The monthly mean temperatures in July, at 18 - 19.5 °C, were 2 – 3 K higher than the long-term reference values. Also the duration of sunshine, at 220 – 270 hours, exceeded the mean values by 10 – 25 %. Precipitation reached 20 – 90 mm, corresponding to 35 – 110 % of the reference values.
August, at mean temperatures between 18.5 and 20 °C, was 2 – 3 K too warm. Despite the typical autumn weather at the end of the month, August had 5 to 12 summer days, twice to three times the normal number. Rainfall, at 20 – 50 mm, was only 30 – 60 % of the long-term mean, and the 240 – 360 recorded
sunshine hours exceeded the mean values by 10 – 30 %.
Also in September, the mean temperatures were 1 K too high, at 15 – 16 °C. Because of prolonged dry spells, only 60 – 70 mm rain was recorded, which was about 80 – 90 % of the long-term mean. However, abundant local rains led to high surpluses in some areas. The recorded 200 to 230 sunshine hours clearly exceeded the long-term mean by 40 – 50 %.
In October, the temperature level decreased continuously and, at mean temperatures between 6.5 and 9.7 °C, the month was 2 – 3 K too cold. With local differences, monthly precipitation ranged from 50 to 100 mm, with mean values being reached or slightly exceeded or fallen short of. 130 – 160 hours of sunshine were recorded, which was 30 – 60 % above the long-term mean.
In November, temperatures fell more slowly and the monthly mean temperatures were 0.7 to 1.5 K above the long-term mean. At 35 – 55 mm of precipitation, only 40 – 65 % of normal rainfall was reached. The duration of sunshine was about normal, at 50 – 60 hours.
Also in December, the weather continued to be too mild for the season, and the monthly mean temperatures of 3.7 – 5.8 °C exceeded the long-term reference values by 1 – 2 K. On average, December had 6 frost days less than the long-term mean and precipitation, at 65 to 80 mm, was about 10 % above or below the monthly means. 50 to 65 hours of sunshine were recorded, which was 30 – 75 % above the mean values.
In June, the reference values were exceeded by 1.7 K, at a mean water temperature of 13.7 °C.
The mean temperature of surface water in July 2003 was 16.0 °C, which was 1.7 K above the climatological value. In August, the mean sea surface temperature rose to 17.5 °C, and was thus 2.5 K above the reference value. Also in September, the mean water temperature of 15.8 °C exceeded the climatological value by 2.1 K. In October, the water temperature of 12.9 °C still exceeded the reference values by 1.1 K. This trend continued in November with a mean SST of 10.5 °C, which was 0.9 K above the climatological value, and in December, when the mean SST of 9.1 °C still was 1.3 K too warm.
Due to the of the mild weather, no ice was reported in the North Sea at the end of 2003.
In late July/early August, oxygen conditions in the North Sea were still good, with only a few low or critical values (e.g. southeast of the Dogger Bank).
In the outer German Bight, very low oxygen levels (up to 3.2 mg/L) were measured in September in near bottom water, the lowest value which the BSH had found in this area since 1989, when weather conditions were comparable.
Coastal waters of Lower Saxony
In the second half of 2003, high concentrations of potentially toxic algae were not observed at any of the sampled stations throughout the period under review (early August – end of October).
During the first algae monitoring cruise of the season around 10 August, no unusual developments as compared to
same period last year were observed despite the exceptionally calm and extremely warm weather. Phytoplankton initially was dominated by diatoms (especially Pseudonitzschia sp.); they disappeared almost completely by the end of August and did not return until late September, with small numbers of individuals. The bioluminescent species Noctiluca miliaris was present in small numbers of individuals at almost all stations throughout the period under review, with an increasing trend observed briefly in the 39th week (22 - 28 September). The toxic dinoflagellate Dinophysis acuminata occurred only at two stations between late August and early September, with an uncritical number of individuals ranging from 100 indiv./L to 300 indiv./L. After that, it was not detectable at any of the stations. The microflagellate Chrysochromulina sp. was observed repeatedly at all stations, but was clearly in the non-critical range, commonly 100 – 3300 indiv./L, up to 8600 indiv./L in early August. The foam-forming alga Phaeocystis globosa was observed only in a few places from late August, with an increasing tendency in the 39th week (22 - 28 September). The ciliate Myrionecta rubrum was observed at two stations at the end of August, with 800 and 400 indiv./L respectively, after which numbers at all stations dropped to about 100 – 200 indiv./L.
