What happened to reef-fish breeding in warmer water with less food?

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Climate change is predicted to warm the ocean and alter plankton communities that feed many marine fishes. To examine how higher sea surface temperatures and fluctuating food levels affect reef-fish reproduction, researchers kept breeding pairs of the coral reef damselfish Acanthochromis polyacanthus through a full summer breeding season in an orthogonal experiment with 3 temperatures and 2 food levels.

The temperatures were 28.5°C, the current-day average summer temperature at the collection location, and 30.0°C and 31.5°C, predicted to become close to the regional average over the next 50 to 100 years. Pairs received either a high- or low-quantity diet based on average and minimum feeding rates in the wild.

Both temperature and food supply affected reproductive output. Fewer pairs bred at elevated temperatures, and no pairs on the lower-quantity diet reproduced at either higher temperature. Eggs produced at 30.0°C and 31.5°C were smaller than those at 28.5°C.

Histological analysis of the gonads and steroid hormone measurement revealed no apparent differences in patterns of oogenesis among treatments. Spermatogenesis, however, was reduced at high temperatures despite some increases in plasma androgen levels. The researchers concluded that reduced breeding at warmer temperatures, combined with reduced sperm production, indicates the potential for significant declines in A. polyacanthus populations as the ocean warms.