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Reservoirs of biodiversity
Deep-sea sponge grounds
Seas
Regional
Reservoirs of biodiversity
Deep-sea sponge grounds
Seas
Regional
UNEP World Conservation Monitoring Centre
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The United Nations Environment Programme World
Con
servation Monitoring Centre (UNEP-WCMC) is the
biodiv
ersity assess ment and biodiversity policy support
arm of the United Nations Environment Programme
(UNEP), the world’s foremost inter governmental envi ron -
mental organization. The Centre has been in operation for
over 25 years, combining scientific research with prac -
tical policy advice.
© UNEP/UNEP-WCMC, 2010
ISBN: 978-92-807-3081-4
CITATION: Hogg, M.M., Tendal, O.S., Conway, K.W.,
Pomponi, S.A., van Soest, R.W.M., Gutt, J., Krautter, M.
and Roberts, J.M. (2010)
Deep-sea Sponge Grounds:
Reservoirs of Biodiversity.
UNEP-WCMC Biodiversity
Series No. 32. UNEP-WCMC, Cambridge, UK.
URL: http://www.unep-wcmc.org/resources/publications/
UNEP_WCMC_bio_series/32.aspx
For all correspondence relating to this report please contact:
info
@unep-wcmc.org
A Banson production
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Printed in the UK by Swaingrove
DISCLAIMER
The contents of this report do not necessarily reflect the views or
policies of UNEP, contributory organizations or the institutions of the
authors. The designations employed and the presentations do not
imply the expressions of any opinion whatsoever on the part of UNEP
or contributory organizations concerning the legal status of any
country, territory, city or area and its authority, or concerning the
delimitation of its frontiers or boundaries.
AUTHORS
Mariana M. Hogg, School of Lif
e Sciences
Heriot-Watt University, Mh222@hw.ac.uk
Ole Secher Tendal, Natural History Museum of Denmark,
University of Copenhagen, ostendal@snm.ku.dk
Kim W. Conway, Pacific Division, Geological Survey of
Canada, kconway@nrcan.gc.ca
Shirley A. Pomponi, Harbor Branch Oceanographic
Institution, Florida Atlantic University,
spomponi@hboi.fau.edu
Rob W.M. van Soest, University of Amsterdam,
R.W.M.vanSoest@uva.nl
Julian Gutt, Alfred Wegener Institute for Polar and Marine
Research, Julian.Gutt@awi.de
Manfred Krautter, Institute for Palaeontology
University of Stuttgart,
manfred.krautter@geologie.uni-stuttgart.de
J. Murray Roberts, School of Life Sciences, Heriot-Watt
University, J.M.Roberts@hw.ac.uk
IMAGES
Front cover and title page (left to right): see pages 11, 35,
42, 33, 20. Back c
over: see page 41. Page 8, top to bottom,
left: see pages 14, 35, 34, 41, 48; right: see pages 21, 65,
43, 15, 29.
UNEP promotes
environmentally sound
practices, globally and in its own
activities. This report is printed on
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and other eco-friendly practices. Our
distribution policy aims to reduce
UNEP’s carbon footprint.
3
L
ong overlooked, deep-water sponge grounds are
now emerging as a key component of deep-sea
ecosystems, creating complex habitats hosting many
other species. They are an important refuge in the deep
ocean and they are also reservoirs of great species diversity,
including commercially important fish. Playing a similar role
to that of cold-water coral reefs with which they often co-
occur, sponge grounds are even more ecologically and
geographically diverse, consisting of many individual species
and occurring in many places around the world.
The rapid development of sophisticated technology has
provided opportunities to observe and study deep-water
sponges in a way that has never been previously possible.
This report highlights what is currently known about deep-
water sponge grounds in terms of their distribution, biology,
ecology and present-day uses in biotechnology and drug
discovery, and introduces case studies of particular deep-
water sponge habitats from around the world.
Worrying findings are presented on the impacts of human
activities, in particular bottom trawling used by commercial
fisheries, and gaps in knowledge are also brought to our
attention. We do not yet know the full global distribution of
deep-water sponges, or fully understand their biological
processes and ecological roles. Furthermore, there is
limited scientific understanding of the ramifications of
climate change and ocean acidification on the health and
continued function of these important and fragile deep-
water habitats.
This report highlights the need to minimize the risk of
damage to deep-sea sponge grounds through appropriate
conservation and careful management, and presents further
evidence of the need to improve awareness and under stand -
ing to ensure that future generations have the opportunity
to explore, study and benefit from these vulnerable deep-
water habitats. I therefore welcome the recommendations
made by the authors. As a result of their work, deep-water
sponge grounds – for so long out of sight – will no longer be
out of mind.
Chris Elliott
Executive Director, Conservation
WWF International
Preface
4
We gratefully acknowledge everyone who contributed to this
report. Many thanks to those who gave permission for
previously published photographic images and illustrations
to be reproduced. The following contributed images for
the report: J. Berman, W. Dimmler, J.H. Fosså, P. Gibson,
Harbor Branch Oceanographic Institution, ICES, D. Jones,
C. Martens, P.B. Mortensen, W.E.G. Müller, NAFO, J. Petri,
B. Picton, H.T. Rapp, A. Starmans, H. Thiel, and C. Wienberg.
Assistance was also given by D. Sipkema in reviewing the
chapter on microbial associations and S. Christiansen and
E. Kenchington who reviewed and made valuable con -
tributions to the chapter on the conservation of deep-water
sponge grounds. Many thanks to T. Hourigan for reviewing
the first draft report and to L.-A. Henry and L. Wicks for
reviewing and editing final stages of the revised document.
In addition we would like to acknowledge support through
the 'Deep-sea Conservation for the UK' project funded by the
Esmée Fairbairn Foundation and the European Community’s
Seventh Framework Programme (FP7/2007-2013) under the
HERMIONE project, grant agreement n° 226354. Finally, we
thank N. Barnard at UNEP-WCMC for her assistance with
editing and producing this report and S. Hain for initiating
this work.
Acknowledgements
5
Preface........................................................................................................................................................................................3
Executive summary....................................................................................................................................................................7
CHAPTER 1: INTRODUCTION...................................................................................................................................................11
CHAPTER 2: RESEARCH ..........................................................................................................................................................13
Technology......................................................................................................................................................................................13
Remote sensing .............................................................................................................................................................................15
Mapping and acoustics..................................................................................................................................................................15
Submersibles .................................................................................................................................................................................16
Remotely operated vehicles ..........................................................................................................................................................17
CHAPTER 3: BIOLOGY ..............................................................................................................................................................18
Anatomy..........................................................................................................................................................................................18
Spicules ..........................................................................................................................................................................................20
Chemical ecology...........................................................................................................................................................................20
Growth, size and longevity.............................................................................................................................................................22
Reproduction..................................................................................................................................................................................22
Disease ...........................................................................................................................................................................................23
CHAPTER 4: BIODIVERSITY......................................................................................................................................................25
Associated fauna............................................................................................................................................................................26
CHAPTER 5: THREATS..............................................................................................................................................................27
Commercial trawling and other fishing gear...............................................................................................................................27
Hydrocarbon exploration and exploitation ...................................................................................................................................29
Cable and pipeline placement.......................................................................................................................................................30
Waste disposal and dumping ........................................................................................................................................................30
Mining of geological resources .....................................................................................................................................................30
Global climate change...................................................................................................................................................................31
Assessing the risks........................................................................................................................................................................31
CHAPTER 6: CASE STUDY 1: Glass sponge reefs off the west coast of Canada – a living fossil ..........................................33
Sponge reefs in Earth’s history.....................................................................................................................................................33
Mapping and sampling ..................................................................................................................................................................34
Distribution and reef form.............................................................................................................................................................35
Sponge reef habitat and sensitivity to human impacts ...............................................................................................................36
CHAPTER 7: CASE STUDY 2: Sponge grounds in the Northeast Atlantic ..............................................................................38
CHAPTER 8: CASE STUDY 3: The bird’s nest sponge (
Pheronema carpenteri
) ....................................................................39
CHAPTER 9: CASE STUDY 4: The deep Antarctic shelf, a ‘sponge kingdom’.........................................................................41
Contents
6
CHAPTER 10: USES OF SPONGES ...........................................................................................................................................45
Historical perspectives ..................................................................................................................................................................45
Current uses in biotechnology ......................................................................................................................................................45
Fibre optics, engineering and design ...........................................................................................................................................49
CHAPTER 11: INTERNATIONAL ACTIONS ...............................................................................................................................51
United Nations General Assembly and UNCLOS.........................................................................................................................51
Food and Agriculture Organization of the United Nations (FAO) ................................................................................................52
Global conventions and partnerships...........................................................................................................................................52
International Union for Conservation of Nature (IUCN) ..............................................................................................................52
European Union .............................................................................................................................................................................52
OSPAR Convention for the Protection of the Marine Environment of the North-East Atlantic................................................53
International Council for the Exploration of the Sea (ICES)........................................................................................................53
Academia........................................................................................................................................................................................53
World Wide Fund for Nature (WWF) .............................................................................................................................................54
Deep-Sea Conservation Coalition.................................................................................................................................................54
CHAPTER 12: CONSERVATION CONSIDERATIONS .................................................................................................................55
Are deep-water sponge grounds vulnerable marine ecosystems? ...........................................................................................55
Assessment of ‘significant adverse impacts’ ...............................................................................................................................59
Mitigation measures......................................................................................................................................................................59
Prospective.....................................................................................................................................................................................64
Are deep-water sponge grounds ecologically and biologically sensitive areas? ......................................................................65
Can deep-water sponge grounds be designated marine protected areas? ..............................................................................68
CHAPTER 13: RECOMMENDATIONS........................................................................................................................................69
Acronyms..................................................................................................................................................................................73
Glossary ....................................................................................................................................................................................74
References................................................................................................................................................................................76
Institutions and experts working on deep-water sponges.....................................................................................................84
7
U
ntil recently, deep-water sponge grounds have
remained Cinderellas of the deep seas, largely
overlooked and poorly understood. However, it is
now clear that these sponges create habitats, support high
biodiversity, provide refuge for fish, and are a storehouse of
novel chemical compounds, some of which show promise
for pharmaceutical drug development.
