Ontogenetic patterns of distribution in coral reef fishes, within the mangroves of a Caribbean atoll

• Main Author: Cavers, Clare Veronika
• Published: University of Edinburgh 2003
• Subjects: 591.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642688

This thesis aims to assess the relative importance of the mangrove forest within a Caribbean atoll, in the early life history stages of coral reef fishes. Three quantitative techniques were used. Stationary light traps and towed plankton nets collected larval stages, and a visual census technique was used to assess juvenile and adult stages. Environmental factors, including habitat structure, were measured simultaneously. The study was conducted over the months of August-September 2000 and June-November 2001. A nested sampling design provided the distribution of fish on three spatial scales, at 10s, 100s and 1000s of metres. A total of 159 species or types of coral reef fish within 50 families were recorded. The proportion of species present as larvae, and therefore available to settle, was greater in the seagrass than in the mangroves. Twelve taxa present in all three life-cycles stages showed contrasting patterns of distribution between the seagrass and mangrove habitats, with 11 appearing to be open populations. The mean body size of each life stage was smaller in the seagrass than in the mangroves, indicating a preference for the mangrove habitat by larger and therefore older individuals. Diel movement between habitats is evident for the larval assemblage, with higher densities in the seagrass during the day and in the mangroves at night. Lunar periodicity was evident, with the greatest abundance, species diversity and species richness of larvae coincident with the three-quarter moon, and a high density also collected during the new moon. Tidal effects were minimal. Temporal variation in the larval assemblage composition correlated with water turbidity in both mangrove and seagrass habitats. The mangrove larval population was related to both the mangrove and the seagrass adult populations, and reflected the larval supply with a time lag of 2 to 4 weeks. Overall juvenile density reflected the larval supply density, with a time lag of two months. The recruitment of <i>Ocyurus chrysurus</i> and members of the family Scaridae, especially <i>Sparisoma</i> sp. was related to the respective spawning stocks in the mangrove and seagrass habitats. The densities of <i>Haemulon flavolineatum</i> and <i>Lutjanus griseus </i>juveniles decreased as the structural complexity of the mangrove habitat increased.