Production ecology in the Northern Baltic

Production biology in the Bothnian Bay is discussed and compared to that of the southern parts of the Baltic. Severe ice-conditions, low water temperatures in spring and early summer and a pronounced water-colouring cause a delay of the spring development of phytoplankton and a low annual production in the Bothnian Bay. This delay makes possible a higher efficiency of the pelagic system as the zooplankton fauna can develop in harmony with the food resources. The downward transport of energy and matter to the bottom communities from an efficient pelagial should be small and temporally unpredictable, which is thought to be an adequate explanation of the observed very low benthic fauna biomasses in the Bothnian Bay.     

Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

Annual Changes of Abundance and Biomass of Planktonic Ciliates in the Gdańsk Basin,Southern Baltic

Seasonal changes in the species composition, abundance and biomass of planktonic ciliates were determined every 2–3 weeks at two sites of 30 m depth and one location of 105 m depth in the southwestern Gdańsk Basin between January 1987 and January 1988. A total of 40 ciliate taxa were observed during this period. Autotrophic Mesodinium rubrum dominated ciliate abundance and biomass: maximal values of 50 · 10⁻¹ ind. ^1-1 and 65 μg C 1⁻¹ were recorded. The annual mean biomass of M. rubrum comprised 6 to 9% of the annual mean phytoplankton biomass. The highest abundances and biomasses of heterotrophic ciliates were noted at all stations in the spring and summer in the euphotic zone with maximum values of 28 · 10³ ind. 1⁻¹ and 23 μg C 1⁻¹. Three ciliates assemblages were distinguished in the epipelagic layer: large and medium-size non-predatory ciliates, achieving peak abundance in spring and autumn; small-size microphagous ciliates and epibiotic ciliates which were abundant in summer, and large-size predacious ciliates dominating in spring. Below 60 m, a separate deep-water ciliate community composed of Prorodon-like ciliates and Metacystis spp. was found. The ciliate biomass in the 60–105 m layer was similar to the ciliate biomass in the euphotic zone. The heterotrophic ciliate community contributed 10 to 13% to the annual mean zooplankton biomass. The potential annual production of M. rubrum comprised 6 to 9% of the total primary production. Carbon demand of non-predatory ciliates, calculated on the basis of their potential production, was estimated to be equivalent to 12–15% of the gross primary production.     

Phytoplankton Spring Bloom Intensity Index for the Baltic Sea Estimated for the years 1992 to 2004

We introduce an index for estimating the annual phytoplankton spring bloom intensity in the Baltic Sea. It is based on chlorophyll a estimates calculated from automatically sampled fluorescence and chlorophyll a measurements on board cargo ships from 1992 to 2004. The intensity is described by an index including information on the chlorophyll a concentration and duration of the spring bloom period. In all of the years studied, the spring bloom was most intense in the Gulf of Finland. In the Gulf of Finland and the Northern Baltic Proper there was a slight tendency for the bloom to start earlier in the spring.     

Effects of nonindigenous species on diversity and community functioning in the eastern Gulf of Finland (Baltic Sea)

An increase of xenodiversity in plankton and benthos in the eastern Gulf of Finland was observed from 1998 to 2004. Nonindigenous species account for 4.8% of all species found and up to 96% of total biomass. Invasive benthic omnivores, the alien amphipods Gmelinoides fasciatus and Pontogammarus robustoides and the predaceous fish Perccottus glenii with their versatile diets strongly affect the community structure. Invasive sessile seston-feeders that directly (through grazing and water clearance) and indirectly (through recycling of nutrients) interact with other ecosystem components, are mainly represented by the zebra mussel Dreissena polymorpha, which affect the structure of benthic and planktonic communities as well as benthic-pelagic coupling. The invasive predatory cladocerans Cercopagis pengoi and Evadne anonyx and larvae of D. polymorpha are only temporary components in the zooplankton, which is limiting their overall effect. Alien benthic bioturbators, the polychaetes Marenzelleria neglecta and the oligochaete Tubificoides pseudogaster account for a high proportion of total abundance and biomass but their effects on native species need further research.     

