Decoupled effects (positive to negative) of nutrient enrichment on ecosystem services

Abstract

Eutrophication is a widespread phenomenon that disrupts natural ecosystems around the globe. Despite the general recognition that ecosystems provide many services and benefits to humans, little effort has been made to address how increasing anthropogenic eutrophication affects those services. We conducted a field experiment to determine the effect of nutrient enrichment on five ecological services provided by a model coastal system, a shallow seagrass community near Mobile Bay, Alabama (USA): (1) the provision of shelter for fauna; (2) the quality of food provided to first‐order consumers; (3) quantity of food provision to first‐order consumers and O2/CO2 exchange; (4) producer carbon and nitrogen storage, and (5) water clarity. The results showed a severe negative impact on seagrass density and biomass, which greatly reduced the structural complexity of the community and provision of shelter to fauna. Water clarity and the standing stock of producer carbon were reduced in the fertilized area in comparison with the control area. In contrast, nutrient addition did not affect in any consistent way the total quantity of food available for first‐order consumers, the net exchange of O2/CO2, or the standing stock of producer nitrogen in the community. The nutritional quality of the food available for first‐order consumers increased with fertilization. These results show that the impacts of nutrient enrichment on the services provided by natural systems may be disparate, ranging from negative to positive. These findings suggest that management policies for anthropogenic eutrophication will depend on the specific ecosystem service targeted. In the case of shallow seagrass beds, the loss of biogenic habitat and drastic impacts on commercially important fauna may be sufficiently alarming to warrant rigorous control of coastal eutrophication.

Modification of a seagrass community by benthic jellyfish blooms and nutrient enrichment

“…However, in this experiment, we did not observe any difference in epiphytic loads on seagrass from fertilized plots, suggesting seagrass loss was not related to this mechanism. These findings mirror results from a recent nutrient enrichment experiment conducted in Mobile Bay, Alabama in which reductions in Halodule wrightii abundance and structural complexity occurred, with no evidence of increased epiphyte loads on seagrass leaves in fertilized plots (Antón et al, 2011). Instead, it is possible that the observed reduction in seagrass abundance and complexity could be attributed to a shift in abiotic conditions (e.g., lowered dissolved oxygen concentrations) at the sediment-water interface as a result of nutrient enrichment (Burkholder et al, 2007).…”

Iron Deficiency in Seagrasses and Macroalgae in the Red Sea Is Unrelated to Latitude and Physiological Performance

“…Understanding what factors limit benthic macrophytes is important given their role sequestering carbon both within blue carbon habitats and in the deep ocean (Fourqurean et al, 2012;Krause-Jensen and Duarte, 2016;Duarte and Krause-Jensen, 2017), as well as their role in supporting food webs (Antón et al, 2011). The results reported in this study contribute to unravel the complex interactions between environmental gradients and poorly-studied Red Sea macrophytes at large spatial scales.…”

Ecosystem structure and services in eelgrass Zostera marina and rockweed Ascophyllum nodosum habitats

“…Although marine vegetated habitats cover < 2% of the global ocean, they contribute to almost half of the oceanic carbon burial, playing a major role in the oceanic carbon cycle (Duarte et al 2005). Increased nutrient loading to coastal ecosystems is shifting the primary producer assemblage from long-lived macrophytes to phytoplankton, benthic micro-, and annual macroalgae, which can decrease the ecosystems' carbon and nitrogen retention (Worm et al 2000, Antón et al 2011. The projected increase in nutrient loading of another 10 to 20% by 2030 (Millennium Ecosystem Assessment 2005a) will have profound repercussions on coastal ecosystems and their storage services.…”