Although July was wet and partly cold, the monthly mean temperature of 16 °C was in the range of long-term means because warm summer weather set in at the end of the month due to high pressure influence. On the whole, the monthly precipitation of 169 mm was more than twice the normal rain volume. Below average monthly precipitation was only recorded in a few places. The duration of sunshine in July was up to 20 %
below average, at 170 to 223 hours.
In August, at monthly mean temperatures between 18.5 and 19.5 °C, temperatures were 2 - 2.5 K higher than normal due to hot weather in the first ten days of the month. Nevertheless, this month was mostly too wet. At 80 - 125 mm rainfall, up to 170 % of the monthly means was reached because the frontal systems of decaying hurricanes as well as low-pressure zones began crossing the coastal areas from 12 August. At 190 to 255 hours of sunshine, the mean values were exceeded by up to 16 %.
September, at monthly mean temperatures of 15 - 16 °C, was 1 K too warm, with temperatures that were very high in the first ten days of the month but dropped to autumnal levels in the course of the second decade. A total of 80 - 130 mm rain fell in September, with mean values exceeded by 20 % (coast of North Friesland) up to 50 % (coast of Lower Saxony). The duration of sunshine, at 170 - 200 hours, was 20 - 40 % above normal.
October, at monthly mean temperatures between 10 and 12 °C, was slightly too warm. It was mostly too dry. Rainfall in northern Lower Saxony, at 40 - 50 mm, was up to 40 % below normal; in other areas 65 - 80 mm was recorded. This month's 100 - 120 hours of sunshine was 10 % above average.
Also November, at monthly mean temperatures of 6 - 7 °C, was 0.5 - 1 K too warm. With maximally three frost days, the long-term mean was not reached. Precipitation, at 60 - 70 mm, was mostly up to 30 % below normal, except on the coast of Lower Saxony where up to 50 % more rain than normal was recorded, at 80 - 110 mm. 50 - 70 hours of sunshine were recorded, which was up to 10 % higher than normal.
December was too mild, at monthly mean temperatures between 3 and 6 °C, which was 1 - 2 K above the mean values. The number of frost days (1 - 9) was 3 - 5 days below normal. Precipitation at the coasts of Lower-Saxony, at 40 - 50 mm, reached about 60 % of normal, and about 90 % of normal, at 60 - 70 mm, in North Friesland. 40 - 50 hours of sunshine were recorded, which was 20 % above the long-term mean.
The monthly means of sea surface temperature (SST) were compared with the so-called climatological value (1971 - 1993), and the ranking among the highest SSTmonthly means since 1971 is given in brackets.
The monthly mean temperature in July, at 14.6 °C, was 0.3 K above the climatological value (15th rank). August brought a mean temperature of 17.1 °C, which was 2.1 K above the climatological value (5th rank). The monthly mean temperature of 15.2 °C in September was 1.5 K above the climatological value (4th rank). The monthly mean of 12.4 °C in October was 0.6 K above the
climatological value (11th rank). November, with a monthly mean that was 0.9 K above the climatological mean, ranked 6th. In December, the mean sea surface temperature was 9 °C, which was 1.2 K higher than the climatological mean value (1st rank).
By the end of 2004, the ice winter of 2004/2005 had not led to occurrences of ice.
Coast of Lower Saxony
Sampling along the coast of East Friesland to determine the abundance of bloom forming and toxic algae was performed by Niedersächsisches Landesamt für Ökologie (NLÖ, Lower Saxony State Agency for Ecology) at seven near-shore stations. The first samples were collected in early August. An analysis of the entire sampling period from early August to mid-October showed that toxic or HAB (harmful algal bloom) forming phytoplankton species never occurred in any critical quantities. The abundance of such species was generally very low during this year.
Some species were not observed at all, for example the dinoflagellates Dinophysis acuta, D. acuminata, and D. norvegica, which are toxic at low concentrations. Very low concentrations of Dinophysis rotunda were found at a single sampling station in early August, but the species was no longer present in samples taken in mid- and late August. It was observed once more at one station in mid-September at a concentration of 100 individuals/L.
