- Email: [email protected]
Oil Spills
Oil Spills R de la Huz, M Lastra, and J Lo´pez, Universidad de Vigo, Vigo, Spain & 2011 Elsevier B.V. All rights reserved.
Introduction Oil spills are regrettably common around the world: the Amoco Cadiz in France in 1978; the Exxon Valdez in Alaska in 1989; the ‘Gulf War’ in Kuwait in 1991; the Erica in France in 1999; the Aegean Sea in Galicia, Spain, in 1992; and the Prestige in Spain and France in 2002, which are some of the most well-known oil spills. Oil spills originate in oil platforms, refineries, or oil tankers that have an accident or that ‘clean’ their tanks in the ocean. The oil reaching the coast in this manner affects different ecosystems – open and protected sandy beaches, estuaries, and rocky shores – or remains in the water to be finally deposited on the sea bottom in deep or shallow waters. The damage caused by oil spills differ depending on the chemical composition of the oil, the area affected, and the cleaning activities applied. The organism affected by an oil spill will be more or less sensitive to the pollution, depending on its nature and life cycle. But apart from the organism directly affected by the spill, other organisms can be indirectly subject to impacts due to changes in community structure and coexistence interactions such as grazing, predation, and competition dynamics.
Oil Oil is the product obtained by a distillation process of petroleum. The basic components of petroleum are hydrocarbons (mainly carbon and hydrogen) and different organic and inorganic components containing sulfur, nitrogen, and oxygen, besides metals such as iron, vanadium, nickel, and chromium. During the distillation, four different fractions are separated, depending on the boiling temperature: gas (methane, ethane, and hydrogen), propane and butane, gasoline, and finally, distillation oil. There is a residue that is not distilled. The persistence and behavior of the oil in the sea is due to the physical properties such as relative density (relation of the density of the oil with pure water), distillation characteristics (defining the volatility – high amounts of resins, asphaltens, wax, etc. make oil less volatile), viscosity (resistance to flow, which changes with temperature), and flow point (temperature below which oil does not flow). The chemical composition of the oil comprises four major compounds: saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltens. High percentages of polycyclic aromatic hydrocarbons (PAHs) increase the
toxicity of the oil. Apart from the PAHs content, oil can contain heavy metals that will increase its toxicity. Initial properties of oil will be more or less altered when oil spills occur at sea. Physicochemical processes, which occur between oil and water, air, and sediment, are known as meteorization (Figure 1). The different processes of meteorization will distribute the oil to different places and in different forms that could increase the exposure and bioavailability of the oil.
Effects of the Oil Spill on Different Ecosystems Oceans and seas comprise a wide variety of habitats characterized by different communities of animals and plants. Physical characteristics such as temperature and salinity of the water, type of substrata (rock, sediment), depth, light intensity, and wave exposure determine the type of marine habitats and the animals and plants that are adapted to life there. These varieties of ecosystems respond in a different way to the oil spill as some zones and the organisms that inhabit there are more sensitive to hydrocarbon contamination. Oil produces effects over a short or long timescale. Short-term effects are due to the toxicity of the oil, the reduction in light transmission (affecting photosynthetic activity), the decrease in dissolved oxygen, asphyxia, and damage to marine birds (reduction in the floatability by impregnation of feathers, and toxicity by ingestion). Long-term effects are related to changes in important biological process, such as reproduction, recruitment, disappearance of food, and destruction of the habitat. Oil dispersed and dissolved in the water column can contaminate plankton, algae, eggs and larva, and finally, animals that feed on these food resources such as fish, birds, marine mammals, and humans. A further problem is the bioaccumulation of the toxic components of the oil that transports the pollutant along the trophic chain. Another consideration necessary to be taken into account when evaluating the negative effects of an oil spill is to determine if there are commercial species affected by the contamination, because then the economic and social consequences will need to be added to the ecological loss. Rocky Shores Rocky shores comprise a wide variety of habitats, mainly depending on the wave exposure (exposed or protected) and the bathymetry. Bathymetry (Figure 2) and the
251
252
Oil Spills Evaporation Expansion
Expansion
Oxidation
Emulsion
Dissolution Dispersion
Biodegradation Sedimentation
Figure 1 Meteorization process that experience the oil in the sea. From ITOPF (2002) Fate of Marine Oil Spill. Technical Information Paper no. 2. London: ITOPF.
