The Environmental Impact of Offshore Wind Farms Part 2

III. Environmental effects on marine life A. Fish and the benthic community Many similar issues affecting birds that arise from offshore turbine construction also adversely affect the marine community. Ohman (2007) argues that during the construction phase sedimentation and underwater noise could influence fish and other marine organisms. During the operation phase, the submerged part of the power plant locally changes the habitat causing a reef effect (the hard structure underwater may act as an artificial reef that provides a habitat for fish and sessile organisms, such as barnacles). Most importantly, the marine environment can be largely affected by the presence of subsea cables underwater that are used to carry electricity from the generator in the turbine to the offshore transformer before it is converted to high voltage (Ohman et al., 2007) Marine animals can be influenced by the electromagnetic fields that the electric current induces, although there are marked differences in cross-species fish behavior when exposed to magnetic fields. Ecologically speaking, examining the three main consequences for marine life – the introduction of new habitats, increased noise, and exposure to electromagnetic fields – will shed some light on the insight Europe has gained from their experiences with offshore wind turbines (Ohman et al., 2007). A bottom-up approach is necessary in analyzing the impact of turbines on the marine community. The collection of organisms that live on or in the sediment of the sea floor is known as the benthic community, or more simply benthos. The benthic community is typically comprised of infauna, animals and bacteria of any size that live in bottom sediments, and epifauna, which refers to animals that are attached to or move on the bottom sediment, such as oysters, mussels, barnacles, snails, starfish, sponges, and sea squirts (EWEA, 2006). Essentially, the introduction of the hard foundation of the wind turbine creates a new habitat for marine 17 epifaunal organisms (EWEA, 2006). As organisms such as mussels and barnacles attach themselves to the base of a turbine, small fish species may become attracted to the area, which can lead to an increase in the number of seabirds present. What is happening here is an ecosystem shift – as the prey shift their location, corresponding predators have no choice but to follow. The point is that the construction of offshore wind farms will modify the relationships of benthic communities, and therefore create new local ecosystems (Koeller et al., 2006). Specifically, evidence about marine ecosystems from Horns Rev wind farm in Denmark is particularly strong. Monitoring studies at the farm have indicated that indigenous infauna habitats have been effectively replaced by an epifauna community associated with hard bottom habitats, with an estimated 60-fold increase in availability of food for fish (Boesen and Kjaer, 2005). The most important news in relation to an increased level of diversity is the presence of two new species: the ross worm (Sabellaria spinulosa) and the white weed (Sertularia cupressina), and both are considered to be threatened in the Horns Rev region of Denmark (Boesen and Kjaer, 2005). This information is valuable because it signifies that the introduction of offshore turbines has actually increased biodiversity and confirms the oft-discussed habitatcreation potential of these farms. The process of wind turbine construction is interesting in an ecological sense because it changes the way the surrounding ecosystem functions – predators such as the Common Eider and the Common Scoter will inevitably move towards the new location of their epifaunal prey as the ecosystem shifts. Other observational studies have heeded results indicating that the construction of Horns Rev and Nysted wind farms has had a negligible impact on fish in terms of creating a new artificial habitat. While fish may have access to greater prey numbers caused by the wind turbines, species composition of fish in and around both Danish farms has remained relatively 18 constant (Koeller et al., 2006). Only the population of sand eels has demonstrated a different pattern, with the population increasing by about 300 percent in Horns Rev and decreasing by 20 percent outside of it (DEA, 2006). However, it is difficult to measure such activity when the colonization process is immature – many European offshore wind farms have existed for less than a decade. The take home point here is that the existence of differing (and sometimes, opposite) results certainly leaves a lot of room for debate as to whether or not ecological effects of offshore projects on marine organisms are significant. Apart from habitat creation and biodiversity, several studies suggest that fish may be influenced by the magnetic fields induced by flowing electric current through cables on the ocean floor (Ohman et al., 2007). First, small amounts of magnetic material actually exist within some species of fish, including the European eel (Anguilla anguilla) and the yellowfin tuna (Thunnus albacores) (Hanson et al., 1984, Walker 1984). It is also important to note that migrating fish, such as the yellowfin tuna, are expected to use magnetic fields for orientation, that