Bulletin of the Sea Fisheries Institute 2 (153) 2001 - CEEMaR

Main phytoplankton assemblages ... 35
ized methods of the Baltic Monitoring Program (Anon. 1988, Anon. 1983, Grasshoff et al.
1983). Results are presented in box-and-whisker plots that were made using the STATISTICA
program. Each box includes the middle 50% of the data (quartile 2 and 3) and the median is
marked. The lines below and above the box, whiskers, present the range of the nonoutliers. The
outliers, located above and below the box, present the data values 1.5 times greater than the
interquartile range (Anon. 1997).
RESULTS
Cluster analysis
In order to emphasize the most important features of phytoplankton diversity in the Gulf of
Gdañsk and the Pomeranian Bay, clustering analysis was carried out on all the phytoplankton
samples from all the cruises in both basins. Ten groups of samples were identified at a similarity
level of 50% (ig. 3). This means that the phytoplankton similarity among samples from different
groups was lower than 50%, while within each group, the phytoplankton similarity among
samples was greater than 50%. The groups in igure 3 have been numbered, from the most
distinct, with the lowest degree of similarity, to the least distinct, with the greatest degree of
similarity. Table 1 presents the location, cruise dates and the number of samples that belong to
each group, and the range of chlorophyll-a concentration at the stations. The other columns
present the dominant species or the higher phytoplankton systematic units (which constitute
about 75% of the sample biovolume) and their percentage of the biovolume, as well as the
20
Bray-Curtis similarity, %
30
40
50
Gulf of Gdañsk
JULY 96
JULY 94
AUG. 95
Jul. 96
63
(max S)
NOV. 94
APRIL 94 MAY 97 Nov. 94 Apr. 94 May 97
111 (min S) 111 (min S) 37
FEB. 96
Jul. 94
111 (min S)
Jul. 96
52a (min S)
Pomeranian Bay
JULY 96
MAY 97
Jul. 96
6, 18, 38, 41
(min S)
OCT. 97 MAR. 96
groups
10
9
8
7
6
5 4
3
2
1
Fig. 3. Sample groups from particular cruises identified based on cluster analysis. Cruises in bold are those in which
the majority of stations were in a given group; italics identify single stations. Values of extreme salinity conditions
are in brackets.