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Resuspended hypnozygotes of Alexandrium fundyense associated with winter occurrence of PSP in inshore Newfoundland waters
Aquaculture 122 (1994) 171-179
ELSEVIER
Resuspended hypnozygotes of Alemndrium fundyense associated with winter occurrence of PSP in inshore Newfoundland waters P. Schwinghame+*,
M. Hawryluk”, C. Powellb, C.H. MacKenzie”
‘DepartmentofFisheries and Oceans, Science Branch, P.O. Box 5667, St. John’s, Nfld., CanaabAlCSXl bDepartment of Fisheries and Oceans, Inspection Services Branch, P. 0. Box 566 7, St. John’s, Nfld CanadaAlC 5X1 “Ocean Sciences Centre, Memorial Universityof Newfoundland, St. John’s, Nfd., Canada AI C 5S7
(Accepted 30 November 1993)
Abstract
Abundance of sediment resting cysts, or hypnozygotes, of the toxic dinoflagellate, Alexin the stomachs of blue mussels, Mytilus edulis, was found to be positively correlated with the level of paralytic shellfish poisoning (PSP) toxins in the mussel flesh during winter in northeastern Newfoundland. In addition, historical maximum levels of mussel toxicity were positively correlated with abundance of cysts in sediments at collection sites around the coast of the island. Several adjacent mussel culture sites were examined to determine the physical mechanisms involved in initiation and maintenance of high levels of mussel intoxication at some sites while others remained clear. We found that cultures located over depositional basins in embayments which had shallow sills and were oriented along the fetch of strong winds had persistently high toxin levels. Cultures located over erosional bottoms in open basins remained free of high levels of PSP toxins. We propose that taking this mechanism for winter intoxication into account when selecting growing sites will greatly benefit the Newfoundland mussel culture industry. andriumfindyense,
1. Introduction The first reported case of paralytic shellfish poisoning (PSP) in Newfoundland occurred on 25 September 1982 at Harbour Grace, Conception Bay, when blue mussels, MytiZus edulis, containing high levels of PSP toxins were ingested (White *Correspondingauthor. 0044-8486/94/$07.00
0 1994
SSDZ0044-8486(93)E0310-6
ElsevierScienceB.V. All rights reserved
172
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
and White, 1985 ). The recent growth of the mussel culture industry, especially along the northeast coast of the island, has been accompanied by a growth in awareness of the PSP problem, increased monitoring by the Department of Fisheries and Oceans, and the detection of PSP in areas previously not known to be affected. PSP intoxication of mussels in Newfoundland has not been confined to the period between May and October, when the planktonic stage of the toxic dinoflagellate Alexundrium jiotdyense, which’causes PSP, may be present. Some sites have been plagued by high levels of toxicity throughout the winter (Inspection Services Branch, Department of Fisheries and Oceans, St. John’s, Nfld. ). Hypnozygotes, the resting cysts of A. fundyense which are found in sediments, have been implicated in the winter occurrence of PSP toxins in shellfish in northern British Columbia (Gaines and Taylor, 1985), the Bay of Fundy (White and Lewis, 1982; J. Martin, Department of Fisheries and Oceans, St. Andrews Biological Station, pers. commun. ), and the Gulf of Maine (Yentsch and Mague, 1979), but ingested cysts have not been demonstrated to be positively correlated with tissue toxin levels. It was our objective in this study to establish whether such a correlation exists in an area of putative cyst involvement in intoxication of cultured mussels. Table 1 Summary of data collected in 1989 survey of coastal Newfoundland sediments for A. findyense hypnozygotes. PSP toxicity is maximum recorded level for mussels collected at each site, expressed as pg saxitoxin equivalents per 100 g mussel tissue Site
Depth (m)
PSP Toxicity
Alexandrium cysts/ml
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
St. Lunaire Trap Cove Jackson’s Arm St. Patricks/Brown’s Arm Triton Northwest Arm Fortune Hr Burnt Arm/Gosham’s Arm Valleyfield Northeast Arm/Beachcove Saulton’s Brook T.N. Catalina St. Jones Without Bellevue Heart’s Content T.B. Harbour Grace Holyrood Great Hr. Sandyville Piccaire
32 40 18 30 2 20 1 5.5
8 0.5 0.5 15 6 24 16 17 16 0.5 22
N.D., none detected. Site numbers refer to Fig. 1.
