Biogeographic distribution
As a taxonomic group, the thecosome pteropods are amongst the most frequent metazoans found in oceanic zooplankton communities, representing a lineage of Mollusca that have successfully colonized the water column. The molluscan foot has been modified into delicate wings, which allows them to ‘fly’ instead of crawl through their lives in the world’s oceans. Thecosome pteropods are widely distributed, and are found in cold, temperate and tropical latitudes (Parra-Flores & Gasca 2009). Their vertical distribution in the water column stretches from surface layers to the bathypelagic zone. However, most euthecosomatous forms, including the genus Creseis are found primarily in the uppermost 200m (Parra-Flores & Gasca 2009).
Creseis acicula is circum-global (50°N-45°S) and has a continuous distribution throughout warmer oceanic waters, preferring temperature ranges between 10–27.9C (Van der Spoel, 1967). It is the one of the most common species found in neritic waters, occurring along the east coast of Australia, along with C. virgula and C. chierchiae (Newman1990). It is epipelagic, occurring primarily in the mixed surface layers of the water column (Singh et al. 2005).
Changes in global climate affect the biogeographic distribution of organisms, through range expansions, dispersal events and increased competition with invasive species (Monge-Najera 2008). Stressors that impact the distribution of planktonic organisms include direct factors, such as changes in water temperature, ocean chemistry, light, ultraviolet radiation (UVR) and nutrient enrichment. Also significant are the indirect effects of climate change, including changes on physical oceanographic processes that influence the mixing of water masses (McKinnon et al. 2007). A comprehensive understanding of the factors that define spatial distribution of Creseis acicula in the present time is critical for developing models for future conservation efforts. |