Náttúrufræðingurinn - 1968, Blaðsíða 127

NÁTTÚRUFRÆÐINGURINN
235
Syrtlingur eruption began and throughout the summer tliis crater island
produced ash and pumice at an average rate of 4—5 cubic yards per second.
The case of tlie puntice that was produced during the first months of
the Surtsey eruption that began in November 1963 was quite different.
This eruption ocurred in the winter when the sea off the South coast of
Iceland was not warm enough to enable Lepas larvae to survive and make
use of the pumice that was available then. And at the beginning of April, 1964,
or before the temperature of the sea off the Icelandic coasts had begun to
rise again to any appreciablc degrce, the Surtsey eruption ceased to produce
jtumice. And as the summer of 1964 advanced the greater part of this pumice
had eitlter been washed upon the mainland shores or drifted away from the
land to the open sea. Besides, the sea tenrperature was never as higli in the
summer of 1964 as in the summer of 1965. This must be the reason why no
traces of goose barnacles were found in the stomachs of 87 gulls that were
shot at Sandvik in the autumn of 1964 and the winter of 1964—1965.
The same is most likely true of the pumice that was produced by the Jolnir
eruption that began at Christmas of 1965. This eruption, which produced
a similar quantity of material as the Syrtlingur eruption, admittedly lasted
until August 10, 1966, and therefore growth of goose barnacles on the pumice
might have taken place that sunnner, too. Unfortunately, however, other work
preventecl us front making a study of this question then.
We can assume that every year larvae of the three Lepas species that were
found on the Surtsey pumice in 1965 are carried to the South coast of Iceland,
but their quantities most likely vary a great deal from one year to another.
Normally, the greater part of this larva rnass probably perishes owing to the
absence of requisite living conditions. This is a good example of the enormous
wastage of life which is characteristic of many invertebrates, their rcproductive
rate therefore being high to the same degree. Such species can witli impunity
stand enormous setbacks and sacrifice countless millions of individuals in their
search of lavourable living conditions. It is because of these relatively aimless
volleys of organisms that the Lepas larvae were able to make use of the Syrtling-
ur pumice in 1965 to the large extent indicated above. Thcti a volley of organ-
isms scored ;i direct hit, a relatively rare occurrence. But in connection witli
this fact the <piestion arises if and to what extenl volcanic eruptions and
pumice production in past geological epochs may have contributed to the
evolution of marine organisms depending on floating objects for their survival.