Connectivity Shapes Functional Diversity and Maintains Complementarity in Surf Zones on Exposed Coasts

Habitat complexity and connectivity can influence the number of species and their diversity across a landscape. For the surf zones of ocean-exposed beaches, globally one of the longest habitat interfaces, the assumed low structural complexity, and apparent homogeneity, of the sandy seafloor habitats predicts low taxonomic and functional diversity. Here, we assessed how the configuration of the seascape and the context of different beach structure functional diversity and functional niche space of fish assemblages in surf zones. We expected that beaches that were well connected with highly productive and complex estuarine and reef habitats would support a greater level of functional diversity, and a greater degree of functional complementarity within different niches. We sampled surf zones at twenty-five beaches along 50 km of coastline in southeast Queensland, Australia. We calculated functional diversity and functional niche space using variation in the functional traits of fish assemblages. We found that increased proximity with nearby subtidal rocky reefs was the key feature of the coastline shaping functional diversity and functional niche space in surf zone fishes. These effects resulted in increased functional complementarity within a number of fish functional group niches when rocky reefs were nearby. We provide empirical evidence that habitat proximity can structure functional diversity and complementarity in the surf zones of ocean beaches, a system traditionally viewed as having low habitat heterogeneity. Our results highlight the focus management must take in conserving these highly connected ecosystems to avoid negative functional consequences.

Automated summary

Habitat complexity and connectivity have implications for the number of species and their diversity. This study focused on surf zones of ocean-exposed beaches, where the low structural complexity of sandy seafloor habitats was expected to lead to low taxonomic and functional diversity. However, the proximity to nearby subtidal rocky reefs was found to be a key factor shaping functional diversity and functional niche space in surf zone fishes. These findings highlight the importance of conserving these highly connected ecosystems.