Deep-water Coral Reefs: Unique Biodiversity Hot-Spots

294 Pages·2008·26.551 MB·English

by  Dr Martin Hovland (auth.)

Deep-water Coral Reefs
UniqueBiodiversityHot-Spots
Martin Hovland
Deep-water Coral Reefs
Unique Biodiversity Hot-Spots
Published in associationwith
PPrraaxxiiss PPuubblliisshhiinngg
Chichester, UK
Dr Martin Hovland
Marine Geology Expert
Statoil
Stavanger
Norway
SPRINGER–PRAXIS BOOKS IN LIFE SCIENCES INCORPORATING AQUATIC AND MARINE SCIENCES
ISBN 978-1-4020-8461-4 Springer Dordrecht Berlin Heidelberg New York
Springer is part of Springer-Science+Business Media (springer.com)
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# Praxis Publishing Ltd, Chichester, UK, 2008
Printed in Germany
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Cover design: Jim Wilkie
Project management: Originator Publishing Services Ltd, Gt Yarmouth, Norfolk, UK
Printed on acid-free paper
Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xxiii
List of abbreviations and acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . xxv
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Coral reefs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Skeleton formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Coral reef ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3 A modern re-discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2 Historical background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3 The Fugløy reef, 1982 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4 Pockmark craters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.5 Why north of the Polar Circle? . . . . . . . . . . . . . . . . . . . . . . 22
3.6 Suspected origin of the Fugløy reef . . . . . . . . . . . . . . . . . . . 23
3.7 Deep-water bioherms at Nyegga . . . . . . . . . . . . . . . . . . . . . 24
3.7.1 Significance of the tubeworm . . . . . . . . . . . . . . . . . . 29
vi Contents
3.8 Ha˚kon Mosby Mud Volcano (HMMV) . . . . . . . . . . . . . . . . 31
3.8.1 Bacterial mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4 Scandinavian coral reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.2 Reefs in Norwegian fjords. . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.2.1 Agdenes and Tautra reefs . . . . . . . . . . . . . . . . . . . . 40
4.2.2 Stjernsund and other Norwegian fjord reefs . . . . . . . . 43
4.3 Reefs on the continental shelf . . . . . . . . . . . . . . . . . . . . . . . 44
4.3.1 The Haltenpipe reefs . . . . . . . . . . . . . . . . . . . . . . . 44
4.3.2 HRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.3.3 Bivalve association near HRC . . . . . . . . . . . . . . . . . 48
4.3.4 Suspected origin of the HRC . . . . . . . . . . . . . . . . . . 55
4.3.5 The Sula Reef Complex . . . . . . . . . . . . . . . . . . . . . 57
4.3.6 The Husmus reefs, Draugen field . . . . . . . . . . . . . . . 62
4.3.7 The Træna Deep Reef Complex . . . . . . . . . . . . . . . . 64
4.4 Reefs associated with hydrocarbon fields . . . . . . . . . . . . . . . . 68
4.4.1 Pockmark reefs at the Kristin field . . . . . . . . . . . . . . 69
4.4.2 The ‘‘bio-expectations’’ for DWCRs . . . . . . . . . . . . . 69
4.4.3 Some relevant emerging results . . . . . . . . . . . . . . . . . 71
4.4.4 Sponge-associated bacteria . . . . . . . . . . . . . . . . . . . . 76
4.4.5 Silted reefs at the Morvin field . . . . . . . . . . . . . . . . . 76
4.4.6 Origin of Kristin and Morvin reefs . . . . . . . . . . . . . . 76
4.4.7 Seep-associated corals and sponges over a leaky field . . 79
4.5 Other reef occurrences off mid-Norway and northern Norway . . 80
4.5.1 Reefs in Breisunddjupet, near A˚ lesund . . . . . . . . . . . . 80
4.5.2 The Floholman reefs, with associated bacteria and gas! . 81
4.5.3 The Malangsreef . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4.6 Reefs on the continental edge . . . . . . . . . . . . . . . . . . . . . . . 89
