Conservation & Threats
Creseis acicula and their planktonic comrades dominate the Great Barrier Reef pelagic ecosystem, both numerically and by mass. Though they are often overlooked in favour of larger and more colourful benthic organisms, the GBR’s pelagic ecosystem comprises 94% of the total water volume of the Marine Park (McKinnon et al. 2007). The micro and mesozooplankton in the pelagic ecosystem are the basis of food webs that support many coastal recreational fisheries and planktonic organic matter supports a large number of suspension feeders and planktivorous fish on coral reefs.
The growth and abundance of planktonic organisms, including C. acicula, is directly influenced by a number of climatic variables including water temperature, ocean chemistry, ultraviolet radiation (UVR) and nutrient enrichment. Each of these climate stressors will likely be influenced by anthropogenic climate change, either directly or indirectly through changes in oceanographic processes and currents that affect the mixing of water bodies. Current studies have focused on the impacts of ocean acidification on temperate thecosome pteropods (Comeau et al. 2010; 2012), though information is lacking on tropical species and it is not yet understood how these changes will specifically impact C. acicula.
This website, also by the author, gives a simple overview of the ocean acidification process, and the potential impacts on thecosome pteropods. When CO2 dissolves in seawater it produces carbonic acid, a fairly innocuous substance found in most sodas, but very damaging to the delicate shells of calcifying marine organisms. Thecosomata, which is an order that contains all shelled pteropods, are important components of the ocean carbonate cycle, as their bodies are stored in a carbon 'sink' in the deep ocean floor (Hunt et al., 2008). Changes in their global abundance may affect the capacity of the ocean to act as a carbon sink, altering the balance of the carbon cycle (Wright & Davidson, 2006).
A study by Roger et al. (2011) identified the paucity of information available on impacts of ocean acidification on tropical thecosome pteropods. The study used C. acicula as a case study to assess “changes in their aragonite shells, shell morphology, growth patterns,structure, size, and porosity” from samples collected over 40 years. Although the results were inconclusive due to incomplete datasets, the work suggests that thecosome pteropods off Northern Australia may have been negatively influenced by the decline in Ωarag. The study found a significant increase in shell porosity over time (C. acicula: +1.43%) and concluded that tropical pteropods may potentially be ‘sentinels of global change’ (Roger et al. 2011).
Click here to view a vulnerability assessment of GBR planktonic organisms to climate change. |