From 8 October 2003, phytoplankton was clearly in decline, reflecting the typical seasonal development.
As in 2002, the first increase in the abundance of phytoplankton was observed in early April, but at lower water
temperatures than last year. After a maximum with a conspicuous abundance of Odontella aurita (in 2002: Thalassiosira rotula), stocks continued at a low level until mid-June. This was followed by a brief maximum dominated by some diatom species, with a further increase in July which was dominated by Ceratium species. In mid-August, stocks decreased sharply and remained low until the end of September. Water temperatures from mid-July to early September exceeded 18 °C.
Phytoplankton was very species-rich, with Rhizosolenia shrubsolei clearly dominant at the end of June, and Ceratium longipes and/or Ceratium horridum in July.
Dinophysis species were observed in May and from late July to late September (maximum of Dinophysis acuminata on
19 August: 1840 cells/ dm³). Larger numbers of Prorocentrum micans and Prorocentrum redfieldii occurred in August and September (with maxima on 9 September, at 4400 and 26600 cells/ dm³ respectively). Phaeocystis spec. occurred only in small quantities. Moderate numbers of Noctiluca scintillans were observed from early June to the end of July, and the autotrophic ciliate Myrionecta rubrum was not particulary frequent this year.
North Sylt Wadden Sea
(2003 Annual Report; J. van Beusekom, H. Halliger, M. Elbrächter)
Weekly plankton monitoring is carried out as part of the ecological monitoring series in the North Sylt Wadden Sea, which also includes analyses of dissolved and particular nutrients. The most important results of the analyses are presented in the 2003 Annual Report:
Water temperatures were relatively low this winter. In early January and mid-February, they dropped below 0 °C. From late February, temperatures rose steadily and reached their annual maximum of 22 - 23 °C in mid-August. By the end of December, water temperatures had dropped to 4 °C.
Winter concentrations of nutrients reached the following maxima:
PO4: 1.2 µM; Si: 35 – 37 µM; NO3: 40 – 50 µM; NO2: ~1.4 µM; NH4: 7 – 10 µM. During the spring bloom, NH4, Si and PO4 decreased to concentrations below 1 µM. NO3 values did not drop below 2 µM until early June, with values below 0.1 µM reached in mid-July. Nutrient concentrations in summer were low: Si: ~0.5 µM; NO3: <1 µM; NO2: <0.1 µM; NH4: 0 - 4 µM. The seasonal cycle of phosphate was slightly different: from mid-May, concentrations rose from about 0.1 µM to about 1 µM in mid-August, after which they decreased again. The summer maximum was probably due to the high water temperatures.
The phytoplankton season ended late this year, in early October when a marked nutrient increase took place. NH4 and NO2 reached their maxima in December (NH4: ~11 µM; NO2: 1.8 µM). NO3 and Si values increased steadily, reaching 13 µM NO3 and 20 µM Si at the end of December.
The seasonal cycle of phytoplankton biomass showed only a single outstanding occurrence: the spring bloom in mid-March, with a maximum of 48 µg chlorophyll/l. The biomass decreased steadily throughout the summer and reached about 3 µg Chl/l in August. At the end of April and in early June, two small blooms occurred (up to 14 and 11 µg Chl/l, respectively).
Figure 1: Seasonal cycle of chlorophyll in the North Sylt Wadden Sea
The phytoplankton spring bloom this year developed relatively early, with a maximum around 20 March (see Figure 1). It was dominated by the diatoms Odontella aurita, Porosira glacialis and, toward the end of the bloom,
Skeletonema costatum. The cause of the early bloom was primarily the good light conditions which were due both to higher light intensity (easterly winds and clear weather) and lower water turbidity. The high phytoplankton biomasses may have been due to the prevailing low temperatures (about 2 °C) and, consequently, relatively low grazing pressure. Of course, also high nutrient concentrations are essential for the development of strong blooms.
