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A preliminary study of idiopathic lesions in the Dungeness crab, Cancer magister, from Rowan Bay, Alaska
Marine Environmental Research 26 (1988) 311-318
Short Communication A Preliminary Study of Idiopathic Lesions in the Dungeness Crab, Cancer magister, from Rowan Bay, Alaska
ABSTRACT Seventeen Dungeness crab, Cancer magister, from a Log Transfer Facility ( LTF) in Rowan Bay, Alaska, were examined in a histopathologieal study because of what appeared to be high prevalences of shell disease that typically involved periopod, arthrodial membranes. Dungeness crab ( N = 9) from a reference site in Rowan Bay were later examined. The severity and prevalence of the most frequently observed idiopathic lesions, melanized nodules and granulomas, in both groups were statistically tested. This paper reports the findings of this preliminary study.
INTRODUCTION There is frequent conjecture on the increased risk of disease in marine organisms, especially fish, that inhabit contaminated waters (Couch & Harshbarger, 1985; Overstreet, 1988; Sindermann, 1983). However, the true role of environmental perturbations (i.e. pollution) as effectors of disease in invertebrates, particularly shellfish, is largely unclear (Mix, 1988). Dungeness crab, Cancer magister, near a Log Transfer Facility (LTF) in Rowan Bay, Kuiu Island, southeast Alaska, were observed to have extensively eroded arthrodial membranes and darkened dactyl segments. As a result, crabs from the LTF (a site for transferring forest industry logs from land to water) and a reference station in Rowan Bay that is beyond the influence of the LTF bark deposit were collected for histopathological 311 Marine Environ. Res. 0141-1136/89/$03'50 © 1989 ElsevierSciencePublishersLtd, England.
Printed in Great Britain
312
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
study. The results indicate a significant difference in the prevalence and severity of granulomas and severity of melanized nodules in crabs between the two areas.
MATERIALS AND METHODS Twenty Dungeness crab were collected from a Log Transfer Facility (LTF) in late December, 1982 from Rowan Bay (latitude 134 ° 25'N, longitude 56 ° 39' W). Because of logistical and weather problems, we were unable to collect 15 crabs from a reference station at the head of Rowan Bay until early April, 1983. Both groups were shipped live to our laboratory where dead individuals were removed from both groups. Sex, size, shell condition and the presence of wounds was noted from the remaining 17 LTF and 9 reference crab. Small random samples of all major organs were removed, fixed in Helly's solution, processed by standard histological techniques, sectioned at 5/~m and stained with hematoxylin and eosin (H&E). Tissue slides of reference and L T F crab were randomly read blind (i.e. without prior knowledge of the collection site and condition of each specimen) along with our other case loads. Normal and pathological conditions were described and recorded. This entailed the noting of any anomaly and the assignment of a quantitative degree of severity from 1 to 10 (1 = minimal; 10 = excessive). When all the cases were read, the data were grouped, and Fisher's exact and Mann-Whitney tests (Zar, 1974) were applied to the prevalence and severity data.
RESULTS
Gross observations The most c o m m o n gross anomalies of L T F crab were darkening of dactyls and erosion and blackening of arthrodial membranes between the dactylus and propodus of the periopods. The majority of L T F crabs (14/17, 82%) had limb joint erosion in contrast to 4 of 9 (44%) from the reference area. The most severe cases occurred in L T F crabs where the underlying tissue was greatly diminished and the dactylus remained attached by only a narrow section of membrane. Several L T F crabs had one or more dactyls missing. Fisher's test indicated that the incidence of joint erosion was significantly different between sites (P < 0.05). All crabs from both locations possessed blackened dactyls.
