Harmful Algae 6 (2007) 218–231 www.elsevier.com/locate/hal Toxicity of Dinophysis spp. in relation to population density and environmental conditions on the Swedish west coast Odd Lindahl *, Bengt Lundve, Marie Johansen The Royal Swedish Society of Sciences, Kristineberg Marine Research Station, SE 450 34 Fiskeba¨ckskil, Sweden Received 29 April 2006; received in revised form 14 May 2006; accepted 28 August 2006 Abstract The aim of this study in the field was to investigate whether there are differences between the outer archipelago (Gullmar Fjord) and a semi-enclosed fjord system (Koljo¨ Fjord) in occurrences of D. acuta and D. acuminata as well as in their content of diarrheic shellfish toxin (DST) per cell. When all data pairs of cell toxicity of D. acuminata and the corresponding number of cells lÀ1 from the two sites were tested in a regression analysis, a statistically significant negative correlation became evident and was apparent as a straight line on a log–log plot ( p < 0.0001). Obviously, there was an overall inverse relationship between the population density of D. acuminata and the toxin content per cell. Plotted on a linear scale, all data-pairs of cell toxicity and cell number made up a parabolic curve. On this curve the data-pairs could be separated into three groups: (i) D. acuminata occurring in numbers of fewer than approximately 100 cells lÀ1, and with a toxin content per cell above 5 rg cellÀ1; (ii) cell numbers between 100 and approximately 250 cells lÀ1 with a cell toxin content from 5 to 2 rg cellÀ1; (iii) when the population became greater than 250 cells lÀ1, the toxicity, with few exceptions, was less than 2 rg cellÀ1. By applying this subdivision, some clear patterns of the distribution of the differently toxic D. acuminata became evident. When comparing the cell toxicity of the two sites, it was obvious that the D. acuminata cells from all depths from the Gullmar Fjord as a mean were significantly more toxic compared to the Koljo¨ Fjord samples. The results have demonstrated that approximately 100 high-toxicity cells in a low-density population at surface may lead to the same accumulation of DST in a mussel as the ingestion of 1500 low-toxicity cells from a high-density pycnocline population. # 2006 Elsevier B.V. All rights reserved. Keywords: Dinophysis; Cell toxicity; Population density; Cell signalling; Diarrheic shellfish poisoning (DSP) 1. Introduction 2002). The problem with toxic mussels has been highlighted in several studies during the last few Diarrheic shellfish poisoning (DSP) is a major decades, however, knowledge about the phenomena is problem for the shellfish industry around the world (Lee still sparse, and the ability to forecast the occurrence of et al., 1989; Haamer et al., 1990; Dahl and Johannessen, Dinophysis and the toxin content in the shellfish has not 2001; Pavela-Vrancic et al., 2002; Morono et al., 2003). been fully developed. On the Swedish west coast the toxic dinoflagellate Dinophysis spp. occurs in coastal waters all over the genus Dinophysis is the main contributor of the mussel world (Hallegraeff et al., 2003), including Scandinavia toxins DST (diarrheic shellfish toxins) (Godhe et al., (Edebo et al., 1988; Belgrano et al., 1999; Andersen et al., 1996; Aune et al., 1996; Godhe et al., 2002,). They vary in the content of toxin per cell and their * Corresponding author. ability to produce different kinds of toxins of different E-mail address: [email protected] (O. Lindahl). poisonouness (Tables 1 and 2). Diarrheic shellfish 1568-9883/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.hal.2006.08.007 O. Lindahl et al. / Harmful Algae 6 (2007) 218–231 219 Table 1 Summary of reported toxicity per cell (rg cellÀ1)ofD. acuminata Country Area OA cellÀ1 DTX-1 cellÀ1 DTX-2 cellÀ1 Reference Denmark Coastal 0–40 Andersen et al. (1996) The Wadden sea 0.3 Andersen et al. (1996) Limfjord 6.1 Andersen et al. (1996) East coast of Jutland 5.3 Andersen et al. (1996) Canada Gulf of St. Lawrence 25.5 Cembella (1989) France Le Havre 1.6 Lee et al. (1989) Japan Tokyo Bay J Trace Lee et al. (1989) Spain Rio de Pontevedra 1–37 0.3–0.6 ? Blanco et al. (1995) Sweden Gullmar Fjord 9.1 0 Johansson et al. (1996) Gullmar Fjord 0.04 0.02 Yasumoto (unpublished) Gullmar Fjord 0–17 Present paper Koljo¨ Fjord 0–2.6 Present paper poisoning (DSP) causes abdominal cramps, diarrhea, have been reported to cause most of the DST toxicity nausea, and vomiting (Daranas et al., 2001). The first (Godhe et al., 2002). D. acuminata has in many incident of illness was reported in the Netherlands in the countries in northern Europe been reported to produce 1960s, and the toxic substance was first isolated from OA (Carmody et al., 1996), while