Rapp. P.-v. Réun. Cons. int. Explor. Mer, 187: 83—88. 1987

Diarrhetic mussel poisoning. Measures and consequences in The Netherlands

Marie Kat

Kat, Marie. 1987. Diarrhetic mussel poisoning. Measures and consequences in The Netherlands. - Rapp. P.-v. Réun. Cons. int. Explor. Mer, 187: 83 - 88.

Several outbreaks of diarrhetic mussel poisoning in The Netherlands in 1961, 1971, 1976, 1979, and 1981 led to the development of a sanitary control system for phytoplankton toxins. Since 1981, it has been established that this phenomenon was caused by a bloom of the dinoflagellate Dinophysis acuminata.

Monitoring of the phytoplankton concentrations in the Dutch coastal waters, together with a rat bioassay used for the detection of DSP (Diarrhetic Shellfish Poison) in mussels provided the necessary information upon which temporary bans on the shellfish fishery in the infested areas could be based.

During the shellfish poisoning periods in 1976, 1979, and 1981 the mussel re-laying areas at Yerseke Bank in the Oosterschelde were not infested by DSP. Therefore, marketing of mussels from this area could be continued (in contrast to 1971) and the economic losses were almost negligible.

As D. acuminata blooms in European coastal waters appear to be widespread, an adequate sanitary control system is required to reduce the risks for the shellfish market and the consumers.

A la suite de plusieurs épidémies d ’intoxications diarrhéiques par les moules aux Pays-Bas en 1961, 1971, 1976, 1979 et 1981 un système de contrôle sanitaire des toxines phytoplanctoniques a été mis en place. Depuis 1981 il a été établi que ce phénomène était dû aux efflorescences du dinoflagellé Dinophysis acuminata.

Une surveillance des concentrations phytoplanctoniques dans les eaux côtières néerlandaises associée à un test rat pour détecter le DSP (Diarrhetic Shellfish Poison) a fourni l’information nécessaire servant de base aux fermetures temporaires de la pêche aux moules dans les zones infestées.

Au cours des périodes de contamination des mollusques en 1976, 1979 et 1981, les aires de reparcage des moules de Yerseke Bank dans l'Oosterschelde n’ont pas été touchées par le DSP. C’est pourqoi la commercialisation des moules dans ce secteur a pu se poursuivre (contrairement à ce qui avait eu lieu en 1971) et les pertes économi­ques ont été quasi négligeables.

En raison de la multiplication des efflorescences de D. acuminata dans les eaux côtières européennes il est nécessaire d'organiser un système de contrôle sanitaire approprié afin de réduire les risques pour le marché des coqillages et les consomma­teurs.

Marie Kat: Netherlands Institute fo r Fishery Investigations, P.O. Box 68, 1970 A B IJmuiden. The Netherlands.

Introduction

Diarrhetic shellfish poisoning: outbreaks and causative agent (history)

The first described outbreak of diarrhetic mussel poi­soning took place in the Oosterschelde (The Nether­lands) in 1961. It resulted from human consumption of the blue mussel (Mytilus edulis). At first, it was sug­gested that this phenomenon was caused by the dinofla- gellates Prorocentrum micans and P. redfieldii ( = P. triestinum), which were abundantly present in both mussel guts and ambient waters. However, re-exam­

ination of the phytoplankton samples, taken in the Oos­terschelde before the outbreak, revealed the occurrence of yet another dinoflagellate, Dinophysis acuminata (Kat, 1979), during this period.

In 1961 (Kat, unpublished), a rat bioassay was devel­oped to detect diarrhetic toxin in mussels, but plans for proper safety control were mainly aimed at phytoplank­ton monitoring. From 1962 to 1971 neither Dinophysis acuminata nor Prorocentrum species produced any blooms in the shellfish-growing areas of the Ooster­schelde.

