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GLERL Tumor-like Anomalies in Lake Michigan Zooplankton Research Project

Henry Vanderploeg

Background and Proposed work:

Tumor-like anomalies (TLAs) have been identified as a serious emerging threat to the food web in Lake Michigan and other Great Lakes due to the high frequency of large TLAs found on zooplankton by GLERL, EPA, and University of Michigan (e.g. Omair et al. 1999; Bridgeman et al. 2000). At a recent workshop on the phenomenon at GLERL, the present state of knowledge of the lesions was reviewed and an agenda for research was developed. At times, TLA's can affect 50-70% of the copepods of certain species. Calanoid copepods appear to be especially vulnerable to infestation. The occurrence of lesions was highly variable temporally and spatially in Lake Michigan.

Gretchen Messick of the Cooperative Oxford Laboratory of NOAA's Center for Coastal Environmental Health and Biomolecular Research and John C. Harshbarger of the Registry of Tumors in Lower Animals at George Washington University classified several TLAs types based on gross appearance and histologic manifestations. The histologic exams showed that the TLAs were not neoplastic, i.e., not cancerous. Histologic studies so far indicate that most TLA's are comprised of either herniated copepod tissue, acellular tissue, or cells that resemble host hemocytes demonstrating a host response. Transparent, pyriform "cysts" occurred with low frequency along with other types of TLAs. These "cyst-like" TLAs which contain numerous round bodies of varying sizes which may be present both within the copepod and the attached TLA are believed to be trophomeres and gonomeres of ellobiopsid parasites (Bridgeman et al. 2000) (Figure 1). Although hernias were experimentally induced by puncturing the carapace in live calanoid copepods (Bridgeman et al. 2000), it is yet to be determined whether the hernias in copepods from Lake Michigan and other areas were caused by ellobiopsid parasites. Additionally, preliminary histologic assays have detected other protozoan parasites in copepods with and without TLA's that include an unidentified microsporidian and hematodinium-like organisms (Messick, unpublished data). Due to the varied TLA types encountered, the intricate and diverse nature of histologic TLA manifestations, and preliminary findings of several protozoan parasites, no one causative agent has been identified. Further investigation is necessary to determine the etiology for these varied types of TLAs and whether these different types of TLA's may be related. There is indication that some TLA's may be a reactive response to unknown irritant(s). Additional microscopic investigations are needed to define etiologic agents, distribution of TLA's on the host's body and whether the TLA location on the host is linked to different TLA types. Additionally, investigations are needed to identify what host species are affected, the prevalence among host life stages, and the geographic and temporal distribution of TLA's among various host species affected. Once this work clarifies the nature of the TLA's, further work will be needed to reproduce TLA's in the lab to confirm the identity of the etiologic agent.

Although several morphological variations of tumor-like abnormalities (TLA's) have been observed, collaborators have found TLAs with similar gross appearances in a small lake near Ann Arbor (Bridgeman et al. 2000), in Lago Maggiore in Italy (Maria Manca), lakes in Europe, Asia; and in brackish waters of Europe, including the Baltic and Black Seas. The first appearance of TLAs in recent years or their recent increase in these systems may indicate the emergence of a global phenomenon with a common etiology.

Workshop participants recommended expanding EPA and GLERL "monitoring" efforts to improve spatial and temporal time series in Lake Michigan in FY 2000 to ensure capturing the development of this spotty phenomenon and getting insights into possible consequences to zooplankton populations.

Ecology: GLERL proposes to build upon the pre-plume (February), plume (March), and post plume survey cruises (April) at all transects and the monthly monitoring at St. Joseph, Muskegon, and Deepwater Station (DWS) by adding monthly cruises at M110 separated by two weeks from the monthly monitoring cruises (Fig. 2). EPA GLNP0 will do 3 instead 2 survey cruises of the offshore stations in Lake Michigan (Fig 2, Table 1). This intense set of data covering the whole of Lake Michigan will be an important complement to GLERL seasonal data collected for 15 years near M110.

