Cascading top-down effects on estuarine intertidal meiofaunal and algal assemblages

ALVAREZ F.; ESQUIUS, K.S.; ADDINO, M.; ALBERTI, J.; IRIBARNE O.; BOTTO, F.

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2013 vol. 440 p. 216 - 224

0022-0981

Interactions between organisms are important determinants of species distributions and abundances. Due to thehigh complexity of interactions between species in natural systems, the outcome of a given interaction can affectothers, finally modifying community composition. In South-Western Atlantic intertidal mudflats, the zonation ofthe burrowing crab Neohelice (Chasmagnathus) granulata and the intertidal snail Heleobia australis rarely overlaps,suggesting that both speciesmight have negative interactions; and, given that both species have different foragingstrategies, these negative interactions can have top-down impacts on community composition. Zonation patternsof both species showed that snails are more abundant in areas without crab burrows, and field experiments revealedthat snail density correlated with a reduction in crab density and that when crabs were excluded, snailswere able to colonize those higher intertidal areas. Bioturbation and not competition seems to drive that pattern,given that crabs have no effects onmicroalgae, but negatively affect infaunal organisms such as copepods, flagellates,nauplli larvae and snails. Conversely, snails negatively affect algal assemblages, specifically cyanobacteria,chlorophytes, and euglenophytes, although diatoms, the most abundant group, was not modified. Our resultsshow that crab–snail competition disrupts snail herbivory upon microalgae by limiting the area over whichalgal consumption occurs and highlight the complex web of interactions that frequently regulates communitystructure in natural systems.