Organic matter release by the dominant primary producers in a Caribbean reef lagoon: Implication for in situ O₂ availability

Coral reef lagoon benthic primary producers may control various processes important for ecosystem functioning, predominately via the release of organic matter, but comparative data are rare. This study therefore comparatively investigated the quantity of particulate and dissolved organic matter released by different benthic primary producers (seagrasses, macroalgae and scleractinian corals) from the coral reef lagoon of Puerto Morelos, Mexican Caribbean. Microbial degradability of the released organic matter was determined along with diurnal in situ measurements of O₂ concentrations at lagoon sites dominated by different primary producers. Particulate organic carbon (POC) release was highest for corals (8.2 ± 4.2 mg m^-2 h ^-1), followed by benthic algae (3.9 ± 0.7 mg m^-2 h^-1) and seagrasses (3.1 ± 2.0 mg m^-2 h ^-1). Dissolved organic carbon (DOC) release rates were highest for seagrasses (15.8 ± 6.0 mg m_-2 h_-1), followed by algae (1.9 ± 2.0 mg m_-2 h_-1), whereas corals displayed net DOC uptake. Benthic algae-derived organic matter stimulated planktonic microbial O₂ consumption significantly more than seagrass- or coral-derived organic matter. In situ O₂ loggers revealed significantly lower average O₂ concentrations, particularly during the night, at algae-dominated sites compared to other benthic lagoon environments. This indicates effects of algae-derived organic matter on in situ O₂ availability. We therefore suggest that shifts in benthic primary producer dominance affect ecosystem functioning owing to differences in quantity, composition and microbial degradability of the released organic matter.