Aquatic Environment and Biodiversity Annual Review 2012

AEBAR 2012: Ecosystem effects: Land-based effects
duration, frequency and magnitude of exposure, temperature, and other environmental variables
(Servizi and Martens 1992).
Increased nutrient addition to the aquatic environment can initially increase production, but with
increasing nutrients there is an increasing likelihood of harmful algal blooms and cascades of effects
damaging to most communities above the level of the plankton (Kennish 2002; Heisler et al. 2008).
This excess of nutrients is termed eutrophication. Eutrophication can stimulate phytoplankton growth
which can decrease the light availability and subsequently lead to losses in benthic production from
seagrass, microalgae or macroalgae and their associated animal communities. Algal blooms then die
and their decay depletes oxygen and blankets the seafloor. The lack of oxygen in the bed and water
column can lead to losses of finfish and benthic communities. These effects are likely to be location
specific and are influenced by a number of factors including: water transparency, distribution of
vascular plants and biomass of macroalgae, sediment biogeochemistry and nutrient cycling, nutrient
ratios and their regulation of phytoplankton community composition, frequency of toxic/harmful algal
blooms, habitat quality for metazoans, reproduction/growth/survival of pelagic and benthic
invertebrates, and subtle changes such as shifts in the seasonality of ecosystems (Cloern 2001). These
effects of eutrophication abound in the literature, for example, the formation of dead (or anoxic) zones
is exacerbated by eutrophication, although oceanographic conditions also play a key role (Diaz and
Rosenberg 2008). Dead zones have now been reported from more than 400 systems, affecting a total
area of more than 245,000 square kilometres (Diaz and Rosenberg 2008). This includes anoxic events
from New Zealand in coastal north-eastern New Zealand and Stewart Island (Taylor et al. 1985,
Morrissey 2000).
Other pollutants such as heavy metals and organic chemicals can have severe effects, but are more
localised in extent than sediment or nutrient pollution (Castro and Huber 2003, Kennish 2002).
Fortunately the concentration of these pollutants in most New Zealand aquatic environments is
relatively low, with a few known exceptions. Examples of this include naturally elevated levels of
arsenic in Northland 27 , Cadmium levels in Foveaux Strait oysters (Frew et al. 1996) and levels of
Nickel and chromium within the Motueka river plume in Tasman Bay (Forrest et al. 2007). The
Cadmium levels have caused market access issues for Foveaux Strait Oysters. Some
anthropogenically generated pollutants such as copper, lead, zinc and PCBs are high in localised
hotspots within urban watersheds. In the Auckland region these hotspots tend to be in muddy
estuarine sites and tidal creeks that receive runoff from older urban catchments 28 . There is a lack of
knowledge on the impacts of these pollutants upon fisheries.
Climate change is likely to interact with the effect of land-based impacts as the main delivery of landbased
influences is through rainfall and subsequent freshwater flows. Global climate change
projections include changes in the amount and regional distribution of rainfall over New Zealand
(IPCC 2007). More regional predictions include increasing frequency of heavy rainfall events over
New Zealand (Whetton et al. 1996). This is likely to exacerbate the impact of some land-based
influences as delivery peaks at times of high rainfall, e.g. sediment delivery (Morrison et al. 2009).
Physical alterations of the coast are generally, but not exclusively (i.e. wetland reclamation for
agriculture), concentrated around urban areas and can have a number of consequences on the marine
environment (Bulleri and Chapman 2010). Changes in diversity, habitat fragmentation or loss and
increased invasion susceptibility have all been identified as consequences of physical alteration. The
effects of physical alterations upon fisheries remain largely unquantified; however the habitat loss or
alteration portion of physical alterations will be dealt with under the habitats of particular significance
for fisheries management (HPSFM) section.
27 Accessible on the www.os2020.org.nz website.
28 Available from the State of the Auckland Region report 2010, Chapter 4.4 Marine, at
http://www.arc.govt.nz/albany/index.cfm?FD6A3403-145E-173C-986A-A0E3C199B8C5
219