Micro-habitats and Associations
 Large adult and small T. niloticus juveniles all occupy the same marco- habitat, but different micro- habitat. Micro- habitat refers to particular niches of the overall habitat, for example rubble covered areas of the reef flat, rather than deep, rock covered areas.
As the trochus mature, habitat changes from small, coral rubble in shallow areas to large rocks around the deeper reef edge (Chambers, 2007).
Differences could be consequence of active substratum selection or differential survival (FAO, 1999). This means that as the animals grows it could actively seek different micro- habitat, or in the case of differential survival the larger fitter animals take over the preferred habitat and juveniles must wait until they are large enough to compete for these areas as well. Shallower areas with more rubble could be safer for smaller T. niloticus as there are less predators. Food preferences corresponding with age could also underlie different substratum selection (FAO, 1999).
Bour (1992 cited in Castell, 1997) found a positive correlation between size and density of the animal: as they got bigger they formed denser aggregates. As juveniles grow their ability to disperse to favorable sites is also likely to increase, leading to areas of higher density.
As juveniles migrate to deeper water as they mature, shell width increases with water depth (Heslinga et al, 1984).
The specimen found in the image to the left was found on the reef flat close to the reef edge on the Heron Island reef, 2011. It is approximately 7cm across the base. |