The Phaeocystis bloom following that of diatoms was not very clearly distinguishable this year. In June, the diatoms Guinardia delicatula and Cerataulina pelagica were dominant. From mid-June to early September, especially Rhizosolenia imbricata was the prevailing phytoplankton species. The frequent occurrence of the diatom Odontella sinensis from late August to early November was particularly noteworthy.
The most frequently observed algae this summer (May – September) were the diatoms Odontella rhombus, Odontella sinensis, Odontella granulata, Biddulphia alternans, Bellerochea malleus, Rhizosolenia imbricata,
Guinardia delicatula, Actinoptychus senarius, Subsilicea fragilarioides, the dinoflagellate Protoperidinium achromaticum and the flagellate Phaeocystis globosa.
Major occurrences this year were the early spring bloom with a high biomass, the prolonged dominance of Rhizosolenia imbricata, and the autumn dominance of Odontella sinensis.
Coastal waters of Schleswig-Holstein
In early July, the distribution of microalgae was rather heterogeneous. At stations farther from the coast, near Helgoland and west of List/Sylt, cell numbers of the autotrophic cilate Myrionecta rubra rose continuously, with the dinoflagellate species spectrum increasing at the end of July and diatoms still the dominant species. Northwest of Sylt, Rhizosolenia imbricata was dominant, while Chaetoceros species prevailed in the south. Diatoms were still dominant in August. Dinoflagellates were rarely observed, except in the vicinity of Helgoland. In September, the diatom spectrum again diversified clearly.
Investigations in July/August of groundfish/fish stocks in the North Sea, with a focus on the German Bight, showed a further biomass decrease. On the basis of 2003 catches, the 2003 year classes of cod, haddock, and whiting did not give rise to much hope, as in the preceding year. This was confirmed at the autumn meeting of the Advisory Committee for Fisheries Management (ACFM) of the International Council for the Exploration of the Sea (ICES) in October. In the North Sea, the condition of cod, plaice, and sole stocks continued to be poor, with a low spawning stock biomass. Only North Sea saithe stocks were in good condition. Numerous 2003 fish stocks had to be classified as "outside safe biological limits", i.e. they can no longer be exploited optimally by fisheries, or not at all. Therefore, a number of recommendations were made regarding management measures and the rebuilding of several stocks.
Examinations of dab for macroscopic diseases largely confirmed last year's findings.
Sea grass and green algae in the Wadden Sea
In the summer of 2003, green algae in the Wadden Sea of the Schleswig-Holstein North Sea coast covered only about half the long-term average area, related to the period after 1994 (i.e. after the mass development in the early 1990s). Nevertheless, the values were still higher than before the 1980s.
Sea grass stocks in the North Frisian Wadden Sea in 2003 continued to be stable and in good condition. Sea grass meadows in the West and East Frisian Wadden Sea as well as between the Jade and Eider rivers had not yet recovered from the decline
during the past decades.
At mean temperatures between 18 and 19.5 °C, July was 2 K too warm, and the number of summer days ranging from 1 (Rügen) to 12 (Kiel) was clearly higher than normal. Precipitation ranged from 25 mm (70 % below mean value) to 110 mm (50 % above mean value). At 230 to 275 hours of sunshine, the monthly mean values were exceeded by 10 %.
August, at mean temperatures of about 19 °C, was 1.5 to 2.5 K too warm. The dry spell of the preceding month continued, with only 2 – 6 days of rain. Only 30 – 90 % of the monthly mean precipitation was reached, depending on the region. The month was very sunny, and the recorded 245 – 272 hours of sunshine were 10 – 20 % above the long-term mean.
September still had typical summer weather with mean temperatures of 15 – 16 °C, which was 1 – 2 K above the long-term mean. With some local exceptions, about 40 to 50 mm rain, corresponding to 80 – 90 % of the long-term mean, was recorded. At 200 – 225 hours of sunshine, the average was exceeded by 25 – 40 %.
