On the occurrence of fishes in relation to corals in Curaçao

During the period from 10.IV.1969 until 14.IV.1970 an inventory was taken of 9 Millepora-fields and 8 Acropora palmata-fields in shallow water along the southcoast of Curaçao. From these fields all fishes were collected and one specimen of every species of coral. With the aid of a method used in the sociology of plants, the corals of both types of field were compared with each other as regards rate of cover and sociability. The fishes were identified, weighed and measured and the data obtained were then statistically evaluated. A significant difference in cover was found between Millepora in Millepora-fields and Acropora palmata in Acropora palmata-fields. No significant differences were found in cover and sociability of accompanying species of coral occurring in both the Millepora and Acropora palmata-fields. The average number of accompanying species of coral in both types of coral field is equal. No significant differences in composition of species were established for either type of coral field. The number of fishes in Millepora-fields is significantly larger than in Acropora palmata-fields. This can at least partly be explained by the occurrence of many juvenile fishes in Millepora-fields, because there is more shelter and less free flow and swell. The fish biomass per m², however, is about equal for both types of fields, viz. 167 g in Millepora and 157 g in Acropora palmata-fields, and corresponds with the figures given by RANDALL (1963) for two “natural reefs” in Puerto Rico (160 and 158 g/m²). A number of fishes show a striking preference for either Millepora or Acropora palmata-fields. Some species, occurring in both types of coral field, reach a significantly higher mean weight in either Millepora or Acropora palmata-fields. The significantly higher total weight of carnivores in Millepora-fields may correlate with the large numbers of juvenile fishes and crustaceae found in these fields. The higher total weight of zoo-plankton feeders in Acropora palmata-fields might be explained by the stronger free flow and, consequently, the larger supply of plankton in this type of coral field. The low biomass of herbivorous fishes, compared with the results of ODUM & ODUM (1955), RANDALL (1963) and TALBOT (1965), may be caused by the poor algal growth in and around these types of coral field.