BSEP116B Biodiversity in the Baltic Sea - Helcom

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52 Macoma baltica where the influence of periodic salt-water inflows is tangible. These patterns are more distinct closer to the Danish Straits and the proximity to the inflows. Since the largest recorded inflow in the 1950s, salinity has decreased in the entire Baltic Proper and the dominance has changed from marine species to typical brackish-water species in the southeastern Gotland Basin (Figure 3.4.2). Similarly, the ‘marine’ elements of the community in the Gulf of Finland, such as the polychaete Terebellides stroemi, have disappeared altogether. The nature and magnitude of the salt-water inflows have a direct influence on the strength of the halocline and, hence, the oxygen dynamics in the Baltic. Stratification of the water column in combination with an increased organic loading (which has been exacerbated by eutrophication) has resulted in widespread hypoxia and anoxia. This poses a severe threat to the biodiversity of benthic invertebrate communities, which is illustrated in the periodically very poor and low diversity communities recorded in the southeastern Gotland Basin and Gulf of Finland (Figure 3.4.2). During the mid-1990s, benthic communities recovered owing to the stagnation period that weakened stratification; however, with the large salt-water intrusion in 1993, the halocline strengthened and oxygen conditions deteriorated (Laine et al. 2007, Norkko et al. 2007). In contrast, changes in species composition are small in the southern Bothnian Sea (SR5) and virtually absent in the Bothnian Bay (BO3). This is due to overall low species diversity. Nevertheless, invasive species, such as the polychaete Marenzelleria spp., are conspicuous elements of the system and have established viable populations in many areas of the Baltic Sea, as exemplified in southern Bothnian Sea. In the Bothnian Sea, large natural variations in abundance of the dominant species, the amphipod Monoporeia affinis, are typical. In this area, the influence of salt-water inflows is minimal and there is not a strong halocline, which would promote the formation of hypoxia. In the Bothnian Sea, the Monoporeia populations have been declining since the mid-1990s for reasons that have not been clarified. However, recent monitoring suggests that these populations may be recovering. When examining long-term trends from data collected in 1965–2006, it becomes immediately obvious that conditions were already disturbed in the mid-1960s. Benthic invertebrate status in the central parts of the Baltic Sea, in particular, is more or less entirely controlled by the presence or absence of hypoxia/anoxia. Already in Hessle’s (1924) seminal work, hypoxia/anoxia was reported in both coastal and open-sea areas. However, he also reported on the presence of species such as the polychaete Scoloplos armiger at over 140 m depth in the eastern Gotland Basin, which indicates that the spatial extent of hypoxic bottom waters was limited at that time. Current evidence suggests that the spatial and temporal extent of oxygen deficiency has increased over the past decades. In the light of historical work (Hessle 1924), it is also likely that reference conditions defined for open-sea areas in this assessment are underestimates. Generally, Baltic benthic macrofauna are characterized by small, shallowdwelling species owing to low salinity and transient hypoxia; historically, it was only in the southern Baltic, where more mature communities composed of deeper-dwelling larger species, e.g., some long-lived bivalves and large polychaetes, could have developed (Tulkki 1965, Rumohr et al. 1996). However, currently macrobenthic communities are severely degraded and abundances are below a 40-year average in the entire Baltic Sea (Norkko et al. 2007). Functional aspects of biodiversity The broad-scale patterns and changes in structural biodiversity also translate into differences in functional biodiversity. While the actual relationship