Supra
tidal z
one Pelagic zone
Neritic environment
Intertidal zone Deep
0m
Subtidal zone
Oceanic environment
Bathyal zone 200 m
ment viron nt Ep nme nviro e ic g nt opela nme Mes nviro e ic g ent ypela onm Bath envir ic g ela ssop Aby ic en ipelag
Abyssal zone 6000 m 3000 m
Hadal zone 200 m deep Continental shelf
Low tide
Continental slope
High tide
Figure 2
Bathymetric zones and environments on the oceans.
affecting conditions such as light, water turbulence, and temperature are responsible for the distribution of the benthic animals and plants into horizons or bands. Typical organisms of rocky shores are epibenthic animals that are fixed to the substrata or move just over it, and algae, lichens, and vascular plants on the upper limits of the marine environment, just inside the terrestrial zone. Some animals are capable of perforating the substrata, as is the case of some sponges, mollusks, polychaetes, and equinoderms. The littoral zone, located between the
upper and lower tidal limits and the shallow sublittoral zone, comprises a high diversity of organisms that are highly adapted to the harsh, variable environmental conditions such as desiccation and changes in the salinity and temperature. This zone is contaminated by oil when the spill reaches the coast, and the extent to which it is affected and restored will vary depending on the exposure to the waves, which are a very effective cleaner, and the capacity of the species to support the toxic and physical effects of the oil.
Oil Spills
Upper levels of rocky shores are characterized by lichens, by some arthropods such as isopods and insects, and diverse species of vascular plants and bryophytes. Such vegetation are altered by oil sills, but specially by the cleaning activities that occasionally remove the vegetation to gain access to the oil deposited on the rocks, and in the case of the lichens, cleaning with pressurized water on the rock removes everything present there. The intertidal zone is characterized by different species of algae; gastropod mollusks such as limpets, Gibbula spp., and Littorina spp.; bivalve mollusks such as mussels; cirriped crustaceans such as barnacles; and cnidarians such as sea firs, stalked jellyfish, and sea anemones. In the wake of the Prestige oil spill, a low effect was observed on this zone 6 months after the spill, but there could be a sublethal effect affecting the reproduction, larval development, and recruitment. The more sensitive species were barnacles and limpets located on the upper level, and some algae were more affected by the cleaning activities. In the case of the Prestige oil spill, most of the intertidal rocky shore affected was directly exposed to wave action, a fact that helps the rapid cleaning of the oilcovered rocks, but in the case of protected shores, the oil contamination may be more dangerous due to a longer permanence of the oil on the rocks. The shallow sublittoral zone is characterized by algae; sponges; ascidians such as sea squirts; decapod crustaceans such as crabs, lobsters, prawns, and shrimps; equinoderms such as sea urchins, sea cucumbers, and starfishes; and different species of gastropod mollusk and sea slugs. This zone supports a lower hydrodynamic condition than the intertidal zone, and a more constant temperature and salinity of the water. The organisms most affected by the oil from the Prestige spill were sea urchins, which practically disappeared from the coastal area of Galicia 6 months after the spill. Sedimentary Shores Sedimentary shores include a wide variety of habitats, chiefly depending on tide depth (Figure 2), sediment type, and exposure to the waves: intertidal and subtidal shores, including subtidal habitats from low shore to abyssal depths; shores composed of sand, mud, or gravel; and exposed or protected beaches. The variety of habitats with the animals and plants that live there responds differently to oil spill, and restoration is more or less swift. Intertidal shores or beaches are characterized by two kinds of macrofaunal community, one purely marine and another semiterrestrial, inhabiting the upper levels of the shore, with a terrestrial life cycle but with a direct dependence on the marine habitat that supplies food and humidity. As a general rule, the upper level of a beach is the most affected by the spill. The oil is deposited on the upper level at high tide, and this oil remains there until
253
the next spring high tide arrives or it is cleaned. This area is especially sensitive because the macrofauna present here does not spread by water, and so recolonizing is more difficult when the community is seriously affected. Apart from the mortality caused by the oil, cleaning activities increase this mortality, because the habitat is destroyed when the polluted material is removed, including algal wrack and the top layer of sand where these animals live. Studies on the meiofauna of exposed sandy beaches in Galicia, 6 months after the Prestige oil spill, showed that relative abundance of the class Oligochaeta of supratidal levels decreased, as a result of higher PAHs. Animals whose main food supply is macrofauna from the wrack, such as birds, are also affected by the disappearance of food and by the destruction of their habitat during cleaning activities. In some cases, it is necessary to invade the dunes and cut the affected vegetation, where these birds live. Upper levels of beaches and dunes have vascular plants and bryophytes, such as Ammophila arenaria – a typical phanerogam that helps to establish the dune. Estuaries present a high abundance and diversity of plants, especially in salt marshes, with Juncus maritimus and Spartina spp. as representative species of these areas. These plants will be affected, to a greater or lesser extent, depending on the part of the plant affected by oil, that is, the aerial part or the rhizome, but especially depending on the cleaning activities that, in many cases, cause a higher impact than the oil, due to trampling underfoot, cutting, and removal of the plants affected. The lower part of the beach appears to be less affected by oil, as observed after the Prestige oil spill in exposed sandy beaches, where polychaetes have practically disappeared, but typical crustaceans of this habitat showed lower mortality rates. The intertidal meiofauna on the exposed sandy beaches of Galicia, 6 months after the Prestige oil spill, was not affected in terms of total density and major taxa occurrence. In the case of protected and estuarine beaches, the effects will probably be more dramatic, and may be measurable for decades after the event, when compared with exposed beaches where the pristine stages will occur after a few years. The hydrodynamic conditions in protected and estuarine beaches are calmer or absent in the case of estuaries, and this environment allows the oil to remain for a longer period of time on the substrata, increasing exposure to hydrocarbons and their toxic and physical (hypoxia) effects. Usually, these ecosystems are rich in commercial species such as clam, oyster, and crab, thus adding commercial loss to the ecological disaster, in the case of these coastal populations. In exposed beaches, waves are a powerful, natural cleaner, removing the oil deposited on the intertidal zone. But, in many cases, waves bury the oil when sediment is moved, leaving the pollutant more or less at depth, appearing again when the waves remove the deposited sediment.
