Quarterdeck Volume 5, Number 1, Spring 1997
Bioavailability of colloidally-bound
metals in penaeid shrimp
Roberta A. Carvalho
Ogilbia cayorum
Little fish in a big ocean
Sabrina F. Criscione
Anthropogenic and natural radionuclides
over the Siberian Shelf
Jon M. Schwantes
Bioavailability of colloidally-bound metals in penaeid shrimp
Roberta A. Carvalho
Bioaccumulation, the concentration of an element in an organism, depends on the chemical form of that element. Living organisms either passively absorb or actively take elements into their bodies. My thesis research shows that metals bound to colloid-sized organic matter can bioaccumulate and be released as quickly as free ionic forms of metals. In natural estuarine environments, metals exist in many physiochemical forms-ionic, organically and inorganically complexed, bound to organic and inorganic particles, or bound to colloid-sized micro-particles and macromolecules. In many instances organisms accumulate or assimilate the ionic or the low-molecular-weight form of metal. Until recently, most bioavail-ability studies examined only the uptake and release of these free ionic forms of metals. Therefore, I wanted to perform experiments to examine the bioavailability of other forms of metals. For example, how do colloidally-complexed trace metals influence the bioaccumulation and subsequent release rates in shrimp? I chose to study penaeid shrimp because they are abundant, easy to maintain in captivity, live in many of the world's oceans, and eat what is on the seafloor-settled trace metals. I also wanted to examine where metals accumulate in the shrimp. I used radioactively tagged forms of metals at low, environmentally realistic concentrations to examine uptake and release rates in the body and tissues of the shrimp. To begin, I made a solution of colloids from estuarine water collected at a local salt marsh. I isolated colloids from seawater with an ultrafiltration apparatus. Once the colloids were collected, I bound the metal, in radioactive form, to the colloidal particles. This was done by mixing and filtering the metal-colloid solution to result in a final product of exclusively colloidally-complexed metals. During my research it was difficult to hold shrimp for extended periods of time without high mortality rates and atypical physiological responses. Animals held in groups were subject to cannibalism, and deteriorating water quality induced stress. To achieve good survival rates, I maintained individual animals in small teflon containers in a pure oxygen atmosphere and periodically removed them for feeding. During the experiment, the shrimp were exposed to colliodally-complexed and free ionic forms of metals for four-teen days. Following that, they spent fourteen days in radio-tracer free water. During both phases I periodically tested the shrimp and water to observe the kinetics of uptake and release of metal. I found that penaeid shrimp accumulated colloidally-complexed forms of metals in amounts comparable to free ionic forms. The hepatopancreas, a digestive gland, was the site of the highest accumulation of radiotracer. This is due to metal binding proteins located in vesicles of the organ. The carapace, which contains gill filaments, was the site of second highest accumulation. This uptake is linked to the intake of water through the gills for respiration. The abdominal tissues accumulated the least amount of radiotracer. The shrimp were able to release a majority of both forms of accumulated radiotracer after 14 days in the release phase of the experiment. My research shows that the current emphasis on ionic forms of trace metals for their bioavailability and toxicity might be overstated. The role of colloidal forms of metals in determining bioavailability and toxicological limitations should be studied and incorporated into kinetic models of bioaccumulation and release. |
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Ogilbia cayorum
Little fish in a big ocean
Sabrina F. Criscione
Ogilbia cayorum (Drawing from Evermann and Kendall's Descriptions
of little known genera and species of fish from the U.S., 1898)
Ogilbia cayorum is a viviparous (live bearing) fish belonging to the family Bythitidae. It inhabits coral reefs in shallow waters off South and Central America, the Florida Keys and the Caribbean. It was first described in 1898 by Evermann and Kendall from Key West, Florida, and it is from this location that the species name was derived. In Latin, cayorum means "of the Keys" and refers to Cayo Hueso or Bone Key, the original name of the island of Key West. The common name for O. cayorum is Key Brotula. Since its discovery little information has been gathered regarding this species. It is found in some of the most popular scuba diving locations, but only the most observant and stealthy diver will glimpse this reef inhabitant. Ogilbia cayorum is a tiny fish ranging from 15 to 75 millimeters long. It spends most of the day hiding in the interstices of the reef, venturing out only at night to feed. Its reproductive strategy of bearing live offspring distinguishes it from the more than 2000 reef species thought to inhabit the Gulf of Mexico and Caribbean. The genus O. cayorum is thought to contain several different and as yet undescribed species found throughout the tropical western Atlantic. The objective of my study was to investigate differences in physical characteristics among fish specimens to determine if the genus is composed of multiple species. To accomplish this I collected body measurements, descriptive data, and fin ray and scale counts