Benthic Primary Production Budget of a Caribbean Reef Lagoon (Puerto Morelos, Mexico)

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 (P(n)) and gross (P(g)) 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 O(2) 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 P(g) was highest for macroalgae and scleractinian corals (87 and 86 mmol O(2) m(−2) specimen area d(−1), respectively), however seagrasses contributed highest (59%) to the lagoon-wide P(g). Macroalgae exhibited highest individual P(n) rates, but seagrasses generated the largest fraction (51%) of lagoon-wide P(n). 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 (P(g): 488 and P(n): 181 mmol O(2) m(−2) lagoon area d(−1)) and overall P(g):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.