T H E PROBLEM OF OIL POLLUTION O F THE SEA
261
years (Fig. 8) was undoubtedly the virtual elimination of the grazing
sea-urchins and abalones. The wrecked tanker did, indeed, provide a
breakwater to protect the initial growth of the young plants, but it
broke up and was dispersed during the first winter, after which the
Macrocystis climax passed through a t least two growth cycles.
No similar catastrophe on the shores of north-west Europe has yet
created such an effect on the North Atlantic equivalents of this kelp,
but observations have been made on the ecological effects of the
" Torrey Canyon " wreck and of several spills in Milford Haven upon
the intertidal zone (Bellamy et al., 1967; Nelson-Smith, 1968a, b ;
Smith, 1968; Crapp, 1969a, b). These effects cannot be ascribed to oil
alone, as in every case solvent-emulsifiers used to clean the shores
probably caused more damage than the oil (although their most toxic
components are themselves aromatic hydrocarbons-see below, p. 284).
On these shores the most obvious seaweeds are three species of FUCUS,
Ascophyllum nodosum (L.) le Jol. and Pelvetia canaliculata ; in large
pools and at the lowest tidal levels, other brown algae such as Halidrys
siliquosa (L.) Lyngb., Himanthalia elongata (L.) S . F. Gray, Laminaria
spp., Xaccorhiza polyschides (Lightf.) Batt. or Alaria esculenta (L.) Grev.
may make a significant contribution. Beneath these there is a '' turf ''
of many species of smaller brown, red and occasionally green algae. The
main grazers on the algae are the limpets Patella vulgata and the less
widespread P. depressa (Pennant) or P. aspera (Lam.) (distantly related
to Haliotis spp., the abalones and ormers), winkles of the genus Littorina
and topshells (Gibbula spp. and Monodonta lineata (da Costa)). Factors
influencing the balance between the seaweeds, their grazers and such
competitors for space as the acorn-barnacles and mussels are considered
by Southward (1956) and Lewis (1964). On the most heavily polluted
and vigorously cleaned shores in Cornwall, which are also exposed to
strong wave-action, all the limpets were killed; within two or three
months they became clothed with the green algae Enteromorpha
intestinalis (L.) Link., E . compressa (L.) Grev., Ulva lactuca L. and
Colpomenia peregrina Sauv., which are normally confined to sheltered
shores and estuaries. During the following year, a vigorous new growth
of fucoids appeared to replace the " green phase ". Young limpets
also began to reappear within a year of the incident, but these graze
sporelings rather than mature plants. A small cove in Pembrokeshire
which showed the same succession of events after a pollution incident
in 1962 still had an unusually dense cover of seaweeds three years later.
During experiments in the Isle of Man in which limpets were systematically removed, a strip of shore also passed through a " green phase "
and produced a dense growth of fucoid algae which persisted for about
261
years (Fig. 8) was undoubtedly the virtual elimination of the grazing
sea-urchins and abalones. The wrecked tanker did, indeed, provide a
breakwater to protect the initial growth of the young plants, but it
broke up and was dispersed during the first winter, after which the
Macrocystis climax passed through a t least two growth cycles.
No similar catastrophe on the shores of north-west Europe has yet
created such an effect on the North Atlantic equivalents of this kelp,
but observations have been made on the ecological effects of the
" Torrey Canyon " wreck and of several spills in Milford Haven upon
the intertidal zone (Bellamy et al., 1967; Nelson-Smith, 1968a, b ;
Smith, 1968; Crapp, 1969a, b). These effects cannot be ascribed to oil
alone, as in every case solvent-emulsifiers used to clean the shores
probably caused more damage than the oil (although their most toxic
components are themselves aromatic hydrocarbons-see below, p. 284).
On these shores the most obvious seaweeds are three species of FUCUS,
Ascophyllum nodosum (L.) le Jol. and Pelvetia canaliculata ; in large
pools and at the lowest tidal levels, other brown algae such as Halidrys
siliquosa (L.) Lyngb., Himanthalia elongata (L.) S . F. Gray, Laminaria
spp., Xaccorhiza polyschides (Lightf.) Batt. or Alaria esculenta (L.) Grev.
may make a significant contribution. Beneath these there is a '' turf ''
of many species of smaller brown, red and occasionally green algae. The
main grazers on the algae are the limpets Patella vulgata and the less
widespread P. depressa (Pennant) or P. aspera (Lam.) (distantly related
to Haliotis spp., the abalones and ormers), winkles of the genus Littorina
and topshells (Gibbula spp. and Monodonta lineata (da Costa)). Factors
influencing the balance between the seaweeds, their grazers and such
competitors for space as the acorn-barnacles and mussels are considered
by Southward (1956) and Lewis (1964). On the most heavily polluted
and vigorously cleaned shores in Cornwall, which are also exposed to
strong wave-action, all the limpets were killed; within two or three
months they became clothed with the green algae Enteromorpha
intestinalis (L.) Link., E . compressa (L.) Grev., Ulva lactuca L. and
Colpomenia peregrina Sauv., which are normally confined to sheltered
shores and estuaries. During the following year, a vigorous new growth
of fucoids appeared to replace the " green phase ". Young limpets
also began to reappear within a year of the incident, but these graze
sporelings rather than mature plants. A small cove in Pembrokeshire
which showed the same succession of events after a pollution incident
in 1962 still had an unusually dense cover of seaweeds three years later.
During experiments in the Isle of Man in which limpets were systematically removed, a strip of shore also passed through a " green phase "
and produced a dense growth of fucoid algae which persisted for about