State of the Bay Report 2010-Final - Anchor Environmental

Table 8.5. W statistics at all stations sampled between 2004 and 2010 in Langebaan Lagoon (1 =
Undisturbed, 0 = moderately disturbed, -1 = Grossly disturbed)(Red indicates a decrease an
green indicates an increase since the previous year)
2004 2008 2009 2010
LL 31 0.276 0.178 0.26497 0.220529
LL 32 0.108 0.303 0.077271 0.232452
LL 33 0.216 0.099 0.415304 0.281207
LL 34 0.233 0.057 0.265976 0.247906
LL 37 0.295 0.362 0.256901 0.333258
LL 38 - - 0.166232 0.183672
LL 39 - - 0.244047 -0.06678
LL 40 - - 0.188317 0.184814
LL 41 - - 0.195189 0.032135
8.4.3 Species Diversity Indices
8.4.3.1 Spatial Analysis
Mean values (± SE) for various diversity indices associated with macrobenthic communities
in Small Bay, Big Bay and Langebaan Lagoon have been represented graphically in Figure 8.14.
Species diversity (H’), species evenness (J), species richness (d) and the total number of species (S) is
notably higher in Big Bay and Langebaan Lagoon when compared to Small Bay, but the difference is
not significant (p > 0.05). These results, coupled with the W statistics and the results of the
sediment analysis (see §6), indicate that macrobenthic communities in Small Bay are subject to the
greatest degree of anthropogenic stress when compared to Big Bay and Langebaan Lagoon.
The species diversity (represented by the Shannon Weiner Index, H’) for Saldanha Bay and
Langebaan Lagoon in 2010 is represented in Figure 8.15. The diversity of species in Small Bay is
lowest at the Yacht Club Basin (SB1), Mussel farm (SB9), along the Multi-Purpose Terminal (SB15)
and in the middle of the bay (SB8). The low species diversity in the Yacht Club Basin is most likely
due to the polluted state of this site (see §6), while the low diversity at the Multi-Purpose Terminal is
most likely due to dredging that occurred in the area in 2007/08. Furthermore both the yacht club
basin and the area below the ore jetty in Small Bay have been recognized as ‘key problem areas’ that
suffer from reduced water movement which leads to the accumulation of fine grained particles and
organic matter, to which toxic substances such as metals and hydrocarbons adsorb (CSIR 2002). The
remaining five sites in Small Bay have low levels of diversity (H’ values ranging from 0.91 to 1.90).
Overall the diversity in Big Bay is low to moderate (H’ values ranging between 1.4 and 2.3).
The diversity of benthic macrofauna in Big Bay was lowest at sites near the ore jetty and Small Bay.
The lower levels of diversity are most likely a consequence of anthropogenic disturbances that have
occurred along the ore jetty (dredging) and within Small Bay (fish factory effluent, mussel farms,
sewerage). Sites BB25 and BB29 both had a relatively high diversity compared to other Big Bay sites.
Examination of the sediment characteristics and the concentration of contaminants provide no
apparent reason for the variation in diversity between sites.
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 177