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UC Toxics News: Fall 2000
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Indicators of Pollution: Studies in San Diego Bay by Paige Jennings Reprinted with permission from Explorations Magazine, a publication of Scripps Institution of Oceanography,UCSD

 

 

 

In the backwater of San Diego Bay, Dmitri Deheyn prepares to dive to one of his research sites. Photographer: Bill Call

Ocean pollution is a serious environmental concern, especially in developed coastal areas where shoreline and bay sediments may become reservoirs of urban and industrial pollutants, including heavy metals, As a consequence, organisms living in or on the sediment, or those that prey upon bottom-living organisms, face heavy-metal exposure.

Marine organisms living in direct contact with contaminated coastal sediments may serve as biological indicators to help scientists determine the locations and severity of pollution. Dimitri Deheyn, a postdoctoral fellow from Belgium, is working in Michael Latz's lab at Scripps to develop new ways of using common bioluminescent brittle stars for this purpose.

"Brittle stars are cousins of starfish, and their name refers to their tendency to release an arm when stressed," explains Deheyn. "They live in contact with the sediment on which they feed and are sensitive to environmental quality, being easily killed by exposure to high enough levels of certain heavy metals,''

Commonly, bioluminescent bacteria are used to determine sublethal effects of toxicity but Deheyn thinks they are not accurate indicators of how heavy-metal toxicity will affect larger multicellular organisms with nervous systems.

Collecting during the dive. Photographer: Bill Call

Deheyn explains, "Bacteria lack the complex organization of tissues and organs found in higher organisms, including humans. The human nervous system can be very sensitive to pollutants, while other tissues in our bodies are less sensitive or even help remove pollutants." This appears to be the case for brittle stars.

In luminescent brittle stars, light production is under the control of the nervous system and originates in photocells in the five arms. By comparing bioluminescence from individual photocells to that from the arms, Deheyn's experiments at Scripps will determine whether the effect of heavy metals on bioluminescence is due to nervous system toxicity or a more general physiological impairment.

One of Deheyn's main field projects is taking place this summer in San Diego Bay at six sites exposed to varying levels of heavy metals. He will transplant brittle stars collected from uncontaminated areas outside of the bay into mesh cages buried in the sediment at each site. The locations range from the relatively clean waters at the mouth of the bay, to the back of the bay, where the sediments support high levels of contamination due to heavy industry and a slow rate of water recirculation.

With a keen eye and a gentle grasp, Deheyn searches for tiny brittle stars living within a locally collected kelp holdfast. Photographer: Marc Tule

During the course of one month, Deheyn will remove samples from each site for evaluation in the lab. He will determine the types and quantities of metals in the tissues and will measure the light production of animals from each site. He will then compare the physiological toxicity to the amount of heavy metals in the tissue as measured by mass spectrometry.

"If light production decreases, pollution might limit the fitness of any individual brittle star. The bay brittle star can be considered a model for other organisms in which such a causal link between anthropogenic pollutants and individual fitness may not be so obvious:' says Deheyn.

Deheyn's field work is being conducted in collaboration with the Marine Environmental Quality Branch of the Space and Naval Warfare Systems Center in San Diego. He also receives research support from NATO, the Belgian-American Educational Foundation, and the UC Toxic Substances Research and Teaching Program.