Turf algae increasingly dominate benthic communities on coral reefs. Given their abundance and high dissolved organic carbon (DOC) release rates, turf algae are considered important contributors to the DOC pool on modern reefs. The release of photosynthetically fixed carbon as DOC generally, but not always, increases with increased light availability. Nutrient availability was proposed as an additional factor to explain these conflicting observations. To address this proposed but untested hypothesis, we documented the interactive contributions of light and nutrient availability on the release of DOC by turf algae. DOC release rates and oxygen production were quantified in incubation experiments at two light levels (full and reduced light) and two nutrient treatments (natural seawater and enriched seawater). In natural seawater, DOC release at full light was four times higher than at reduced light. When nutrients were added, DOC release rates at both light levels were similar to the natural seawater treatment at full light. Our results therefore show that low light in combination with low nutrient availability reduces the release of DOC by turf algae and that light and nutrient availability interactively determine DOC release rates by this important component of Caribbean reef communities.

Benthic cyanobacterial mats (BCMs) have increased in abundance on coral reefs worldwide. However, their species diversity and role in nitrogen fixation are poorly understood. We assessed the cyanobacterial diversity of BCMs at four coral reef sites in Curaçao, Southern Caribbean. In addition, nitrogen fixation rates of six common mats were measured. Microscopic examinations showed 22 cyanobacterial species, all from the order Oscillatoriales. Species diversity was similar among sites despite differences in overall BCM abundance. Dominant mats were primarily composed of Hydrocoleum glutinosum, Oscillatoria bonnemaisonii or Lyngbya majuscula. However, some mats exhibited highly variable species composition despite consistent macroscopic appearance. 16S rRNA-based phylogeny revealed similar species as those identified by microscopy, with additional sequences of unicellular (Xenococcus and Chroococcidiopsis) and heterocystous (Rivularia and Calothrix) cyanobacteria. Vice versa, morphotypes of Tychonema, Schizothrix and Dichothrix were found by microscopy only. The detection of similar species at the same sites in a study conducted 40 years ago indicates that changes in environmental conditions over these years may have favored indigenous species to bloom, rather than facilitated the introduction and proliferation of invasive species. Nitrogen fixation rates of mats were 3-10 times higher in the light than in the dark. The highest areal nitrogen fixation rate (169.1 mg N m-2 d-1) was recorded in the cyanobacterial patch dominated by O. bonnemaisonii. A scale-up of nitrogen fixation at a site with 26% BCM cover at 7 m depth yielded an aerial rate of 13 mg N m-2 reef d-1 , which exceeds rates reported in open ocean blooms of Trichodesmium in the Caribbean. Our results suggest that

This guide on performance monitoring and evaluation (evaluation) is intended for practitioners responsible for planning and managing marine areas. Practitioners are the managers and stakeholders who are responsible for designing, planning, implementing, monitoring, and evaluating marine management plans. While its focus is on the performance monitoring and evaluation of MSP, planners and managers should know how to incorporate monitoring and evaluation considerations into the MSP process from its very beginning, and not wait until a plan is completed before thinking about how to measure “success”. Effective performance monitoring and evaluation is only possible when management objectives and expected outcomes are written in a way that is measurable, either quantitatively or qualitatively.

Terrestrial runoff after heavy rainfall can increase nutrient concentrations in waters overlying coral reefs that otherwise experience low nutrient levels. Field measurements during a runoff event showed a sharp increase in nitrate (75-fold), phosphate (31-fold) and ammonium concentrations (3-fold) in waters overlying a fringing reef at the island of Curaçao (Southern Caribbean). To understand how benthic reef organisms make use of such nutrient pulses, we determined ammonium, nitrate and phosphate uptake rates for one abundant coral species, turf algae, six macroalgal and two benthic cyanobacterial species in a series of laboratory experiments. Nutrient uptake rates differed among benthic functional groups. The filamentous macroalga Cladophora spp., turf algae and the benthic cyanobacterium Lyngbya majuscula had the highest uptake rates per unit biomass, whereas the coral Madracis mirabilis had the lowest. Combining nutrient uptake rates with the standing biomass of each functional group on the reef, we estimated that the ammonium and phosphate delivered during runoff events is mostly taken up by turf algae and the two macroalgae Lobophora variegata and Dictyota pulchella. Our results support the often proposed, but rarely tested, assumption that turf algae and opportunistic macroalgae primarily benefit from episodic inputs of nutrients to coral reefs.