is, the sense of their surroundings (Walker, 1984). The human-introduced magnetic fields that occur due to turbine construction have in fact had some negative effects. For instance, magnetic exposure was observed to modify hormone levels in brook trout, while it was also shown to have slowed down embryonic development (Lerchl et al., 1998). In the laboratory, Krzemieniewski his colleagues (2004) decreased biomass and increased mortality in European catfish when exposed to a constant magnetic field with an intensity ranging from 0.4 to 0.6. Additionally, there have been a few studies on the effects of pile driving on fish. In general, these studies have placed fish in cages at various distances from piledrivers and found measured, although minimal, increases in mortality and other injuries (Hastings and Popper, 2005). There have also been a few studies on the effects of noise on stress levels in fish. Chronic 19 noise exposure is known to increase stress levels in humans with consequential effects on health, and there is clear reason to believe similar effects could take place in aquatic species. It has also been found that a continuous 170 dB noise showed no effect on corticosterone (a stress hormone) levels in goldfish and found no statistically significant results (Smith, et al., 2004). Although not conducted in European waters, more subtle effects on fish have been found in a range of international studies. Canadian studies have shown that the catch rate of haddock and cod decreased in areas after air gun use but returned to normal several days later suggesting that fish left the area and gradually returned (Engas and Lokkeborg, 2002). This study shows valuable evidence of learning, and is pertinent regardless of its location; that is, if the same study took place in European waters, it is probable that a similar outcome would have resulted. In a separate study, it was also determined that salmon and cod show significant avoidance behavior in areas of intense noise – the two species moved away from loud disturbances at distances of 1.4 km and 5.5 km, respectively (Nedwell et al., 2004). This section outlines the literature regarding offshore turbines and the effects that they have had (and could possibly have in the future) on a variety marine species. In terms of habitat creation, some studies found that wind turbines actually increase available habitat and act as a catalyst for increased biodiversity, while other studies found no change in the surrounding environment. As to be expected with a young industry, widely differing hypotheses and results are likely to be prevalent. Importantly, like birds, fish have displayed the ability to learn and practice avoidance in the presence of loud underwater noises. Taken together, while different species of fish are likely to display vastly different responses to different disturbances, electromagnetic field effects, noise, and other consequential factors of turbine construction were found to have negligible effects on fish species surrounding European offshore wind farms. 20 There are additional concerns and limitations about the presence of wind turbines with regard to fish populations. Current available technology has limited wind turbine placement to areas where the water depth is less than approximately 30 m (Musial et al., 2004). However, floating wind turbines capable of being installed in depths of up to 200 m are currently being designed and manufactured – a good sign for the potential available area for wind power. It has been argued that floating offshore wind turbines are likely to act as fish aggregating devices (FADs); FADs have been used for centuries to concentrate marine fish to facilitate capture (Wilhelmsson et al., 2006, Vella et al., 2001, Rodmell et al., 2005, Castro et al., 2002). Here, the foundation of the wind turbine adds three-dimensional complexity to the environment and serves as a substrate for benthic invertebrates, attracting large numbers of fish (Snyder and Kaiser, 2009). Many variables have an impact on these predictions, such as the baseline concentration of fish in an area, movement patterns of species of interest, changes in catchabilities, and changes in effort distributions (the amount that and frequency with which one fishes) (Fayram and Risi, 2007). In order to measure these variables, longitudinal case studies once again become quite valuable, as it is important to know the condition of the marine ecosystem under study before a disturbance and to document incremental change over time. Fisheries management is difficult to begin with, as overfishing of profitable species has proven to be a major concern for marine species overseers. The use of FADs results in increased catch rates for a number of fish species; for example, catch rates of some tuna species may be 10-100 times greater near FADs than in open-water areas based on tag releases and recaptures (Itano, 2000). It can be stated that increased catch rates contribute positively to the argument for 21 offshore wind power. However, constant caution should be exercised given the uncontrolled effort that exists in most recreational fisheries. One potential mechanism that could potentially minimize conflicts with both recreational and commercial fisheries management is the