Idiopathic lesions in the Dungeness crab
313
Histopathology Joint erosion was accompanied by a chronic inflammatory reaction (Fig. 1). The arthrodial membrane was eroded and the surface of the wound was covered by layers of flattened hemocytes; the outermost layers were necrotic and melanized. Deeper into the wound, normal hemocytes were evident in both whirling and encapsulating patterns. Underlying connective tissue and muscle were disrupted by the intense wound healing process. Muscle fibers were commonly infiltrated with hemocytes. The epithelium abutting the wound was necrotic but with increasing distance from the wound, the epithelium changed from simple squamous to simple columnar. Granulomas were the most c o m m o n lesion observed in crab tissues from both stations (Tables 1 and 2). Granulomas were found in 13 of 17 (76%) L T F crabs and in 3 of 9 (33%) reference crabs. The prevalence of these lesions was significantly different between the two stations (Fisher's, P < 0.05). They occurred in almost all organs and tissues, but were most prevalent in the gills (both stem and lamellae; Figs 2 and 3), hindgut, heart and connective tissue of the hepatopancreas. Fisher's test indicated that the prevalence of these lesions in the gills, hindgut and heart was significant (P < 0-05) between the two groups. To determine if the granulomas were more or less severe in crabs from
Fig. 1. Intense host reaction involving walling off by hemocytes and melanization in response to erosion of arthrodial membrane (small arrows). Large arrow is at area of epithelium abutting host reaction. H&E. x 100.
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
314
TABLE 1 Prevalence and Severity of Granulomas in LTF Dungeness Crab. Numbers in table refer to severity of the lesion (0 = no lesion)
Case no.
82371 82372 82373 82374 82375 82376 82377 82378 82379 82380 82381 82382 82383 82384 82385 82386 82387 Organ prevalence
Antennal g~nd
Eye
0 0 0 0 0 5 4 0 5 4 0 0 0 0 6 0 0 5
0 0 0 0 5 0 5 0 0 0 4 0 0 0 0 0 0 3
Gill
4 4 5 5 7 5 6 3 6 3 4 4 5 7 3 7 0 16
Heart
Hepatopancreas
Hindgut
Organs affected
0 0 5 0 0 0 6 5 0 4 4 4 0 6 7 4 0 9
4 0 5 5 0 4 4 0 5 0 0 0 0 0 0 4 0 8
0 5 6 4 6 5 5 5 5 5 5 6 6 0 4 5 0 13
2 2 4 3 3 4 6 3 4 4 4 3 2 2 4 4 0
TABLE 2 Prevalence and Severity of Granulomas in Reference Dungeness Crab. Numbers in table refer to severity of the lesion (0 = no lesion)
Case no.
83220 83221 83222 83223 83224 83225 83226 83227 83228 Organ prevalence
Antennal gland
Eye
Gill
Heart
Hepatopancreas
Hindgut
Organs affected
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 3 0 0 0 0 0 0 4 2
5 0 0 0 0 0 0 0 0 1
0 2 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
1 2 0 0 0 0 0 0 1
Fig. 2.
Small unmelanized nodule (arrow) and granuloma (G) in the gill stem. H&E. x 280.
O
Fig. 3.
Small unmelanized nodule (arrow) and melanized granuloma (G) in the tegrnental gland area of the gill stem. Tegmental gland: TG. H&E. x 420.
316
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
either location, the Mann-Whitney test was applied to the granuloma data. The test indicated that the general severity between the two stations was significant (P < 0"05). The severity of lesions in the gills, hindgut and heart between the two stations was also significant (P < 0.05). Melanized nodules were also observed in the majority of organs and tissues. No significant difference in prevalence was evident between either station (Fisher's test at P < 0.05), nor was there a significant difference in general severity. However, the severity of the lesion in the gills was significant (Mann-Whitney, P < 0.05) between the two stations.
