Recolonization of Rocky Shores in Cornwall After Use of Toxic Dispersants to Clean Up the Torrey Canyon Spill

Abstract

Fourteen thousand tons of Kuwait crude oil, reduced from 18 000 tons by weathering at sea, was stranded along 150 km of the coast of West Cornwall, England, in March 1967. The oil was treated with 10 000 tons of toxic dispersants during cleaning operations. By itself the oil was not very toxic, although it killed some limpets and barnacles, and most of the mortalities that followed cleaning were due to the dispersants. There was a graded effect. Most animals and some algae were killed on the shores treated heavily with dispersants, while a few animals and most algae survived in places less heavily treated. However, long stretches of coast were contaminated to some extent by drifting of patches of oil and dispersants along the shore and by indiscriminate dispersant use in remote coves. The general sequence of recolonization was similar to that which has been found after small-scale experiments, where the rocks were scraped clean, or where limpets were removed, but took longer to complete. There was first a rapid "greening" by the alga Enteromorpha; then a heavy settlement and growth of perennial brown algae (Fucus species), leading to loss of surviving barnacles. A settlement of limpets and other grazing animals followed, with eventual removal or loss of the brown algae. The final phases were a reduction in the limpet population and a resettlement of barnacles. Lightly oiled, wave-beaten rocks that received light dispersant treatment showed the most complete return to normal, taking about 5–8 yr; heavily oiled places that received repeated application of dispersants have taken 9–10 yr and may not be completely normal yet. Most common species returned within 10 yr, but one rare hermit crab is still missing from places directly treated with dispersants. The early recolonization by algae resulted in a raising of the upper limit of Laminaria digitata and Himanthalia elongata by as much as 2 m in wave-beaten places, demonstrating that grazing pressure by limpets must be one of the factors controlling the zonation of these plants. Later, other species of plants and animals were found higher up the shore than usual, under the shade and shelter provided by the dense canopy of Fucus. Fluctuations in the populations of algae and herbivorous animals during the course of the recolonization illustrate the importance of biological interactions in controlling the structure of intertidal communities. Pollution disturbance affects the herbivores more than plants, hence the point of stability of the community is shifted towards the sheltered shore condition of low species richness and greater biomass. Key words: petroleum, dispersant, rocky shore, Torrey Canyon, recolonization, coastal ecology, pollution

Recovery of the brown alga Fucus gardneri following a range of removal intensities

“…Canopy-forming algae have also been shown to enhance (McCook and Chapman, 1991;Albrecht and Reise, 1994) or suppress (Dethier and Duggins, 1988) herbivore abundance, and thus may indirectly influence recovery rates, but herbivore abundances in our experiment did not differ between treatments. Similarly, the removal of Fucus canopies often leads to blooms of other algal species (Southward and Southward, 1978;van Tamelen et al, 1997), which may suppress recovery. Ephemeral algal cover was weakly, if at all, correlated with the initial disturbance intensity in our experiment.…”

“…The response of fucoids to individual natural and anthropogenic disturbance events, such as ice-scour and oil spills, has been well documented (Southward and Southward, 1978;Chapman, 1991, 1997;Rolan and Gallagher, 1991;Highsmith et al, 1996;Houghton et al, 1996;Kiirikki and Ruuskanen, 1996;van Tamelen and Stekoll, 1996). Studies to date have focused on the effect of presence versus absence of adult cover, but generally have not examined the effect of a range of adult cover densities on recovery.…”

Modelling patch dynamics on rocky shores using deterministic cellular automata

“…Waves of limpets advancing into remaining stands of macroalgae were seen on some shores 4 to 5 yr after the major disruption caused by dispersant application following the Torrey Canyon oil spill in southwest England in 1967 (Southward & Southward 1978, Hawkins & Southward 1992. Littorinids advance in waves into patches of ephemeral green algae (R. L. Vadas pers.…”

“…Loss of Fucus plants so anchored tears barnacles out of the surrounding matrix of fused barnacle shells. Fucus plants fixed to bare rock can also be weakened by grazing of limpets on the stipe (Southward & Southward 1978). Barnacles under the Fucus plants are also eaten by the sheltering dogwhelks.…”

“…Poor limpet recruitment facilitates escapes, while good limpet recruitment inhibits escapes. Qualitative models (Southward 1964, Southward & Southward 1978, Hawkins & Hartnoll 1983a, Hartnoll & Hawkins 1985 have been developed which propose that patchiness on Northeast Atlantic moderately exposed rocky shores is generated and maintained by a combination of the above intrinsic deterministic processes and stochastic events (see Fig. 2).…”