N.D. N.D. 580 43 N.D. N.D. N.D. N.D. N.D. N.D. N.D. 46 N.D. N.D. 1200 N.D. N.D. 38 150
0 0
24 0 0 0 0 0 0 0 0 2 0 0 256 0 6 0 2
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
173
2. Methods
We have begun a program of water, sediment, and stomach content sampling to determine the factors which lead to elevated levels of PSP toxins in shellfish assayed by Inspection Services Branch, Department of Fisheries and Oceans, St. John’s, Nfld. From 3 May to 15 June 1989, we sampled inshore sediments near mussel (Mytilus e&&s) farms and wild collection sites along the south and east coasts of Newfoundland (Table 1, Fig. 1) . Surface sediments were collected using a 15 cm x15 cm Ekman corer where sampling sites were reached by small boat. Duplicate 5-ml subsamples were collected with cut-off lo-ml syringes from the surface of the Ekman samples. Where sites were accessible by foot using chestwaders at low tide, duplicate 5-ml samples of surface sediment were collected directly with cut-off lo-ml syringes. The samples were placed in 20-ml plastic scintillation vials and stored unpreserved, in the dark, at 4”C, prior to analysis. The resting cysts of Alexundriumfindyense were separated from the surface sediments for enumeration using the density-gradient centrifugation technique of
Fig. 1. Sampling locations for 1989 survey of Alexandrium fundyense hypnozygotes in coastal sediments around Newfoundland. Inset illustrates the Pilley’s Tickle area, where mussels were collected for analysis of PSP toxicity and enumeration of A. findyense hypnozygotes in the stomach in winter 199 1-92. Site numbers refer to Table 1.
174
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
Schwinghamer et al. ( 199 1). Abundances were estimated as numbers per ml in the surface 3 cm of sediment (the depth to which a cut-off lo-ml syringe penetrates for a 54 sample). We examined the stomach contents of cultured mussels collected in the fall and winter of 199 l-92 from sites in Pilley’s Tickle, Notre Dame Bay, on the northeast coast of Newfoundland (Fig. 1 and Fig. 2 ) . Animals were taken at random from batches sent to Inspection Services Branch for testing for paralytic shellfish toxins by the standard mouse bioassay. The entire stomach contents were collected from the dissected digestive gland mass using a micropipette. The toxin levels reported here are average values for pooled subsamples of 20-25 individual mussels (minimum of 100 g wet wt. flesh) from each population sampled, therefore no esti-
Little H&our BarredIsland Cove
Big Island
Kelly Cove 2
Fig. 2. Bathymetry and sample collection locations at five mussel farms in Pilley’s Tickle. The mussel rafts extended over most of each cove. Scale and direction for all sites are indicated on the Big Island chart.
175
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-179
i
‘oooo u
0
1000
0
aI z
1
10 Cysts
100
ml -’
Sediment
1000 (n+l)
Fig. 3. Logarithmic plot of maximum recorded PSP toxin levels in mussels vs. abundance of A. fundyense hypnoxygotes in sediments at 19 coastal sites around Newfoundland. The square symbol at the origin represents 12 sites with no record of PSP and no cysts in the sediment.
loo0 j 100
@
-------______
*-----a
i
10 7 1
10 Cysts
ml -’
1000
100 Stomach
Contents
(n+l)
Fig. 4. Logarithmic plot of PSP toxin levels in pooled samples of 20-25 mussels from three sites at Barred Island Cove and two sites at Little Harbour, Pilley’s Tickle vs. abundance of A. findyense hypnoxygotes in stomach contents of mussels taken from the same populations. •i represents three mussels and 0 represents four mussels from Little Ha&our.
176
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
mate of population variability is available. The cyst numbers, on the other hand, were determined on individual animals, so estimates of population variation could be calculated. Cyst numbers are given per ml of stomach contents. Meteorological records for the study period were collected at Kings Point, Southwest Arm, Green Bay, near the Pilley’s Tickle area, by Department of Fisheries and Oceans Inspector Vey Stoodley. Bathymetry of the study locations was taken from Canadian Hydrographic Service chart no. 4593 and records at Department of Fisheries and Oceans, Inspection Services Branch, St. John’s, Nfld.
