Combined engineering effects of clams and crabs on infaunal assemblages and food availability in intertidal systems

FERNANDA ALVAREZ; MARIANA ADDINO; OSCAR IRIBARNE; FLORENCIA BOTTO

MARINE ECOLOGY PROGRESS SERIES

INTER-RESEARCH

Lugar: Oldendorf/Luhe; Año: 2015

0171-8630

ABSTRACT: In softsediments, ecosystem engineers (EEs) may play key roles in modifying habitats andtherefore affecting bottom-assemblage species. In the southwestern Atlantic mudflats, 2 EEs coexist: the stout razor clam Tagelus plebeius andthe burrowing crab Neohelice (Chasmagnathus) granulata.Clams create small depressions (i.e. millimeters), while crabs build large burrows(i.e. centimeters) generating crab beds covering many hectares. We hypothesizedthatthese differences in the bioturbation scale may have different consequencesfor infaunal assemblages. We found that (1) microscale sediment-surfaceheterogeneities created by clams (e.g.holes and surrounding depressions) were relatedto higher organic-matter content and micro -phytobenthic biomass (measured aschlorophyll a), (2)abundances of meiofaunal groups (copepods,ostracods, and nematodes) were higherin clam holes than outside at all tidal levels, and (3)habitats with a moreheterogeneous structure?such as clam holes inside a crab bed?had a higher foodavailability and an abundance of several meiofaunal groups (e.g. ostracods, andprincipally nematodes). Large-scale bioturbation (crab-bed formation) alsoaffected primary producers, infaunal assemblages, and clam distribution,because at the highest intertidal levels clams were absent outside the crabbeds. Our results thus demonstrate the differential effects of 2 contrasting EEson the organization of soft-bottom communities and the key role ofmicroheterogeneities in adding specific structures to already modified systemson a larger scale.