Physiological and biochemical energetics of larvae of Teredo navalis L. and Bankia gouldi (Bartsch) (Bivalvia : Teredinidae)

Abstract

The biochemical composition of larvae of Teredo navalis L. and Bankia gouldi (Bartsch) (Bivalvia: Teredinidae) was examined throughout larval development at 23°C and 30–32%. salinity in the presence of the phytoplankton food Isochrysis aff. galbana (clone T-ISO), during a delay of metamorphosis in the presence of food but absence of a wood substratum and during periods of enforced starvation. Newly released Teredo navalis larvae had a mean length ( L) and height ( H) of 89.3 and 76.1 μm respectively. The first appearance of pediveliger larvae at 212.1 μm L and 230.0 μm H occurred 27 days after release. Larval dry weight increased from 0.29 μg to 1.96 μg during this period. Newly formed straight hinge larvae of Bankia gouldi had dimensions of 62.8 μm L and 49.8 μm H. Metamorphically competent B. gouldi larvae had dimensions of 230.0 μm L and 282.9 μm H and were first observed 20 days after fertilization. Larval dry weight increased from 0.06 μg to 2.20 μg during this period. During enforced delay of metamorphosis the ash-free dry weight of Teredo navalis larvae decreased whereas the ash free dry weight of Bankia gouldi larvae increased. During the early period of shelled larval development both species showed similar decreases in lipid, protein and carbohydrate levels (μg·mg dry weight −1); however, this was reflected in a decrease in biochemical content (μg·larva −1) only in Teredo navalis. During enforced starvation the major proportion of both the weight and caloric losses were due to protein. Lipid also contributes significantly to these losses whereas the contribution of carbohydrate was small. Larval oxygen consumption rates were determined directly by manometry and indirectly by estimates of decrease in caloric content during periods of enforced starvation. Direct and indirect determinations for T. navalis are described by the relationships R = 1.16 W 1.05 and R = 0.98 W 1.24 respectively where R is the respiration rate in nl O 2 · larva −1 · h −1 and W is dry weight inclusive of shell in μg. Direct and indirect determinations for Bankia gouldi are described by the relationships R = 1.37 W 1.25 and R = 1.81 W 1.25 respectively. When data for both assay procedures are combined for each species the relationships R = 1.10 W 1.07 and R = 1.44 W 1.18 are obtained for Teredo navalis and Bankia gouldi respectively.