3. Results Our sediment samples indicate a positive correlation (linear r=0.94, log-log r= 0.86, P-c 0.001) between the abundance of resting cysts, or hypnozygotes, of Akxundrium in sediments and the maximum recorded levels of PSP toxins in mussels (Fig. 3). While the cysts form the seed populations of the planktonic stage which shellfish ingest during the summer and early fall, the historical incidence of high toxin levels in mussels in the late fall and winter at some Newfoundland sites implicates cysts as the direet agents of intoxication. Mussels from some sites in embayments of Notre Dame Bay on the northeast coast contained a wide range of toxin levels during winter, 199.1-92. We have found a positive correlation (linear r=0.85, log-log r=0.77, P-zO.001) between the numbers of cysts in the stomachs and toxin levels in tissues of mussels from the Pilley’s Tickle area (Fig. 4, Table 2). Neither the mussel stomachs nor water samples taken 10 days earlier at the same sites contained any planktonic A. findyense. The heavy (average density= 1.22 g cmm3) resting cysts may be introduced into the water column with sediment resuspension by strong winds. Fig. 5 illusTable 2 Abundance of A. findyense hypnozygotes in stomachs of mussels from Barred Island Cove and Little Harbour, Pilley’s Tickle. PSP toxicity is expressed as pg saxitoxin equivalents per 100 g mussel tissue Sample site
Barred Island Cove Pilley’s Tickle BIC, Pilley’s Tickle (Centre of site) BIC, Pilley’s Tickle (North end of site) Little Hr Pilley’s I (North end of site) Little Hr. Pilley’s I (Centre of site)
Date sampled
PSP toxicity
Alexandrium cysts/ml
Stomach vol. (ml)
N
Mean
Range
331
200-620
0.07
8
10/12/91
515
28/2/92
110
94.2
O-267
0.04
4
2812192
45
16.7
O-67
0.03
4
2812192
37
36.4
o-71
0.07
4
28/2/92
43
0
0
0.06
4
N, number of stomachs analyzed.
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
--
Barrrd Llttle
Island
177
Cow
Harbour
= < 800 .- > x: i 600
100 i
I
E 5 % c :: xi > u .5 3
80 60 40 20 0 11/2
11/16
11/30
12/14
Date (1991) Fig. 5. PSP toxin levels in mussels, and average daily wind velocity and direction at Barred Island Cove and Little Harbonr, PilIey’s Tickle between 2 November and 24 December 199 1. The horizontal dashed line in the PSP panel is at 80 fig*100 g-l, the maximum acceptable level for edible mussels.
trates that a sudden increase in toxin levels in mussels from Barred Island Cove and Little Harbour, Pilley’s Tickle occurred after several days of strong northeasterly winds, and levels remained high for at least a month while sustained westerly winds ranged from 25 to 65 km h- ’ (daily average). Toxins in mussels from Barred Island Cove assayed immediately after the northeasterly storm were not detectable, but levels 3 days later, after the winds had shifted to the west, had risen to near 1000 ~0 100 g-l. The levels decreased within 10 days to about half the peak values, but remained at 300 to 400 m. 100 g- ’through December as the westerlies continued. In Fig. 2, the bathymetry of PSP positive and negative sites in the Pilley’s Tickle area is shown. While Barred Island Cove and Little Harbour were positive, adjacent sites at Big Island and Kelly Cove remained negative. Both of the posi-
178
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-I 79
tive sites are depositional (soft bottom) basins protected by shallow sills at their entrance. The negative sites do not have sills and are located over hard bottom.
