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CHAPTER FIVE- SYNTHESIS AND CONCLUSIONS
5.1- Factors controlling the bathymetric distribution of species and their
effects on early life-history stages of echinoderms
The factors that control the diversity of communities and also the bathymetric
distribution of individual species are likely to involve a number of mechanisms that
act during the larval stage. These mechanisms may include larval physiological
tolerances to temperature and pressure, inherent larval behaviours and the availability
of food. Factors that limit depth of occurrence may place limits on the invasion of
deeper water by shallow water species, but in most deep-sea animals, such limiting
factors for individual species are unknown (Tyler & Young, 1998). In addition, there
are only a few physiological experiments on early life-story stages of deep-sea benthic
animals. (Dayton et al., 1982; Young & Tyler, 1993; Young et al., 1996ab, 1997;
Tyler & Young, 1998).
Tyler & Young (1998) examined temperature and pressure tolerances of the
dispersal stages of congeneric species of echinoids with different bathymetric
distributions, and it was inferred that physiological tolerances of the larvae influenced
the adult distribution.
Young et al. (1996b) experimented with early embryos of 7 littoral species of
tropical echinoids from Hawaii and the Bahamas and 3 bathyal species from the
Bahamas. In every case, embryos tolerated pressures greater than those of their adult
normal distributional ranges, but at temperatures found in shallow water. This
suggests that pressure does not set actual depth limits for most species and would not
prevent recruitment or invasion of depths as great as 2000 m.
Sewell & Young (1999) concluded that the geographic distribution of the
echinoid Echinometra lucunter does not appear to be limited by the temperatures at
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