from 231 specimens of O. cayorum. Fish specimens were examined from eleven different locations throughout the Gulf of Mexico and Caribbean Sea. I then analyzed the raw data using various statistical tests to determine if specimens from any of these locations were significantly different from one another. Results from the analysis failed to show that several different species of Ogilbia inhabit this region. Physical differences were found to be slight. Due to the subtle nature of the variation, Ogilbia is considered a species composed of three populations-an island population and northern and southern populations-which differ slightly in regards to body proportions. Physical differences among the populations were not considered significant enough to warrant the establishment of an entirely new species. The reproductive strategy of Ogilbia may be a factor in promoting the evolution of different populations. The life history of most coral reef fish includes a stage in which local tides and currents transport newly hatched young. This larval period is thought to provide the primary opportunity for species dispersal. Ogilbia cayorum is one of only a few species of reef fish that lack this pelagic life history stage, therefore its ability to disperse is limited. This barrier to gene flow may allow the development of physically distinct species over short distances. A thorough revision of the genus Ogilbia is needed. This study clarifies only a small piece of the taxonomic puzzle. Additional studies involving taxonomic as well as life history components are needed to determine an accurate classification hierarchy and the ecological importance of O. cayorum within the reef community. |
Anthropogenic and natural radionuclides over the Siberian Shelf
Jon M. Schwantes
The Arctic Ocean remains one of the least understood oceans in the world. Its remote, harsh nature makes scientific investigation there very difficult in all but the summer months. During the summers of 1994 and 1995, in conjunction with the Geochemical and Environmental Research Group (GERG) at Texas A&M University, I sampled Siberian Shelf waters for several naturally occuring and man-made radioactive isotopes. For my thesis research, I used man-made radionuclides (cesium 137 and plutonium 238, 239, and 240) and natural radionuclides (lead 210, radium 226 and 228, and thorium 234) to trace the fate of radioactive contaminants in waters over the Siberian Shelf. The purpose of this study was to help delineate man-made sources of radioactive pollutants on the Siberian coast and to assess the effect such sources have on that environment. The Arctic marine environment is perhaps more vulnerable to human influence than the world's other oceans. The capacity of the Central Arctic Ocean to cleanse itself of particle-reactive pollutants, pollutants that readily bind to particles suspended in water, is low compared to the Atlantic and Pacific Oceans due to lower particle concentrations and lower settling fluxes. Since scavenging and subsequent settling and burial by suspended particles remains the significant pathway by which particle-reactive pollutants are removed from the marine environment, low suspended-particle concentrations often translate into longer residence times in the water column. In addition, the flushing rates of Arctic surface waters are relatively fast. Pollution from point sources introduced into these surface waters could quickly spread over the entire Arctic Ocean surface in less than ten years. Fast circulation, however, also helps dilute potential pollutants, thus ameliorating the problem. Seasonal processes, such as pulsed primary productivity, pulsed river influence, and melting ice help increase particle concentrations in the water column over the shelf during the summer months. Coastal areas, which introduce high concentrations of suspended particles to the water column, are also important in controlling pollutant concentration in the Arctic Ocean. Major sources of radioactive isotopes that pollute the ocean are grouped into two categories: global fallout or other-than-global fallout. Low plutonium activity ratios estimated from Siberian Shelf water showed little or no contribution of pollutants from sources other than global fallout. Processes related to estuarine mixing over the shelf control radioactive and other pollutants entering surface waters of the Arctic Ocean. The highest concentrations of man-made cesium and plutonium were found near the mouths of the Siberian Rivers. These radionuclides were probably coming from underlying estuarine sediments due to increased salinity and destruction of binding sites. I used particle-reactive, naturally occurring radioisotopes such as thorium and lead as tracers for particle scavenging in Siberian Shelf waters. I evaluated the magnitude and efficiency by which particle-reactive pollutants like plutonium are scavenged by comparing the percentage of the pollutant bound to particles to the percentage of thorium and lead tracers bound to particles. By studying radium tracers, I found that the flushing rate of the Kara Sea is about one and a half to three years. Results showed that on the Siberian Shelf, flushing is relatively fast, settling fluxes for suspended particles are high, and there is little or no plutonium pollution from sources other than global fallout. This study indicates that the seasonal introduction of suspended particles is important for controlling the concentrations of particle-reactive pollutants in Siberian Shelf waters. |
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