Seasonal and interannual change in a Chesapeake Bay eelgrass community: Insights into biotic and abiotic control of community structure

Abstract

We characterized the seasonal and interannual variation in macrophytes, epiphytes, invertebrate herbivores, small demersal predators, and physicochemical characteristics of an eelgrass (Zostera marina) bed in Chesapeake Bay, Virginia, over 10 yr, to explore the relative importance of abiotic and biotic forcing on community composition and abundance. Our hypotheses were (1) physicochemical drivers affect community structure directly, (2) bottom‐up trophic control is evidenced by positive covariance among trophic levels, (3) top‐down control generates inverse patterns of abundance at adjacent trophic levels, and (4) species diversity among herbivores contributes to temporal stability. Composition and abundance of eelgrass‐associated species varied strongly among seasons and years. Much of this variation correlated with temperature and salinity anomalies, and multivariate analysis grouped communities roughly by season, supporting our first hypothesis. Severe seagrass loss during the hot summer of 2005 shifted the community toward a novel composition, but community structure rebounded within a year. Evidence for trophic control was mixed: selected taxa showed patterns consistent with top‐down or bottom‐up control, but these patterns generally disappeared at the level of whole years and entire trophic levels. Our ability to detect trophic effects may have been limited, however, by consumer movement or changing behavioral responses to resource availability and predation. There was also little evidence that diversity stabilized total herbivore abundance. Although consumer effects on lower levels were inconsistent, the strong physicochemical forcing of community structure supports suggestions that eelgrass communities are highly vulnerable to natural and anthropogenic changes in climate and hydrography.

Seasonal variation in carbon sources of ­mesograzers and small predators in an eelgrass community: stable isotope and fatty acid analyses

“…Resale or republication not permitted without written consent of the publisher grazers and their food (Edgar & Shaw 1995, Nelson & Waaland 1997, Douglass et al 2010. In temperate systems, abiotic and biotic conditions change considerably in the course of the year with possible consequences for food web interactions (Polis et al 1996).…”

“…The use of stable isotope analysis is well established in the research of seagrass ecosystems (Kharlamenko et al 2001, Connolly et al 2005, Douglass et al 2010, but most studies focus on 1 or 2 temporal sampling points. As a high temporal variability in the abundance of consumers and their food is common in benthic ecosystems (Edgar & Shaw 1995, Nelson & Waaland 1997, Douglass et al 2010, a broader approach is necessary to assess the effect of mesograzers in seagrass meadows.…”

“…As a high temporal variability in the abundance of consumers and their food is common in benthic ecosystems (Edgar & Shaw 1995, Nelson & Waaland 1997, Douglass et al 2010, a broader approach is necessary to assess the effect of mesograzers in seagrass meadows. We used stable isotope and fatty acid analyses to study the seasonal variation in carbon sources of common mesograzer and small predator species in an eelgrass system in the Baltic Sea.…”

Seasonal and diel changes in the structure of a crustacean decapod assemblage associated to a shallow Cymodocea nodosa meadow in northern Tunisia (Mediterranean Sea). An overview of the Mediterranean decapod taxocoenoses.

“…In this way, movements -migrations of P. adspersus have been related to water temperature (Hagerman & Østrup, 1980;Bilgin et al, 2008) but not always (Bilgin et al, 2009). Anthropogenic pressure (Douglass et al, 2010), stronger during summer, should not be forgotten either. Furthermore, the location of the meadows (depth, emplacement) and the influence of the different surrounding habitats are important factors in the decapod assemblage structure, and they are responsible for the differences between geographic areas and sites (species composition and dominance).…”

Effects of grazing and fertilization on epiphyte growth dynamics under moderately eutrophic conditions: implications for grazing rate estimates

“…The seagrass itself, sediment microalgae, epiphytic algae, loose macroalgal mats and phytoplankton constitute the trophic base of food webs in seagrass beds (Cebrian 2004, Hauxwell & Valiela 2004. Understanding the complex set of trophic interactions between seagrass fauna and their prey has presented a challenge (Hemminga & Duarte 2000, Duffy et al 2003, Mateo et al 2006, Douglass et al 2010. Anthropogenic eutrophication often stimulates epiphytic and macroalgal growth, further complicating these interactions (Sand-Jensen & Borum 1991, Duarte 1995, Borum & Sand-Jensen 1996.…”