by Ann Green; photographs by Scott D. Taylor
As a tiny wave ripples onto a sandy marsh off the Cape Fear River, North Carolina Sea Grant researcher Martin Posey stands knee deep in soft mud.
Dressed in knee-high olive boots, a checkered shirt and jeans, Posey places a cage on the muddy sand flat.
The cage will keep out fish and crabs and stay in place for a month, along with six other cages. Some of the cages have nutrients added. Others are nutrient-free.
A short, compact researcher with boundless energy, Posey relishes his hands-on work in the flat, muddy marsh. “I love going out in the field instead of pushing paper,” says Posey while digging in the mud. “This is where it is actually happening. It is easy to get lost in the numbers.”
Posey also wades in the shallow copper-colored water and helps his assistants pull in a seine net filled with small predators, including flatfish, blue crabs and juvenile croakers.
The marsh's isolation — in the shallow shoulder areas along the Cape Fear River — provides an excellent laboratory for Posey and his colleagues to study the effects of nutrient loading on estuaries.
Although there have been numerous studies on the detrimental effects of nutrients in fresh water, this is one of the first times scientists have experimentally studied the effects of nutrient loading on bottom communities in North Carolina tidal creeks.
Posey, along with colleagues and graduate students, found that low levels of nutrients increased the growth of benthic microalgae — single-celled algae living on the bottom of North Carolina's estuaries.
However, added nutrients did not result in more or larger small bottom animals, including the many small invertebrates that are food sources for fish and crabs.
Algae are a major source of plant production on tidal flats and form the base of many food chains. Posey says the results suggest that the effects of added nutrients may be more complex than often thought.
“Within several weeks, low nutrient loading created a greater biomass of algae,” says Posey, a professor at the University of North Carolina at Wilmington. “We know the grazing animals sometimes can keep algae under control and that increased algal production can lead to increased number and/or sizes of the animals that feed on them.
“One of our questions was whether increased nutrients may lead to increased numbers of bottom animals — the food for many fish and crabs. Surprisingly, small increases in nutrients led to more algae but not more fauna, making the issue of nutrient additions in coastal waters much more complex than we had previously thought.”
Posey says the study may have important implications for the state's water quality.
“Even though water quality is meeting the Environmental Protection Agency's guidelines, biology and the food web also affect and are affected by water quality,” he says. “Our results suggest that the health of the fish population may influence food-web response to moderate nutrient loading. We are seeing small differences in communities with low to moderate nutrient loading. This suggests there may be a threshold for change at higher nutrient loadings.”
Because of his groundbreaking research, Posey received the Faculty Scholarship Award from UNC-W last year. He was one of only two professors to receive the award.
“Martin is one of our most engaged faculty members,” says Scott Quackenbush, chair of the UNC-W Department of Biological Sciences. “He has more to do on one given day than three people.”
Troy Alphin, a research associate and long-time collaborator with Posey, agrees. “He is probably one of the most enthusiastic people in the research field,” says Alphin. “He doesn't do anything half way. His interest in water quality issues is tied together in all his projects.”
Posey developed an affinity for the water while growing up in rural southern Maryland on the Chesapeake Bay.
“I lived on a creek,” he says. “My dad was a small-time fisherman. I helped with the nets — all small stuff.”
His interest in estuarine systems led him to study zoology at the University of North Carolina at Chapel Hill where he did an honors thesis on mud shrimp.
“The diversity of organisms got me into benthic ecology from worms to mud shrimp,” he says. “The diversity on flats is so amazing. It all intrigues me.”
In Posey's doctoral thesis at the University of Oregon, he continued his interest in ghost shrimp — an invertebrate that can kill oysters and is used as bait for fisheries.
“Once, I sunk in the mud,” he says. “I had to swim and crawl my way out of a mud slurry.”
For several years, Posey worked in the Pacific Northwest on seagrass beds and other projects. In the fall of 1989, Posey began teaching atUNC-W.
At UNC-W, Posey juggles several jobs — from teaching and research to managing, along with Alphin, a staff of 14 assistants and students in the Benthic Ecology Lab where they conduct experiments on bottom fauna.
“The lab is a beehive of activity because Martin has to collaborate with 10 other faculty members,” says Quackenbush.
One of the lab's ongoing projects is its involvement with the Cape Fear River Program, a collaborative program that involves numerous researchers and focuses on the dynamics of the state's largest river system as well as the effects of development on the river's health.