International concern is now focused on the vulnerability
of deep-water sponge grounds. Sponges are slow-growing
and long-lived, and therefore slow to recover from per tur -
bations, including physical damage. The impacts of climate
change on sponges are largely unknown, but bottom
trawling is currently considered to be the most per vasive
and damaging deep-water human activity. This has been
recognized in a number of international arenas.
This report outlines what is known about deep-water
sponge grounds in terms of their distribution, biology,
ecology and present-day uses in biotechnology and drug
discovery. It also reviews the policy environment within
which deep-water sponges can be conserved, discusses
options for future policy development, and concludes with a
series of recommendations focusing upon:
■ Under UN General Assembly Resolution 61/105:
❑ formally identifying sponges as a vulnerable
marine ecosystem;
❑ adopting precautionary management of sponges,
including refinement of sponge bycatch thresholds
for fishing vessels;
■ Under the Convention on Biological Diversity’s 2012
target for marine protected areas:
❑ ensuring the representation of sponges in
marine protected area networks;
❑ supporting broad international engagement in
the scientific research needed to:
– map and predict sponge distribution globally,
– understand sponge ecology, particularly the role
of secondary metabolites;
■ Enhancing monitoring through the use of vessel
monitoring and fishery observer approaches;
■ Developing regional monitoring programmes with
full stakeholder involvement;
■ Ensuring effective science-policy interactions to
promote better management of sponge grounds
and other vulnerable deep-water ecosystems.
Sponge grounds form structurally complex habitats
supporting locally rich biodiversity. They have provided
society with a range of ecosystem goods and services for
thousands of years, dating back to the times of Homer and
Aristotle. For generations, some local communities have
relied on shallow-water bath sponge fisheries as a source
of income. More recently – since the 1970s – a growing and
significant bio technological industry has developed, which
extracts potential drugs from marine organisms. As a
group, sponges produce a particularly diverse array of
secon dary metabolites – compounds that have powerful
metabolic effects on other species, comparable to the
antibiotics produced by bacteria. A number of drugs have
now been discovered from sponges and taken through
clinical trials. Understanding secondary metabolites in
sponges and their role in sponge biology has tremendous
potential for future drug discovery. For example, whereas
up to 10,000 compounds may have to be synthesized in
the laboratory for a single drug to pass through clinical
trials, only around 200 secondary metabolites are typically
screened to produce a successful new drug. However,
despite their inherent and biotechnological value, we
risk irreversibly damaging deep-water sponge grounds
before we have been able to study their ecology and
explore their wider potential for providing ecosystem
goods and services.
As with all deep-water ecosystems, sponge grounds
remain poorly mapped and understood. Current knowledge
of the global distribution of sponges is biased to those
areas of the world with a history of deep-sea surveys,
although recent technological advances now allow three-
dimensional seabed surveys and remotely operated
vehicles to map and explore the deep sea as never before.
Where scientific studies have been carried out, the scale
and significance of deep-water sponge grounds have been
unexpectedly high.
Deep-water sponge grounds often occur as distinct bands
where local environmental conditions are suitable for their
growth. In the Northeast Atlantic, such bands of ‘
Holtenia
grounds’ formed by the glass sponge
Pheronema
were first
Executive summary
Madrid
Siliceous
sponge
reef belt
fibrinogen
FIBG
FK
tyrosine
kinase
GLUBP
GLUBPp
nin
(1,3)-ß-
D
-glucan (1,3)-ß-
D
-glucan (1,3)-ß-
D
-glucan
gene expression
discovered in the 19th century. Sponge grounds are typically
found in truly oceanic waters with suitable hard substrate
on which to settle and local water currents to supply food
particles from the surface ocean. There are thought to be
more than 500 sponge species in the well-developed
‘sponge kingdom’ on the deep continental shelf of
Antarctica. However, a global map of sponges does not exist
and the recent discovery of giant glass sponge reefs off
western Canada – a throwback to Jurassic times – shows
that more mapping is a priority for future work.
Sponges are long-lived and slow-growing. For example,
today’s Canadian sponge reefs are up to 9,000 years old,
with individual sponges reaching ages of more than 100
years. They are also fragile structures that are easily
damaged by physical perturbations. As scientific surveys
record deep-water sponge distribution and discover new
sponge habitats, many also bring back clear evidence that
they have been damaged by bottom trawling. Bottom
trawling of sponge grounds physically injures, dislodges
and captures sponges. If returned to the sea after having
been caught, they rarely survive. Seabed sediments
disturbed by the passage of a trawl also clog the complex
filtering apparatus that sponges use to catch their food.
Similar concerns have been raised over the deep-sea
disposal of cuttings from oil and gas drilling and the
localized seabed impact associated with cable and pipeline
laying and seabed mining. There is almost no scientific
understanding of the impacts of climate change and ocean
acidification on deep-water sponge grounds.
To date, management and conservation of deep-water
sponges is widely considered to be inadequate and
uncoordinated. However, there are various existing frame -
works which can be used to rectify this. Perhaps the most
notable is the adoption in December 2006 by the United
Nations General Assembly (UNGA) of Resolution 61/105.
This resolution calls upon states and regional fishery
management organizations to ensure that vulner able
marine ecosystems do not suffer significant adverse
environmental impacts from bottom trawling. International
guidelines on the identification of such vulnerable areas
were published by the Food and Agriculture Organization of
the United Nations (FAO) in 2009. Following these guide -
lines, deep-water sponge grounds meet the criteria of
being vulner able marine ecosystems on a number of levels:
■ they are limited to discrete areas with suitable
environmental conditions;
■ they support high biodiversity of other species;
■ they are fragile and unlikely to recover from trawl
damage;
8
Deep-sea sponge grounds
9
Executive summary
■ they are slow-growing, long-lived and form struc -
turally complex habitats.
However, while UNGA Resolution 61/105 provides a mecha -
nism for states and regional fisheries organizations to
prevent damage from bottom trawling, the effectiveness of
this is currently limited by a number of factors. For example:
■ there remains uncertainty over the formal defi -
nition of a vulnerable marine ecosystem;
■ current guidelines on the level of sponge bycatch
needed to require a fishing vessel to move on to a
different area can be as much as 800 kg; there is
growing consensus that this limit is too high;
■ guidelines do not currently consider the rate of
bycatch, which is important given the highly
variable geographic distribution of sponges;
■ upon encountering a vulnerable marine ecosystem,
vessels are required to move on 2-5 nautical miles,
which may not be far enough to reduce the spread
of trawl impact to nearby habitats.
The conservation of sponge grounds may also be achieved
through the Convention on Biological Diversity (CBD), in two
ways. The first is the target to establish a global, repre sent -
ative network of marine protected areas by 2012, adopted by
the Parties to the Convention in 2006, which should include
representation of sponges. Secondly, deep-water sponge
grounds meet several of the criteria adopted by the CBD in
2008 to identify ecologically and biologically sensitive areas
of the open ocean and deep seas (including areas beyond
national jurisdiction). These criteria are being used to sup -
port countries’ identification of areas in need of improved
management or protective measures, including marine
protected areas, but the process is still in its infancy.
While there are currently no known marine protected areas
that have been created explicitly to protect deep-water
sponges, there are some examples of successful sponge
conservation at the regional level, particularly the estab -
lishment in 2009 of several fishery closures by the
Northwest Atlantic Fisheries Organization (NAFO) in res -
ponse to UNGA Resolution 61/105, to protect sponge
grounds off Atlantic Canada. Furthermore, the Commission
for the Conser vation of Antarctic Marine Living Resources
(CCAMLR) and the New Zealand government have adopted
far more precautionary move-on rules than those currently
provided in UNGA Resolution 61/105. Such precautionary
measures may be more effective, especially in the case of
New Zealand where these rules are combined with a repre -
sentative network of closed areas.
These examples of successful deep-sea sponge manage -
ment and conservation are encouraging, but there is much
more to do. There is a clear need to bring the research
community together to focus efforts on understanding
deep-water sponge grounds and to provide the funding and
infrastructure needed for this work. Given the expense and
technically challenging nature of such research, strong
col laborations and international partner ships should play
an important role, including transfer of exper tise and infra -
structure from developed to less developed nations. Efforts
to improve fishery observer coverage and gather infor -
mation on sponge ground distribution from fishers should
be increased.
Finally, and perhaps most importantly, there is a great need
to improve awareness and understanding of deep-water
sponge grounds. Without this, future generations may be
denied the opportunity to explore, study and benefit from
these important and fragile architects of the deep sea.
11
O
ver the last decade there has been a resurgence of
both scientific and public interest in sponge grounds,
with increasing recognition of their importance to
the biodiversity and functioning of marine ecosystems.
Scientific research has revealed new insights into how
deep-water sponges provide habitat for many species and
influence biodiversity (Klitgaard 1995). Uncertainties over
the current ecological state of sponge grounds, coupled with
significant gaps in our knowledge of their global distribution,
have also caused great concern among regional, national
and international agencies. This has largely been in res -
ponse to the threats posed by deep-water bottom trawling.
Large habitat-forming deep-water sponges are particularly
slow-growing, and these long-lived creatures could take
many decades – probably several human generations – to
recover, if at all (Klitgaard 1995).
