Problems in Studying Nitrogen Cycling through Filter-Feeding Bivalve and Phytoplankton : A Review

Abstract

This article reviews recent studies on filtration and ammonium excretion rates of filter-feeding bivalves. Many of the studies emphasized the controlling role of filter-feeding bivalves in material cycling between the water column and the sediments. However, the application of metabolic rates measured in vitro to in situ nitrogen cycling includes some problems. For example, measurements of metabolic rate without sediments cause an artificial stress on infaunal bivalves. Concentration of suspended materials also affects the rates of filtration and ammonium excretion of filter-feeding bivalves. Constructing a desirable apparatus for measuring bivalve metabolism therefore requires considerable effort to simulate in situ environment. From this point of view, batch type experiments are not suitable because they require a measurable change in concentration of the objectives in a closed system, which usually induces artificial stress on bivalves. Continuous incubation technique in an open system is presumed to create less stress, and it also enables the repeated measurement with same animal. Another problem in recent works is that they mostly concentrated on the effect of bivalves on either taking up or supplying nutrients to Phytoplankton. Since both effects take place simultaneously, studies must pay attention the concomitant analysis of both effects in the natural environment.