Spatio-temporal dynamics of surf zone tropical fish assemblages: Stability in a complex system

Abstract

Fish assemblages in the surf zone can be influenced by the proximity to other habitats and environments, exposure to waves, and variability in abiotic factors. This study assessed the interactive processes that influence and control the species composition, diversity, relative abundance, and size structure of inner surf zone fish assemblages in a highly diverse tropical region. Beach seine sampling was conducted at three distinct sampling sites for 12 consecutive months during the new and first quarter moon phases, with replicates collected during both day and night periods, on Serrambi Beach, Pernambuco State, northeast Brazil. Generalized Linear Models (GLM) were applied to assess the relationships between species richness and abundance and explanatory environmental variables. A set of environmental variables was measured at each sampling point. A total of 19,026 individuals belonging to 84 taxa were caught, with fourteen taxa comprising 87.5% of the total number of individuals, representing an equitable and constant composition throughout the year. GLM results showed that the sampling point alone explained 16% and 38% of the richness and abundance models, respectively. Temperature had a stronger influence on the structure of the fish assemblage than salinity. Fish size distribution ranged from 8 to 450 mm SL, and individuals between 10- and 120-mm SL represented up to 97% and occurred systematically throughout the year. Our results suggest that proximity to reefs results in a fish assemblage that is more abundant, diverse, and temporally stable. The presence of small individuals of the dominant species is likely an ontogenetic strategy, where juveniles use the shallow areas of the surf zone as a “standby transient habitat,” finding protection from predators and food while seeking suitable conditions to later move to nearby coastal environments and complete their life cycle or even remain within the surf zone itself. This study highlights the surf zone's critical role within the mosaic of coastal habitats, emphasizing its importance for the diversity of tropical fish.