Rocky shore biodiversity: Separating the effects of anthropogenic impacts from natural variation and climate change impacts

The marine environment of Orkney has been subject to a variety of pressures over the years and there is a history of marine monitoring programmes investigating the potential impacts of different activities such as those associated with the oil terminal on Flotta, aquaculture, introduction of non-native species and climate change. The rocky shores around Orkney range from extremely sheltered, fucoid-dominated shores to extremely wave-exposed animal-dominated shores.

Long-term monitoring sites were set up in the 1970s, alongside intermittent survey efforts as part of the UK MarClim programme (2008, 2015, 2021) and recent baseline sites established to assess effects of two newly proposed developments - the extension of the Hatston Pier (Kirkwall) on the northern coast of the Orkney Mainland and the Scapa Deep-Water Quay on the eastern coast of Scapa Flow.

At both these locations there are existing potential pressures from various activities as well as the impacts of climate change. It will be important to be able to separate the effects of these existing pressures from those of any additional impacts that may arise from the proposed developments to help inform any mitigation measures that could be put in place.

Rocky shore communities are subject to considerable natural variation in the composition and abundances of key species that can mask the impacts of other pressures and the long-term effects of climate change through sea-level rise, increasing sea water temperature and increased wave action as well as increasing air temperature and changes in rainfall patterns. When seeking to develop and implement a monitoring programme to detect the impact from specific developments (e.g. a pier extension of new major coastal infrastructure and the associated subsequent operations) it is important the monitoring programme is designed in such a way that 'cause and effect' can be confidently attributed.

Established survey designs such as 'Before/After-Control/Impact' (BACI) can help localise ecological changes to the time and location of the anticipated impacts, and will be used in this study.

The rocky shore monitoring programme in Orkney was established before climate change and the introduction of non-native species were considered significant threats. The data from the historical programme do provide an excellent baseline and provide an insight into the scale of natural variability at several sites over 40+ years. The use of fixed-line transects, however, have some significant limitations in being able to distinguish between natural variation and climate change driven effects.

The MarClim surveys that have been undertaken at various times over the last 15-years also provide an important baseline for assessing future change.

The focus of the monitoring programme on the two new proposed development sites provides the opportunity to explore a combination of well-established monitoring approaches such as line transects, but also introduce new approaches: (i) biological traits analysis (BTA) to examine the functional change in these ecosystems, and (ii) evaluation of ecological changes in the context of location within the geographical and thermal ranges of the component species.