important cosmopolitan representatives (Messing et al.,
2008; Roberts et al., 2009a).
Dimensions and time constraints of cold-water
coral reefs
Cold-water coral reefs are self-sustained and spatially welldefined coral framework-sediment systems measuring tens
of meters to kilometers in lateral extension and up to 40 m in
thickness, thus influencing local current regimes (Dorschel
et al., 2007; Mienis et al., 2007). Most cold-water coral
reefs occur in water depths of 200–1500 m, where light is
almost reduced or absent, although some reefs exist in much
shallower depths due to specific hydrographic conditions,
that is, in some upwelling fjord settings (Freiwald et al.,
2004; Försterra et al., 2005; Roberts et al., 2006). Reefs
generally occur in groups of hundreds if not thousands in
a given area like on many places of the Norwegian continental shelf, or off Apulia, Ionian Sea (Fosså et al., 2005;
Savini and Corselli, 2010). A focus on the Norwegian coral
systems may underpin the substantial reef-constructing
capability of these unexpectedly large coral build-up seabed
structures. The last glacial ice shields vanished from the
shelf about 13–12 ka ago, and the first appearance of
Lophelia corals was dated 11 ka, short after the last major
cold spell, the Younger Dryas Event, from one of the northernmost coral reef provinces in northern Norway (Lopez
Correa, unpublished data). This coral age and the high latitudinal position coincides with the onset of the modern
oceanographic regime in the north eastern Atlantic, the full
establishment of the poleward flowing Atlantic Current system, which seemingly had carried coral larvae as North as to
the Stjernsund, Finnmark District. This allows the following assumption. All the cold-water reefs in Norwegian shelf
and fjord settings formed within the past 11 ka. This is
a relatively short time span to develop mature biogenic seabed structures with the dimensions given above.
Performing a first conservative calculation of the CaCO 3
flux and production rates for cold-water corals, Lindberg
and Mienert (2005) concluded that Norwegian corals contribute with flux and production rates reaching 4–12% of
that of warm-water reefs. Further south, post-glacial onset
of cold-water coral growth in the Porcupine Seabight and
southeast Rockall Bank recolonized fossil cold-water carbonate mounds at and after 11 ka, contemporaneously with
the onset of the Norwegian coral spread towards the North
(Frank et al., 2009). Even further south, cold-water corals
fade off just after the Younger Dryas period in the Gulf of
Cádiz (Wienberg et al., 2009). The least we can conclude
from these data of rise and decline ages is that reefconstructing Lophelia and Madrepora quickly responds to
changing climates and productivity regimes along the
northeastern Atlantic continental margin.
Colony, thicket, coppice, reef
Another apparent character is the low diversity of the primary coral framework constructing species. In contrast to
warm-water coral reef framework, only one to three
colonial scleractinian species form the backbone of coldwater reefal framework in a given area (Stanley and Cairns,
1988), thus acting as typical ecosystem engineers. Most significant framework-forming azooxanthellate scleractinians
are L. pertusa, M. oculata, Solenosmilia variabilis,
Goniocorella dumosa, Enallopsammia profunda, and
Oculina varicosa. The latter species lives with endosymbiotic zooxanthellae in the photic zone but without
photo-endosymbionts in aphotic depths (Reed, 2002).
The initiation of what will become a reef eventually
with time starts with a dense larval spatfall of one or two
of the above-mentioned species within a relatively localized area. After metamorphosis of the settled larvae, the
corals develop colonies that steadily intermingle with
neighboring colonies with time, thus increasingly monopolizing the seabed to form low-relief thickets of 10–30 cm
height (Squires, 1964). Such thickets provide support and
shelter for other organisms that become attracted to the
newly created habitat. The corals protect themselves efficiently against competitors with their anti-fouling ability
– the skeleton-overcoating tissue or coenosarc. The tissue
spread upon those organisms that try to settle onto the
coral skeleton, which subsequently becomes encalcified
by tissue-controlled precipitation of faint aragonite layers
to entomb the epizoans (Harmelin, 1990; Freiwald and
Wilson, 1998). With continuing growth of coral colonies
within a thicket, a separation of live from dead and tissue-barren framework induces a further important step in
the evolution of a complex ecosystem, which is called
the coppice stage. The tissue-barren framework is now
prone to colonization by other sessile organisms, such as
foraminifers, hydrozoans, octocorals, serpulids, molluscs,
bryozoans, brachiopods, and a diverse array of sponges
among others. Therefore, species richness of the coralassociated assemblage of sessile organisms is more
diverse in the tissue-barren part of a coral colony than in
the upper live part of the colony resulting in a clear faunal
zonation pattern (Freiwald, 2002; Mortensen and Fosså,
2006). Of some importance is the infestation of the tissue-barren coral framework by boring and endolithic
organisms, which opens a new dimension in micro-habitat
colonization but also tend to weaken the framework stability through bioerosion. Most effective bioeroders are boring alectonid, clionaid, and phloeodictyid sponges, which
deeply excavate the coral skeleton, thus facilitating the
collapse of a colony or even larger parts of thickets (e.g.,
Beuck and Freiwald, 2005; Beuck et al., 2007, 2010). In
the coppice stage, accumulation of coral fragments and
remains of the associated skeletal fauna becomes prominent. However, another pre-requisition is needed to transform coppices into a high-relief reef stage – continuous
trapping and baffling of suspended particles advected by
the bottom-near current regimes. These imported particles
entirely consist of the remains of pelagic organisms, such
as planktonic foraminifers, coccolithophorids, and pteropods, or they represent a mixture of pelagic and terrigenous silt and clay particles, which are then called
hemipelagic sediments. In any case, the matrix infill
226
COLD-WATER CORAL REEFS
2008; Roberts et al., 2009a).