4. Discussion Results presented here provide evidence that, in the absence of planktonic A. fin&en.se, resuspended hypnozygotes ingested by cultured mussels Mytilus eduZisare the probable cause of PSP intoxication in the bays of northeastern Newfoundland during the winter months. In this area, strong winds stir up the muddy bottoms in depositional embayments to produce local intoxication of mussels. The orientation of the embayment is probably either a mitigating or exacerbating factor, depending on the fetch of winds from a particular direction. Local topographic and hydrographic features, particularly those which affect advective dispersal of resuspended sediments, must be taken into account in defining more general spatial relationships of shellfish intoxication with sediment cyst concentrations. It is important to ensure that growers understand that the cysts themselves can intoxicate their mussels, and take suitable precautions to avoid contamination of growing sites by transfer of mussels from areas that contain cysts in the sediments. Processors who also grow their own mussels should ensure that animals they receive from other growers are from uncontaminated sites. Research must be directed at developing criteria for location of mussel culture sites to minimize the risk of intoxication by hypnozygotes.
5. Acknowledgements
We thank the numerous individuals whose conscientious efforts were necessary parts of this study: the mussel growers of the Pilley’s Tickle area cooperated throughout the study; Glen Worthman and Denis Riche collected the sediment cyst samples in the 1989 survey program; Fisheries Inspectors Vey Stoodley, Pat Singleton, and Clyde Follett collected Pilley’s Tickle samples and provided weather data; Steve Keats (Inspection Services Branch) dove for sediment samples at the Pilley’s Tickle sites; Doug Downey and Cyril Morrissey performed the laboratory assays for PSP. We extend our sincere thanks to Dr. D.R.L. White for his support and encouragement of this work. 6. References Gaines, G. and Taylor, F.J.R., 1985. An exploratory analysis of PSP patterns in British Columbia: 1942-1984. In: D.M. Anderson, A.W. White and D.G. Baden (Editors), Toxic Dinoflagellates. Elsevier Science, New York, pp. 439-444. Schwinghamer, P., Anderson, D.M. and Kulis, D.M., 1991. Separation and concentration of living
P. Schwinghamer et al. / Aquaculture 122 (I 994) 171-I 79
179
dinoflagellate resting cysts from marine sediments via density-gradient centrifugation. Limnol. Oceanogr., 36: 588-592. White, A.W. and Lewis, C.M., 1982. Resting cysts of the toxic, red tide dinoflagellate Gonyaulax excavata in Bay of Fundy sediments. Can. J. Fish. Aquat. Sci., 39: 1185-l 194. White, D.R.L. and White, A.W., 1985. First report of paralytic shellfish poisoning in Newfoundland. In: D.M. Anderson, A.W. White and D.G. Baden (Editors), Toxic Dinoflagellates. Elsevier Science, New York, pp. 5 1 l-5 16. Yentsch, C.M. and Mague, F.C., 1979. Motile cells and cysts: two probable mechanisms of intoxication of shellfish in New England waters. In: D.L. Taylor and H.H. Seliger (Editors), Toxic Dinoflagellate Blooms. Elsevier/North Holland, New York, pp. 127- 130.
ELSEVIER
Resuspended hypnozygotes of Alemndrium fundyense associated with winter occurrence of PSP in inshore Newfoundland waters P. Schwinghame+*,
M. Hawryluk”, C. Powellb, C.H. MacKenzie”
‘DepartmentofFisheries and Oceans, Science Branch, P.O. Box 5667, St. John’s, Nfld., CanaabAlCSXl bDepartment of Fisheries and Oceans, Inspection Services Branch, P. 0. Box 566 7, St. John’s, Nfld CanadaAlC 5X1 “Ocean Sciences Centre, Memorial Universityof Newfoundland, St. John’s, Nfd., Canada AI C 5S7
(Accepted 30 November 1993)
Abstract
Abundance of sediment resting cysts, or hypnozygotes, of the toxic dinoflagellate, Alexin the stomachs of blue mussels, Mytilus edulis, was found to be positively correlated with the level of paralytic shellfish poisoning (PSP) toxins in the mussel flesh during winter in northeastern Newfoundland. In addition, historical maximum levels of mussel toxicity were positively correlated with abundance of cysts in sediments at collection sites around the coast of the island. Several adjacent mussel culture sites were examined to determine the physical mechanisms involved in initiation and maintenance of high levels of mussel intoxication at some sites while others remained clear. We found that cultures located over depositional basins in embayments which had shallow sills and were oriented along the fetch of strong winds had persistently high toxin levels. Cultures located over erosional bottoms in open basins remained free of high levels of PSP toxins. We propose that taking this mechanism for winter intoxication into account when selecting growing sites will greatly benefit the Newfoundland mussel culture industry. andriumfindyense,
