Marine Invertebrates of Bermuda Atlantic Pearl Oyster (Pinctada imbricata) By Erin Leonhardt and James B. Wood (Ed) Abstract Taxonomy  Habitat  Ecology  Recent Research  Commercial Importance  Bermuda Laws  Personal Interest  References  Links

Abstract


The Atlantic pearl-oyster, Pinctada imbricata, is biologically and economically important. Pinctada imbricata is a filter-feeding bivalve that grows in a diverse geographic range (Urban, 2000; O’Connor and Lawler 2004a). The growth and reproduction of P. imbricata depends on salinity, temperature, suspended particulate matter (SPM), and food (Ward and MacDonald, 1996; Urban, 2000; O’Connor and Lawler, 2004a). Recent research on P. imbricata focuses on commercial oyster farmers and shellfish hatcheries (O’Connor and Lawler, 2004b). In Bermuda P. imbricata is found in Harrington Sound and protected under Bermudian Laws(Balzer and Wefer, 1981; Laws of Bermuda, 1989; Urban, 2000).

Taxonomy


Phylum: Mollusca
  Class: Bivalvia
    Order: Pterioida
      Family: Pteriidae


The Atlantic pearl oyster, Pinctada imbricata, is in the class Bivalvia because it has bilateral symmetry, a two valved shell, is dorsally hinged, and has an intestine that passes through the heart (Sterrer, 1986). The Atlantic pearl oyster lacks a head, radula, and cephalic eyes (Sterrer, 1986). P. imbricata are in the order Pterioida because they have both a nacreous (pearl layer) and a notch in the right valve that byssally attaches to the substrate (Sterrer, 1986). Characteristics that P. imbricata share in the family Pteriidae are an ovate shell, a straight hinge line, and an interior nacreous or pearl layer (Sterrer, 1986). The species Pinctada imbricata is known for having a thin and brittle shell, appearing brown to tan with darker brown lines, and being able to produce pearls (Sterrer, 1986).

Habitat


The Atlantic pearl-oyster, Pinctada imbricata, has a broad range of habitats. Common geographic locations that P. imbricata can be found are Australia (specifically New South Wales and Port Stephens), India, Caribbean Sea of Columbia (specifically Guajira province), and Bermuda (Urban, 2000; O’Connor and Lawler, 2004a). P. imbricata were brought to Japan to help improve economic loss due to disease in Japanese native pearl oyster species; furthermore, the introduction of P. imbricata to Japan led to cross-breeding between both pearl oysters species (Masaoka and Kobayashi, 2005). Pearl oysters, including P. imbricata, were in abundance off the coast of Venezuela (primarily coast of Cubagua) until the early 1500s when high demands for pearls eventually depleted the pearl oyster population (Romero, 2003). P. imbricata populations geographically vary depending on habitat conditions.

The Atlantic pearl-oyster use byssi to attach to hard substrates (Ward and MacDonald, 1996). Pinctada imbricata are found in rocky, sandy, and shallow areas in bays, sounds, lagoons, and harbors in both the Northern and Southern hemispheres (Ward and MacDonald, 1996; O’Connor and Lawler, 2004a).

Ecology


Growth in P. imbricata embryos, juveniles, and adults is affected by seawater temperature changes, salinity fluxes, food availability, and suspended sediments (Ward and MacDonald, 1996; Urban, 2000; O’Connor and Lawler, 2004a). Temperature and salinity tolerance depends on the geographical location of P. imbricata; correspondingly, stable populations of P. imbricata are found near estuarine systems where water flow helps regulate salinity and temperature levels (O’Connor and Lawler, 2004a). When water flow is minimum during salinity changes bivalves can close their valves, this is called isoosmotic intracellular regulation (O’Connor and Lawler, 2004a). Juvenile Atlantic pearl oysters responded to reduced salinities by closing their valves, which decreased the rate of byssal attachment (O’Connor and Lawler, 2004a). Under the conditions of 18 degrees Celsius and 29 to 32 parts per thousand (ppt) 80% of P. imbricata spat formed byssal attachment (O’Connor and Lawler, 2004a). One specific example is in Port Stephens, Australia where the temperature range for P. imbricata is 14 to 26 degrees Celsius and spawning primarily occurs during the summer when the temperature is above 18 degrees Celsius (O’Connor and Lawler, 2004a; O’Connor and Lawler, 2004b). In India P.imbricata is tolerant of salinities between 24 to 50 ppt for 2 to 3 days; whereas, in Japan P. imbricata spat needs a minimum of 22.7 ppt to survive (O’Connor and Lawler, 2004a). Spawning of P. imbricata occurs at different temperatures because of the geographical area to which the species has adapted (O'Connor and Lawler, 2004a). Temperature can also be affected by the amount of upwelling in an area, which can affect the rate of reproduction (Urban, 2000). Upwelling can lower water temperature; correspondingly, upwelling increases surface nutrients supplying more energy for gonad development and reproduction (Urban, 2000). The growth of P. imbricata is not only dependent on salinity and temperature, but also dependent on suspended particulate matter (Ward and MacDonald, 1996).

