Summer metabolism and seasonal changes in biochemical composition of the Antarctic brachiopod Liothyrella uva (Broderip, 1833)

Oxygen consumption and ammonia excretion were measured in Liothyrella uva (Broderip, 1833) held in the laboratory under simulated summer conditions. The mean oxygen consumption of a 50 mg AFDW brachiopod was 0.205 μg-at. O · h ^?1 while the ammonia excreted was 0.022 μg-at. NH₃-N · h ^?1. The exponents of the regressions relating these parameters to AFDW were not significantly different from each other and the common slope was 0.83. The rise in metabolism over previously published winter levels was 15–20%. The difference between simulated summer and winter conditions was the presence or absence of food. The rise in metabolism was seen in both oxygen consumption and ammonia excretion whilst the oxygen to nitrogen ratio remained virtually unchanged at 9.2 (9.3 in winter), showing that, as in winter conditions, protein was the main metabolic substrate. Oxygen consumption rates were around five times lower than those of temperate brachiopods, even after applying a Q₁₀ temperature correction, and they were two to seven times lower than Antarctic bivalve and gastropod molluscs. An investigation of the biochemical components of field specimens showed strong seasonal variation in protein and carbohydrate, although carbohydrate levels were only as ≈5–10% of protein contents at any one time. There was no significant seasonal variation in lipids, although there was some evidence to suggest that they may be involved, with protein, in the gametogenic cycle. Shell tissues (the caeca) were identified as a site of nutrient storage and may be implicated in short-term storage of material for reproduction as well as the long-term storage of overwintering energy reserves.