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strategy described by Winemiller and Rose (1992) and appear to be related to
environmental and population conditions. They possess small body size and low
fecundity per spawning event, and aseasonal reproduction with probably multiple
spawning frequency, although their large egg size probably follows the general trend
in cold waters in order to provide the larvae with energy sufficient for a high survival
probability. The opportunistic strategists are distinctive of highly disturbed and
unpredictable environments (Winemiller and Rose, 1992; McCann and Shuter, 1997).
The zone between 1100 and 3000 m coincides with the transitional zone
proposed by Howell et al., (2002) where boundaries at 2500, 2800 and 3300 m are
thought to demonstrate a region of transition between bathyal and abyssal fauna. This
region of pronounced faunal change occurs at ~2500 m where bathyal fauna meet, and
overlap with, abyssal fauna.
Previous studies have found this overlap in other megafaunal taxa
(Vinogradova et al., 1959, Hansen, 1975; Billett, 1991). Vinogradova et al. (1959)
claimed this boundary is a well-defined intermediate region at a depth of 2500-3500
m, and they noted the disappearance of large numbers of species at around 3300 m, as
well as entire taxonomic groups, to be replaced by a large number of new species,
genera and families pertaining only to ocean depths greater than 3000 m.
Within an evolutionary context, bathyal species are likely to have a mixed
origin, with some species from the shelf and some originating from abyssal depths
(Rogers, 2000). Data for the temperature and pressure effects on the later stages of
development of the shallow water asteroids Asterias rubens Linnaeus and
Marthasterias glacialis (Linnaeus) (Chapter 3, section 3.3.2 this thesis) show that all
the developmental stages have a potentially wider depth distribution than their
respective adults. Therefore, the larvae of shallow water species could survive
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