The wider availability of deep-sea survey and sampling
technologies, including remotely operated and autono mous
underwater vehicles, is now allowing the first detailed
obser vations of deep-water sponges in their natural
habitats. The widespread perception that sponges are
‘simple’ and ‘primitive’ in their functioning is being over -
turned as the complexity of their biology and ecology is
revealed. Many different kinds of deep-water sponge
1. Introduction
Figure 1.1:
Stryphnus
ground off Norway. The yellow
sponge is an
Aplysilla
species encrusting the lumpy
Stryphnus
.
J.H. Fosså, Bergen.
BOX 1.1: DEFINITION OF SPONGES
The Phylum Porifera (Grant 1836): ‘Sessile meta -
zoans with a differentiated inhalant and exhalant
aquiferous system with external pores, in which a
single layer of flagellated cells (choanocytes) pump
a unidirectional water current through the body,
con taining a highly mobile population of cells
capable of differentiating into other cell types
(totipotency) and conferring a plasticity to growth
form, and with siliceous or calcitic spicules present
in many species.’ (From Hooper
et al.
2002.)
12
Deep-sea sponge grounds
grounds have been explored, mostly at high latitudes,
including glass (hexactinellid) sponge reefs off the coast
of British Columbia, western Canada. Carbon dating
techniques have revealed that these reefs have been
growing for up to 9,000 years and geological records show
that these sponges have existed for many millions of years,
making them true living fossils (Conway
et al.
1991).
The sponges (Porifera) form one of the most ancient
animal groups on the planet, with a fossil record reaching
back to the Cambrian, 580 million years ago. The sponge
body is multicellular, comprising several cell types with
different functions. Sponges have no true tissues or organs,
but are considerably more differentiated than single-celled
organisms (protozoans). Despite their relatively simple
structure the group is highly diverse, comprising around
8,000 present-day (or extant) species, an estimated 7,000
undescribed species and hundreds of fossil species (Hooper
et al.
2002).
Apart from 150 freshwater species, sponges are a marine
group and are found in all the oceans and at all depths,
including at depths greater than 8,000 m. The number of
species described to date is highest in tropical shelf areas,
decreasing toward polar regions and with greater depth on
the continental slope. Most species live on hard substrata like
rock, gravel and coral reefs. A small number are soft-bottom
dwellers, and have special arrange ments to keep them above
the muddy surface, such as a stalk, a basal tuft or a fringe
along the lower edge of the body.
Sponges are highly effective filter feeders, both in terms of
the size spectrum of particles they can catch and the volume
of water they can filter. Their filtering system is a com pli -
cated interior arrangement of canal-like structures – the
unique hallmark of this group. Different subgroups of
sponges have evolved their aquiferous canal system in dif -
ferent ways, the most surprising being a reduction of the
filtering capacity in favour of a carnivorous mode of life
(Brusca and Brusca 2003).
This report summarizes the recent growth in understand -
ing of deep-sea sponge habitats to brief policy decision
makers, environmental stakeholders and the public about
the central issues and our existing state of knowledge. It
pre sents key concepts, current thinking and approaches for
manage ment and conservation as well as providing recom -
men da tions for appropriate measures that can be taken to
protect the most vulnerable deep-water sponge habitats.
Figure 1.2: Illustration of the biological structure and
skeleton of some glass sponges (Hexactinellida).
E. Haeckel, Kunstformen der Natur 1904.
BOX 1.2: DEFINITION OF ‘SPONGE GROUNDS’
Aggregations of large sponges that develop under
certain geological, hydrological and biological con -
ditions to form structural habitat. Sponge-dominated
habitats have variously been called sponge beds,
sponge fields, sponge accumulations, sponge grounds,
sponge associations, sponge mass occur rences, ostur
and sponge reefs. These terms are ambiguous,
although the last three are to some degree defined in
the literature. In this report we will adopt the term
‘sponge ground’ and refine this broad term with
reference to the sponge species dominating in body
size and abundance, and also often by the accumu -
lation of its skeletal remains on the seabed.
13
M
ost of the 20th-century information gathered
on deep-sea sponges is centred in the Atlantic
Ocean, but even here datasets are sporadic and
infrequent. However, they provide valuable information
about the richness of sponge life in bathyal waters (200-
2,000 m depth) and build on pioneering historic oceano -
graphic expeditions. In the 19th century the ships HMS
Porcupine
,
Lightning
and
Challenger
used dredging tech -
niques to collect deep-sea samples, with the
Challenger
expedition (1872-76) providing particularly detailed records
of sponges. The samples collected during the cruises of
HMS
Porcupine
are described extensively by Carter in his
reports of 1874 and 1876. These cruises marked the birth
of oceanography as a science and were fundamental in
showing that animal life could persist at depths greater
than 600 m.
Other cruises sampling deep-sea life at around the same
time as HMS
Challenger
included, amongst others, the
Norwegian cruises of Michael Sars, which also reported
marine life at great depths. Amongst the many different
sponges hauled from the deep during these Norwegian
expeditions,
Cladorhiza
must have been one of the most
start ling in appearance. To modern eyes, this sponge re -
sembles a ‘space-age microwave antenna’; in the 19th
century they were observed to be ‘sponges with a long stem
ending in ramifying roots, sunk deeply in the mud. They act
as a bush-like seafloor cover lying over extensive tracts
of the sea bottom’ (Alexander Agassiz in Heezen and
Hollister 1971).
TECHNOLOGY
The vision of building a diving vessel that could go to the
greatest depths of the ocean was first initiated by pioneers
like Auguste Piccard. A so-called bathyscaph, FNRS-3, built
for underwater exploration was supported by the French
navy. In February 1954, FNRS-3 reached 4,049 m in the
mid-Atlantic, although it had no gear with which to collect
samples. The year before, US-Italian bathyscaph
Trieste
reached the near-deepest spot in the Mediterranean,
achieving 3,167 m, and in January 1960 off the coast of
Guam it sealed a record of 10,916 m. But despite these
exciting advances, the bathy scaph was still cum bersome
and difficult to operate in remote areas far from its
home base.
After the success of
Trieste,
the USA created an even more
advanced submersible named
Alvin
. The submersible had a
remote-control arm with a claw for sampling and a propeller
for horizontal propulsion. By the 1970s, improvements in
deep-sea engineering meant that higher strength steel and
titanium pressure hulls permitted
Alvin
to reach depths
of more than 3,000 m. Geological mapping in the Gulf of
Maine off the northeast coast of North America and the
discovery of deep-sea hydrothermal vents was a piece of
ground breaking research that
Alvin’s
high manoeuvrability
and strength enabled it to achieve. Since then, many innova -
tions have followed, particularly in the use of remotely
operated vehicles or ROVs. Indeed, the most recent vehicle
to visit the greatest depths of the ocean was the
Nereus
hy -
brid ROV from Woods Hole Oceanographic Institution (USA),
which dived to 10,902 m in May 2009. Equipped with sophisti -
cated cameras and sampling devices,
Nereus
and vehicles
like it illustrate the potential we now have to explore and
under stand the deep sea and its ecology as never before.
Carrying out deep-sea research requires rigorous planning
combined with technical expertise. Recent advances in
deep-sea sonar and submersible technologies have been
hugely significant in developing a greater understanding
of deep-water sponge fields. However, before these tech -
nolo gies emerged, historical data from fishermen’s charts
pro vided the foundation for what was known about deep-
water sponge grounds and coral banks that lasted for more
than 100 years.
The discovery of areas with high abundances of sponges
dates back nearly 150 years. At that time investigations were
made with early dredges and trawls, and only occasionally
reached depths of more than 1,000 m. The early records
most often came from localities widely scattered on a
long-distance expedition route, and therefore precise
positioning is rarely available. With better mapping of near-
coast and slope areas and the establishment of national sea
territories, there followed an interest in regional investiga -
tions typically based on a grid of sampling stations. A need
for better know ledge of local resources arose when fishery
limits were established and, over time, extended to greater
dis tances offshore to reach present-day limits at 200 nauti -
cal miles (or in some cases 400 nm). Many nations now
run regular multidisciplinary or bottom trawl fish sampling
2. Research
14
Deep-sea sponge grounds
surveys in their fishery areas along annually repeated
transects. These surveys may also record bycatch infor ma -
tion including data on sponges, corals and echino derms,
amongst others. Examples of recent mapping based on
trawling efforts are shown in Figures 2.1 and 2.2.
The recent BIOFAR programme (on marine benthic fauna
of the Faroe Islands) provided important insights into the
Northeast Atlantic. The region’s deep-water sponge ground
or ‘ostur’ distribution is defined in two arc-shaped bands
related to the flow paths of the Norwegian Atlantic Current
and the Irminger Current (Klitgaard and Tendal 2004). The
bands are not continuous but instead form a series of
patches influenced by local topography. The majority of
sponge grounds are found on the shelf plateau near the
shelf break, as well as along slopes and ridges.
Fishing records alongside scientific research cruises using
classical sampling approaches (e.g. dredging, trawling, grab -
bing, box coring) have led to our present-day under standing
of sponge distribution and biodiversity. Scandinavian studies
Figure 2.1: Distribution of
Geodia
and
Stryphnus
sponge
grounds in the Northeast Atlantic.
Ole Secher Tendal.
Greenland
Canada
USA
Labrador SeaLabrador SeaLabrador Sea
Davis
Strait
Baffin
Island
Hudson
Strait
—70ºN
—60ºN
—50ºN
I
70ºW
I
60ºW
I
50ºW
I
40ºW
N
Figure 2.2: Survey-trawl coverage between 2005 and
2008 in the Canadian exclusive economic zone (EEZ)
(red line). Different trawl types were used down to
depths of 1,450 m and different colours refer to different
surveying institutions.
ICES 2009.
15
Research
(Klitgaard and Tendal 2004) have integrated other wise frag -
mentary information to address key issues of taxonomy,
biology and observed distributional patterns. With a sub -
stantial collection of evidence in support of their key role in
deep-sea ecosystems, it is now important that ad di tional
research is undertaken so that the vulner a bility of sponges
to both global climate change and human activity can be
assessed and their potential recovery explored.
