BSEP116B Biodiversity in the Baltic Sea - Helcom

Average number of species
20
15
10
5
0
Arkona Basin
strains species distributions (Figure 3.4.1). In this
broad-scale assessment, eight basins were evaluated
and reference conditions, i.e., the average
number of species that should be found, varied
between 18.3 in the Arkona Basin and 2.0 in the
Bothnian Bay. For the years 2000–2006, benthic
invertebrate status varied considerably between
sub-basins and was related to the widespread
occurrence of hypoxia and anoxia in the Baltic
Proper and the Gulf of Finland (Figure 3.4.1). None
of the sub-basins can be regarded as pristine, even
though the Gulf of Bothnia and the Arkona Basin
are in a reasonable condition (as defined by the
good-moderate border set by acceptable deviation;
Bornholm Basin
SE Gotland Basin
N&CE Gotland Basin
Northern Baltic Proper
Reference value
G/M border
Assessment 2000-2006
Gulf of Finland
Bothnian Sea
Bothnian Bay
Figure 3.4.1. Reference values and the border between good
and moderate (G/M) ecological status in the different subbasins
of the open-sea areas in the Baltic Sea depicted as Ecological
Quality Ratio (EQR) and the average number of species.
Benthic invertebrate status is described as an average for the
period (2000–2006).
see HELCOM 2009a). The entire Baltic Proper, from
the Bornholm Basin to the northern Baltic Proper,
and the Gulf of Finland are in a severely disturbed
state (Figure 3.4.1).
Some univariate measures of biodiversity were
calculated for selected representative stations in
each sea area, which highlight the nature of the
overall diversity gradient in the Baltic Sea (Table
3.4.1). The total number of species recorded
for the assessment period 2000–2006 ranged
from 27 in the Arkona Basin (BY2) to only 3 in
the Bothnian Bay (BO3), while average species
diversity ranged from 13.7 to 1.4. Correspondingly,
the Shannon-Wiener diversity index ranged
from 2.4 to 0.02 (Table 3.4.1). In the low-diversity
Baltic Sea, these traditional measures, such
as Shannon-Wiener, are not very informative
(Magurran 2008). Several stations, in particular,
the Bornholm Basin (BY5) and the northern Baltic
Proper (IBSV9), demonstrate the degraded state
of macrobenthic communities over the assessment
period. Interestingly, Cody’s measure of
species turnover (β c
; beta diversity) provides
useful insights into the transient and dynamic
nature of the benthic communities in the southern
Baltic Sea (Table 3.4.1). In the Arkona Basin
(BY2), Cody’s measure reached 4.4 (which translates
into an average actual species turnover of
8.8 between the years 2000–2006). In contrast,
species turnover in the Bothnian Bay (BO3) gave
an index value of 0.5. This obviously reflects the
large differences in available species pools as well
as the overall difference in biodiversity along the
gradient. In addition, the dynamic nature of the
southern Baltic is intimately linked to the periodic
salt-water inflows.
Table 3.4.1. Stations from each sea area provide examples of the benthic communities during the assessment period
2000–2006. Diversity is measured as the total and average number of species ± std (standard deviation) and Cody’s
measure (β) represents the average species turnover ± std. Diversity is also calculated as the Shannon & Wiener (H’
(log 2
)) index (Shannon & Weaver 1963).
50
Sea area Station Depth Total nr Average nr of species Shannon-Wiener H' (log 2
) Cody's measure ß C
m of species x std x std x std
Bothnian Bay BO3 110 3 1,43 0,53 0,02 0,03 0,50 0,32
Bothnian Sea, north US6B 82 3 2,14 0,69 0,07 0,06 0,25 0,42
Bothnian Sea, south SR5 125 5 3,86 0,90 0,88 0,37 0,17 0,26
Gulf of Finland LL11 67 7 3,14 1,21 0,34 0,16 0,83 0,93
Gulf of Finland LL4A 58 10 5,86 1,86 1,46 0,39 1,33 0,68
N Baltic Proper IBSV9 88 0 0,00 0,00 0,00 0,00 0,00 0,00
NE Gotland basin LF1 67 7 3,43 1,27 0,57 0,22 0,75 0,52
SE Gotland basin BCSIII10 90 3 1,71 0,76 0,33 0,47 0,42 0,38
Bornholm basin BY5 89 0 0,00 0,00 0,00 0,00 0,00 0,00
Bornholm basin HBP216 53 13 10,00 1,63 2,16 0,40 1,33 0,58
Arkona basin BY2 48 27 13,67 3,01 2,37 0,24 4,40 0,74