The diarrhetic mussel-poisoning episode in 1971

H orth Ssa

C30C2Sete

North/Sea

Rhine/Meuse

N o f de te c te d

13-15 SEP '7 8 2 5 -28 A U G »80 21-23 SEP *82

Figure 1. Maximal observed blooms of Dinophysis acuminata in the Dutch coastal area 1973-1982. Dotted lines, isohalines for the summerperiod; encircled numbers, salinities (Kat, 1983b).

again coincided with the presence of D. acuminata, though they were far outnumbered by Prorocentrum micans. However, when a decrease in the toxicity of the mussels occurred, in spite of continuing high numbers of

P. micans, D. acuminata became a suspected dinoflagel­late. This opinion was fortified by the occurrence of extraordinary blooms of D. acuminata in the Dutch coastal area (Fig. 1) about two weeks before short-term

84

, 0 4 : °5

1 «3

E A S T E R N S C H E L D T

SEP '81

O Non toxic areas

• Slightly toxic

# Moderately toxic

^ Seriously toxic

JUL

Figure 2. Maximal toxicity observed at Dutch mussel sites in the Waddensea and the Oosterschelde (Kat, 1983a).

outbreaks of diarrhetic mussel poisoning in the Dutch Waddensea in 1976 and 1979. Finally, during the diar­rhetic mussel-poisoning episode in 1981, a Dinophysis- type of toxin was isolated from toxic mussels from the most infested sites in the Dutch Waddensea and identi­fied by Yasumoto (1982, personal communication). D. acuminata must, therefore, be considered the most likely causative organism.

Monitoring

The occurrence of these poisoning episodes necessitated the establishment of a stringent control system, based on effective monitoring of phytoplankton and mussel tissues. Every year from June till October, net hauls were analysed for suspected dinoflagellates, in partic­ular D. acuminata, in a weekly monitoring programme. In addition the rat bioassay was carried out in mussels from sites in every mussel location in the Oosterschelde and the Dutch Waddensea, both shellfish-growing ar­

85

eas. In this bioassay white rats are fed the hepato- pancreas of raw mussels; the presence of DSP toxin leads to diarrhea. This test has proved to be effective. The test method from 1961 has been improved in the course of the years so that the degree of toxicity can now be measured on an arbitrary scale (Kat, 1983a).

The presence of D. acuminata in the phytoplankton samples leads to a more frequent sampling programme for mussel toxicity. A positive reaction by the test ani­mals then leads to a temporary ban on the shellfish fishery in the infested area during the period of mussel poisoning.

The distribution pattern of the mussel poisoning has been found to be very patchy (see e.g.. Fig. 2) because of the unpredictable route of D. acuminata-bearing wa­ter masses, which demonstrates the need to sample the total shellfish-growing area on a sufficiently frequent basis.

Economic consequencesIn the shellfish-growing areas in the Dutch Waddensea and the Oosterschelde, mussels are harvested from July to April. According to official Dutch regulations, shell­fish from both areas must always be re-layed before

0 .2 .

1979-80

0.4.

0.2

1980-81

0.4.

0.2.

1981-82

0.6

0.4

0.2

Figure 3. Home market, July 1979—April 1983.

1.0.

1979-80

1-0.

1980-81

1.0.

isselpoisoning

1.0.

1982-83

Figure 4. Export market (Belgium and France), July 1979— April 1983.

2.0.

1.0.

1971-72

J sA O DN J MF

Figure 5. Export market (Belgium and France), July 1970- April 1972.

marketing. This takes place on the Yerseke Bank, a designated area in the Oosterschelde, where the envi­ronmental conditions are optimal (Fig. 2, station G).

In 1961 and 1981, DSP toxicity did not penetrate as far as the re-laying sites in the Oosterschelde and in consequence there was no reason to ban shellfish trans-

86

G1 G2F2 F3 F4 F5

50

49

60

47

46

45

44N o r w d 1

43

57

42

40

39

38

Bnfai

35

33

30cells per litre

29> 1 0 0 0

Figure 6. Distribution of Dinophysis acuminata, 15 August—9 September 1983.

portation from the Yerseke Bank. In Figures 3 and 4, the home and export sales are depicted for the period July 1979 to April 1983. The short-term decline in Octo­ber 1981 in both markets was probably the result of bad publicity, although fluctuations of the same order also were recorded in 1982 under quite harmless circum­stances. In July 1971, however, the marketing of mus­sels had to be banned for a 4-week period (Fig. 5), because a Dinophysis acuminata bloom had advanced into the eastern part of the Oosterschelde, where toxic­ity of mussels was detected (Fig. 2, E and F).

