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Macroalgal assemblages as indicators of the broad-scale impacts of fish farms on temperate reef habitats


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Oh, E 2009 , 'Macroalgal assemblages as indicators of the broad-scale impacts of fish farms on temperate reef habitats', Honours thesis, University of Tasmania.

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Intensive fish culture in open sea pens can deliver large amounts of nutrients to coastal ecosystems.
Sheltered areas with high water quality are predominately chosen for this type of mariculture, and
these systems may be adversely affected by the presence of the farms. Since macroalgal community
composition has been shown to be a good indicator of environmental disturbance on reef, the present
study investigated the effect of salmon farms on macroalgae in a semi-enclosed coastal waterway in
southern Tasmania. Data on the macroalgal community were collected from two depths at 44 sites of
varying distance from twelve active fish farm leases. This included reference sites at distances of 5
km or more. The sites were widely distributed throughout the study area, and varied in their exposure
to wave action. The macroalgal community composition differed significantly between sites at 100 m
from fish farms and sites at 5 km or more. Sites at 400 m varied in their response to farms, with some
sites showing characteristics similar to 100 m sites. Impacts varied between swell exposed sites and
sites only subjected to wind-generated waves. Chaetomorpha spp. and Ulva spp. were abundant near
fish farms at exposed sites, whereas the abundance of filamentous green algae increased at sites near
fish farms in sheltered sites. The percentage cover of indicator groups such as epiphytes and
opportunistic algae in total provided the best indicators of fish farm impacts on a broad scale. The
percent cover of canopy forming perennial algae did not decrease near fish farms indicating that their
growth and recruitment has not been greatly affected by high levels of sedimentation from fish farms
or prolonged fouling by opportunistic algal epiphytes to the present, however further study is needed
to examine this in more detail.
The above analysis utilised photographic quadrats to quantify community composition. Most other
broad-scale sampling methods used to measure macroalgal composition require expertise to identify
species in situ. However, this reduces the capacity of monitoring programs to collect large amounts
of data. Using data collected from a subset of 36 sites, the photographic method was compared with a
manual quadrat sampling method. The two methods produced similar multivariate results but manual
quadrats had a slightly greater capacity to detect the impacts of the fish farms. This indicates that
photographic quadrats are likely to be conservative in quantifying effects of fish farms, but still
deliver appropriate resolution to detect major changes in dominant macroalgal cover and composition.
Some adjustments to the photographic methods used will allow better resolution for algae obstructed
by canopy or epiphytic overgrowth.

Item Type: Thesis - Honours
Authors/Creators:Oh, E
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