The bioluminescent alga Noctiluca scintillans, a heterotrophic dinoflagellate which does not produce any toxins, occurred at all stations in early August, with maximum cell counts of 180 cells/L, but decreased in abundance until the end of August, when samples at some of the stations were completely free of cells. From mid-September, samples again showed densities of up to 22 cells/L. In mid-October, cell counts again showed slightly higher densities of max. 61 individuals/L.
In mid-October, also Ceratium furca (dinoflagellate) was more abundant.
The foam-forming alga Phaeocystis globosa, which belongs to the class of Prymnesiophyceae, was found at three stations in early August in small numbers of colonies (max. 18 colonies/L), after which its abundance decreased continuously. It recurred only once, in mid-September, at all stations with maximally 33 colonies.
In early August, nanoflagellates of the genus Chrysochromulina (Prymnesiophyceae) and the Raphidophyceae species Chattonella marina and Fibrocapsa japonica, all three of which produce toxins, were not found at any of the stations. In mid-August, Chrysochromulina cell counts showed 5,800 to 11,700 cells/L at some of the stations, but none of the toxic species C. polylepis and C. leadbeateri from the IOC list (IOC = Intergovernmental Oceanographic Commission). At the end of August, population densities still reached 7,800 cells/L, after which cells of these species were no longer present until the end of the sampling period.
Negligible concentrations of Chattonella marina were found at a single station in mid-August but, like Fibrocapsa japonica, the species was not observed afterwards at any of the stations.
Diatoms of the potentially toxic genus Pseudo-nitzschia, at cell concentrations of up to 18,200 cells/L, were found in early August, increasing to 42,100 cells/L by mid-August. Their abundance then decreased to 2,400 cells/L by the end of the month, rising again to a maximum abundance of 6,200 cells/L in mid-September. Between the end of September and the last sampling date in mid-October, maximally 2,900 and 2,700 cells/L, respectively, were found, with local occurrences of very small numbers of individuals or the complete absence of cells.
Low population densities of the ciliate Myrionecta rubra, which is capable of photosynthesis due to the presence of endosymbiontic algae, were found only in early August, at three stations.
Throughout the sampling period, diatoms were dominant among the non-toxic and non-dangerous algae of the relatively species-rich phytoplankton. Frequently found species were: Odontella sinensis, Lithodesmium undulatum, Thalassiosira spp., Chaetoceros socialis, Chaetoceros spp., Eucampia zodiacus, Rhizosolenia spp., Biddulphia alternans, Coscinodiscus wailesii, C. granii, and Guinardia flaccida.
Helgoland Roads (synopsis 1st and 2nd half of the year)
In March, after low carbon values in winter, a carbon content of 17 µg/dm³ was measured due to the presence of the diatom Thalassionema nitzschoides.
In the course of April, phytoplankton stocks increased as in the preceding year, from 7 to 63 µg C/dm³. The dominant species were diatoms of the genus Thalassiosira as well as Thalassionema nitzschioides, Rhizosolenia setigera, and Guinardia delicatula.
In May, stocks increased to 125 - 216 µg C/dm³. The dominant species among diatoms, which decreased toward the end of the month, was Guinardia delicatula, with a maximum of 43 µg C/dm³ on 11 May. Also the
Haptophycea Phaeocystis globosa was abundant, which also had its maximum of 157 µg C/dm³ on 11 May.
In early June, phytoplankton decreased in abundance, increasing again from mid-June. Values ranged between 15 µg C/dm³ on 1 June and 71 µg C/dm³ on 22 June. Besides diatoms (dominant species: Guinardia delicatula with a maximum of 50 µg C/dm³ on 22 June), also Phaeocystis globosa was present until the middle of the month (maximum of 12 µg C/dm³ on 8 June), and a relatively large population of small naked flagellates of about 8 µg C/dm³ and, at the end of June, the autotrophic ciliate Myrionecta rubra (maximum of 6 µg C/dm³ on 22 June) were observed as well.