D. acuta has been the black sponge Halicondria okadai (Hallegraeff et al., reported to produce OA, DTX-1, or DTX-2 (Tables 1 2003). There are three kinds of DSP toxins: the okadaic and 2). In Sweden D. acuta has been observed to cause acid (OA) group, the pectenotoxin-group, and the OA in mussels in the outer archipelago, while the co- yessotoxin group. In Sweden the okadaic acid has occurrence of DTX-1 in mussels and algae was previously been the most commonly observed DST observed in confined fjord areas (Svensson, 2003a,b). toxin (Edebo et al., 1988). The OA group also includes In the review of Maestrini (1998) it was concluded DTX-1 and DTX-2 and several derivatives (Quilliam, that little is known about the taxonomy of Dinophysis 2003). These compounds are lipid-soluble long-chain- spp. and about how they thrive and survive in the linked polyether rings and are accumulated in the pelagic. Further, it was concluded that knowledge is hepatopancreas of the blue mussel (Mytilus edulis) especially limited concerning whether the species have (Yasumoto et al., 1985; Hallegraeff et al., 2003). several life stages, exactly what they take from the sea There are several species of DST-producing in order to live and grow, and to what extent dense, Dinophysis: for example, D. acuta, D. acuminata, D. vertically patchy populations result from active or norvegica, D rotundata, D. caudata, D. fortii, D. passive concentration, from growth, or from a mixture sacculus,andD. dens (Hallegraeff et al., 2003; Graneli of both processes. It is generally clear that at times of et al., 1997). In Sweden D. acuta and D. acuminata greatest cell density, cells of Dinophysis can be Table 2 Summary of reported toxicity per cell (rg cellÀ1)ofD. acuta Country Area OA cellÀ1 DTX-1 cellÀ1 DTX-2 cellÀ1 Reference Spain Vigo 9.4 Lee et al. (1989) Norway Sogndal 4 4.2 Lee et al. (1989) Sweden Gullmar Fjord 20 Riisgaard (1991), Edler and Hageltorn (1990) Sweden Kulefjord 100–160 Haamer et al. (1990) Sweden Gullmar Fjord 0 6.6 Johansson et al. (1996) Sweden Gullmar Fjord 0.52 0.01 1.57 Yasumoto (unpublished) Ireland Southwest coast 58 78 Kevin et al. (1998) Spain Ria de Pontevedra 0.6–94 0.4–169 ? Blanco et al. (1995) Portugal Northwest coast Detected Vale and Sampayo (2000) Ireland Bantry Bay Detected Draisci et al. (1998) Gullmar Fjord Detected Present paper Koljo¨ Fjord 0.4–7.8 Present paper 220 O. Lindahl et al. / Harmful Algae 6 (2007) 218–231 concentrated in a layer of water that represents only a The aim of this study was to investigate whether small fraction of the water column. This could be a there are differences between the outer archipelago and result of the sinking of senescent cells accumulating in the semi-enclosed fjord system in occurrences of D. the pycnocline; active vertical migration; better growth acuta and D. acuminata as well as in their content of due to the occurrence of organic material at the DST per cell, which in turn may explain the observed pycnocline suitable for Dinophysis nutritional require- occurrences of DST in mussels. The most obvious and ments; or, finally, reduction or absence of grazing conspicuous result of the present study was the clear (Maestrini, 1998). negative correlation between the population density and DST occurrence in the blue mussel has been the toxicity per cell of D. acuminata. This relationship monitored along the Swedish west coast since the was more or less present regardless of site and depth end of the 1980s. After analysis of this data set, a pattern during a period of 2 months. This result seemed to be a in toxin occurrence has become apparent (Rehnstam- novel finding. Holm and Hernroth, 2005). Most obvious was the annual cycle of DST with peaks from late summer/early 2. Materials and methods autumn to winter (August–January), when DST levels occasionally were over the limit for human consump- 2.1. Study areas tion (160 mgkgÀ1). This pattern has, at least partly, been thought to result from cold water temperatures and Water samples were taken from the Koljo¨ Fjord a lack of non-toxic phytoplankton (diatoms) during (588130.6N; 118330.4E), which is the northern part of the winter (Edebo et al., 1988). Along the Swedish west Orust-Tjo¨rn Fjord system (Fig. 1). This chain of coast the occurrence of DST in mussels has often connected fjords and sill basins is open at both ends, differed considerably between sites situated on the outer and there is a counterclockwise (=north-going) net archipelago (high toxic mussels) compared to the semi- current of 70 m3 sÀ1 (Bjo¨rk et al., 2000). This net current enclosed fjord system (low toxic mussels) inside the is mainly driven by salinity differences in the surface large islands Orust and Tjo¨rn (Fig.