Sampling datasets for deep-sea sponges are still relatively
scarce and are restricted in their geographical locations.
Most of the available data are from the Atlantic and North
Pacific, with very few records from other parts of the world’s
ocean, notable exceptions being the Southwest Pacific (New
Caledonia), eastern Australia and New Zealand (Schlacher
et al.
2007). In contrast, because their skeletal remains can
form distinctive reef structures, data on cold-water corals
are more abundant, although again large areas of the global
ocean remain very poorly known. Cold-water coral reefs
can be identified with multibeam echosounder surveys and
then surveyed visually using deep-sea camera systems,
manned submersibles or remotely operated vehicles. This
has allowed cold-water coral habitats to be observed
in situ
so that not only can they be mapped and samples be taken,
but ecological roles and biological processes can be studied
(Roberts
et al.
2009b).
REMOTE SENSING
The first permanent photograph was an image made in
1825, and within just 15 years people began experimenting
with remote sensing by tethering cameras to balloons to
help map local topography. In the 1960s the first images of
planet Earth were taken from space, helping to crystallize
our view of Earth as a discrete system and promoting envi -
ron mental movements around the world.
In the marine environment light travels only short distances
whereas sound waves resonate over great distances. Thus
marine remote sensing usually relies on acoustic tech -
niques which grew out of military sonar applications in the
Second World War (see Fosså
et al.
2005).
MAPPING AND ACOUSTICS
Acoustic mapping has become an efficient method to map
and survey the seabed and the habitats that form upon it.
Although the use of acoustic mapping is limited for deep-
water sponge grounds because they tend to absorb sound
waves, certain forms of sponges, such as the hexactinellid
‘glass’ sponge reefs off the coast of Canada, have been
successfully surveyed using this approach. Techniques used
include side-scan sonar, seismic profiling and bathy metric
surveys derived from multibeam echosounders.
The first of these, side-scan sonar, can map a large area of
seabed relatively quickly and at certain frequencies sono -
grams can depict characteristics in the uppermost deposits
of the seafloor. The sonar ‘towfish’ is typically towed behind
the vessel, and transducers in the towfish transmit sound -
waves from each side and receive the reflected signals. An
image is produced as an echogram and, typically, where
higher sound frequencies are used, a higher mapping
resolution will be obtained. However, using this system is
not without its challenges, and there is a trade-off between
the area mapped in a given time and the resolution of the
seabed features within the defined area (Kenny
et al.
2003).
This means that side-scan sonar is often used in conjunction
with other, wide-area mapping methods and is frequently
used to help identify particular objects on the seafloor.
Seismic profiling uses low- and intermediate-frequency
sound pulses of approximately 10 herz to several kilohertz
emit ted from a system operated by survey vessels. The
sound pulses penetrate the seabed and are reflected from
interfaces of different densities or acoustic impendence.
These reflections or echoes are received by hydrophones
that are either towed by or mounted in the hull of the vessel.
Seismic data and profiling of the sub-seafloor generates
broad-scale information in two-dimensional form about the
geological setting surrounding deep-water sponge grounds
that would be unavailable through other systems of remote
sensing. However, this technique does not provide detailed
local habitat mapping information and cannot confirm the
definite existence of sponge grounds or cold-water coral
reefs, or estimate their horizontal extent.
Multibeam echosounders use a wide range of frequencies,
often employing more than a hundred beams transmitted at
different angles from the same transducer unit. They create
GPS antenna
Swath
Transducer
Single beams
Surveyed seabed
Figure 2.3: Diagram showing how a multibeam echo -
sounder sonar would operate from a scientific research
vessel.
C. Wienberg
/
MARUM, Germany.
16
Deep-sea sponge grounds
a fan which travels perpendicular to the direction of the
survey vessel, and the angle of this fan (the swath angle),
along with the water depth, determines the width of
the corridor mapped (Figure 2.3). This process produces
shaded-relief topographic maps which are very valuable
in helping to identify marine habitats and the wider
topographic context in which they are found.
The strength of the reflected echoes from multibeam
echosoundings can also be extracted and used to create
‘backscatter’ maps of the seabed that contain information
on sediment types (Kenny
et al.
2003). Echo strength
depends on the hardness, roughness and homogeneity of
the seabed. The combination of shaded-relief bathymetry
and backscatter maps, together with slope analysis, can
help to understand relict and cur rent processes including
erosion and deposition. Recent advances have made it
possible to display the acoustic survey data collected in real-
time whilst at sea by using software packages, such as Olex
(Ocean DTM), which allow for the immediate identification
of potentially important seabed terrain for deep-water
sponges. (It is important to note that as yet it has not proved
possible to detect deep-water sponge grounds using purely
acoustic methods, apart from the large sponge reefs off the
west coast of Canada, see Case study 1.)
SUBMERSIBLES
The use of
in situ
techniques such as remotely operated
vehicles (ROVs) and submersibles allows detailed under -
standing of small areas of seabed. Therefore these tools
are most effective when used alongside wide-area habitat
maps based on acoustic datasets, such as multibeam
bathy metry and backscatter data. This may, for example,
allow observations made during submersible surveys to
be extrapolated beyond the limited track covered by the
visual survey.
The first manned research submersibles appeared in
the 1960s as part of scientific and technological advance -
ments catalysed during the two World Wars. They allowed
scientists to observe and survey deep-sea animals in their
natural habitat on the seabed for longer periods of time
than ever before. They also allowed inhospitable environ -
ments such as mid-ocean ridge and vent communities to
be explored. In 1964, the submersible
Alvin
was used to
investigate cold-water coral mounds on the Blake Plateau
off South Carolina (USA). On the other side of the Atlantic,
another manned submersible,
Pisces III,
was used to exam -
ine
Lophelia pertusa
coral colonies growing on Rockall
Bank off the west coast of Scotland (Roberts
et al.
2009b).
Use of submersibles for surveying deep-water sponge
grounds is relatively rare, although there has been a re -
surgence of interest in recent years. For example, the vast
hexactinellid sponge reef complexes off the west coast of
Canada have been surveyed using submersibles, revealing
siliceous sponge reefs that were previously thought to be
extinct. Their discovery enabled a greater understanding of
fossil taxa and the process of sponge reef building. Direct
observation from submersibles also revealed that these
sponge reefs had been damaged over the past decade by
bottom trawling (Krautter
et al.
2001).
A survey of bioherms on the Pourtalès Terrace off the
south coast of Florida used Johnson-Sea-Link (JSL) manned
submersibles to explore the high diversity of Porifera, where
66 different taxa were identified. This method allowed
benthic population densities and micro habitat asso ciations
of the individual species to be studied (Reed
et al.
2005).
The JSL manned submersibles, which have been used for
biomedical sponge research since 1984 by the Harbor
Branch Oceanographic Institution group in Florida, USA,
provide platforms that enable research ers to go deeper, stay
longer and visit unusual sites (e.g., steep walls, rocky bot -
toms and vent communities) that cannot be accessed using
conventional methods. Sampling from these submersibles
has allowed researchers to be more precise and selective
in sampling than conventional deep-sea collection methods
would allow. Some submersible systems now have the ability
to maintain samples at ambient conditions of high pressure
and low temperature. These vehicles go to increasingly
greater depths, stay for longer periods of time and collect
significant amounts of environmental data. With steadily
decreasing funding for ship operations, manned sub -
mersibles have now reached a critical juncture between cost
and logistical requirements. This has created a shift towards
building a new generation of smaller, more sophisticated
Figure 2.4: A Johnson-Sea-Link manned research
submersible in action.
Florida Atlantic University/HBOI.
17
Research
submersibles that can be dep loyed from smaller research
vessels (Adkins
et al.
2006).
The advantage of manned submersibles is the degree to
which the benthic environment may be examined in a
‘natural sense’ by a human observer, where the flat video
monitors and lack of wide-angle vision opportunities asso -
ciated with ROVs limit the perspectives of scientists. Of the
few who have dived in manned research submersibles,
almost all report the unique value of having personally
visited the environments they have often spent a lifetime
studying from the surface.
REMOTELY OPERATED VEHICLES (ROVs)
ROVs have developed since the 1970s, largely to serve the
needs of industrial applications such as the offshore oil
industry. They come in a diverse array of shapes and sizes
and are normally designed for specific tasks. For scientific
appli cations the trend has been towards vehicles with greater
capacities for detailed visual survey, experimental mani pu -
lation and equipment deployment at increasing depths.
ROVs rely on a combination of visualization, propulsion,
manipulation, sonar and navigation to produce high-quality
data for sampling, mapping and ground-truthing (Orange
et al.
2002). Increasingly, acoustic tools such as sector scan -
ning sonars and multibeam systems are being mounted
directly onto ROVs. Often as costly as manned sub mersibles
and requiring considerable technical expertise, ROVs are
useful for high-resolution imagery and investi gation for the
characterization of habitats and for observing processes
in
situ
. They have been instrumental in giving researchers
a deeper understanding of habitats which are otherwise
both hard to reach and difficult to observe. The success of
ROVs often depends on the quality of their support systems,
such as precise underwater navigation and positioning
techniques. Alongside ROVs, autonomous underwater
vehicles (AUVs) and hybrid vehicles which can both act in
tethered ROV and untethered AUV modes are becoming
increasingly important in deep-sea survey and sampling.
The importance of surveying and sampling deep-water
sponge grounds using habitat mapping approaches linked
to ROV surveys lies in their reduced impacts on the habitat
being explored, unlike historic destructive sampling using
deep-sea trawls and dredges. Finally, it is also important
to note that sponge species can rarely be identified from
visual information alone and that samples, such as those
that can be taken and stored by ROV, are needed for micro -
scopic examination.
Figure 2.5: The
Victor
remotely operated vehicle from the
French marine research institution Ifremer.
J.M. Roberts.