In July, phytoplankton initially decreased from 45 µg C/dm³ on 6 July to 18 µg C/dm³ on 13 July, after which the abundance increased up to 145 µg C/dm³ by the end of the month. The dominant diatoms were initially Guinardia delicatula (maximum on 6 July, at 27 µg C/dm³), followed by Guinardia striata (62 µg C/dm³ on 20 July) and, on 27 July, Guinardia striata (38 µg C/dm³) and Thalassiosira rotula (40 µg C/dm³). On 20 July, also Phaeocystis globosa (10 µg C/dm³) and many small naked flagellates (10 µg C/dm³) were observed. The abundance of Ceratium fusus peaked on 20 July, at 9 µg C/dm³. Myrionecta rubra ranged between 7 and 10 µg C/dm³ in July.
In August, the phytoplankton biomass decreased from an initially high level of 170 µg C/dm³ to 9 µg C/dm³ at the end of the month. On 3 August, the diatoms Detonula pumila (= Schroederella delicatula), at 43 µg C/dm³, Chaetoceros socialis (26 µg C/dm³), and Guinardia striata (6 µg C/dm³) were the dominant species, followed later by Guinardia delicatula
(5 µg C/dm³ on 10 Aug.) and Bacteriastrum hyalinum (4 µg C/dm³ on 17 August). Flagellates, too, were rather abundant on 3 August: small naked flagellates reached 8 µg C/dm³, and Ceratium fusus 10 µg C/dm³. Myrionecta rubra reached its highest population density of the year 2004 on 10 and 17 August, at 23 and 22 µg C/dm³, respectively.
In September, phytoplankton was species-rich without any particularly dominant species. Its biomass ranged from
34 µg C/dm³ (on 7 and 22 September) to 15 µg C/dm³ (on 28 September). Flagellates were composed of many small naked species (4 µg C/dm³) at the end of the month. Ceratium furca still was relatively abundant, at C values between 2 and 11 µg C/dm³ (on 22 September).
At the beginning of October, the phytoplankton biomass was low, from 13 to 15 µg C/dm³.
Comparison of the abundance at Helgoland Roads with the 2003 data
In April 2004, the abundance of diatoms was lower than in 2003, whereas in May 2004 there were more diatoms and, particularly, more phytoplankton because of Phaeocystis, which was absent in 2003. In June 2003, more phytoplankton was found than in 2004 due to abundant diatoms, and in July 2003 due to a mass development of Ceratium spec.. The abundance of phytoplankton in August 2004 was slightly higher than in 2003, which was attributable to more Myrionecta rubra than in 2003. In September, plankton was about equally abundant in both years.
North Sylt Wadden Sea
After a steady decrease in the phytoplankton biomass to about 3 µg Chl/L during early summer, a small bloom (up to 7 µg Chl/L occurred in early July. Until mid-July, Phaeocystis was observed regularly. In early July, the diatom Rhizosolenia imbricata was abundant, in late July Guinardia striata.
Rather frequently observed algal species during this summer (May to September) were the diatoms
Actinoptychus senarius, Cylindrotheca closterium, Odontella granulata, Odontella rhombus, Odontella regia, Odontella sinensis, Brockmaniella brockmannii, Lithodesmium undulatum, Delphineis surirella, Skeletonema costatum, Eunotogramma dubium, Chaetoceros densus, as well as the flagellates Phaeocystis globosa, Hemistasia phaeocysticola, and Noctiluca scintillans.
Potentially toxic algae (Alexandrium, Dinophysis, Chattonella, Chrysochromulina, Pseudo-nitzschia) were observed several times.
Until mid-September, chlorophyll values were below 5 µg/L. In autumn, as usual, a very species-rich diatom phytoplankton was observed. At the end of September and in late November, small blooms with biomasses of up to 9 µg/L were observed. Odontella sinensis was rather frequent at the end of October.
Outstanding occurrences in this year were the relatively late and rather weak spring bloom in mid-April followed by a long and intensive bloom of Phaeocystis in mid-May, and the early onset of the seasonal nutrient increase in autumn.
The annual cycle of the phytoplankton biomass is shown in Figure 1.
Figure 1: Annual cycle of phytoplankton biomass in 2004
Schleswig-Holstein coastal waters
In July, the number of summer species still was slightly too low, though with an upward trend. Diatoms showed a higher diversity of species and higher cell counts. Guinardia flaccida, G. delicatula, G. striata, and Rhizosolenia imbricata occurred everywhere. The occurrence of other species differed locally. Dinoflagellates were still below normal.
