Habitat suitability of drift macroalgae in two shallow coastal estuaries of the northern Gulf of Mexico

Abstract

Drift macroalgae, often associated with seagrass habitats, may provide resources and habitat to seagrass associated fauna, increasing faunal abundance and diversity. Yet, excessive amounts of drift macroalgae can be harmful, reducing the abundance of both aquatic angiosperms and animals by causing localized hypoxia. To ascertain the effects of drift macroalgae at biomasses commonly found in the northern Gulf of Mexico, we quantified recruitment into drift macroalgae without the presence of seagrass and measured associated changes to temperature, dissolved oxygen, and flow in Redfish Bay, Texas and Big Lagoon, Florida, USA. These locations comprise different coastal ecosystems with different compositions of drift macroalgae. In both locations, the presence of macroalgae significantly increased recruitment of small nekton, with higher abundances and species richness found within macroalgae relative to adjacent artificial macroalgae. Flow velocity and dissolved oxygen levels were lower in macroalgae than in adjacent artificial or bare substrate, but still remained above hypoxic levels over daily fluctuations. Despite lower oxygen levels at night, and overall lower water flow, organisms readily recruited into drift macroalgae more so than the artificial habitats nearby. However, the reduction in oxygen reveals that in higher biomasses, macroalgae could adversely affect animals.