Abstract
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.
Highlights
Turf algae increasingly dominate benthic communities on coral reefs
A positive relation between dissolved organic carbon (DOC) release and light availability was only observed in the natural seawater treatment, i.e. indicating that the occurrence of light-dependent DOC release depended on nutrient availability
In this study we demonstrate that DOC release by turf algae increases with increasing light availability under naturally occurring nutrient concentrations
Summary
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. They exhibit fast growth rates[29], rapidly take up nutrients[30] and are capable of nitrogen fixation due to the presence of cyanobacteria within these communities[31,32] Their high surface to volume ratio facilitate the exchange of metabolic products (e.g., DOC) between these algal communities and their environment[33] and makes them one of the most productive benthic primary producers on coral reefs[34,35]. These contrasting observations are certainly not mutually exclusive[46,47] and suggest that actual DOC release rates likely depend on more than one environmental condition (e.g., light and nutrient availability)
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