At the end of July/beginning of August, seasonal "red tides" occurred in the waters around Helgoland and southwest of Eiderstedt, caused by the dinoflagellate Noctiluca scintillans and the autotrophic ciliate Myrionecta rubra. In the southern part of the North Sea coastal waters of Schleswig-Holstein, especially diatoms showed a large species diversity. Cell counts of the dinoflagellate Heterocapsa rotundata were high. In the northern part, the species diversity was markedly lower, showing a conspicuously low proportion of dinoflagellates and, in some areas, an increasing abundance of the foam-producting alga Phaeocystis globosa (Prymnesiophyceae). By the end of August, phytoplankton had decreased strongly, with diatoms still most abundant and dinoflagellates occurring only sporadically. The transition to autumn plankton species in 2004 was not gradual but characterised by a breakdown in the cell counts and species diversity of phytoplankton.
Surveys conducted in the North Sea and Baltic Sea to determine the incidence of viral and bacterial skin diseases and liver tumours in dab, flounder, and cod confirmed the regional differences observed in the past years. On the whole, a lower incidence than in earlier years was found, and particularly skin ulcers in cod in the western Baltic were less frequent.
Although fish stocks have not shown a decrease in total biomass in the North Sea during the past two decades, the 2004 year classes of cod, haddock, and whiting leave little hope for a recovery of stocks, and also plaice stocks continue to be low. This loss of commercially valuable species was compensated by an increase in herring stocks, in particular, but also stocks of dragonet and solenette.
At the autumn meeting of the Advisory Committee for Fisheries Management (ACFM) of the International Council for the Exploration of the Sea (ICES), a reduction of fishing pressure was urgently recommended. Scientific recommendations for total allowable catches were only partially accepted by the EU Commission's Fisheries Council at the end of the year. The same applies to other stock rebuilding measures such as catch bans, fisheries exclusion zones, reduction of fishing days.
Seal counts in the Wadden Sea in 2004 provided evidence for a beginning recovery of stocks, after a mass mortality had been caused by the phocine distemper virus in 2002. In early August 2004, 12,803 seals were counted in the entire Wadden Sea area, which was an 18 % increase over 2003. Seal stocks are expected to return to their 2002 levels in 2008.
June 2004 was too cold and too wet, with too little sunshine.
Also July temperatures, with monthly means between 15.5 and 16.6 °C, were up to 1 K too low because warm summer weather did not set in until the end of July. Precipitation was high, with major regional differences. Rainfall varied between 60 and 115 mm, exceeding the monthly means by up to 80 %. There were few hours of sunshine, only 190 - 237 hours, which was up to 20 % below the monthly means.
At monthly mean temperatures between 18 and 19 °C, August was 1.5 - 2.0 K too warm. Precipitation, at 60 - 100 mm, showed major regional differences and exceeded the monthly mean values by up to 70 %. The rainfalls of 40 - 50 mm recorded at the coast of Mecklenburg-Vorpommern were up to 25 % below normal. The duration of sunshine, at 220 - 260 hours, was mostly up to 10 % above normal.
In September, the mean temperatures, at 14 - 15 °C, were 0.5 - 1 K above the long-term means. The beginning of the month was characterised by typical late-summer anticyclonic weather conditions, whereas stormy autumn weather prevailed at the end of the month. With 50 - 80 mm rainfall on the western Baltic coast, mean values were exceeded by up to 30 %. On the coast of Vorpommern, only 35 - 45 mm precipitation was recorded, which was 70 - 85 % of the mean values. The duration of sunshine, at 180 - 215 hours, was 15 - 30 % above normal.
Also October was 0.5 - 1 K too warm, at monthly mean temperatures between 10 and 11 °C. Precipitation showed major regional differences. In the western part of Mecklenburg, the recorded precipitation of 30 mm was about 30 % below normal, whereas 70 - 75 mm was measured west of Rügen - a surplus of about 70 %. A total of 100 - 126 hours of sunshine was recorded in this area, exceeding the monthly means by up to 17 % west of Rügen, and up to 10 % east of Rügen.
