POLYCHAETES AS ENVIRONMENTAL INDICATORS: RESPONSE TO LOW OXYGEN AND ORGANIC ENRICHMENT
Levin, L. A.
Marine Life Research Group, Scripps Institution of Oceanography, La Jolla, CA 92093-0218, USA
Strong gradients in organic enrichment and in oxygen availability occur throughout the world's oceans. These gradients occur naturally, for example along continental margins exposed to persistent or seasonal hypoxic waters, but are also generated by anthropogenic activities such as aquaculture or sewage disposal. Polychaetes are among the marine organisms most tolerant to stress associated with organic loading and low oxygen, and are often used as environmental indicators. This presentation will examine polychaete responses to organic matter and oxygen gradients at the population and community level, and will compare these responses in deep- and shallow-water systems. In North America, genera such as Capitella, Mediomastus, Streblospio and Prionospio inhabit enriched areas in shallow water. The tolerances of these taxa to hypoxia and the extent to which sulfides are toxic (versus beneficial) probably explain their relative dominance patterns in different places. In organophilic species, population-level responses to enrichment can include changes in abundance, reproductive parameters, maturation time, body size and population growth rate. Shifts in polychaete community structure along organic matter and oxygen gradients have been recognized in shallow water for several decades. These will be reviewed and compared to patterns of polychaete abundance, biomass, dominance and species richness at deep-water sites associated with oxygen minimum zones in the Arabian Sea and eastern Pacific Ocean and with enrichment in the NW Atlantic. Because oxygen and organic-matter availability often vary inversely, their effects are difficult to separate. Multiple regression analyses of environmental parameters on polychaete diversity data lead to the hypothesis that low oxygen influences primarily patterns of species presence (richness), while organic enrichment most affects dominance and evenness measures. Other topics to be addressed in this presentation include shifts in polychaete dwelling and feeding modes that occur along oxygen and organic-matter gradients, and whether these are consistent in shallow vs deep water.