18
S
ponges are among the most ancient animal groups
on Earth, with a fossil record reaching back to the
Cambrian over 580 million years ago. Reef-building
sponges were most widespread during the Late Jurassic,
when siliceous sponges formed a vast sponge reef belt more
than 7,000 km in length on the northern shelf of the Tethys
Sea and the adjacent North Atlantic basins.
Four sponge classes are presently recognized, the extant
Demospongiae, Hexactinellida and Calcarea, and the
extinct Archaeocyatha, all dating back at least to the Early
Cambrian (Hooper
et al.
2002). More than 8,000 valid extant
species have been formally described (van Soest
et al.
2008:
www.marinespecies.org/porifera), and it is predicted that
another 7,000 species have yet to be discovered (Hooper
et al.
2002). In addition, there are several hundred fossil
species which need to be described or redescribed and then
classified. Thus, despite great efforts from many sponge
specialists reviewed in
Systema Porifera: A Guide to the
Classification of Sponges
(Hooper
et al.
2002), the classi -
fication of sponges at higher taxonomic levels, the phylo -
genetic relationships between the classes and the relations
to other Metazoa remain the subject of lively debate (Boury-
Esnault 2006).
ANATOMY
The body form of a sponge is related to the interior
arrangement of the aquiferous system (Figure 3.1), the skel -
etal configuration, the age of the individual and influences
from the wider environment (e.g. water currents, food supply
and substratum). For some sponges, especially at generic
level, their shape is characteristic (meaning that it is
shared by a number of species in that genus). Shapes can
be difficult to define, and are described using simple, broadly
applicable terminology, such as ‘thinly encrusting’, ‘thickly
encrusting’, ‘lumpy’, ‘globular’, ‘urn-shaped‘, ‘funnel-
shaped’, ‘fan-shaped’, ‘branching’, etc.
A unique characteristic shared by all adult sponges is
the interior aquiferous system of canals and flagellated
cham bers through which water is pumped. This water
supplies food and oxygen and removes waste and repro -
ductive elements. The walls of the aquiferous system form
the internal cellular layer of the sponge body, consisting of
cells called endopinacocytes lining the incurrent and
excurrent canals. There are also choanocytes (flagellated
cells which maintain water currents and extract food) lining
larger or smaller chambers (choanoderm). The outer surface
3. Biology
Water out Osculum Water out Osculum
Osculum
Body wall
Ostia
Water
in
Spongocoel
Choanocytes
Asconoid Syconoid Leuconoid
Incurrent
canal
Spongocoel
Water in
Water out
Choanocyte
chambers
Figure 3.1: Diagram illustrating patterns of seawater
flow through three different sponge body structures:
asconoid (a simple vase or tube shape); syconoid (with a
pleated body wall); and leuconoid (with a network of
chambers).
J. Berman, University of Wellington, New Zealand.
19
Biology
of a sponge is formed by a layer of thin, epithelia-like cells,
the pinacoderm. While the Demospongiae and Calcarea have
discrete individual cells, the Hexactinellida have their pinaco-
and choanoderm composed by syncytia, large cell-like struc -
tures containing many nuclei. These layers are con sid ered
to be particular to the sponge body plan and differ from the
entoderm and ectoderm of other multi cellular animals.
Between the aquiferous system and the outer pinacoderm
surface is a more or less well developed gelatinous layer,
the mesohyl, with functionally different cell types and
skeletal elements. The skeletal elements are produced by
some of the cells and differentiated into protein fibres
(spongin), collagen fibres and mineral ‘needles’ called
spicules. The skeleton supports the canal system and the
soft parts of the sponge, and forms many variations with
respect to both its form and the amount and arrangement
of organic and inorganic elements. Finally, although
sponges are multi cellular, they do not possess true tissues
and organs (this means that sponges do not have a
muscular or nervous system).
Most sponge cells are mobile and some show totipotency,
meaning that the individual sponge cell has the potential to
transform itself into another cell type and play another role.
Archaeocytes are large amoeboid totipotent cells regulating
the relative number of cell types in the sponge. Choanocytes
have a rounded cell body with a long flagellum (tail) and
a filtering device around the base of the flagellum.
Amoebocytes perform different functions in connection with
digestion, storing food reserves, waste discharge and
reproduction. Collencytes secrete collagene and perform a
similar function to connective tissue cells. After catching
particles from the filtered water current, the amoebocytes
wander within the sponge body digesting the food, delivering
nutrients to other cells (notably egg cells) and discharging
waste into the excurrent canals. Some amoebocytes receive
the particles caught by the choanocytes and digest them.
Finally, sclerocytes produce the mineral spicules that are so
important to sponge skeletal structure.
Figure 3.2: A few sponges are carnivorous. They have a
reduced canal system and are able to catch small prey
(typically crustaceans) on protruding spicules. These
species can be numerous in certain places and some
are often found in or near sponge grounds. This image
shows the carnivorous sponge
Cladorhiza gelida
(about
40 cm high) colonized by a prominent crinoid (feather
star). In the background is another carnivorous sponge,
Chondrocladia gigantea
. The photograph was taken in the
Faroe-Shetland Channel in October 2009 at about 1,000 m
depth.
D. Jones, The Serpent Project (www.serpentproject.com).
Figure 3.3: A
Geodia barretti
sponge.
P. Mortensen, Institute
of Marine Research & MAREANO project (www.mareano.no).
Figure 3.4: A habitat-forming sponge ground off the
coast of Norway.
P. Mortensen, Institute of Marine Research &
MAREANO project (www.mareano.no).
The choanocytes, which in most sponges are concentrated
in spherical, oval or finger-shaped chambers in the canal
walls, pump water through the canal system. The water
enters the sponge through many small surface pores (ostia)
and is led through fine canals to the flagellar chambers.
From here it flows through successively larger canals to a
few large openings in the sponge surface (oscula), where it
leaves the sponge. In effect, the water is taken in slowly
close to the sponge surface, and leaves the sponge under
some pressure, avoiding any recirculation (Figure 3.5).
SPICULES
Other than a few exceptions without a skeleton, the vast
majority of species of the classes Demospongiae and
Hexactinellida form spicules of silica (SiO
2
) to support the
soft body parts formed by the mesohyl, canal system and
cells. Sponges of the third class, Calcarea, produce calcium
carbonate (CaCO
3
) spicules. In most demosponges the
silicious spicule skeleton of the mesohyl is combined with
spongin, a fibrous collagenous substance, allowing the for -
m ation of a great variety of skeletal structures and body
forms in the group. Spicules and their role in skeletal con -
figuration are the main taxonomic characteristics used to
identify sponge species and have been the subject of much
descriptive research (Figure 3.6).
Silicon uptake is an important process for sponges, both in
relation to the general growth of individuals and to ensure
that they can generate a sufficient density of spicules. It
seems to be an energy-demanding process, since starving
sponges and those in reproductive phases produce fewer
spicules than under normal conditions (Frølich and Barthel
1997). The retention of silica by sponges can be so significant
that it alters local geochemical conditions: spicules from
dead sponges become incorporated in seabed sediment
and influence both the composition and structure of the
sedimentary record (Maldonado
et al.
2005), and the distri -
bution of other animals as well (Bett and Rice 1992). As
some hexactinellid sponges lay down more silica per unit
biomass than many demosponges, they are probably most
common in silica-rich environments such as the deep sea,
Antarctica and regions of local upwelling (Barthel 1995; Uriz
et al.
2003).
CHEMICAL ECOLOGY
As sessile animals, sponges cannot move to avoid predators
or other organisms competing for space, and this dual
pressure of predator defence and spa tial competition has
been a critical evolutionary driver. Sponges have developed
a bewildering array of secondary meta bolites (Thoms and
Schupp 2008), making them one of the most prolific sources
of secondary metabolites in the ocean, and accounting for
50 per cent of natural products found in marine inverte -
brates (McClintock and Baker 2001).
Sponge chemical defences vary both temporally and
spatially. Until very recently, it was generally believed that
the potency of chemical defence in sponges and other
marine inverte brates was higher in the tropics than at
temperate latitudes (Hay 1996). However, new research
found a similar potency of chemical defence in sponges from
a tropical latitude in the Indo-Pacific (Guam) and a tem -
perate latitude in the Mediterranean (Spain) (Beccero
et al.
2003). Thus, contrary to conventional wisdom, the potency of
chemical defence in sponges was equal at both tropical and
temperate lati tudes (Thoms and Schupp 2008).
Secondary metabolites from deep-sea sponges include
compounds such as triterpene glycosides that play a wide
range of roles not only in defending the sponges from
Figure 3.5: Sponge filtration shown by allowing giant
barrel sponges (
Xestospongia muta
) in the Florida Keys
to take up a fluorescent dye. This dye can be seen
leaving the sponge in a strong water current from the
sponge oscula.
C. Martens and P. Gibson, University of North
Carolina at Chapel Hill.
20
Deep-sea sponge grounds
21
Biology
pre dation and spatial competition, but also in supporting
sym biotic fauna. It has been suggested that some of
these chemical metabolites may be ‘evolutionary baggage’
with no specific role, but this probably accounts for only a
small proportion of the compounds that sponges produce
(Wang 2006).
Sponges are sophisticated in using their chemical pro cesses,
and are selective in their filtering of trace nutrients, metals,
sediment and detritus in order to meta bolize the most use -
ful ingredients for their survival. For example, a system of
cell coordination in sponge tissues facilitates the incorpo -
ration of foreign material such as quartz (in sand grains),
used in the production of collagen (Cerrano
et al.
2007).
Medical researchers conducted immune-system studies by
using antibodies against the enzyme lysozyme to identify
how sponges use it. What transpired was that the sponge
targeted it towards potentially harmful extracellular bacteria
while protecting the bacteria that are symbionts and use the
sponge as a host (Thoms and Schupp 2008). These reactions
were studied using immunofluorescence, and revealed
how sponges distinguish finely between different bacterial
organisms. The chemical ecology of sponges is of special
interest in medical studies of tissue metabolism and evo -
lutionary biology and has become a valuable source of
chemical compounds for the pharmaceutical industry.