Temperatures in November were 1 K above the long-term reference values and reached mean values ranging between 4.4 °C (Szczecin Lagoon) and 6.5 °C (Fehmarn). Up to 3 frost days were recorded, which was half the mean values; the mean value of 8 frost days was only reached east of Rügen. It was mostly too dry, with precipitation of 30 - 45 mm on the German Baltic islands, which was only up to 50 % of the monthly reference values. Sunshine hours were up to 36 % above normal, at 62 - 72 hours.
Also in December, the monthly means of 3 - 4 °C were about 2 K above the long-term reference values. Precipitation was below average. With 25 - 45 mm precipitation in Mecklenburg-Vorpommern, only 55 - 75 % of the monthly means was reached; at the coast of Schleswig-Holstein, where up to 70 mm was measured, mean precipitation levels were reached locally. In the eastern coastal regions (between Rügen and Szczecin Lagoon), the duration of sunshine was 25 - 30 hours corresponding to 65 - 80 % of normal. At Boltenhagen, 47 hours were recorded, which is 132 % of the monthly mean.
(Values for the Baltic coast of Mecklenburg-Vorpommern could not be determined from May - October because of data failure)
In July, the mean water temperature at the coast of Schleswig-Holstein, at 17.2 °C, was slightly below the reference data. In August, the mean water temperature of 19.1 °C corresponded to the reference values. That was also the case in September, at 16.3 °C. In October, the mean temperature of 11.7 °C still corresponded to the reference value. In November, only the mean value for Mecklenburg-Vorpommern could be determined (8.2 °C). Water temperatures corresponded to the values of the reference series. Water temperatures in December were slightly above the reference series, at 4.2 °C (Schleswig-Holstein) and 5.1 °C (Mecklenburg-Vorpommern) on average.
Water levels on the Baltic coasts of Schleswig-Holstein and Mecklenburg-Vorpommern in July showed monthly mean values up to 11 cm above the reference series. The lowest water level was recorded in Flensburg on 11 July, at 455 cm, and the highest level of 561 cm was measured in Lübeck on 20 July. Mean water levels in August corresponded to the values of the reference series. This month's minimum of 457 cm was recorded at Eckernförde on 19 August, and the maximum of 549 at Wismar on 14 August. Also in September, the monthly mean values corresponded to the reference series, with the exception of Kiel where they were 7 cm below it. The minimum value of 412 cm was also measured at Kiel, on 14 September, whereas the maximum value of 577 cm was recorded at Koserow on 30 September. The monthly means in October were up to 13 cm above the values of the reference series. The lowest water level was measured at Flensburg and Eckernförde on 22 October, at 444 cm. Flensburg also reported the maximum of 578 cm, on 11 October. The monthly means in November were up to 8 cm above the reference series. The lowest water level (387 cm, 1.13 m below generalised mean sea level) was observed in Flensburg and Travemünde on 12 November, the highest level of 640 cm at Koserow on 23 November. The monthly means in December were 12 cm above the reference series. The lowest value of 389 cm was recorded at the Wismar gauge on 23 December, and the highest value of 570 cm in Koserow on 6 December.
Also in July - December 2004, runoff volumes in the Odra area (gauge Hohensaaten-Finow) in some cases were clearly below the respective mean values of the period 1941 - 2000.
In the 2004/2005 ice season on the German Baltic Sea coast, no ice occurrences had been reported by the end of December 2004.
In the northern Baltic, this season's first ice formation began on the north coast of the Bay of Bothnia on 17/18 November, about one week later than average. Due to mostly mild weather in December, there was only minor new ice formation. Fresh SW winds pushed the new ice toward the fast-ice edge, which led to temporarily strong ridging in the NE part of the Bay of Bothnia toward the end of the year.
Baltic coast of Schleswig-Holstein
At the end of June and in early July, the development of the summer plankton species was slow. Cool and windy weather delayed the seasonal sequence of micoalgal communities by several weeks. Small flagellate species with high cell counts prevailed, and there were only a few areas with medium to high cell counts of summer diatoms. Dinoflagellates continued to be underrepresented.
By mid-July, the typical assembly of summer plankton had developed in the Baltic coastal waters despite relatively low water temperatures, with higher cell counts of diatoms and dinoflagellates (especially Ceratium species). Filamentous blue-green algae of the species Anabaena became more abundant, especially in the Bay of Lübeck, but did not accumulate on the surface.
