Influence of temperature and nutrients on species richness of deep water corals from the western coast of the Americas

Abstract

Studies on biogeography of stony corals from the eastern Pacific have been conducted in detail only for reef species, and to date there have been no attempts to explain the differences of regional species richness on the basis of oceanographic conditions. The objective of this work was to determine the relationship between deep-water (<200 m) scleractinian species richness along the western coast of the Americas, and four oceanographic variables (temperature, nitrates, phosphates and silicates), and the feasibility to use this information to model effects of global warming on those associations. Data on coral distribution were gathered from bibliography and museum collections, while information on oceanographic conditions from 200 to 2000 m depth was obtained from NOAA atlases. Species richness, estimated for intervals of 5 degrees of latitude, was correlated with abiotic factors using the Spearman rank coefficient. In the Northern Hemisphere, total species richness was positively influenced by temperature, but negatively by nutrients. In contrast, there was no effect of those factors on coral diversity in the Southern Hemisphere. At the family level, high temperatures favored species richness of Caryophylliidae and Dendrophylliidae north of the Equator, but diversity was reduced in areas of high concentration of silicates. In the Southern Hemisphere, temperature was not associated with deep-water coral richness, but correlated negatively with diversity of Caryophylliidae. Nutrients also showed an inverse relationship with richness of the latter family. In the rest of the families analyzed, there was no apparent effect of oceanic conditions on species richness in the Southern Hemisphere. The results indicated that richness may be influenced by changes in oceanographic factors (especially temperature and silicate concentration). Then, it is feasible to develop numerical models to predict possible changes in deep-water coral diversity on the basis of scenarios from global warming models.