ASPECTS OF STRESS IN THE TROPICAL MARINE ENVIRONMENT
241
(Moore and Lbpez, 1966), total tissue production continues fairly
constant but, over a three year period, changes over from all somatic
to all gonad. Under conditions of stress, gonad production is generally
given preference over somatic production. Thorson (personal communication) states that, in the Arctic, protandrous hermaphroditism is
common, the " cheaper " male phase allowing somatic growth to
continue up to the time when the animals become female. It seems
likely that the amount of growth taking place after sexual maturity may
reflect general degree of stress.
We have assembled all the data we could which included size at
sexual maturity and maximum size. These were cubed to give values
related approximately linearly to tissue weight. For each species, the
size increase after maturity was then expressed as a percentage of the
maximum size. Figure 19 shows the results for the four groups on which
we have information. In temperate waters, growth after maturity is
characteristically large. In cold and warm waters it may be large, but,
on the average, is considerably less than in temperate waters. In these
regions of stress the variation in rate is also much greater than in
temperate waters.
G. Longevity
There is a considerable literature on lengevity in marine invertebrates, much of which has been reviewed by Comfort (1966) and
SegerstrAle (1960). Unfortunately many listed records are misleading
in that they refer to maximum recorded age, such as on a fouling test.
panel, whereas it may be known that the species actually lives much
longer. It is generally accepted, that there is an inverse relationship
between growth rate and longevity, and that longevity is greater, and
growth rate less in cold waters than in warm waters. The relation of
longevity has been clearly shown by Weymouth and McMillin (1931) in
the case of Siliqua patula.
In Fig. 20 we have assembled data for a number of species of
molluscs. The number is not large but we consider the longevities to
be valid maxima for the population in question. The trend towards
shorter life span in the tropics is clear. The smaller size in the tropics
is less pronounced and will be examined in more detail, and from more
extensive data, in a later section.
H. Extremes of size
There are many instances in which stress is accompanied by reduction in size. Examples are dwarf races at abnormally high or low
salinities. It seems likely, then, that there may be a size gradient
241
(Moore and Lbpez, 1966), total tissue production continues fairly
constant but, over a three year period, changes over from all somatic
to all gonad. Under conditions of stress, gonad production is generally
given preference over somatic production. Thorson (personal communication) states that, in the Arctic, protandrous hermaphroditism is
common, the " cheaper " male phase allowing somatic growth to
continue up to the time when the animals become female. It seems
likely that the amount of growth taking place after sexual maturity may
reflect general degree of stress.
We have assembled all the data we could which included size at
sexual maturity and maximum size. These were cubed to give values
related approximately linearly to tissue weight. For each species, the
size increase after maturity was then expressed as a percentage of the
maximum size. Figure 19 shows the results for the four groups on which
we have information. In temperate waters, growth after maturity is
characteristically large. In cold and warm waters it may be large, but,
on the average, is considerably less than in temperate waters. In these
regions of stress the variation in rate is also much greater than in
temperate waters.
G. Longevity
There is a considerable literature on lengevity in marine invertebrates, much of which has been reviewed by Comfort (1966) and
SegerstrAle (1960). Unfortunately many listed records are misleading
in that they refer to maximum recorded age, such as on a fouling test.
panel, whereas it may be known that the species actually lives much
longer. It is generally accepted, that there is an inverse relationship
between growth rate and longevity, and that longevity is greater, and
growth rate less in cold waters than in warm waters. The relation of
longevity has been clearly shown by Weymouth and McMillin (1931) in
the case of Siliqua patula.
In Fig. 20 we have assembled data for a number of species of
molluscs. The number is not large but we consider the longevities to
be valid maxima for the population in question. The trend towards
shorter life span in the tropics is clear. The smaller size in the tropics
is less pronounced and will be examined in more detail, and from more
extensive data, in a later section.
H. Extremes of size
There are many instances in which stress is accompanied by reduction in size. Examples are dwarf races at abnormally high or low
salinities. It seems likely, then, that there may be a size gradient