1. Introduction The first reported case of paralytic shellfish poisoning (PSP) in Newfoundland occurred on 25 September 1982 at Harbour Grace, Conception Bay, when blue mussels, MytiZus edulis, containing high levels of PSP toxins were ingested (White *Correspondingauthor. 0044-8486/94/$07.00
0 1994
SSDZ0044-8486(93)E0310-6
ElsevierScienceB.V. All rights reserved
172
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
and White, 1985 ). The recent growth of the mussel culture industry, especially along the northeast coast of the island, has been accompanied by a growth in awareness of the PSP problem, increased monitoring by the Department of Fisheries and Oceans, and the detection of PSP in areas previously not known to be affected. PSP intoxication of mussels in Newfoundland has not been confined to the period between May and October, when the planktonic stage of the toxic dinoflagellate Alexundrium jiotdyense, which’causes PSP, may be present. Some sites have been plagued by high levels of toxicity throughout the winter (Inspection Services Branch, Department of Fisheries and Oceans, St. John’s, Nfld. ). Hypnozygotes, the resting cysts of A. fundyense which are found in sediments, have been implicated in the winter occurrence of PSP toxins in shellfish in northern British Columbia (Gaines and Taylor, 1985), the Bay of Fundy (White and Lewis, 1982; J. Martin, Department of Fisheries and Oceans, St. Andrews Biological Station, pers. commun. ), and the Gulf of Maine (Yentsch and Mague, 1979), but ingested cysts have not been demonstrated to be positively correlated with tissue toxin levels. It was our objective in this study to establish whether such a correlation exists in an area of putative cyst involvement in intoxication of cultured mussels. Table 1 Summary of data collected in 1989 survey of coastal Newfoundland sediments for A. findyense hypnozygotes. PSP toxicity is maximum recorded level for mussels collected at each site, expressed as pg saxitoxin equivalents per 100 g mussel tissue Site
Depth (m)
PSP Toxicity
Alexandrium cysts/ml
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
St. Lunaire Trap Cove Jackson’s Arm St. Patricks/Brown’s Arm Triton Northwest Arm Fortune Hr Burnt Arm/Gosham’s Arm Valleyfield Northeast Arm/Beachcove Saulton’s Brook T.N. Catalina St. Jones Without Bellevue Heart’s Content T.B. Harbour Grace Holyrood Great Hr. Sandyville Piccaire
32 40 18 30 2 20 1 5.5
8 0.5 0.5 15 6 24 16 17 16 0.5 22
N.D., none detected. Site numbers refer to Fig. 1.
N.D. N.D. 580 43 N.D. N.D. N.D. N.D. N.D. N.D. N.D. 46 N.D. N.D. 1200 N.D. N.D. 38 150
0 0
24 0 0 0 0 0 0 0 0 2 0 0 256 0 6 0 2
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
173
2. Methods
We have begun a program of water, sediment, and stomach content sampling to determine the factors which lead to elevated levels of PSP toxins in shellfish assayed by Inspection Services Branch, Department of Fisheries and Oceans, St. John’s, Nfld. From 3 May to 15 June 1989, we sampled inshore sediments near mussel (Mytilus e&&s) farms and wild collection sites along the south and east coasts of Newfoundland (Table 1, Fig. 1) . Surface sediments were collected using a 15 cm x15 cm Ekman corer where sampling sites were reached by small boat. Duplicate 5-ml subsamples were collected with cut-off lo-ml syringes from the surface of the Ekman samples. Where sites were accessible by foot using chestwaders at low tide, duplicate 5-ml samples of surface sediment were collected directly with cut-off lo-ml syringes. The samples were placed in 20-ml plastic scintillation vials and stored unpreserved, in the dark, at 4”C, prior to analysis. The resting cysts of Alexundriumfindyense were separated from the surface sediments for enumeration using the density-gradient centrifugation technique of
Fig. 1. Sampling locations for 1989 survey of Alexandrium fundyense hypnozygotes in coastal sediments around Newfoundland. Inset illustrates the Pilley’s Tickle area, where mussels were collected for analysis of PSP toxicity and enumeration of A. findyense hypnozygotes in the stomach in winter 199 1-92. Site numbers refer to Table 1.
