seagrass explorer

Ecological effects of seagrass genetic diversity

Eelgrass beds are highly productive marine ecosystems that provide nursery habitat for a number of commercially valuable fish species, buffer coastlines during storms, and act as blue carbon sinks. Unfortunately, their nearshore location makes them especially vulnerable to damage from human activity. To better predict the capacity of these systems to respond to global and local anthropogenic stressors, we are examining trait variation and genetic structure within beds across a depth gradient to determine whether eelgrass on the shallow and deep edges are locally adapted. Local adaptation, the mechanism by which a particular environment shapes the genotypic and phenotypic makeup of its population, selects for traits that allow the local population to perform better in its home environment than non-local individuals of the same species.

To assess patterns of local adaptation within natural, subtidal seagrass meadows in Massachusetts, we are examining phenotypic variation and genetic structure across depths in the foundation species Zostera marina (common eelgrass). Our study combines reciprocal transplant and common garden experiments, with the goal of linking trait variation to local environmental conditions, population demographics, and gene flow across depths. In addition, we are examining the abiotic and biotic selective forces that may be contributing to the presence/absence of patterns consistent with local adaptation by conducting experiments across multiple life history stages, from seeds to seedlings to adult shoots, and considering the effects not only of the environment, but also of the composition of the surrounding population on survival, growth, and performance. A better understanding of genetic structure and trait variation within seagrass meadows will benefit managers and restoration practitioners and aid in effective management and restoration of these ecosystems.

Genetic variation can have significant effect on populations, communities, and ecosystems (Hughes et al. 2008 Ecology Letters), generating increasing interest in the potential for eco-evolutionary feedbacks. My graduate and postdoctoral research examined genotypic (i.e., clonal) diversity in eelgrass (Zostera marina), a habitat-forming seagrass species that is found in shallow coastal systems throughout the northern hemisphere. Working with Jay Stachowicz at UC Davis, I demonstrated the variation in clonal diversity can have large and lasting effects on eelgrass productivity and response to disturbance in experimental systems (Hughes and Stachowicz 2004 PNAS; Hughes and Stachowicz 2011 J. Ecology), and these positive effects of eelgrass genetic diversity can be detected in natural eelgrass populations (Hughes and Stachowicz 2009 Ecology). Grazer presence and identity can also interact with eelgrass genotypic diversity to influence productivity (Hughes et al. 2010 Marine Ecology Progress Series). These studies suggest that seagrass genetic variation should be a key component of conservation and restoration efforts in these valuable coastal systems.

The Hughes Lab is a collaborative partner with ZEN (Zostera Experimental Network; http://zenscience.org), a global network of seagrass ecologists examining the effects of bottom-up and top-down forces and biodiversity on eelgrass beds worldwide. In 2014 and 2015, we conducted detailed field surveys of local seagrass sites in Nahant, MA and Gloucester, MA. We also ran controlled lab and field experiments to examine species interactions, identifying the mechanisms underlying local patterns and contributing to an understanding of global trends in biodiversity and ecosystem function in seagrasses.

Seagrasses are highly productive coastal ecosystems, providing critical habitat for a wide variety of commercially and ecologically important species. Unfortunately, seagrasses are declining globally in areal extent, and the rates of decline have increased in recent years (Waycott et al. 2009, PNAS).  As a consequence, species that depend on seagrasses for food and/or habitat are also of conservation concern (Hughes et al. 2009, Frontiers in Ecology and the Environment). Various factors can contribute to seagrass declines, including increases in water column nutrients and reductions in epiphyte grazers (Hughes et al. 2004, Marine Ecology Progress Series).  Currently, awareness of seagrass loss and its potentially dramatic effects on marine ecosystems lags behind that of other coastal habitats such as coral reefs and mangroves (Orth et al. 2006, BioScience).

Parasites and pathogens are integral components of marine communities and can drive community change. In seagrasses, the pathogen Labyrinthula zosterae causes eelgrass wasting disease, which can cause large-scale losses of this critical foundation species. Through our partnership with ZEN, the Hughes Lab is investigating global patterns in wasting disease prevalence. We are also examining the independent and potentially interactive effects of host density and genetic diversity on wasting disease incidence in eelgrass.