Other studies have also shown how the chemical reactions
and compound conversions observed in sponges can both
give a deeper understanding of sponge biology and be used
in medical and other applications. For example, chemical
secretions from sponges in the Caribbean were found to
contain antifungal activity (limiting fungal attack in the field)
that could help overcome problems of resistance to con -
ventional fungicides in the paper industry and to treat
common fungal infections in skin, hair and nails (Gaspar
et
al.
2004). Further, the process of spicule formation in which
amorphous silica is synthesized by the enzyme silicatein has
helped establish that the process begins intracellularly and
is completed extracellularly, closing a contentious debate
(Schröder
et al.
2007). This latter study has also out lined key
Figure 3.6: Example of sponge spicules from
Paratimea
sp. viewed through the microscope. This image shows
long spicules (up to 2 mm in length) along with smaller
star-shaped microscleres known as asters.
B. Picton,
National Museums Northern Ireland.
22
Deep-sea sponge grounds
enzymes that could be synthesized in the labora tory and
used for the surface modification of biomaterials and the
encapsulation of biomolecules, amongst other applications.
Although pharmaceutical companies have been successful
in discovering biologically active compounds, our under -
stand ing of their wider eco logical significance is in its
infancy. Major un certainties remain; for example, are these
compounds syn the sized by the sponges themselves, by
microorganisms associated with the sponges or by an
interaction between the two?
Recent leaps in knowledge about deep-sea sponges in the
midst of a revival of interest has fostered emerging taxo -
nomic and geographic trends in chemical ecology and its
applications, as well as in the biology of these ubiquitous
metazoans as a whole. Integrative research has certainly
helped to consolidate current knowledge, and it is clear that
further exploration of the biology, chemistry and ecology of
sponges can only move this research field forward.
GROWTH, SIZE AND LONGEVITY
Throughout their lifecycles, sponges undergo growth,
shrinking, division and fusion, and have extra ordinary
regenerative capabilities. These are in part res ponses and
strategies to deal with substratum compe tition and the
environment surrounding them (Garrabou and Zarbala
2001). In the 1980s it was observed that growth pat terns in
sponges were irregular over time, and that rates of tissue
regeneration were far more rapid than undisturbed growth
rates (Ayling 1983; Hoppe 1988). In a more recent and
detailed study in British Columbia, Canada, the average
growth rate for temperate deep-water hexactinellid sponges
was found to be 1.98 cm per year. In contrast, the rates of
tissue regeneration were up to 20 times higher (Leys and
Lauzon 1998). However efficient, regeneration is dependent
on many intrinsic and extrinsic factors, and requires sig -
nificant resource investment by the sponge, which con se -
quently compromises sponge growth, reproduction and
defensive capacities (Henry and Hart 2005).
Individual sponge growth rates are variable due to the
organism’s ability to change its characteristics in response
to its environment (phenotypic plasticity), so body size is not
a reliable indicator of age. Thus, age is deter mined by carbon
and strontium isotopic dating in both living and fossil sponge
specimens (Xiao
et al.
2005). The extraordinary longevity of
some sponges has been demon strated, with some sponges
hundreds of years old (Leys and Lauzon 1998). Therefore the
capacity for sponges to provide ecosystem services such as
habitat formation, nutrient cycling, trophic structuring and
energy exchange must be stated in terms of long ecological
timescales. The implication of these findings is that damage
to or death of these often long-lived creatures will take, at a
minimum, several human generations to regenerate to their
current standing, making damage irreversible over several
human generations.
REPRODUCTION
Most sponge species are hermaphrodites or, more rarely,
egg and sperm cells are produced by separate individuals
(dioecious). Patterns of sexual reproduction vary from one
group to another, but in general they are poorly known.
Egg cells originate from transformed archaeocytes or
choanocytes. Sperm is formed from single choanocytes
or whole choanocyte chambers lowered from the canals
into the mesohyl. Ripe spermatozoa are released from the
mesohyl into the excurrent canals and carried out with
the water through the osculae. Thus the spermatozoa must
be transported to other sponges within reach by local water
currents before the spermatozoa die (Spetland
et al.
2007).
Eggs are either embedded in slimy strings and released
into the surroundings where they are fertilized by the sperm,
or retained in the mesohyl and fertilized internally. However,
during internal fertilization, which is by far the most com -
mon, spermatozoa enter the sponge with the incurrent
water and are caught by choanocytes, which lose their
flagellae and collars, migrate into the mesohyl and trans -
port the spermatozoa to the egg cells.
Most sponge species are viviparous, with larval develop -
ment occurring in the maternal mesohyl. Cleavage of the
egg is total (the whole egg divides, rather than forming a
separate yolk and embryo), but with great variation in
developmental pattern be tween sponge groups. Division
and differentia tion of cells is appreciable and leads in the
majority of cases to a solid, large parenchymella larva that
settles a few days after leav ing the sponge (Fell 1974;
Ruppert
et al.
2004). In ovi parous sponges and some
viviparous species, cleavage of the fertilized egg is also
total, with all cells of the embryo of about the same size,
and leads to a small coelo blastula larva. Cells develop and
dif ferentiate during the short free-swim ming stage (one to
three days), after which the larva attaches to the sub -
stratum and develops into a juvenile sponge.
Many sponge species also reproduce asexually, producing
genetically identical but somatically distinct individuals
(clones). Clonal reproduction can be induced intrinsically,
but probably of more interest for conservation and protec -
tion measures is the effect of anthropogenic influences on
sponge cloning. The use of mobile fishing gear is particularly
destructive to sponges, which can snap or fragment upright
and encrusting sponges. Demographically, this increases
23
Biology
the number of individuals (providing they survive) in that
population, but reduces both the average sponge size and
genetic diversity, making the sponges more susceptible to
disease or inbreeding.
Overall, the variety of reproductive methods in sponges is
so vast and complex that the strategies of particular species
and groups are only just emerging. The ability to be sexual
or asexual, viviparous or oviparous and to have gametes
of both sexes gives sponges some of the most plastic stra -
te gies for reproduction. Studies to date mostly concentrate
on a par ticular element of the reproductive process for a
spe cific species (e.g. Ereskovsky 2000; Lanna
et al.
2007;
Gonobobleva 2007). However, two recent studies have exam -
ined reproductive processes more clearly. From a strategic
point of view, it is possible to identify some of the repro duc -
tive challenges that deep-water sponges face as disting -
uish able from those of sponges in shallow–water habitats.
In the first of these studies, Maldonado and Uriz (1999)
drew attention to the strategic role of deep-water sponge
reproduction. They recognized that the fragmented habitats
characteristic of the deep sea often produce apparently
discrete, spatially separated animal populations. They sug -
gested that for sessile species including sponges, it is
important that they have the capacity to disperse and colon -
ize new areas. As sponge larvae are only dispersed over
short distances it is not clear how this is achieved, although
ocean currents clearly play an important role. It is also
possible that sponge fragments (clones) may be transported
by ocean currents to settle and colonize new areas. A final
surprising finding from this study was the high genetic
variability within a sponge population, indicating contri bu -
tions from both asexual and sexual reproduction.
In the second study, Spetland
et al.
(2007) examined the
dense communities of
Geodia barretti
(Bowerbank, 1858)
found in many Scandinavian fjords. This species undergoes
gametogenesis in annual cycles. As a dioecious and ovi -
parous sponge,
G. barretti
has either spermatic cysts or
oocytes that are clustered within its mesohyl. The annual
reproductive season is triggered by phytoplankton blooms
in the fjords and gametes are released in early summer
at the end of these blooms. This event is therefore syn -
chronous with peaks in organic matter sedimentation
that occur as a result of the blooms, with each popula tion
exhibiting a ‘spawning phase’ with gametes being released
simultaneously. More research on the repro ductive cycles
of sponges of the Order Astrophorida, such as
G. barretti,
are necessary to understand population dynamics and
the potential for periodicity in the chemical ecology
of astrophorids.
For most deep-water sponge species that experience
seasonality in food supply, reproduction may be seasonal
and occur during the summer months (January to March
in the southern hemisphere). A rise in water temperature
and/or primary production are key triggers for egg
production (oogenesis), which runs through a multi-stage
process of development, from oocytes, a mixture of zygotes
and larvae, to a larva-dominated spawning ground (Lanna
et
al.
2007). In the deep sea, large habitat-forming sponges are
likely to be ‘K-strategists’, with long lifespans and low
reproduction rates and reproductive efforts, coupled with
adaptation to a specialized ecological niche (Ereskovsky
2000). Further, a case study of
Pheronema carpenteri
pop -
ulation dynamics off the coast of Morocco by Barthel
et al.
(1996) indicated that shifts in age can occur across a bathy -
metric range so that the sponge grounds appear to be
‘wandering’. Spicule mats, which form when an individual
sponge dies and its skeleton disintegrates, were found below
a maximum abundance band of smaller and younger
individuals higher along the slope. This was taken to show
that the population of
P. carpenteri
had effectively relocated
or ‘wandered’ to a slightly shallower depth. More studies are
needed to examine whether other sponge grounds show
similar capacities. Encouraging more investigation into how
particular deep-water sponge species reproduce will help to
define their ecological niches and therefore predict their
likely distribution on both regional and global scales.
DISEASE
The study of sponge disease first began when epidemics
that periodically affected commercial sponge populations
were discovered. For example, early reports in the mid-
1880s of diseased sponges in British Honduras received
much attention and speculation about the mechanisms
governing the spread of the disease, such as transmission
by water currents (Smith 1941). Later, after observations of
sponge disease in the Indian Ocean and eastern Gulf of
Mexico, fungal infection was also cited as a possible source
(Lauckner 1980).
