MARINE BIOLOGY AT SKIPPER'S ISLAND
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The seawater flowing round the island is heavily laden with
particular matter, including much detritus. Its salinity lies
between 31‰ and 31.5‰. Even in early March 1958 its
corrected salinity was found to be 31.5‰. There appears to be
little land drainage into Hamford Water and, in a biological
sense, the sea water is reasonably pure.
Aurelia aurita, the common jellyfish, is plentiful during the
summer. Sampling of the outgoing tide in mid-channel below
the dam (July 1958) showed that the following were present in
the plankton. The Cystoflagellate, Noctiluca, in large numbers;
an unidentified Anthomedusan and numbers of specimens of the
sea gooseberry Pleurobrachia pileus (O. F. Muller); Littorina and
Crepidula larvae, small Syllid worms, post-larval Nereids; zoaea
and megalopa crab larvae (probably Carcinus) and zoaea larvae
of prawns: Cirripede nauplii and metanauplii; tadpole larvae of
tunicates and strangely, a number of nematode worms, species
unidentified. The last find suggests the possibility of their tidal
dispersion in this region of inshore channels and creeks.
The dam is particularly interesting as an island site for
sedentary forms both plant and animal. The algae await
accurate identification and this work is being undertaken by
Dr. Alvin. The following have been noticed: Laminaria
saccharina, Fucus vesiculosus, both in quantity, and an extensive
growth of Ulva lactuca.
The animals are representative of most marine phyla and
are interesting not only for the presence of unexpected, but also
for the absence of expected forms. Among sponges present are
two calcareous forms, Sycon ciliatum (Fabricius) and Grantia
compressa (Fabricius); also Halichondria bowerbanki Burton
near low water and Halichondria panicea (Pallas) and Polymastia
in large quantities at mid-tide level. The latter are referred to
again below as they are members of an interesting commensal
association on the dam (figure 3).
A fair range of coelenterates is present. The following
hydroids are found in quantity: Kirchenpaueria pinnata (L.),
Obelia geniculata (L.), O. dichotoma (L.) and Dynamena pumila
(L.). No Athecate hydroids have yet been found, although
Anthomedusae are present at times in the plankton of the creeks.
The anemones are of particular interest. Neither the opelet
(Anemonia sulcata) nor the beadlet (Actinia equina) has been
found, although the latter is present on parts of the coast outside
Hamford Water. On and adjacent to the dam members of the
Ilianthidae, Diadumenidae, Metridiidae and Sagartiidae are to be
found. Small specimens of the burrowing anemone Peachia
hastata Gosse are present in mud-filled holes and fissures on the
dam. Colonies of the plumose anemone, Metridium senile (L.)
var. dianthus (Ellis) are present in sheltered situations: these are
of two colour varieties, flame red and brown, with an occasional
white specimen associated with the latter.