Potential phytoplankton indicator species for monitoring Baltic coastal waters in the summer period

Abstract

There are very few time series documenting clear trends of change in the biomass of total phytoplankton or single taxa that coincide with trends of increasing nutrient concentrations. Weekly or biweekly monitoring since 1997 on a cross section of the central Gulf of Finland (NE Baltic Sea) with similar climatic and hydrographic conditions, but different nutrient levels, provided a uniform dataset. In order to evaluate seasonal (June-September) patterns of phytoplankton succession, more than 1,200 samples were statistically analyzed by selecting 12 dominant taxa using wet weight biomass values. In addition, the continuously measured hydrographic parameters on board the ships of opportunity, and simultaneous nutrient analyses gave high frequency information on the water masses. The objective of this study was to identify the taxa that may prove indicative in the assessment of eutrophication in the appropriate monitoring time periods. None of the most common bloomforming species (Aphanizomenon sp., Nodularia spumigena, and Heterocapsa triquetra) showed reliable correlations with enhanced nutrient concentrations. The species we suggest as reliable eutrophication indicators-oscillatorialean cyanobacteria and the diatoms Cyclotella choctawhatcheeana and Cylindrotheca closterium-showed the best relationships with total phosphorus concentrations. Their maxima appear toward the end of July or in August-September when phytoplankton community structure is more stable, and less frequent observations may give adequate results. Another diatom, Skeletonema costatum, exhibited stronger correlations with dissolved inorganic and total nitrogen in June, during the period of the summer phytoplankton minimum.

Coastal eutrophication research: a new awareness

“…The diagnostics of these impacts require that robust indicators be developed that help assess the responses of coastal ecosystems to eutrophication (e.g., Jaanus et al, 2009). The search for reliable ecosystem-level indicators of eutrophication impacts is not driven by an academic interest in better understanding eutrophication, but by the requirements of legislation and policy to identify and abate coastal eutrophication, as exemplified by the EU Water Framework Directive and the OSPAR Convention (e.g., Claussen et al, 2009;Duarte et al, 2009;Henriksen, 2009).…”

“…We now have a better appreciation of the scale of problem (e.g., Nixon, 2009), a better understanding of its processes and dynamics (e.g., Cloern, 2001;Boesch, 2002;Howarth & Marino, 2006;Conley et al, 2009;Duarte et al, 2009;Soetaert & Middelburg, 2009), improved diagnostic tools and indicators (e.g., Eyre & Ferguson, 2009;Jaanus et al, 2009), and have taken action to mitigate it (e.g., Nørring & Jørgensen, 2009, Petersen et al, 2009Savchuk & Wulff, 2009), as clearly exemplified by the papers compiled in this issue. Collectively, these papers portray a major development of the field over the past decade.…”

Effects of nitrogen concentration on the taxonomic and functional structure of phytoplankton communities in the Western Baltic Sea and implications for the European water framework directive

“…Spatharis et al (2007) demonstrated that the abundance of the potentially toxic diatom Pseudonitzschia calliantha was related to very high nutrient concentrations in coastal waters of the Mediterranean Sea. In the Baltic Sea, as far as we know, only the small diatom Skeletonema costatum and the cyanophycean small colony forming Woronichinia compacta were found to be strongly correlated to nitrogen concentrations (Toming & Jaanus, 2007;Sagert et al, 2008b;Jaanus et al, 2009).…”

“…Since the salinities are higher in our part of the Baltic Sea and therefore these taxa, especially Chlorophyceae, rarely constitute a relevant part of total phytoplankton biomass, this system could not be adopted untested for the western German coastal regions with salinities higher than 15 PSU. Other studies revealed that the diatom species Skeletonema marinoi had a significant correlation to nitrogen concentrations in the Gulf of Finnland (NE Baltic Sea, salinity 5-6 PSU), whereas ocillatorialean Cyanophyceae and the diatoms Cyclotella choctawhatcheeana and Cylindrotheca closterium showed the best relationship with total phosphorus concentrations (Toming & Jaanus, 2007;Jaanus et al, 2009).…”

Untitled

“…Nevertheless, based on physico-chemical parameters and phytoplankton biomass expressed as chlorophyll a concentration the Bay is considered as a system where natural eutrophication still prevails over anthropogenic (Krivokapić, Pestorić, Bosak, Kušpilić, & Riser, 2011). For getting a better biological quality assessment of the ecosystem, a trophic estimation based on physico-chemical parameters and phytoplankton biomass expressed as chlorophyll a concentration need to be showed together with information on the phytoplankton taxonomic composition (Toming & Jaanus, 2007;Jaanus, Toming, Hallfors, Kaljurand, & Lips, 2009). Eutrophication causes numerous physical and chemical changes in the marine environment which lead to pressure on algal populations, and all those changes can result in intensive growth of harmfultoxin producing species.…”