At the end of July, cell counts of typical diatom summer species (Skeletonema costatum, Leptocylindricus danicus, Proboscia alata, and Cerataulina pelagica) increased also in the inner areas of the Flensburg and Kiel Fjords. Also cell counts of the autotrophic ciliate Myrionecta rubra were elevated for some time.
In the Fehmarn Sound, western Mecklenburg Bight, and Bay of Lübeck, the typical flocs and accumulations of blue-green algae on the surface were observed temporarily in early August. However, they were much weaker in intensity and areal extent than in 2003.
Monitoring station "Seebrücke Heiligendamm"
From 2.6.2004, the large diatom Dactyliosolen fragilissimus developed very strongly (2757 mg/m³ on 22.6.2004) but disappeared almost completely by 6.7.2004 (week 28). It was replaced by the large diatom Cerataulina pelagica (316 mg/m³) on 20.7.2004 (week 30). By 3.8.2004, it had decreased to 56 mg/m³ while the summer cyanobacteria Nodularia spumigena, Aphanizomenon sp. and Anabaena spp. developed. However, in contrast to the previous year, the cyanobacteria did not form a bloom. By 10.8.2004 (week 33), concentrations of the cyanobacteria Nodularia spumigena, Aphanizomenon sp. and Anabaena spp. had already decreased. Also the summer diatoms (Cerataulina pelagica, Proboscia alata, Dactyliosolen fragilissimus) disappeared, whereas the slow growth of the typical dinoflagellate Ceratium tripos continued. Cryptophyceae (Plagioselmis prolonga) developed as well. All species decreased by 24.8.2004 (week 35). A large biomass of dinoflagellates (Ceratium tripos, Prorocentrum micans, Heterocapsa rotundata) appeared on 31.8.2004 but decreased only one week later. Surprisingly, Nodularia spumigena reappeared in week 37 but finally disappeared in week 39 (21.9.2004). Dinoflagellates (Ceratium tripos, C. fusus, Prorocentrum micans) continued to grow. An unusual bloom of the potentially toxic diatom Pseudonitzschia cf. pungens (349 mg/m³) was observed; the last bloom of this species was recorded in October 1999. At the same time (5.10.2004, week 41), also Cerataulina pelagica, Guinardia flaccida and Ceratium tripos were frequent.
The typical autumn dinoflagellates (Ceratium tripos, C. fusus, Prorocentrum micans) dominated on 19.10.2004 and 2.11.2004 (weeks 43 and 45). Afterwards, their biomass decreased sharply. Nevertheless, the diversity was rather high in mid-December, with more than 40 identified taxa. It consisted mainly of diatoms (Proboscia alata, Guinardia flaccida, Thalassiosira anguste-lineata, Thalassionema nitzschioides, Chaetoceros curvisetus, Ditylum brightwellii, Cerataulina pelagica), dinoflagellates (Ceratium tripos, Heterocapsa rotundata) and cryptophyceae (Teleaulax sp., Plagioselmis prolonga).
Figure 2: Chlorophyll-a concentration and composition of phytoplankton biomass (wet weight) from 6.1. to 28.12.2004 at the coastal
station Heiligendamm (surface water).
Outer coastal waters of Mecklenburg-Vorpommern
In June, chlorophyll-a concentrations ranged between 1.1 µg/L (northwest of Hiddensee) and 4.7 µg/L (Pomeranian Bight), clearly exceeding the long-term means (LTM) between Boltenhagen and Fischland. The phytoplankton biovolume ranged from 0.1 mm³/L northwest of Hiddensee to 1.1 mm³/L north of Boltenhagen.
In July, Chl-a concentrations dropped below LTM, to values between 1.1 µg/L (north of Darsser Ort) and 6.7 µg/L (Pomeranian Bight). At the end of the month, potentially toxic blue-green algae were observed in an area extending from the waters northwest of Hiddensee to east of Sassnitz (Aphanizomenon flosaquae, at up to 128,000 filaments/L).