4.6.1 The Røst Reef Complex . . . . . . . . . . . . . . . . . . . . . 90
4.7 Corals and reefs in the North Sea and Kattegat . . . . . . . . . . . 91
4.7.1 The Fedje reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.7.2 Corals inside a pockmark, Troll field . . . . . . . . . . . . . 92
4.8 Lophelia colonies on man-made structures . . . . . . . . . . . . . . . 93
4.8.1 The Brent Spar Buoy . . . . . . . . . . . . . . . . . . . . . . . 93
4.8.2 Statfjord . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.8.3 UK Block 22/4, blowout site . . . . . . . . . . . . . . . . . . 95
4.9 Swedish/Norwegian reefs. . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.9.1 Kosterfjord reefs . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.10 Danish ‘‘bubbling reefs’’ . . . . . . . . . . . . . . . . . . . . . . . . . . 98
4.11 Reefs off the Faroe Islands . . . . . . . . . . . . . . . . . . . . . . . . 100
4.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Contents vii
5 North Atlantic coral reefs and giant carbonate mounds. . . . . . . . . . . . 103
5.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.2 The Atlantic margin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
5.2.1 Porcupine Seabight Mounds . . . . . . . . . . . . . . . . . . . 106
5.2.2 Seep or non-seep, could drilling resolve the issue? . . . . 114
5.2.3 The Rockall Trough margin mounds . . . . . . . . . . . . . 120
5.2.4 Lophelia within the deep Rockall Trough, the Darwin
Mounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
5.2.5 Observed acoustic plumes associated with mounds . . . . 127
5.2.6 Possible sources of seeping fluids off Ireland . . . . . . . . 127
5.2.7 Serpentinisation, the most important geobiological pro-
cess? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
5.3 Gulf of Cadiz, west of Gibraltar . . . . . . . . . . . . . . . . . . . . . 129
5.3.1 The lower slope, mud volcanoes, and gas hydrates . . . . 130
5.3.2 The Pen Duick occurrence . . . . . . . . . . . . . . . . . . . . 132
5.3.3 Carbonate mounds off Mauritania . . . . . . . . . . . . . . 137
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
6 Other deep-water coral reefs, worldwide . . . . . . . . . . . . . . . . . . . . . 141
6.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
6.1.1 The Campos and Santos Basin reefs, off Brazil . . . . . . 142
6.1.2 The Gulf of Mexico (GoM) . . . . . . . . . . . . . . . . . . . 144
6.1.3 Deep-water corals off Belize . . . . . . . . . . . . . . . . . . . 147
6.1.4 The Florida Straits . . . . . . . . . . . . . . . . . . . . . . . . . 150
6.1.5 The Blake Ridge occurrences . . . . . . . . . . . . . . . . . . 153
6.1.6 Off Nova Scotia . . . . . . . . . . . . . . . . . . . . . . . . . . 153
6.1.7 Orphan Knoll, off Newfoundland . . . . . . . . . . . . . . . 154
6.1.8 The Mid-Atlantic Ridge . . . . . . . . . . . . . . . . . . . . . 155
6.2 The eastern Atlantic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
6.2.1 Small mounds off Congo . . . . . . . . . . . . . . . . . . . . . 156
6.3 The Mediterranean Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
6.4 The Pacific Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
6.4.1 Coral gardens off the Aleutian Islands . . . . . . . . . . . . 158
6.4.2 Davison Seamount off California . . . . . . . . . . . . . . . 159
6.4.3 Australian carbonate knolls . . . . . . . . . . . . . . . . . . . 160
6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
7 Ancient and modern analogues . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
7.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
7.2 Waulsortian-like mounds from the Carboniferous . . . . . . . . . . 164
7.2.1 A key to the present? . . . . . . . . . . . . . . . . . . . . . . . 165
7.2.2 Petroleum-filled mounds . . . . . . . . . . . . . . . . . . . . . 167
