The importance of marine subsidies for terrestrial consumers in coastal Peru

The Peruvian coast is one the best examples of cross-ecosystem food web exchanges, in which resources from one of the richest marine ecosystems subsidize consumers in one of the driest deserts on Earth. Marine subsidies are resources that originate in the marine ecosystem, and that contribute to increase the density of consumers in the recipient ecosystem. I examined the effects of marine subsidies on animal populations in the Peruvian coastal desert. ^ I combined several approaches to study the linkages between marine resources and terrestrial consumers, such as surveying the spatial distribution and estimating the relative abundance of terrestrial consumers, studying the diet of geckos and lizards through stomach content analyses, and examining the desert food web with carbon and nitrogen stable isotope analyses. ^ I found that the distribution and diet of desert consumers were tightly coupled to the availability of marine subsidies. I revealed linkages along two pathways of nutrient fluxes: tidal action that washes ashore macroalgae and cadavers of marine organisms, and animal transport in places where pinnipeds and seabirds congregate for reproduction. In the first pathway, intertidal algivivores made marine resources available to terrestrial consumers by moving between the intertidal and supratidal zone. The relative contribution of terrestrial and algal carbon sources varied among terrestrial consumers, because scorpions assimilated a lower proportion of energy from macroalgae than did geckos and solifuges. In the second pathway, I found that pinniped colonies influenced the diet of desert consumers, and contributed to support large populations of lizards and geckos. By combining field observations, and stomach and stable isotope analyses, I constructed a simplified food web for a large sea lion colony, showing the number of trophic levels that originate from pinniped-derived nutrients. ^ My study demonstrates the enormous importance of marine resources for the diet of desert consumers. The near absence of rainfall along the Peruvian coast promotes an extreme dependence of terrestrial consumers on marine resources, and causes permanent food web effects that are affected by temporal variability in marine productivity, rather then temporal patterns of desert plant growth. ^

The importance of marine subsidies for terrestrial consumers in coastal Peru

The Peruvian coast is one the best examples of cross-ecosystem food web exchanges, in which resources from one of the richest marine ecosystems subsidize consumers in one of the driest deserts on Earth. Marine subsidies are resources that originate in the marine ecosystem, and that contribute to increase the density of consumers in the recipient ecosystem. I examined the effects of marine subsidies on animal populations in the Peruvian coastal desert. I combined several approaches to study the linkages between marine resources and terrestrial consumers, such as surveying the spatial distribution and estimating the relative abundance of terrestrial consumers, studying the diet of geckos and lizards through stomach content analyses, and examining the desert food web with carbon and nitrogen stable isotope analyses. I found that the distribution and diet of desert consumers were tightly coupled to the availability of marine subsidies. I revealed linkages along two pathways of nutrient fluxes: tidal action that washes ashore macroalgae and cadavers of marine organisms, and animal transport in places where pinnipeds and seabirds congregate for reproduction. In the first pathway, intertidal algivivores made marine resources available to terrestrial consumers by moving between the intertidal and supratidal zone. The relative contribution of terrestrial and algal carbon sources varied among terrestrial consumers, because scorpions assimilated a lower proportion of energy from macroalgae than did geckos and solifuges. In the second pathway, I found that pinniped colonies influenced the diet of desert consumers, and contributed to support large populations of lizards and geckos. By combining field observations, and stomach and stable isotope analyses, I constructed a simplified food web for a large sea lion colony, showing the number of trophic levels that originate from pinniped-derived nutrients. My study demonstrates the enormous importance of marine resources for the diet of desert consumers. The near absence of rainfall along the Peruvian coast promotes an extreme dependence of terrestrial consumers on marine resources, and causes permanent food web effects that are affected by temporal variability in marine productivity, rather then temporal patterns of desert plant growth.

