Long Term Ecological Impacts of Marine Oil Spills

It has been apparent that the Obama Administration misread the consequences to the BP oil spill. Obama will use any excuse to cover up his poor judgement and reaction to the calamity. The consequences to marine oil spills has been well documented and known for some time.

We will see where we go from here.

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Long Term Impacts of Marine Oil Spills

Torrey Canyon, 1967 - The impacts of the clean-up of rocky shores following the Torrey Canyon spill are now legendary. The large volumes of highly toxic first generation dispersants caused massive mortality of the shore life and tainted (pun intended!) the name of dispersants to this day. Rapid recovery from the oil was recorded from the un-treated shores, but disruption of the treated shore communities was reported to last at least 10 years and possibly as much as 15 years (Hawkins
and Southward1992).

This is all the more remarkable because the disruptions continued in the absence of oil and without any physical clean-up damage to the shore – i.e. only through the natural recovery processes. This is far longer than any other example found, although at least some of the disruptions described were in the form of unusually large fluctuations in abundance of the dominant species. Reductions in biodiversity of the affected shores is only apparent by the very protracted return of one limpet species (Patella depressa), which took 10 years. This limpet was at the edge of its geographical range, which will have limited its recruitment potential. Abundances of the other species documented all rose rapidly and many then fluctuated even more than typical natural variability.
Florida, 1969 - Although relatively small, this fuel oil spillage caused heavy oiling of significant areas of saltmarsh. After 7 years, oil remaining in the sediment was still having notable effects (poor recruitment, survival and abundance and abnormal behaviour) on populations of burrowing fiddler crabs. Signs of recovery were correlated with sediment naphthalene removal (Krebs and Burns 1978). High concentrations of oil still remain in sub-surface sediments (below 6 cm) at the monitoring sites (Reddy et al. 2002) and studies after twenty years (Teal et al. 1992) showed that crabs from the heavily oiled sites had much higher oil concentrations in their tissues and that detoxification enzyme indicators (EROD activity) were significantly higher in marsh fish from those sites. Continued ecological effects do not appear to have been studied beyond the first 7 years.

Arrow, 1970 - Thomas (1978) describes effects on sediment infauna from a spill of heavy fuel oil into a very sheltered bay. Six years after the spill, toxic levels of oil still remained in the sediment and analysis of clam (Mya arenaria) growth rates (from length and weight frequency data) from oiled and unoiled sites showed significant reduction at oiled sites. Lee et al. (1999) have carried out bioassay studies in more recent years (last in 1999) on sediments from the same area. They showed that sediments from the oiled sites (which were still conspicuously contaminated by oil) had low toxicity, as measured by bioassays using amphipods.

Metula, 1974 - thick and extensive deposits of tar and asphalt pavement still remain on areas of saltmarsh and upper intertidal mixed-sediment beaches at this classic oil spill site (Owens et al. 1999). Recovery of the marsh vegetation is likely to take many more decades, but chemical composition of the oil’s toxicity is now low and breaking up the deposits would accelerate recolonisation (Wang et al. 2001).

Amoco Cadiz, 1978 – this very large spill severely affected a wide variety of coastal resources around Brittany, but its ecological impact is now best known for the erosion and slow re-growth of trampled saltmarsh areas; while similarly oiled but uncleaned marsh returned to natural vegetation in less than 5 years (Baca et al. 1987). The physical alteration of the marsh was therefore the primary cause of long term effects in this case.

