Analysis of fish abundance in the Gulf of California and projection of changes by global warming

The Gulf of California is considered as a key area for conservation worldwide, and has high endemism and diversity of its reef fish fauna. This group might be affected by global warming, because they are ectotherms and temperature may increase several degrees by 2100. This study analyze the latitudinal patterns of abundance of the 20 most abundant reef fishes in the Gulf of California, and evaluate possible changes caused by the temperature increment. Stationary censuses of fishes (N= 147) were done in six regions, from Los Angeles Bay (28°N) to Los Cabos (22°N). For each region we obtained the following information: mean, minimum and maximum surface temperature, photosynthetic pigments, and nitrate, phosphate and silicate concentrations. These factors were included in stepwise regressions to evaluate its influence on each species, and the equations were used to project change in numbers as a result of warming, by changing the coefficients linked to mean temperature in 1°, 2° and 3° C. The results of the models indicated that as temperature increases, four species reduce their abundance, fourteen became very similar in numbers along the gulf, and two were unaffected. Ten species will extend its range to areas where they are currently absent. Finally, richness and diversity (H') of the "future" communities will increase significantly; the highest value occurred in the 1°C increase model, but afterwards the values reduce gradually. Our conclusions are: a) the Gulf of California reef fish fauna will not react homogeneously to temperature increase; b) some species may change their distribution; c) ecological indices reflect the predicted qualitative shift in assemblage composition; and d) the differential responses of the species may cause an ecological imbalance in teleost assemblages of the gulf in following decades.