262
FINDLAY E. RUSSELL
11. PROTISTA
Most of the toxic protista are of the order Dinoflagellata. These
organisms are widely distributed throughout neritic waters and in the
high seas from the polar oceans to the tropics. " Blooms " of toxic
dinoflagellates sometimes occur during weather disturbances, or under
certain other conditions, and result in the phenomenon frequently
referred to as " red water ", " red tide " or " brown water ". However,
the bloom may appear yellowish, greenish, bluish, or even milky in
color, depending on the protistan involved and a number of ecological
factors. When excessive numbers of these unicellular organisms collect
there may be a mass mortality of fishes and other marine organisms
in the area. Such occurrences are frequently reported (Kofoid, 1911 ;
Hornell, 1917 ; Nightingale, 1936 ; Galtsoff, 1948 ; Connell and Cross,
1950 ; Fish and Cobb, 1954 ; Smith, 1954 ; Brongersma-Sanders, 1957 ;
Grindley and Taylor, 1962). Halstead (personal communication, 1964)
lists a number of conditions which favor plankton blooms. These
include changes in weather conditions that bring about upwellings or
other alterations in water masses, changes in nutrient salt concentrations, changes in water temperature and in sunlight; and changes in
those factors which affect water turbulence, transparency, surface
illumination, passive sinking of the phytoplankton themselves to depths
beyond the photic zone, and the grazing action of the zooplankton
population.
The possible causes for the mass mortality of marine life during and
following plankton blooms has been the subject of considerable discussion. Among the factors that have been implicated are: oxygen
depletion in the water, due either to the number of plankton present
or to the release of decay products by these organisms and the dying
fish; asphyxiation through a blanketing of the fish with a mass of
plankton ; or the production of a toxin by the protistan. It is known
that the early larvae of certain molluscs and crustaceans which respire
through their body surfaces are not affected by blooms, while those
forms with specialized respiratory gills die when these organs become
covered with the disintegrating bodies of the plankton (Motoda,
1944). It would appear that the evidence to date favors the conclusion that in most instances the mass mortality of fishes and
certain other marine forms during these maxima can be ascribed
to physical rather than chemical phenomena, although there is
evidence to the contrary.
FINDLAY E. RUSSELL
11. PROTISTA
Most of the toxic protista are of the order Dinoflagellata. These
organisms are widely distributed throughout neritic waters and in the
high seas from the polar oceans to the tropics. " Blooms " of toxic
dinoflagellates sometimes occur during weather disturbances, or under
certain other conditions, and result in the phenomenon frequently
referred to as " red water ", " red tide " or " brown water ". However,
the bloom may appear yellowish, greenish, bluish, or even milky in
color, depending on the protistan involved and a number of ecological
factors. When excessive numbers of these unicellular organisms collect
there may be a mass mortality of fishes and other marine organisms
in the area. Such occurrences are frequently reported (Kofoid, 1911 ;
Hornell, 1917 ; Nightingale, 1936 ; Galtsoff, 1948 ; Connell and Cross,
1950 ; Fish and Cobb, 1954 ; Smith, 1954 ; Brongersma-Sanders, 1957 ;
Grindley and Taylor, 1962). Halstead (personal communication, 1964)
lists a number of conditions which favor plankton blooms. These
include changes in weather conditions that bring about upwellings or
other alterations in water masses, changes in nutrient salt concentrations, changes in water temperature and in sunlight; and changes in
those factors which affect water turbulence, transparency, surface
illumination, passive sinking of the phytoplankton themselves to depths
beyond the photic zone, and the grazing action of the zooplankton
population.
The possible causes for the mass mortality of marine life during and
following plankton blooms has been the subject of considerable discussion. Among the factors that have been implicated are: oxygen
depletion in the water, due either to the number of plankton present
or to the release of decay products by these organisms and the dying
fish; asphyxiation through a blanketing of the fish with a mass of
plankton ; or the production of a toxin by the protistan. It is known
that the early larvae of certain molluscs and crustaceans which respire
through their body surfaces are not affected by blooms, while those
forms with specialized respiratory gills die when these organs become
covered with the disintegrating bodies of the plankton (Motoda,
1944). It would appear that the evidence to date favors the conclusion that in most instances the mass mortality of fishes and
certain other marine forms during these maxima can be ascribed
to physical rather than chemical phenomena, although there is
evidence to the contrary.