Benthic microbial mats: important sources of fixed nitrogen and carbon to the Twin Cays, Belize ecosystem

Abstract

We collected surface microbial mats at sites on Twin Cays, Belize to determine rates of primary production and nitrogen transformations. A diverse array of cyanobacteria including filamentous, coccoidal and heterocystous cyanobacteria, as well as purple sulfur bacteria and heterotrophic bacteria, were important components of microbial mat communities. Sediment chlorophyll a concentrations illustrated a high photosynthetic biomass in surface sediments. Rates of primary carbon fixation, measured as gross oxygenic photosynthesis, and nitrogen fixation and denitrification, measured using specific metabolic inhibitors, were determined during day-and-night incubations. Primary production rates were similarly high across different mat types. Nitrogen fixation rates were substantial under in situ conditions and nighttime activity frequently exceeded daytime activity. In situ denitrification rates were very low in all incubations. In the presence of added nitrate, however, denitrification rates increased significantly during daytime and nighttime incubations so that they equaled or exceeded nitrogen fixation rates. Collectively, our data show that microbial mats are a significant source of fixed carbon and nitrogen to the Twin Cays ecosystem and suggest that mats may serve as an important component of the ecosystem's food web.

Seasonal patterns of nitrogen fixation and denitrification in oceanic mangrove habitats

“…), clearly showing that benthic processes serve as an important net source of N to the oligotrophic Twin Cays mangrove ecosystem (Joye & Lee 2004).…”

Nutrient Addition Differentially Affects Ecological Processes of Avicennia germinans in Nitrogen versus Phosphorus Limited Mangrove Ecosystems

“…The difference in patterns of nutrient limitation at the two sites was due to a combination of physical and biogeochemical factors. For example, stunted forests at offshore islands such as Twin Cays received a very low supply of exogenous nutrients, but the N:P ratio of the substrate was relatively high due to benthic N 2 fixation (Joye and Lee 2004). There has been little human impact on the nutrient regime at Twin Cays (Rü tzler and others 2004).…”

Proceedings of the Smithsonian Marine Science Symposium

“…Although both of these locations are associated with low-nutrient coral reef ecosystems, Twin Cays receives negligible terrigenous inputs of freshwater or sediments whereas Bocas mangroves experiences a high fl ux of nutrients from several rivers draining into the archipelago. In addition, patterns of nutrient limitation in these systems may be affected by local patterns of N 2 fi xation (Joye and Lee, 2004;Borgatti, 2008).…”

“…Although both of these locations are associated with low-nutrient coral reef ecosystems, Twin Cays receives negligible terrigenous inputs of freshwater or sediments whereas Bocas mangroves experiences a high fl ux of nutrients from several rivers draining into the archipelago. In addition, patterns of nutrient limitation in these systems may be affected by local patterns of N 2 fi xation (Joye and Lee, 2004;Borgatti, 2008).Resorption of phloem-mobile nutrients from leaves during senescence is an important nutrient conservation strategy for plants that infl uences many ecological processes, including primary production, nutrient uptake, competition, and nutrient cycling (Chapin, 1980). To resolve the relative degree to which latitude and nutrient enrichment affect the ability of R. mangle to conserve nutrients invested in foliage, we examined resorption of N, P, and K. Across location, zone, and nutrient treatment levels, our results indicate that a major control of the nutrient concentrations in senesced leaves was nutrient concentration in green leaves, which is consistent with a global dataset compiled by Kobe et al (2005).…”