Variable recruitment and changing environments create a fluctuating resource: The biology of Anadara Uropigimelana (Bivalvia: Arcidae) on Tarawa atoll

Abstract

The arcid bivalve Anadara uropigimelana (te bun) is the most important shellfish resource in the central atolls of Tungaru (former Gilbert Islands), with a yearly catch of ca. 1400 tons on South Tarawa alone. Species of Anadara s.s. are also important in artisanal shellfisheries on several central Pacific islands. Tungaru atolls lying in the highly productive zone of equatorial upwelling harbor dense te bun beds, while those occurring outside this zone have fewer Anadara. Te bun are abundant in seagrass beds, lagoonal shoals, and shallow-lagoon bottoms. They reproduce year round with a lunar spawning periodicity. Size frequency data and observations on the occurrence of small juveniles indicate that, despite frequent reproduction, there is high spatio-temporal variation in recruitment within the Tarawa lagoon. One massive recruitment event in 1993 opened a novel fishery in Bonriki village, where no te bun were available for two decades previously. Highly variable recruitment, as well as changes in the extent of seagrass habitats, may explain marked historical fluctuations in the abundance of this important resource.