A sharp temperature drop occurred in October which, at mean temperatures between 6 and 8 °C, was 2 – 3 K too cold. 9 frost days were recorded instead of the normal 2 frost days. The dry spell came to an end, with precipitation of 40 – 60 mm exceeding the long-term mean by up to 40 %. Nevertheless, the 130 – 150 hours of sunshine in October exceeded the long-term reference values by 20 – 40 %.
After the cold month of October with monthly mean temperatures of 6 – 7 °C, November was 1.5 – 2.0 K too warm. With rainfalls of 25 to 40 mm, there was a deficit of 30 – 50 %. Up to 10 % more hours of sunshine than normal were recorded.
December, too, was 1.5 to 2 K too mild, at monthly mean temperatures between 3 and 4.3 °C, and there were about 6 frost days less than normal. Precipitation at the Baltic Sea coasts, at about 40 mm and 10 – 20 % below normal, was clearly lower than at the North Sea. The duration of sunshine exceeded the long-term means by about 30 – 60 %.
In July 2003, the mean temperatures of 17.7 °C to 18.9 °C measured in the Baltic Sea coastal waters of Schleswig-Holstein and Mecklenburg-Vorpommern were about 1 K above the reference values. Also the August temperatures, which ranged from 18.4 °C to 20.6 °C, exceeded the reference values by about 1 K. The water temperatures in September (15.9 – 16.7 °C) and October (11.3 – 11.5 °C) corresponded to the long-term means. In November, the mean temperatures from 7.0 to 8.4 °C were again 1 K too high, and the same applies to December, when the mean temperatures still ranged from 4.4 °C to 5.7 °C.
The balanced curve of water levels in July 2003 had its lowest value of 471 cm on 4 July and its maximum of 59 cm above MSL on 1 July, both in Flensburg. The monthly means exceeded the reference values by up to 8 cm.
In August, the lowest water level of 426 cm was measured in Flensburg, on 15 August, and the maximum of 583 cm in Wismar, on 30 August. The monthly means exceeded the reference values by up to 6 cm.
The September peak value of 565 cm was recorded in Lübeck on 1 September, while that month's minimum level of 442 cm was measured in Flensburg on 23 September. On the whole, the monthly means were up to 5 cm above the reference series.
The monthly means in October were up to 19 cm above the reference values.
The maximum level of 598 cm was measured in Flensburg on 20 October, and the lowest level of 417 cm on 28 October, also in Flensburg.
Also in November, both the maximum value of 569 cm (9 Nov.) and the minimum value of 455 cm (19 November) were measured in Flensburg. The monthly means were 3 – 7 cm lower than the reference values.
Normal monthly means were reached in December despite the storm surge of 6 December, which raised the water level to a peak value of 666 cm in Wismar. Also the lowest level of 390 cm was measured in Wismar, on 24 December.
On the first days of the last November week, ice formation began on the North coast of the Bay of Bothnia, two weeks later than the long-term mean. From mid-December, navigation was restricted in some Finnish harbours, and the first ice report was issued on 15 December. Despite a marked increase in ice coverage by the end of December 2003, ice conditions
in the northern Baltic lagged about two and a half weeks behind the normal end-of-the-year ice development.
In the outer coastal waters of Mecklenburg-Vorpommern, phosphate concentrations increased again in July (0.04 to 0.52 µmol/L) and reached values from <0.02 – 1.13 µmol/L in September. Nitrate concentrations in August ranged from <0.10 – 0.88 µmol/L, and in September from 0.17 – 1.30 µmol/L. In oxygen depleted areas, ammonia released by anoxic sediments was found in the bottom water.
In the inner coastal waters of Mecklenburg-Vorpommern, phosphate concentrations in July were about two to three times higher than in June (<0.02 – 3.36 µmol/L) and increased somewhat in September (0.25 – 4.79 µmol/L). Nitrate levels in July were slightly lower than the month before (<0.01 – 1.20 µmol/L) and reached values up to 1.50 µmol/L in September.
