Asymmetrical distribution of Distichopora violacea (Cnidaria: Hydrozoa) in four Maldivian atolls

Description

Stylasterids belong to one of the few calcifying hydroid families that are commonly found in shallow tropical coral reefs. Although these corals are accurately described from a taxonomic point of view, information about their ecology is scarce. Distichopora violacea is one of the most common stylasterids of the Indo-Pacific region; however, no information is yet available on its distribution and abundance. To fill this gap data we gathered data during three scientific expeditions on four Maldivian atolls. In each atoll investigations were carried out at three depths, both in the ocean and in the lagoon reef, to examine differences in colony density and distribution. Distichopora violacea was observed in all the studied atolls; however, its distribution and density were not homogeneous among them. This species was more abundant in the ocean reefs than in the lagoon ones, suggesting a strong influence of water movement. Moreover, we found a high variability in colony density in the eastern ocean reefs that was tentatively attributed to a different topography of the reef: colonies were more abundant on the gentle slopes of Malè atolls than on the steep reefs of Felidhoo. Oceanographic features, mainly due to the seasonal monsoons, are likely to interact with the biological requirements of the species in determining the observed asymmetrical geographical distribution. The present investigation provides new insights on the stylasterid D. violacea and, for the first time, quantitative data on its distribution and density that can be useful for conservation and management of this CITES regulated species.

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