State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Benthic macrofauna
macrofauna data from Saldanha Bay and Langebaan Lagoon. In the intervening years between the
1975 and 1999 studies, significant development took place in Saldanha Bay (previously described in
this report) including ore export and dredging of Small Bay in 1997/98. The 1999 study was
conducted approximately 12 months after dredging and is representative of a recovering benthic
community. Direct comparisons between earlier studies are further complicated due to different
equipment being used in 1975 than in 1999-2009. The study conducted in 1975 in Saldanha Bay
(Moldan 1978) made use of a modified von Veen grab sampler weighted to 20 kg which sampled an
area of 0.2 m 2 from the surface fraction of sediment whilst that of 1999-2009 made use of a diveroperated
suction sampler which sampled an area of 0.24 m 2 to a depth of 30 cm. The former
sampling technique (von Veen grab) would be expected to sample a smaller proportion of benthic
macrofauna due to its limited ability to penetrate the sediment beyond the surface layers. The
suction sampler effectively sampled to a depth of 30 cm, which is the range in which larger species,
like prawns and crabs, are expected to occur. The study conducted in 1975 in Langebaan Lagoon
(Christie and Moldan 1977) and those conducted by Anchor Environmental Consultants both made
use of a diver-operated suction sampler which sampled an area of 0.24m 2 . However, in 1975 a
depth of 60 cm was sampled while in surveys since 2004 a depth of only 30 cm was sampled. Thus,
considering the differences in sampling techniques employed, it is likely that the changes reflected
by the data between the 1975 and 1999-2008 in Saldanha Bay and Langebaan Lagoon are a function
both of real changes that occurred in the Bay and an artefact of differences in sampling
methodology. The exact location of sites sampled during 1975 and 1999-2008 studies also differed
slightly (Figure 7.1), however, the broad distribution of sites throughout the sampling area ensures
that the data collected are representative of Small Bay, Big Bay and Langebaan Lagoon and such can
be compared with one another.
7.3 Approach and methods used in monitoring benthic macrofauna in 2011
7.3.1 Sampling
A total of 30 sites were sampled for benthic macrofauna in 2011, ten of which were in Small Bay,
seven in Big Bay, nine in Langebaan Lagoon, two in Salamander Bay and two in Donkergat (Figure
7.1). The water depth ranged from 1.8 m to 21 m, with the shallowest sites being those in
Langebaan Lagoon (Table 7.1). Samples were collected using a diver-operated suction sampler,
which sampled an area of 0.08 m 2 to a depth of 30 cm and retained benthic fauna >1 mm in size in a
muslin bag. Three suction samples were taken at each site and pooled, resulting in a total sampling
surface area of 0.24 m 2 per site. These methods correspond exactly with those employed in 1999,
2004 and 2008-2010 and thus facilitate comparisons between these sets of data. Samples were
stored in plastic bottles and preserved with 5% formalin.
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