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

8 Professional Paper NMFS 12
Bering Sea each year – more than four times the weight
of corals landed there as fisheries bycatch (NMFS 5 ).
All emergent epifauna are susceptible to disturbance
from fishing gear (Stone, 2006) and most species of
deep-water sponges are to some degree vulnerable to
disturbance (also see Hogg et al., 2010, for a recent
review). Fishing operations affect the seafloor from
depths of 27 m to about 1200 m in the Aleutian Islands,
with most effort at depths shallower than 200 m (Stone,
2006). The degree to which a particular gear type affects
sponge habitat depends on its configuration (i.e.,
physical area of contact), operation (i.e., physical forces
on the seafloor), spatial and temporal intensity of operation,
seafloor bathymetry and substratum type, and
the resiliency of sponges to disturbance. Both direct
and indirect effects from fishing activities on sponges
likely occur. Direct effects include removal as bycatch,
damage caused by physical contact, or detachment
from the seafloor and translocation to unsuitable habitat.
Indirect effects include increased vulnerability to
predation, especially for sponges detached from the
seafloor, and habitat alteration. Furthermore, there
is some evidence that reproduction is suppressed in
damaged shallow-water scleractinian corals due to a
reallocation of energy reserves to tissue repair and
regeneration (Wahle, 1983), and similar effects may
occur in sponges.
Most of the factors that control the degree to which
sponges provide habitat structure are the same factors
that control the degree to which they are vulnerable to
disturbance. For example, large species with arborescent
growth forms are more likely to be contacted by
passing fishing gear. Species such as Plakina tanaga have
low vulnerability to disturbance due to their encrusting
habitus and absence in areas where bottom trawling is
known to occur. Some species such as Poecillastra tenuilaminaris
are highly vulnerable to disturbance due to
their large size and high relative abundance. Artemisina
stipitata is moderately vulnerable to disturbance due to
its large size, erect form, and presence in areas where
bottom trawling and longline fishing are known to occur.
Some sponges, for example those with holdfast
structures rather than root-like attachment systems, may
be more vulnerable to detachment, and it is unknown
if intact but otherwise undamaged sponges detached
from the substrate (e.g., roller sponges; Reiswig, unpubl.
data, 2010) can survive.
The recovery rate of disturbed benthic ecosystems in
Alaskan waters is of keen interest to fisheries managers
but is still little more than conjecture due to limited
5 National Marine Fisheries Service. 2004. Final programmatic
supplemental groundfish environmental impact statement for Alaska
groundfish fisheries. Alaska Region, NOAA, NMFS, P.O. Box
21668, Juneau, AK 99802-1668.
knowledge of species distribution and basic life history
processes. Rates of recovery will depend on growth rates
and rates of sexual and asexual reproduction or speed of
regeneration, which are unknown for most species. Two
key components of ecosystem persistence are resistance
(i.e., the ability to resist changes from disturbance) and
resiliency (i.e., the ability to absorb changes and the
speed with which it returns to its original condition)
(Holling, 1973). In the case of sponges, resistance to
disturbance depends largely on their physical size, morphology,
and distribution relative to the disturbance.
We know from studies in the Aleutian Islands and Gulf
of Alaska that benthic emergent epifauna, especially
sponges, have low resistance to fishing gear disturbance
(Freese et al., 1999; Stone, 2006; Heifetz et al., 2009;
Stone, unpubl. data, 2004–2005). We know little about
the resiliency of emergent epifauna, however.
Resiliency depends on several factors, including
growth rate, recruitment rate, and reproductive ecology.
Like deep-water corals, sponges have life history
attributes such as slow growth rates and high longevity
(Dayton, 1979), indicating that long periods of time
would be necessary for habitats dominated by sponges
to recover from disturbance (Freese, 2001). Growth
rates for deep-water sponges are generally slow (see
above) and therefore inherently difficult to study.
Reference sites, such as undersea cables that provide
a known time-line for recruitment and subsequent
growth, show promise in studies of sponge habitat recovery
(Levings and McDaniel, 1974) but have not yet
been identified or targeted for such study in Alaska.
The only known study to address the recovery dynamics
of sponges in Alaska reported no visually detectable
growth or regeneration one year post-disturbance with
a bottom trawl (Freese, 2001). Due to the opportunistic
nature of that study (observations were subjective, not
quantifiable; not repeatable since specimens were not
georeferenced; and made in an area subjected to high
background disturbance), the findings are questioned.
Contrastingly, a study conducted off the southeastern
coast of the U.S. indicated that some sponges were
capable of recovering completely within one year from
damage caused by a research trawl (Van Dolah et al.,
1987).
Monitoring bycatch of sponges
Appendix II provides a list of all sponges for which we
have provided species descriptions in this guide. For
each species, the importance as fish habitat and the vulnerability
to disturbance from fishing activities is ranked
from low (1) to high (3). Ranks for the two measures
are averaged to provide a score. We recommend that
species with scores greater than 2.0 be considered a