Comparison of growth of the reef fish species Haemulon flavolineatum (French grunt) between seagrass beds, mangroves and the coral reef, as a test for the nursery hypothesis

Juvenile French grunts (Haemulon flavolineatum) were caught, measured in length and weight and introduced in cages for 6 to 8 weeks to grow in their natural environments, the reef, the seagrass beds and the mangroves. After this period, weighing and measuring length was repeated and the growth could be calculated. The mangroves and seagrass beds are identified as nursery habitats for juvenile reef fish and are supposed to increase their survival chances. The nursery hypothesis claims nurseries are beneficial to the juveniles in several ways, including higher growth rates. This research, conducted on the Caribbean islands of Curaçao and Aruba proved the opposite for juveniles between 3.5 and 4 cm. The growth in length and weight of the fishes were higher, although only significantly in Aruba, in the reef habitat compared to the nurseries. Food samples collected on Aruba at each site were comparable with the growth results, because the highest food availability was found in th reef habitat. When comparing the growth of the fishes between two different locations (each location containing all three habitats) on the island of Aruba, significant differences in growth in length were found. Apart from the fact that the highest growth was found on the reef on both islands, there were little similarities found in growth between the islands. The correlation between environmental factors and the growth of the fishes were small, with only a correlation detected between water clarity and growth in weight and weight/length ratio on Aruba. Differences between the two main areas on Aruba and between the islands could, however, not be explained by this. In conclusion, mangrove and seagrass nurseries do not contribute to a higher growth rate of small juvenile French grunts.

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