254
Oil Spills
The quality of organic sediment matter, estimated from carbohydrates, proteins, and lipids concentration, and the biopolymeric carbon, estimated as the fraction potentially available to deposit feeders, were analyzed in exposed sandy beaches before the Prestige oil spill. These biochemical components of the sediment and water indicated the food availability for the meiofauna and macrofauna present in these habitats. It was observed that there was no limitation in food availability in the sediments on the beaches studied 6 months after the Prestige oil spill. This could be due to the fact that the oil spill did not affect these biochemical components or due to the lower presence of higher trophic consumers. Sediment type, size, and form have an important effect on the permanence and degradation time of the hydrocarbons. Finer, more compact sediments are less permeable to oil, whereas coarse sediments allow the oil to percolate and remain below the surface for a longer time, because they are not eroded by waves. This was observed in the gravel beaches of Alaska, following the Exxon Valdez oil spill, where a layer of subsurface oil persisted in some beaches for as long as 8 years after the spill. In some exposed sandy beaches of Galicia, with coarse sand and steep slopes, a layer of subsurface oil was observed when the storms eroded the slope. Subtidal shores present a different response to oil spills depending on the depth involved. Shallow subtidal regions, down to 20 m, showed a massive decline in benthic amphipods, especially the families Ampeliscidae and Phoxocephalidae, and an increase in the abundance of opportunistic families of polychaetes, such as Capitellidae and Spionidae, following the Amoco Cadiz, Exxon Valdez, and the Aegean Sea spills. At greater depths, from 40 to 100 m, no disturbance of the benthos was detected, as noted in Prince William Sound, Alaska, following the Exxon Valdez spill. In this case, the formation of neutrally buoyant oil–clay flocculates inside oil slicks and the major currents in the zone were apparently important in preventing subtidal oil accumulation at depth. Furthermore, during the followup of this oil spill, high abundance values of benthic fauna were observed that may reflect a flux of unusual amounts of phytoplankton to the bottom when low levels of grazing zooplanktons were present, resulting in increasing availability of food resources for the benthos. Bathyal and abyssal zones were considered as marine deserts, with low and very specialized species, but during the studies made following the Prestige oil spill (the remains of the ship lie at depths of 3565 and 3830 m), these zones showed a high number of species, the majority being new species. These zones that apparently present homogeneous environmental conditions are characterized by the total absence of light, low temperatures, and high salinities and pressure. The animals typically found in these areas include errant and swimming animals, the
predominant species being echinoderms, crustaceans, fishes, and cephalops; sessile animals comprising sponges, cnidarians, crinoids, and tunicates; macrofauna mainly constitutes of annelid polychaets, peracarid crustaceans, and mollusks; meiofauna basically includes nematods, harpacticoid copepods, ostracods, tardigrads, and kinorhynchs. The few studies conducted on these zones made it very difficult to evaluate the effect of oil spills, although studies carried out on the continental platforms have shown a drastic reduction in organisms of the benthic community found in this area.
