– a look at the ramifications of species extinction for biogeochemistry and ecosystem functioning.
Around Sydney there is a tiny species that every developer hates: the Cumberland Plain Land Snail. This species has stopped, delayed or significantly changed many developments across the Sydney basin, and is even said to be the snail that rules Sydney. Recently we also learnt that the world’s biggest coal mine development, the Carmichael coal mine in central Queensland, Australia, has been delayed due to an obscure snake and skink.
The usual argument is why does it matter that a seemingly insignificant species, such as a snail, should go extinct? Why should a snail prevent thousands of jobs and millions in investment?
The Cumberland Plain Land Snail rules development across western Sydney, Australia. Image Source: The Royal Botanic Gardens and Domain Trust.
The arguments for why we should not let any species go extinct have been made previously across many forums. Research conducted with Unisense microsensors and laboratory instruments demonstrate how species diversity, or lack of it, can affect biogeochemistry and ecosystem functioning.
Biogeochemistry is the science studying the relationship between the geochemistry of an area and how it affects, and is affected by, flora and fauna. Biogeochemists are particularly interested in the circulation of elements, such as carbon, oxygen and nitrogen, between organisms and their environment. A natural question for biogeochemists to ask is what effect does species diversity have on the circulation of elements.
Waldbusser et al (2004), from the University of Connecticut, examined how species diversity impacted on oxygen and pH in nearshore sediments. Their experiment was conducted on microcosms in the laboratory with five treatments: a control sediment that was sterilised so it contained no large species, three separate sediments that contained only a single species, and the fifth sediment that contained all three species.
The species in the experiment were Clymenella torquate (the bamboo worm), Spio setosa, and Leitoscoloplos fragilis: three different types of marine worms also known as polychaetes. The three species were chosen based on their widespread, frequent distribution and functional differences.
The polychaet worm species, Clymenella torquate (the bamboo worm), was one of three species in the Waldbusser et al experiment. Image Source: http://www.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxid=27310
The bamboo worm in its native habitat. The photo gives an example of the near-shore sediment in which the experiment was conducted. Image Source: http://www.dpr.ncparks.gov/photos/fromNRID.php?sciName=Clymenella%20torquata&pid=22261&source=pub&page=1
In the experiment, the scientists were interested in the sediment pore water oxygen and pH values across the different treatments. Profile measurements were made from the top of the sediment towards the bottom. As the experiment was conducted in a microcosm, or a very small area, it was necessary to perform the measurements with oxygen and pH microsensors connected to an instrument such as the OXY-Meter and pH/mV Meter. The length of the sediment profile was 40mm and measurements were made every 2mm (for oxygen) and 5mm (for pH). In order to achieve consistent measurements at such precision, the use of a micromanipulator was necessary.
Below are three figures presented by the scientists in their paper of particular interest:
Figure 1. pH profile to 40mm depth in the experimental sediment.
Figure 2. Oxygen profile to 15mm depth in the experimental sediment.
Figure 3. The cumulative variability in oxygen and pH measurements across experimental treatments. The taller the column, the higher the variability, or variance, in the measured values.
The first two figures show the oxygen and pH profile in the sediment across the experimental treatments. The first graph highlights the change in pH down the sediment profile. At the bottom of the sediment, the control treatment was more acidic than the multispecies assemblage treatment.
The third graph shows the cumulative variance, or variability, in oxygen and pH across the treatments. The third graph highlights that in the control treatment, which did not have any polychaete worms, had a large amount of variability. When compared against the multispecies assemblage treatment, the control treatment had approximately 3 times the amount of variability in oxygen and pH content.
This experiment by these marine scientists highlights how species diversity can influence the biogeochemistry of a system. In a species poor system, the variability of oxygen and pH was three times greater than a species rich system. The species poor system was also more acidic. This experiment highlights that species diversity can lead to greater stability in ecosystem functioning. Such a result is not only limited to marine microcosms in the laboratory, but has also been observed across multiple and varied ecosystems, as reviewed by Naeem et al (1999).
Preventing species extinction in its own right is important, however it also is practical and beneficial for humans. Diverse species assemblages leads to ecosystem stability and can even improve ecosystem services such as water and air purification. The loss of species and subsequent ecosystem functioning can actually lead to greater economic harm than good.
Naeem et al (1999). Biodiversity and Ecosystem Functioning: Maintaining Natural Life Support Processes. Issues in Ecology, 4: 2-11. Link
Waldbusser et al (2004). The effects of infaunal biodiversity on biogeochemistry of coastal marine sediments. Limnology and Oceanography, 49: 1482-1492.