DISCUSSION Since 1977, the tissues of approximately 900 Dungeness crab throughout the waters of Puget Sound, Hood Canal, the Pacific Coast of Washington and southeast Alaska have been examined for infectious and non-infectious diseases. Regardless of etiology, the lesions and host responses have been remarkably similar, and the prevalences of the lesions not significantly different from site to site. Prior to this study, the severity of the lesion was not critically evaluated. It is difficult to draw a clear relationship between pollution and disease in crustaceans because of the ubiquitous distribution and similarity of lesions. We have, therefore, been skeptical of the use of crustaceans as indicators of pollution. Shirley & Shirley (1988) reported appendage injury prevalences of 25% in Dungeness crab from another Southeast Alaska location. They concluded that adult Dungeness crab from Southeast Alaska, Washington and Oregon are in comparable condition with respect to appendage injury. Tanner crabs, Chionoecetes bairdi, exposed to oil-contaminated sediments for a 1-year period failed to show any significant pathological differences between the five exposure groups (unpublished personal data). Sawyer et al. (1984) noted that almost all pathological conditions of C. irroratus could be found in specimens from both clean and polluted environments. Increased prevalences of shell erosion and melanization of diseased tissue have been reported to occur in many crustaceans collected near ocean disposal sites of New York and New Jersey (Gopalan & Young, 1975; Sawyer et al., 1979). However, shell erosion has been reported in crustaceans from all aquatic environments. Sawyer et al. (1984) reported that localized lesions in the gills, referred to as black foci or spots in otherwise clean gills, were similarly not necessarily associated with degraded environments. Sawyer (1982) and Sawyer et al. (1983) observed extensive gill blackening in C. irroratus in moribund or live specimens caught only at or near ocean disposal sites. It was later determined that extensive gill blackening was only rarely observed at unimpacted sites (Sawyer et al., 1984).
Idiopathic lesions in the Dungeness crab
317
We examine the major organs and tissues of all specimens because we believe that this provides us with a comprehensive index on the state of health of an organism. We were, therefore, able to confirm the effects of, and host reaction to, shell erosion initially described by Gopalan & Young (1975) and Young & Pearce (1975). However, erosion in our study typically involved the arthrodial membranes o f the joints and not the calcified portion of the exoskeleton. Shell disease has been reported to cause mortalities in the American lobster, Homarus americanus (Rosen, 1970). However, the possible role of the highly virulent bacterium, Aerococcus viridans var. homari, was not determined. Granulomas in crustaceans were first reported by Sparks (1980) from the midgut of the Dungeness crab and were believed to be biotic in origin. Since they were observed in virtually all organs and tissues with no apparent causative agent, it is likely that those in this study were of abiotic causation. Rowan Bay is undeveloped and not influenced by industry other than the LTF, which began operations in the summer of 1973. The introduction of organic debris resulting from LTF operations has changed the sediment strata of the area and the decomposition of organic debris typically increases oxygen demand. Under aerobic conditions, few toxic chemicals would accumulate but under anaerobic conditions or reduced oxygen tension, several toxic chemicals are produced during the normal decomposition processes of organic material (Rheinheimer, 1976). It is conceivable that these chemicals may have participated in the production of the described crab tissue lesions. The present study is the first in which certain lesion prevalences and severity appear to be significant in a disturbed habitat. It is important to point out that the data in this study are limited in time and scope, and consist of discontinuous collections. However, this report indicates that a more critical evaluation of lesions and how they are reported may be necessary when investigating environmental disturbances of any type and their possible effects on native organisms. REFERENCES Couch, J. A. & Harshbarger, J. C. (1985). Effects of carcinogenic agents on aquatic animals: An environmental and experimental overview. Environ. Carcinogenesis Revs., 3, 63-105. Gopalan, U. K. & Young, J. S. (1975). Incidence of shell disease in shrimp in the New York Bight. Mar. Pollut. Bull., 6, 149-53. Mix, M. C. (1988). Shellfish diseases in relation to toxic chemicals. Aquat. Toxicol., 11, 29-42. Overstreet, R. M. (1988). Aquatic pollution problems, Southeast US coasts: Histopathological indicators. Aquat. Toxicol., 11, 213-39.
