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

State of Saldanha Bay & Langebaan Lagoon 2011
Benthic macrofauna
Table 7.1. Depth at each of the sites sampled in 2011.
Small Bay
Depth
(m) Big Bay Depth (m)
Langebaan
Lagoon
Depth (m)
Salamander/
Donkergat
SB1 10 BB20 20.9 LL31 5.5 D1 4.1
SB2 7.8 BB21 10 LL32 4.4 D2 3.5
SB3 5.2 BB22 11 LL33 3 S1 2.8
SB8 10.9 BB25 10.3 LL34 4.1 S2 6.3
SB9 14.7 BB26 15 LL37 3
SB10 7.1 BB29 15 LL38 6.6
SB14 15 BB30 3.4 LL39 5.7
SB15 12 LL40 2.4
SB16 16 LL41 0.8
SB42 9.1
Depth
(m)
In the laboratory, samples were rinsed of formalin, stained with Rose Bengal to aid in
identification of biological material. All fauna were removed and preserved in 1% phenoxetol
(Ethylene glycol monophenyl ether) solution. The macrofauna were then identified to species level
where possible, but at least to family level in all instances. The biomass (blotted wet mass to four
decimal places) and the abundance of species were recorded for each sample.
7.3.2 Statistical Analysis
The data collected from this survey were used for two purposes 1) to assess spatial variability in the
benthic macrofauna community structure and composition between sites in 2011 and 2) to assess
changes in benthic community structure over time (i.e. in relation to the 1999, 2004, 2008, 2009 and
2010 surveys). Both the spatial and temporal assessments are necessary to provide a good
indication of the state of the system.
7.3.2.1 Community structure and composition
Changes in benthic species composition can be the first indicator of disturbance, as certain species
are more sensitive (i.e. likely to decrease in abundance in response to stress) while others are more
tolerant of adverse conditions (and may increase in abundance in response to stress, taking up space
or resources vacated by the more sensitive species). Monitoring the temporal variation in
community composition also provides an indication of the rate of recovery of the ecosystem
following disturbances in different areas of the system. This allows one to more accurately predict
the impacts of proposed activities. “Recovery” following environmental disturbance is generally
defined as the establishment of a successional community of species which progresses towards a
community that is similar in species composition, density and biomass to that previously present (C-
CORE 1996 and Newell 1998). The rate of recovery is thus dependent on the reference
environmental conditions and the communities supported by such conditions. Given the spatial
variability of environmental conditions (largely influenced by depth and exposure) as well as
anthropogenic disturbances it is expected that recovery will vary spatially throughout the Saldanha
Bay and Langebaan Lagoon system.
Certain species are able to rapidly invade and colonise disturbed areas as they have high
fecundity, rapid growth and rather short life-cycles (Newell 1998). These species are known as “rstrategists”
or opportunistic species and their presence generally indicates unpredictable short-term
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