Distribution, growth rate, and death from octopod and gastropod predation ofTawera bollonsi(Bivalvia: Veneridae) at the Auckland Islands

Abstract

Abstract Tawera bollonsi, originally described from five valves whose colour suggested their derivation from a comparatively late fossiliferous deposit, is a common bivalve living at the Auckland Islands. Discoloration occurs during life and not after death. Its shell is more inflated than in any other Tawera species. It lives in mud, sandy mud, and fine sand in the inlets and harbours, often with the crustaceans Callianassa filholi and Heterosquilla tricarinata and the bivalve Chione aucklandica. The size frequency of both living specimens and valves is bimodal. For the living specimens the main peak is at 6–8 mm, with a secondary peak at 38–40 mm. The main peak for valves is at 25–37 mm with a secondary peak at 5 mm. Growth rate is very variable and may be genetically determined. Predation rates for both octopus and gastropod predation varied considerably but, with one exception, were less than 20%. Octopus predation, not previously been reported from waters as cold as the subantarctic Auckland Islands, is a more common cause of death than gastropod predation.