etween changes in the functional biodiversity and ecosystem function is difficult to quantify, it is apparent that there is a strong gradient in functional biodiversity in the Baltic Sea (Bonsdorff & Pearson 1999), which affects the trophic structure and energy flow in the ecosystem. Biological trait analysis can be useful to identify functions that are important for ecosystem function or may help interpret the effects of disturbances (e.g., Bremner et al. 2003). Traits can be exemplified by the longevity or size of particular species and their developmental mechanisms and mobility, which are all species characteristics that play important roles in classifying the state of benthic communities or reflect their potential for recovery after disturbance and are therefore important in defining resilience. The differences in benthic functional diversity between sub-basins during the period 2000–2006 are illustrated in a basic classification at some representative stations along the Baltic Sea salinity gradient (Table 3.4.2, Figure 3.4.3). Biological traits (BT) were used to describe the characteristic functions of individual benthic infaunal species. The main BT included were feeding type, feeding habit, mobility, size, adult longevity, larval development, living habit and environmental position. Existing BT at each station are expressed as a percentage of Table 3.4.2. Biological traits (BT) at selected stations in the Baltic Sea, expressed as a percentage of the total number of BT identified for the respective main group during 2000–2006. The following main traits were included: feeding type, degree of mobility, feeding habit, size, adult longevity, developmental mechanism (larvae), living habit and environmental position. 31-45 % 46-60 % 61-75 % 76-90 % >90 % Bothnian Bay Bothnian Sea Gulf of Finland NE Gotland Basin SE Gotland Basin Bornholm Basin Arkona Basin Biological trait/Stations BO3 US6B SR5 LL11 LL4A LF1 BCSIII10 HBP216 BY2 Feeding type 57 % 57 % 57 % 57 % 86 % 71 % 57 % 86 % 71 % Mobility 75 % 75 % 75 % 100 % 100 % 100 % 100 % 100 % 100 % Feeding habit 75 % 75 % 100 % 100 % 100 % 100 % 75 % 100 % 100 % Size 40 % 40 % 60 % 80 % 60 % 80 % 40 % 80 % 100 % Adult longevity 40 % 40 % 40 % 60 % 80 % 80 % 40 % 80 % 100 % Development 75 % 75 % 75 % 100 % 75 % 100 % 50 % 100 % 75 % Living habit 75 % 75 % 75 % 100 % 75 % 100 % 50 % 100 % 75 % Environmental position 80 % 80 % 80 % 80 % 80 % 80 % 40 % 100 % 100 % Increasing salinity 31 45 % Number of expressed traits 60 50 40 30 20 Feeding type Mobility Feeding habit Size Adult longevity Development Living habit Environmental position 10 0 Bothnian Bay (BO3) Bothnian Sea (US6B) Bothnian Sea (SR5) Gulf of Finland (LL11) Gulf of Finland (LL4A) NE Gotland Basin (LF1) SE Gotland Basin (BCSIII10) Bornholm Basin (HBP216) Arkona Basin (BY2) Increasing salinity Figure 3.4.3. The number of biological traits expressed in each main group (feeding type, mobility, feeding habit, size, adult longevity, development, living habit and environmental position) during 2000–2006 for selected stations (Villnäs & Norkko, unpublished). Note that one species may express several traits; hence, the number of traits often exceeds the total number of species at a station. Biological traits include: (a) feeding type: suspension feeder, surface detritivore, burrowing detritivore, omnivore, carnivore, scavenger, herbivore; (b) degree of mobility: stationary, swim, crawl, burrow (c) feeding habit: jawed, tentaculate, pharynx/proboscis, other mechanism; (d) size (measured in biomass): xs, s, m, l, xl; (e) adult longevity (years): 1–2, 2–3, 3–5, 5–10, >10; (f) developmental mechanism: planktotrophic, lecitotrophic, direct (brood protection), other; (g) living habit: tube-dweller, burrow dweller, crevice dweller, free living; and (h) environmental position: epifaunal, infaunal, pelagic, epibenthic, nectobenthic. 53
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Baltic Sea Environment Proceedings
Page 4 and 5: Published by: Helsinki Commission K
Page 6 and 7: TABLE OF CONTENTS PREFACE . . . . .
Page 8 and 9: 6.6 Hazardous substances . . . . .
