REGIONAL-SCALE COMPOSITIONAL AND SIZE FIDELITY OF ROCKY INTERTIDAL COMMUNITIES FROM THE PATAGONIAN ATLANTIC COAST

Fernando M Archuby,Gabriela M Boretto,Julieta C Martinelli,Sandra Gordillo,Mariana Adami,Mariano E Malvé

doi:10.2110/palo.2014.054

Abstract

The use of rocky intertidal assemblages in paleoecology and conservation paleobiology studies is limited because these environments have low preservation potential. Here, we evaluate the fidelity between living intertidal mussel bed communities (life assemblages or LAs) and mollusk shell accumulations (death assemblages or DAs) from the environmentally harsh Patagonian Atlantic Coast. LAs were sampled from rocky mid-intertidal and mussel-dominated habitats while DAs were collected from the high water mark at beaches in close proximity to the living intertidal community to assess live-dead mismatch at regional scales. DAs were restricted to the subset of species in the DAs that inhabit rocky intertidal habitats. A total of 37,193 mollusk specimens from 15 intertidal species were included in the analysis. Ten species were present in LAs, 14 in DAs, and nine were shared by LAs and DAs. DAs showed higher diversity, less dominance, and more rare species than LAs. Despite finding good agreement in species composition between DAs and LAs within the same region, smaller species are underrepresented, as shown by differences in size-frequency distributions. Our findings indicate that the composition of DAs is a result of the combined effects of spatial and temporal averaging, size-related biases, and biases related to low detectability of boring and vagile species in LAs. Thus, DAs do not accurately detect within-provincial latitudinal gradients in composition. However, DAs clearly capture differences between the Argentine-Magellanic Transition Zone and the Magellanic Province, indicating that DAs are informative tools at regional scales despite the environmental harshness to which they are subjected.

Highlights

The degree of fidelity between living communities and their fossil counterparts constrains the usefulness of preserved assemblages to reconstruct past ecosystems
Death assemblages consist of a mix of intertidal and subtidal species inhabiting soft and hard substrates, caused by the mosaic distribution of rocky, muddy, and sandy substrates along the sampling area
FIG. 3.—Pie charts with details of the distribution of abundance and species richness of death assemblages for data pooled across samples

Summary

Introduction

The degree of fidelity between living communities and their fossil counterparts constrains the usefulness of preserved assemblages to reconstruct past ecosystems. The dissimilarities between LAs and DAs in marine soft-bottom environments can be largely explained by the effect of time averaging and probably less by taphonomic biases (Tomasovych and Kidwell 2009, 2010, 2011; Kidwell and Tomasovych 2013). This finding has been established in several other contributions both from terrestrial and marine ecosystems (Kidwell and Tomasovych 2013 and references therein). A conservative estimation of the effects of time averaging on DAs indicates that in a few decades to centuries, alpha diversity increases and beta diversity decreases at small spatial scales, species dominance is reduced, and rare species become more common (i.e., rank abundance distributions become flatter) (Tomasovych and Kidwell 2010)

Methods

Results

Discussion

Conclusion