Prey abundance can be indicative of predator abundance but migration and dispersal phenomena of prey, together with attraction of predators to prey may overwhelm any simple correlation. In this study, 24 inter-tidal species of starfish were located at Heron and Wistari Reefs and there was a large range in the abundances of different starfish species. 12 species (50%) of the species were found by sampling less than 6 hectares (5%) of the total sampled area. No specimens of the giant triton (Charonia tritonis) were located during this study conducted over several years.
When most species of starfish are rare then interestingly, there appears to be a density at which they don’t appear to occur. Is this indicative of predators? Whether a relatively abundant species such as Echinaster luzonicus or a rarer species they seem to not occur at 0.3 individuals per hectare. What could this mean about predator density?
If an assemblage of starfish species is controlled by predator abundance, would the abundance distributions of these prey species reflect the underlying predator abundance. Could the minimum at 0.3 individuals / hectare indicate something related to predator density or is it just an artifact related to sample size limitations?
If sampling could have been more intensive or extensive would the number of traverses / log abundance categories in Echinaster luzonicus for example have demonstrated a different minimum than for a rarer species? If it existed, would such variation indicate a predator’s prey preference, particularly at low prey densities?
1 species of starfish (Echinaster luzonicus) occurred with an average density of greater than 10 individuals per hectare. 8 species occurred at 1 individual per hectare. 6 species occurred at each of 0.1 and 0.01 individuals per hectare and 3 species occurred at less than 0.01 individuals per hectare. It is notable that starfish of all species were uncommon at Heron and Wistari Reefs compared with studies on reefs that have carried population outbreaks of the crown-of-thorns starfish (Acanthaster planci). It is also notable that neither the crown-of-thorns starfish (Acanthaster planci) nor the giant triton (Charonia tritonis) were located on any inter-tidal traverse during this study of 120 hectares over several years.