ECOSYSTEM ENGINEERING BY BIOTURBATING POLYCHAETES IN EVENT BED MICROCOSMS

Modification of event beds by the burrowing nereidid polychaete Alitta virens (Sars) was examined using laboratory microcosms, to assess its importance as an ecosystem engineer in pristine sediments. In all microcosms, the nereidids modified their environment to permit long-term occupation, but different behavioral strategies and burrow morphologies were observed based on sediment characteristics and nutrient availability. Alitta virens utilized scavenging, surface deposit feeding, suspension feeding, microbial gardening, deposit feeding at depth, and cannibalism. Suspension feeding using mucus nets is used by many nereidids but has not been documented previously in A. virens; extended use of the technique may indicate low availability of biotic sediments for deposit feeding. Alitta virens typically produced burrows similar to Arenieolites and Skolithos, but morphologies resembling Polykladichnus, Planolites, Palaeophycus, and Thalassinoides were formed under differing sedimentary conditions and over different time scales. In the rock record, such ichnological diversity might be interpreted as indicating paleoecological diversity, rather than the response of one taxon to changing conditions. Alitta virens is an allogenic ecosystem engineer, its behavior changing the physical and geochemical characters of its environment. These changes, combined with the widespread occurrence and population longevity of A. virens, demonstrate that burrowing polychaetes are important ecosystem engineers in shallow marine environments, and are likely to have been so over geological time scales.