Increased sea-surface temperatures cause fundamental changes to plankton communities, which form the basis of all marine ecosystems. The rise in surface temperatures and the change in plankton availability negatively affect the growth rate, swimming ability, behavior and reproductive rates of tropical reef fish. Donelson et al. (2010) studied the effects of increased sea-surface temperatures and limited food availability on the reproductive output and body conditions of the coral reef fish, Acanthochromis polyacanthus. Breeding pairs were exposed to high and low temperatures and were randomly assigned to a high ration diet or a low ration diet. The results indicated that the fish exposed to elevated temperatures had lowered reproductive fitness. The fish in the low ration treatments had significantly lower growth rates, indicating that they have impaired reproductive performance compared to those in the high ration treatment. Thus, even a small rise in surface temperature can have a significant impact on the reproductive success of tropical fish, A. polyacanthus. .— Sachi Singh
Donelson, J. M., Munday, P. L., McCormick, M. I., Pankhurst, N. W. Pankhurst P. M. 2010. Effects of elevated water temperature and food availability on the reproductive performance of a coral reef fish. Marine Ecology Progress Series 40, 233–243.
Tropical reef fishes have evolved in a thermally stable environment and are sensitive to small changes in sea-surface temperatures. Elevated sea-surface temperatures not only affect the growth rate and behavior of the tropical fish, but also have the potential to decrease reproductive success of these organisms. Doneslon et al. studied the effects of increased sea-surface temperature and limited food availability on the reproductive success and growth rates of Acanthochromis polyacanthus. They collected the fish from the Palm Island region in the Great Barrier reef; they exposed the fish to three temperature treatments—average sea-surface temperatures in the Palm Island, 1.5 °C higher than the average temperature and 3 °C higher than the average temperature—which reflected the predicted rise in temperatures in the Palm Island region. The authors randomly assigned breeding pairs to different feeding treatments—high and low ration diets—at each of the three temperature conditions. The results indicated that egg size, clutch size and embryonic duration of the fish decreased with the rise in surface temperature. The egg size of fish is usually a useful indicator of larval success, as smaller eggs are likely to produce progeny with reduced fitness. The increased water temperature also led to reduced levels of spermatozoa in the male fish. While food ration did not affect egg size or reproductive output, it negatively affected the growth rate of the fish, as the fish in the low ration treatment were significantly smaller than the ones in the high ration treatment. Previous studies have shown that increased body size can be beneficial for many components of reproduction, like fecundity and egg size; consequently, a reduction in growth rate could result in fish producing fewer offspring. Thus, the results of this study indicate that even a small rise in sea-surface temperature could have disastrous consequences for the reproductive fitness and—consequently, the population stability—of many tropical reef fish.