318
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
Rheinheimer, G. (1976). Aquatic Microbiology. John Wiley & Sons, London. Rosen, B. (1970). Shell disease of aquatic crustaceans. In A Symposium on Diseases of Fishes and Shellfishes. ed. S. F. Snieszko, American Fisheries Society, Special Publication, 5, 409-15. Sawyer, T. K. (1982). Distribution and seasonal incidence of'black gill' in the rock crab, Cancer irroratus. In Ecological Stress and the New York Bight: Science and Management. ed. G. F. Mayer, Estuarine Research Foundation, Columbia, SC, 199-211. Sawyer, T. K., Lewis, E. J., Galasso, M., Bodammer, S., Ziskowski, J., Lear, D., O'Malley, M. & Smith, S. (1983). Black gill conditions in the rock crab, Cancer irroratus, as indicators of ocean dumping in Atlantic coastal waters of the US. Rapp. P.-v. Reun. Cons. int. Explor. Mer., 182, 91-95. Sawyer, T. K., Lewis, E. J., Galasso, M. E. & Ziskowski, J. J. (1984). Gill fouling and parasitism in the rock crab, Cancer irroratus Say. Mar. Environ. Res., 14, 355-69. Sawyer, T. K., MacLean, S. A., Bodammer, J. E. & Harke, B. A. (1979). Gross and microscopical observations on gills of rock crabs (Cancer irroratus) and lobsters (Homarus americanus) from near-shore waters of the eastern United States. In Proc. Second Biennial Crustacean Workshop. ed. D. H. Lewis & J. K. Leong, Sea Grant Publication, Texas A&M Univ., pp. 79-114. Shirley, S. M. & Shirley, T. C. (1988). Appendage injury in Dungeness crabs, Cancer magister, in southeastern Alaska. Fish. Bull., 86, 156-60. Sindermann, C. J. (1983). An examination of some relationships between pollution and disease. Rapp. P.-v. Cons. int. Explor. Mer., 82, 3743. Sparks, A. K. (1980). Multiple granulomas in the midgut of the Dungeness crab, Cancer magister. J. Invertebr. PathoL, 35, 323~,. Young, J. S. & Pearce, J. B. (1975). Shell disease in crabs and lobsters from New York Bight. Mar. Pollut. Bull., 6, 101-5. Zar, J. H. (1974). Biostatistical Analysis, Prentice-Hall, Inc., Englewood Hills, NJ.
J. Frank Morado, Albert K. Sparks National Marine Fisheries Service, Northwest and Alaska Fisheries Center, Division of" Resource and Conservation Engineering, 7600 Sand Point Way N.E., Seattle, Washington 98115, USA & Charles E. O'Ciair National Marine Fisheries Service, Northwest and Alaska Fisheries Center, Auke Bay Laboratory, PO Box 210155, Auke Bay, Alaska 99821, USA (Received 16 October 1987; revised version received 1 November 1988; accepted 10 November 1988)
Short Communication A Preliminary Study of Idiopathic Lesions in the Dungeness Crab, Cancer magister, from Rowan Bay, Alaska
ABSTRACT Seventeen Dungeness crab, Cancer magister, from a Log Transfer Facility ( LTF) in Rowan Bay, Alaska, were examined in a histopathologieal study because of what appeared to be high prevalences of shell disease that typically involved periopod, arthrodial membranes. Dungeness crab ( N = 9) from a reference site in Rowan Bay were later examined. The severity and prevalence of the most frequently observed idiopathic lesions, melanized nodules and granulomas, in both groups were statistically tested. This paper reports the findings of this preliminary study.
INTRODUCTION There is frequent conjecture on the increased risk of disease in marine organisms, especially fish, that inhabit contaminated waters (Couch & Harshbarger, 1985; Overstreet, 1988; Sindermann, 1983). However, the true role of environmental perturbations (i.e. pollution) as effectors of disease in invertebrates, particularly shellfish, is largely unclear (Mix, 1988). Dungeness crab, Cancer magister, near a Log Transfer Facility (LTF) in Rowan Bay, Kuiu Island, southeast Alaska, were observed to have extensively eroded arthrodial membranes and darkened dactyl segments. As a result, crabs from the LTF (a site for transferring forest industry logs from land to water) and a reference station in Rowan Bay that is beyond the influence of the LTF bark deposit were collected for histopathological 311 Marine Environ. Res. 0141-1136/89/$03'50 © 1989 ElsevierSciencePublishersLtd, England.
Printed in Great Britain
312
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
study. The results indicate a significant difference in the prevalence and severity of granulomas and severity of melanized nodules in crabs between the two areas.