Pinctada imbricata filter feeds suspended particulate matter (SPM) from the water column (Ward and MacDonald, 1996). Abiotic factors such as storms and wind resuspend bottom sediments and increase the amount of SPM in the water; furthermore, an increase in SPM affects light penetration and nutrient levels (Ward and MacDonald, 1996). High levels of sedimentation can clog the gills of P. imbricata (Ward and MacDonald, 1996). P. imbricata is able to regulate the ingestion rate of SPM through bulk rejection and then reject the material in pseudofeces (Ward and MacDonald, 1996). The purpose of pseudofecal production is not only to remove bulk amounts of excess or irritating material, but also to reject unwanted material to improve the quality of ingested matter (Ward and MacDonald, 1996). Sediments contain varying levels of nutrients including nitrogen and carbon; nevertheless, P. imbricata does not select out nitrogen or carbon particles from SPM (Ward and MacDonald, 1996). The amount of suspended matter has an affect on the growth of P. imbricata because of the amount of nutrients available in the SPM (Ward and MacDonald, 1996).

P. imbricata can be found in the subtropical environment of Harrington Sound, Bermuda (Balzer and Wefer, 1981; Urban, 2000). Further studies need to be done on the number of P. imbricata in the sound and how the P. imbricata is ecologically affected. Characteristics of Harrington Sound are large amounts of green algae (Cladophora prolifera), one inlet (Flatt’s inlet) providing surface water flushing, a deep basin (Devil’s Hole), and fish species primarily composed of grunts and sea-breams that transport sediments from deep to shallow water (Balzer and Wefer, 1981; Alheit, 1983; Lapointe and O’Connell, 1989). These ecological variables may effect the survival, growth, and reproduction of P. imbricata in Harrington Sound, but further studies need to done on correlating these variables with anthropogenic variables of Atlantic pearl-oyster populations in the sound.

Recent Research


Genetic techniques have been used to test the genes of Japanese oysters for identification purposes (Masaoka and Kobayashi, 2005). Pinctada imbricata is considered genetically similar to Pinctada martensii and Pinctada fucata (both Indian-Pacific pearl oysters) (Masaoka and Kobayashi, 2005). To replenish the loss of many Japanese native pearl oysters other pearl oyster species, including P. imbricata, were brought to Japan (Masaoka and Kobayashi, 2005). This makes identifying pearl oyster species in Japan difficult because of the combination of many pearl oyster species (Masaoka and Kobayashi, 2005).

Research on the reproduction and spawning of P. imbricata is used to benefit oyster farmers and shellfish hatcheries (O’Connor and Lawler, 2004b). In Port Stephens, Australia oyster spat was not available for farmers when the farmers needed the spat (O’Connor and Lawler, 2004b). To be economically successful, oyster farmers in Australia need spat in September, but P. imbricata was not ready till December or January; as a result, hatcheries were built to control oyster reproduction and spat availability (O’Connor and Lawler, 2004b). In the hatchery, oysters were conditioned in July and then spawned in August, which made spat available in September (O’Connor and Lawler, 2004b). Variables that were observed during reproduction and growth included shell growth, byssal attachment, mantle thickness, and mucoprotein layers (O’Connor and Lawler, 2004b). O’Connor and Lawler (2004b) found that P. imbricata commonly has two reproduction peaks, sometimes one or three peaks, and peaks usually occur in the summer. Reproduction varies depending on the latitude of the area; furthermore, spawning activity was found to decrease when latitude increased (O’Connor and Lawler, 2004b). Researching reproduction is important because the information will help farmers know when to collect wild spat and spawn oysters in the hatchery (O’Connor and Lawler, 2004b).

