two fisheries3. Cursory phylogenetic surveys have shown the two to be closely related (4), but the genetic and morphological similarities between P. parvimensis and P. californicus have yet to be studied in depth. Historically, sea cucumbers cucumber species’ ossicle characteristics are used as distinguishing characteristics for taxonomic differentiation. Ossicles are calcareous structures embedded in sea cucumbers’ body wall tissue.2 They are the miniscule remnants of ancestral species’ skeletal material. More importantly, each species has uniquely patterned ossicles, and it’s these patterns that scientists have often used as key identifying features when defining sea cucumber taxonomy. In the case of the externally similar P. parvimensis and P. californicus, ossicle characterization becomes particularly important for species identification; ossicle descriptions have been published for P. californicus but have not yet been described for P. parvimensis.2 In this study I use molecular as well as the ossicle-based, traditional morphological techniques to investigate the delineation between P. parvimensis and P. californicus. Molecular techniques have outstripped morphological techniques in quantifying how distinct two species are, and can be used to investigate the extent to which two species share genes. This study supplements molecular with morphological techniques in order to establish a knowledge base concerning in what ways P. parvimensis and P. californicus differ: ossicle identification guides can provide a simple means of telling two ostensibly similar species apart. California’s sea cucumber fisheries have seen population effects due to fishing since the 1980s and their management is ongoing.1,5 That management can be refined by garnering more sophisticated information about how and to what extent two species differ – in particular, biodiversity conservation strategy and marine reserve design both benefit from natural history studies.6 13 Investigating species diversity contributes to the scientific knowledge base that policymakers and marine managers draw from.