Binding of phosphate in sediment accumulation areas of the eastern Gulf of Finland,Baltic Sea

The relationships between P and components binding P were studied by analysing the concentrations of N, P, Fe, Mn, Ca and Al in sediments and pore water along the estuarine transect of the River Neva in August 1995. The high sediment organic matter concentration resulted in low surface redox potential and high pore-water o-P concentration, whereas the abundance of amphipods resulted in high surface redox potentials and low pore-water o-P concentration. However, despite the variation in sediment organic matter and the abundance of amphipods, very reduced conditions and slightly variable concentrations of Tot-P (0.7–1.1 mg g^–1 DW) were observed in the 10–15 cm sediment depth along the estuarine gradient, indicating that the pools of mobile P were largely depleted within the depth of 0–15 cm. Multiple regression analysis demonstrated that organic matter and Tot-Fe concentration of the sediment were closely related to the variation in Tot-P concentration of the sediments (r ² = 0.817, n=32). In addition, the high total Fe:P ratio suggested that there is enough Fe to bind P in sediments along the estuarine gradient. However, low Fe_diss concentrations in the pore water of reduced sediment (redox-potential <–50 mV) indicated efficient precipitation of FeS (FeS and FeS₂), incapable to efficiently bind P. Consequently, the low Fe_diss:o-P ratio (< 1) recorded in pore water in late summer implied that Fe³⁺ oxides formed by diffusing Fe_diss in the oxic zone of the sediments were insufficient to bind the diffusing o-P completely. The measured high o-P concentrations in the near-bottom water are consistent with this conclusion. However, there was enough Fe_diss in pore water to form Fe³⁺ oxides to bind upwards diffusing P in the oxic sediment layer of the innermost Neva estuary and the areas bioturbated by abundant amphipods.     

Fin abnormalities of pikeperch in coastal areas off the Finnish south coast

Pikeperch Stizostedion lucioperca from two different water areas off the Finnish south coast were affected by three types of fin abnormalities: fin anomalies, acute fin erosion (fin rot) and healed fin erosion. Fin erosion occurred at high prevalences at both areas, while fin anomalies occurred mainly in the area polluted by sewage.     

Seasonal variations in the physiological condition of the benthic amphipods Monoporeia affinis and Pontoporeia femorata in the Gulf of Riga (Baltic Sea)

Seasonal variations in the physiological condition of two benthic deposit-feeding amphipods were studied in two environmentally differing areas in the Gulf of Riga (Baltic Sea) with the purpose of estimating their role in benthic mineralisation. At the shallower (26 m) nearshore station, Monoporeia affinis exhibited low ammonia excretion rate (VNH ₄ ⁺ ) throughout the year. After intensive accumulation of lipids in spring, the lipid reserves of the individuals became rapidly depleted during autumn. Gravid females in winter-early spring showed exceedingly low lipid and triacylglycerol (TAG) levels compared to studies carried out in open-sea areas. Pontoporeia femorata studied at the deeper (43 m) offshore station exhibited a higher VNH ₄ ⁺ at all times with no significant seasonal variation. Lipid and TAG accumulated continuously until November, reaching higher levels than recorded previously for this species. Experiments showed that the temperature coefficient Q ₁₀ determined for VNH ₄ ⁺ is likely to depend on the recent feeding history of the amphipods. Mineralisation of nitrogen and carbon by the amphipod populations at the study sites was estimated to be 1.7-3.0 g C and 11.3-13.5 mmol NH ₄ ⁺ m^–2 yr^–1. Conclusively, both biotic and abiotic factors affect the condition of the amphipods, while the species also have genuine differences in their metabolic characteristics.     

典型低纬度海区(南海、孟加拉湾)初级生产力比较

南海和孟加拉湾有着相似的纬度范围,均处于低纬度季风区,但环境的开放性和水体交换特征有所不同。将南海和孟加拉湾的初级生产力进行对比,有助于加深人们对低纬度海区生物生产过程的认识。南海有着复杂的物理过程,存在涡旋、上升流、黑潮、台风和冲淡水等多种现象,显著地影响着初级生产力大小和时空分布。南海初级生产力有以下几个特点:(1)受冲淡水和沿岸上升流的影响,沿岸海域常常高于开阔海区;(2)初级生产力的高值通常不出现在表层,大都出现在次表层;(3)在开阔海区受水体交换(黑潮等)和中尺度现象影响(涡旋)显著。此外,南海初级生产力的季节变化也比较明显,但季度变化规律有较强的区域性。孟加拉湾物理环境与南海差别明显,初级生产力主要受淡水输入、涡旋和光照的影响,受台风和上升流影响不如南海明显。在沿岸区,高温低盐水覆盖了沿岸上层水体,使得混合层较稳定,抑制了深层富含营养盐水体的涌升补充,导致初级生产力下降;光强(悬浮物多、多云天气多)也限制了初级生产力。孟加拉湾开阔海区常常有涡旋形成,也对初级生产力有一定影响。沿岸区初级生产力南海高于孟加拉湾,而在开阔海区两者差别不大,因此整体上南海初级生产力水平高于孟加拉湾。     

Seasonal changes in condition indices in adult mature and non-maturing burbot, Lota lota (L.), in the north-eastern Bothnian Bay, northern Finland

The population structure and seasonal changes in condition factors of the burbot in a shallow coastal region of the north-eastern Bothnian Bay are described. The significance of the so-called rest years is examined by comparing condition indices in immature or sterile and mature burbot. The somatic condition index ( K ₂), liver index ( K ₁), intestine index ( K ₁) and gonad index ( K_g ) are determined monthly in terms of organ weight in relation to body length. Approximately 30% of the whole catch of 1052 burbot were non-maturing but were 40 cm or more in length. K ₂, K ₁ and K ₁ were lowest in the autumn, when the first sign of gonad recrudescence was observed in mature burbot. The non-maturing burbot were never in poorer condition than mature ones. As mature and non-maturing burbot dissipated their energy stores during the warmest period of the summer, it is concluded that burbot spending a rest year do not accumulate and store energy reserves over the summer for the next year, and that such rest years, if they exist, do not occur for nutritional reasons.     

