Patterns and drivers of reef fish agonistic interactions along a latitudinal gradient in the Atlantic Ocean

Abstract

Aim. Biotic interactions are among the most fundamental components of life. The structure and drivers of interactions are, therefore, a central research topic in ecology. In coral reefs, reef fish enroll in numerous interactions, and play an essential role in maintaining ecosystem functioning. We investigated the structure and drivers of reef fish agonistic interactions in 38 reef sites across the Atlantic Ocean. 

Location. Atlantic Ocean.Time period. Current.

Major taxa studied. Tropical reef fishes.

Methods. We collected data on reef fish species richness and agonistic interactions using Remote Underwater Videos (RUVs) in 38 reef sites distributed in 9 localities across the Atlantic Ocean. In each locality, we sampled 30 RUVs, totaling 270 videos and over 45 hours of footage. We employed four network metrics to assess the structure of reef fish agonistic interactions: weighted unipartite nestedness (WUNODF), modularity, centrality, and clustering. We further tested the influence of environmental variables (sea surface temperature, pH, and salinity) on interaction networks using a mixed linear model. 

Results. Agonistic interactions were more frequent in the tropics (12°N to -17°S latitude) in Curaçao Island, in the Caribbean, and Rocas Atoll and the Abrolhos Archipelago, in the Southwestern Atlantic Ocean. Agonistic interaction networks were predominantly modular (41% of sites) across the latitudinal gradient, while network centrality was observed in 8% of sites. Stegastes species, known for their territorial and aggressive behaviour, initiated 75% of agonistic interactions (high out-degree centrality). Interaction frequency was driven by regional richness and maximum SST. Agonistic interactions decreased with increasing regional richness, and increased with increasing SST.  

Main conclusions.  We demonstrate that, despite varying latitudes, reef fish agonistic interaction networks are modular. Also, interaction frequency in agonistic systems is strongly influenced by SST, highlighting the need to consider how global warming may reshape species interactions in a rapidly changing ocean.