Karenia mikimotoi

3 Toxic Phytoplankton
3.1 Toxic diatoms and dinoflagellates causing
shellfish poisoning
Various species of the diatom Pseudonitzschia produce the toxin domoic acid that is
the cause of amnesic shellfish poisoning (ASP). Certain species of the dinoflagellate
genus Alexandrium, e.g. A. minutum and A. tamarense, produce various toxins
belonging to the saxitoxin group that are the cause of paralytic shellfish poisoning
(PSP), as does Gymnodinium catenatum, and the dinoflagellates Dinophysis
acuminate, acuta and norvegica produce toxins in the okadaic acid group, that are
responsible for diarrhetic shellfish poisoning (van Egmond et al., 2004; Leftley and
Hannah, 2008). The shellfish that feed on these algae concentrate the toxins in their
tissues and because they filter large volumes of water, e.g. mussels may filter several
litres per hour, the algae do not need to be present in high concentrations. For
example, one to two hundred cells per litre of toxic Alexandrium may be sufficient to
engender toxicity in the shellfish sufficient to cause poisoning if eaten (Townsend et al.,
2001 and refs. therein) and blooms of Alexandrium and Dinophysis do not approach
the densities of ‘nuisance algae’ blooms such as Phaeocystis spp. - see notes to Table
6.
The WHO guidelines (Anon., 2003) note the absence of evidence of adverse effects
due to ingestion of seawater containing seawater containing species of algae
responsible for ASP, PSP and DSP as well as those responsible for neurotoxic
shellfish poisoning (NSP). This is discussed further in sect. 4. It was also noted also
that there is little information on adverse effects of dermal contact with marine waters
containing these groups of toxic algae and no incidents appear to have been reported
in the scientific literature since 2003.
3.2 Prorocentrum lima
The epibenthic and epiphytic dinoflagellate Prorocentrum lima is widely distributed in
coastal seas and estuaries in both temperate and tropical regions around the world and
is common in UK waters. It produces diarrhetic shellfish poisoning (DSP) toxins,
primarily okadaic acid and dinophysistoxin-1 (Quilliam, 2004 and refs. therein) and also
the toxic macrolide prorocentrolide (Leftley and Hannah, 2008).
P. lima has been found associated with seaweed and seagrass in Fleet Lagoon,
Dorset. This is a coastal area where shellfishery closures have occasionally been
enforced due to elevated levels of DSP toxins in shellfish (Foden et al., 2005) and P.
lima is probably the cause. (See also notes (5) and (6) in Table 6).
Although normally epiphytic or epibenthic in habit, planktonic blooms of P. lima have
been described, for example in locations in the W Adriatic (Ingarao et al., 2007)
reaching densities of ca. 4.7 x 10 5 cells.L -1 .
There is no evidence from the literature that. P. lima is a danger to human health other
than due to consumption of DSP toxins via shellfish vectors. One of the authors of this
report (JWL) can add this anecdotal evidence: He has cultured hundreds of litres of
DSP toxic Prorocentrum lima as part of experiments to toxify shellfish. He has been
exposed to cultures for many hours and has even immersed his hands in dense
cultures and can report no short-term ill-effects.
12 A Literature review of the potential health effects of marine microalgae and macroalgae