Detailed visual seabed survey at drilling site 7218/11-1
Detailed visual seabed survey at drilling site 7218/11-1
Detailed visual seabed survey at drilling site 7218/11-1
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Figure14. Photosfrom Mercier(2012)showing(left) a sea-penfield and (right) developinglarvaeof the redfish<br />
Sebastestuckedamong the polypsof the seapens.Sizeof the seapensis not given,but the scalebarson the<br />
right are both 1 mm.<br />
The ecologicalrole of sponges,and their responsesto environmentalconditionsare to someextent<br />
documentedfor shallow-w<strong>at</strong>ers (seefor exampleBell & Smith,2004),we have few studieswhich<br />
clarify the role of coralsand spongesas autogenic engineersin deeperw<strong>at</strong>er (Miller et al., 2012).<br />
Thoseauthors further st<strong>at</strong>e"[…]nevertheless,many fishes and macroinvertebr<strong>at</strong>esinhabit deepw<strong>at</strong>er<br />
coral (Rogers,1999, Husebøoet al., 2002, Mortensen & Buhl Mortensen, 2005 and Stone,<br />
2006) and sponge(Beulieu,2001, Marliave et al., 2009) habit<strong>at</strong>s. Unlike shallow-w<strong>at</strong>er systems,<br />
where the processesconnectinghabit<strong>at</strong> with popul<strong>at</strong>ionsand communitiesof dependantorganisms<br />
are rel<strong>at</strong>ively well understood,the role of habit<strong>at</strong> structure, includingth<strong>at</strong> of autogenicecosystem<br />
engineers,in deep-w<strong>at</strong>er communitiesis still uncleardue to lack of small-scaleobserv<strong>at</strong>ionaland<br />
experimentalstudies(Auster,2007).<br />
Obviously,the role of spongesas ecosystemengineersis a question of scale.At a small scale,an<br />
individual spongeprovides a habit<strong>at</strong> for a range of other organisms,but to be significant<strong>at</strong> an<br />
ecosystemscalerequiresth<strong>at</strong> large areasand/or large amountsof spongesare involved. Thisbegs<br />
the question to which we have no clear answer – how many sponges, or how large an area<br />
constitutes a resource of ecosystemsignificance?Further, how can we then assessissuesof<br />
vulnerabilityto humanactivities,or conserv<strong>at</strong>ionst<strong>at</strong>us.<br />
The UK Biodiversity Action plan (http://jncc.defra.gov.uk/pdf/UKBAP_BAPHabit<strong>at</strong>s -12-<br />
DeepSeaSpongeComms.pdf ) contains some interesting remarks, about sponge abundances,<br />
extractedfrom OSPAR(2008). "Densitiesof occurrenceare hard to quantify,but spongesin the class<br />
Hexactinellidahave been reported <strong>at</strong> densities of 4-5 per m², whilst ‘massive’growth forms of<br />
spongesfrom classDemospongiahave been reported <strong>at</strong> densitiesof 0.5-1 per m 2 (B. Bett, pers.<br />
comm.)." In this context,we canassumeth<strong>at</strong> "massivegrowth forms" meanslargeindividuals,such<br />
asthe Geodiaspecimensin the BarentsSea, whichcanmeasure30-40 cm andmorein diameter.<br />
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