Virginia Coastal Program: 2004 Coastal Grant Project Description and Final Summary
Project Task:
FY2004 Task 11.05
Grantee:
University of Virginia/Virginia Institute of Marine Science
Project Title:
Seaside Heritage Program - Trophic Interactions of Fish Predators Using Restored Sea grass Beds
Project Description as Proposed:
This project will
document the impact of restored seagrasses in South Bay on higher
trophic organisms through both direct and indirect techniques. VIMS
will sample resident predators throughout their residency in restored
beds, examine their feeding habits directly and quantify their integrated
response to habitat changes by analyzing isotopic tracers in the
tissues of predators, their prey and the primary producers upon
which they ultimately depend. This project will emphasize utilization
of seagrass transplant sites by transient, higher trophic level
predators. These transient predators likely feed in re-established
SAV beds and algal habitats by tidally modulated activities. They
serve to link SAV-based production to other adjacent ecosystems
when they move out after feeding. Such predatory activities are
detectable isotopically, since stable isotopic compositions of nitrogen
and carbon increase in the heavy isotope with trophic level, in
a linear fashion of about 1 per mil for carbon and 3 per mil for
nitrogen. The influence of the replanting areas would potentially
be able to be extended to these non-resident species.
The long-term aim is to revisit South Bay after seagrasses are successfully
restored so that we can document changes in energy flow in resident
plant/animal communities using similar approaches. These long-term
objectives will allow documentation of changes in ecosystem-level
processes, water quality and food web structure as the South Bay
system progresses from one dominated by salt marsh and algae (both
mico- and macro) primary producers to one where seagrass becomes
a significant component.
Federal Funding:
$44,000
Project Contact:
Jacques van Montfrans, 804.684.7391; vanm@vims.edu
Project Status:
Project Completed
Final Product Received:
Project Summary Provided by Grantee:
This study investigated the importance of recently established eelgrass (Zostera marina) beds in Eastern Shore coastal embayments (South Bay) for numerous resident and seasonal species of fishes.
Evidence of fish reliance on various carbon sources was examined using two approaches.
First, resident fish predators were sampled within two habitat types (seagrasses and algae) to obtain instantaneous feeding habit data.
Secondly, resident fishes were examined for stable isotopes of carbon, nitrogen, and sulfur (d13C, d15N, and d34S) to evaluate the integrated influence of primary producers over the long term in the diet of resident species.
Over two years (2004 and 2005), monthly samples were taken randomly from June - September in restored seagrass beds and in algal-dominated habitats using a 150-foot seine.
Fishes from 24 samples (12 seagrass and 12 algae) each year were processed for length, weight, stomach contents (VIMS) and tissue sample analysis (UVA). Overall, more than twice as many fishes were collected in 2005 than in 2004.
Fish abundance varied seasonally among the 33 species and 5400 individuals collected in 2004 and among the 28 species and 11,290 individuals caught in 2005. Generally, fish abundance was highest in July, decreased in August and was lowest in June and September when similar levels of low abundance occurred.
Among the dominant species, silver perch (Bairdiella chrysura) and Alantic silversides (Menidia menidia) were strongly associated with SAV habitats in 2005 but this relationship was weaker (perch) or reversed (silversides) in 2004. Pig fish (Orthopristis chrysopterus), Northern pipefish (Sygnathus fuscus), bay anchovies (Anchoa mitchelli) and tautog (Tautoga onitis) occurred consistently in higher abundances in SAV than in algal habitats. Pig fish were more abundant in 2004 and occurred in highest abundance in July. Northern pipefish are known to be linked to SAV habitats and were always more numerous in SAV than algae. Atlantic croaker (Micropogonias undulatus) were uncommon in 2004, but occurred in greater numbers in 2005. Silver perch, pig fish and Atlantic croaker are often preyed upon during their juvenile phase by other predatory fishes and therefore are considered a forage base for these predators.
The fact that seagrass habitats contained higher numbers of these prey species than algal beds indicates the potential importance of the transition of primary producers from ephemeral algae to more permanent SAV in coastal embayments.
Such transitions could potentially have a positive effect on the trophic ecology of these systems by supporting higher prey populations. However, the fish species investigated in this study fed on similar prey that were often common to both SAV and algal habitats thereby confounding any attempt to make unique inferences about the importance of each habitat as a source of nutrition.
The marine landscape in South Bay is in a state of transition as SAV primary production in the system expands. It is likely that SAV habitats may positively influence the ecology of the area over the long term.
The data collected in this study will serve as a baseline from which changes in energy flow within the community can be compared. Each species that has begun to utilize seagrass primary production may have a unique response to this new food source. Over time, and as the trophic interactions in restored South Bay seagrass plots evolve, it is likely that seagrass primary production will become a more important source of nutrition for a variety of species, including those that have recreational or commercial value.
Disclaimer: This project summary provides the federal dollars initially awarded to the grantee. Due to underexpenditure or reprogramming of grant funds, this figure may change. For more information on the allocation of coastal grant funds, please contact Laura McKay, Virginia Coastal Program Manager, at 804.698.4323 or email: Laura.McKay@deq.virginia.gov
A more detailed Scope of Work for this project is available. Please direct your request for a copy to Virginia.Witmer@deq.virginia.gov
