Movement and Bioturbation

Echinoderms on the abyssal plain have very limited spatial and temporal patchiness in food supply and must be able to move suitably to optimize net energy intake. Due to a wide diversity of body forms echinoderm classes show a wide variety of movement strategies in the deep sea.

The most fascinating of these movements, are the body undulations or ‘swimming’ in benthoplegaic holothurians who travel large distances for food and mating by this technique (Pages et al. 2007). However this is a rare form of movement as most echinoderms move in direct contact with the sea floor leaving tracks in the soft (60-90% water) sediments (Gage and Tyler, 2001). Deep sea irregular echinoids such as Spatangus raschi will move semi-buried in sediments using shorten spines to leave a meandering path whereas regular sea urchins Hygrosoma petersii will move over sediment surface using tube feet leaving few visible tracks (Rex and Etter, 2010).

Figure 4. Example of a deep sea Holothurian grazing leaving a smooth track behind (Young et al. 1985)

Locomotion, burrowing and grazing of benthic echinoderms in the deep sea plays a significant role in structuring and altering the sediment (Figure 4; Turnewitsch et al. 2000). Movement related actives of echinoderms on the abyssal plain displaces sediment creating a greater surface area over which chemical flux can occur as well as increasing burial rates (bioturbation). Bioturbation in the upper centimeters of marine sediments significantly increases the depth of the mixed layer and rate of nutrient cycling, creating more potential food resources on the abyssal plain (Teal et al. 2008). Bioturbation is not only important for abyssal plain organisms but also in the role of alteration, burial and remineralisation of particulate organic carbon from the euphotic zone, contributing to maintaining the biogeochemical equilibrium of the earth (Hughes and Gage, 2004).

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