Environmental statement - Flyndre and Cawdor - Maersk Oil

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Flyndre and Cawdor Environmental Statement Section 3 Environmental Baseline planktonic species (fish, benthic invertebrates and algae). This meroplankton population may have a very different seasonal cycle depending on the life cycle strategy of the fish species and benthic organisms which inhabit the area. The composition and abundance of plankton communities varies throughout the year and are influenced by several factors including depth, tidal mixing, temperature stratification, nutrient availability and the location of oceanographic fronts. Species distribution is directly influenced by temperature, salinity, water inflow and the presence of local benthic communities (Robinson, 1970). Produced water from oil and gas extraction may include dissolved hydrocarbons, organic acids and phenols which are used in biocides, corrosion and scale inhibitors and gas treatment. Plankton may be exposed to these contaminants through passive diffusion, active uptake or through eating contaminated prey. As plankton spend most of their lives in the water column, they will be particularly exposed to those contaminants that remain in solution (Sheahan et al., 2001). Produced water has been shown to affect recruitment in calanoid copepods (Hay et al., 1988). The toxicity of produced water will decrease as it disperses away from the source. Stomgren et al. (1995) found that acute toxicity in the diatom Skeletonema spp. was only likely in individuals in the immediate vicinity of the source of produced water, while at distances greater than 2 km the effects are negligible. Although plankton communities are vulnerable to continuous exposure to low levels of hydrocarbons and chemicals, work after the Sea Empress spill (72,000 tonnes of oil released) off the coast of southwest Wales found no significant effects on the plankton (Batten et al., 1998). This suggests that plankton communities are less vulnerable to one‐off incidents than they are to the continuous exposure associated with produced water release. 3.5.2. BENTHOS Bacteria, plants and animals living on or within the seabed sediments are collectively referred to as benthos. Species living on top of the sea floor may be sessile (e.g. seaweeds) or freely moving (e.g. starfish) and collectively are referred to as epibenthic organisms. Animals living within the sediment are termed infaunal species (e.g. clams, tubeworms and burrowing crabs) while animals living on the surface are termed epifaunal (e.g. mussels, crabs, starfish and flounder). Semi‐infaunal animals, including sea pens and some bivalves, lie partially buried in the seabed. As shown in Table 3‐10 benthic species may also be classified in terms of their size. Bacteria and benthic organisms play a major role in the decomposition of organic material that originates from primary production by phytoplankton in surface water and settles on the seabed (North Sea Task Force, 1993). For example bacteria degrade hydrocarbons through their utilisation as a food source (Clark, 1996). Benthic animals display a variety of feeding methods. Suspension and filter feeders capture particles which are suspended in the water column (e.g. sea pens) or transported by the current (e.g. mussels). Deposit feeders (e.g. sea cucumbers) ingest sediment and digest the organic material contained within it. Other benthic species can be herbivorous (e.g. sea urchins), carnivorous (e.g. crabs) or omnivorous (e.g. nematodes). Sessile infaunal species are particularly vulnerable to external influences that may alter the physical, chemical or biological community of the sediment as they are unable to avoid unfavourable conditions. Each species has its own response and degree of adaptability to changes in the physical and chemical environment. Consequently the species composition and relative abundance in a particular location provides a reflection of the immediate environment, both current and historic (Clark, 1996). Surveys of the North Sea show that the benthic fauna is characterised by water depth 3 ‐ 24 D/4114/2011
Flyndre and Cawdor Environmental Statement Section 3 Environmental Baseline and seabed type, with depth mainly influencing epifauna, whilst sediment characteristics are more important for the infauna (Basford et al., 1990). The recognition that aquatic contaminants may alter sediment benthos, together with the relative ease of obtaining quantitative samples from specific locations, has led to the widespread use of infaunal communities in monitoring the long‐term impact of disturbance to the marine environment. Size Categories Macrobenthos (>1 mm) Meiobenthos (50 µm to 1 mm) Microbenthos (
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Figure 1‐2 Flyndre and Cawdor Dev
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1.5. ENVIRONMENTAL MANAGEMENT Flynd
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Inspections Reviews Investigation
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Ensure the installation meets
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