Temperature-related timing of the spring bloom and match between phytoplankton and zooplankton

Figures & data

Table I. Description of data on phytoplankton used in this study with information on collection year, sampling station, methods, references and the time of ice retreat.

Year	Station	Unit	Sampling depth	Sampling frequency	Ice retreat	Reference
1979	XII	PP	Whole water column	Biweekly	Mid-April	Forsskåhl et al. (1982)
1980	P3	mg C m^−2	0–10 m integrated samples	2–3 times month^−1	Early April	Kuparinen et al. (1984)
1983	XII	Chl a	0–10 m	1–3 times month^−1	Mid-April	Kivi (1986)
1984	XII	Chl a	0.2–2 m	Every second or third day	Mid-April	Niemi and Åström (1987)
1985	XII	Chl a	0–5 m	7 times during the vernal bloom	late April	Lignell (1990)
1988	P3	PP	0.2, 1, 2.5, 5, 7, 9 m	Weekly	early April	Lignell et at. (1993)
1992	XII	Chl a	0, 2.5, 5, 7.5, 10 m	Weekly	no ice	Viitasalo et al. (1999)
2000	XII	Chl a	0–10 m integrated samples	Weekly	no ice	Tamelander and Heiskanen (2004)
2015	XII	Chl a	1 m	Weekly	no ice	Elovaara et al. (2020)
2016	XII	Chl a	0, 2, 4, 7, 15 m	Weekly	January	Elovaara et al. 2020
2018	XII	Chl a	0.5, 5, 10, 15 m	Weekly	Mid-April	Almén and Tamelander (unpub.)

Notes: Data were gathered from the Tvärminne area, Southwestern Finland, from sampling station XII (Storfjärden) and P3 (Storgadden). Detailed descriptions of the methods can be found in the original publications.

Table II. Description of data on zooplankton used in this study with information on collection year, sampling station, methods and references.

Year	Station	Unit	Sampling depth and net	Sampling frequency	Reference
1979	XII	C m^−3	Vertical net 25–0 m, 150 µm	Biweekly	Forsskåhl et al. (1982)
1980	P3	C m^−2	Vertical net 25–0 m, 150 µm	2–3 times month ^−1	Kuparinen et al. (1984)
1983	XII	Ind m^−3	Vertical net 25–0 m, 150 µm	Every tenth day	Viitasalo et al. (1995)
1984	XII	Ind m^−3	Vertical net 25–0 m, 150 µm	Every tenth day	Viitasalo et al. (1995)
1988	P3	C m^−2	Vertical net 10–0 m, unknown net	Weekly	Lignell et al. (1993)
1992	XII	C m^−2, Ind m^−2	Vertical net 25–0 m, 100 µm	Weekly	Koski et al. (1999)
2016	XII	Ind m^−3	Vertical net 25–0 m, 100 µm	Weekly	Tamelander (unpubl.)

Note: Data were gathered from the Tvärminne area, from sampling station XII (Storfjärden) and P3 (Storgadden).

Figure 1. Temperature and time (day of year) of the spring bloom peak at Tvärminne Storfjärden. Temperature is the average seawater temperature between 0 and 10 m in April (temperature for 1997 is missing).

Figure 2. Annual time series of Chlorophyll a in the Tvärminne region, Southwestern Finland, based on data retrieved from publications listed in Table I.

Figure 3. Time integrated biomass for spring and summer blooms in the Tvärminne area. Bloom conditions were defined as Chl a concentration exceeding 3 μg l⁻¹. The spring bloom was defined as the period starting in March when Chl a uninterruptedly exceeded the threshold, i.e. one peak. The summer bloom included multiple peaks between June and October after which Chl a did not exceed the threshold. The biomasses of these peaks were pooled into one summer bloom. In 1983 Chl a did not exceed the threshold after the spring bloom. (* indicates missing summer data).

Figure 4. Time lag (days) between phytoplankton and zooplankton biomass peaks against average seawater temperature in April in Tvärminne (●Storfjärden and ◆Storgadden).

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