In spite of the occurrence of diarrhetic mussel poison­ing, the annual turnover of mussels shows an agreeable increase for the last few years (Table 1).

Discussion

The Netherlands

Phytoplankton research in the Dutch coastal area, car­ried out since 1973, has revealed that Dinophysis is a common dinoflagellate in the phytoplankton concentra-

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Table 1. The annual turnover of mussels 1970-1983 (x lO 6 kg).

Period Home market Export market(Belgium and France)

1970-1971 ........... No data 43-61971-197 2 ........... No data 53-51973-1978........... No data1979-198 0 ........... 8-3 34 11980-1981 ........... 9-1 35-01981-198 2 ........... 10-0 50-81982-198 3 ........... 11 0 56-3

tions in August, usually reaching maximum population density in September at salinities of 30—33 g/kg (Fig. 1). Blooms of D. acuminata appeared to be correlated to wind speed rather than to water temperature.

Concentrations of more than 10 000 cells per litre only arose after a period of at least one week with mean wind speed not exceeding wind force 2 Beaufort, whereas during periods when wind force 3 Beaufort or more prevailed, D. acuminata concentrations remained below 1000 cells per litre. Water temperatures during the bloom periods ranged between 15-8°C and 19-5°C.

Based upon these experiences, the outbreak of a nox­ious D. acuminata bloom and its possible consequences can be more or less predicted in Dutch coastal waters.

Other North Sea coastal areas

Results of an incidental phytoplankton survey between 54°N and 58°30'N in the North Sea carried out from 15 August to 9 September 1983 (a period of maximal D. acuminata occurrence, at least in Dutch coastal waters) show that D. acuminata was observed in high numbers in the coastal waters of Scotland, England, Germany, Denmark, and The Netherlands, but not in the open waters of the central northern North Sea (Fig. 6). As the presence of D. acuminata has been a yearly recur­

ring phenomenon in The Netherlands, the same is to be expected in other North Sea coastal areas.

Atlantic coastal areas

D. acuminata blooms have also been observed along the European Atlantic coast. Marino et al. (MS) correlated a bloom of D. acuminata of less than 16000 cells per litre in August 1978 with diarrhetic mussel poisoning in Ri'a de Ares y Betanzos in Spain. Along the French coast, blooms of D. acuminata have been infrequently observed since 1975 (Lassus, 1983). However, the pres­ence of D. acuminata in the coastal waters of Brittany and Normandy during the summer of 1983 led to in­festation of bivalves by a diarrhetic toxin (Alzieu et al., 1983).

The ubiquity of D. acuminata in the coastal waters of Europe urges the development of stringent national DSP controls in shellfish-growing areas.

ReferencesAlzieu, C., Lassus, P., Maggi, P., Poggi, R., and Ravoux, G.

1983. Contamination des coquillages des côtes bretonnes et normandes par une algue unicellulaire toxique (Dinophysis acuminata). Rapp, techn. ISTPM, No. 4.

Kat. M. 1979. The occurrence of Prorocentrum species and coincidental gastro intestinal illness o f mussel consumers. In Toxic dinoflagellate blooms. Developments in marine biol­ogy, Vol. 1, pp. 215-220. Ed. by D .L . Taylor and H .H . Seliger. Elsevier/North Holland, New York. 505 pp.

Kat, M. 1983a. Diarrhetic mussel poisoning in The Nether­lands related to the dinoflagellate Dinophysis acuminata. Antonie van Leeuwenhoek, 49: 417-427.

Kat, M. 1983b. Dinophysis acuminata blooms in the Dutch coastal area related to diarrhetic mussel poisoning in the Dutch Waddensea. Sarsia, 68: 81—84.

Lassus, P. 1983. Bilan des eaux colorées observées sur le litto­ral français entre 1975 et 1982. 1CES CM 1983/L:29.

Marino, J ., Campos, M. J ., Nunes, M .T ., and Iglesias, M. L. Variaciôn estacional de los ambietales y del fitoplankton en la zona de Lorbe (Rîa de Ares y Betanzos) en 1978. Manu­script.