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Contributions to Zoology, 74 (3/4) (2005)

Desmacella austini sp. nov. from sponge reefs off the Pacific coast of Canada

Helmut Lehnert1, Kim W. Conway2, J. Vaughn Barrie2, Manfred Krautter3

1.  Eichenstr. 14, 86507 Oberottmarshausen, GermanyLehnert@spongetaxonomics.de

2.  Geological Survey of Canada - Pacific P.O. Box 6000 Sidney, B.C. Canada V8L4B2

3.  Institut für Geologie und Paläontologie Eichenstr. 14, 86507 Oberottmarshausen, GermanyLehnert@spongetaxonomics.de

Keywords: Porifera, Desmacellidae, taxonomy, new species, sponge reefs, Pacific, Canada

Abstract


A new species of a very thinly encrusting Desmacella (Porifera, Demospongiae, Poecilosclerida, Desmacellidae) is described from Queen Charlotte Basin and Georgia Basin, off the Canadian Pacific coast. It is compared with all known species of the genus, differing in the geometry and size of spicules, and the persistent epizoic growth.

Introduction


Siliceous sponge reefs had a wide distribution in prehistoric times and once constructed the largest reefs known on earth, reaching an acme in the Upper Jurassic when a deep-water reef belt on the northern Thetis shelf existed that was 7,000 km long (Krautter et al., 2001). In present times hexactinellid sponges of the order Hexactinosida have constructed reefs at several localities off the coast of British Columbia, Canada. The reefs occur on relict glaciated seafloor areas with a low sedimentation rate and a high dissolved silica concentration in the Queen Charlotte Basin and in Georgia Basin (Conway et al., 2004; Conway et al., 2005) and the reefs represent stable communities that have been growing for up to 9,000 years. The main framebuilders include the hexactinosidan species Aphrocallistes vastus, Farrea occa and Heterochone calyx in Queen Charlotte Basin, and A. vastus and H. calyx in Georgia Basin (Conway et al., 2004). The framework of these reefs is constructed through several processes of framebuilding, and the reef matrix is derived from trapping of suspended sediments (Krautter et al., 2001). Similar framebuilding processes are thought to have contributed to the formation of the ancient reefs (Krautter et al., 2006). Upwelling and downwelling oceanographic processes in a biologically productive coastal sea have contributed to the development of large reef complexes (Whitney et al., 2005). The reefs form as bioherms (mounds) and biostromes (beds or sheets) that may rise up to 21 m above the seafloor and they cover around 1000 km2 on the continental shelf. Individual reef complexes may cover areas of more than 300 km2 and occur in 90-240 m depth range (Conway et al., 2001; Conway et al., 2005). The three-dimensional framework structure of the reefs is comparable to coral reefs and provides habitat for a variety of sessile and motile organisms from different phyla. Among the sessile epifauna of the sponge reefs are sponges of the class Demospongiae, although the magnitude of epifaunal sponge (and other) species growing on the reef-framework is presently unknown. Only a relatively small number of epifaunal sponge species have been examined and of these one is undescribed.

It is the purpose of the present paper to describe this new species of the genus Desmacella and compare it with other known species.

Methods


Samples of hexactinosidan sponges with adhering epifaunal organisms were collected by KC and MK during a research cruise aboard CCGS John P. Tully, using Shipek and Van Veen grab samplers and also sampling using the submersible Delta in July 1999 and in June 2002 using an HD2+2 remote operated vehicle (ROV). Photo and video-documentation was made in situ during the dives. In October 2003 the ROV ROPOS was deployed from the research vessel CCGS Vector to survey, photograph and sample sponge reefs in Georgia Basin. Samples were stored in 95% ethanol or alternatively in 4% formalin/seawater after collection. For the identification of the sponges semi-thin sections parallel and perpendicular to the surface were made with a razor blade and embedded in Canada balsam. For spicule preparations small pieces of sponge were boiled in sodium hypochlorite solution, washed in distilled water and transferred into ethanol in several steps using a centrifuge to avoid loss of spicules. Ethanol-spicule suspension was pipetted on glass slides and spicules were embedded in Canada balsam after evaporation of the ethanol. SEM observations were made at the Institute for Zoology in Erlangen, Germany with a Hitachi S800 on gold sputtered spicules.

Systematic description

Class Demospongiae

Order Poecilosclerida

Family Desmacellidae Ridley and Dendy, 1886

Genus Desmacella Schmidt, 1870

Desmacella austini sp. nov.

Material. Holotype. Originally labeled VEC0301. Type locality. Georgia Basin, Georgia Strait, coordinates: 49°36.76’N 123°07.19’W, 169 m, deposited at the Senckenberg Museum, Frankfurt am Main, Germany, registration number: SMF 9760. A schizotype is kept at the Zoological Museum Amsterdam, registration number: ZMA Por. 18340.

Additional material. Tul99A-17, Queen Charlotte Basin, Queen Charlotte Sound, 51º34.61’N 128º08.11’W, 205 m; Tul0233A-56, Queen Charlotte Basin, N. Hecate Strait, 53º13.66’N 130º05.43’W, 165 m; Tul02-33A-57, Queen Charlotte Basin, N. Hecate Strait, 53º16.15’N W 130º04.24’W, 169 m; Tul02-52B, Queen Charlotte Basin, N. Hecate Strait, 53º17.3’N 130º04.4’W, 165 m; Tul02-46A, Tul02-46B, Queen Charlotte Basin, N. Hecate Strait, 53°09.63’N 130°04.84’W, 163 m.

