Changes in biodiversity and environmental stressors influence community structure of an experimental eelgrass Zostera marina system

Abstract

Changes in biodiversity can result in decreased ecosystem functioning and loss of ecosystem services, but altered biodiversity is only one of many stressors impacting ecosystems. In many estuaries, environmental stressors such as warming water temperatures and eutrophication are increasing and negatively impacting biological communities, particularly seagrasses such as the important habitat-forming species Zostera marina (eelgrass). These negative impacts may change the diversity, composition, and functioning of this important ecosystem, but the interactions of stressors with changes in biodiversity are poorly understood. We manipulated eelgrass communities in a factorial experiment to test how changes in crustacean grazer diversity, warmer water temperatures, and nutrient enrichment interact to affect ecosystem biomass, stability, and community composition. We found that the presence and richness of crustacean grazers had a larger effect on grazer, algal, and sessile invertebrate biomass than experimental warming or nutrient enrichment. Diverse grazer assemblages stabilized epiphytic algal biomass in the face of stressors, and counteracted the promotion of epiphytic microalgae by stressors. Nutrient enrichment and warming both promoted epiphytic microalgae, while reducing macroalgae and eelgrass. A more diverse grazer assemblage stabilized epiphytic algal biomass, but we did not detect interactions among environmental stressors and grazer diversity. These results emphasize that loss of herbivore diversity can exacerbate the impacts of environmental stressors on grazing, relative dominance of microalgae versus macrophytes, producer biomass, and stability. KEY WORDS: Diversity · Stressors · Eelgrass · Grazers Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 470: [41][42][43][44][45][46][47][48][49][50][51][52][53][54] 2012 in marine systems (Stachowicz et al. 2007. The impacts of biodiversity change and other stressors in marine systems are an increasing concern because we know little about their interactions, especially in the context of global climate change.Climate change is a primary threat affecting marine systems around the globe, and the impacts are predicted to increase as more CO 2 is dissolved in the oceans, global temperatures continue to warm, and ocean circulation patterns change (Doney et al. 2012). Climate warming, an important stressor, is predicted to increase both extreme temperatures as well as mean temperatures (Najjar et al. 2010, Doney et al. 2012. Warming temperatures can lead to changes in oceanic physical processes and chemical properties such as ocean circulation, sea level, and dissolved oxygen concentrations that can impact other components of marine communities. Increased water temperatures can alter ecosystem properties, services, and functions indirectly through effects on the diversity of organisms in a community, or directly through effects on biomass and primary production. Water temperatures in most shallow temperate es...

Predicting consequences of climate change for ecosystem functioning: variation across trophic levels, species and individuals

“…3) and feeding rates (Fig. Direct effects on algae have been neutral or positive depending on experimental duration (O'Connor, 2009); strongly positive, resulting in a doubling of algal biomass (Ekl€ of et al, 2012); positive for microalgae but not macroalgae (Blake & Duffy, 2012); or either positive or negative for different species in the same functional group (Olabarria et al, 2012). Previous mesocosm experiments with comparable temperature manipulations (+ 2-6°C) have shown variable effects on both algal producers and invertebrate consumers.…”

“…5) of some but not all amphipod species, and no direct effect of temperature on algae growth (Table 1: Change in Ulva biomass). Direct effects on grazer population growth have also been neutral (O'Connor, 2009), or neutral or negative depending on the species (Blake & Duffy, 2012;Ekl€ of et al, 2012). Direct effects on algae have been neutral or positive depending on experimental duration (O'Connor, 2009); strongly positive, resulting in a doubling of algal biomass (Ekl€ of et al, 2012); positive for microalgae but not macroalgae (Blake & Duffy, 2012); or either positive or negative for different species in the same functional group (Olabarria et al, 2012).…”

Wave action modifies the effects of consumer diversity and warming on algal assemblages

“…Empirical research has begun to address consumer diversity effects in relation to multiple stressors in marine systems (e.g., Blake andDuffy 2012, Eklo¨f et al 2012). Although previous studies have assessed the effects of grazer diversity on ecosystem processes in rocky shore habitats in the northeast Atlantic (O'Connor and Crowe 2005, Griffin et al 2010), little work has been done to examine the context dependency of these effects in relation to abiotic variables reflecting predicted environmental change.…”

Consumers mediate the effects of experimental ocean acidification and warming on primary producers

“…Partitioning net effects into direct and indirect effects, and estimating their relative importance, is readily achieved using structural equation modeling (SEM) (31), a framework for understanding causal processes (32). Consequently, SEM is being increasingly used to disentangle complex community-or ecosystem-level effects of environmental and climate change (33)(34)(35).…”