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Life-history and population dynamics of the range extending Octopus tetricus (Gould, 1852) in south-eastern Australia

Ramos Castillejos, JE (2015) Life-history and population dynamics of the range extending Octopus tetricus (Gould, 1852) in south-eastern Australia. PhD thesis, University of Tasmania.

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Ocean warming may impact the physiology, morphology, or behaviour of marine
organisms that are already living close to their limits of thermal tolerance. In response
to warming, many marine species are contracting, relocating or extending their
geographic range in order to keep pace with their preferred thermal environments.
However, variation in the magnitude of range shift responses to ocean warming is
great and the mechanisms behind those range shift responses are poorly understood.
Most of our understanding on how life history characteristics and population
dynamics relate to range shifts is based on studies on terrestrial or marine invasive
species but these may differ from climate-driven marine range shifting species.
Moreover, examining climate-driven marine range shifts of long-lived species is
challenging. The use of short-lived marine range-shifting species may thus facilitate
examining how life history characteristics and population dynamics relate to climate-driven
marine range shifts, which may allow us to increase our capacity to anticipate
changes in species distributions, assess their potential impacts, and develop
appropriate management strategies. In the southern hemisphere, Octopus tetricus
(Gould, 1852) has undergone a recent polewards range extension from southern
Queensland and New South Wales into Victorian and Tasmanian waters, likely
associated with the strengthening of the East Australian Current. Therefore, this study
investigated how life history characteristics, population dynamics and genetics may
relate to the rapid range extension of O. tetricus.
In Tasmanian waters, Octopus tetricus had a maximum total weight of 2.3 kg,
demonstrated fast growth rates and a short lifespan of approximately 11 months.
Temperature, food availability, and gender appeared to influence growth rate.
Individuals that hatched during cooler and more productive conditions, but grew
during warming conditions, exhibited faster growth rates and reached smaller body
sizes than individuals that hatched into warmer waters but grew during cooling
conditions. Fast growth and the associated rapid population turnover may provide an
advantage over longer-lived native species, facilitating the range extension of O.
tetricus. Mature females with developing eggs were found off north-eastern Tasmania.
Fecundity was high and more mature females were observed during the austral spring
and summer compared to other seasons of the year; the reproductive cycle of females
thus seemed to be timed to favourable seasonal environmental conditions, whereas
mature males were observed all year round. Females matured later and had larger
body size at maturity compared to males. Octopus tetricus has the capacity to
reproduce in the new parts of its range and the population has the potential to be self-sustainable,
which may enable the size of the emerging population to increase at the
extended zone. The population at the range extension zone was sub-structured with a
distinct group predominately comprised of individuals from Tasmania. Genetic
diversity within the range extension zone was maintained compared to the historical
distribution area. The range extension of O. tetricus is likely to be facilitated by high
and constant dispersal of paralarvae, high gene flow from a diversity of source areas,
and high genetic diversity. These features would favour adaptation to new
environments and facilitate establishment beyond the historical geographic limits,
potentially allowing O. tetricus to prevail at the range extension areas. These results
suggest that fast growth rate, rapid population turnover, high reproductive capacity,
synchronization with favourable environmental conditions, high gene flow from a
diversity of source areas, and high genetic diversity are some of the enabling factors
that may allow the establishment and prevalence of the population of O. tetricus in the
range extension zone.

Item Type: Thesis (PhD)
Keywords: Growth rates, population turnover, reproductive biology, fecundity, population genetic structure, population connectivity, genetic diversity
Copyright Information:

Copyright 2015 the Author

Date Deposited: 21 Nov 2016 00:31
Last Modified: 21 Nov 2016 00:31
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