Case studies UK
Case studies elsewhere
Many chemicals foreign to the marine environment are toxic, whether
they are naturally occurring (e.g. crude oil) or man-made (many pesticides). Locally
lethal concentrations may have a direct impact on communities by eliminating many or most
species. Frequently, toxic compounds become concentrated during progress along a food
chain, accumulating in and selectively depleting the top predators; not only are these
conspicuous species (such as otters or seals) often of special public or conservation
interest, but their removal may have knock-on consequences for the whole structure of a
particular ecological community. Only recently has it been widely appreciated that
relatively low concentrations of many toxic compounds may affect species through subtle
mechanisms leading to, for example, immune system impairment, reduced reproductive
success, or developmental aberrations. The toxic effects of oil pollution fall into two
categories (Lobban & Harrison, 1994):
- those associated with the coating of the organism
- those due to disruption of metabolism by the uptake of hydrocarbons
Regarding the first of these, the mucilaginous slime covering of kelps
is thought to act (serendipitously) as a protective device against coating by oil
(OBrien & Dixon, 1976). Although the oil retained in the canopy of offshore Macrocystis
beds, following a spill at Santa Barbara, adhered tightly to the kelp blades reaching the
surface, removal of the oil layer revealed healthy tissue beneath it. Observable damage to
the kelp plants in the beds was negligible, presumably because they were "saved"
by mucus secretions.
The metabolic effects of hydrocarbons on kelp physiology may be
serious. The application of three different crude oils to the thallus surface of Laminaria
digitata reduced photosynthetic rates during emersion relative to controls (Schramm,
1972). In Macrocystis, 10-100 ppm of unspecified fuel oils in emulsion with sea
water reduced photosynthesis by 50% during 4-day exposures (OBrien & Dixon,
1976). In young blades, the photosynthetic capacity was completely reduced after 3 days
exposure to a 1% emulsion of diesel oil in sea water; boiler fuel, containing a higher
proportion of toxic components, was even more algicidal. More recently it has been found
that reductions in rates of photosynthesis vary with the type of crude oil, its
concentration, the length of exposure, the method of preparing the oil-seawater mixture,
and the irradiance used during the experiments (Lobban & Harrison, 1994). Although Macrocystis
fronds may be exposed directly to floating oil because of their buoyancy, Laminaria
hyperborea fronds, being almost exclusively subtidal, would not come into contact with
freshly released oil, but only to sinking emulsified oil and oil adsorbed onto particles.
The kelps are relatively insensitive to the dispersants used in
oil-spill cleanups, but faunal elements of kelp biotopes may be seriously damaged by oil
pollution. Oil is known to interfere with the ability of lobsters to detect the sex
pheromone that triggers mating, and with the normal feeding behaviour of sea-anemones
(Beveridge et al., 1997).
Case studies UK
Early oil-spills in the UK, such as that of the Torrey Canyon on the
Scilly Isles, are now not particularly relevant as it is widely believed that much of the
ecological damage was due to the use of highly toxic dispersants which have now been
replaced by relatively non-toxic chemicals.
Information on the effects of the Milford Haven oil spill (Sea Empress)
on kelp biotopes are due for publication in late 1998.
Case studies elsewhere
In Norway, Laminaria digitata grown in large concrete basins was
continuously exposed to diesel oil for two years. With diesel oil at 130 µg per litre,
lengthwise growth was reduced by about 50% (Lobban & Harrison, 1994). At the lower
concentration of 30 µg per litre there was no overall inhibition of growth. After two
years of continuous exposure, the plants completely recovered during a subsequent oil-free
The Amoco Cadiz oil spill in Brittany had no significant effects on Laminaria
spp. (Lobban & Harrison, 1994). The consequences for other faunal and floral
components of the kelp biotopes are not known.