Today the sponge reefs discontinuously cover about 1000 km2 of seafloor
in Queen Charlotte Sound and Hecate Strait in depths between 165 and 240
metres. Four separate locations have been identified where sponge reef
complexes have formed. The reefs consist of very dense populations of
living hexactinosidan sponges, often more than 1 m in height. The mounds
are up to 21 metres high and often many kilometres wide. Sometimes they
show remarkably steep slopes, up to 90°, on the flanks. In addition
to the mound, or biohermal structures, there are also large biostromal
structures which cover many square kilometres of seafloor. These reach
thicknesses from 2 to 10 m in southern and central Queen Charlotte Sound.
Smectite 42-50% (mean 46%),
Chlorite 3-10% (mean 7%),
Illite/Smectite 23-30% (mean 26%),
Illite 4-8% (mean 6%) and
Kaolinite 12-20% (mean 15%).
The sponge fauna of the reefs consist of only 7 hexactinellid species,
and of these only three of them are very abundant and form the framework
of the reefs. They include the hexactinellid hexactinosidan species Heterochone
calyx, Aphrocallistes vastus and Farrea occa. Siliceous sponges that were
often abundant in the reefs, but are not considered to be reef builders,
included the hexactinellid lyssacinosidan (rossellid) species Rhabdocalyptus
dawsoni, Acanthascus platei, Acanthascus cactus and Staurocalyptus dowlingi.
In some areas the reef surface has a dense coverage of monospecific sponges
over many square metres. Farrea occa often form such large clusters.
Taxa identified in association with the sponge reefs include several
species of annelid worms (Terebella sp., serpulids), bryozoans (often
encrusting dead sponge skeletons), bivalves and gastropods (both very
rare). Several species of rockfish (e.g. Yellow eye, Sebastes ssp.) occur
in some areas of the reefs utilizing openigs and niches between the sponges.
It is possible these fish are using the reefs as a "kindergarten"
during their juvenile stage. Species of spider crab and King crabs, shrimps,
prawns and euphausids are locally very abundant. Many different species
of echinoderms, notably seastars and urchins, were common in those parts
of the sponge reefs, where sponges are dying or obviously in poor condition.
The relative amount of these echinoderms can thus be used as an indicator
for the state (health) of the sponge reefs.
All modern and most fossil hexactinosidan sponges need a hard substrate
to settle. This hard substrate was provided by icebergs, grounding and
ploughing the sea floor. The fine grained sediment fraction of the berms
on both sides of the iceberg scours was washed out and the remaining cobbles
and boulders form a suitable substrate for the initial settlement of Hexactinosida.
After the death and mazeration of hexactinosan individuals, their skeleton
plays an important role as a substrate for other hexactinosidan sponges.
Their larvae attach to these skeletons and develop into a juvenile sponge
using the fibres of the substrate skeleton for a solid fixation. Little
is known about the larval stage of hexactinellid sponges. Our investigations
cannot contribute to understanding of this early stage of sponge development
and we have to refer to OKADA (1928). The skeleton of juvenile hexactinosidan
sponges cannot be used for a sound taxonomical identification as the size,
shape and architecture of the juvenuiles spicules differ remarkably from
the adult individuals. Juvenile sponges of Lyssacinosida, for example, have
a rigid skeleton whereas the spicules of adult lyssacinosidans are isolated
not fused together (Mehl, 1992). The skeletons investigated are fairly
irregular without a obvious (visible) prefered orientation. The size of
very young sponges is around 1 mm in diametre and globular in shape. In
later stages of development, the shape is more variable, and depends mostly
on the orientation of the substrate skeleton.
No direct observation or measurement was done to establish the growth
rates of hexactinosidan sponges. Long term observations in the Antarctic
indicate a very slow growth rate of rossellid Lyssacinosida (Hexactinellida).
Over 10 years of observation there was no remarkable change in body size
In order to estimate the age of hexactinellid sponges, the growth rates alone are not sufficient data, because the volume of the sponge body increases to the power of three while the length increases only linearly. A better way to estimate the age is by means of the increasing volume of the sponge body. After Leys& Lauzon (1998) a mean growth rate of 2 centimetres per year corresponds to 167 ml. A sponge, 32 centimeter tall with a volume of 5,8 l, would be 35 years old (if the growth rate is constant. Large individuals (e.g. 36,8 l and nearly 1 m long) are at least 220 or more years old (calculated with a constant average growth rate of 167 ml per year). Growth rates are usually not constant, but vary within broad limits and decrease as the sponges increase in size. Therefore we consider the above mentioned arithmetical ages to be fairly reliable.
