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UNIVERSITY OF SOUTHAMPTON
ABSTRACT
FACULTY OF SCIENCE
SCHOOL OF OCEAN AND EARTH SCIENCE
Doctor of Philosophy
REPRODUCTION AND LARVAL BIOLOGY OF NORTH ATLANTIC ASTEROIDS
RELATED TO THE INVASION OF THE DEEP SEA
by Francisco Benitez Villalobos
A very important objective of ecological research is to explain the evolution of life histories,
more specifically how natural selection modifies reproduction and development in order to
generate the patterns that are observed in nature. With few exceptions, the reproductive
mechanisms and patterns found in deep-water echinoderms are entirely similar to those found
in shallow-water species. The aims of this study were 1) to examine the reproductive biology
of the many deep-sea asteroids found on the continental slope to the west of Europe in order
to determine if the reproductive adaptations are a function of depth, distribution or are
phylogenetically controlled, and 2) to conduct experiments on the effects of pressure and
temperature on larval development of Atlantic asteroids, to investigate the physiological
potential for deep sea invasion by shallow-water species. Eggs of the shallow-water asteroids
Asterias rubens Linnaeus and Marthasterias glacialis (Linnaeus) were fertilized in vitro and
incubated through the early embryonic cleavages until the larval stage. They were subjected
to different temperature/pressure regimes. Early embryos were able to tolerate pressures up to
150 atm at 15 o C and 100 atm at 10 o C. Survivorship of A. rubens swimming bipinnaria
remained high (> 70%) after incubation at all the pressure/temperature combinations. In M.
glacialis the highest survival of swimming larvae was 100% at 1 atm/5, 15 and 20 o C and 50
atm/15 and 20 o C. Data for the temperature and pressure effects on the later stages of
development suggest that all the larval stages are more temperature/pressure tolerant than the
early embryos and survivorship becomes greater with larval age. Therefore, the larvae of
these two species could survive transport to deeper waters and these species may be capable
of sending colonists to the deep sea. In the deep NE Atlantic the habitat has selected for
species with specific reproductive traits, which provide them with successful and
advantageous life history strategies. This can be clearly observed in the upper bathyal zone
between 700 and 1100 m, where the environmental conditions have selected for small species
with low fecundity and large eggs, plus habits related directly or indirectly with suspension
feeding. These species exhibit reproductive features with trends to the opportunistic strategy
and are distinctive of unpredictable environments, although their large egg size probably
follows the general trend observed in species from cold waters in order to provide the larvae
with energy sufficient for a high survival possibility. Conversely, phylogenetic and
evolutionary factors are also important and seem to be decisive at the deepest waters where
basically mainly species belonging to the strict deep-sea family Porcellanasteridae are found.
All these species possess a mixture of features typical of classical K strategists and
equilibrium strategists, which enable them to persist in a relatively stable environment with
low energy availability. A comprehensive knowledge of the reproductive processes of the
deep-sea fauna is essential in order to evaluate the level of variability caused in the
environment principally by human activity and the possible effects on life-history of the
species.
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