Effects of nutrient enhancement and predation on estuarine communities.
Over the last two decades development around our estuarine and coastal areas has increase dramatically. Likewise the impacts associated with increased development (increase organic and inorganic inputs, loss of riparian wetlands, and habitat degradation) have been seen, yet we know surprising little about how these systems cope with these stressors.
Since 1993 we have conducted a variety of studies (producing several articles, with more in press) dealing with the top-down vs bottom-up control of estuarine systems. Specifically these projects deal with the infaunal response to controlled nutrient additions in the presence of predators and in the absence of predation at a variety of sites representing a range of background nutrient and developmental inputs. We also deal with the issue of scale in regard to eutrophication, for example small tidal creeks do not respond to nutrient additions in the same way as larger river dominated systems do. The bulk of these studies have been supported by North Carolina Sea Grant
Fear River Program
As part of the Cape Fear River Program, the Benthic Lab examines trophic dynamics and anthropogenic impacts in the Cape Fear River. Specifically, we examine seasonal benthic infaunal composition and abundance at several subtidal stations along the lower Cape Fear River and in the lower Northeast Cape Fear.
Additionally, samples of epibenthic organisms, such as juvenile fish, mysid shrimp, and crabs are collected using epibenthic sled tows. This data allows for examination of timing and magnitude of recruitment events, and establishment of baselines to understand causality of changes in the river. Recently this data has been useful in determining the impact of large scale events such as hurricanes and chronic problems such as pollution inputs. Results to date indicate the benthic communities in the Cape Fear River estuary have high resistance and resilience to disturbance. However, there are some sites that indicate lose of species richness over the last four years. While this trend may be due in part to repeated natural disturbance events it is an area we will watch closely to see if the trend continues. The data collected for this project has been made available to concerned industries, as well as state agencies, to assist in improving resource management practices. This project expands our understanding of trophic linkages and controls within the estuary.
program at UNCW
This is a multi-disciplinary program that brings combines ecology, multiple aspects of physiology, endocrinology, and genetics to study the biology of the early juvenile stages of Callinectes sapidus the blue crab within the estuarine systems of southeastern North Carolina. Our main focus in the program is to evaluate the distribution of early juvenile blue crabs, Callinectes sapidus, (<30 mm carapace width) across the estuarine gradient. Work conducted in other systems indicated that blue crab megalopae settle at the mouth of the estuary, around preferred habitats, then metamorphose into first crabs and at around 30 mm carapace width begin to move up the estuary into lower salinity areas. Observations from the Cape Fear and New Rivers indicated juveniles may utilize low salinity habitats at a much smaller size class. Monthly sampling over the past two years has shown that a large proportion of the early juveniles are found in the oligohaline regions of these estuaries.
In order to evaluate possible benefits of utilizing low salinity regions of the estuary we must understand the tradeoff involved. Initial indications are that the utilization of low salinity habitats places a greater energy demand on the early juveniles, therefore they must receive some benefit, possibly in the form of reduced predation pressure. For this reason we sample the suite of potential predators at all sites.
We also evaluate the size distribution of early juveniles across the estuarine gradient. This information is vital in determining the potential benefits that juvenile blue crabs receive from utilizing low salinity regions of the estuary. While this study focuses in the early juveniles (< 30mm carapace width) there are several size classes that may respond differently and affect the strength of the cost/benefit from using a particular habitat. Results of the last two years indicate even the smallest size class (<10mm carapace width) can be found in the oligohaline regions of the estuary, although the size distribution shifts among seasons.
Aside from their value as a food source, oyster reefs may serve a variety of other ecological functions. Among these are potential effects on local water quality and habitat for fish and decapods. We have been examining use of oyster reefs by fish and decapods in order to determine their importance as a refuge and/or foraging habitat. We have found that intertidal and shallow subtidal reefs are utilized to a greater degree than adjacent habitats by several species of fish, shrimp, and crabs. Moreover, smaller predators using oyster reef areas also forage over adjacent sandflats having consequences for the distribution and abundance of organisms in those areas.