The degradation of marine ecosystems is a global issue due to the many
human-mediated impact pathways such as agriculture and horticultural
discharges of fertilizers and stock effluent (Howarth et al. 2002, Smith
et al. 2006), and point-source inputs of human and industrial wastes
(Taylor et al. 1998, Bothner et al. 2002). An effect that is common to
most of these stressors is the enrichment of the water column and seabed
from additional nutrients. As a result, most environmental monitoring
programs will include enrichment indicators, such as direct measures of
nutrient concentrations (more common in the water column),
concentrations and prevalence of nutrient responsive organisms (e.g.
phytoplankton and benthic macrofauna), and several associated
physico-chemical indicators relating to the oxygen status. The
reliability and informative nature of these indicators is critical to
our ability to detect change and status in relation to any real or
perceived environmental thresholds.
Benthic macrofauna analysis is generally viewed as the ‘gold standard’
for assessing benthic condition, and with it, marine ecological quality
status (), however, the method has two key limitations that are
increasingly pertinent and therefore restrictive of its use.
Importantly, the composition of the macrofauna community (i.e. the 1-20
mm sized animals that live within the sediments) provides a tangible,
time-integrated picture of recent environmental influences by virtue of
their presence and prevalence. Understanding of the relative
sensitivities and the roles that each of the various macrofauna species
play during disturbance and subsequent ecological succession reliably
permits conclusions regarding the general level of ecological
modification and disturbance. The limitations of this approach stem from
the time it takes to sieve, sort, correctly identify and enumerate all
of the individuals in a sediment sample. The labour costs of having
skilled personal undertake this task in developed countries are
significant, with analytical costs on the order of $100-1500 USD per
sample (Author Pers. Obvs.). Such high costs can influence survey
design, affecting both the frequency and intensity of sampling, and in
doing so can adversely impact our ability to understand a system
(temporally) and the reliability of the estimates (spatial replication).
Moreover, the time consuming analytical process has the potential to
create a major bottleneck in the work stream which can delay the
provision of the results by several months, and with that our ability to
report on and respond to the results in a timely manner.
This problem is not new, and much effort has gone in to developing other
potential more cost effective indicators of enrichment, but as yet there
is presently no universally accepted replacement. Biogeochemical
indicators, such as redox potential ( Wildish) and total free sulphides
(Hargrave) have gone some way to addressing this as they are both
relatively cost effective and rapid, and often correlate reasonably well
with biological indicators (Hargrave, Keeley, ??). However, they have
one distinct limitation, in that they are one step removed from ecology
and exceptions often exist where the correlations are poor, and as such
they tend to be viewed as a compromised assessment, providing a proxy
for ‘ecological health’. This may be in part related to differences in
response times, and therefore indicator-specific time lags and the
degree to which the chemical indicators are providing a temporally
integrated picture of effects. Therefore there remains a clear and
immediate need for an alternative method for evaluating ecological
quality status that is both rapid and cost-effective, and directly
related to ecology and biodiversity.
Another popular approach to evaluating benthic effects involves the
application of biotic indices, which still require a full macrofauna
assessment, and aim to condense what is effectively multivariate data in
to a single number. There is presently a plethora of such indicators
(for reviews see Pinto et al and ???) that use a variety of approaches,
many of which are region and/or environment specific (e.g. MEDDOCC,
mmmm). Some do this very effectively, have proven to be reasonably
transferable and are becoming more broadly utilised as a result. One
such group indicator utilise the Eco-Group approach developed by Borja
et al. () for the application of the AZTI marine biotic index (AMBI).
The basic premise here is that knowledge of the disturbance/enrichment
tolerance of the dominant macorfauna taxa can be used in conjunction
with their relative prevalence to calculate a scaled index. to
composition and knowledge of species-specific sensitivities down in Some
do it fairly well ().
Salmon farms as a case study - induce pronounced seabed enrichment
In this paper we… exploit the strong enrichment gradients that
are commonly observed in association with salmon farms (Ref, Keeley) to
test the potential for using NGS of foraminiferal communities to
determine benthic ecological quality status. To do this we use the
overall synthesis indicated by multiple established indicators of
benthic enrichment to elucidate the ecological characteristics of lesser
known foramifera taxa and then to allocate Eco-Groups (Borja et al) in a
manner analogous to established macrofauna methods (see Keeley et al.
2012). The Eco-Group allocations are then used to derive and test the
suitability of a variety of established indicators for purposes of
discerning benthic enrichment stage.