A guide to the deep-water sponges of - NMFS Scientific Publications ...

that readers can definitively confirm specimen identification.
For most species, we provide photographs of
specimens on deck (shortly after collection) or archived
specimens and photographs of specimens in situ. The
former will be most useful to fisheries observers and
fishers to identify specimens on fishing and survey vessel
decks shortly after collection. The latter will be useful
to scientists attempting to identify and quantify sponge
fauna in situ, with submersibles and remotely operated
cameras. We provide the known zoogeographic
range and information about the physical habitat and
oceanographic habitat (i.e., temperature and salinity),
if available (Koltun, 1959), of each species both within
Alaskan waters and throughout its known range. Finally,
we include for each species special remarks with regard
to taxonomic history, biology, and ecology.
We used the following literature to construct the species
lists and determine the zoogeography and other
published information for each species: Austin (1985),
Blake and Lissner (1994), Boury-Esnault and Rützler
(1997), Brøndsted (1993), Burton (1934), Dickinson
(1945), Hooper and Van Soest (2002), Koltun (1958,
1959, 1970), Lamb and Hanby (2005), Lambe (1900),
Laubenfels (1953), Sim and Kim (1988), Van Soest
et al. (2008), and de Weerdt (1986a, 1986b).
Appendix I provides a current and comprehensive
taxonomic list of all sponges now known to occur in the
deep waters (>80 m) of Alaska. Appendix II provides
a ranking for all the species included in this guide in
terms of their importance as fish habitat and vulnerability
to disturbance from fishing activities. The average
score for these two factors is used to prioritize species for
monitoring as bycatch in commercial fisheries and stock
assessment surveys. Appendix III includes a glossary of
terms commonly used in the species descriptions. The
terminology used in the section on skeletal structure is
not included in Appendix III. We refer the reader to the
Thesaurus of Sponge Morphology (Boury-Esnault and
Rützler, 1997) for a comprehensive glossary of skeletal
structure terminology. Appendix IV includes scanning
electron microscopy (SEM) images of spicules from select
calcareous, hexactinellid, and demosponges found
in Alaskan waters. The purpose of Appendix IV is to
provide readers with a representative collection of spicule
images so that they may gain an understanding of
the terms used in the guide and an appreciation for the
variation between species and among spicule types. This
collection also serves as a source of reference material
for those who wish to microscopically examine sponges.
Zoogeography of sponges
All three major groups of sponges—Class Calcarea
(calcareous sponges), Class Hexactinellida (hexacti-
nellid or glass sponges), and Class Demospongiae (demosponges)—are
well represented in Alaska. Only 12
(6.1%) of the 196 species of sponges now known from
Alaskan waters are calcareous sponges. They have skeletons
composed entirely of calcium carbonate laid down
as calcite and are consequently one of the faunal groups
at high risk from increased acidification of North Pacific
Ocean waters. They are principally found in shallow
water and are very rare at depths below 250 m.
Glass sponges are represented by 52 species (26.5%
of the total) in Alaskan waters. Glass sponges have a siliceous
skeleton consisting of spicules with a hexactinal
or 6-rayed pattern. They are generally more abundant
in deeper water but have a very broad depth distribution
in Alaska, ranging from 20 m in the fjords of Southeast
Alaska to more than 2800 m on the Aleutian Island
slope. Hexactinellid sponges are common throughout
Alaska but form different habitats depending on geographical
region. In the deeper slope habitats of the
Aleutian Islands, we have observed large debris fields
comprised mainly of glass sponge skeletons that provide
attachment substrate for other invertebrates, including
gorgonians and hydrocorals. In the Gulf of Alaska, glass
sponges are generally solitary but do form low-diversity
dense patches in areas of exposed hard substrate (Stone,
unpubl. data, 2005). In southern Southeast Alaska, in
Portland Canal along the border of Alaska and British
Columbia, we have found small sponge reefs, similar in
species composition to, but much smaller in size than,
the massive bioherms reported farther south in British
Columbia (Conway et al., 1991, 2001, 2005; Krautter et
al., 2001). Small patches of hexactinellid reef, believed
to be biohermal, have also been observed in northern
Southeast Alaska near Juneau, possibly indicating that
these structures are more common than originally
hypothesized and may extend up through the inside
waters of the Alexander Archipelago in areas where
favorable conditions exist for reef formation.
Demosponges are by far the dominant group of
sponges in Alaskan waters, with 132 documented species.
Demosponges also have a siliceous skeleton but the
spicules are not hexactinal in pattern and the skeleton
may be replaced or largely supplemented with an organic
collagenous network of spongin. They are found
throughout Alaskan waters and over a very broad depth
range (intertidal to more than 2800 m). High diversity
sponge “gardens” recently discovered in the Aleutian
Islands (Fig. 1) are dominated by demosponges but
also include some hexactinellid and calcareous sponges.
A few deep-water sponges (e.g., Guitarra fimbriata,
Halichondria sitiens, and Hymeniacidon assimilis) are cosmopolitan
in distribution (Dickinson, 1945), but recent
research indicates that the occurrence of sibling species
worldwide might also be common. Deep-water sponges
are found throughout Alaska and have been reported
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