Randall Hughes Research

Loss of Coastal Seagrass Habitat Accelerating Globally

Many species dependent on seagrasses are also of conservation concern

I recently participated in a comprehensive global evaluation of seagrass observations that was published in the Proceedings of the National Academy of Sciences. Based on more than 215 studies and 1,800 observations dating back to 1879, the study found that 58 percent of world's seagrass meadows are currently declining. We also show that there has been an acceleration of annual seagrass loss from less than 1 percent per year before 1940 to 7 percent per year since 1990. This study illustrates that seagrasses are disappearing at rates similar to coral reefs and tropical rainforests.

We estimate that seagrasses have been disappearing at the rate of 110 square-kilometers (42.4 square-miles) per year since 1980, primarily due to (1) direct impacts from coastal development and dredging activities and (2) indirect impacts of declining water quality. With 45 percent of the world's population living on the 5 percent of land adjacent to the coast, pressures on remaining coastal seagrass meadows are extremely intense. In addition, as more and more people move to coastal areas, conditions only get tougher for seagrass meadows that remain.

Despite the high ecological and economic value of seagrasses, public awareness of these critical habitats and the threats they face lags far beyond that of other marine habitats such as coral reefs. With this comprehensive analysis, we hope to highlight the magnitude of the problem and focus attention on preventing future losses,” she added.

“While the loss of seagrasses in coastal ecosystems is daunting, the rate of this loss is even more so,” said co-author Dr. Robert Orth of the Virginia Institute of Marine Science of the College of William and Mary. “With the loss of each meadow, we also lose the ecosystem services they provide to the fish and shellfish relying on these areas for nursery habitat. The consequences of continuing losses also extend far beyond the areas where seagrasses grow, as they export energy in the form of biomass and animals to other ecosystems including marshes and coral reefs.”

Seagrasses profoundly influence the physical, chemical and biological environments of coastal waters. A unique group of submerged flowering plants, seagrasses alter water flow and can help mitigate the impact of nutrient and sediment pollution. In addition, they provide habitat for a wide variety of associated species, many of which are commercially or recreationally valuable.

These dependent species are vulnerable to seagrass declines; a separate analysis (Hughes et al. 2009) shows that there is, on average, more than one species of conservation concern for every seagrass species across the globe.

“This is the wake- up call for northwest Florida,” says Dr. Felicia Coleman, Director of the FSUCML. “Here we have three aquatic preserves --the Big Bend, Alligator Harbor, and Apalachicola Bay Aquatic Preserves-covering nearly 104,000 acres of submerged land with the most extensive expanses of seagrass left in the United States. These are gifts we shouldn't squander with overzealous development.”

“Accelerating loss of seagrasses across the globe threatens coastal ecosystems,” appeared in the Proceedings of the National Academy of Sciences Early Edition on June 29. The article was authored by 14 scientists from the United States, Australia and Spain, including Drs. Michelle Waycott (lead author), Carlos Duarte, Tim Carruthers, Bob Orth, Bill Dennison, Suzanne Olyarnik, Ainsley Calladine, Jim Fourqurean, Ken Heck, Randall Hughes, Gary Kendrick, Jud Kenworthy, Fred Short, and Susan Williams. To view the complete article, please go to http://www.pnas.org/content/early/2009/07/07/0905620106.abstract?sid=3953921a-b64d-4ebf-946e-8d59eeb75ba0

“Associations of concern: declining seagrasses and threatened dependent species” appeared in the June 2009 issue of Frontiers in Ecology and the Environment. The authors included Randall Hughes, Susan Williams, Carlos Duarte, Ken Heck, and Michelle Waycott.

Both studies were conducted as a part of the Global Seagrass Trajectories Working Group, supported by the National Center for Ecological Analysis and Synthesis (NCEAS) in Santa Barbara, California, through the National Science Foundation.