State of the Bay Report 2010-Final - Anchor Environmental

growing, large bodied species in Big Bay between 2009 and 2010 suggesting that disturbance had
been reduced. It is possible that the slightly reduced level of disturbance occurring in Big Bay
between 2009 and 2010 allowed for a greater diversity of species (both r and K strategists) to coexist.
This is a sign of the recovery of the system following disturbance.
The average diversity of macrofauna in Langebaan Lagoon was relatively low in 2004, but
increased between 2004 and 2008 and 2008 and 2009 such that the lagoon supported a moderate
level of diversity. The 2010 survey revealed that there had been a very slight decrease in the
diversity of macrofauna. The W statistic revealed that there had been a slightly increased level of
disturbance in the lagoon between 2009 and 2010. This was most likely a natural fluctuation in
response to community interactions and natural changes to the physical environment. Indeed the
results of the 2010 sediment survey suggest that there had been improved flushing of fine sediments
in the southern reaches YEAR; of LS Means the Lagoon, suggesting stronger water movements YEAR; LS Means in the area.
Diversity (H')
Diversity (H')
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
Current effect: F(4, 54)=7.9270, p=.00004
Effective hypothesis decomposition
Vertical bars denote 0.95 confidence intervals
Include condition: V3="SB"$
1999
YEAR; LS Means
Current effect: F(3, 24)=.39626, p=.75686
Effective 2004 hypothesis 2008 decomposition 2009
Vertical bars denote 0.95 confidence intervals
Include condition: YEAR V3="LL"$
2010
Langebaan Lagoon
Small Bay
2004 2008 2009 2010
YEAR
Current effect: F(4, 33)=.68502, p=.60741
Effective hypothesis decomposition
Vertical bars denote 0.95 confidence intervals
Include condition: V3="BB"$
1999 2004 2008 2009 2010
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 180
Diversity (H')
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
Big Bay
Figure 8.16. Average Shannon Weiner diversity indices (H’) (± 0.95 confidence intervals) for Big Bay, Small
Bay and Langebaan Lagoon in 1999, 2004, 2008, 2009 and 2010.
8.4.4 Linking Ecological Indices to Environmental Variables
MDS plots were generated from macrobenthic abundance data to detect any similarities in
community structure between samples drawn from different areas of the Bay and Lagoon.
Environmental data was then superimposed on top of the MDS plots in the form of bubbles that are
scaled in accordance with the magnitude/concentration of the parameter in question (i.e. larger
bubbles represent higher concentrations of metals for example). The aim of superimposing bubble
plots onto the macrobenthic MDS was to assess whether the spatial variability in the benthic
community composition was linked to any specific contamination gradients or environmental
variable(s).
Depth and the percentage mud appear to be the principle abiotic factors that correlate with,
and most likely lead to distinctions in the benthic macrofauna community composition between
Langebaan Lagoon and Saldanha Bay. Saldanha Bay is deeper and the sediments contain a higher
YEAR