Freshwater Ostracoda from Tarawa, Kiribati: their implications for dispersal mechanisms

Abstract. Tarawa Atoll, Gilbert Islands (1° 30′N, 173° 00′E) is an isolated place, comparatively recently emergent – 2500 years bp and 2 – 3 m above present sea-level (Marshall & Jacobson, 1985). During the course of a study of the marine ostracods (Eagar, in press) it was noted that there are relatively few places where freshwater is visible on the surface of the atoll. This is not unusual, given the low precipitation (154 mm a⁻¹) and the daytime temperatures of Tarawa (27–30°C). Five freshwater ponds on South Tarawa (Fig. 1) were examined and two species of Ostracoda were found: Cyprinotus cingalensis Brady, 1886 and Limnocythere notodonta Vávra, 1906. At Bairiki (locality A), a pond adjacent to the causeway linking Bairiki with Betio was sampled and yielded abundant Cyprinotus cingalensis. Other ponds were found at Ambo (Locality B) and Temaiku Bight (Localities C and D with two ponds). Only the pond (Locality B), an established babai pit (taro; Cyrtosperma chamissonis), adjacent to the roadside at Ambo yielded further specimens of the ostracod Limnocythere notodonta, although in low numbers.

The question of how these species were introduced onto Tarawa Atoll is intriguing. C. cingalensis is known from Ceylon (Brady, 1886), Hawaii and the Sandwich Islands. The record by Vávra (1906) from Australia may be incorrect. Limnocythere notodonta was previously recorded only from Java (Vávra, 1906). Both species may have been distributed in the same way that Sars (e.g., Sars, 1896) transported species from different parts of the world to Norway to describe . . .