Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Marine Biodiversity
worked up under the latter project (see Clark et al. 2009).). Analyses comparing the 3 surveys
of the Graveyard complex between 2001 and 2009 indicate there are changes in some taxa
following cessation of fishing operations on one of the features in 2001, but little sign of any
recovery of stony coral species and associated benthic communities . Preliminary results were
presented at the 2012 Deep Sea Biology Symposium (Clark et al. 2012).
ZBD2009-03 The vulnerability of rhodoliths to environmental stressors and characterisation of
associated biodiversity.
Rhodoliths are free-living calcified red algae. They occur worldwide, forming structurally and
functionally complex benthic marine habitats. Rhodolith beds form a unique ecosystem with a
high benthic biodiversity supporting many species, including some that are rare and unusual.
Recent international studies show that these fragile algae are at risk from the impacts of a range
of human activities e.g., physical disruption, reduction in water quality, alterations to water
movement, and aquaculture installations. Impacts of fragmentation may be critical in terms of
biodiversity and abundance associated with rhodolith beds.
The focus of this programme was to improve knowledge about the location, extent or ecosystem
functioning of rhodolith beds in New Zealand. The ecology of subtidal rhodolith beds was
been investigated for the first time in New Zealand, characterising two rhodolith species,
Lithothamnion crispatum and Sporolithon durum, examining the structure and physical
characteristics of beds at two locations and documenting their associated biodiversity. In
addition the responses of these rhodolith species to environmental stressors were investigated
for the first time.
This study documented high biodiversity in two subtidal rhodolith beds sited in relatively
close proximity in the coastal zone, with significant differences in biotic composition. The
rhodolith beds studied (located in the Bay of Islands) differed significantly in terms of water
motion, sediment characteristics and light levels. Biodiversity of the rhodolith beds was
investigated sampling (1) invertebrates at three levels of association (epifauna, infauna,
cryptofauna), (2) macroalgae, (3) fishes, as well as recording the biogenic and non-biogenic
substrates:
• a number of undescribed taxa were discovered as well as new records for the
New Zealand region, and range extensions of species known elsewhere,
• more than double the number of invertebrate taxa were present in the rhodolith
beds than found outside the beds,
• both rhodolith beds harboured high diversity of associated macroalgae and
invertebrates but with markedly different species composition,
• the floral and faunal composition differed significantly between sites.
Both species of rhodolith were found to be vulnerable to the impacts of increasing
temperature and decreasing pH. There was a significant difference between the effects of
treatments on the two species and further statistical analysis showed significant interaction
between temperature and pH level on growth. Overall the greatest effect on growth rate came
with the combination of high temperature (25° C) and low pH (7.65) on Lithothamnion
crispatum which showed negative growth, indicating probable dissolution. In experiments
investigating other environmental stressors, temperature was found to be more important for
the survival and growth of the rhodolith species examined than the effects of burial, light and
fragmentation.
The extent of rhodolith beds in other parts of the New Zealand region remain to be
documented, including those in coastal areas (including intertidal beds) and subtidal beds on
the shelf.
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