Spatial patterns in reef fish biomass and trait structure along a natural environmental gradient

Biodiversity loss is a fundamental concern across marine and terrestrial ecosystems in virtue of continued and increasing localized and global human activities. Accordingly, it is essential to discern how communities vary in space across a range of environmental and disturbance scales. Increasingly, ecological traits are providing important mechanisms for understanding communities based on the trait's species provide, building upon traditional assessments of taxonomic identity. This study investigated trait and biomass indices constructed from fish communities from 94 reefs along 2000 kms of latitude along the Red Sea. Fish communities were recorded through in situ visual surveys and covered varying coastal population density and a natural linear gradient in environmental parameters (sea surface temperature, productivity, salinity). From these communities, a total of 153 unique functional entities (FEs) were recorded. Using key components of trait diversity, Red Sea reefs contain low trait redundancy and high vulnerability, with 71% of FEs represented by a single species. Despite the strong linear gradient in environmental variables along the latitudinal range, functional richness and diversity did not reflect this, suggesting that local scale environmental variability and stressors may have a greater, and or additive influence. Standing biomass and biomass productivity was highest in the Farasan Banks (southern Red Sea) while biomass productivity was lowest in the two far northern regions. The high biomass in the Farasan Banks was largely driven by planktivore species, suggesting a link with higher levels of primary productivity and warmer water temperature in the south. The region with the highest trait vulnerability was adjacent to a major city and industrial port, suggesting a link between vulnerability and coastal population. This study provides a baseline for the region and a mechanism to support recommendations on the assessment of vulnerable reef fish communities at regional scales beyond taxonomic assessments.