“We have discovered information about the effects of hurricanes on the bottom community,” says Posey. “We found dramatic deterioration after hurricanes Fran and Bonnie and to a lesser extent after Floyd. However, we also found that the bottom community recovered the spring after the hurricane, indicating that bottom animals are resilient.”
In his work on the Cape Fear, Posey also documented a gradual and steady decline of bottom species at certain locations over the past five years. “That may indicate chronic effects or gradual deterioration in our river system or the cumulative effects of multiple hurricanes,” he says.
When Posey isn't teaching or overseeing the lab, he is motoring on a vessel to one of his research sites.
For his ongoing Sea Grant project on blue crab habitats — particularly juvenile crabs — he samples areas near the Cape Fear and New rivers. In North Carolina, blue crabs are the top commercial fishery, generating more than $32 million from hard crab harvests in 2000, according to the N.C. Division of Marine Fisheries.
In the past, most researchers had thought that young crabs, which face the greatest danger from the claws of bigger crabs, would rather migrate to seagrass beds.
While studying the thumbnail-sized young crabs, Posey discovered that marsh areas along the state's southeastern coast may be used extensively as nursery areas for blue crabs.
What makes Posey's research so useful is his choice of a region — one that hasn't been studied much for its crab habitats and has no seagrass beds.
“These crabs may use low-salinity areas — especially in the absence of submerged vegetation.” Posey says. The study emphasizes the potential management importance of these riverine systems, he adds.
Through a North Carolina Fisheries Resource Grant administered by North Carolina Sea Grant, Posey and Sea Grant researcher Larry Cahoon studied the effects of experimental shrimp and crab trawling on bottom communities. They worked alongside veteran fisher Henry Daniels.
In recent years, there has been no shortage of opinions about the environmental impacts of inshore trawling.
Some say trawling is good for productivity of inshore waters, “cultivating” the bottom sediments and stimulating growth of the tiny creatures that live there. Others say trawling is bad for these waters, unsettling the communities and disrupting their biomass or weight and volume and ability to reproduce.
The study is important because the bottom areas affected by trawling are a prime habitat for soft-bottom organisms that are important food for larger fish, shrimp and crabs.
The research targeted three types of organisms. Benthic microalage are important plant producers, especially for small bottom-dwelling animals. Meiofauna live in-between sand grains and are small enough to be prey for shrimp and small bottom-feeding fishes. Macrobenthos include worms, amphipods and clams and are a food source for larger fishes, shrimp and crabs.
“We found no significant effects of experimental trawling on soft bottom organisms,” says Posey. “However, there were some differences between trawled and untrawled areas. The differences vary between areas, between years, and among different types of organisms. More work is needed to determine which, if any, of these differences are actually due to the chronic effects of trawling.”
Healthy oysters serve as a natural water-filtration system by cleansing estuaries of suspended material, consuming excess algae and promoting growth of vegetation.
As more people move to coastal areas, water-quality problems are expected to increase.
“The development of oyster populations that are tolerant to low water-quality parameters, especially turbidity and increased nutrients, is important,” says Posey. “The establishment of populations of tolerant oysters would help to create a source of larvae to replenish dwindling stocks, enhancing fishery habitats and possibly affecting the water quality through filtering.”
To develop a tolerant strain of native oysters, Alphin, Posey, and Sea Grant researcher Ami Wilbur are examining natural adult populations in two different water-quality environments.
“Results obtained will be a first step in determining possible selection among oyster populations,” he says.
Posey also is investigating the value of oyster reefs as a fishery habitat.
“Because currently employed harvesting practices for oysters are destructive to the entire reef, evaluating the use of reefs is important for properly managing, protecting and restoring these habitats and associated fisheries,” he says.
It has been well documented that reefs are critical habitats for oysters, Posey says. “However, we have not determined if oyster reefs qualify as essential fish habitat for other important species,” he adds. “We currently are looking at how reefs are used by fish, crabs and shrimp under a variety of conditions.”
Both North Carolina and Virginia have efforts underway to restore oyster reefs for their habitat value. However, these restoration efforts require a firm understanding of factors that influence the quality of oyster reefs as habitat, such as the vertical relief of a reef, the size of oysters, or closeness to other habitat types, says Posey.
As Posey looks into the Cape Fear River, he says that all his projects are interrelated.
“All our projects are centered on the food web,” he says. “We need to develop a better understanding of food-web dynamics in estuarine systems. Many nearshore estuaries are important habitats for shrimp, blue crabs and oysters.”
To find out more about Posey's research, log onto: www.uncwil.edu/cmsr/benthic.