Tracking beach ecosystems in wake of oil spill
TAMPA, Fla. – In the aftermath of the BP oil spill, the focus on Florida beaches has been whether they are cleaned of oil or not.
But USF Professor Susan Bell, chair of the Department of Integrative Biology, is investigating a more complex set of questions about beaches and their inhabitants: whether the interwoven communities of plants, small crabs, clams, turtles, birds and other critters are a functioning food web or have feeding relationships become altered on beaches impacted by the nation’s largest environmental disaster.
This summer, Bell, along with University of South Florida post-doctoral researcher, Alex Tewfik, and students have scoured both urban and pristine beaches -- from the Panhandle to the lower southwest Florida coast, and up the Atlantic coast to North Carolina -- in an effort to understand the colonies of creatures that inhabit beaches and the food items consumed by the diverse group of animals.
In a research effort funded through a National Science Foundation Rapid Research Grant issued in the aftermath of the Deepwater Horizon spill, Bell is meticulously documenting an ecosystem few beachgoers notice when they’re sprawled out on the sand.
“You think there’s nothing going on here, that it’s a static environment, but it’s not,” Bell said. “It’s ever-changing.”
Many of the organisms that make up the food web live within the sediments or are most active at nighttime. In tracking these creatures and their feeding activities, Bell hopes to provide new understanding on how beach dwellers are dependent on these food sources and those delivered to the beach by waves from deeper waters.
Because some beach environments depend on the sea to continually nourish the shores with food sources, the impact of oil on these young animals is not well understood but could eventually show up if fewer of the creatures make their way back to beaches, she said.
Surprisingly scant scientific information has been documented about how beach food webs develop and how the animals interact, especially in Florida, Bell said. A dearth of baseline data led Bell to propose the one-year project, which will likely provide the foundation for longer examinations of the environmental impact of the spill on beach ecology.
So when shore birds stick their beaks into the sand to nab a small coquina, are they ingesting oil? What about the sea grasses that wash ashore that break down, providing yet another food source, if they too are coated by crude? And for those organisms hatched offshore that make their way to the beach to live, how might oil and dispersants which spread through the northern Gulf affect their existence?
“If there is oil in the water column, they are encountering it,” Bell said on a recent morning surveying St. Pete Beach. “Even if the oil is not here, it could have an impact on the coastal environments – environments need not be in close proximity to the spill to be vulnerable.
“They are resilient,” Bell said of the beach dwelling organism. “But there is a point beyond which the ecosystem may not recover.”
One key focus of Bell’s project is the lowly ghost crab, known as the “custodian” of the beach for its wide-ranging appetite and the central role it plays in the beach food web. Ghost crabs release their eggs offshore and the small crabs work their way to the beaches where they burrow into sediments and sometimes in the dunes. They forage at nighttime for food – dead fish, small clams, spiders and even turtle eggs.
In turn, the crabs make a tasty meal for raccoons and sea gulls.
“The soft sediments are prime habitat for the ghost crabs,” Bell explained. “Interestingly the highest numbers of burrows are often found right in the area where a lot of both food items and oiled material washed ashore, and where oil residue is also retained in the sand.”
The area of the beach where the incoming waves deposit seaweed and algae -- called “wrack” -- along with small shrimp and crabs is highly important to the beach food web. Machines that are being used to clean oiled beaches often leave deep tire tracks in sand, which may pose a whole new challenge especially for smaller crabs who have to navigate deep tire tracks or which have very shallow burrows.
“You think the grass - like material here is garbage, but it really is a food supply,” Tewfik said. “You might want to clean up oil material, but you are also moving a food supply.”
The investigators will continue to assess not only how many ghost crabs are found on oiled beaches but also whether crab feeding on oiled beaches has changed because of the contamination.
The investigators are interested in how food webs might vary depending on the amount of human influence on beaches. Beaches in urban locales where machines remove washed up materials on a daily basis and where contaminants can enter from nearby parking lots have fewer ghost crabs than beaches that are undeveloped and have fewer visitors, they’ve found.
“Unlike many other coastal ecosystems comparatively few organisms do well in beach habitats because it’s so tough to live in,” Tewfik said. “If we lose those guys, there are not many replacements that can serve as substitutes in the food web.”
Filed under:Arts and Sciences Research School of Natural Sciences and Mathematics Integrative Biology
Author: Vickie Chachere