MAP Technical Reports Series No. 106 UNEP

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which occur in all the seas of the world, however, the mechanisms of the deaths of the marine
animals have not been sufficiently studied yet. Recently, the problem has represented a notable
scientific interest, both in Japan and Europe because of the health and economic damage
caused.
The effects of phytoplankton blooms on animals are direct and indirect, primary or
secondary. The primary or direct effects are those caused by the blocking of the branchial
apparatus by the phytoplanktonic biomass, the effect on the branchial cells of specific
ichthyotoxins, and on the cellular metabolism of biotoxins adsorbed via the digestive system
(Taylor, 1990). The indirect or secondary effects, however, are due to lack of O 2 and to the
production of H 2S and NH 3, which can reach really toxic levels for fish.
Harmful algal blooms which create problems for fishery and aquaculture in the coastal
area in the world and in the Mediterranean sea are due to organisms belonging to the following
algae classes: Dinophyceae, Prymnesiophyceae, Raphidophyceae, Dictyochophyceae
(= Silicoflagellates).
6.1.1 Dinophyceae
The toxic blooms of dinoflagellates fall into three categories (Steidinger, 1983): (a)
blooms that kill fish but few invertebrates (Gymnodinium breve Davis, the Florida red tide
organism, is an example); (b) blooms that kill primarily invertebrates (several species of
Gonyaulax are of this type); (c) blooms that kill few marine organisms but the toxins are
concentrated within the siphons or digestive glands of filter-feeding bivalve molluscs (clams,
mussels, oysters, scallops, etc.) causing paralytic shellfish poisoning (PSP).
It has been noted for some time that the mortality of fish during the blooms of
dinoflagellates of the species Ptychodiscus breve (= Gymnodinium breve) and Alexandrium (=
Gonyaulax), responsible for NSP and PSP in man, is due to neuromuscular lesions caused by
the same biotoxins absorbed via the digestive system (Ray, 1971; Steidinger et al., 1973) (see
chapter 7).
The information presently available indicates the possible link between dinoflagellates
toxins (saxitoxins and brevetoxins) and recent mass mortalities of marine mammals (humpback
whale and bottlenose dolphins) along the eastern coast of the United States (Anderson and
White, 1989).
Genus GYMNODINIUM Stein
In Florida, the mortality in fish is due to Gymnodinium breve which was identified in
1948 as the aetiological agent and is considered to be the sole agent responsible for all the
outbreaks described since 1844. As regards benthic fish, the toxins may have a complex effect
on the neuromotor system, but this is not true for various invertebrates for which the anoxic
condition is probably the only cause of death (Steidinger et al., 1973). Ray and Aldrich (1965),
Spikes et al. (1969), Martin and Chatterjee (1969) found that the lipid extract of G. breve
produces toxins that have effects on fish, chicks and mice. The abundance and annual
periodicity pattern of the unarmoured dinoflagellate G. breve (Davis) was studied also in the
Mediterranean sea in an eutrophic environment (Saronikos Gulf, Aegean Sea) during 1977-1983
and 1987 (Pagou and Ignatiades, 1990). In the Aegean Sea, fish kills are to date not reported.