Marshes along the South Carolina coast have been less salty following an influx of rain water late last year. Low levels of salinity for a sustained period of time can change the homes and breeding grounds for fish and other animals.
Scientists at the University of South Carolina are studying how this temporary environmental change may affect the ecology of the marsh. Research Specialist Paul Kenny slips a small metal measuring device into the water.
"The temperature at the surface is 17.7 degrees centigrade and salinity is back to normality,” he said to Director of the Baruch Marine Field Laboratory Dennis Allen.
Allen’s team takes these readings at the top and bottom of the Georgetown marsh just about 60 miles north of Charleston. Allen said the salt levels are starting to return to normal after six months. But it’s still quite a bit lower than would have been the case had we not had so much rain and inflow of lower salinity water,” he said.
Allen and his team are working on a 10 month study as part of USC’s efforts to research the short and long term impacts on natural ecosystems and human communities. But he is no stranger to the North Inlet Estuary, he’s been studying the marsh since 1981. As he looks down at the brownish tea colored water, he explains he’s been finding different kinds of animals recently.
"What we have seen with the incursion of freshwater, is fish that are normally found in the lower ends of the river systems in the salt marsh,” Allen said referring to catfish, longnose gar, white perch and a some types of shrimp normally only found in freshwater.
Allen said fish need the right amount of salt and temperature to survive. Much like humans can’t withstand extreme hot or cold temperatures.
He attributes some of the ecological changes he’s seeing to the lower salinity levels along with the rising temperatures. He says the fish have it easier because they can swim to the type of saltwater they need to survive, but the creatures that live in the mud – well they are stuck.
"What we have already seen by visual inspection of oyster reefs is some adult oysters have succumbed to the stress and died,”Allen said. "Reefs that have been established for a century or more have been knocked back and have to start over again.”
Allen and his team have been testing the same way every two weeks in this marsh for 35 years. He believes that long recorded history will provide important context when determining the temporary or potentially longer term effects of these low salt levels. Assistant Director of the USC Baruch Marine Field Lab Matt Kimball says those previous measurements provide a reference point.
"This baseline stuff is critical,” he said. You don’t know where you need to go back to or where you came from without it."
Kimball and the others take the fish back to the lab where they measure, weigh and inspect them.
Allen adds marshes like these, are nurseries for a lot of the seafood we eat like shrimp and crab, drum, trout and flounder. He warns that changes in the marsh may eventually reach our plates. That’s something David Bolanger hopes to prevent. Clammer Dave as he is nicknamed sloshes through the banks of a marsh near Awendaw during low tide in his wetsuit. He checks clam bags and oyster baskets for those that are ready to be washed, packed and sold.
He said the low salt levels affected his oyster producers shortly after the October 2015 floods.
We actually took oysters from other areas and put them on my lease to make them more saline until we sold them,” he said.
Bolanger said at the time it was the only way to sell the product. The floods also brought higher than normal levels of silt that suffocated some of his clams.
The climate in parts of the marsh he grows his clams in has yet to return to normal. The ecosystem is so interconnected, he said, one change can have a ripple effect.
The scientists in Georgetown agree. They will continue to study the effects of low salt levels in the marsh until the end of the summer.