How to Work after an Oil Spill As discussed earlier, the problems caused by an oil spill depend on the nature of the hydrocarbons, the type of ecosystem affected, and the length of the spill, but the cleaning activities also can increase the problems. It is very important to identify the type of area affected: intertidal, subtidal, sedimentary, or a rocky shore, and to apply the most adequate and least aggressive method to remove the oil spilled. The first step is to ensure adequate coordination of the cleaning activities and for the authorities involved to make all the material and personal means available. The most important thing is to preserve the unaffected areas and, in the polluted areas, to remove the larger quantities of oil when it arrives massively. The next stage is to adapt the cleaning activity to the specific characteristics of the area affected: Rocky shores with animals and plants that live all or • part of their life cycle on the substratum require
•
manual removal of the oil, which can be performed using pressurized water. However, this system is recommended in areas where there are no animals and plants that can be removed by the pressure of the water, such as in urban and port areas. Another recommendation when this method is used is to apply a filtration system to collect the oil removed, which, in some cases, appears in an emulsion form that increases the toxicity and availability of the hydrocarbons. In the course of regenerating the rocky shore following the Prestige oil spill, the affected coast was cleaned by adding nutrients that enriched the microorganism of marine water. These microorganisms degraded the hydrocarbons and the results were satisfactory as they increased the velocity of oil degradation while preserving the substratum. Sedimentary shores present a very sensitive area, located on the upper limit of the intertidal zone, where semiterrestrial animals and specialized plants live. These areas are usually affected by high amounts of oil deposited by tides. In the first moments after the spill, maximum quantity of the spilled oil needs to be
Oil Spills
removed, but after that a manual selection of material and sediment contaminated must be done, trying to keep clean algae because it is the habitat of the specialized semiterrestrial animals typical of the upper levels. Manual cutting of marsh and dune vegetation contaminated by oil should only be considered in areas where oil may persist, where significant impacts to wildlife are likely, or where less destructive cleanup techniques have been proven to be insufficient. It is very important to have pre-spill information of the different ecosystems for baseline data. These studies will be very important for the postspill analysis and for recommendation on how to act and restore the affected areas. See also: Oil and Chemical Spills, Oil Industry and the Health of Communities in the Niger Delta of Nigeria.
Further Reading Besteiro C (2004) Evaluacio´n del impacto en las comunidades y especies de intere´s comercial y ecolo´gico en las zonas costeras. Periodo primaveral. Informe final del Programa Nacional: Accio´n urgente Prestige-Recursos naturales. Ministerio de Ciencia y Tecnologı´a. de la Huz R, Lastra M, Junoy J, Castellanos C, and Vie´itez JM (2005) Biological impacts of oil pollution and cleaning in the intertidal zone of exposed sandy beaches: Preliminary study of the ‘‘Prestige’’ oil spill. Estuarine, Coastal and Shelf Science 65: 19--29.
255
Feder HM and Blanchard A (1998) The deep benthos of Prince William Sound, Alaska, 16 months after the Exxon Valdez oil spill. Marine Pollution Bulletin 36(2): 118--130. Go´mez Gesteira JL and Dauvin J-C (2005) Impact of the Aegean Sea oil spill on the subtidal fine sand macrobenthic community of the Ares-Betanzos Ria (Northwest Spain). Marine Environmental Research 60: 289--316. Gonza´lez Laxe F (2003) El impacto del Prestige. Ana´lisis y evaluacio´n de los dan˜os causados por el accidente del Prestige y dispositivos para la regeneracio´n medioambiental y recuperacio´n econo´mica de Galicia. Instituto de Estudios Econo´micos de Galicia, Fundacio´n Pedro Barrie´ de la Maza. Hayes MO and Michel J (1999) Factors determining the long-term persistence of Exxon Valdez oil in the gravel beaches. Marine Pollution Bulletin 38(2): 92--101. ITOPF (2002) Fate of Marine Oil Spill. Technical Information Paper no. 2. London: ITOPF. Mora J, Garmendia JM, Go´mez Gesteira JL, et al. (1996) Seguimiento mensual del bentos infralitoral de la rı´a de Ares y Betanzos antes y despue´s de la marea negra del ‘Aegean Sea’. In: Ros J (ed.) Seguimiento de la contaminacio´n producida por el accidente del buque Aegean Sea, pp. 137--150. Madrid: Ministerio de Medio Ambiente, serie monografı´as. Ornitz BE and Champ MA (eds.) (2002) Oil Spill First Principles: Prevention and Best Response. Amsterdam: Elsevier Science. ISBN 0080428142. Peterson CH (2001) The ‘‘Exxon Valdez’’ oil spill in Alaska: Acute, indirect and chronic effects on the ecosystem. Advances in Marine Biology 39: 1--103. Rodrı´guez JG, Incera M, de la Huz R, Lo´pez J, and Lastra M (2007) Polycyclic aromatic hydrocarbons (PAHs), organic matter quality and meiofauna in Galician sandy beaches, 6 months after the Prestige oil-spill. Marine Pollution Bulletin 54: 1046--1052. Whitfield J (2003) How to clean a beach. Nature 422: 464--466. Zengel SA and Michel J (1996) Vegetation cutting as a clean-up method for salt and brackish marshes impacted by oil spill: A review and case history of the effects on plant recovery. Marine Pollution Bulletin 32(12): 876--885.