Seasonal and spatial variations of fish trophic guilds in a shallow,semi-enclosed tropical estuarine bay

A study on seasonal and spatial variations of feeding habits and trophic guilds of dominant fish species in Pattani Bay during March 2003 to February 2004 was aimed at classifying diet composition, identifying dominant food components of each species, categorizing trophic guilds of the community and evaluating effects of habitat characteristics and seasonality on guild organization. Most fishes showed high food intake, fed on a diverse range of food items but relied heavily on calanoid copepods and shrimps. All species, with the exception of Epinephelus coioides, were classified as specialist feeders. Four main dietary guilds were classified. Three of these were classified as the guilds dominated by at least two major food items. Significant variations in trophic guilds of 28 fish species based on habitat types and seasons were also identified. They could be divided into three seasonal groups and three site-groups and a single site. Trophic organization for each season and habitat ranged from two to four groups. This information identifies groups of fishes that seasonally and spatially utilize different food resources within a semi-enclosed estuarine bay ecosystem.     

Population dynamics, growth and production of the neozoon Marenzelleria cf. viridis (Verrill, 1873) (Polychaeta: Spionidae) in a coastal water of the southern Baltic Sea

The propagation of an immigrant from North America, viz. the spionid Marenzelleria cf. viridis in the Darss-Zingst Bodden (DZB) (southern Baltic Sea), was studied at three stations from March 1992 to December 1995. Highest mean abundances (over 28 000 ind. m^-2) and wet weights (400 g m^-2) were recorded at station 2 in 1994. The spionid also reached its highest dominances in terms of biomass (40 to 90%) at this station, which was selected for the population dynamics, growth and secondary production studies. The spionid has a life span of about 3 years, and many individuals achieved sexual maturity after one year. Their growth curve is steepest during the first year of life, during which the animals grow to a length of about 180 segments. However, growth depression was observed during the ripening of the gametes in April, May and June. Secondary production was in the region of 55 to 85 g AFDW m^-2 y^-1. Productivity (P/B) varied considerably from generation to generation, ranging between 0 and 4.8 with an average between 1.2 and 1.6.     

Population decline of amphipod Monoporeia affinis in Northern Europe: consequence of food shortage and competition?

In the present study, we investigate the effects of food quality (with three distinct algal diets) and quantity (high vs. low carbon and nitrogen contents) and competition (with natural polychaete competitor, Marenzelleria spp) on the semelparous amphipod Monoporeia affinis fitness and reproduction. Contrary to other studies on this species, our results showed that amphipod females have the ability to adjust their offspring investment when conditions were significantly altered before mating in terms of food quantity, while food quality was of less importance. In fact, there was only a low beneficial effect on amphipod reproduction and embryonic development of a presumed high quality diatom diet. Also, the presence of a natural competitor did not affect amphipod reproductive outcome. The results are viewed in the context of a dramatic decline observed on the amphipod populations in the Gulf of Bothnia. Though, several plausible hypotheses have been suggested for the decline, including competition, new anthropogenic substances, hypoxia and predation, we hypothesize that the population decline is related to food shortage and malnutrition due to an increased percentage low quality terrestrial carbon (rich in humus) from river outflow into the Gulf of Bothnia. Concomitantly, the bacterial food web was enhanced, which has a lower trophic efficiency. We also suggest that a secondary effect of malnutrition is an increased susceptibility to other types of stressors such as contaminants and parasites.     

