A critique on the relationship of surface area of live coral with total number of fishes as well as the biomass of fish in a coexisting system of Chromis caeruleus and Dascyllus aruanus (Pomacentridae) at Minicoy atoll

摘要

The pomacentrid fishes Chromis caeruleus (Cuvier) and Dascyllus aruanus (Linn.) coexist onudramose live corals without apparently displaying aggressive reactions. The population in audcoral colony is of many size groups, an obvious result of continual s ettlement of postlarvae of fishes fromudplankton, probably a strategy in nature to prevent in breeding in resident fishes. The relationship betweenudthe total number of fishes residing on a coral and the upper surface area of the habitat (coral colony)udcan be expressed as : Y - 0.2117 — 0.000064 X, where Y is the number of fishes per unit area of theudcoral and X the upper surface area of the coral sampled ; the correlation coefficient (r) being — 0.486.udThe relationship between the fish biomass and the upper surface area of the habitat can be expressedudas : Y = 0.07888 - 0.00005225 X, where Y is the wei^t of fish per unit area of the coral sampled andudX is the upper surface area of the coral; the correlation coefficient (r) being —0.99. As indicated byudthese correlation coefficients, there exists a closer relationship (inverse) between the biomass of fishudand the surface area of the microhabitat (live isolate coral) than between the total number of fish andudthe surface area at a time in a coexisting system of resident reef fishes. The ratio of the fish biomassudand the upper surface area of the coral (an index of density of fish) is also found to vary in differentudsamples, within a range of 380.3 to 934.25 cm' of the coral and a fish biomass of 22.42 to 30.87 gmudweight of fish sampled. The total length of the fishes ranged from 7 mm to 40 mm in the samples. Theudptesratt study also indicates that neither a numerical nor biomass consistency of fishes can be anticipatedudin a microhabitat over a prolonged time. Both these factors are ever changing as also the areaudof the living habitat viz. the live coral colony. This is due to the interplay of many natural and artificialudfactors, such as, continual recruitment of postlarvae, growth of fish at sites, migration andudmortality of fishes as well as the partial death or growth of corals that cause a dwindling or expansionudof living space for resident fishes. The above factors in nature control the density of fish population inuda coral live isolate. The maximum carrying capacity of the habitat perhaps is never allowed to reachudso that coexistence is made possible without the fishes displaying apparent agonistic reaction.. However,udthe present data did not clearly indicate the maximum carrying capacity of unit area of Acroporaudcorymbosa sampled; the systems analysed were in different stages of density level.