Histology and Behavior: We propose to use R/V Lake Guardian in offshore surveys since it's lab facilities allow quick sorting and fixation of fresh animals for histologic examinations. Before fixation, appearance and behavior of live animals with TLAs will be documented on video. Additionally, live specimens with TLAs will be set aside for observation of swimming behavior and short-term survival later in the laboratory to evaluate the effect of the TLAs on affected zooplankton. Gretchen Messick will direct histologic processing and examination at the Cooperative Oxford Laboratory. Various steps leading up to histologic characterization include collecting and sorting zooplankton both with and without TLAs, placing them quickly into appropriate fixatives, embedding specimens in paraffin, sectioning, staining, and finally microscopic examination of tissues. We also propose to histologically compare specimens from collaborators to determine if TLAs from Europe are similar to those collected in Lake Michigan.

2002 Plans

Other samples from EEGLE or archived zooplankton samples from 1984-1994 may be counted and examined for TLAs.
Submit final report on findings to EPA and present findings at 8th International Conference on Copepoda in Taipei, Taiwan, July 21-26, 2002.
Figure 1. Gross morphology and histologic sections of elongate cyst-like TLA on copepod. Top right: Gross morphology. Top left: Tissue section of external TLA (right arrow) and internal round bodies associated with TLA (left arrow). Bottom left: histologic section of same TLAs shown in top right. Note round bodies along outer periphery with no nuclear material (bottom arrow), nuclei of various sizes among inner granular material (middle arrow) and round body undergoing cleavage (heavy arrow). These round bodies are characteristic of spore development in ellobiopsid parasites.

Figure 2. Survey cruise transects southern Lake Michigan

2001 Accomplishments

Very few TLAs were found on copepods on the special Lake Guardian cruise. So far 183 copepods with external abnormalities have been processed for histology. Most of the protrusions appear to be herniated host tissue consisting of muscle, lipid, hemocytes, gonad or gut tissue. In some instances herniated tissue is necrotic and unidentifiable. As reported in Bridgeman et. al (2000), some ribbon-like projections are an unusual ellobiopsid parasite. In some nauplii, glassy structures embedded in herniated tissues may be diatom outer frustules. Histologically, non-cellular, refractile, glassy areas are seen in protrusions and in some cases within internal tissues. Thus, no causative agent has been identified. The possibility exists that some herniations may be a result of wounding from diatom frustules during collection.

2000 Accomplishments

We applied for and received funds from EPA to hire the histology technician and 10 months of time of a zooplankton technician to help with zooplankton counting. Work to date, much of it done in a small lake near Ann Arbor, has shown that some of the TLAs are ellobiopsid parasites and that the most common TLA can be induced experimentally by puncturing the carapace of copepods with a fine needle. The co-occurrence of the parasites and common TLA led to the hypothesis that TLAs were caused by parasites wounding the copepods (Bridgeman et al. 2000). Few TLAs were observed in Lake Michigan in 2000.

Products

Publications

Omair, M. B. Naylor, D.J. Jude, J. Quddus, T.F. Beals, and H.A. Vanderploeg. 2001. Histology of herniations through the body wall and cuticle of zooplankton from the Laurentian Great Lakes. J. Invertebrate Pathology 77: 108-113.

Bridgeman, T.B., Messick, G., and Vanderploeg, H.A. 2000. Sudden appearance of cysts and ellobiopsid parasites on zooplankton in a Michigan lake: a potential explanation of tumor-like anomalies. Can. J. Fish. Aquat. Sci. 57: 1539-1544.

Presentations

Cavaletto, J.F., Vanderploeg, H.A., and Pothoven, S. Status of Lake Michigan Zooplankton 1994-1999: Seasonal distribution and the presence of tumor-like anomalies . 43rd International Association of Great Lakes Research Conference, May 2000, Cornwall, Ontario.

Vanderploeg, H.A., Omair,M., and Naylor, B. 1999. Tumors in zooplankton and their implications for monitoring programs. Lake Michigan: State of the Lake '99. Convened by Grand Valley State University November 8-9, 1999. Muskegon Michigan.

References:

Haney, JF, & Hall, DJ 1973. Sugar-coated Daphnia: a preservation technique for Daphnia. Limnol. Oceanogr. 18: 331-333. Luna, LG 1968. Manual of Histologic Staining Methods of the Armed Forces Institute of Pathology. 3d ed. McGraw-Hill Book Co., New York. 258 p.

Omair, M., H.A. Vanderploeg, D.J. Jude, and G.L. Fahnenstiel. 1999. First observations of tumor-like anomalies (exophytic lesions) on Lake Michigan zooplankton. Can. J. Fish. Aquat. Sci. 56: 1711-1715.

Last updated: 2004-04-23 mbl