Benthic foraminifera as a novel bio-monitoring tool in the assessment of environmental impacts linked to marine aquaculture
Abstract
The present thesis describes the behaviour of benthic foraminiferal
species in response to various levels of natural and/or anthropogenic
organic matter enrichment in the benthic environment. Loch Creran, on
the west coast of Scotland, was chosen as representative of such
environments, with both organic matter accumulation from natural
sources and an active marine aquaculture industry. An improved,
quantitative understanding of foraminiferal response to the variation in
benthic environmental gradients associated with fish is established.
Furthermore, the performance of these foraminiferal species as a novel
bio-monitoring tool to assess the impact of marine aquaculture is
evaluated. In order to address how aquaculture has influenced the benthic
environment at Loch Creran, foraminifera, sediment grain-size, organic
matter (OM) content and abundances were analysed in surface samples
collected from beneath and around floating fish cage complexes. In this
study, we followed the Foraminiferal Bio-Monitoring (FOBIMO)
protocol (Schönfeld. et al., 2012), which proposed a standardised
methodology of using foraminifera as a bio-monitoring tool to assess the
quality of the marine ecosystem and applied these protocols to the rapidly
expanding marine aquaculture sector in Scotland.
The thesis quantified the potential of benthic foraminifera for use
in reconstructing paleoenvironments from areas the pre-impacted
environmental status in areas exposed to environmental stress (e.g.
accumulation of organic matter) following the onset of marine
aquaculture. Twenty stations were sampled within Loch Creran to
describe the spatial and down-core (temporal) distribution pattern of
benthic foraminiferal assemblages. For the spatial distribution study, triplicate, Rose-Bengal stained samples from an interval of (0_1cm) below
the sediment surface were studied at each station from below the fish cages
(impacted stations) to a distance of over 1 km from the farming sites and
from the upper basin, where fish caged are absent and a natural source of
organic matter exists from the River Creran. Morphospecies counts were
conducted, and the organic carbon and the grain size distributions
determined. For the down-core study, two short sediment cores, SC-02-A
and SC-04-B were examined to present the fish farming site and a more
distant, non-fish farming site. The two cores were analysed to assess the
temporal (down-core) changes in benthic foraminiferal distribution. The
total organic matter (TOM) content was determined and indicates
temporal changes in OM accumulation rate and associated benthic
foraminiferal responses.
The results indicated 4 foraminiferal assemblage groups within the
surface sediments: (i) A1 (the reference site), (ii) A2-1 (non-fish farming
sites), (iii) A2-2 (fish farming sites) and (iv) the upper basin assemblage
group (River Creran). The assemblages were found to be well adapted to
a high input of OM contents and a minimum dissolved oxygen (DO2)
penetration depth into the sediment. The majority of foraminiferal species
at the impacted sites were agglutinated species (e.g. Eggerella scabra),
likely related to the presence high sediment (OM) contents and low
dissolved oxygen concentrations. Down-core distribution data indicated
that a faunal shift has taken place, correlating with changes in OM
enrichment in the sediment. The species diversity of foraminifera
decreases above this OM enrichment horizon in the fish farming core.
Specimens of Ammonia beccarii were dominant in the lowermost
sediment core (i.e. the pre-impacted sediment). Above 7 cm, the
assemblages change and become dominated by Eggerella scabra,
coinciding with a marked change in sediment colour. The results of this
study highlight the potential of using benthic foraminifera as reliable
indicators of pre-impacted marine habitats, with great potential to
understand environmental history around the globe.
Type
Thesis, MPhil Master of Philosophy
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