Visual Observations of Particle Manipulation During Feeding in Larvae of a Bivalve Mollusc
Abstract:Suspension-feeding in various larval stages of the bivalve Mercenaria mercenaria (Linne) was observed and characterized using high speed video microscopy (60–240 images·s−1). Larvae were tethered in a micro flow-through chamber and exposed to varying prey type (Isochrysis aff. galbana, TISO and Synechococcus spp., SYN) and concentration (102 to 106 cells·ml−1). Feeding appeared to consist of a series of distinct, independent steps: (1) capture of a cell by the pre- and post-oral cirri of the velum, (2) transport to the mouth by the food groove, (3) concentration of cells into a bolus at the mouth, (4) selection or rejection of cells for entry into the esophagus and, (5) activation of a ciliated sphincter either to allow a cell to enter the stomach or to reject it from the esophagus. Probabilities of steps one and two appeared to be a function of the encounter rate with cells in the medium as both prey types were captured and transported to the mouth with equal efficiency. However, steps three, four and five were related to particle characteristics and the degree of gut satiation. Ingestion rate of Isochrysis cells was proportional to the encounter rate between concentrations of 102 and 103 cells·ml−1, but declined to an incipient level specific to larval size at cell concentrations above 104 cells·ml−1. The rate of cell rejection increased with increasing concentration and was inversely proportional to ingestion rate above 103 cells·ml.−1 Both the water flow through the velum per unit velar edge and clearance rate per unit edge increased by a factor of two between 2 and 10 days of development. Ten-day-old larvae with empty guts were exposed to a constant concentration of Isochrysis cells. Ingestion was high for the first 6 min (93 cells·min−1) and proportional to the rate of capture and transport to the mouth, but then fell to 4.3 cells·min−1 within 9 min of initial exposure. A total of 635 cells were ingested before rejection exceeded ingestion rate after 9 min of feeding.
Document Type: Research Article
Publication date: 1988-11-01
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