creation of a marine protected area (MPA) in waters surrounding the wind power generating facility (Fayram and Risi, 2007). Marine protected areas designate locations that are intentionally preserved, as human disturbances could cause more than proportional damage to either marine species or the marine environment. Fishing, and in this case, overfishing, can be prohibited in these areas. Rules and regulations surrounding a particular MPA depend on the species living in the area and the typical purpose of the marine habitat (National Marine Protected Areas Center, 2000). A study of a planned project in the Adriatic Sea serves as a telling case study for the interaction between offshore wind farms and fish populations. Essentially, several fish species (both commercially and recreationally relevant) found in waters associated with floating offshore wind power generating facilities in the Adriatic Sea are characterized as unknown or overfished. Some examples include the bluefin tuna (Thunnus thynnus), Atlantic mackerel (Scomber scombrus), amberjack (Seriola dumerili), dolphinfish (Coryphaena hippurus), albacore (Thunnus alaluguna), and swordfish (Xiphias gladius), as well as other less common tuna species (Fayram and Risi, 2007). Additionally, the Mediterranean bluefin tuna stock is and has been of concern for a number of years due in part to unreported harvesting, lack of fishing effort enforcement, inappropriate allowable catch limits, and poor data quality (Fayram and Risi, 2007). The presence of floating turbines would likely increase the congregation of low-stock species in areas close to the turbines, which in turn could increase the probability of irresponsible overfishing practices. 22 From these studies, it is clear that the problem of overfishing could be enhanced by the presence of floating offshore wind turbines. However, the creation of an MPA in the vicinity of wind power generating facilities in the Adriatic Sea could have a measurable benefit on recreational anglers, commercial fisherman, and fisheries managers (Fayram and Risi, 2007). Fisherman and managers would benefit because total harvest could be more closely controlled, increasing the likelihood that the fishery can be sustainably managed. Bluefin tuna are highly migratory and therefore would receive less benefit from MPAs than sedentary species (benthic species), but protecting juveniles and adults present in the waters surrounding a wind farm would probably decrease the likelihood of overfishing (Fayram and Risi, 2007). Still, the aim for environmentalists in terms of offshore wind ecology is to minimize the probability of a particular species from encountering dangerous conditions as a result of man-made structures. Thus far, studies are able to offer only indicators of potential environmental danger associated with the construction of offshore wind turbines. While the information available is limited, it can be argued that wind turbines may have the potential to increase habitat availability to some marine organisms and at the same time hamper the physiology of some fish through magnetic field conduction. In addition, the presence of floating turbines could have a detrimental affect on fishing practices, as floating turbines can cause the formation of large congregations of fish. As stated before, it would be valuable to be able to do longitudinal studies of marine populations both before and after the construction of turbines. Nonetheless, in moving towards the future, it is critical to examine the ways in which the European offshore movement has affected the marine environment thus far. 23 The construction of wind farms has also had quantifiable effects on cetaceans, or mammals that spend their entire lives underwater (Merriam-Webster Dictionary). Many cetaceans use echolocation 1 to find their food, and many more communicate using acoustic signals (Snyder and Kaiser, 2009). As a result, cetaceans with very sensitive hearing (such as porpoises) can be damaged by the loud noises associated with wind farms, particularly the sounds of pile driving. At the site of construction, the sound pressure level of pile driving a foundation into the seabed for a 1.5 MW turbine is 228 dB, and 400 m away from pile driving the sound pressure level is 189 dB (DONG, et al., 2006). This level of noise should cause hearing loss in seals (DONG, et al., 2006). Pile driving would be audible to porpoises and seals for at least 80 km and might cause behavioral responses up to 20 km away (DONG, et al., 2006). During wind farm operation, the noise from the turbines may be detectable for porpoises and seals up to about 1 km from the source (DONG, et al., 2006). The extent to which this noise would cause cetaceans to alter their daily life is presently unknown, but any interference with echolocation could plausibly hinder their ability to communicate, and hearing loss would severely inhibit their ability to survive. At the Nysted wind farm, the population of harbor and grey seals was monitored before, during, and after turbine construction. Wind farm operation did not have a significant impact on seal abundance, however pile driving operations occurring at one selected site did decrease the number of seals observed at a nearby breeding site (Snyder and Kaiser, 2009). Also, while the total annual population remained stable, after construction fewer harbor seals were present on nearby land sites in June (the breeding season) but more were present in July and August. This In echolocation, a high-pitched sound is sent out by the cetacean. The sound essentially reflects off of the object in question and returns to the cetacean. The cetacean interprets this returning echo to determine the object's shape, direction, distance, and texture. 