Sponges of the New Caledonian lagoon - IRD

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70 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.
Actual proportions of endemic species may vary greatly between different groups of sponges. Some species are obviously capable of maintaining relatively widespread distributions, perhaps due to more successful dispersal mechanisms of their reproductive products. These include several species of xestospongia. in the family Petrosiidae. which are very Widely distributed in shallow waters throughout the Indo-Malay region. Other groups of sponges. such as Mycale and Clathria. both in the order Poecilosclerida. have many hundreds of species in shallow-water habitats within the Indo-west Pacific. Only few of these are truly Widespread. suggesting that their ancestors colonised these coastal waters and subsequently speciated in them relatively successfully. The sponge fauna of New Caledonia is also clearly stratified in relation to different depth distributions. There is very little apparent mixing between deeper and shal low-water faunas. and each of these faunas has distinct biogeographical relation ships. These two faunas are considered separately. Deeper-water species Although there ore undoubtedly mony more deeper-woter species (>400 m depthl yet to be discovered in this region, our knowledge of this founo is relotively good, thonks largely to the work of Orstom, in comparison to adjacent provinces, such os Australia, New Zealand and other southwestern Pacific islands (where fewer comparable deeper-water sponge faunas hove been investigatedI. ApprOXimately 72% of deeper-water sponges are endemic to the New Caledonian region, and we already hove some good ideas on their biogeographical relationships, supported to some extent by palaeontological evidence. Recently, 0 remarkably rich fauna of desma-bearing sponges l'Lithistida') was described from the deeper waters of the Norfolk Rise, to the south of the island. These 'Iithistids' are firm' bodied sponges with rigid interlocking skeletons formed by desma spicules, producing 0 relatively good fossilisation potentiallunlike many of the soft-bodied speciesl. This fossil record gives us the ability to compare species living today with those that lived in the more diverse Cretaceous fauna, during the time of the Tethys Sea. Fossil 'Iithistids' (from western Europe) show remarkably close resemblance to living species from New Caledonia, certainly related at the generic level, and it is thought that the living 'Iithistids' from New Caledonia hove evolved from this ancient Tethyan fauna, unchanged in their morphology over the 80 100 million years that they hove been separated. That these lithistids now exist and are isolated, 'relict' species of 0 once widely-dispersed founa 0150 suggests that oceanographic conditions in these deeper waters may be similar to those of ancestral seas, and these conditions are relatively stable compared with the more transitory shallaw-water habitats of the lagoon. This ideo is confirmed by the relict distribution of other groups in deep waters off New Caledonia, such os crinaid echinoderms, bryazaans or lace corals and some crustacean groups, which also hove numerous "living fossils" Many deeper-water, 50ft-bodied [non-lilhislidl demasponges from New CoIedania are similar 10 those that lived during the Late Eocene fauna 158-37 mya) of New Zealand. This evidence comes from comparisons between these living deeper-woter populatians and isolated fossil spicules in uplifted sediments from southeastern New Zealand. The New Caledonian and New Zealand papulations were probably in contact prior to this time but hove since become isolated by geographiC and/or oceanographic barriers os indicated by the high proportion of endemiC 71 Sponge diversity, distribution and biogeography
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Claude Levi Ed itor Pierre Laboute,
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8 Cel ouurage est le resu/lat d'une
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This work is the result of a long s
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Author profiles Chris Battershill i
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Clive WiIkinson is Principal Resear
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18 Sponges of the New Caledonian La
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Page 25 and 26: Sponges are fascinating. Each spong
Page 29 and 30: a What IS sponge .- Cll0anocytes in
Page 31 and 32: Sponge structure s ponge adults are
Page 33 and 34: ., Matrix cyanobacleria (photo J. V
Page 35 and 36: whiCh are always present irrespecti
Page 37 and 38: How con you s identi fy sponge? o p
Page 39 and 40: Soft parts of the sponge (photo J.
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Page 51 and 52: Anchorate isochela (pl,oto P.R. Ber
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Page 57 and 58: The role of sponges In carol reefs
Page 59 and 60: the production of much coral rubble
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Page 63 and 64: The fascinating world of sponge che
Page 65 and 66: It was originally assumed that spec
Page 67 and 68: Sponge diversity, distribution and
Page 69 and 70: predators. Nor do many have adequat
Page 71: where its life forms were capable o
Page 86: Order Astrophorida 84 I SteJlerro (
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Further reading Brien (P.), Levi (C
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Glossary Acantho- Addition of spine
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incorrectly interchanged with the t
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Clathrate Interwoven tubular constr
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Ectosome Peripheral region of the s
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198 Sponges of the New Coledonion L
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202 Sponges of the New Caledonian l
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List of general illustrations provi
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115 Mycale (Zygomycale) parishi (BO
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