Introduction Oil spills are regrettably common around the world: the Amoco Cadiz in France in 1978; the Exxon Valdez in Alaska in 1989; the ‘Gulf War’ in Kuwait in 1991; the Erica in France in 1999; the Aegean Sea in Galicia, Spain, in 1992; and the Prestige in Spain and France in 2002, which are some of the most well-known oil spills. Oil spills originate in oil platforms, refineries, or oil tankers that have an accident or that ‘clean’ their tanks in the ocean. The oil reaching the coast in this manner affects different ecosystems – open and protected sandy beaches, estuaries, and rocky shores – or remains in the water to be finally deposited on the sea bottom in deep or shallow waters. The damage caused by oil spills differ depending on the chemical composition of the oil, the area affected, and the cleaning activities applied. The organism affected by an oil spill will be more or less sensitive to the pollution, depending on its nature and life cycle. But apart from the organism directly affected by the spill, other organisms can be indirectly subject to impacts due to changes in community structure and coexistence interactions such as grazing, predation, and competition dynamics.
Oil Oil is the product obtained by a distillation process of petroleum. The basic components of petroleum are hydrocarbons (mainly carbon and hydrogen) and different organic and inorganic components containing sulfur, nitrogen, and oxygen, besides metals such as iron, vanadium, nickel, and chromium. During the distillation, four different fractions are separated, depending on the boiling temperature: gas (methane, ethane, and hydrogen), propane and butane, gasoline, and finally, distillation oil. There is a residue that is not distilled. The persistence and behavior of the oil in the sea is due to the physical properties such as relative density (relation of the density of the oil with pure water), distillation characteristics (defining the volatility – high amounts of resins, asphaltens, wax, etc. make oil less volatile), viscosity (resistance to flow, which changes with temperature), and flow point (temperature below which oil does not flow). The chemical composition of the oil comprises four major compounds: saturated hydrocarbons, aromatic hydrocarbons, resins, and asphaltens. High percentages of polycyclic aromatic hydrocarbons (PAHs) increase the
toxicity of the oil. Apart from the PAHs content, oil can contain heavy metals that will increase its toxicity. Initial properties of oil will be more or less altered when oil spills occur at sea. Physicochemical processes, which occur between oil and water, air, and sediment, are known as meteorization (Figure 1). The different processes of meteorization will distribute the oil to different places and in different forms that could increase the exposure and bioavailability of the oil.
Effects of the Oil Spill on Different Ecosystems Oceans and seas comprise a wide variety of habitats characterized by different communities of animals and plants. Physical characteristics such as temperature and salinity of the water, type of substrata (rock, sediment), depth, light intensity, and wave exposure determine the type of marine habitats and the animals and plants that are adapted to life there. These varieties of ecosystems respond in a different way to the oil spill as some zones and the organisms that inhabit there are more sensitive to hydrocarbon contamination. Oil produces effects over a short or long timescale. Short-term effects are due to the toxicity of the oil, the reduction in light transmission (affecting photosynthetic activity), the decrease in dissolved oxygen, asphyxia, and damage to marine birds (reduction in the floatability by impregnation of feathers, and toxicity by ingestion). Long-term effects are related to changes in important biological process, such as reproduction, recruitment, disappearance of food, and destruction of the habitat. Oil dispersed and dissolved in the water column can contaminate plankton, algae, eggs and larva, and finally, animals that feed on these food resources such as fish, birds, marine mammals, and humans. A further problem is the bioaccumulation of the toxic components of the oil that transports the pollutant along the trophic chain. Another consideration necessary to be taken into account when evaluating the negative effects of an oil spill is to determine if there are commercial species affected by the contamination, because then the economic and social consequences will need to be added to the ecological loss. Rocky Shores Rocky shores comprise a wide variety of habitats, mainly depending on the wave exposure (exposed or protected) and the bathymetry. Bathymetry (Figure 2) and the
251
252
Oil Spills Evaporation Expansion
Expansion
Oxidation
Emulsion
Dissolution Dispersion
Biodegradation Sedimentation
Figure 1 Meteorization process that experience the oil in the sea. From ITOPF (2002) Fate of Marine Oil Spill. Technical Information Paper no. 2. London: ITOPF.
