Sponges of the New Caledonian lagoon - IRD

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Sponges
of the New
Caledonian
Lagoon
closing passages that might act as routes of dispersal and faunal exchange
between permanent land masses). Similarly, during this period there were several
periods when temperatures changed substantially, particularly during the Eocene
(58-37 MYA), Miocene (24-5 MYA) and Pleistocene (1.6-0.1 MYA) eras, partially due
to the gradual northwards movement of the whole Indo-Australian plate into the
tropics but also to the periodic events of glaciation and consequent sea level
changes, and changes to sea circulation as a result of opening or closure of major
passages between land masses.
It is these tectonic processes of rifting, drift, uplifting, isolating and the subsequent
oceanographic and climatic changes which have influenced the development of the
living sponge fauna of New Caledonia. Nevertheless, this fauna may not be completely
isolated, with some marine species still continually migrating into thiS region riding
the sea currents or perhaps rafting on the surface of the sea attached to other floating
objects. The biogeographical histories of marine invertebrates are especially
influenced by the dispersal of these 'foreign invaders'. For some groups of animals,
such as reef-building corals, continual colonisation from adjacent provinces is a
major feature of present day distributions. Conversely, for animals like sponges
with apparently more restricted means of dispersal the present day distributions
may be influenced less by 'invasion' than by subsequent evolution of the once
widespread ancestors. In fact both mechanisms are true, as will be shown below.
Present patterns
of sponge distribution
and abundance
Within the New Caledonian lagoon ecosystem and its outer reefs and deeper
waters surrounding these reefs it is estimated that there may be up to 600 species
of sponges. So far, however, we only know the identity of about half of these, and
it is likely that many of the others are new to science (undescribed). Generally,
including all the described species of sponges from all habitats, most (71 %) are
unique (endemic) to New Caledonia, whereas only a smaller proportion also lives in
adjacent waters surrounding neighbouring land masses. A few species (perhaps 5%
of the fauna) may be truly widely distributed within the Indo-west Pacific region,
apparently closely linked to the distribution of coral reefs.