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Range and distribution

 

All marine animals live in an environment that will usually be within a limited range of physical constraints such as depth, temperature and pH. Often a few individuals of each species may exist on the outer limits or extremes of their usual habitat range, and it is often in these locations that changes in species abundance may be first recognised. Increasing or decreasing species abundance may be a sign that the marine environment is changing in some way, resulting in habitats that are either more or less acceptable to a particular species.

In many areas, species have demonstrated a trend of expanding their habitat ranges, increasing their abundance and/or undergoing poleward shifts, which in the southern hemisphere would be a southerly shift in distribution. These changes have been linked to physical changes in the environment; in particular, warming waters as a result of global climate change. Along the east coast of Tasmania the underlying ocean warming is further intensified by the presence of the East Australian Current (EAC), which is extending further south into Tasmanian waters bringing with it warmer northern sub-tropical waters.

Scientists have identified changes to the distribution of Australian marine species that suggest our marine ecosystems are changing. These include species expanding their ranges and/or increasing in abundance, localised populations expanding, and records of species occurring outside of their usual range. The Redmap website will record sightings of species which are extending their distributional range or changing their distribution, these are discussed in more detail below.


Range extensions: newcomers to Tasmania

 As Tasmanian coastal waters warm and the effects of the EAC become more prominent, the Tasmanian environment has become a more suitable habitat for species that would otherwise have been unable to survive in the usually cooler southern waters.

There are clear examples of species commonly associated with the mainland such as the long spined sea urchin (Centrostephanus rogersii) and the green rock lobster (Jasus verreauxi), both more commonly associated with New South Wales waters, becoming more common in Tasmania and, in the case of the urchin, adapting so well that they have become pests. 

The increased distribution and abundance of the long spined sea urchin in Tasmania has created a threat to macroalgal (seaweed) beds on the east coast. Through overgrazing by the urchin, whole regions have been left without any usual vegetation such as seaweed and algae, resulting in cleared rocks and reefs referred to as sea urchin barrens. The term ‘barren’ refers to the fact that many of the usual species have disappeared leaving mostly just rocks and urchins.

Centrostephanus rogesii grazing on algae (Image: G. Edgar, TAFI)



Some initial habitat extensions may provide additional food source for existing species, create new fisheries or enhance current ones, and may in some cases appear to have positive outcomes. However, in time as populations of some species increase, these same extensions may prove to be detrimental to existing Tasmanian species which will be under increasing pressure from greater competition and an environment that is warmer than what they are adapted to. Some new species may be no problem at all and may add value to our fisheries or act as an additional food source for existing species. The impact of new species (and change in general) on the Tasmanian environment will not be clear in the short term.

Green rock lobster (Jasus verreauxi) (Image: Gary Carlos, TAFI)

 

 

Relatively recent arrivals that have been happily received by the Tasmanian fishing communities include snapper (Pagrus auratus) and the yellowtail kingfish (Seriola lalandi). The relative abundance of these newcomers has increase significantly in Tasmanian waters, so much so that for the first year ever they have been included in the Department of Primary Industries, Parks, Water and Environment ‘Tasmanian Recreational Fishing Guide’ with a bag limit.

Yellowtail kingfish illustration (Image: Peter Gouldthorpe, DPIPWE)

 

Changes to distribution: Time to move on – it is just too hot here!

For some Tasmanian species, their usual environment is becoming unsuitable; it is too hot and in order to survive they have to move south to find cooler waters. Species that live in habitats on the continental shelf (and slope) or on inshore reefs will be unlikely to extend their distribution in response to warming waters as there is no shelf or inshore reef habitat between Tasmania and Antarctica. Southern rock lobsters for example, are a cool water species and cannot move further south in order to find preferred environmental conditions.

 

The research

Meet Dr Peter Last and Dr Dan Gledhill. They are two Tasmanian ichthyologists (they study fish) from CSIRO in Hobart who are looking at how climate change may be affecting the range and distribution of Tasmanian marine species. They have studied historical manuscripts, field surveys, fishing data and scientific research from the 1800s, 1980s and 1990s, to determine what changes have been recorded over time. Each record, like a piece of a puzzle, gives a little more information about the particular species.

 

In work soon to be published, they have shown that there have been changes to the distribution of a number of fish species in Tasmanian waters that are all consistent with the trends expected from warming waters as a result of climate change. The implications of these extensions and shifts are unclear but some issues scientists need to consider are

  • What impact will ‘new’ species have on existing ecosystems?
  • Will new species thrive without their usual predators and become pests?
  • Will new species out-compete local species for resources?
  • Will the new species become the preferred food for a local predator leading to an expansion in the population of another species?
  • How will local species adapt and change in response to more competition?
  • What management is required to ensure fishing of these changing marine populations is at a sustainable level?

 For a list of species that may be undergoing changes to their range and distribution in Tasmania go to the REDMAP marine species page or download a coloured pdf of the Fish Species.


Acknowledgement and Source Information:


Climate Change and Biodiversity, Intergovernmental Panel on Climate Change IPCC, April 2002.

Last PR, White WT, Gledhill D, Hobday AJ, Brown R, Edgar GJ, Pecl G (unpublished) Long-term shifts in abundance and distribution of a temperate fish fauna: a response to climate change and fishing practices

Ling SD, Johnson CR (2009) Population dynamics of an ecologically important range extender: kelp bed versus barrens sea urchins. Marine Ecology Progress Series 374, 113-125.

 

 

 

Pecl G, Frusher S, Gardner C, Haward M, Hobday A, Jennings S, Nursey-Bray M, Punt A, Revill H, van Putten I (2009). The east coast Tasmanian rock lobster fishery – vulnerability to climate change impacts and adaptation response options. Report to the Department of Climate Change, Australia.