State of the Bay Report 2010-Final - Anchor Environmental

Taxon
Anchor Environmental
Occurrence
in Saldanha
Bay Origin Vector
Spartina maritima Confirmed Europe BS
12.1 The occurrence and spread of the Western pea crab Pinnixa
occidentalis in Saldanha Bay
The Western Pea crab Pinnixa occidentalis was originally described from California by M. J.
Rathbun in 1893, but is presently reported to occur along the whole west coast of North America
from Alaska to Mexico (Ocean Biogeographic Information System 2011). The depth range
distribution for this species is reported to range from 11-319 m. This species was recently (in the
latter part of 2010) identified in the collections from the Saldanha Bay: State of the Bay surveys
(Clark et al. 2011), previously being listed as unidentified owing to it not having been previously
reported from South Africa waters. Sampling for the State of the Bay surveys entails the collection of
three replicate sediment samples from 20-25 sites in Salnaha Bay and Langebaan using a diveroperated
suction sampler, which sampled an area of 0.08 m 2 to a depth of 30. It appears to be an
alien species that established itself in the Bay in the period between 1999 (at which time no
specimens were recorded in a comprehensive set of samples from the Bay) and 2004 when it was
recorded at four of the 30 sampling sites in the Bay. Subsequent to it becoming established in the
Bay, both the abundance and range occupied by this species expanded fairly rapidly (increasing from
4 sites and 10.1 individuals m -2 ) to a maximum of 8 sites and 37.2 individuals m -2 in 2009 and 2010,
respectively (Figure 12.1). The initial distribution (2004) took the form of a narrow swathe extending
right across Saldanha Bay from Hoedjiesbaai to the Lagoon entrance, which filled out a little in 2008,
and then extended through into the upper reaches of Langebaan lagoon in 2009 (Figure 12.1). The
distribution in 2010 was similar to that in 2008 and 2009 but did not include any sites in the lagoon
which suggests that the habitat here may not be entirely suited to the species which favours deeper
water (>10 m) in its native area (Ocean Biogeographic Information System 2011).
No. sites
Abundance (no. ind. m -2 )
10
8
6
4
2
0
40
30
20
10
0
1999 2004 2008 2009 2010
1999 2004 2008 2009 2010
Figure 12.1 No of sites (top) at which the Western Pea crab Pinnixa occidentalis has been recorded in
Saldanha Bay and Langebaan lagoon in the period 2004 and top number of individuals
collected from these sites (bottom).
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 255