Estimation of export production in the coastal Baltic Sea: effect of resuspension and microbial decomposition on sedimentation measurements

Hydrography, nutrient concentrations, primary production and sedimentation of particulate matter were studied during spring, late summer and autumn in the coastal area of the northern Baltic Sea, SW Finland. Vernal phytoplankton productivity peak and biomass maximum in early May were followed by high sedimentation rates of organic matter at the end of May. In summer, sedimentation rates of organic material were generally low. The decay rates of organic carbon in the sediment traps, estimated by measuring oxygen uptake of settled organic matter, varied between 0.005 to 0.08 d^–1 and were on average 0.02 d^–1. Decomposition of organic matter inside the sediment traps was mainly controlled by temperature, while also organic contents of settled material were significant. Microbial decomposition decreased sedimentation rates of organic carbon and nitrogen on average by 11% and 15%, respectively, during the whole study period of ca. 6 months. Resuspension of organic matter from sediment surface was estimated to contribute ca. 17 and 24% of the total sedimentation of organic carbon during spring and summer, respectively. Export production (i.e. primary sedimentation of organic carbon corrected by decomposition) was estimated to be 32% of the net primary production during the whole productive season and 42% in spring when the flux of primary settling material was greatest. Sedimentation of the spring bloom was the major annual supply of organic matter to the benthos (>80% of the total primary sedimentation).     

大亚湾基础生物生产力及潜在渔业生产量评估

通过对大亚湾海域初级生产力及浮游动物次级生产力的现场调查数据,对该海域潜在渔业生产量及最大可持续渔获量进行了评估。结果表明,大亚湾春季及秋季初级生产力平均值分别为765.23 mgC.m-2.d-1和1786.33 mgC.m-2.d-1,浮游动物次级生产力春季及秋季平均值分别为175 mgC.m-2.d-1和679 mgC.m-2.d-1。采用Tait模式和Cushing模式估算的大亚湾潜在渔业产量分别为3.30万吨和4.78万吨。数据分析结果表明,基于基础生物生产力的评估方法很可能高估了该海区的实际渔业产量,这与基础生物群落结构的改变密切相关;高生物多样性及生态系统结构与功能的健康性是维持渔业资源产量与质量的重要基础。     

Photosynthesis and nitrogen fixation in a cyanobacterial bloom in the Baltic Sea

Daily integrals of photosynthesis by a cyanobacterial bloom in the Baltic Sea, during the summer of 1993, were calculated from the vertical distributions of light, temperature and the organisms in the water column and from photosynthesis/irradiance curves of picoplanktonic and diazotrophic cyanobacteria isolated from the community. The distribution of chlorophyll a in size-classes <20?µm and >20?µm was monitored over 9 days that included a deep mixing event followed by calm. Picocyanobacteria formed 70% of the cyanobacterial biomass and contributed 56% of the total primary production. Of the filamentous diazotrophs that formed the other 30%, Aphanizomenon contributed 28% and a Nodularia-containing fraction 16% of the primary production. For the whole population there was little change in standardized photosynthetic O₂ production, which remained at about 31?mmol?m^?2 before and after the mixing event. There were differences, however, between the classes of cyanobacteria: in picocyanobacteria primary production hardly changed, while in Aphanizomenon it increased by 2.6 and in Nodularia it fell below zero. Total phytoplankton photosynthesis was strongly dependent on total daily insolation with the compensation point at a photon insolation of 22.7?mol?m^?2?d^?1. Similar analyses of N₂ fixation showed much less dependence on depth distribution of light and biomass: Aphanizomenon fixed about twice as much N₂ as Nodularia their; their fixation exceeded their own N demand by about 12%. Together, these species contributed 49% of the total N demand of the phytoplankton population. Computer models based on the measured light attenuation and photosynthetic coefficients indicate that growth of the cyanobacterial population could occur only in the summer months when the critical depth of the cyanobacteria exceeds the depth of mixing.     

Viral production in the Gulf of Trieste (Northern Adriatic Sea): Preliminary results using different methodological approaches

Although the temporal and spatial variability of virioplankton in the northernmost part of the Adriatic Sea has been repeatedly explored suggesting that viruses constitute an extremely dynamic component of the plankton community and hypothesizing their importance in marine food webs and mucilage events, there is still no information about viral replication rates. Hence, the contribution of viruses to bacterial mortality and the cycling of organic matter in this part of the Adriatic basin are still not fully comprehended. Assessment of the role of viral lysis requires a robust means of estimating viral production. Since, up to now, none of the available methods evolved to a state of a standard yet, in this preliminary study 3 different experimental approaches were simultaneously assayed (viral production estimated by radiotracer incorporation method [TdR], dilution technique for the estimate of viral production in already infected bacteria [DIL] and serial dilution method in manipulated phage-host assemblage [SER]). The present study provided the first evidence of viral production rates in this study area, that resulted in comprising between ∼ 3.5-15 × 10⁸ viruses L^− 1 h^− 1 and critically faced up the results obtained by different techniques with the consideration that they suffer from different biases. Based on TdR and DIL viral proliferation estimates, viral lysis was responsible for the loss of 54 to 95% of the bacterial standing stock, while the viral-induced mortality by SER (325% d^− 1) was likely consistently overestimated. These results indicate that viral lysis is a significant factor for prokaryotic mortality suggesting its implication as an important pathway for the cycling of dissolved organic matter in the Gulf of Trieste.