Architectural vs. biological effects of a habitat-altering, exotic mussel, Musculista senhousia

Abstract

Musculista senhousia Benson in Cantor is a small mytilid mussel that has been introduced from Asia onto three continents, including the Pacific coast of North America. The mussel often forms dense mats that can increase infaunal density and species richness. This research experimentally examines the relationship between the physical structure of the mussel mat habitat and the biological activities of the mussel as it relates to the macrofaunal assemblages in Mission Bay, San Diego, California, USA. The results of this experiment demonstrate that the effects of physical structure consistently outweigh the effects of living mussels. Total macrofaunal densities, species richness, and densities of a variety of taxa (e.g. the snail Barleeia subtenuis Carpenter, nemerteans, and amphipods) were enhanced by the presence of the artificial mats. The tube-building, planktonically-developing polychaete , Pseudopolydora paucibranchiata Okuda, however, was apparently inhibited by mats, as were planktonic developers as a group. The effects of structure provided by mussel shells themselves appeared to be weaker than the mat effects, although some taxa, such as the gastropod B. subtenuis , responded to shells alone. The influences of living mussels also were less pronounced than that of artificial mats, although non-planktonic developers, including midge larvae and the tanaid Leptochelia dubia Kroger, showed positive responses to live mussels. In general, these results are consistent with observed effects of other habitat-creating exotics, and suggest that facilitation of biota by non-native species capable of creating physical complexity in ecosystems may be a major and predictable consequence of biological invasions.