7.3 Fossil seep carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168
7.3.1 Ancient deep-water fossil reefs, Algerian Sahara . . . . . 169
7.3.2 Kess-Kess formations, Morocco . . . . . . . . . . . . . . . . 170
viii Contents
7.4 Seamounts and carbonates . . . . . . . . . . . . . . . . . . . . . . . . . 170
7.5 ‘‘Living fossil’’ structures?. . . . . . . . . . . . . . . . . . . . . . . . . . 172
7.5.1 Stromatolites and microbialites . . . . . . . . . . . . . . . . . 172
7.5.2 Are they seep bioherms? . . . . . . . . . . . . . . . . . . . . . 173
7.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
8 Competing theories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
8.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
8.2 Reefs that didn’t drown . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
8.3 A null hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
8.3.1 Water-related factors. . . . . . . . . . . . . . . . . . . . . . . . 181
8.4 A hydrodynamical case study . . . . . . . . . . . . . . . . . . . . . . . 184
8.5 External or internal control? . . . . . . . . . . . . . . . . . . . . . . . . 186
8.5.1 A case of life and death . . . . . . . . . . . . . . . . . . . . . 189
8.6 A question of geophysical interpretation, linear reefs . . . . . . . . 192
8.6.1 Case 1: the Sula Ridge reefs . . . . . . . . . . . . . . . . . . 193
8.6.2 Case 2: the Træna Deep reefs . . . . . . . . . . . . . . . . . . 195
8.6.3 Case 3: other linear reefs . . . . . . . . . . . . . . . . . . . . . 198
8.7 Reefs associated with local depressions . . . . . . . . . . . . . . . . . 198
8.7.1 Moats and other depressions . . . . . . . . . . . . . . . . . . 198
8.8 New support for the hydraulic model . . . . . . . . . . . . . . . . . . 199
8.9 Geodiversity and biodiversity, a link? . . . . . . . . . . . . . . . . . . 202
8.10 Summary and a re-iteration of the hydraulic theory. . . . . . . . . 204
9 An unintended extinction? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
9.1 Threats to deep-water coral reefs . . . . . . . . . . . . . . . . . . . . . 207
9.1.1 Mechanical disturbance and burial . . . . . . . . . . . . . . 209
9.1.2 Climate change and acidification . . . . . . . . . . . . . . . . 210
9.2 A glimmer of hope? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
9.2.1 Biological response . . . . . . . . . . . . . . . . . . . . . . . . . 212
9.2.2 Climate change? . . . . . . . . . . . . . . . . . . . . . . . . . . 213
10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
10.1 Summary of main conclusions . . . . . . . . . . . . . . . . . . . . . . . 215
APPENDIXES
A Some additional photographs and images. . . . . . . . . . . . . . . . . . . . . 217
B Epilogue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
Acontributiontotheresourcesthemeof
the International Year of Planet Earth
Preface
Welcome to a journey beneath the oceans a journey Captain Nemo would have
envied us ...
Hovland and Mortensen (1999)
Maybeonedaywewillseethemountainsaheadofus.Maybeonedaywewillseethe
sevenmountainsofourmysteriousdestiny.Maybeonedaywewillseethatbeyond
our chaos there could always be a new sunlight, and serenity.
Okri (1993).
WhenAliceinWonderlandwentthroughthelookingglass,sheenteredaworldwith
differentrules.Fewofushavehadtheexperienceofdiscoveringthattherulesthat
hadbeenguidingourresearchforthepastyearsordecadeswereallwrong,thatthe
predictions ofour theories were wrong, that the assumptions were wrong, that our
professorswerewrong,thatourtextbookswerewrong.Thishashappenedfamously
in astronomy, cosmology, physics, and chemistry.
Anderson (2007)
Lopheliaisthecoralthatbreaksalltherules.Itisatruehardcoralproducedbya
colony of individual polyps but it is found in deep cold water. Unlike its tropical
counterparts, Lophelia does not contain zooxanthellae and so does not rely on
sunlight.
