268
A. NELSON-SMITH
under anaerobic conditions requires about 4 mg nitrate ; sea water may
contain as little as 0.1 mg per litre and rarely has more than 2 mg
(Pilpel, 1968). Izyurova (1952) has achieved four- to ten-fold increases
in the rate of anaerobic degradation by the addition of nitrate. Crosby
et al. (1954) reported the periodical abundance of sulphur bacteria in
a refinery effluent holding-pond and ZoBell and Prokop (1966) concluded that bacteria of the genus Desulfovibrio or Desu&muculum
can definitely degrade mineral oil under anaerobic conditions. Davies
and Hughes (1968) disagree, but only over the precise definition of
anaerobiosis. These authors reviewed the basic pathways of crude oil
degradation. Treccani (1965) gives a concise account of the bacterial
metabolism of individual pure hydrocarbons, on which there is a large
and specialized literature. The final products of aerobic oxidation are
carbon dioxide and water. Many of the intermediate products are
water-soluble and almost all are readily susceptible to further attack
by micro-organisms commonly present in coastal waters (Brown et al.,
1951).
Intermediate products of degradation, as well as the bacteria themselves, provide support for many higher micro-organisms. Protozoa,
fungi and lower algae contribute to the slime in a brackish refinery
effluent described by Crosby et al. (1954). Spooner (1968a, b) reported
many ciliates amongst oil droplets, some with oil in food-vacuoles, and
Voroshilova and Dianova (1950) refer to an increase in the numbers of
protozoans following that of oil-degrading bacteria in polluted waters.
Orton (1925) observed numbers of the small polychaete Ophryotrochu
burrowing into weathered oil, he assumed to feed on bacteria. Larger
animals can contribute directly to the removal of oil, although probably
not actually digesting it. George (1961) reported that limpets Putella.
were capable of scraping weathered oil from the rocks in the normal
process of browsing. Oil appeared in the faeces, mixed with rock fragments and plant debris, while the limpets apparently remained unharmed. Some months after a fairly severe spill, he found the shore
cleared of oil except for a band deposited above the highest level which
limpets could reach. On the worst-affected shores in Cornwall after the
" Torrey Canyon " wreck, all limpets were killed by emulsifier spraying
(see below), but it was seen that Patella and the topshell Xonodonta had
been grazing oil from the few unsprayed reefs (Holme, 1967 ; Spooner,
1967; Smith, 1968) and in Brittany (Fig. 9). Spooner and Spooner
(1968) observed that chitons-which occupy a similar ecological niche
to limpets but are there nearly twice as large-removed from coral rock
in the Bahamas much of the fuel-oil spilt from the stranded " General
Colocotronis " (Figs. 10, 11).
A. NELSON-SMITH
under anaerobic conditions requires about 4 mg nitrate ; sea water may
contain as little as 0.1 mg per litre and rarely has more than 2 mg
(Pilpel, 1968). Izyurova (1952) has achieved four- to ten-fold increases
in the rate of anaerobic degradation by the addition of nitrate. Crosby
et al. (1954) reported the periodical abundance of sulphur bacteria in
a refinery effluent holding-pond and ZoBell and Prokop (1966) concluded that bacteria of the genus Desulfovibrio or Desu&muculum
can definitely degrade mineral oil under anaerobic conditions. Davies
and Hughes (1968) disagree, but only over the precise definition of
anaerobiosis. These authors reviewed the basic pathways of crude oil
degradation. Treccani (1965) gives a concise account of the bacterial
metabolism of individual pure hydrocarbons, on which there is a large
and specialized literature. The final products of aerobic oxidation are
carbon dioxide and water. Many of the intermediate products are
water-soluble and almost all are readily susceptible to further attack
by micro-organisms commonly present in coastal waters (Brown et al.,
1951).
Intermediate products of degradation, as well as the bacteria themselves, provide support for many higher micro-organisms. Protozoa,
fungi and lower algae contribute to the slime in a brackish refinery
effluent described by Crosby et al. (1954). Spooner (1968a, b) reported
many ciliates amongst oil droplets, some with oil in food-vacuoles, and
Voroshilova and Dianova (1950) refer to an increase in the numbers of
protozoans following that of oil-degrading bacteria in polluted waters.
Orton (1925) observed numbers of the small polychaete Ophryotrochu
burrowing into weathered oil, he assumed to feed on bacteria. Larger
animals can contribute directly to the removal of oil, although probably
not actually digesting it. George (1961) reported that limpets Putella.
were capable of scraping weathered oil from the rocks in the normal
process of browsing. Oil appeared in the faeces, mixed with rock fragments and plant debris, while the limpets apparently remained unharmed. Some months after a fairly severe spill, he found the shore
cleared of oil except for a band deposited above the highest level which
limpets could reach. On the worst-affected shores in Cornwall after the
" Torrey Canyon " wreck, all limpets were killed by emulsifier spraying
(see below), but it was seen that Patella and the topshell Xonodonta had
been grazing oil from the few unsprayed reefs (Holme, 1967 ; Spooner,
1967; Smith, 1968) and in Brittany (Fig. 9). Spooner and Spooner
(1968) observed that chitons-which occupy a similar ecological niche
to limpets but are there nearly twice as large-removed from coral rock
in the Bahamas much of the fuel-oil spilt from the stranded " General
Colocotronis " (Figs. 10, 11).