Siliceous sponge spicules consist of amorphous biogenic silica. This
opaline material is supposed to dissolve shortly after the death and maceration
of the sponge. This is discussed by numerous authors, mainly dealing with
fossil or sub-fossil sponges (e.g., Friedman et al., 1976; Land, 1976;
Lang, 1989; Narbonne & Dixon, 1984; Rigby, 1986).
Bornhold, B.D. (1978): Carbon/nitrogen ratios (C/N) in surficial marine sediments of British Columbia. - Current Research, part C, Geological Survey of Canada, Paper 78-1C, Ottawa.
Conway, K. W., Barrie, J. V., Austin, W. C. & Luternauer, J. L. (1991): Holocene sponge bioherms on the western Canadian continental shelf. - Continental Shelf Research 11: 771-790, 10 figs., 1 tab., London.
Dayton, P. K. (1978): Observations of growth, dispersal and population dynamics of some sponges in McMurdo Sound, Antarctica. - In: LÚvi, C. & Boury-Esnault, N. (eds.) Observations of growth, dispersal and population dynamics of some sponges in McMurdo Sound, Antarctica. - Colloques Internationaux du Centre National de la Recherche Scientifique, 291: 271-282, Paris.
Freiwald, A., Wilson, J. B. & Henrich, R. (1999): Grounding Pleistocene icebergs shape recent deep-water coral reefs. - Sedimentary Geology 125: 1-8, 3 figs., Amsterdam.
Friedman, G. M., Syed, A. A. & Krinsley, D. H. (1976): Dissolution of Quartz accompanying Carbonate Precipitation and Cementation in Reefs: Example from the Red Sea. - Journal of Sedimentary Petrology 46(4): 970-973, Tulsa.
Land, L. S. (1976): Early dissolution of sponge spicules from reef sediments, North Jamaica. - Journal of Sedimentary Petrology 46(4): 967-969, 3 figs., Tulsa.
Lang, B. (1989): Die Schwamm-Biohermfazies der Noerdlichen Frankenalb (Urspring; Oxford, Malm): Mikrofazies, Paloekologie, Palaeontologie. - Facies 20: 199-274, 26 figs., 9 pl., 3 tab., Erlangen.
Levings, C. D. & McDaniel, N. G. (1974): A unique collection of baseline biological data: benthic invertebrates from an underwater cable across the Strait of Georgia. - Fisheries Research Board of Canada, Technical Report 441: 1-19.
Leys, S. P. & Lauzon, N. R. J. (1996): Hexactinellid ecology: Growth and seasonal regression in Rhabdocalyptus dawsoni. - Abstract, International Conference on Sponge Biology, pp. 29, March 12.-16., 1996 Otsu, Japan.
Leys, S. P. & Lauzon, N. R. J. (1998): Hexactinellid sponge ecology: growth rates and seasonality in deep water sponges. - Journal of Experimental Marine Biology and Ecology 230: 111-129, 8 figs., Amsterdam.
Narbonne, G. M. & Dixon, O. A. (1984): Upper Silurian lithistid sponge reefs on Sommerset Island, Arctic Canada. - Sedimentology 31(1): 25-50, Amsterdam.
Neuweiler, M. (2000): Untersuchungen an Kieselnadeln rezenter hexactinellider Schwaemme. - Thesis Universitaet Stuttgart, 166 pp., 165 figs., Stuttgart.
Okada, Y. (1928): On the Development of a Hexactinellid Sponge, Farrea sollasi. - Journal of the Faculty of Science Imperial University of Tokyo, Sect. 4 Zoology 2: 1-27, 22 figs., 8 pl., Tokyo.
Rigby, J. K. (1986): Sponges of the Burgess shale (Middle Cambrian), British Columbia. - Palaeontographica Canadiana 2: 1-105, 27 figs., 20 pl., Toronto.
last changes 18.02.2011