Abstract:
High temperature anomalies
associated with global warming have been shown to be responsible for a
reduction in live coral cover on reefs. Prolonged episodes of warmer seawater
temperatures are known to cause adult corals to undergo bleaching after which
the corals may die. However, the effect
of elevated temperatures on early life-stages of corals remains poorly studied.
If elevated temperatures reduce survival and settlement of coral larvae, the
recovery of coral populations will be impeded. Temperature effects on the
survivorship and settlement of Favia fragum (Esper 1797) larvae
were observed during a series of laboratory experiments. Larvae maintained at
elevated temperatures (30-33 ēC) exhibited reduced survivorship and settlement
abilities as compared to those maintained at control temperatures (27-29 ēC).
The observed decrease in survivorship corresponded with the induction of
settlement. A transplant experiment showed that larvae maintained for a 48 hour
settlement period at control temperatures survived and settled poorly when
transplanted to elevated temperatures. Larvae maintained for the same
settlement period at elevated temperatures survived and settled more
successfully when transplanted to control temperatures. Additionally, larvae
maintained at elevated temperatures for an extended period of time had severely
reduced settlement abilities at ambient temperature. These results indicate that Favia fragum larvae
are sensitive to and negatively impacted by elevated temperatures. The
settlement step appears to be particularly sensitive to temperature. We suggest
that this developmentally complex metamorphosis is a life-stage of corals that
is likely impacted by elevated temperatures.