Supra
tidal z
one Pelagic zone
Neritic environment
Intertidal zone Deep
0m
Subtidal zone
Oceanic environment
Bathyal zone 200 m
ment viron nt Ep nme nviro e ic g nt opela nme Mes nviro e ic g ent ypela onm Bath envir ic g ela ssop Aby ic en ipelag
Abyssal zone 6000 m 3000 m
Hadal zone 200 m deep Continental shelf
Low tide
Continental slope
High tide
Figure 2
Bathymetric zones and environments on the oceans.
affecting conditions such as light, water turbulence, and temperature are responsible for the distribution of the benthic animals and plants into horizons or bands. Typical organisms of rocky shores are epibenthic animals that are fixed to the substrata or move just over it, and algae, lichens, and vascular plants on the upper limits of the marine environment, just inside the terrestrial zone. Some animals are capable of perforating the substrata, as is the case of some sponges, mollusks, polychaetes, and equinoderms. The littoral zone, located between the
upper and lower tidal limits and the shallow sublittoral zone, comprises a high diversity of organisms that are highly adapted to the harsh, variable environmental conditions such as desiccation and changes in the salinity and temperature. This zone is contaminated by oil when the spill reaches the coast, and the extent to which it is affected and restored will vary depending on the exposure to the waves, which are a very effective cleaner, and the capacity of the species to support the toxic and physical effects of the oil.
Oil Spills
Upper levels of rocky shores are characterized by lichens, by some arthropods such as isopods and insects, and diverse species of vascular plants and bryophytes. Such vegetation are altered by oil sills, but specially by the cleaning activities that occasionally remove the vegetation to gain access to the oil deposited on the rocks, and in the case of the lichens, cleaning with pressurized water on the rock removes everything present there. The intertidal zone is characterized by different species of algae; gastropod mollusks such as limpets, Gibbula spp., and Littorina spp.; bivalve mollusks such as mussels; cirriped crustaceans such as barnacles; and cnidarians such as sea firs, stalked jellyfish, and sea anemones. In the wake of the Prestige oil spill, a low effect was observed on this zone 6 months after the spill, but there could be a sublethal effect affecting the reproduction, larval development, and recruitment. The more sensitive species were barnacles and limpets located on the upper level, and some algae were more affected by the cleaning activities. In the case of the Prestige oil spill, most of the intertidal rocky shore affected was directly exposed to wave action, a fact that helps the rapid cleaning of the oilcovered rocks, but in the case of protected shores, the oil contamination may be more dangerous due to a longer permanence of the oil on the rocks. The shallow sublittoral zone is characterized by algae; sponges; ascidians such as sea squirts; decapod crustaceans such as crabs, lobsters, prawns, and shrimps; equinoderms such as sea urchins, sea cucumbers, and starfishes; and different species of gastropod mollusk and sea slugs. This zone supports a lower hydrodynamic condition than the intertidal zone, and a more constant temperature and salinity of the water. The organisms most affected by the oil from the Prestige spill were sea urchins, which practically disappeared from the coastal area of Galicia 6 months after the spill. Sedimentary Shores Sedimentary shores include a wide variety of habitats, chiefly depending on tide depth (Figure 2), sediment type, and exposure to the waves: intertidal and subtidal shores, including subtidal habitats from low shore to abyssal depths; shores composed of sand, mud, or gravel; and exposed or protected beaches. The variety of habitats with the animals and plants that live there responds differently to oil spill, and restoration is more or less swift. Intertidal shores or beaches are characterized by two kinds of macrofaunal community, one purely marine and another semiterrestrial, inhabiting the upper levels of the shore, with a terrestrial life cycle but with a direct dependence on the marine habitat that supplies food and humidity. As a general rule, the upper level of a beach is the most affected by the spill. The oil is deposited on the upper level at high tide, and this oil remains there until
253
the next spring high tide arrives or it is cleaned. This area is especially sensitive because the macrofauna present here does not spread by water, and so recolonizing is more difficult when the community is seriously affected. Apart from the mortality caused by the oil, cleaning activities increase this mortality, because the habitat is destroyed when the polluted material is removed, including algal wrack and the top layer of sand where these animals live. Studies on the meiofauna of exposed sandy beaches in Galicia, 6 months after the Prestige oil spill, showed that relative abundance of the class Oligochaeta of supratidal levels decreased, as a result of higher PAHs. Animals whose main food supply is macrofauna from the wrack, such as birds, are also affected by the disappearance of food and by the destruction of their habitat during cleaning activities. In some cases, it is necessary to invade the dunes and cut the affected vegetation, where these birds live. Upper levels of beaches and dunes have vascular plants and bryophytes, such as Ammophila arenaria – a typical phanerogam that helps to establish the dune. Estuaries present a high abundance and diversity of plants, especially in salt marshes, with Juncus maritimus and Spartina spp. as representative species of these areas. These plants will be affected, to a greater or lesser extent, depending on the part of the plant affected by oil, that is, the aerial part or the rhizome, but especially depending on the cleaning activities that, in many cases, cause a higher impact than the oil, due to trampling underfoot, cutting, and removal of the plants affected. The lower part of the beach appears to be less affected by oil, as observed after the Prestige oil spill in exposed sandy beaches, where polychaetes have practically disappeared, but typical crustaceans of this habitat showed lower mortality rates. The intertidal meiofauna on the exposed sandy beaches of Galicia, 6 months after the Prestige oil spill, was not affected in terms of total density and major taxa occurrence. In the case of protected and estuarine beaches, the effects will probably be more dramatic, and may be measurable for decades after the event, when compared with exposed beaches where the pristine stages will occur after a few years. The hydrodynamic conditions in protected and estuarine beaches are calmer or absent in the case of estuaries, and this environment allows the oil to remain for a longer period of time on the substrata, increasing exposure to hydrocarbons and their toxic and physical (hypoxia) effects. Usually, these ecosystems are rich in commercial species such as clam, oyster, and crab, thus adding commercial loss to the ecological disaster, in the case of these coastal populations. In exposed beaches, waves are a powerful, natural cleaner, removing the oil deposited on the intertidal zone. But, in many cases, waves bury the oil when sediment is moved, leaving the pollutant more or less at depth, appearing again when the waves remove the deposited sediment.
