caulerpa taxifolia in moreton bay - Centre for Marine Science ...

1. ABSTRACT
Caulerpa taxifolia in Moreton Bay
Caulerpa taxifolia is a green macroalga that has gained notoriety in the last two decades
as an invasive species following its introduction and subsequent invasion of large areas
of the north-western Mediterranean Sea. It is native to Moreton Bay in south-east
Queensland, where it shares its soft-sediment niche with seven species of seagrass. The
current distribution of C. taxifolia in Moreton Bay was mapped, and compared with its
distribution five years ago to detect any changes. To explore interactions between
C. taxifolia and Moreton Bay seagrasses, experiments investigated the effect of
C. taxifolia extract and of physical disturbance on seagrasses.
There was a significant increase in C. taxifolia distribution in Moreton Bay in the last
five years, particularly in western and southern regions with more sites and increased
cover. In western Moreton Bay, C. taxifolia mainly colonised bare sediments, while
in the southern Bay and Pumicestone Passage it replaced seagrass. It is interesting to
note that at the sites where C. taxifolia cover decreased in western Moreton Bay, it
was replaced by seagrass, which indicates the potential for seagrasses to recover after
colonisation by C. taxifolia. There were dense populations present around Dunwich
at North Stradbroke Island in eastern Moreton Bay, however C. taxifolia was only
present at low densities on the eastern banks.
Planthouse experiments showed some significant results, with seagrass shoot
density being negatively affected by the addition of C. taxifolia extract, however the
results were highly variable. Reciprocal transplants of C. taxifolia and the seagrass
Zostera capricorni indicated that Z. capricorni is more susceptible to physical
disturbance than C. taxifolia, which can utilise disturbance as an opportunity for
expansion.
Five processes are hypothesised to synergistically affect C. taxifolia distribution and
seagrass interactions in Moreton Bay, including sustained high seawater temperatures,
water quality decline, physical disturbance, allelopathic interactions from C. taxifolia
toxins, and the accumulation of sulphide in the sediments.
Jane Thomas -1-
Abstract