Tolerance to high temperatures and potential impact of sea warming on reeffishes of Gorgona Island (tropical eastern Pacific)

Knowledge of upper thermal-tolerance limits of marine organisms in the trop ical eastern Pacific (TEP) is important because of the influence of phenome na such as El Nino and global warming, which increase sea temperature. Labo ratory experiments were conducted to determine the critical thermal maximum (CTM) of reef fishes from the TEP. In 15 reef fishes of Gorgona Island (TE P) the CTM was between 34.7 degreesC and 40.8 degreesC. None of these CTMs was exceeded by sea temperature in the TEP during any of the strongest El N ino events in this century (32 degreesC during El Nino 1982-1983 and 1997-1 998). which indicates that all species studied here may tolerate El Nino ma ximum temperatures. In addition, the CTM of the least-tolerant species was 8 degreesC above the current mean sea temperature in a wide range of latitu des in the TER This suggests that fishes live far from their upper thermal tolerance limits and that the current global-warming trend is still unlikel y to be dangerous for these species. If sea temperature continues to increa se at the current rate, in about a century sea temperature could exceed the thermal tolerance of some reef fishes and threaten them with extinction. S uch risk. however, might occur sooner if the sea temperature during El Nino also increased in step with the global warming, but also because other pro cesses involved in maintaining population, such as reproduction, can be aff ected at lower temperatures. The possible ability, of reef fishes to adapt to increases in sea temperature is discussed.