1 24 could suggest that fewer seals were using the area around the wind farm for breeding which could have an important effect on the viability of the population (Snyder and Kaiser, 2009). While there is some suggestive evidence for habitat displacement and potential reproductive reduction, the fact that more seals were present in July and August of the study period again shows some evidence of adaptation and learning. The study might also suggest that seals did not find the areas around wind farms to be safe breeding grounds, but found them to be safe foraging or living grounds. The study did not show that seals experienced greater levels of mortality; it seems as though seals simply used a level of caution while near the turbines, particularly during the breeding season. In another study, harbor porpoises were shown to occur less frequently in the area around a wind farm during construction at both Nysted and Horns Rev (DONG, et al., 2006, Carstensen et al., 2006). This result is primarily due to animals fleeing the noise caused by piledriving, as described above. At Horns Rev, the porpoises returned following the construction period, although just two years later porpoises at Nysted were less numerous than they were in baseline census numbers (DONG, et al., 2006). Although porpoise numbers were lower after the construction period, it is still difficult to deem the absence of porpoises as being caused by the presence of turbines. Determining a causal relationship requires other variables, such as weather, pollution, and food availability to be held constant. In a location as dynamic and ever-changing as the sea, it is particularly difficult to state that the reason that harbor porpoises no longer frequent the area is because of wind turbines. Taken together, the effects of wind turbine construction on mammals are ambiguous. Here, there is documented evidence that porpoises and seals have a tendency to leave the area in which there is loud noise. In the same way that humans exercise caution and practice avoidance 25 measures in times of danger, the fact that these creatures have left the area should probably be viewed as a species trying to protect itself against an unknown disturbance. The encouraging aspect of these studies is that they take a longitudinal approach that runs over a period of years. Nonetheless, mammals, much like birds, fish, and other marine species have shown a propensity for adaptation and learning, as many were able to stay in the area of the wind farm after its construction. IV. Conclusions and a look forward Overall, this paper serves to provide lessons as to organism behavior in response to the construction of offshore wind turbines. Studies have shown that avian mortality due to collision risk is a real but relatively insignificant issue that can be augmented by severe weather, wind, or a variety of other factors. In this light, it is difficult to determine a causal relationship between the construction of offshore turbines and avian mortality. Separately, electromagnetic fields and underwater noise, as well as the presence of turbines as FADs, have all shown to have some effects on marine populations and activity. 26 The common threads that run throughout all studies mentioned in this paper are, in reality, quite interesting. The first is that birds, fish, and mammals alike have shown some ability to be able to adapt to their surroundings, and in some cases, take advantage of the man-made structures. For instance, because benthic species attach themselves to turbine foundations, fish are provided with an expanded food supply. In the case of seals and porpoises, the animals often returned to their original living areas regardless of the turbines, once a diminished level of danger had been detected (loud noise during the construction phase could indicate a high level of danger). The second common thread is that longitudinal studies are the key to unveiling the true effects of offshore wind farm construction. Without studies that take places over a long period of time, it is impossible to determine whether or not animal activity occurs as a result of a disturbance or because of normal, day-to-day variation. Longitudinal effects are often timeconsuming and tedious to reveal, but will highlight substantiated relationships (or, the lack thereof) between wind turbines and organism activity. A continued push for longitudinal studies is necessary to truly understand the environmental impact of offshore turbine construction. Examining the existing offshore projects in Europe is a critical piece of evaluating the potential ecological impact of an offshore farm in the United States. However, the ways in which the United States can yield similar information is of great relevance as well. 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