Reef Fish Community Structure Across an Ecological Transition Zone

Abstract

Transition zones exhibit a unique combination of abiotic characteristics derived from the merging of two distinct areas, hosting communities with different thermal tolerance and distribution ranges. Given these characteristics, these zones are key to unmasking the effects of climate change on biodiversity since rapid changes in the sea temperature can favor some populations more than others. This study aimed to investigate the community structure of reef fish in seven islands of the southwestern Atlantic in a transition zone. Our results revealed distinct patterns of thermal affinity separating reef fish communities from the north to south islands, indicating a higher tolerance for species experiencing colder and seasonal temperatures. We also found that the abundance distribution pattern corresponds to the presence of many rare and few dominant species. Planktivores were the most abundant trophic group in the northern islands, while omnivores prevail in the south, potentially due to differences in the oceanographic conditions of the region, such as water turbidity. Our findings underscore the importance of understanding how communities differ or shift in space, which is crucial for predicting the consequences of environmental changes on biodiversity and ecosystem functioning.

Keywords: α-diversity, community structure, southwestern Atlantic, transition zone, thermal tolerance