Multiple stressors and disturbance effects on eelgrass and epifaunal macroinvertebrate assemblage structure

Abstract

Multiple forms of environmental change and anthropogenic pressure co-occur in coastal marine ecosystems. These external forces affect ecosystem structure, functioning, and, eventually, services to humans. Studies that include more than 2 simultaneous stressors are still needed to understand potential interactions among multiple stressors. We evaluated single and interactive effects of density reduction of Zostera marina L. (a habitat-forming species), shading, and sediment nutrient enrichment on the response of Z. marina and its associated epifauna over 10 wk. Shading had the greatest effect on reducing the eelgrass relative leaf elongation rate (RLE), non-structural carbohydrate reserves, and eelgrass shoot density. A reduced eelgrass density sustained higher epifaunal densities and increased the eelgrass RLE. Sediment nutrient enrichment increased eelgrass shoot density but decreased epifaunal richness, diversity, and total abundance. Our disturbance and pair of stressors differed in their influence on diversity measures, but all affected assemblage structure. Most of the changes to the epifaunal assemblage and diversity likely occurred due to altered habitat availability and epiphytic algae load. We observed additive, antagonistic, and negatively synergistic interactions among our treatments, while most of the cumulative effects showed dominance by one stressor over another. Our results highlight the importance of field experiments that are based on multiple disturbances and stressors to determine their interaction type on communities.

Remote Sensing of Coastal Vegetation Phenology in a Cold Temperate Intertidal System: Implications for Classification of Coastal Habitats

“…For eelgrass, the growth continued until the beginning of October, while the LAI showed an increase between May and June, remained constant until September, and was followed by a small decrease at the end of the season. Similar results were shown in other studies [56][57][58].…”

Seagrass and epiphyte seasonality in a biogeographic transition zone

“…Micro-and macroalgae outcompete seagrasses for nutrients and reduce the quantity and quality of light the plants receive through shading (Bulthuis and Woelkerling 1983, Brodersen et al 2015, Ruesink 2016), which can directly in uence the physiological and reproductive success of their host (Sand-Jensen 1977, Ow et al 2020). This results in reduced leaf growth/turnover rate, shoot density, and increased nonstructural carbohydrate content (Cimon et al 2021). Epiphytes can also increase oxidative stress, reduce chlorophyll b levels (Costa et al 2015), and alter plant metabolism (Ow et al 2020).…”

“…Epiphyte biomass varies spatially and temporally among seagrass meadows (Larkum et al 2006a) and is in uenced by a myriad of factors including seagrass leaf turnover rate (Hemminga 1998, Douglass et al 2010, herbivory (Hoffmann et al 2020), epiphyte accumulation rate (Bulthuis and Woelkerling 1983), diversity of both seagrass and grazer (Duffy et al 2015), as well as environmental conditions such as nutrient availability (Jaschinski and Sommer 2011) and irradiance (Burnell et al 2014). Top-down factors such as species richness of grazers and herbivory are important in mediating epiphyte abundance (Hughes et al 2004, Pillay and Waspe 2019, Cimon et al 2021. Notably, the biodiversity of grazers has a stronger in uence on epiphyte biomass than the grazer biomass itself, and a reduction in grazers stimulates epiphytic algae growth more signi cantly than nutrient addition (Reynolds et al 2014).…”