38
P. Tett
2
4
6
8
1
2
3
4
5
6
7
8
years 1979-1981
(c) reference envelope
(log10) PD/L
(log10) MAD / L
2
4
6
8
1
2
3
4
5
6
7
8
(d) PCI for 2006
(log10) PD/L
(log10) MAD / L
New points : 8; Outside envelope: 5
PCI : 0.38
0
31
59
90
120 151 181 212 243 273 304 334 365
2
4
6
8
day in year
(b) medium-sized armoured
dinoflagellates, 1979 to 1981
log
10 cells / L
0
31
59
90
120 151 181 212 243 273 304 334 365
2
4
6
8
day in year
log
10 cells / L
(a) pelagic diatoms, 1979 to 1981
4
5
Fig. 1.7 Evaluation of a Phytoplankton Community Index illustrated with data from loch Creran.
Part (a) shows the seasonal cycle of pelagic diatoms (PD), illustrated by the common species
Skeletonema costatum, and was obtained by plotting abundances in all phytoplankton samples
taken in the loch during 1979, 1980 and 1981. The vertical scale is logarithmic, in order to show,
clearly, the wide range in abundance. The horizontal scale gives days in the year, with day 1 being
1st January. The data from 1979–1981 is plotted as open circles; the small set of filled circles
shows observations made during 2006. Part (b) shows a similar graph for the medium-sized
autotrophic dinoflagellates (MAD), illustrated by drawings of a typical species of the genera
Gonyaulax and Scrippsiella. In part (c) the 1979–1981 data from (a) and (b) have been plotted
onto a surface whose axes are the abundances of the PD and the MAD, and an envelope has been
drawn around the points to define reference conditions. In part (d) the envelope has been redrawn,
and points from 2006 plotted onto the surface. The PCI is the proportion of new points that remain
inside the reference envelope
P. Tett
2
4
6
8
1
2
3
4
5
6
7
8
years 1979-1981
(c) reference envelope
(log10) PD/L
(log10) MAD / L
2
4
6
8
1
2
3
4
5
6
7
8
(d) PCI for 2006
(log10) PD/L
(log10) MAD / L
New points : 8; Outside envelope: 5
PCI : 0.38
0
31
59
90
120 151 181 212 243 273 304 334 365
2
4
6
8
day in year
(b) medium-sized armoured
dinoflagellates, 1979 to 1981
log
10 cells / L
0
31
59
90
120 151 181 212 243 273 304 334 365
2
4
6
8
day in year
log
10 cells / L
(a) pelagic diatoms, 1979 to 1981
4
5
Fig. 1.7 Evaluation of a Phytoplankton Community Index illustrated with data from loch Creran.
Part (a) shows the seasonal cycle of pelagic diatoms (PD), illustrated by the common species
Skeletonema costatum, and was obtained by plotting abundances in all phytoplankton samples
taken in the loch during 1979, 1980 and 1981. The vertical scale is logarithmic, in order to show,
clearly, the wide range in abundance. The horizontal scale gives days in the year, with day 1 being
1st January. The data from 1979–1981 is plotted as open circles; the small set of filled circles
shows observations made during 2006. Part (b) shows a similar graph for the medium-sized
autotrophic dinoflagellates (MAD), illustrated by drawings of a typical species of the genera
Gonyaulax and Scrippsiella. In part (c) the 1979–1981 data from (a) and (b) have been plotted
onto a surface whose axes are the abundances of the PD and the MAD, and an envelope has been
drawn around the points to define reference conditions. In part (d) the envelope has been redrawn,
and points from 2006 plotted onto the surface. The PCI is the proportion of new points that remain
inside the reference envelope