174
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
Schwinghamer et al. ( 199 1). Abundances were estimated as numbers per ml in the surface 3 cm of sediment (the depth to which a cut-off lo-ml syringe penetrates for a 54 sample). We examined the stomach contents of cultured mussels collected in the fall and winter of 199 l-92 from sites in Pilley’s Tickle, Notre Dame Bay, on the northeast coast of Newfoundland (Fig. 1 and Fig. 2 ) . Animals were taken at random from batches sent to Inspection Services Branch for testing for paralytic shellfish toxins by the standard mouse bioassay. The entire stomach contents were collected from the dissected digestive gland mass using a micropipette. The toxin levels reported here are average values for pooled subsamples of 20-25 individual mussels (minimum of 100 g wet wt. flesh) from each population sampled, therefore no esti-
Little H&our BarredIsland Cove
Big Island
Kelly Cove 2
Fig. 2. Bathymetry and sample collection locations at five mussel farms in Pilley’s Tickle. The mussel rafts extended over most of each cove. Scale and direction for all sites are indicated on the Big Island chart.
175
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-179
i
‘oooo u
0
1000
0
aI z
1
10 Cysts
100
ml -’
Sediment
1000 (n+l)
Fig. 3. Logarithmic plot of maximum recorded PSP toxin levels in mussels vs. abundance of A. fundyense hypnoxygotes in sediments at 19 coastal sites around Newfoundland. The square symbol at the origin represents 12 sites with no record of PSP and no cysts in the sediment.
loo0 j 100
@
-------______
*-----a
i
10 7 1
10 Cysts
ml -’
1000
100 Stomach
Contents
(n+l)
Fig. 4. Logarithmic plot of PSP toxin levels in pooled samples of 20-25 mussels from three sites at Barred Island Cove and two sites at Little Harbour, Pilley’s Tickle vs. abundance of A. findyense hypnoxygotes in stomach contents of mussels taken from the same populations. •i represents three mussels and 0 represents four mussels from Little Ha&our.
176
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
mate of population variability is available. The cyst numbers, on the other hand, were determined on individual animals, so estimates of population variation could be calculated. Cyst numbers are given per ml of stomach contents. Meteorological records for the study period were collected at Kings Point, Southwest Arm, Green Bay, near the Pilley’s Tickle area, by Department of Fisheries and Oceans Inspector Vey Stoodley. Bathymetry of the study locations was taken from Canadian Hydrographic Service chart no. 4593 and records at Department of Fisheries and Oceans, Inspection Services Branch, St. John’s, Nfld.
3. Results Our sediment samples indicate a positive correlation (linear r=0.94, log-log r= 0.86, P-c 0.001) between the abundance of resting cysts, or hypnozygotes, of Akxundrium in sediments and the maximum recorded levels of PSP toxins in mussels (Fig. 3). While the cysts form the seed populations of the planktonic stage which shellfish ingest during the summer and early fall, the historical incidence of high toxin levels in mussels in the late fall and winter at some Newfoundland sites implicates cysts as the direet agents of intoxication. Mussels from some sites in embayments of Notre Dame Bay on the northeast coast contained a wide range of toxin levels during winter, 199.1-92. We have found a positive correlation (linear r=0.85, log-log r=0.77, P-zO.001) between the numbers of cysts in the stomachs and toxin levels in tissues of mussels from the Pilley’s Tickle area (Fig. 4, Table 2). Neither the mussel stomachs nor water samples taken 10 days earlier at the same sites contained any planktonic A. findyense. The heavy (average density= 1.22 g cmm3) resting cysts may be introduced into the water column with sediment resuspension by strong winds. Fig. 5 illusTable 2 Abundance of A. findyense hypnozygotes in stomachs of mussels from Barred Island Cove and Little Harbour, Pilley’s Tickle. PSP toxicity is expressed as pg saxitoxin equivalents per 100 g mussel tissue Sample site
Barred Island Cove Pilley’s Tickle BIC, Pilley’s Tickle (Centre of site) BIC, Pilley’s Tickle (North end of site) Little Hr Pilley’s I (North end of site) Little Hr. Pilley’s I (Centre of site)
Date sampled
PSP toxicity
Alexandrium cysts/ml
Stomach vol. (ml)
N
Mean
Range
331
200-620
0.07
8
10/12/91
515
28/2/92
110
94.2
O-267
0.04
4
2812192
45
16.7
O-67
0.03
4
2812192
37
36.4
o-71
0.07
4
28/2/92
43
0
0
0.06
4
N, number of stomachs analyzed.