Commercial Importance


In the early 1500’s there were many oyster beds containing P. imbricata off the coast of Venezuela, the coast later became know as Costa de las Perlas (Pearls’ Coast) (Romero, 2003). Trade between indigenous people and European settlers not only kept pearls in high demand, but also led to pearls becoming an unsustainable resource (Romero, 2003). Pearls from oysters were the most valuable commodity carried on Spanish ships and were in high demand by wealthy people (Romero, 2003). Prior to the year 1530 the value of pearls shipped from the American continent to Europe was one-third greater than the production of gold and silver mines on the American continent in a year (Romero, 2003). As the demand for pearls increased the supply quickly decreased resulting in the depletion of pearl oyster beds off the coast of Venezuela (Romero, 2003).

Even though pearl oyster beds off the coast of Venezuela were depleted, pearls remain economically important in many places. In Australia pearl oysters are the primary basis for the Australian aquaculture industry (O’Connor and Lawler, 2004b). Other than Australia, Pinctada imbricata is economically important in Japan (O’Connor and Lawler, 2004b; Masaoka and Kobayashi, 2005).

Bermuda Laws


In 1978 Bermuda Fisheries Laws declared the Atlantic pearl-oyster, Pinctada imbricata, as a protected species (Laws of Bermuda, 1989).

Personal Interest


My interest in oysters began while studying at college. Through my university I was fortunate enough to work for an oyster gardening program that aims to restore and enhance the oyster population in Narragansett Bay, Rhode Island USA. Oyster populations are biologically important because they filter large amounts of water per day and provide habitats for other organisms to live underneath or around. While studying in Bermuda I learned that in Bermuda the Atlantic pearl-oyster is primarily found in Harrington Sound and immediately became interested as to why they were mainly found in the sound. I became interested in what the population size of these oysters in the sound may be and what effects the population size of these oysters. I learned that the Atlantic pearl-oyster is not only biologically important, but also economically important in many cultures. The combination of biology and anthropology makes the discussion of the Atlantic pearl-oyster even more intriguing and valuable to the earth and society.

References

Alheit J. 1983. Sediment transport by fishes in Harrington Sound, Bermuda. Estuaries, Coastal and Shelf Sciences. 17:547-554.

Balzer W, Wefer G. 1981. Dissolution of carbonate minerals in a subtropical shallow marine environment. Marine Chemistry. 10:545-558.

Lapointe BE, O’Connell J. 1989. Nutrient-enhanced growth of Cladophora prolifera in Harrington Sound, Bermuda: Eutrophication of a confined, phosphorous-limited marine ecosystem. Estuarine, Coastal and Shelf Sciences. 28:347-360.

Laws of Bermuda. “Fisheries (Protected Species) Order 1978” 1989. Accessed Nov 11th. 2007 .

Masaoka T, Kobayashi T. 2005. Species identification of Pinctada imbricata using intergenic spacer of nuclear ribosomal RNA genes and mitochondrial 16S ribosomal RNA gene regions. Fisheries Science. 71:837-846.

O’Connor WA, Lawler NF. 2004a. Salinity and temperature tolerance of embryos and juveniles of the pearl oyster Pinctada imbricata Roding. Aquaculture. 229:493- 506.

O’Connor WA, Lawler NF. 2004b. Reproductive condition of the pearl oyster, Pinctada imbricata, Roding, in Port Stephens, New South Wales, Australia. Aquaculture Research. 35:385-396.

Romero A. 2003. Death and taxes: the case of the depletion of pearl oyster beds in the sixteenth-century Venezuela. Conservation Biology. 17:1013-1023.

Sterrer, W. (1986). Marine Fauna and Flora of Bermuda (ed. W. Sterrer), pp. 460-467. Canada: John Wiley & Sons, Inc.

Urban HJ. 2000. Culture potential of the pearl oyster (Pinctada imbricata) from the Caribbean. I. Gametogenic activity, growth, mortality and production of a natural population. Aquaculture. 189:361-373.

Ward JE, MacDonald BA. 1996. Pre-ingestive feeding behaviors of two sub-tropical bivalves (Pinctada imbricata and Arca zebra): Responses to an acute increase in suspended sediment concentration. Bulletin of Marine Science. 59:417-432.

Links


Australian Aquaculture Portal, Pinctada maxima
History of the Atlantic pearl oyster, Pinctada imbricata, industry in Venezuela and Colombia
Pearl Oyster Aquaculture
The Present Status of Shellfish Culture in Japan
A History of the Pearl Oyster Fishery in the Archipielago de las Perlas, Panama