This article appears in the following ICES Journal of Marine Science issue: Marine Environmental Indicators: Utility in Meeting Regulatory Needs [View the issue table of contents]
Use of a Phytoplankton Community Index to assess the health of coastal waters
1 School of Life Sciences, Napier University, 10 Colinton Road, Edinburgh EH10 5DT, United Kingdom
2 The Centre for Environment, Fisheries and Aquaculture Science, Pakefield Road, Lowestoft, Suffolk NR33 0OT, United Kingdom
3 Fisheries Research Services, Marine Laboratory, PO Box 101, 375 Victoria Road, Torry, Aberdeen, AB11 9DB, United Kingdom
4 Agri-Food and Biosciences Institute, Belfast BT9 5PX, UK
Correspondence to P. Tett: tel: +44 131 4552633; fax: +44 131 4552291; e-mail: p.tett{at}napier.ac.uk
Tett, P., Carreira, C., Mills, D. K., van Leeuwen, S., Foden, J., Bresnan, E., and Gowen, R. J. 2008. Use of a Phytoplankton Community Index to assess the health of coastal waters. – ICES Journal of Marine Science, 65: 1475–1482.Monitoring of marine-ecosystem status and health requires indicators of community structure and function. As a structural indicator, we propose a Phytoplankton Community Index (PCI) based on the abundance of "life-forms" such as "pelagic diatoms" or "medium-sized autotrophic dinoflagellates". To calculate the PCI, data showing seasonal variation in these abundances are plotted in "life-form space" of two or more dimensions. Data from a "type-specific reference condition" are then enclosed within a reference envelope. Comparison data are plotted into the same coordinate system, and the PCI is the proportion (between 0 and 1) of these new data that fall within the reference envelope. Results from initial applications of this method are shown for UK coastal waters in the northern North Sea (near Stonehaven), a Scottish fjord (Loch Creran), and the eastern Irish Sea (including Liverpool Bay). The Stonehaven data (1997–2005) were used to compare values obtained from weekly sampling with those from monthly sampling. A spatial comparison between more- and less-nutrient-enriched waters in the eastern Irish Sea (1991–2003) showed little difference in phytoplankton community structure. Loch Creran has experienced a large change in the "balance of organisms", and hence a reduction in the PCI, between 1979–1981 and 2006/2007, associated with a decrease in chlorophyll but no apparent change in nutrients. These results are discussed in relation to the intended uses of the PCI as an index of biological quality for the Water Framework Directive (WFD) and an index of ecosystem health in the context of eutrophication. Although the method only measures change, it can also be used as an indicator of biological quality if the reference conditions are those defined for a WFD waterbody, and as an indicator of health if appropriately calibrated. Suggestions are made for further development.
Keywords: Irish Sea, life-forms, Loch Creran, nutrients, PCI, phytoplankton, Stonehaven
Received 23 November 2007; accepted 8 May 2008; advance access publication 10 September 2008.