MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12992

Macroalgal biomass, growth rates, and diversity are influenced by submarine groundwater discharge and local hydrodynamics in tropical reefs

Florybeth Flores La Valle*, Florence I. Thomas, Craig E. Nelson

*Email: lavallef@berkeley.edu

ABSTRACT: It is critical to evaluate the in situ effects of multiple stressors on coastal community dynamics, especially those harboring high diversity such as coral reefs, in order to understand the resilience of these ecosystems, prepare coastal management for future scenarios, and aid in prioritizing restoration efforts. In this in situ study, at two sites with gradients of submarine groundwater discharge (SGD), a suite of physical parameters (wave exposure index, wind exposure index, and depth) and an all-encompassing SGD chemical parameter (average N+N daily load) were measured along spatially cohesive and temporally relevant scales and used to model macroalgal growth, biomass, and diversity in Maunalua Bay, Hawaiʻi. We show that (1) species-specific macroalgal biomass is significantly related to SGD and one of the two exposure indices (i.e. wind exposure or wave exposure), (2) SGD and wave exposure play key roles in species-specific growth rates, and (3) SGD supports low diversity and increased biomass of species that can tolerate the biogeochemistry associated with SGD. Our work suggests that SGD and local hydrodynamics predict local variation in macroalgal growth, biomass, and diversity in tropical reefs.