West coast Scotland
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Loch Ewe (Site 37, 57 50.14'N 5 36.61'W), a sea loch on the west coast of Scotland, has been part of the Marine Scotland Science Coastal Ecosystem Monitoring Programme since 2002. This site acts as a reference site to fulfill the requirements of EU Water Framework Directive and to test the development of tools to identify Good Environmental Status for the Marine Strategy Framework Directive. Samples have been collected by Isle of Ewe Shellfish and their input to the success of the programme is gratefully acknowledged.
The Loch Ewe monitoring site is 40 m deep and located at the northerly face of the sea loch. Samples are collected weekly. Samples to measure temperature, salinity, and nutrients are collected using a reversing bottle and digital thermometer from surface (1 m) and bottom (35 m) depths. A 10m integrated tube sampler is used to collect samples for Chlorophyll and phytoplankton community analysis. Phytoplankton samples are preserved in Lugol s iodine and analysed using the Utermohl method (Utermohl, 1958).
Seasonal and interannual trends
Water movement in this loch is strongly influenced by wind and tide. The loch faces north and has variable exchange with the North Minch, which is influenced by influxes of Atlantic water. Temperature and salinity show a strong seasonality. The lowest temperatures are observed during spring (ca. 7 C) and the warmest towards late summer. The temperature at this site rarely exceeds 14 C. The temperature at this and other west coast sites can be up to 1-2 C warmer during spring than the sites at the east coast, Orkney, and Shetland. Salinity follows a similar pattern, with lowest salinity observed in spring and highest in late summer.
Nutrients show a seasonal pattern typical to high latitudes, with concentration of total nitrates, phosphate, and silicate accumulating over winter, when phytoplankton abundance is reduced and concentrations decrease during the phytoplankton growing period.
The phytoplankton community observes a similar seasonal pattern to other sites in Scotland, with a strong spring bloom dominated by Diatoms. The spring bloom occurs earlier on the west coast (February/March) than on the east (March/April), likely the result of the warmer water temperature. Dinoflagellates become an important component of the phytoplankton community during summer. The autumn Diatom bloom is more intensive than on the east coast and is dominated by larger Diatoms, such as the Rhizosolenia and Pseudo-nitzschia spp. type species.
Annual average plots show an increase in Dinoflagellates over the last five years. Increased numbers of athecate Dinoflagellates have been observed during summer. The pattern of Diatom abundance during the spring bloom is similar to that on the east coast, with an increase in abundance of Skeletonema observed since 2005 at this site. Chlorophyll data demonstrate an increase, primarily occurring during winter over the last three years. Similar to other sites, a decrease in the abundance of Ceratium has been observed over the last decade. This site also experienced a devastating Karenia Mikimotoi bloom in late summer 2006 (Davidson et al., 2009), with significant mortalities of benthic fauna recorded.
This site was the focus of an intensive study of the presence of shellfish toxin-producing species and algal toxins (Bresnan et al., 2005). Further information and links to the data collected at this site can be found at the Marine Scotland website ( https://www.scotland.gov.uk/Topics/marine/science/MSInteractive/Themes/Coastal).