In early July, oxygen levels in the western Baltic were still good, and even in the Flensburg Fjord oxygen
levels were as high as 3.8 mg/L. In September, satisfactory oxygen conditions prevailed in the deep water between the central area of Kiel Bight and the eastern part of Fehmarn Belt (between 3.5 and 6.4 mg O2/L in deep water). By contrast, substantially lower levels were measured in the Mecklenburg, Lübeck, and Neustadt Bays, at values between 0.5 and 2.8 mg/L. In the Flensburg Fjord and Gelting Bay, oxygen levels dropped to less than 1 mg/L.
Monitoring in the area between Kiel Bight and the northern Gotland Basin in late July/early August showed anoxic conditions in the deep water of the western Gotland Sea, in the Karlsö, Landsort, and Faroe Deeps. The situation continued unchanged until October, while the deep water at all other stations was free of hydrogen sulphide.
In the outer coastal waters of Mecklenburg-Vorpommern, the surface water in July had very good oxygen levels, and the bottom water good oxygen levels. In early August, the bottom water in the Bay of Lübeck and in the Mecklenburg and Pomeranian Bights had very low levels between 0.4 and 3 mg/L. This situation improved clearly at the end of the month.
In the inner coastal waters of Mecklenburg-Vorpommern, the surface water in July was slightly oversaturated, and the bottom water only had some sporadic local oxygen deficits. Also in August, oxygen deficiencies occurred only locally.
In the Pomeranian Bight and seaward of the Oder estuary, an exceptionally high oxygen deficit (0.5 to 1.5 mg/L) was found in the bottom water. The situation continued until stronger winds set in.
Baltic coast of Schleswig-Holstein
When sampling started in early June, diatoms in the Flensburg and Kiel Fjords had already increased strongly and were forming first algal blooms. In the other areas off Heiligenhafen and in the Bay of Lübeck, relatively little plankton was observed. Filamentous blue-green algae occurred only in the outer Bay of Lübeck. The situation continued largely unchanged until the end of June.
From early July, the species spectrum – especially that of diatoms – began to change. Proboscia alata was ubiquitous, but dinoflagellates were still rare. In the inner parts of the Flensburg and Kiel Fjords, a flagellate bloom was observed in addition to the existing diatom bloom (Skeletonema costatum).
In early August, masses of algae (filamentous blue-green algae) were observed increasingly in the coastal waters of Heiligenhafen, Fehmarn Sound and Bay of Lübeck. In the middle of the month, filamentous blue-green algae were also observed in the area of Kiel and in the Flensburg Fjord. Stronger winds at the end of the month dispersed the blue-green algae. Phytoplankton decreased markedly in all areas, and filamentous blue-green algae were hardly observed any more.
In September, no special observations were reported, the species spectrum was rather homogenous throughout the area, and diatoms increased again.
Monitoring station "Seebrücke Heiligendamm"
The phytoplankton biomass was small until mid-February. At the end of February, there was an explosive growth of diatoms, with the Skeletonema costatum bloom continuing until mid-March. This was followed by the development of Cryptophyceae (especially Teleaulax sp.). The usual replacement of diatoms by large, athecate dinoflagellates was very weak in 2003. In late April, mainly Dictyocha speculum and Pseudopedinella sp. were found. A phase of very low phytoplankton biomass dominated by Cryptophyceae (Hemiselmis, Teleaulax, Plagioselmis) continued until the end of May. After a moderate increase in biomass in mid-June, Ceratium tripos for the first time became clearly noticeable. The typical summer bloom of diatoms began in late June, represented by Guinardia flaccida, which reached a maximum of 1398 mg/L in early July and remained dominant until the end of July.
At the end of July, nitrogen fixing cyanobacteria (Nodularia spumigena, Aphanizomenon sp.) occurred spontaneously at the monitoring station, so that warnings had to be issued for several bathing beaches. By 11 August, the bloom had disappeared again. Wind events at the end of August led to a strong decrease of phytoplankton biomass. Rapid changes in the species composition occurred in September (Ceratium tripos, at 437 mg/L in early September, was replaced by Dactyliosolen fragilissimus, at 444 mg/L, by mid-September), probably due to the passage of different water bodies having different phytoplankton stocks. At the end of September, the diatom Dactyliosolen fragilissimus was replaced by the typical autumn diatom of the Baltic Proper, Coscinodiscus granii. By the end of November, a stable bloom of Ceratium tripos and C. fusus had developed, accompanied by the diatoms Cerataulina pelagica, Thalassiosira baltica, Th. anguste-lineata and Th. eccentrica as well as the Cryptophyceae Teleaulax sp. and Mesodinium rubrum. Chlorophyll concentrations in mid-December indicated a decline of the algal bloom.
