最新天美传媒

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Seagrass ecosystems along the northern half of Florida鈥檚 Gulf Coast have remained relatively healthy and undisturbed for the last several thousand years, according to and co-authored by researchers from the 最新天美传媒 College of Marine Science.

Elsewhere, seagrasses have not fared as well. have disappeared since 1879 and an estimated seven percent of seagrass beds were lost each year between 1990 and 2009. Those that remain are often struggling 鈥� the discovery of a healthy refugium is a rare event.

To assess the long-term health of seagrass communities along Florida鈥檚 Nature Coast, the study authors turned to fossils of mollusks, which can be used as a surrogate for species that aren鈥檛 normally preserved. If fossils indicate that mollusks have been doing well, it鈥檚 likely that other organisms in the ecosystem have been doing well, too.

The team sampled from 21 locations in six estuaries, from the mouth of the Steinhatchee River in the north to that of the Weeki Wachee River in the south. At each site, they used a long hose made from PVC pipe to suction up sections of the seafloor.

鈥淲e collect sediment samples while scuba diving, and then we sieve those samples and extract all that we find in it,鈥� said , senior author of the study and chair of invertebrate paleontology at the Florida Museum of Natural History. 鈥淭he samples are dominated by dead material, because it has accumulated there over many centuries. Typically, for every live bivalve or snail, we find thousands of dead specimens.鈥�

The odious task of counting and identifying the specimens took the team several years to complete. Once they鈥檇 crunched the numbers, their results showed that mollusk diversity 鈥� and the health of seagrass meadows, by extension 鈥� hasn鈥檛 changed much over the last several millennia, including the most recent one in which humans have left their mark on environments across the globe.

Establishing that the seagrass meadows found along the Nature Coast are relatively unchanged is also important because they can be now used with more confidence as a benchmark for assessing the state of heavily altered seagrass habitats and guiding their restoration.

Just 50 miles south of the study鈥檚 sampling area, seagrass communities haven鈥檛 been as lucky. Between 1950 and 1980, the city of Tampa鈥檚 population increased from about 125,000 people to 270,000. During that same period, 46 percent of seagrass meadows in Tampa Bay disappeared.

Aggressive nutrient reduction efforts in the region led to water quality improvements and the recovery of seagrass in Tampa Bay between 1999 and 2018 鈥� however, recent assessments have again shown significant reductions in seagrass followed by modest recoveries. On the opposite coast, a survey from 1999 indicated as much as had been lost in a 56-mile stretch of the Indian River Lagoon.

Read more: Seagrass areal cover in Tampa Bay over the last 30 years (1990- 2021) observed by satellites

This loss of seagrass is primarily caused by nutrient pollution from inland farms and coastal cities. Plumes of single-celled microalgae and photosynthetic bacteria feast on excess nutrients and multiply in the water column, creating what are, in effect, marine clouds. This significantly reduces the amount of light that reaches the seafloor, which seagrasses don鈥檛 tolerate well.

The Nature Coast, which was designated an aquatic preserve in 2020, has largely avoided these challenges.

鈥淭here鈥檚 not a lot of development in those watersheds, particularly from the area around Weeki Wachee all the way up into the Panhandle, so the effects of excess nutrient delivery are not as pronounced as is in other places that have suffered as a consequence,鈥� said study co-author Thomas Frazer, dean and professor of biological oceanography at the 最新天美传媒 College of Marine Science.

Many of the meadows have since rebounded with the aid of pollution mitigation and habitat restoration efforts. But algal blooms are now an annual occurrence in areas across Florida, and these will continue to have negative effects on seagrasses.

Climate change creates additional challenges, particularly for species along the Nature Coast. Though they鈥檙e doing well now, temperate and subtropical species are being pushed toward the planet鈥檚 poles by increasing global temperatures. But Florida species in Gulf waters can only migrate so far before they hit land.

鈥淭here鈥檚 nowhere for them to go,鈥� Frazer said.

Read more: Hungry herbivores threaten subtropical seagrass meadows

Backed up against the Panhandle, Florida鈥檚 Gulf Coast seagrasses will encounter marine climate refugees from further south. This has the potential to disrupt the tenuous balance within seagrass ecosystems. A single seagrass leaf can host a bazaar of tentacled hydroids, encrusting bryozoans, olive-shaped sea squirts, bacterial colonies and algal fuzz. As little as is actual plant.

In a healthy seagrass meadow, these seagrass dwellers are kept in check by grazing fish and invertebrates, but as these ecosystems change along with the Earth鈥檚 climate, the continued diversity and existence of grazers is far from guaranteed.

鈥淲e鈥檙e already seeing range extensions of mobile fauna,鈥� Frazer said. 鈥淎 number of fishes, for example, are moving up north along the Gulf Coast, and they may either eat seagrass or consume grazers that help keep seagrasses clean of organisms that live on them.鈥�

Seagrass ecosystems were around before the dinosaurs went extinct, and the consequences of losing something this old and diverse are not trivial.

Seagrasses stabilize sediment, reducing erosion and enhancing the accumulation of nutrient-rich biomatter. They鈥檙e so good at doing this that even though seagrass meadows cover only 0.2 percent of the ocean floor, they鈥檙e responsible for .

All of these tightly packed resources attract animals. Sea turtles, manatees and fish eat seagrass, while countless other species make the meadows their home.

鈥淭hey provide very important nursery habitat,鈥� Frazer said. 鈥淚n Florida alone, more than 80 percent of the fish caught by commercial fisherman and recreational anglers spend some part of their life history in those seagrass beds.鈥�

The deep roots and slender green blades of seagrass also protect coastal environments on land. Most seagrasses average only a foot or two in length, but a bunch of them together creates a substantial amount of drag. In near-shore environments, where the water is shallow, .

鈥淭hey鈥檙e a front line for storm protection,鈥� Frazer said.

For now, that protection remains in place. Florida鈥檚 Nature Coast Aquatic Preserve has the largest seagrass bed in the Gulf. With good management, it may stay that way.

Funding for the study was provided in part by the University of Florida IFAS seed grant.