Impact of Oyster (Crassostrea virginica) Reef Restoration on Benthic Invertebrates and Coastal Birds in a Subtropical Estuary

Jessica L Copertino,Linda J Walters,Katherine Harris,Lyndsey Chute

doi:10.3390/su14042371

Abstract

In order to mitigate the degradation of eastern oyster (Crassostrea virginica) reefs in Mosquito Lagoon (ML) along the east coast of central Florida, oyster reef restoration efforts have been in place for over 14 years. These restored reefs are successful in terms of universal oyster metrics (i.e., density, shell height, reef height) and are similar to natural reefs. However, little is known about the impact of this restoration on bird populations. ML provides a habitat for many bird species, including several listed as “threatened” by the Florida Fish and Wildlife Conservation Commission. Many of these birds rely on oyster reefs for foraging and loafing habitats. As benthic invertebrates serve as an important food source for coastal birds, we monitored the abundances and diversity of these organisms on live, restored, and dead reefs. We collected sediment samples from the reef sites pre-restoration, and one month, six months, one year, two years, and three years post-restoration. We counted benthic invertebrates present in the sediment samples, and sorted them by taxa (polychaetes, amphipods, isopods, gastropods, bivalves, decapods). Benthic invertebrate abundances on restored reefs became similar to live reefs over time (species composition, density), indicating that the prey base on restored reefs was similar to that of live reefs within 6 months. A second objective of this study was to determine if restored oyster reefs reach the same abundances, foraging behaviors, and diversity of bird species on natural, live reefs. We conducted monthly bird surveys to assess bird utilization of live, restored, and dead reefs. After three years, the abundances, behaviors, and assemblages of birds on restored reefs were similar to live reefs.

Highlights

Shorebirds, wading birds, and seabirds rely on coastal ecosystems for foraging and nesting habitats (e.g., [1,2,3,4])
Goss-Custard and Moser [9] found that loss of foraging grounds due to the spread of the cordgrass Spartina anglica led to decreases in Calidris alpina (Dunlin) abundances in several estuaries in Europe
Of the birds observed on live reefs, 2.2% on restored reefs, and 87.0% on dead reefs

Summary

Introduction

Shorebirds, wading birds, and seabirds rely on coastal ecosystems for foraging and nesting habitats (e.g., [1,2,3,4]). The ability of any coastal habitat to support communities of foraging birds is dependent on two main factors: prey availability and habitat extent [5]. The study found that wading birds were negatively impacted by decreased prey density and decreased prey vulnerability, and all experienced population declines [6]. As foraging densities increase, density-dependent factors, such as competition, take effect and can lead to an overall reduction in bird abundance [5,7,8]. If the foraging habitat in an ecosystem is lost, the capacity of that site to support bird populations would decrease. Meire [10] found that reductions in intertidal foraging habitat due to the construction of several dams resulted in declines in Haematopus ostralegus (Eurasian Oystercatcher) populations in an estuary in the Netherlands

Methods

Results

Discussion

Conclusion