The Amoco Cadiz spill also impacted subtidal sediments in the Bay of Morlaix and Dauvin (1998) has suggested that impacts to the benthos lasted for up to 12 years (and in the absence of any oil). He has shown that densities of tubiculous amphipods (primarily Ampelisca - which are well known to be extremely sensitive to oil in water) in a fine sand seabed habitat (17m depth) were much reduced for that period, even though they have a high fecundity. He suggests that Ampelisca populations in this habitat and location are naturally at a stable ‘climax’ state but that
this state was severely disturbed and that recovery was slow because the population was geographically isolated.
Esso Bernicia, 1978 - fuel oil from this spill contaminated shores within Sullom Voe and outside and is still present as patches of tar and asphalt pavement on some very sheltered rocky and mixed sediment shores. Annual monitoring showed rapid return of the communities of epibiota at most of the affected sites except some boulder/shingle shores where aggressive physical clean-up (with bulldozers) caused long-term instability of the substrata (Moore et al. 1995). This instability resulted in continued depression of both species richness and abundance of some algae and molluscs on those shores for at least nine years, presumably by reducing recruitment and survival. By 1989 species richness had returned and abundances had also returned to normal levels, but substratum levels were still surprisingly changeable for many more years and abundances still fluctuated greatly (annual reports and personal observations).

The Esso Bernicia spill also killed large numbers of wintering birds. Frequent monitoring showed that most of the local populations affected quickly returned to pre-spill numbers except for the great northern diver (Gavia immer). Heubeck (1997 and pers. comm.) showed that abundances in Yell Sound were still much reduced from their pre-spill levels. He suggests that the Yell Sound wintering population may also all breed in the same location (somewhere in the Nearctic) and that the cause of the poor recruitment may be due to environmental factors affecting that location.

TROPICS experiment, 1984 - Baca et al. 2005 review 20 years of results from this study on the effects of chemically dispersed crude oil on mangroves. They show that the oil did not persist and no long term impacts were detected at the dispersed oil and reference sites; while the undispersed oil site was still characterised by persistent oil residues, significantly reduced mangrove condition (smaller tree size) and substratum erosion.

Vivita, 1986 - A tropical example of the long term impacts of tar residues has been shown by Nagelkerken and Debrot (1995). They found that substantial tar cover in rubble shores of Curacao, still present more than 7 years after oiling despite moderate wave exposure, was causing a 35% reduction in species richness of molluscs (snails, limpet and chitons). They suggested that this reduction was in large part due to the loss of micro-habitats (under, between and within the rubble) caused by the cementation of rubble by the tar deposits.

Galeta, 1986 - Five years after this crude oil spill there were still severe impacts on biodiversity and productivity of red mangroves (Garrity et al.1994, Levings et al. 1994) and the structure of the mangrove had been so badly altered that recovery would clearly take a long time, even if oil had not still been present. Relatively undegraded oil was present in the anoxic muds and were expected to remain toxic for at least 20 years (Burns et al. 1994). Unfortunately no follow up studies appear to have been published. Recovery of corals on reef edge and reef flat habitats was also very slow (Cubit and Connor 1993), although complicated by natural stresses.

Exxon Valdez, 1989 - there is still a lack of consensus between researchers with different perspectives on the impacts of the Exxon Valdez spill of crude oil (Shigenaka 2005). Appreciable quantities of oil still persist on and beneath the surface of some sheltered boulder/cobble and coarse gravel shores (Short et al. 2004) and elevated tissue concentrations in some bivalves is correlated with oiled shores, but the long-term effect that it is having on ecology, beyond some localised
smothering, is confused by conflicting claims. The very limited pre-spill data and many confounding factors has made it difficult to detect impacts in populations of mobile species (fish, birds, mammals), and many studies that link sublethal effects (e.g. biomarkers) to heavily oiled sites may not have taken sufficient account of background oil. Page et al. (2004) have shown that substantial background levels of hydrocarbons from a variety of sources, including Exxon Valdez oil, are present in seabed sediments. Detoxification enzyme indicators (EROD activity) in coastal rock fish were induced by those background levels but were no more elevated at Exxon Valdez contaminated sites than at other sites. There are many ecological studies that suggest that biodiversity and productivity of the majority of affected communities and populations quickly returned to normal levels (e.g. Gilfillan, 1995, Wiens et al., 1999).

Effects of aggressive clean-up activity (hot water washing) on sheltered shore epibiota were described by Houghton et al. (1997). They showed that large fluctuations in abundance of the community dominants were still occurring at the cleaned sites (but were not so great at unoiled sites and oiled uncleaned sites) seven years after the spill. These population fluctuations were therefore similar to those described from the Torrey Canyon spill; but it also seems that the period when species richness and species abundances were continuously reduced was much shorter (apparently only 2 or 3 years).

