Náttúrufræðingurinn - 1968, Blaðsíða 126

234
NÁTTÚRUFRÆÐINGURINN
had fed on goose barnacles did tliey amount to half or more of the stomach
contents.
The explanation of the unexpected quantity of goose barnacles in many of
the gulls collected at Sandvik was not far to seek. Tlie beaches on the South and
West of the Reykjanes Peninsula were dotted with heaps of pumice covered
by vast quantities of goose barnacles. l’heir presence there can be accounted
for as follows:
On November 14, 1963, a submarine volcanic eruption began off the West-
man Islands, about 120 km (75 miles) to the southeast of Sandvik, and this gave
rise to a new permanent island, Surtsey. In late May 1965 a second eruption
began close to Surtsey, and soon another island of tephra rose frorn the sea
(Syrtlingur). Later on a third island (Jolnir) was formed, but these two subsi-
diary crater islands disappeared again (see Thorarinsson, 1966, for an exact
chronology of events). Tlie term „Surtsey pumice" is used in this paper for
pumice produced during this whole period of submarine eruptions.
On October 27, 1965, we collected samples of pumice with goose barnacles
that had been washed upon the shores of the Reykjanes Peninsula. Collections
were made at four stations on the south side of the peninsula (Herdisarvik,
Thorkötlustadabot, Arfadalsvik and Sandvik), and at one station on the west
side (Stora-Sandvik). Three species of Lepas were found on the pumice samples.
Lepas fascicularis was by far the most common species. Next in abundance was
Lepas anatifera, while the third species, Lepas pectinata, was rare compared
with the other two. This species had not previously been recorded in Iceland,
but was now found at three of the five stations where collections were made.
The material collected at Herdisarvik contained 7 specimens of L. pectinata,
the material from Thorkötlustadabot contained 15 specimens, and the material
from Arfadalsvik 33 specimens of this species.
Unfortunately it is not known when pumice with goose barnacles began to
drift onto the beaches of the Reykjanes Peninsula. No gulls were collected there
during the summer and autumn of 1965 before October 8. And during the
same period no search for pumice with goose barnacles was made along the
shores of the peninsula. It may be mentioned, however, that during the winter
of 1964—1965 no traces of goose barnacles were found in 87 gulls collected in
the Sandvik area during the period October 5, 1964 — February 2, 1965. Neitlier
were any traces of goose barnacles on pumice found on the shores of Stora-
Sandvik on March 9, 1966. However this may be, it is obvious that the great
abundance of goose liarnacles found on pumice in various parts of Reykjanes
in the autumn of 1965 could not have reached maturity unless certain conditions
were present simultaneously: Vast numbers of larvae ol the spccies in question
must liave reached the waters off South Iceland at a time when very large
quantities of floating purnice were available and when the temperature of tlie
sea was exceptionally higli. All these requirements were apparently fulfilled
during the summer of 1965. The temperature of the sea off South Iceland was
then well above the average, which means that there must have been a strong
influx of Atlantic water, probably carrying vast numbers of viable Lepas larvae
into the areas of floating pumice off South Iceland. And in April, 1965, tlie