Chlorophyll-a concentrations measured in August in the waters between Boltenhagen and Hiddensee ranged from 1.4 - 2.5 µg/L, which was below LTM. In the area between Cape Arkona and Greifswalder Oie, the measured values of 3.8 - 11.0 µg/L were slightly above LTM. In the Pomeranian Bight, the measured Chl-a values of 5.5 µg/L and
6.3 µg/L reached barely 50 % of LTM. The phytoplankton biomass ranged from 0.1 mm³/L (north of Boltenhagen) to 1.0 mm³/L (north of Ahlbeck) in the eastern part, and 0.1 to 0.8 mm³/L, corresponding to 6.6 % to 46 % of LTM, in the western part, in the sea area north of Warnemünde. Dominant species were the dinoflagellate Ceratium tripos (north of Boltenhagen) and, farther east, Aphanizomenon flos-aquae (north of Ahlbeck).
During special surveys of the abundance of blue-green algae, large algal mats of Nodularia spumigena and
Aphanizomenon flos-aquae were observed in the waters of Greifswalder Bodden and Pomeranian Bight from early August. On 11 August 2004, these species of blue-green algae and, additionally, Anabaena spp. were also found east of Sassnitz and north of Cape Arkona, where they formed flocs on the water surface. On 16 August, also Nodularia spumigena and Aphanizomenon flos-aquae, as a subdominant form, were found besides the typical summer algae of the genera Prorocentrum, Dinophysis, Chaetoceros, and Ceratium in the western Baltic coastal waters (northwest of Hiddensee extending to the area north of Warnemünde). They occurred in the form of algal mats or flocs.
Farther west, in the area of the Mecklenburg Bight extending from the waters north of Bug to the area north of Boltenhagen, Aphanizomenon flos-aquae, Anabaena cf. lemmermannii and Nodularia spumigena, including some larger accumulations,
were observed on 17 August. However, there was no formation of floating algal mats.
Inner coastal waters of Mecklenburg-Vorpommern
Also in June, the Chl-a values were mostly below the long-term means. Values ranged from 1.5 µg/L in the brackish "Salzhaff" to 107 µg/L in the Stettiner Haff, with long-term means clearly exceeded; this was partly due to the typical early summer growth of the diatom species Coscinodiscus (biovolumes of 7.0 mm³/L at 237,000 cells/litre).
In July, chlorophyll-a concentrations increased to different levels but remained below LTM. Phytoplankton biovolumes ranged between <0.1 mm³/L (Wismar Bight) and 10.4 mm³/L in the Szczecin Lagoon, where the typical early-summer growth of the diatom Coscinodiscus led to cell counts of 237,000 cells/L (=0.7 mm³/L).
In August, chlorophyll-a concentrations between 5.5 µg/L (Salzhaff) and 130 µg/L (Peenestrom) were observed in the inner coastal waters. In the Lower Warnow, the unusually low value of 9.1 µg/L only reached 30 % of LTM; elevated Chl-a levels of 29.5 µg/L (228 %) in the waters of Greifswalder Bodden were caused by a strong growth of blue-green algae. The phytoplankton biovolume consisted of cryptoflagellates of the genera Plagioselmis, Teleaulax, and Dictyocha speculum. In the Szczecin Lagoon, Cyanophyceae species such as Aphanizomenon flos-aquae, Microcystis aeruginosa/M. flos-aquae as well as Anabaenopsis elenkinii were dominant. The biovolume remained small, however, at 5.6 mm³/L (LTM: 15.3 mm³/L).
Surveys conducted in the North Sea and Baltic Sea in September to determine the incidence of viral and bacterial skin diseases and liver tumours in dab, flounder, and cod confirmed the regional differences observed in the past years but generally a lower incidence than in earlier years. Especially the decline of skin ulcers in cod from the western Baltic, which has been observed since 1998, has continued.
Surveys of the development of cod stocks in the western Baltic in November confirmed a good to very good cod year-class 2003. However, the 2004 cod year-class is expected to be average to weak, and also the weakness of adult cod stocks has been confirmed.
The EU Fisheries Council's decisions at the end of the year placed Baltic cod under special protection and established additional fisheries exclusion zones and a prolonged catch ban in summer.
The results of the herring larvae survey in 2004 have shown a good 2004 year-class of herring in the western Baltic Sea, the Kattegat, and Skagerrak.