Abstract
High photosynthetic benthic primary production (P) represents a key ecosystem service provided by tropical coral reef systems. However, benthic P budgets of specific ecosystem compartments such as macrophyte-dominated reef lagoons are still scarce. To address this, we quantified individual and lagoon-wide net (Pn) and gross (Pg) primary production by all dominant functional groups of benthic primary producers in a typical macrophyte-dominated Caribbean reef lagoon near Puerto Morelos (Mexico) via measurement of O2 fluxes in incubation experiments. The photosynthetically active 3D lagoon surface area was quantified using conversion factors to allow extrapolation to lagoon-wide P budgets. Findings revealed that lagoon 2D benthic cover was primarily composed of sand-associated microphytobenthos (40%), seagrasses (29%) and macroalgae (27%), while seagrasses dominated the lagoon 3D surface area (84%). Individual Pg was highest for macroalgae and scleractinian corals (87 and 86 mmol O2 m−2 specimen area d−1, respectively), however seagrasses contributed highest (59%) to the lagoon-wide Pg. Macroalgae exhibited highest individual Pn rates, but seagrasses generated the largest fraction (51%) of lagoon-wide Pn. Individual R was highest for scleractinian corals and macroalgae, whereas seagrasses again provided the major lagoon-wide share (68%). These findings characterise the investigated lagoon as a net autotrophic coral reef ecosystem compartment revealing similar P compared to other macrophyte-dominated coastal environments such as seagrass meadows and macroalgae beds. Further, high lagoon-wide P (Pg: 488 and Pn: 181 mmol O2 m−2 lagoon area d−1) and overall Pg:R (1.6) indicate substantial benthic excess production within the Puerto Morelos reef lagoon and suggest the export of newly synthesised organic matter to surrounding ecosystems.
Highlights
Tropical coral reefs are among the most productive global ecosystems on account of a diverse community of benthic photoautotrophs sustaining reef community biomass and ecosystem productivity [1]
From a more detailed perspective, particular reef ecosystem compartments show considerable differences in benthic primary production (P) and R, which in turn underlie considerable variability [8]. This results from variable contributions of the main functional groups of photoautotrophic primary producers to benthic community composition, and from their individual metabolic activity [2,3]
Individual Pg, R and Pn rates were used to calculate the contribution of each investigated taxon and their respective functional groups to lagoon-wide benthic metabolism taking into account the specific percentage cover related to the entire lagoon area and respective mean 2D to 3D conversion factors
Summary
Tropical coral reefs are among the most productive global ecosystems on account of a diverse community of benthic photoautotrophs sustaining reef community biomass and ecosystem productivity [1]. This results from variable contributions of the main functional groups of photoautotrophic primary producers (e.g., seagrasses, macroalgae and scleractinian corals) to benthic community composition, and from their individual metabolic activity [2,3].
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