MATERIALS AND METHODS Twenty Dungeness crab were collected from a Log Transfer Facility (LTF) in late December, 1982 from Rowan Bay (latitude 134 ° 25'N, longitude 56 ° 39' W). Because of logistical and weather problems, we were unable to collect 15 crabs from a reference station at the head of Rowan Bay until early April, 1983. Both groups were shipped live to our laboratory where dead individuals were removed from both groups. Sex, size, shell condition and the presence of wounds was noted from the remaining 17 LTF and 9 reference crab. Small random samples of all major organs were removed, fixed in Helly's solution, processed by standard histological techniques, sectioned at 5/~m and stained with hematoxylin and eosin (H&E). Tissue slides of reference and L T F crab were randomly read blind (i.e. without prior knowledge of the collection site and condition of each specimen) along with our other case loads. Normal and pathological conditions were described and recorded. This entailed the noting of any anomaly and the assignment of a quantitative degree of severity from 1 to 10 (1 = minimal; 10 = excessive). When all the cases were read, the data were grouped, and Fisher's exact and Mann-Whitney tests (Zar, 1974) were applied to the prevalence and severity data.
RESULTS
Gross observations The most c o m m o n gross anomalies of L T F crab were darkening of dactyls and erosion and blackening of arthrodial membranes between the dactylus and propodus of the periopods. The majority of L T F crabs (14/17, 82%) had limb joint erosion in contrast to 4 of 9 (44%) from the reference area. The most severe cases occurred in L T F crabs where the underlying tissue was greatly diminished and the dactylus remained attached by only a narrow section of membrane. Several L T F crabs had one or more dactyls missing. Fisher's test indicated that the incidence of joint erosion was significantly different between sites (P < 0.05). All crabs from both locations possessed blackened dactyls.
Idiopathic lesions in the Dungeness crab
313
Histopathology Joint erosion was accompanied by a chronic inflammatory reaction (Fig. 1). The arthrodial membrane was eroded and the surface of the wound was covered by layers of flattened hemocytes; the outermost layers were necrotic and melanized. Deeper into the wound, normal hemocytes were evident in both whirling and encapsulating patterns. Underlying connective tissue and muscle were disrupted by the intense wound healing process. Muscle fibers were commonly infiltrated with hemocytes. The epithelium abutting the wound was necrotic but with increasing distance from the wound, the epithelium changed from simple squamous to simple columnar. Granulomas were the most c o m m o n lesion observed in crab tissues from both stations (Tables 1 and 2). Granulomas were found in 13 of 17 (76%) L T F crabs and in 3 of 9 (33%) reference crabs. The prevalence of these lesions was significantly different between the two stations (Fisher's, P < 0.05). They occurred in almost all organs and tissues, but were most prevalent in the gills (both stem and lamellae; Figs 2 and 3), hindgut, heart and connective tissue of the hepatopancreas. Fisher's test indicated that the prevalence of these lesions in the gills, hindgut and heart was significant (P < 0-05) between the two groups. To determine if the granulomas were more or less severe in crabs from
Fig. 1. Intense host reaction involving walling off by hemocytes and melanization in response to erosion of arthrodial membrane (small arrows). Large arrow is at area of epithelium abutting host reaction. H&E. x 100.
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
314
TABLE 1 Prevalence and Severity of Granulomas in LTF Dungeness Crab. Numbers in table refer to severity of the lesion (0 = no lesion)
Case no.
82371 82372 82373 82374 82375 82376 82377 82378 82379 82380 82381 82382 82383 82384 82385 82386 82387 Organ prevalence
Antennal g~nd
Eye
0 0 0 0 0 5 4 0 5 4 0 0 0 0 6 0 0 5
0 0 0 0 5 0 5 0 0 0 4 0 0 0 0 0 0 3
Gill
4 4 5 5 7 5 6 3 6 3 4 4 5 7 3 7 0 16
Heart
Hepatopancreas
Hindgut
Organs affected
0 0 5 0 0 0 6 5 0 4 4 4 0 6 7 4 0 9
4 0 5 5 0 4 4 0 5 0 0 0 0 0 0 4 0 8
0 5 6 4 6 5 5 5 5 5 5 6 6 0 4 5 0 13
2 2 4 3 3 4 6 3 4 4 4 3 2 2 4 4 0
TABLE 2 Prevalence and Severity of Granulomas in Reference Dungeness Crab. Numbers in table refer to severity of the lesion (0 = no lesion)
Case no.