Description. Alive blue or yellow, thinly encrusting sponge (Figs. 1 and 2) on Heterochone calyx , light brown or greyish in preservative. Oscules not apparent. Surface hispid. The ectosome consists of densely spaced spicule brushes of tylostyles, points facing outwards forming bouquets (Fig. 3). In some specimens the spicule brushes are basally prolonged and from short polyspicular tracts. Occasionally these tracts are branching and lead to two spicule brushes. A direct connection of the polyspicular tracts or the ectosomal spicule brushes to the rigid hexactinellid skeleton could not be observed. The spicule tracts of the Desmacella seem to end between the spicules of the hexactinellid sponge. Strewn in between are the three categories of sigmas. The choanosome in thin specimens is situated where the rigid skeleton of Heterochone is still present and tylostyles are clearly more rare in this region, but sigmas are visible between the hexactinellid spicules. Tylostyles (Fig. 4) are 170-495 x 6-10 μm; large sigmas, 55-65 μm; medium size sigmas, 26-42 μm and small sigmas, 15-20 μm (Figs. 4 and 5).

Remarks. This species seems to show specific adaptations for overgrowing Heterochone calyx and possibly other hexactinellid sponges. While it constructs a typical desmacellid skeleton near the surface, it produces mainly microscleres where it settles deeper in the rigid hexactinellid skeleton. There is also some evidence of a succession of species growing on the hexactinellid substratum. In several cases we observed Halichondria disparilis growing over Desmacella austini sp. nov. In all cases D. austini sp. nov. was growing directly on Heterochone calyx . If Halichondria disparilis was present it grew on the Desmacella . On living Heterochone calyx we found the yellow growth form of Desmacella austini sp. nov. while the blue Desmacella was growing on dead Heterochone . Living Heterochone calyx is coloured white or pale yellow.

The occurrence of D. austini sp. nov., growing specifically on hexactinosidan skeletons, within hexactinellid sponge reefs has implications for sponge reef ecology. The sponge is in competition for, or at least limits availability of, hard subtrate growing space for the reef forming hexactinellid

FIG2

Figs. 1-5. Desmacella austini sp. nov. (1) In situ photograph, blue growth form on dead Heterochone calyx in Georgia Strait on Mc Call Bank, 169 m depth. (2) Yellow, growing among living, pale yellow Heterochone calyx in N. Hecate Strait at 165 m depth. (3) Surface spicule brushes. (4) Tylostyles and three categories of sigmas. (5) Three size categories of sigmas.

sponges. Considering that on sponge reefs the only available hard substrate is dead and macerated hexactinosidan skeletons (Conway et al., 1991, Krautter et al., 2001) this competition could potentially become a factor limiting reef growth or recovery. Many reef areas have been impacted by bottom trawling (Conway et al., 2001) and in situ observations suggest that D. austini sp. nov. where abundant, may limit the ability of hexactinosidan sponges to re-colonize reef areas that have been damaged by trawling by occupying the available substrate of sponge skeletons and skeletal fragments of the reef surface.

Discussion


 

missing

As the distribution of deep-water species is not known very well we compared our new species with all known species of the genus (Table 1). Comparing the categories and sizes of spicules, D. democratica (Sollas, 1902) has the most similar set of spicules. Sollas (1902) did not report different size categories for the sigmas of D. democratica but the size range of 10-80 μm is within the size range of all size classes of our new species and it could be argued that Sollas overlooked their occurrence in distinct size classes. Conspecifity nevertheless, seems unlikely as the tylostyles Sollas reported are longer and considerably thinner than in D. austini sp. nov. There are two other species of Desmacella which also have three size-categories of sigmas, D. campechiana (Topsent, 1889) and D. ithystela Hooper, 1984. Desmacella campechiana has two size-categories of tylostyles, the large category being much longer than styles in D. austini sp. nov. and the small category of sigmas being only half the size of the small sigmas in the species described in this publication. Desmacella ithystela from the Northwest Shelf, western Australia, differs in having again two size categories of tylostyles which are considerably smaller than in our new species and it differs also in the large category of sigmas which are two to three times larger than reported for D. austini sp. nov. All three species have very different distributions from D. austini sp. nov., the Caribbean, Australia and New Zealand respectively, which makes conspecifity again more unlikely from a biogeographic perspective. Desmacella vestibularis (Wilson, 1904) and D. vagabunda Schmidt, 1870 occur roughly sympatric on the American Pacific coast, though known only from Galapagos and California. However, these species differ clearly in spicule categories and sizes (see Table 1). Hentschel (1929) and Koltun (1959) transferred Desmacella capillifera Levinsen, 1887, Desmacella hamifera Lundbeck, 1909 and Desmacella groenlandica Fristedt, 1887 to Biemna as they found commata as microscleres. As both authors report the occurrence of commata it seems probable that the first authors of these species overlooked the commata and so we assume this transfer correct, and therefore do not include these species in Table 1. However, spicule categories and sizes differ clearly from our new species.

Etymology. Named after Dr W.C. (Bill) Austin in recognition of his contributions to the understanding of sponge biology and ecology.

Acknowledgements


Thanks are due to officers and crews of the research vessels Vector and John P. Tully. The Geological Survey of Canada and the German Research Foundation (DFG KR 1902/2-2) kindly supported this study. Many thanks to Dr W. Heimler who made the SEM photos at the Zoological Institute at the University of Erlangen, Germany. Rob Van Soest and John Hooper improved the mansucript with their constructive reviews.

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