Impairments of Endocrine Functions: Case Studies - Ecological Biomarkers: Indicators of Ecotoxicological Effects - page 229

45

Dogwhelk abundance at e Kames (12)

40

All dogwhelks
in edged
Juveniles (<16 mm)

35

30

25

20

15

10

5

0

1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011

Year

FIGURE 9.7
Increasing abundance of adult, subadult (thin edged shells), and juvenile (<16 mm shell length) dogwhelks at
monitoring site close to The Kames (site 6). Abundances are semiquantitative, expressed as a sampling rate
(time taken to collect individuals by the same field sampler).

6

Scatsta Ness 1, mid shore
Scatsta Ness 2, mid shore
Jetty 3, lower shore

5

4

3

2

1

0

FIGURE 9.8
Temporal changes in relative abundance of dogwhelks (all size classes) at three monitoring sites close to the oil
terminal in Sullom Voe. Abundances are based on the following classification: 0 = absent, 1 (rare) <0.25/m 2 , 2
(occasional) 0.25-0.5/m 2 , 3 (frequent) 0.5-2.5/m 2 , 4 (common) 2.5-7.5/m 2 , 5 (abundant) 7.5-25/m 2 .

of the populations, leading to even more profound and lasting effects on ecosystem struc-
ture, may occur.
Finally, it is also worth noting that imposex is a unique bioindicator due to its “sex-
ual orientation.” In contrast to all other known sex change phenomena that feminize or
demasculinize (see below), it causes masculinization.