Page 10 and 11: 1 INTRODUCTION 8 1.1 An integrated
Page 12 and 13: Box 1.1. Biodiversity The term biod
Page 14 and 15: of saline water from the North Sea
Page 16 and 17: 14 On a global scale, marine ecosys
Page 18 and 19: Box 1.2. Regime shifts in the Balti
Page 20 and 21: 2 MARINE LANDSCAPES AND HABITATS 18
Page 22 and 23: From an ecological point of view, a
Page 24 and 25: Box 2.1.2. The Baltic marine landsc
Page 26 and 27: • A coherent data set on benthic
Page 28 and 29: Denmark Estonia Finland Germany Lat
Page 30 and 31: Mud-sandflat, Greifswald Lagoon, Ge
Page 32 and 33: 3 COMMUNITIES Communities are assem
Page 34 and 35: 32 Spring bloom index 1200 1000 800
Page 36 and 37: 34 Unusual events and new species i
Page 38 and 39: 36 Depth limit (m) the Gulf of Both
Page 40 and 41: Number of species 16 14 12 10 8 6 4
Page 42 and 43: Figure 3.2.7. Left panel shows pred
Page 44 and 45: Implications for the Baltic Sea Act
Page 46 and 47: Biomass (wet weight, mg per m 2 ) B
Page 48 and 49: the other hand, is not selected by
Page 50 and 51: iomass can be used to assess enviro
Page 52 and 53: Average number of species 20 15 10
Page 56 and 57: the total BT identified for each ma
Page 58 and 59: Recruitment (thousands) 8000000 700
Page 60 and 61: Alien species Several alien fish sp
Page 62 and 63: 4 SPECIES The number of species in
Page 64 and 65: Table 4.1.1. Results of dedicated a
Page 66 and 67: Number of stranded porpoises 180 16
Page 68 and 69: is recommended to survey harbour po
Page 70 and 71: Number of individuals 12000 10000 8
Page 72 and 73: Mean blubber thickness (mm) 40 35 3
Page 74 and 75: Breeding pairs 60000 50000 40000 30
Page 76 and 77: predation on nests and nesting adul
Page 78 and 79: sites outside the Baltic, decreased
Page 80 and 81: Table 4.3.1. Development of the pop
Page 82 and 83: 80 Number of breeding pairs 3000 25
Page 84 and 85: The strategic goal of the BSAP to h
Page 86 and 87: for a given site or area. The secon
Page 88 and 89: Mussel bed reef community, Jasmund,
Page 90 and 91: Table 5.3. Assessment results of th
Page 92 and 93: Aerial photo of harbours seals (Pho
Page 94 and 95: 6 HUMAN PRESSURES ON BIODIVERSITY A
Page 96 and 97: Table 6.1.1. Catch range during the
Page 98 and 99: Baltic herring trawling, Bothnian B
Page 100 and 101: 6.1.3 Major international framework
Page 102 and 103: 100 Oil turnover (millions of tonne
Page 104 and 105:
NOx emissions and sewage Macrophyte
Page 106 and 107:
Communication links There are a num
Page 108 and 109:
Figure 6.3.3. Left: concrete-stone
Page 110 and 111:
ecommendations would contribute to
Page 112 and 113:
Tourist fishing 110 cial fishery fo
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112 Figure 6.5.1. Integrated classi
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can be considered as having been a
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Although no direct, dramatic mass m
Page 120 and 121:
Bearing in mind the complex hydrogr
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Box 6.7.1. Invasion status of the B
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Table 6.7.1. Examples of ecological
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munities that formerly consisted of
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6.8.2 Activities generating noise i
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128 and fish in the Baltic Sea area
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800 700 600 bag of the two German B
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Fish swarm on kelp (Laminaria sp.)
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tion of ice cover, either through r
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7 STATUS OF THE NETWORK OF MARINE A
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Box 7.1. Natura 2000 network of pro
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25 20 on how the criteria on ecolog
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estrial, nearshore marine, and offs
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144 >30 psu 18-30 psu 11-18 psu 7.5
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Permission needed Restricted Forbid
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Figure 7.8.a. MARXAN ’best portfo
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The BSPA network is relatively well
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Mammals. Among the mammals, the pop
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154 taxonomic groups and communitie
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156 provided by an ecosystem. Use o
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158 Reduction of human pressures Wh
Page 162 and 163:
160 fishing on fish population dyna
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162 Baden, S., Boström, C. (2001).
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164 Season 2001-2002. Acta Zoologic
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166 Gasiūnaitė, Z.R., Cardoso, A.
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168 HELCOM & OSPAR (2003): Joint HE
Page 172 and 173:
170 ICES (2008c). Report of the Bal
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172 area: density-dependent effects
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174 Noer, H., Clausager, I., Asferg
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176 Scheffer M., Carpenter S.R., Fo
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178 by passive acoustic monitoring.
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180 Warzaw, Poland Vilhunen, Jarmo,
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182 6.7 Alien speices Authors: Lepp
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ANNEX III: CONSERVATION STATUS OF T
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ANNEX IV: HABITAT OR SPECIES DISTRI
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ANNEX V: STATUS OF BREEDING AND WIN
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