Late Summer Trophic Conditions in the North-east Gulf of Finland and the River Neva Estuary, Baltic Sea

The fate and effects of high nutnent loadlng from the River Neva -St Petersburg (NW Russia) region was studied in the Neva Estuary and adjacent waters of the eastern Gulf of Finland (Baltic Sea) under late suinmer conditions Special emphasis was given to the role of N and P as productlon limiting factors The data originated from 5 crulses performed in 1990-1992 and include CTD measurements and spatlal distributions of different nutnent fractions as well as nutrlent depletion measurements onboard The results revealed quick losses of both total and inorganic nutnents from the euphotic layer of the inner estuary under varying physlcal conditions On the basis of nutrient depletion exper~ments, the very strlking non-conservative behaviour of inorganic nutrients was explained by effective biological fixation of nutrients into planktonic blomass, followed by sedimentation For total nutrients, physico-chemical loss processes might also be important in the salinlty gradient prevailing in the inner estuary The theo~etical hmiting nutnent for planktonic production varied according to the physical state of the water mass, especially to vertical mixing conditions In general the inner estuary was P limited, while the open eastern Gulf was mainly N liinited In the outer estuary low mixed layer depth (MLD) favoured N limitation, while thick MLD (l e windy weather) favoured P limitation Thls indicates that reduction of both N and P load into the eastern Gulf would improve water quality in thls area However, effective N removal would probably induce the most extensive improvement in the trophic status of the entire Gulf of Finland

Section: Study Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nitrogen and phosphorus as production limiting factors in the estuarine waters of the eastern Gulf of Finland

Pitkänen¹,

Tamminen²

1995

“…Effects of winds are commonly reported, for example, in San Francisco Bay estuary (Cloern 1996), Chesapeake Bay estuary (Horrigan et al 1990), and in coastal oceans such as the one off the coast of Washington, USA (Dortch & Poste1 1989) and Dogger Bank in the North Sea (Riegman et al 1990). Blooms often occur in summer after wind events (Iverson et al 1974, Hitchcock et al 1987, Pitkanen et al 1993.…”

Section: Introductionmentioning

confidence: 99%

Importance of wind and river discharge in influencing nutrient dynamics and phytoplankton production in summer in the central Strait of Georgia

Yin¹,

Rh²,

Harrison³

et al. 1997

A cruise was conducted during August 6-14, 3 991 to investigate the d y n a m~c s of nutrients and phytoplankton pi-oduction in the central Strait of Georgld, British Columbia, Canada, dunng a period when strong stratification resulted In nitrogen-l~mited primary productivity. High resolution vertical profiles of salinity, temperature, fluorescence and nutrients (nitrate and phosphate) were taken daily along a transect. A wind event occurred on August 7 and a rapid increase in the Fraser River discharge took place from August 8 to 14. The wind event mixed the water column and nutrients increased at the same time. Phytoplankton responded to the incrcdscb in nutrients and a bloom occurred soon after the wind event. The rapid increase in river discharge caused the entrainment of nltrate in the estuanne plume and, a s a result, a subsurface maxlmum of chl a was developed. Our results clearly demonstrated that summer phytoplankton productivity in the central Strait of Georgia is fueled by a supply of nutrients from the nitracline through vertical mixing induced by the interaction of winds, rlver discharge and tidal cycles. Of these 3 factors, winds are the most variable and therefore a summer with frequent wind events could result in higher than normal productivity. The mechanism for t h~s is that part of the nitracline was maintained above the euphotic zone d u e to various physical processes in spite of the strong stratification, and therefore, nutrients were frequently available for phytoplankton uptake caused by across-pycnocline mixing due to w~n d , rlver dischdrge and tides.

“…The trend is in fact gen-198 Lehtiniemi & Gorokhova: Alien cladoceran affects native copepods eral for zooplankton biomass distribution in the Gulf (Telesh 2004), suggesting that both species maintain residency in the proximal part of the estuary. Several mechanisms could be responsible for this, including low salinity water (3 to 4 PSU) and low rate of water exchange (Pitkänen et al 1993), elevated concentrations of food available due to higher nutrient loading (Telesh 2004), and reproduction mode of these zooplankters, which is favored in estuarine shallow water conditions (both species carry their eggs/embryos until the release, and produce resting eggs). In the water column, C. pengoi is most abundant above the thermocline, although it also occurs in deeper waters (this study), while in E. affinis, the major part of the population is confined to the thermocline during daytime and migrates upwards to the surface at night (Vuorinen 1987).…”

mentioning

confidence: 99%

Predation of the introduced cladoceran Cercopagis pengoi on the native copepod Eurytemora affinis in the northern Baltic Sea

Lehtiniemi¹,

Gorokhova²

2008

We studied the potential of an introduced species, the predatory cladoceran Cercopagis pengoi, to influence native zooplankton populations in the Baltic Sea. Feeding rates (FRs) of different instars of C. pengoi on Eurytemora affinis, a dominant copepod species, were determined experimentally. The FRs of C. pengoi varied from 0.7 to 4.8 prey predator -1 d -1 and were significantly higher in older instars. Based on the experimental results and long-term zooplankton abundance data from the Gulf of Finland, we estimated the in situ predation rates. Our results imply that at maximum abundance, the C. pengoi population feeding in dense prey patches could consume as many as 10 5 E. affinis m -3 d -1. This could explain the observed drastic decrease in copepod abundances in the eastern Gulf of Finland, the region with the highest C. pengoi abundance after the expansion of this species. Such a decline may strengthen food competition between other zooplanktivores, i.e. planktivorous fish and mysids, feeding on the same copepod prey in regions where C. pengoi may reach high abundances. In the Gulf of Finland, especially in the eastern parts, a collapse of E. affinis, a key species in the pelagic system, would cause major changes in virtually all trophic levels, because the food web structure is simple with only a few species of zooplankton, planktivores, and piscivores. 362: 193-200, 2008 alterations in demographic structure of zooplankton communities (Benoît et al. 2002, Ojaveer et al. 2004, Litvinchuk & Telesh 2006 or using stable isotope analysis (Gorokhova et al. 2005). These studies suggest that C. pengoi feeds on small zooplankton (Laxson et al. 2003, Lehtiniemi & Lindén 2006 and may therefore have negative effects on these populations by direct predation (Benoît et al. 2002, Ojaveer et al. 2004, Witt et al. 2005. Accurate estimates of the predation rates are lacking, hampering the evaluation of the impact of this cladoceran on prey communities. KEY WORDS: Introduced species · Predation · Food web dynamics · Cercopagis pengoi · Eurytemora affinis Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerThe aim of this study was to investigate if and how Cercopagis pengoi may affect the population size of the calanoid copepod Eurytemora affinis Poppe through predation. We chose this copepod species because (1) it is one of the few dominant mesozooplankton species in the northern Baltic during the growing season (Viitasalo 1992), (2) it is a preferred prey for the dominant zooplanktivores, i.e. herring, sprat, and mysids (Flinkman et al. 1998, Peltonen et al. 2004, and (3) it has been suggested that its seasonal population development is influenced by C. pengoi predation (Ojaveer et al. 2004). To assay feeding rates (FRs) of C. pengoi on E. affinis, several feeding experiments were conducted to test for differences in consumption rates between: (1) smaller and larger C. pengoi preying on small and large copepods, (2) parthenogenic and gametogenic females of C. pengoi,...