Figure 2: Chlorophyll a concentration and composition of phytoplankton biomass (wet weight) from 7.1. to 17.12.2003 at
the coastal station Heiligendamm (surface water).
Outer coastal waters of Mecklenburg-Vorpommern
In July, both the chlorophyll-a concentrations and biovolumes in the entire sea area were below the long-term means. The long dry spell with low nutrient input to the coastal waters has been discussed as a possible cause. The species spectrum had changed only negligibly from June. Almost along the entire coast, the cryptoflagellate Plagioselmis prolonga reached cell concentrations between 175,000 and 856,000.
In August, chlorophyll-a values at nearly the entire outer coast were clearly below the long-term monthly mean. The phytoplankton biovolume varied between 0.3 mm³/litre (northwest of Hiddensee) and 1.7 mm³/litre (east of Sassnitz). The phytoplankton species composition at the end of August was typical of the season.
Chlorophyll-a values in September reached up to 90 % of the long-term mean. As a typical feature of late summer, Ceratium and Prorocentrum dinoflagellates were dominant in the western coastal areas of the Baltic.
Inner coastal waters of Mecklenburg-Vorpommern
In July, chlorophyll-a levels were very high locally (Wismar Bight, Unterwarnow), while concentrations at other stations were below normal or even extremely low (e.g. Kubitzer Bodden, at only 2.0 µg/L). Also the biovolumes were far below the long-term means at some stations. As regards phytoplankton, very large volumes of µ-algae were measured in the Strelasund and Greifswalder Bodden (between 122 and 235 million cells/litre). In the waters of Kleines Haff, the potentially toxic blue-green alga Microcystis aeruginosa/flosaquae reached concentrations of up to 74 million cells/litre. In the Unterwarnow, a Skeletonema costatum diatom bloom was observed.
Chlorophyll-a measurements in August showed values clearly above the long-term monthly mean (LMM) in some areas, e.g. the Saaler Bodden, at 123 µg/L (or 173 % of LMM), and in other areas extremely low levels, e.g. 5.2 µg/L (9 % of LMM) in the Barther Bodden.
The measured biovolumes ranged from >0.1 mm³/litre in the Wismar Bight to 8.7 mm³/litre in the Strelasund, where a peak value was reached in the long-term data series for August. Large concentrations of the potentially toxic dinoflagellates Prorocentrum minimum and P. micans contributed to this development. In the waters of Stettiner Haff, species of the potentially toxic blue-green algae genus Microcystis prevailed, but their biovolume was relatively small. That was also true for the blue-green alga Aphanizomenon "balticum".
In September, the phytoplankton development was normal, and the biovolumes of the characteristic species decreased strongly, especially in the Stettiner Haff, Strelasund, and Greifswalder Bodden.
Surprisingly, a major accumulation of the filamentous blue-green alga Aphanizomenon "balticum" was observed in
the Stettiner Haff in November, an unprecedented occurrence in that season.
The rate of Baltic cod affected by acute skin diseases, which was determined in August, varied between 1.8 % and 10.4 % in four areas investigated and was thus on the same order as last year.
In September, the biological diversity and stock situation of the main fish species in the Arkona Sea was investigated. Flounder catches confirmed an above-average 2001 year class, while plaice and turbot catches were below average. Also the precarious situation of cod stocks was confirmed. Positive trends were expected for pike-perch and perch.
The outcome of the larval surveys in the Greifswalder Bodden and Strelasund (the most important spawning ground of the so-called "Rügen herring") in October 2003 indicated a strong 2003 year class of herring in the western Baltic, Kattegat, and Skagerrak.
In November/December, surveys confirmed the poor condition of the adult cod stock in the southwestern Baltic. Good catches of age group 0, the 2003 year class of cod, have raised hopes of a recovery of stocks.