What is an oyster reef
Oyster reefs, often referred to as oyster bars, are common submerged habitats in the southern United States. Oyster reefs in Florida are found in nearshore areas and estuaries of both coasts, but grow especially vigorously near estuarine river mouths where waters are brackish and less than 10 meters deep. For example, the Apalachicola River in northern Florida is a particularly productive area for oysters, and supplies over 90% of the states annual oyster catch. Within the Indian River Lagoon, oyster reefs may be found in the vicinity of spoil islands and impounded areas. In addition to being commercially valuable, oyster reefs serve a number of important ecological roles in coastal systems: providing important habitat for a large number of species; improving water quality; stabilizing bottom areas, and influencing water circulation patterns within estuaries.
Oyster reefs are built primarily by the eastern oyster, Crassostrea virginica, through successive reproduction and settlement of larvae onto existing reef structure. Oysters in Florida spawn from late spring through the fall. The planktonic larvae that develop require a hard substratum to settle upon in order to complete development to the juvenile stage, and prefer to settle on the shells of other oysters. Thus, over time, continued settlement and subsequent growth of generations of oysters may form massive reef structures consisting of staggering numbers of individuals. Luntz (1960), estimated that 5,895 oysters, the equivalent of 45 bushels, occurred within a single square yard of oyster reef.
As successive generations of oysters settle and grow, reefs become highly complex, with many structural irregularities and infoldings that provide a wealth of microhabitats for many different species of animals. Wells (1961) listed 303 different species utilizing oyster reef as habitat in North Carolina. Common Indian River Lagoon species associated with oyster reefs include bivalves such as the hard clam (Mercenaria mercenaria) and bay scallop (Argopecten irradians concentricus); space competitors such as the scorched mussel (Brachidontes exustus), ribbed mussel (Geukensia demissa), the jingle shell (Anomia simplex), and barnacles of the Balanus genus; gastropod mollusks such as the conchs (Melongena spp. and Strombas spp.) and rocksnails (Thais spp.); numerous sponge species; flatworms; polychaete worms; amphipods; isopods; shrimp; and fishes such as blennies, gobies, spadefish, snappers, drum, and seatrout, among others.
Beyond providing smaller organisms with habitat, oyster reefs also provide food to a wide variety of secondary consumers. Many species of fish prey upon oyster reef associates; while others such as the black drum (Pogonias cromis) and cow-nosed ray (Rhinoptera bonasus) prey upon oysters themselves. Other species that utilize oyster reefs for foraging and feeding include the xanthid crabs, also known as mud crabs; swimming crabs of the genus Callinectes; mollusks such as the thick lipped oyster drill (Eupleura caudata), the sharp-rib drill (E. sulcidentata), the Atlantic oyster drill (Urosalpinx cinerea), the Tampa drill (U. tampaensis), the knobbed whelk (Busycon carica), the lighthire whelk (B. contrarium), and the pear whelk (B. spiratum pyruloides); flatworms such as oyster leeches (Stylochus spp.); boring sponges (Cliona spp.); and annelid worms (Polydora spp.).
Oyster reefs also contribute to improved water quality in areas where they occur. Oysters are filter feeders which strain microalgae, suspended particulate organic matter, and possibly dissolved organic matter from the water column over their gills in order to feed. Under optimal temperature and salinity conditions, a single oyster may filter as much as 15 liters of water per hour, up to 1500 times its body volume. Spread over an entire reef, for an entire day, the potential for oysters to improve water clarity is immense. Additionally, since oysters are sessile, and bioaccumulate some potential toxins and pollutants found in the water column, they have been used to assess the environmental health of some areas.
