Can no-bubble methane seeps affect biological traits of benthic macroinvertebrates in coastal systems?

Abstract

Methane seep studies often target sites where methane gas is actively bubbling from the sea floor to the water column. However, gas bubbles often remain trapped in surficial seabed sediments, especially in coastal systems; notably few ecological studies exist for these systems. These environments form patches on the seafloor in the Bahia Blanca estuary that, based on taxonomic analysis, represent a distinct benthic habitat. Here we examine whether taxonomic changes in benthic communities associated with trapped methane gas bubbles are related to functional changes. We found significant differences in biological traits of macroinvertebrates weighted by abundance and by species between two sites differing in gas presence and between spring and winter seasons. Compared with the control (no gas) site, the gas site had subsurface-deposit feeders and large sessile animals partially calcified with suspension-feeding mode. In contrast, at the control site the small and non-calcified animals are discretely motile, building burrows and tubes and feeding on surface deposit material. Trapped methane gas, detected with seismic methods, changes biological traits in benthic fauna and can lead to alteration of some ecosystem functions. This suggests the utility of high-resolution seismic methods for detect these benthic habitats with high spatial accuracy, and a need to further understanding of ecosystem processes associated with gas presence in the context of both direct anthropogenic and climate-change pressures.