Factors affecting the distribution of the introduced goby Tridentiger trigonocephalus Gill (Gobiidae) in south eastern Australia
- Publication Type:
- Thesis
- Issue Date:
- 2008
Closed Access
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01Front.pdf | contents and abstract | 1.01 MB | |||
02Whole.pdf | thesis | 54 MB |
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Studies of biological invasion have often noted the tendency of invaders to accumulate in
disturbed habitats. While this pattern has been observed repeatedly it has been difficult to
establish a mechanism: do these habitats possess attributes, such as fewer native species, vacant
niches and lower biotic resistance, which make them more susceptible to invasion? The
presence of introduced species that persist in such habitats but fail to establish outside these
regions suggests that there are factors characteristic of disturbed habitats' that allow the initial
invasion of these species, while outside these regions invasion is suppressed. The introduced
gobiid T. trigonocephalus (Gill 1858; Family: Gobiidae) was introduced to SE Australia, to
Port Jackson in Sydney Harbour (33°51' S) and Port Phillip Bay in Melbourne (37°52' S) in the
early 1970's and while populations have persisted since that time the species remains restricted
within these estuaries to the .
Populations of T. trigonocephalus reach their greatest density around the commercial regions of
Port Jackson and Port Phillip Bay and densities are positively associated with physical
properties of these regions, such as relief and sediment size. While recruitment to regions
outside these core areas does occur, adult populations apparently fail to establish. In Port Phillip
Bay, the population of T. trigonocephalus reaches significantly greater densities and is
distributed over a broader area than the population in Port J ackson. The positive association in
densities of this species with physical and biological indicators (low visibility, deep water, fine
sediment grain size and a fish assemblage typical of these regions), suggests that predation may
prevent establishment of this species outside the regions where these factors are present.
However, pre-settlement factors such as poor reproductive output may also limit the distribution
of this species. Field and laboratory studies demonstrated that adult populations in both
locations completed a normal reproductive cycle up to the point of gamete production
(ovulation in females). Reproduction occurs from early Spring until mid-Summer at both
locations, when water temperatures increasing above 22°C appear to trigger gonadal regression.
Temperature in Port Jackson reaches this point earlier in the year than Port Phillip Bay and as a
result, the reproductive season of T. trigonocephalus is significantly shorter in Port Phillip Bay.
Similar temperatures (about 22°C) trigger gonadal regression in both locations and while
regression in the Port Jackson population is triggered at a slightly higher temperature, this is not
enough to compensate for the more rapid increase and higher maximum and regression occurs
approximately one month earlier than in Port Phillip Bay. In females, temperature affects
reproduction by inhibiting ovulation, resulting in oocyte over-ripening and subsequent oocyte
atresia and resorption. Males have a slightly higher tolerance to temperature in that testicular
regression occurs at temperature slightly higher than those triggering ovarian regression,
however the mechanism is less apparent.
Temperature also appears to have substantial flow-on effects on the abundance/output of egg
and larval stages of T. trigonocephalus. Ichthyoplankton samples from Port Jackson taken in the
region supporting the highest population densities of T. trigonocephalus showed a diverse
gobiid fauna but, except for a single specimen, a complete absence of T. trigonocephalus.
Recruits of this species were observed in Port Jackson indicating that some degree of larval
settlement, however this was significantly lower than that recorded in Port Phillip Bay.
The success of the invasion of T. trigonocephalus into south-eastern Australia appears to
depend on several factors. Disturbed habitats do appear to possess attributes that make them
more easily invaded by T. trigonocephalus than other regions; however these appear to be
physical attributes rather than biological ones. Thus, there is the potential for T. trigonocephalus
to invade any habitat with these attributes, most notably newly dredged regions of harbours or
regions of freshwater and sediment input. Outside these habitats biotic resistance does appear to
play a role in limiting the invasion success of this species.
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