83220 83221 83222 83223 83224 83225 83226 83227 83228 Organ prevalence
Antennal gland
Eye
Gill
Heart
Hepatopancreas
Hindgut
Organs affected
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 3 0 0 0 0 0 0 4 2
5 0 0 0 0 0 0 0 0 1
0 2 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
1 2 0 0 0 0 0 0 1
Fig. 2.
Small unmelanized nodule (arrow) and granuloma (G) in the gill stem. H&E. x 280.
O
Fig. 3.
Small unmelanized nodule (arrow) and melanized granuloma (G) in the tegrnental gland area of the gill stem. Tegmental gland: TG. H&E. x 420.
316
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
either location, the Mann-Whitney test was applied to the granuloma data. The test indicated that the general severity between the two stations was significant (P < 0"05). The severity of lesions in the gills, hindgut and heart between the two stations was also significant (P < 0.05). Melanized nodules were also observed in the majority of organs and tissues. No significant difference in prevalence was evident between either station (Fisher's test at P < 0.05), nor was there a significant difference in general severity. However, the severity of the lesion in the gills was significant (Mann-Whitney, P < 0.05) between the two stations.
DISCUSSION Since 1977, the tissues of approximately 900 Dungeness crab throughout the waters of Puget Sound, Hood Canal, the Pacific Coast of Washington and southeast Alaska have been examined for infectious and non-infectious diseases. Regardless of etiology, the lesions and host responses have been remarkably similar, and the prevalences of the lesions not significantly different from site to site. Prior to this study, the severity of the lesion was not critically evaluated. It is difficult to draw a clear relationship between pollution and disease in crustaceans because of the ubiquitous distribution and similarity of lesions. We have, therefore, been skeptical of the use of crustaceans as indicators of pollution. Shirley & Shirley (1988) reported appendage injury prevalences of 25% in Dungeness crab from another Southeast Alaska location. They concluded that adult Dungeness crab from Southeast Alaska, Washington and Oregon are in comparable condition with respect to appendage injury. Tanner crabs, Chionoecetes bairdi, exposed to oil-contaminated sediments for a 1-year period failed to show any significant pathological differences between the five exposure groups (unpublished personal data). Sawyer et al. (1984) noted that almost all pathological conditions of C. irroratus could be found in specimens from both clean and polluted environments. Increased prevalences of shell erosion and melanization of diseased tissue have been reported to occur in many crustaceans collected near ocean disposal sites of New York and New Jersey (Gopalan & Young, 1975; Sawyer et al., 1979). However, shell erosion has been reported in crustaceans from all aquatic environments. Sawyer et al. (1984) reported that localized lesions in the gills, referred to as black foci or spots in otherwise clean gills, were similarly not necessarily associated with degraded environments. Sawyer (1982) and Sawyer et al. (1983) observed extensive gill blackening in C. irroratus in moribund or live specimens caught only at or near ocean disposal sites. It was later determined that extensive gill blackening was only rarely observed at unimpacted sites (Sawyer et al., 1984).
Idiopathic lesions in the Dungeness crab
317
We examine the major organs and tissues of all specimens because we believe that this provides us with a comprehensive index on the state of health of an organism. We were, therefore, able to confirm the effects of, and host reaction to, shell erosion initially described by Gopalan & Young (1975) and Young & Pearce (1975). However, erosion in our study typically involved the arthrodial membranes o f the joints and not the calcified portion of the exoskeleton. Shell disease has been reported to cause mortalities in the American lobster, Homarus americanus (Rosen, 1970). However, the possible role of the highly virulent bacterium, Aerococcus viridans var. homari, was not determined. Granulomas in crustaceans were first reported by Sparks (1980) from the midgut of the Dungeness crab and were believed to be biotic in origin. Since they were observed in virtually all organs and tissues with no apparent causative agent, it is likely that those in this study were of abiotic causation. Rowan Bay is undeveloped and not influenced by industry other than the LTF, which began operations in the summer of 1973. The introduction of organic debris resulting from LTF operations has changed the sediment strata of the area and the decomposition of organic debris typically increases oxygen demand. Under aerobic conditions, few toxic chemicals would accumulate but under anaerobic conditions or reduced oxygen tension, several toxic chemicals are produced during the normal decomposition processes of organic material (Rheinheimer, 1976). It is conceivable that these chemicals may have participated in the production of the described crab tissue lesions. The present study is the first in which certain lesion prevalences and severity appear to be significant in a disturbed habitat. It is important to point out that the data in this study are limited in time and scope, and consist of discontinuous collections. However, this report indicates that a more critical evaluation of lesions and how they are reported may be necessary when investigating environmental disturbances of any type and their possible effects on native organisms. REFERENCES Couch, J. A. & Harshbarger, J. C. (1985). Effects of carcinogenic agents on aquatic animals: An environmental and experimental overview. Environ. Carcinogenesis Revs., 3, 63-105. Gopalan, U. K. & Young, J. S. (1975). Incidence of shell disease in shrimp in the New York Bight. Mar. Pollut. Bull., 6, 149-53. Mix, M. C. (1988). Shellfish diseases in relation to toxic chemicals. Aquat. Toxicol., 11, 29-42. Overstreet, R. M. (1988). Aquatic pollution problems, Southeast US coasts: Histopathological indicators. Aquat. Toxicol., 11, 213-39.
