The effect of changes in quantity and quality of food on the feeding behaviour of the soft-shelled clam, Mya arenaria, using a new technique to determine gut retention time

Scarratt, Alison Margaret (1994) The effect of changes in quantity and quality of food on the feeding behaviour of the soft-shelled clam, Mya arenaria, using a new technique to determine gut retention time. Masters thesis, Memorial University of Newfoundland.

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Abstract

This study investigates the effect of changes in the quantity and quality of food on the feeding behaviour of Mya arenaria, the soft-shelled clam. M. arenaria is a suspension- feeding bivalve, ingesting particles suspended in the water column. The laboratory component of this study presented M. arenaria with an artificial diet, consisting of silicon dioxide (SiO2) particles and the single-celled diatom Chaetoceros muelleri, for inorganic and organic components respectively. These feeding experiments were performed using a flow-through apparatus. This included measurements of clearance and ingestion rates, absorption efficiencies, and gut retention times of both organic and inorganic fractions. -- In response to a 3-fold increase in food concentration, M. arenaria decreased clearance rale by almost 9-fold, and therefore ingested less material, even though more food was available. These clams with lower ingestion rate also had a shorter gut retention time, and thus a smaller amount of material in the gut. It is possible that clams feeding on the low quantity diet were expending more energy in obtaining particles (higher ingestion rate despite lower food concentrations) but perhaps less energy in digesting them (clams feeding on the low quantity diet had an absoiption efficiency equal to those feeding on the 10 mg diet, but over a longer gut retention time. If the net energy gained in the digestive process (i.e. lower amounts of enzymes working over a longer time) was greater than that expended in filtering, this would be an effective feeding strategy for clams to adopt when experiencing low quantities of food. -- In response to an increase in the quality of the food (proportion of organic material increases), clams decreased clearance rate and ingestion rate, to maintain a constant ingestion rate of organic material. Although gut retention time lengthened, absorption efficiency remained unchanged. Therefore, clams regulated both their intake of food and gut retention time to keep their ingestion rate of organic material constant, and to maintain absorption efficiency levels. -- This study also measured the clearance rate, ingestion rate, gut retention time and absorption efficiency of A/, arenaria feeding on natural particle assemblages at a clam flat in Platter's Cou\ Terra Nova National Park, NF. Clearance rates were significantly higher than any measured in the laboratory study. Field measurements of gut retention time were comparable to those measured in the laboratory study, however, field measurements of absorption efficiency were strongly negative, indicating possible metabolic faecal loss or periodicity of digestion in the intertidal population. -- This study also describes the development and use of a new technique to assess the gut retention time of suspension-feeding bivalves, lite green alga Tetraselmis suvcka was used as an organic marker, detectable in faecal pellets by high performance liquid chromatography because of its characteristic chlorophyll b signature. The inorganic marker used was silicon carbide particles which can be detected in faecal pellets by particle size analysis using a Coulter Multisizcr. Results obtained by this method are comparable to those of other studies, and the technique is sensitive enough to detect post-ingestive selection of particles within the gut of individual clams.

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