Seagrass populations are facing major declines in the midst of global climate change and increasing urban development along coasts, according to a study conducted at the request of the International Union of the Conservation of Nature (IUCN). Frederick Short from Jackson Estuarine Laboratory in New Hampshire and colleagues reported that, of the 72 species of known seagrass, 10 species are classified at a higher risk of extinction and 3 qualify as endangered.
Seagrass meadows are responsible for many vital functions in marine ecosystems, explained Robert J. Orth from the College of William and Mary and colleagues in a 2006 study. They are directly linked to mangroves, coral reefs, salt marshes and other marine habitats. These meadows provide a haven for species of finfish and shellfish in their juvenile stages. Manatees, dugongs and green sea turtles are also heavily dependent on seagrasses: They provide the primary source of nutrients for these endangered marine animals. Reduction in the area of seagrass coverage available to these endangered species would undoubtedly decrease their already diminishing populations, according to Orth and colleagues. Seagrass is also a large source of carbon, some of which is transported deeper into the ocean, serving as a nutrient source for organisms that live in food-limited environments. Seagrass also captures and holds carbon within its rhizomes, roots and leaves. Much like tropical ecosystems, seagrass meadows serve as biodiversity hotspots, providing shelter and allowing various species to flourish in the nutrient-rich environment.
Seagrasses serve as effective bioindicators because changes in their environment can cause changes in their development and ability to serve as filters. According to Orth and colleagues, changes in water quality are easily identified by the health of seagrasses because of their high reliance on light—for example, when a decline in seagrasses is linked to an increase in nutrient deposits from coastal development. The environmental advantages of seagrass can be noted by the after-effects of the “eelgrass wasting disease” of the 1930s: Substantial amounts of seagrass were destroyed on coasts surrounding the North Atlantic Ocean due to the wasting disease and in turn caused alterations in current patterns. Food chains and fisheries were damaged, and sedimentation was negatively affected.
Research conducted by Orth and colleagues suggested that, although seagrass species were able to undergo evolutionary adaption during periods of environmental fluctuations, current environmental changes are occurring too rapidly to allow them to adapt. Increases in sea surface temperature, sea level and the frequency of storms, which cause surges and swells, have all played a part in impacting seagrass populations, wrote the researchers. Tsunamis and hurricanes have frayed seagrass communities and in turn affected their ability to provide the ecological services necessary to support other organisms. Sediment stirred up by extreme weather events clouds waters surrounding seagrasses, decreasing the seagrasses’ ability to photosynthesize; less light means poorer growth. According to Orth and colleagues, seagrass populations are not just threatened by climate change but by environmental stress brought about by human activities, like coastal developments, increased water pollution and harmful fishing practices as well.
And according to Frederick Short and colleagues, urban development along U.S. coasts is further damaging seagrass ecosystems. Along with this development is an increase in pollution levels, which directly affect watersheds and alter the landscape. There are different problems in different biomes: In temperate and industrialized areas, issues stem from discharge of waste containing high levels of nitrogen and phosphorous. Any increase in these nutrients can offset the delicate balance in marine ecosystems. In tropical areas the main threats to seagrass meadows are caused by wrongful subsistence fishery practices, like using fishing gear that damages seagrass beds. Deforestation in tropical regions causes sediment discharge to cloud up the water, directly affecting the seagrass productivity levels, claimed Short and colleagues.
Some argue that seagrasses go unrecognized by the conservation community because they are underwater–out of sight, out of mind. Do you think of seagrasses as ecosystem engineers? How do you view their role compared with other marine habitats, and where would you place them as a conservation priority?
Photo Credit: Florida Fish and Wildlife Conservation Commission