Bioclimate Envelope Models … predicting the future

I have addressed in the past the concept of invasive species – organisms which invade a regions outside their native environment, often impacting the environment and it’s native creatures in negative, and sometimes irreversible ways. An important development in the study of marine invasive species is to determine where they may move to next before it happens … identifying regions that are at risk of invasion. This was the focus for my Master research paper and I thought I’d share my findings …

 

Bioclimate models are employed to predict the current and future distributions of species by comparing known species distributions to associated environmental variables. The environmental conditions which characterize the “preferred” habitat of the the species are identified. Potential matching environmental conditions for future years are then identified through climate modelling and it is assumed that the species has the ability to inhabit the identified regions in the future.

 

Study Objectives

The intent of this study was to apply ecological niche modelling to 4 introduced marine species which are known to have/or have previously had negative impacts in Australian waters. The current suitable habitat of each species was determined from online distributional databases, allowing the identification of preferred environmental characteristics. By modelling the projected climate conditions of Australia in the future, the projected distributions of each species could then be determined. Those habitats which are preferred by the 4 species was identified according to sea surface temperature.

 

Species of Interest

Four marine invasive species were chosen:

Sabella spallanzanii – is a fan worm which has established large populations competing with other organisms for both space and food. The species has been discovered in many locations around Australia.

sabella spallanzaniiSabella spallanzanii

Original image by: Manuel Sanchez-Mateos

Carcinus maenas – the North Atlantic shore crab has been recorded in large populations in Australia since the 1800s and is a strong competitior of many local species.

carcinus maenasCarcinus maenas

Original image by: John Haslam

Asterias amurensis – the Northern Pacific seastar is known for large population outbreaks throughout south-eastern Australia. It has affected significant impacts on fisheries and structural changes to communities residing in and on the ocean sediments.

asterias amurensi

Asterias amurensis

Original image by: Dean Franklin

Mytilopsis sallei – is the black-striped mussel made famous after it was completely eradicated from northern Australia. the species can attach to almost any surface, completely altering natural and man-made structures and preventing native species from settling.

mytilopsis cut

 Mytilopsis sallei

Original image from Google

Modelling Techniques

The ensemble modelling platform BIOMOD2, was selected based on its ability to combine modelling algorithms and produce a consensus projection. In other words, multiple models could be forecast together providing a single, more accurate projection, rather than getting many projections that show different possibilities. Modelling was undertaken with the freeware and open-source R software. Each species was modelled with 3 distinct algorithms – a Generalized Linear Model (GLM), a Generalized Additive Model (GAM), and a Generalized Boosting Model (GBM).

 

Species Distribution & Environmental Data

The distributions for each species was gleaned from 2 online global databases: The Global Biodiversity Information Facility  catalogs species occurrence records and classifications; and the Ocean Biogeographic Information System is a portal to multiple marine species’ datasets. Sea surface temperature conditions were derived for the three coldest months of the year and the three warmest months of the year under future climate change scenarios. Current global sea surface temperature was obtained from NASA’s MODIS Aqua Ocean Color website. For future predictions, sea surfaces (Australia only) were obtained from Australia’s CSIRO: Ozclim website. Two future climate change scenarios were selected – one for low greenhouse gas emissions and one for high greenhouse gas emissions. Both the high and low climate scenarios demonstrated a shift in the characteristic sea surface temperatures around Australia in a southward direction, resulting in the warmer northern waters extending further down the eastern and western coastlines, and a smaller region of the colder, temperate waters in the southern latitudes.

 

So what did I find?

Initially, the possible distribution of each species was modelled (determined) based on current, known, sea surface temperature – S. spallanzanii, C. maenas, and A. asterias  prefer the cooler, southern waters of Australia, and M. sallei prefers the warmer, northern waters of Australia. The high and low climate scenarios projected a southward shift in suitable habitat range for S. spallanzanii, C. maenas and A. asterias, as would be expected if the temperate waters they favour also shifted southward. Likewise, the range of suitable habitat for M. sallei increased under both high and low climate scenarios, extending southward along the eastern and western coastline, mirroring the shift in sea surface temperature.

 

What does this mean?

This study offers insight into the possibilities of applying ecological niche models based on environmental preferences. On a broad scale, the projected distribution of the selected species resembled the projected shift in climate as indicated via modelled climate change. If the projections are to eventuate, the 3 species which prefer the cooler, southern waters will eventually find no suitable range in Australia waters – great news!. On the other hand, M. sallei will find suitable habitat along most of Australia’s coastline.  This does not bode well for Australian marine life considering how easy the species is transported and the ability of the mussel to attach to almost any surface. The study has identified a risk which warrants further attention.

However, the study suggests that sea surface temperature alone is not a sufficient indicator of environmental suitability for marine species. One cannot assume that climate alone limits the movements and ability of a species to inhabit a region. For example, a species may be limited by the depth of the water, surface geology, elevation and more. With this in mind, a larger scale study is warranted and could provide great insight into the possible future changes to Australia’s marine environments. Let’s remember though, that a Master research project undertaken in just 6 months must have its limits.

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