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-l 79
--
Barrrd Llttle
Island
177
Cow
Harbour
= < 800 .- > x: i 600
100 i
I
E 5 % c :: xi > u .5 3
80 60 40 20 0 11/2
11/16
11/30
12/14
Date (1991) Fig. 5. PSP toxin levels in mussels, and average daily wind velocity and direction at Barred Island Cove and Little Harbonr, PilIey’s Tickle between 2 November and 24 December 199 1. The horizontal dashed line in the PSP panel is at 80 fig*100 g-l, the maximum acceptable level for edible mussels.
trates that a sudden increase in toxin levels in mussels from Barred Island Cove and Little Harbour, Pilley’s Tickle occurred after several days of strong northeasterly winds, and levels remained high for at least a month while sustained westerly winds ranged from 25 to 65 km h- ’ (daily average). Toxins in mussels from Barred Island Cove assayed immediately after the northeasterly storm were not detectable, but levels 3 days later, after the winds had shifted to the west, had risen to near 1000 ~0 100 g-l. The levels decreased within 10 days to about half the peak values, but remained at 300 to 400 m. 100 g- ’through December as the westerlies continued. In Fig. 2, the bathymetry of PSP positive and negative sites in the Pilley’s Tickle area is shown. While Barred Island Cove and Little Harbour were positive, adjacent sites at Big Island and Kelly Cove remained negative. Both of the posi-
178
P. Schwinghamer et al. /Aquaculture 122 (1994) 171-I 79
tive sites are depositional (soft bottom) basins protected by shallow sills at their entrance. The negative sites do not have sills and are located over hard bottom.
4. Discussion Results presented here provide evidence that, in the absence of planktonic A. fin&en.se, resuspended hypnozygotes ingested by cultured mussels Mytilus eduZisare the probable cause of PSP intoxication in the bays of northeastern Newfoundland during the winter months. In this area, strong winds stir up the muddy bottoms in depositional embayments to produce local intoxication of mussels. The orientation of the embayment is probably either a mitigating or exacerbating factor, depending on the fetch of winds from a particular direction. Local topographic and hydrographic features, particularly those which affect advective dispersal of resuspended sediments, must be taken into account in defining more general spatial relationships of shellfish intoxication with sediment cyst concentrations. It is important to ensure that growers understand that the cysts themselves can intoxicate their mussels, and take suitable precautions to avoid contamination of growing sites by transfer of mussels from areas that contain cysts in the sediments. Processors who also grow their own mussels should ensure that animals they receive from other growers are from uncontaminated sites. Research must be directed at developing criteria for location of mussel culture sites to minimize the risk of intoxication by hypnozygotes.
5. Acknowledgements
We thank the numerous individuals whose conscientious efforts were necessary parts of this study: the mussel growers of the Pilley’s Tickle area cooperated throughout the study; Glen Worthman and Denis Riche collected the sediment cyst samples in the 1989 survey program; Fisheries Inspectors Vey Stoodley, Pat Singleton, and Clyde Follett collected Pilley’s Tickle samples and provided weather data; Steve Keats (Inspection Services Branch) dove for sediment samples at the Pilley’s Tickle sites; Doug Downey and Cyril Morrissey performed the laboratory assays for PSP. We extend our sincere thanks to Dr. D.R.L. White for his support and encouragement of this work. 6. References Gaines, G. and Taylor, F.J.R., 1985. An exploratory analysis of PSP patterns in British Columbia: 1942-1984. In: D.M. Anderson, A.W. White and D.G. Baden (Editors), Toxic Dinoflagellates. Elsevier Science, New York, pp. 439-444. Schwinghamer, P., Anderson, D.M. and Kulis, D.M., 1991. Separation and concentration of living
P. Schwinghamer et al. / Aquaculture 122 (I 994) 171-I 79
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