Intertidal Death Assemblages as Proxies of Marine Biodiversity. An Example from Northern Patagonia, Argentina

Abstract

Marine conservation biologists have identified mollusks as one of the appropriate surrogate taxa for characterizing marine benthic diversity. In turn, live/dead comparison studies have overwhelmingly demonstrated that mollusk remains are faithful proxies of the mollusk composition of the living communities from which they come, with positive consequences for the paleoecological evaluation of fossil assemblages. In this contribution, we evaluate the way in which mollusk biodiversity is distributed along the lower intertidal to supratidal (high water mark) dead shell assemblages accumulated on a northern Patagonian rocky shore, in order to explore the usefulness of these assemblages as paleontological proxies and potential surrogates of regional biodiversity . A diversity gradient from the lower intertidal to the supratidal was identified which is probably associated with vertical transport, although the influence of gradients of the living community should be tested to confirm this. The outstanding result of this study is the discovery of high levels of diversity among dead shells (31 bivalves and 39 gastropod species) in a single locality and with a moderate sampling effort. The supratidal death assemblage has higher species richness than expected, possibly caused by stranding of the fauna after storms. Nevertheless, this level shows the lowest level of evenness and a strong bias when samples are not sieved through a fine mesh. The record of marine benthic diversity in death assemblages is a promising area of research that deserves to be explored in depth.