Abstract
Benthic primary producers in coastal ecosystems provide important habitat for marine organisms through the provision of complex 3D habitat. Primary producers produce organic matter, while simultaneously producing reactive oxygen species, including hydrogen peroxide (H2O2), a driver of oxidative stress. Through their high biomass, productivity and effect on local hydrodynamics, benthic primary producers can potentially increase H(2)O(2)concentrations surrounding the biogenic structures they form. The aim of this study was to identify the potential role of H(2)O(2)produced by benthic primary producers as an external stressor in coastal ecosystems. This was achieved by measuring H(2)O(2)concentrations within sea lettuce blooms (Ulvasp.), giant kelp forests (Macrocystis pyrifera), and seagrass meadows (Zostera muelleri); quantifying H(2)O(2)production rates of these species; and testing heterotrophic bacterial response to relevant H(2)O(2)concentrations.Ulvasp. produced five times more H(2)O(2)than other species. At in situ concentrations, H(2)O(2)inhibited bacterial production and carbon flow through the microbial loop by 75%. This study reveals H(2)O(2)as an additional stressor in bloom-formingUlvasp. with higher H(2)O(2)production compared to the ecosystem engineersM. pyriferaandZ. muelleri. H(2)O(2)production by benthic primary producers can affect carbon flow through the microbial loop, with the potential to propagate a stress signal up the food web.