254
Oil Spills
The quality of organic sediment matter, estimated from carbohydrates, proteins, and lipids concentration, and the biopolymeric carbon, estimated as the fraction potentially available to deposit feeders, were analyzed in exposed sandy beaches before the Prestige oil spill. These biochemical components of the sediment and water indicated the food availability for the meiofauna and macrofauna present in these habitats. It was observed that there was no limitation in food availability in the sediments on the beaches studied 6 months after the Prestige oil spill. This could be due to the fact that the oil spill did not affect these biochemical components or due to the lower presence of higher trophic consumers. Sediment type, size, and form have an important effect on the permanence and degradation time of the hydrocarbons. Finer, more compact sediments are less permeable to oil, whereas coarse sediments allow the oil to percolate and remain below the surface for a longer time, because they are not eroded by waves. This was observed in the gravel beaches of Alaska, following the Exxon Valdez oil spill, where a layer of subsurface oil persisted in some beaches for as long as 8 years after the spill. In some exposed sandy beaches of Galicia, with coarse sand and steep slopes, a layer of subsurface oil was observed when the storms eroded the slope. Subtidal shores present a different response to oil spills depending on the depth involved. Shallow subtidal regions, down to 20 m, showed a massive decline in benthic amphipods, especially the families Ampeliscidae and Phoxocephalidae, and an increase in the abundance of opportunistic families of polychaetes, such as Capitellidae and Spionidae, following the Amoco Cadiz, Exxon Valdez, and the Aegean Sea spills. At greater depths, from 40 to 100 m, no disturbance of the benthos was detected, as noted in Prince William Sound, Alaska, following the Exxon Valdez spill. In this case, the formation of neutrally buoyant oil–clay flocculates inside oil slicks and the major currents in the zone were apparently important in preventing subtidal oil accumulation at depth. Furthermore, during the followup of this oil spill, high abundance values of benthic fauna were observed that may reflect a flux of unusual amounts of phytoplankton to the bottom when low levels of grazing zooplanktons were present, resulting in increasing availability of food resources for the benthos. Bathyal and abyssal zones were considered as marine deserts, with low and very specialized species, but during the studies made following the Prestige oil spill (the remains of the ship lie at depths of 3565 and 3830 m), these zones showed a high number of species, the majority being new species. These zones that apparently present homogeneous environmental conditions are characterized by the total absence of light, low temperatures, and high salinities and pressure. The animals typically found in these areas include errant and swimming animals, the
predominant species being echinoderms, crustaceans, fishes, and cephalops; sessile animals comprising sponges, cnidarians, crinoids, and tunicates; macrofauna mainly constitutes of annelid polychaets, peracarid crustaceans, and mollusks; meiofauna basically includes nematods, harpacticoid copepods, ostracods, tardigrads, and kinorhynchs. The few studies conducted on these zones made it very difficult to evaluate the effect of oil spills, although studies carried out on the continental platforms have shown a drastic reduction in organisms of the benthic community found in this area.