Dimensions and time constraints of cold-water
coral reefs
Cold-water coral reefs are self-sustained and spatially welldefined coral framework-sediment systems measuring tens
of meters to kilometers in lateral extension and up to 40 m in
thickness, thus influencing local current regimes (Dorschel
et al., 2007; Mienis et al., 2007). Most cold-water coral
reefs occur in water depths of 200–1500 m, where light is
almost reduced or absent, although some reefs exist in much
shallower depths due to specific hydrographic conditions,
that is, in some upwelling fjord settings (Freiwald et al.,
2004; Försterra et al., 2005; Roberts et al., 2006). Reefs
generally occur in groups of hundreds if not thousands in
a given area like on many places of the Norwegian continental shelf, or off Apulia, Ionian Sea (Fosså et al., 2005;
Savini and Corselli, 2010). A focus on the Norwegian coral
systems may underpin the substantial reef-constructing
capability of these unexpectedly large coral build-up seabed
structures. The last glacial ice shields vanished from the
shelf about 13–12 ka ago, and the first appearance of
Lophelia corals was dated 11 ka, short after the last major
cold spell, the Younger Dryas Event, from one of the northernmost coral reef provinces in northern Norway (Lopez
Correa, unpublished data). This coral age and the high latitudinal position coincides with the onset of the modern
oceanographic regime in the north eastern Atlantic, the full
establishment of the poleward flowing Atlantic Current system, which seemingly had carried coral larvae as North as to
the Stjernsund, Finnmark District. This allows the following assumption. All the cold-water reefs in Norwegian shelf
and fjord settings formed within the past 11 ka. This is
a relatively short time span to develop mature biogenic seabed structures with the dimensions given above.
Performing a first conservative calculation of the CaCO 3
flux and production rates for cold-water corals, Lindberg
and Mienert (2005) concluded that Norwegian corals contribute with flux and production rates reaching 4–12% of
that of warm-water reefs. Further south, post-glacial onset
of cold-water coral growth in the Porcupine Seabight and
southeast Rockall Bank recolonized fossil cold-water carbonate mounds at and after 11 ka, contemporaneously with
the onset of the Norwegian coral spread towards the North
(Frank et al., 2009). Even further south, cold-water corals
fade off just after the Younger Dryas period in the Gulf of
Cádiz (Wienberg et al., 2009). The least we can conclude
from these data of rise and decline ages is that reefconstructing Lophelia and Madrepora quickly responds to
changing climates and productivity regimes along the
northeastern Atlantic continental margin.
Colony, thicket, coppice, reef
Another apparent character is the low diversity of the primary coral framework constructing species. In contrast to
warm-water coral reef framework, only one to three
colonial scleractinian species form the backbone of coldwater reefal framework in a given area (Stanley and Cairns,
1988), thus acting as typical ecosystem engineers. Most significant framework-forming azooxanthellate scleractinians
are L. pertusa, M. oculata, Solenosmilia variabilis,
Goniocorella dumosa, Enallopsammia profunda, and
Oculina varicosa. The latter species lives with endosymbiotic zooxanthellae in the photic zone but without
photo-endosymbionts in aphotic depths (Reed, 2002).
The initiation of what will become a reef eventually
with time starts with a dense larval spatfall of one or two
of the above-mentioned species within a relatively localized area. After metamorphosis of the settled larvae, the
corals develop colonies that steadily intermingle with
neighboring colonies with time, thus increasingly monopolizing the seabed to form low-relief thickets of 10–30 cm
height (Squires, 1964). Such thickets provide support and
shelter for other organisms that become attracted to the
newly created habitat. The corals protect themselves efficiently against competitors with their anti-fouling ability
– the skeleton-overcoating tissue or coenosarc. The tissue
spread upon those organisms that try to settle onto the
coral skeleton, which subsequently becomes encalcified
by tissue-controlled precipitation of faint aragonite layers
to entomb the epizoans (Harmelin, 1990; Freiwald and
Wilson, 1998). With continuing growth of coral colonies
within a thicket, a separation of live from dead and tissue-barren framework induces a further important step in
the evolution of a complex ecosystem, which is called
the coppice stage. The tissue-barren framework is now
prone to colonization by other sessile organisms, such as
foraminifers, hydrozoans, octocorals, serpulids, molluscs,
bryozoans, brachiopods, and a diverse array of sponges
among others. Therefore, species richness of the coralassociated assemblage of sessile organisms is more
diverse in the tissue-barren part of a coral colony than in
the upper live part of the colony resulting in a clear faunal
zonation pattern (Freiwald, 2002; Mortensen and Fosså,
2006). Of some importance is the infestation of the tissue-barren coral framework by boring and endolithic
organisms, which opens a new dimension in micro-habitat
colonization but also tend to weaken the framework stability through bioerosion. Most effective bioeroders are boring alectonid, clionaid, and phloeodictyid sponges, which
deeply excavate the coral skeleton, thus facilitating the
collapse of a colony or even larger parts of thickets (e.g.,
Beuck and Freiwald, 2005; Beuck et al., 2007, 2010). In
the coppice stage, accumulation of coral fragments and
remains of the associated skeletal fauna becomes prominent. However, another pre-requisition is needed to transform coppices into a high-relief reef stage – continuous
trapping and baffling of suspended particles advected by
the bottom-near current regimes. These imported particles
entirely consist of the remains of pelagic organisms, such
as planktonic foraminifers, coccolithophorids, and pteropods, or they represent a mixture of pelagic and terrigenous silt and clay particles, which are then called
hemipelagic sediments. In any case, the matrix infill
226
COLD-WATER CORAL REEFS