There is an increasing body of evidence that
suggests increasing temperature is correlated
with the growth and success of invasive species.
The marine heat wave that occurred along
Western Australia’s coast created a body of
water that raised ambient temperatures between
3 and 5 °C. In Cockburn Sound where the HMAS
Arunta was berthed water temperatures for this
February to March predicted ‘spawning period’
were up to 3 ºC higher than average (Marsh,
unpublished data). While there is no direct proof
of causality between the oceanic heat wave and
the spawning of Perna viridis documented in this
study there is a strong correlative relationship.
The thermal shock experienced during the heat
pulse is believed to be the trigger that initiated
the spawning of this population. The spawning
of Perna viridis in more tropical locals such as
India has been linked to changes in water
temperature (Rajagopal et al. 1988; Narisimham
1980). Shafee (1989) also report that in
subtropical environs spawning in this species is
restricted to warmer months. Hicks et al. (2001)
report that increased water temperatures
triggered spawning in Perna perna. Another
species of Perna, Perna canaliculus is also
reported to have increased rates of spawning
associated with increased water temperature
(Buchanan 1998). The increased reporting of
invasive species settlement, growth and
dominance linked to increasing temperature
regimes add further weight to this hypothesis.
Temperature is often thought of as one of the key
limiting factors determining the geographic
spread of many marine species. For tropical
species such as Perna viridis it is predominantly
colder waters that are perceived as a limiting
factor. Perhaps one of the primary consequences
of climate change will be the creation of suitable
physical habitats for a non-indigenous species,
such as P. viridis, to move outside its current
native range through the removal of
physiological (temperature) constraints in areas
where it currently can not survive. A period of
elevated sea temperature in the 1990s allowed a
previously temperature-confined P. viridis
population in Tokyo Bay to spread through
Japan’s Seto Inland Sea (Matsuyama 1999;
Umemori and Horikoshi 1991). The average
temperature ranges experienced within Cockburn
Sound, Western Australia (14-24°C) are within
the large range of documented thermal tolera