How to Work after an Oil Spill As discussed earlier, the problems caused by an oil spill depend on the nature of the hydrocarbons, the type of ecosystem affected, and the length of the spill, but the cleaning activities also can increase the problems. It is very important to identify the type of area affected: intertidal, subtidal, sedimentary, or a rocky shore, and to apply the most adequate and least aggressive method to remove the oil spilled. The first step is to ensure adequate coordination of the cleaning activities and for the authorities involved to make all the material and personal means available. The most important thing is to preserve the unaffected areas and, in the polluted areas, to remove the larger quantities of oil when it arrives massively. The next stage is to adapt the cleaning activity to the specific characteristics of the area affected: Rocky shores with animals and plants that live all or • part of their life cycle on the substratum require
•
manual removal of the oil, which can be performed using pressurized water. However, this system is recommended in areas where there are no animals and plants that can be removed by the pressure of the water, such as in urban and port areas. Another recommendation when this method is used is to apply a filtration system to collect the oil removed, which, in some cases, appears in an emulsion form that increases the toxicity and availability of the hydrocarbons. In the course of regenerating the rocky shore following the Prestige oil spill, the affected coast was cleaned by adding nutrients that enriched the microorganism of marine water. These microorganisms degraded the hydrocarbons and the results were satisfactory as they increased the velocity of oil degradation while preserving the substratum. Sedimentary shores present a very sensitive area, located on the upper limit of the intertidal zone, where semiterrestrial animals and specialized plants live. These areas are usually affected by high amounts of oil deposited by tides. In the first moments after the spill, maximum quantity of the spilled oil needs to be
Oil Spills
removed, but after that a manual selection of material and sediment contaminated must be done, trying to keep clean algae because it is the habitat of the specialized semiterrestrial animals typical of the upper levels. Manual cutting of marsh and dune vegetation contaminated by oil should only be considered in areas where oil may persist, where significant impacts to wildlife are likely, or where less destructive cleanup techniques have been proven to be insufficient. It is very important to have pre-spill information of the different ecosystems for baseline data. These studies will be very important for the postspill analysis and for recommendation on how to act and restore the affected areas. See also: Oil and Chemical Spills, Oil Industry and the Health of Communities in the Niger Delta of Nigeria.
Further Reading Besteiro C (2004) Evaluacio´n del impacto en las comunidades y especies de intere´s comercial y ecolo´gico en las zonas costeras. Periodo primaveral. Informe final del Programa Nacional: Accio´n urgente Prestige-Recursos naturales. Ministerio de Ciencia y Tecnologı´a. de la Huz R, Lastra M, Junoy J, Castellanos C, and Vie´itez JM (2005) Biological impacts of oil pollution and cleaning in the intertidal zone of exposed sandy beaches: Preliminary study of the ‘‘Prestige’’ oil spill. Estuarine, Coastal and Shelf Science 65: 19--29.
255
Feder HM and Blanchard A (1998) The deep benthos of Prince William Sound, Alaska, 16 months after the Exxon Valdez oil spill. Marine Pollution Bulletin 36(2): 118--130. Go´mez Gesteira JL and Dauvin J-C (2005) Impact of the Aegean Sea oil spill on the subtidal fine sand macrobenthic community of the Ares-Betanzos Ria (Northwest Spain). Marine Environmental Research 60: 289--316. Gonza´lez Laxe F (2003) El impacto del Prestige. Ana´lisis y evaluacio´n de los dan˜os causados por el accidente del Prestige y dispositivos para la regeneracio´n medioambiental y recuperacio´n econo´mica de Galicia. Instituto de Estudios Econo´micos de Galicia, Fundacio´n Pedro Barrie´ de la Maza. Hayes MO and Michel J (1999) Factors determining the long-term persistence of Exxon Valdez oil in the gravel beaches. Marine Pollution Bulletin 38(2): 92--101. ITOPF (2002) Fate of Marine Oil Spill. Technical Information Paper no. 2. London: ITOPF. Mora J, Garmendia JM, Go´mez Gesteira JL, et al. (1996) Seguimiento mensual del bentos infralitoral de la rı´a de Ares y Betanzos antes y despue´s de la marea negra del ‘Aegean Sea’. In: Ros J (ed.) Seguimiento de la contaminacio´n producida por el accidente del buque Aegean Sea, pp. 137--150. Madrid: Ministerio de Medio Ambiente, serie monografı´as. Ornitz BE and Champ MA (eds.) (2002) Oil Spill First Principles: Prevention and Best Response. Amsterdam: Elsevier Science. ISBN 0080428142. Peterson CH (2001) The ‘‘Exxon Valdez’’ oil spill in Alaska: Acute, indirect and chronic effects on the ecosystem. Advances in Marine Biology 39: 1--103. Rodrı´guez JG, Incera M, de la Huz R, Lo´pez J, and Lastra M (2007) Polycyclic aromatic hydrocarbons (PAHs), organic matter quality and meiofauna in Galician sandy beaches, 6 months after the Prestige oil-spill. Marine Pollution Bulletin 54: 1046--1052. Whitfield J (2003) How to clean a beach. Nature 422: 464--466. Zengel SA and Michel J (1996) Vegetation cutting as a clean-up method for salt and brackish marshes impacted by oil spill: A review and case history of the effects on plant recovery. Marine Pollution Bulletin 32(12): 876--885.