In the 20th century, surveys of deep-water ‘wild’ sponge
populations have revealed other possible causes of disease.
Rützler (1988) investigated diseased specimens of the
mangrove species
Geodia papyracea
, which had difficulty
balancing the number of cyanobacterial symbionts within its
tissues. This imbalance was caused by the rapid multi -
plication of cyanobacteria at a rate faster than the sponge
archaeocytes could remove the excess. This caused des -
truction of the sponge host tissue, which may have involved
the secretion of toxic substances from the cyanobacteria.
The response of
G. papyracea
to this disease paralleled
that observed in other species, i.e. producing a spongin
24
Deep-sea sponge grounds
barrier of collagen consistency and sloughing off tissue that
had decayed.
Evaluating the role of disease in sponge population dyna -
mics has proved difficult since sponge skeletons disin -
tegrate into spicule mats after death. Smith (1941) observed
diseased sponges of medium size disintegrate within just
three weeks. However, studies of sponge community dyna -
mics and the influence of disease amongst coral reefs in
Florida and the Caribbean are now giving a better under -
standing of these processes in shallow, tropical eco systems
(Wulff 2007). These studies build on earlier work, which
suggested that keratose sponge genera such as
Spongia
and
Hippospongia
are especially vulnerable to pathogen
infection in warmer waters because they evolved in cooler,
deeper seas (Vicente 1989).
It also seems that climate change may alter the vulner a -
bility of sponge grounds to disease. Periodic episodes of
mass sponge mortality related to higher water temp era -
tures have been recorded in the northwest Mediterranean
and in Scandinavian fjords. In the latter case, large-scale
necrosis linked to local seawater warming has recently
been observed in popu lations of
Geodia barretti
(T. Lundälv,
pers. comm. 2009). The last major event in the northwest
Mediterranean occurred in July 1999. A general warming
of 2-3ºC at the sea surface was observed, with this warm -
ing reaching a depth of 40 m (Perez
et al.
2000). The first
sign of mortality was the appearance of a white bacterial
veil on the sponge epidermis. This was followed by rot
occurring underneath the layer of bacteria and sponge
death within just two days. For commercial sponge species
(
Spongia
and
Hippospongia
), the combined action of
intense har vesting and temperature-induced disease has
taken a number of populations to the brink of extinction
(Pronzato 1999).
The symbiosis between sponges and the communities of
bacteria that surround them are limited by environmental
thresholds. If these factors change, environmental com -
munity shifts in bacteria can cause pathogenic outbreaks
harmful to the sponge. The temperature thresholds for
these bacterial symbioses have been studied in the warm-
water sponges
Spongia
and
Hippospongia
, occurring at
temp eratures between 27 and 33ºC (Gaino
et al.
1992).
Between temperatures of 27 and 31ºC no change in sponge
health or bacterial community composition was detected.
But sponges exposed to temperatures of 33ºC lost their
bacterial symbionts within 24 hours and showed cellular
necrosis after three days (Webster
et al.
2008). A dramatic
shift in bacterial community composition was observed
between 31 and 33ºC. The heat shock protein hsp70 found
in
Geodia cydonium
is also a useful biomarker in following
these biological responses to physical stress (Koziol
et al.
1997). The breakdown of symbioses and stress in sponges
occurred at very similar temperatures to those reported
during tropical coral bleaching events.
Other than the initial reports of
Geodia
necrosis from
Scandinavian fjords, very little is understood about the vul -
ner ability of deep-water sponge grounds to temperature
change, but it is imperative that this research be prioritized
given the threats posed by global climate change and the
effects of ocean acidification.
25
R
ecent research in the Northeast Atlantic has shown
how diverse deep-water sponge assemblages can be.
On the Rockall Bank west of Scotland and Porcupine
Bank west of Ireland, van Soest
et al.
(2007) recorded be -
tween 105 and 122 sponge species in just three localities. In
this study, both depth (500-900 m) and the presence of
live cold-water corals were found to be primary influences
on sponge species composition and spatial variation. A bio -
diversity census from the Mingulay cold-water coral reef
complex, west of Scotland, reported 100 sponge species
in a very localized area (Roberts
et al.
2009a). Thus it is
becoming clear that, alongside the diversity of associated
fauna found with deep-water sponge grounds, there is
an appreciable biodiversity of deep-water sponges, notably
among thinly encrusting species associated with cold-water
coral habitats.
Other trophic groups including fish, molluscs, crustaceans
and echinoderms all graze sponges, often non-fatally (Taylor
et al.
2007). A survey of hexactinellid sponges on the Weddell
Sea shelf in Antarctica greatly influenced future research
by illustrating the importance of substratum texture and
composition (Barthel 1992). Species-poor associations
appeared to be linked with muddy, soft-bottom seabeds,
whereas species-rich associations were linked with more
solid sponge spicule mats and bryozoan debris. From
these observations another more revealing finding was
made. One hexactinellid sponge,
Rosella racovitzae,
was
present on both softer bryozoan debris and hard spicule
mats, with markedly different population structures char -
acterizing each one. The bryozoan mats supported small,
young specimens whereas the spicule mats were home to
older, more established specimens. This suggests that
these Antarctic sponges colonize the bryozoan debris and
alter the quality of the substratum by depositing spicules
which then develop into spicule mats. The biomass volume,
shelter and probably also food supply all increase with
the presence of spicule mats, and sponge communities –
including these hexactinellid sponges – then become a
major biological structuring agent providing habitat in the
Antarctic deep sea.
4. Biodiversity
Figure 4.1: A sponge ground of
Geodia
sponges found
around Norway.
H.T. Rapp, University of Bergen.
26
Deep-sea sponge grounds
ASSOCIATED FAUNA
Many sponges have microbial associations and some host
specific assemblages of microbes. The microbial associates
occur throughout the sponge, both inter- and intracellu -
larly, and can constitute up to 40 per cent of the sponge’s
volume (Osinga
et al.
2001). A distinction can be made
between epibionts, which are organisms living on the sur -
face of the sponge, and endosymbionts which live in the
sponge mesohyl.
These microbes come from each of the following major
groups: archaea, bacteria, cyanobacteria, microalgae,
hetero trophic eukaryotes and fungi. As well as playing roles
in sponge nutrition and carbon fixing, these micro -
organisms are also thought to play an important part in
sponge metabolism through the production of other com -
pounds (known as secondary metabolites), which pro vide
the sponge host with protection against predation and
spatial competition.
In the shallow-water tropics, studies have revealed that a
substantial increase in bacterial biomass can be found
surrounding sponges, which also helps to support diverse
assemblages of symbionts. In some cases, deep-water
sponge grounds can also be important centres of chemo -
synthetic activity (Hentschel
et al.
2002). In addition,
sponges are known as sinks for dissolved organic carbon
in tropical coral-reef habitats where they play an important
role in coral reef energy budgets (De Goeij and Van Duyl,
2007). The mutual symbiosis between sponges and their
asso ciated microbes is therefore also likely to be of crucial
importance in the deep sea. The expected sponge diversity
of 15,000 species probably holds an even larger number
of undis covered microorganisms that are only found in
sponges, and may significantly increase currently known
microbial biodiversity. For instance, a new bacterial Phylum,
the Poribacteria, has been discovered with members
at present only known to occur in sponges (Fieseler
et
al.
2004).
As well as forming intricate symbioses with a variety of
micro bial organisms, deep-water sponge grounds are
emerg ing as significant centres of invertebrate species
diversity. In the Northeast Atlantic, over 242 epi- and in -
faunal species (living on and in seabed sediments) were
reported with deep-water sponges from around the Faroe
Islands, 115 of which were related to sponges for the first
time (Klitgaard 1995). This study also demonstrated that
com munity composition was often spe cific to a particular
species of sponge. For instance, the habitat-forming sponge
Geodia cydonium
has an internal structure that particularly
favours certain endosymbionts and polychaetes.
Sponge morphology is thought to play an important role
in the composition of associated fauna, although more
research is needed to examine this in detail. In her 1995
study, Klitgaard only found one predator, the chiton mollusc
Hanleya nagelfar,
and this low predator diversity was ex -
plained by the inhospitable texture of the sponges, or by an
artefactual failure to sample predators adequately. However,
the production of secondary metabolites may also help
to protect sponges from predation (Clavico
et al.
2006) and
explain the rarity of sponge predators observed.
Close associations between sponges and crustaceans
have also been documented. Klitgaard (1991), working in
the North Atlantic, observed the isopod
Caecognathia
abyssorum
living in a hollowed-out crevice in sponges,
where it creates a territorial harem. Off Kamchatka,
Russia, young-of-the-year red king crabs
Paralithodes
camtschaticus
were associated with sponges, bryozoans
and hydroids (Tsalkina 1969). Further, laboratory experi -
ments found that recently moulted red king crab glau cothoe
larval stages preferred to settle on complex sub stratum
(hydroids, bryozoans, algae and plastic mesh) rather than
sand (Stevens and Kittaka 1998; Stevens 2003).
Fish often use the structural habitat that sponge grounds
provide for shelter and reproduction and to forage for food.
The intricate architecture of sponge grounds also provides
important nursery grounds for juvenile fish in their early
stages of growth (Auster 2005). Rockfish (or ‘redfish’) of
the genus
Sebastes
are particularly prevalent in sponge
grounds, living in and between sponges. Other groundfish
including cod and ling are often found in trawl catches
along with sponges, demonstrating in their abundance
the importance of sponge-formed habitat for commercial
species of fish (Hixon
et al.
1991). There is also some
evidence that, over time, removal of the sponge grounds by
trawling changes composition of the fish fauna (Sainsbury
1988 in Klitgaard and Tendal 2004). Thus, it seems that
sponge grounds are a crucial refuge and habitat for fish,
although little ecological work has been carried out to
understand the exact nature of this habitat use in the deep
sea and studies to date are limited to tropical waters (e.g.