318
J. Frank Morado, Albert K. Sparks, Charles E. O'Clair
Rheinheimer, G. (1976). Aquatic Microbiology. John Wiley & Sons, London. Rosen, B. (1970). Shell disease of aquatic crustaceans. In A Symposium on Diseases of Fishes and Shellfishes. ed. S. F. Snieszko, American Fisheries Society, Special Publication, 5, 409-15. Sawyer, T. K. (1982). Distribution and seasonal incidence of'black gill' in the rock crab, Cancer irroratus. In Ecological Stress and the New York Bight: Science and Management. ed. G. F. Mayer, Estuarine Research Foundation, Columbia, SC, 199-211. Sawyer, T. K., Lewis, E. J., Galasso, M., Bodammer, S., Ziskowski, J., Lear, D., O'Malley, M. & Smith, S. (1983). Black gill conditions in the rock crab, Cancer irroratus, as indicators of ocean dumping in Atlantic coastal waters of the US. Rapp. P.-v. Reun. Cons. int. Explor. Mer., 182, 91-95. Sawyer, T. K., Lewis, E. J., Galasso, M. E. & Ziskowski, J. J. (1984). Gill fouling and parasitism in the rock crab, Cancer irroratus Say. Mar. Environ. Res., 14, 355-69. Sawyer, T. K., MacLean, S. A., Bodammer, J. E. & Harke, B. A. (1979). Gross and microscopical observations on gills of rock crabs (Cancer irroratus) and lobsters (Homarus americanus) from near-shore waters of the eastern United States. In Proc. Second Biennial Crustacean Workshop. ed. D. H. Lewis & J. K. Leong, Sea Grant Publication, Texas A&M Univ., pp. 79-114. Shirley, S. M. & Shirley, T. C. (1988). Appendage injury in Dungeness crabs, Cancer magister, in southeastern Alaska. Fish. Bull., 86, 156-60. Sindermann, C. J. (1983). An examination of some relationships between pollution and disease. Rapp. P.-v. Cons. int. Explor. Mer., 82, 3743. Sparks, A. K. (1980). Multiple granulomas in the midgut of the Dungeness crab, Cancer magister. J. Invertebr. PathoL, 35, 323~,. Young, J. S. & Pearce, J. B. (1975). Shell disease in crabs and lobsters from New York Bight. Mar. Pollut. Bull., 6, 101-5. Zar, J. H. (1974). Biostatistical Analysis, Prentice-Hall, Inc., Englewood Hills, NJ.
J. Frank Morado, Albert K. Sparks National Marine Fisheries Service, Northwest and Alaska Fisheries Center, Division of" Resource and Conservation Engineering, 7600 Sand Point Way N.E., Seattle, Washington 98115, USA & Charles E. O'Ciair National Marine Fisheries Service, Northwest and Alaska Fisheries Center, Auke Bay Laboratory, PO Box 210155, Auke Bay, Alaska 99821, USA (Received 16 October 1987; revised version received 1 November 1988; accepted 10 November 1988)