Rocky reef fish community composition remains stable throughout seasons and El Niño/La Niña events in the southern Gulf of California

Abstract

Abstract The main effects of El Nino and La Nina on fish are increases in mortality rates, abundance and recruitment variation, and expansion/restriction in the range of distribution and spawning areas. Potentially, the interactions with seasonal effects can further exacerbate or dampen fluctuations in these parameters. The objective of this work, therefore, was to characterize the possible differences in the reef fish community structure in two seasons of the year (warm/cold) and between years (2010/2012) following El Nino-La Nina events. There were no significant differences in mean species richness between years. Furthermore, although more than twice the number of individuals was observed in the year after La Nina (2012) compared to the year following El Nino (2010), there were no significant differences with respect to mean abundance per transect. The total number of species recorded was slightly higher in the cold season, with 68 species across both years. In contrast, the total abundance was higher in the warm season. However, differences between seasons were neither significant for mean species richness nor for mean abundance. Neither season nor year exhibited a significant effect on community composition. The cold season in the Gulf of California is characterized by intense winds which generate a greater mixed layer; this, in turn, increases productivity, with cascading effects on higher trophic levels. In contrast, the presence of nitrogen-fixing picocyanobacteria which increase the levels of primary production may be a factor leading to maintaining a similar fish abundance in the warm season. Fluctuations between seasons and years of study were observed for some individual species, which may be related to oceanic productivity and reproductive periods. The results obtained in this work indicate that seasonality and climatic phenomena such El Nino and La Nina do not have a marked effect on community attributes of rocky reef fish in the southern Gulf of California, which apparently form a seasonally stable community, despite some fluctuations in individual species.