FOR IMMEDIATE RELEASE
Contact: Jana Goldman
Zooplankton, near the bottom of marine and freshwater food chains, can develop tumors like those of higher life forms, according to scientists at the Commerce Department's National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory and the University of Michigan Center for Great Lakes and Aquatic Sciences in Ann Arbor, Michigan.
The evidence, including photographs, will be presented on May 27 during the annual meeting of the International Association for Great Lakes Research, which begins on May 24 in Cleveland, Ohio. Although tumors in zooplankton were reported in 1994 from an area of the Baltic Sea, this is the first time photographs have been taken of the abnormalities and that preliminary evidence has been presented that the tumors are cancerous. The affected zooplankton are copepods and Cladocera (water fleas), which are crustaceans that are usually less than an eighth of an inch in size.
Tumors, or neoplasms, have been found in a variety of invertebrates such as molluscs, insects, and flatworms, but reports of tumors on crustaceans are rare.
Earlier research speculated that tumors might form in zooplankton, but the organisms would die at molting before tumors would be obvious. The team found large tumors on juveniles and on young, recently molted adult zooplankton in Lake Michigan.
Researchers found tumors in several species of copepods and Cladocera. Predatory species were more likely to have tumors than herbivorous species. Preliminary analyses suggest that tumors are more common nearshore than offshore.
The work is the effort of a team of five scientists: Drs. H.A. Vanderploeg of NOAA's Great Lakes Environmental Research Laboratory (GLERL); G. L. Fahnenstiel of GLERL's Lake Michigan Field Station; M. Omair and D.J. Jude of the Center for Great Lakes and Aquatic Sciences; and T.M. Rizki, Department of Biology, University of Michigan. All but Fahnenstiel, who works in Muskegon, Mich., are based in Ann Arbor, Mich.
Zooplankton showing the tumors were collected during 1995 and 1998 as part of GLERL's food web and water-quality monitoring program and as part of Michigan Sea Grant-supported research by D. Jude on larval fish and zooplankton interactions in the nearshore zone. Analysis of the tumors by T. Rizki showed a high frequency of dividing cells, which is suggestive of cancerous growths. M. Omair was the first one to observe the abnormalities in a contract to identify and count zooplankton in preserved samples from GLERL's monitoring study. Only a few samples have been analyzed so far.
"We can only speculate as to when the tumors first occurred in Lake Michigan zooplankton," said Dr. Vanderploeg. "Because such tumors have never been seen until now, despite the many programs on the Great Lakes that have monitored or collected zooplankton, we suspect the occurrence of the tumors is a recent phenomenon in the Great Lakes in general and in Lake Michigan in particular."
It is also possible that previous monitoring efforts, restricted to a few spring and late summer collections, would have missed the tumors because of their limited seasonal coverage and focus on offshore surface waters. The research team plans to examine archived collections and make new collections at many nearshore and offshore sites to find hot spots that might be associated with some environmental factor. Careful microscopic analyses of the tumors also may give some insight into their cause.
NOAA's mission is to describe and predict changes in the Earth's environment and manage wisely the nation's coastal and marine resources.
Editor's Note: Images of the zooplankton showing the growths discussed above are available at: ftp://ftp.glerl.noaa.gov/publications/
All images must be credited to: University of Michigan and NOAA/ Great Lakes Environmental Research Laboratory.
Captions for the images follow.
Figure 1: Appearance of neoplasms or growths on a predatory copepod Limnocalanus macrurus: (Upper left) An individual with a large multi-lobed tumor on the ventral surface of the prosome (anterior body) between the swimming feet and mouthparts. (Upper right) Dorsal view of an individual with a large nearly spherical tumor (large arrow) attached by stalk-like structure (small arrow) to right side of prosome. (Bottom) Individual with tumors (arrows) on the ventral prosome and first segment of urosome (posterior body). Prosome length is approximately 1.7 mm in all cases.
Figure 2: Another predatory copepod with tumors: lateral view of three Epischura lacustris copepodids with neoplasms (at arrows). Prosome length of these individuals is 1.0 mm.
Figure 3: Appearance of tumors on ventral prosome of Diaptomus sp., an ominivorous copepod. (Prosome length is ~ 0.7 mm in both cases)
Figure 4: Appearance of tumors (at arrows) in Cladocera: (Upper left) Dorsal view of Diaphanosoma sp. (Body length = 0.9 mm); (Upper right) Polyphemus pediculus (body length =0.7 mm); and (Bottom) Daphnia galeata mendotae (body length -1.1 mm) with abnormalities on the helmet near compound eye, abdominal claw, and body carapace.