McCormick 1994; Cleary and de Voogd 2007).
The scarcity of complex structural habitat in the deep sea
means that sponges play a crucial role by enhancing the
number and complexity of microhabitats and, ultimately,
biodiversity in the deep sea. Deep-water sponges form a
network of habitat ‘patches’ in deep-sea settings around the
world, but our understanding of the roles these play in sus -
tain ing deep-water biodiversity and the ecological connect -
ivity of these habitats remains at best descriptive.
27
T
he major threats to sponges are deep-water bottom
trawling and fishing with other gears that touch the
seabed. By the late 1980s, the intensive use and
exploit a tion of resources in marine coastal regions had
severely depleted stocks of commercial fish, especially the
more common continental shelf species such as cod. As a
result, fishing effort has shifted, targeting the deep sea in
an attempt to maintain fish catches (Roberts 2002). Other
activities have been directed at valuable biological, mineral
and hydrocarbon resources; this exploration developed mar -
kets for deep-water fish such as the roundnose grenadier
(
Coryphaenoides rupestris
)
.
The result has been an increase
in both vessel capacity and the spatial scale of fishing
operations, which has raised international concern over the
sustainability of fish stocks in both shallow and deep waters.
Sponge grounds provide refuge, local food webs and nursery
grounds for fish in the deep sea where structural habitat can
be scarce, and photographic surveys carried out over the last
decade have revealed widespread damage caused by
commercial fishing (Hernkind
et al.
1997; Roberts
et al.
2000; Ryer
et al.
2004).
Sponges are often slow-growing with long lifespans, and
consequently their recovery and regeneration after damage
or disturbance may take decades (Jones 1992). In recent
years, collaborative initiatives advocating caution over deep-
sea fishing and calls for the protection of the deep-sea
habi tats on which these fish depend have received consider -
able attention. Consortia such as the Deep-Sea Conser -
vation Coalition (DSCC) and the IUCN World Conservation
Con gress supported the United Nations General Assembly
(UNGA) resolutions on sustainable fisheries of 2006 (61/105)
and 2009 (64/72), which called upon Member States to
close bottom fishing in areas where ‘vulnerable marine
eco systems’ are likely to occur, in clud ing cold-water coral
areas, deep-water sponge grounds and sea mount habitats.
Observed threats to sponge grounds are:
■ commercial bottom trawling and other mobile
fishing gear;
■ hydrocarbon exploration and exploitation;
■ cable and pipeline placement.
Potential threats include:
■ deep sea mining;
■ altered geochemistry of the ocean;
■ carbon dioxide sequestration.
COMMERCIAL TRAWLING AND OTHER FISHING GEAR
The deep seas that extend beyond the exclusive economic
zones (EEZ) of national boundaries hav
e operated on open-
access policies which, combined with generous subsidies,
have led to the overexploitation of fisheries using bottom
5. Threats
Figure 5.1: Photographs illustrating a trawl mark through
an area of seabed previously abundant with sponges: (a)
shows an untrawled area with an intact stalked deep-sea
glass sponge (
Hyalonema
); (b) shows linear marks from a
trawl and the broken stalk of a glass sponge.
Roberts
et al
.
2000/Springer publishing.
a
b
28
Deep-sea sponge grounds
trawls and dredges. There is a general consensus that
fishing is the single most influential anthropogenic impact
on continental shelves worldwide (Auster and Langton 1999;
Norse and Watling 1999; Halpern
et al.
2008), and the
expansion of the deep-sea fishing industry has consolidated
this opinion in recent years. There is also growing ack -
nowledgement that the collapse of fish stocks is only one
consequence and arguably a symptom of wider impacts
caused by bottom trawling.
The complex three-dimensional structure of ses sile
animals such as sponges, bryozoans and cold-water corals
is broken up into rubble with the passage of a trawl,
which eliminates habitat for commercially important fish
(Wassenberg
et al.
2002). It has been reported that some
species of sponge appear to be so fragile that they even
disin te grate on contact with a pressure wave induced by
trawl gear (UNGA 2006 paragraph 53). Rare hexac ti nellid
sponge reefs off the coast of British Columbia, Canada,
where extensive trawl damage has been observed, exhibited
a low presence of usually abundant rockfish for which
sponge debris could no longer be used as a nurturing
habitat (Conway 2007). Rockfish were therefore less abun -
dant on trawl-damaged hexactinellid sponge reefs than on
intact sponge reefs.
A second, more indirect way that suspension-feeding
sponges are affected by trawling is through smothering.
Bottom fishing re-suspends large quantities of seafloor
sediments that could smother sponges. While this is not
easily observed or measured, remote-sensing images
illustrate the kilometre-long plumes of re-suspended
sediment generated by trawling vessels in shallow waters
(Amos 2008), and point to the spatiotemporal scales at which
this activity could impact sponge grounds. A third, rarely
considered, threat is that fishing gear can inflict sub-lethal
injury on sponges, which are left to regenerate from their
partial mortality. However, injured sponges have fewer
energetic and cellular resources to grow, reproduce, and
defend themselves against predators and disease (Henry
and Hart 2005).
Mobile fishing gear that contacts the seabed, particularly
trawling, is the fishing apparatus that poses the greatest
threat to deep-water sponge grounds. Bottom trawls consist
of bag-shaped nets towed behind a vessel. Deep-water
trawls are held open by vanes (or ‘doors’) made of wood or
steel which can weigh up to 1 tonne (Jones 1992), and trawl
nets can be as large as 55 m across and 12 m high. Chains
and cables with heavy discs or rollers may also be mounted
along the bottom of the net so that rough seabed does not
obstruct the passage of the fishing equipment or damage
the nets. This gear inflicts significant damage and mortality
on many animals living on the seabed, the extent of which
depends on the weight of the gear on the seabed, the nature
of bottom sediments, the towing speed at which the equip -
ment is dragged and the tidal and current strength, and the
species themselves (Jones 1992).
The impacts of trawling on cold-water coral reefs have
been well documented and, although deep-water sponge
grounds have yet to be given the same attention, it is reason -
able to assume that the extent and degree of damage is
similar. On an average 15-day trip in the Rockall Trough in
the Northeast Atlantic, one trawling vessel covers an area of
approximately 33 km
2
of seabed (Hall-Spencer
et al.
2002).
Fishermen usually attempt to avoid extensive sponge
grounds as these obstruct and damage trawling gear,
representing a rather time-consuming nuisance in cleaning
and re-deploying nets that are full of massive quantities
of sponges. Nevertheless, given the rich abundance and
diversity of fish that these sponge grounds harbour, the
edges of the grounds often receive direct, physically devas -
tat ing damage, which has been supported by visual
observations. Recording the impact of bottom trawling
requires regular and consistent monitoring of sponge
grounds and fisheries bycatch if meaningful observations
and measurements are to be obtained.
The first records of deep-sea trawl marks on the seabed to
the west of Scotland were made in the late 1980s (Roberts
et
al.
2000). Sponge and coral bycatch in the Aleutian Islands,
which contain some of the most pristine cold-water coral
and sponge habitats on Earth, is 12 times the rate observed
in the wider Gulf of Alaska or Bering Sea. From 1990 to 2002,
US federal data from fishery observers recorded approxi -
mately 2 million kg of mostly sponge bycatch from the
Aleutian Islands. This figure is a cause for much concern and
must be considered in appropriate conservation measures
(Shester and Ayers 2005; Heifetz
et al.
2009). In 2005 and
2006, the US National Oceanographic and Atmospheric
Administration (NOAA) froze the footprint for bottom trawl -
ing in the Aleutian Islands and the Bering Sea respectively as
precautionary measures to protect sensitive essential fish
habitat. Regularly updated reports on this can be found at
www.fakr.noaa.gov.
Dredges are another form of fishing gear, similar to bottom
trawling, used typically to catch clams, scallops and oysters.
They remove all sediments, rocks and organisms in their
path, vastly reducing habitat complexity and function, with a
large bycatch of non-target marine fauna including sponges.
Communities living in the wake of the sediment-laden
plumes created by dredging activities are often smothered.
29
Threats
The anchors and weights of demersal longlines and gillnets
also cause damage to the fauna on the seabed, and result in
potentially substantial bycatch with the hooks set close to
the bottom. Mechanical longline sets can extend to a length
of 50 km or more; deep-water gillnets, trammel nets and
combinations are deployed in sets of 300-1,000 nets x 50 m
(15-50 km length) – on average 20 km in the monkfish
fishery, for example. Each vessel in this fishery, which takes
place on the upper slope, uses approximately 5,000-8,000
nets, a total length of 250-400 km. The relative rate of loss of
bottom-set gillnets increases with depth, reaching 15 per
cent of nets set in the Greenland halibut fishery at 700 m
depth (Hareide
et al.
2005). Due to their non-biodegradable
material, such nets continue to catch fish for very long
periods, and can, when moved by currents, also destroy or
trap other fauna such as corals or sponges.
HYDROCARBON EXPLORATION AND EXPLOITATION
The wealth of oil reserves in the Gulf of Mexico attracted
some of the first hydrocarbon production in the deep sea in
1979 (French
et al.
2006, in Davies
et al.
2007). Diminishing
conventional terrestrial and shallow-water oil reserves, com -
bined with rising extraction costs and intense consumer
demand, have increased pressure for new stores of oil and
gas to be found. The Brazilian oil company Petrobras is now
working at depths of over 2,000 m, and newly discovered oil
reserves in water depths greater than 1,000 m off the coast
of West Africa suggest than hydro carbon production in the
deep sea will continue to grow (Polunin 2008).
The release of drilling muds and cuttings from hydrocarbon
exploration and production are important benthic impacts
and threats to sessile suspension-feeding fauna and ben