Gulf War, 1991 - Tar and asphalt pavement still smothers extensive areas of the intertidal sand flats, halophyte zones and mangrove of the Saudi Arabian coast (Michel et al. 2005 and personal observations). Ecological impacts (particularly to halophytes and burrowing crab populations) in the upper intertidal and supratidal are severe and there are few signs of recovery (Getter et al. 2005 and personal observations).

Haven, 1991 - Considerable deposits of soft tar and hard burnt residues from the Haven spill are still present on the seabed off Genoa. Studies on sublethal effects in fish (genotoxic and hepatic tissue damage, Pietrapiana et al. 2002) and PAH concentrations in some sediment samples (Amato et al. 2002) have been linked to the contamination, but no effects were detected in the macrobenthos (Guidetti et al. 2000). Without better evidence of ecological effects (i.e. reduced species richness, population abundance or growth rates) it is not yet possible to show a long term impact, although some small smothering effects are likely just from the presence of the deposits.

Braer, 1993 - even acute impacts of the Braer spill were much less than might have been expected from the size of this spill in coastal waters; but the rapid natural dispersal of the oil and strong downward currents did result in unusually high seabed deposition. Very high concentrations (>1000ppm) of oil were found in muddy sediment sinks south of Shetland in deep water (Kingston et al. 1997) but impacts were mostly limited to reduced abundance and species richness of amphipods. Follow-up studies did not go beyond 1 year.

Sea Empress, 1996 – no significant residues of Sea Empress oil remain and a recent review of all available information, on its ten year anniversary, (Moore 2006) found very little evidence of long term impacts. This is not due to a paucity of data, as the local environment of the oil port and extremely rich coastal habitats were already very well described and monitored. However, the review did identify a few notable impacts:
While no significant long-term impacts on local seabird populations were detected, some localised long-term effects did occur, as can be shown from detailed inspection of seabird monitoring data. For example, one small breeding colony of guillemots was apparently wiped out and the site not reoccupied in 10 years – probably because first time breeders are not attracted to empty cliff sites and older birds habitually return to the same nests (Haycock pers. comm.). Of greater significance, Votier et al. (2005) have shown that the spill did kill many individual guillemots that they were monitoring in breeding colonies on Skomer Island, and that this had a notable effect on the demographics of the population. The long-term effects of this are unclear. Their results also suggested that available nest sites were reoccupied by a pool of birds that might otherwise not have been able to breed. Productivity and population numbers were therefore buffered by the substantial number of non-breeders in the population.

The spill also threatened the survival of a well studied population of the rarely recorded cushion starfish (Asterina phylactica) in shallow rockpools that were severely oiled. Mortality of the cushion stars, which brood their young in situ (therefore no recruitment from planktonic larvae), was very high (>95%) and recovery of the population seemed unlikely. However, a return to pre-spill densities was faster than expected (within 6 years, Crump, pers. comm.) due primarily to self fertilisation by the five remaining isolated animals. This is therefore an example of a species that had a greater recovery potential than might have been expected. Although moderately well studied compared to many benthic species, the spill created a situation that highlighted important gaps in our knowledge of its population ecology. It also appears that Asterina phylactica is not as rare as it was once considered to be, as many more records have been reported.

Finally, splash zone lichens of rocky shores are very slow growing and long term impacts to some well developed colonies were identified following the spill. Impacts are still evident, with abundance of dominant species and hence productivity (such as it is) is greatly reduced at some sites, but reductions in species richness were not found (Crump, pers. comm.).

Estrella Pampeana, 1999 – severe trampling during operations to remove oiled vegetation from brackish water marshes, resulted in substantial oil being pressed down into marsh sediments and extensive damage to root systems (personal observations). Ecological monitoring showed a rapid recovery of unoiled and oiled-but-not-cleaned sites, but delayed recovery of the ‘cleaned’ marsh (Moreno et al. 2004 and personal observations). The worst affected of the ‘cleaned’ marshes were still not fully recovered in 2003.