Stable isotopes reveal complex changes in trophic relationships following nutrient addition in a coastal marine ecosystem

Complex links between the top-down and bottomup forces that structure communities can be disrupted by anthropogenic alterations of natural habitats.We used relative abundance and stable isotopes to examine changes in epifaunal food webs in seagrass (Thalassia testudinum) beds following 6 months of experimental nutrient addition at two sites in Florida Bay (USA) with different ambient fertility. At a eutrophic site, nutrient addition did not strongly affect food web structure, but at a nutrient-poor site, enrichment increased the abundances of crustacean epiphyte grazers, and the diets of these grazers became more varied. Benthic grazers did not change in abundance but shifted their diet away from green macroalgae + associated epiphytes and towards an opportunistic seagrass (Halodule wrightii) that occurred only in nutrient addition treatments. Benthic predators did not change in abundance, but their diets were more varied in enriched plots. Food chain length was short and unaffected by site or nutrient treatment, but increased food web complexity in enriched plots was suggested by increasingly mixed diets. Strong bottom-up modifications of food web structure in the nutrient-limited site and the limited top-down influences of grazers on seagrass epiphyte biomass suggest that, in this system, the bottom-up role of nutrient enrichment can have substantial impacts on community structure, trophic relationships, and, ultimately, the productivity values of the ecosystem.

A Hydrological Budget (2002–2008) for a Large Subtropical Wetland Ecosystem Indicates Marine Groundwater Discharge Accompanies Diminished Freshwater Flow

Water budget parameters are estimated for Shark River Slough (SRS), the main drainage within Everglades National Park (ENP) from 2002 to 2008. Inputs to the water budget include surface water inflows and precipitation while outputs consist of evapotranspiration, discharge to the Gulf of Mexico and seepage losses due to municipal wellfield extraction. The daily change in volume of SRS is equated to the difference between input and outputs yielding a residual term consisting of component errors and net groundwater exchange. Results predict significant net groundwater discharge to the SRS peaking in June and positively correlated with surface water salinity at the mangrove ecotone, lagging by 1 month. Precipitation, the largest input to the SRS, is offset by ET (the largest output); thereby highlighting the importance of increasing fresh water inflows into ENP for maintaining conditions in terrestrial, estuarine, and marine ecosystems of South Florida.

Photo-Reactivity of Natural Dissolved Organic Matter from Fresh to Marine Waters in the Florida Everglades, USA

Natural dissolved organic matter (DOM) is the major absorber of sunlight in most natural waters and a critical component of carbon cycling in aquatic systems. The combined effect of light absorbance properties and related photo-production of reactive species are essential in determining the reactivity of DOM. Optical properties and in particular excitation–emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) have been used increasingly to track sources and fate of DOM. Here we describe studies conducted in water from two estuarine systems in the Florida Everglades, with a salinity gradient of 2 to 37 and dissolved organic carbon concentrations from 19.3 to 5.74 mg C L−1, aimed at assessing how the quantity and quality of DOM is coupled to the formation rates and steady-state concentrations of reactive species including singlet oxygen, hydroxyl radical, and the triplet excited state of DOM. These species were related to optical properties and PARAFAC components of the DOM. The formation rate and steady-state concentration of the carbonate radical was calculated in all samples. The data suggests that formation rates, particularly for singlet oxygen and hydroxyl radicals, are strongly coupled to the abundance of terrestrial humic-like substances. A decrease in singlet oxygen, hydroxyl radical, and carbonate radical formation rates and steady-state concentration along the estuarine salinity gradient was observed as the relative concentration of terrestrial humic-like DOM decreased due to mixing with microbial humic-like and protein-like DOM components, while the formation rate of triplet excited-state DOM did not change. Fluorescent DOM was also found to be more tightly coupled to reactive species generation than chromophoric DOM.

Stable Isotope Biogeochemistry of South Florida Coastal Marine Ecosystems

Southeast Florida’s continual urban expansion will potentially increase anthropogenic pollution in adjacent coastal marine systems. Furthermore, increased nutrient loads could have detrimental effects on the already threatened Florida Reef Tract. The present study uses a stable isotopic approach to determine the sources and the impact of nutrients on the Florida Reef Tract. δ13C and δ15N analysis of macroalgae, sponges, and sediment were analyzed in order to determine nutrient inputs in this region. While δ13C data did not display any significant trends spatially, δ15N values of the majority of biota exhibited a strong East to West gradient with more enriched values close to shore. Relative enrichment in δ15N values were measured for sediments sampled along the Florida Reef Tract in comparison to a pristine Marquesas Keys sediment core. The δ15N data also implies that shoreline anthropogenic nutrients have more nutrient loading implications on reefs than major point sources.