Research

Selected Research Articles 2005–Present
1998–2000 | 2001–2004

Below are abstracts of Rhode Island Sea Grant–funded research articles. To order a copy of the article, contact Rhode Island Sea Grant Communications at (401) 874-6842.

The National Sea Grant Library is the official Sea Grant archive. Library staff lend documents all over the world and maintain a searchable bibliographic database where you may obtain citations and abstracts of Sea Grant publications and, in many cases, a full text copy of the document.

Topics:
Coastal Ecosystems | Estuaries | Fisheries | Invasive Species

Coastal Ecosystems

• C. Mullan Crain and M. Bertness, 2006. Ecosystem Engineering across Environmental Gradients: Implications for Conservation and Management. BioScience 56(3): 211–218.
RIU-R-06-003; 7pp; $3

Ecosystem engineers are organisms whose presence or activity alters their physical surroundings or changes the flow of resources, thereby creating or modifying habitats. Because ecosystem engineers affect communities through environmentally mediated interactions, their impact and importance are likely to shift across environmental stress gradients. We hypothesize that in extreme physical environments, ecosystem engineers that ameliorate physical stress are essential for ecosystem function, whereas in physically benign environments where competitor and consumer pressure is typically high, engineers support ecosystem processes by providing competitor- or predator-free space. Important ecosystem engineers alleviate limiting abiotic and biotic stresses, expanding distributional limits for numerous species, and often form the foundation for community development. Because managing important engineers can protect numerous associated species and functions, we advocate using these organisms as conservation targets, harnessing the benefits of ecosystem engineers in various environments.

Estuaries

• K. Addy, A. Gold, B. Nowicki, J. McKenna, M. Stolt, and P. Groffman. Denitrification Capacity in a Subterranean Estuary below a Rhode Island Fringing Salt Marsh. Estuaries 28(6):896–908.
RIU-R-05-001; 12 pp.; $3

Coastal waters are severely threatened by nitrogen (N) loading from direct groundwater discharge. The subterranean estuary, the mixing zone of fresh groundwater and seawater in a coastal aquifer, has a high potential to remove substantial N. A network of piezometers was used to characterize the denitrification capacity and groundwater flow paths in the subterranean estuary below a Rhode Island fringing salt marsh. N-enriched nitrate was injected into the subterranean estuary to evaluate the denitrification capacity of the saturated zone at multiple depths below different zones (upland-marsh transition zone, high marsh, and low marsh). The warm season (groundwater temperature >12ºC) low marsh groundwater denitrification capacity was significantly higher than all other zones and depths. In the cool season (groundwater temperature <10.5ºC), elevated groundwater denitrification capacity was only found in the low marsh. Through this study, researchers concluded that as much as 29–60 mg N could be removed from 1 liter of water flowing through the subterranean estuary below the low marsh, arguing for the significance of subterranean estuaries in annual watershed-scale N budgets.

• A. Altieri and J. Witman, 2006. Local Extinction of a Foundation Species in a Hypoxic Estuary: Integrating Individuals to Ecosystem. Ecology 87(3):717–730.
RIU-R-06-001; 13 pp.; $3

Researchers integrated across individual, population, community, and ecosystem levels to understand the impact of environmental stress by tracking the foundation species Mytilus edulis in the hypoxic estuary Narragansett Bay. Initial surveys revealed that the mussels occurred in nine extensive, dense, subtidal reefs that attracted a diverse suite of predators (sea stars, crabs, and gastropods). Hypoxia occurred in the summer of 2001, and a mussel transplant experiment revealed overall reduced growth rates of individuals and higher mortality rates among larger mussels. At the population level, large decreases in densities and cover of mussels were correlated with dissolved oxygen concentrations, leading to extinction at one site and reductions of over an order of magnitude at others. At the ecosystem level, the initial infiltration rate of the mussel reefs was estimated as equivalent to filtering the volume of the Bay 1.3 times during the average 26-day average residence time. That function was reduced by more than 75 percent following hypoxia.

Fisheries

• C. Anderson and J. Sutinen, 2005. A Laboratory Assessment of Tradable Fishing Allowances. Marine Resource Economics 20:1–23.
RIU-R-05-002; 22 pp.; $3

Transferable allowance management systems are receiving increased attention from fishery managers and stakeholders alike. Researchers used a laboratory experiment in which human subjects play the role of fishermen to evaluate the promised economic efficiency of tradable allowance systems. In an experiment designed to parallel the most common rules for trading allowances, researchers found that allowance prices are only weakly associated with the value of the fishing right it provides. Instead, researchers found a high degree of price variability, consistent with field experiences. In the lab, this variability hampers convergence and supports speculation, leading to average prices much higher than the equilibrium value of allowances. During this protracted price discovery, allowances are misallocated and efficiency falls. Modifications to the market institutions used in most tradable allowance systems to improve price discovery and enhance efficiency are discussed.

Invasive Species

T. Minchinton, J. Simpson, and M. Bertness, 2006. Mechanisms of exclusion of native coastal marsh plants by an invasive grass. Journal of Ecology 94: 342–354.
RIU-R-06-002; 12; $3

Determining the mechanisms by which invasive species exclude natives is critical for conserving and restoring native populations in impacted habitats. In recent decades the grass Phragmites australis has been aggressively invading coastal marshes of North America, with monocultures often replacing diverse assemblages of plants. The researchers' objective was to quantify how P. australis modifies the abiotic and biotic environment and to determine the mechanisms by which it excludes two common forbs, the annual chenopod Atriplex patula var. hastata and the perennial aster Solidago sempervirens, from the highest tidal elevations of brackish marsh in southern New England. In a 3-year field experiment researchers added seeds of both forb species to stands of P. australis, where they manipulated shoots and litter in an orthogonal design, and to uninvaded marsh areas dominated by the rush Juncus gerardi, where they manipulated the shoots of the marsh vegetation. In general, seedling establishment and the number of plants surviving until the end of the growing season were substantially greater in areas not invaded by P. australis, and both shoots and litter limited the abundance of forbs within stands. Forbs surviving within stands of P. australis grew larger and produced more seeds than those in uninvaded areas, indicating that changes to the soil resulting from invasion do not preclude the survival of established forbs. This was confirmed by a glasshouse study where the performance of forbs in soil collected from within stands of P. australis was better than in soil from areas dominated by J. gerardi. Similar to many invasive grasses in terrestrial communities, P. australis excludes native forbs through competition, modifying the biotic environment of the marsh at both the ground and above-ground levels. The results suggest that successful invaders, such as P. australis, are likely to be the ones that can engineer habitats in multiple ways and limit populations of native species across several critical stages of their life history.