Roberts (1997)
Seafloorlandscapesandfeaturesareoftenfascinatingandawe-inspiring.Fewofthe
processes known to occur on land are active on the oceanic seafloor. Therefore,
underwaterlandscapesatdepthsbeyondlightpenetrationneedourfullimagination
for their interpretation. Ever since I got responsibility for explaining seafloor
phenomena important for human-made seafloor installations and constructions
x Preface
Figure 0.1. The‘‘crown’’ofaLopheliareefoffmid-Norway,atawaterdepthof300m.This
mature Lophelia pertusacolony isabout 2m in diameter.
(pipelines, platforms, and well-templates, at the engineering department of Statoil,
nowStatoilHydro),Ihavetriedtobehonestandtruetothegeophysical,geochemical,
andotherdataweobtained.Thishasledtonumerousdiscussionswithotherscientists
and marine geologists. These constructive ‘‘battles’’, where facts and ‘‘truth’’ are
sought, have often been arduous and long-lasting. In some cases, lacking to under-
standaprocessmaynotbeimportantforengineeringandfoundationconsiderations.
In other instances it is crucial for the safety of installations. For example, when gas
Preface xi
andliquidsmigratingthroughdeep-seasedimentscausetheformationofgashydrates
in near-surface sediments, then any man-made disturbance can lead to seabed
instability.
Biologyhasproventobeaninescapableandintimatepartofnaturalsub-seafloor
processes,oftenbeingthesolevisiblemanifestationoffluidmigration.Wherevergases
and liquids emerge through or onto the seafloor, there may be a dramatic effect,
especially on the composition of the local fauna. Although this book deals with the
deep-water(orcold-water)coralreefsofourplanet,myfavouritesubjectovernearly
30 years, that of natural underground fluid migration processes, also permeates the
text of this book. In this respect, I may be criticised for having a too personalised
descriptionandaccountofdeep-watercoralreefs.But,althoughIhaveattemptedto
leave out these discussions, I failed. Fluid migration is indeed intimately linked to
deep-water coral reefs, and one cannot present one without the other.
However,ithasbeenapleasuretoputallofour(StatoilHydro’s)andsomeofthe
otheroldandnewlygainedknowledgebymanyothers(mainlyacademians)ondeep-
watercoralreefsandthemuchlargercarbonatemoundstructurestogetherinthisway.
Therefore,thetextisnotonlydescriptive,butalsooneofdiscussionandpossibleways
of understanding (i.e., interpreting) what we observe. In this book, I and my fellow
researchers report on biological structures that are not only interesting for an
integrated oil (resource) company in several ways, but also for the public at large,
andformarinescientists,ingeneral.Inthisway,thebookisalsoacontributiontothe
resources theme of the UN InternationalYear of Planet Earth with its emphasis on
resource baselines in relation to sustainable use (see www.yearofplanetearth.org).
I hope thebook will provide a useful overview ofvarious aspects ofdeep-water
coralreefsandcarbonatemounds,providinginsightsintothephysicalprocesses,and
inspireandstimulatefurtherresearchintothesefascinatingnaturalsystems.Although
Iwouldhavelikedto,ithasnotbeenpossibletoincludeeachandeverydocumented
deep-water coral reef. Mapping of the seafloor is becoming very efficient and new
discoveries are being made every week. Keeping abreast with this development is
futile. This book, therefore, presents and discusses only a selection of the world’s
discovered deep-water coral reefs.
Ihavechosentoincludethosereefsandmoundsthatinmyviewarebestdescribed
in the literature I am most familiar with (i.e., literature dealing with seafloor
topography, geology, geophysics, and physical aspects). I do not pretend to under-
stand everything about biology, and biologists may therefore find there is too little
biological focus in this book. Furthermore, because discoveries made on the virgin
seafloorareoftenunique,first-handaccounts,Ihaveoftenfounditrighttoquotethe
actualtextusedfordescriptionbytheoriginalauthors.Inthisway,nothingshouldbe
lost in translation or by my own second-hand interpretation of their text.