Proceedings of the Fourth International Coral Reef Symposium, Manila, 1981, Vol. 1 
AHERMATYPIC CORAL BANKS: LIVING AND FOSSIL 
COUNTERPARTS 
Stephen D. Cairns 
National Museum of Natural History. Smithsonian Institution, Washington, D.C. 20560. USA 
and 
George D. Stanley, Jr. 
Department of Geology, University of Montana, Missoula. MT ,59812. USA 
ABSTRACT 
Reef-like structures referred to as banks are produced by framework-building ahermatypic scleractinians in 
cool water at various depths, usually below those of hermatypic shallow-water reef corals. The distribution of 
Holocene banks is closely related to the ecological requirements of the ahermatypic corals. Fifteen major regions 
of bank development are known today in the Atlantic and Pacific and these banks vary widely in composition and 
ecological structure. Newly discovered living banks come from the Subantarctic South Pacific and off the coast of 
Chile. Emphasis is given to the high fauna! content but low coral species diver.sity as well as the potentially high 
predation pressures which can exist on these banks. 
Only eight widely scattered fossil examples are known. These range from Triassic to Tertiary in age and, Uke 
living examples, each varies in composition and structure. It is suggested that the earUest scleractinian corals of 
the Triassic were ahermatypic and that the development of extensive shallow-water coral reefs in post-Triassic 
time was related to the acquisition of symbiotic algae (zooxanthellae). 
Caution is urged in the interpretation of all ancient reef-like coral accumulations since deep-water banks can 
superficially resemble shallow-water reefs. Increasing amounts of new information of Holocene examples can 
yield considerable insight into recognition of ancient counterparts. 
INTRODUCTION 
The mention of rich deposits of scleractinian 
corals almost invariably brings to mind the visual 
image of a tropical shallow water reef environment 
dominated by massive hermatypic Scleractinia. 
However, not all coral-dominated assemblages are 
necessarily tropical or shallow water. Reef-life struc- 
tures constructed by colonial ahermatypic corals 
also occur in cold (4?-20?C), deep (60-1500m) water. 
Whereas hermatypic corals are severely restricted 
geographically and bathymetrically by the eco- 
logical requirements imposed by their algal sym- 
bionts (zooxanthellae), ahermatypes are not limited 
by these requirements and are much more widely 
distributed (Fig. 1). Hermatypes are relegated to 
shallow (0-70 m), tropical waters; ahermatypes occur 
from 0-6200 m, -1 ? to 29?C, and from the Norwegian 
Sea (70? N) to the Ross Sea, Antartica (78 24'S). 
Ahermatypic species form a significant compo- 
nent of the Holocene Scleractinia both in species 
diversity and abundance. Ninety of the approx- 
imately 190 Holocene genera (47%) and about 560 of 
the approximately 1500 Holocene species (37%) are 
primarily ahermatypic. Although most coral species 
are either hermatypic or ahermatypic ? and often 
the higher taxa are exclusively one or the other ? it 
is stressed that this character is ecologically in- 
fluenced  and  therefore  not  a  good  conservative 
taxonomic character. For instance, oftentimes 
families, genera and even species have hermatypic 
and ahermatypic components: Madracis pharensis 
pharensis is ahermatypic and M. p. luciphila is her- 
matypic; Oculina varicosa occurs naturally in both 
the hermatypic and ahermatypic conditions. 
HOLOCENE CORAL BANKS 
Ahermatypic corals are often incorrectly referred 
to as "deep-water" or "solitary" corals. As in- 
dicated above, ahermatypes do occur in shallow 
water and, although the deepest Scleractinia 
(2000-6200 m, i.e., Fungiacyathus and Leptopenus) 
are invariably small, fragile, solitary species, at con- 
tinental slope depths, large, robust colonial species 
do occur. For instance, Lophelia prolifera (Pallas 
1766) (=L. pertusa). most common between 500-800 
m (Cairns 1979), forms colonies up to 1 m tall and 
has a growth rate of about 5-7 mm/year (Wilson 
1979). (In contrast, growth rates of 100 mm/year are 
not uncommon for branching hermatypic corals). 
Furthermore, when environmental conditions are 
favorable these large, arborescent corals produce an 
extensive reef life framework, trap sediment, and 
provide niches for other benthic organisms. Such 
deep water associations are referred to as coral 
banks. They are usually very diverse assemblages of 
612 CAIRNS AND STANLEY 
100 
500 
UJ 
1000 
a. 
UJ 
Q 
1500 
2000 
?'   6000 
6 200 
Figure 1. Distribution of modern hermaiypic and ahermatypic corals. Modified after Teichert (1958) and Squires (1963). 
IttUititbTropical coral reefs. EZSESIl Hermatypic corals. DUITTTTI Depth and geographic hmit for ahermatypic corals, 
???Ma Effective depth and geographic limit for calcareous algae, .... Extreme depth and geographic limit for 
calcareous algae. Numbered rectangles correspond to deep-water coral structures listed in Table 1. Isotherms are 
AHERMATYPIC CORAL BANKS 613 
species and can become massive structures with 
great relief above the sea floor. Squires (1964) in- 
troduced the genetic classification scheme of: colony 
-? thicket -? coppice -? bank, for such deep-water 
coral structures, and this terminology has been 
generally accepted. 
Deep-water coral banks and coppices were first 
discovered in 1865 (Sars) off the coast of Norway 
and they are now known to be widely distributed 
(Fig. 2, Table 1). Reviews of all or some of these 
structures are included in LeDanois (1948), Teichert 
(1958), Allen and Wells (1962), Stetson, Squires, and 
Pratt (1962), and Squires (1963, 1964, 1965). Deep- 
water coral structures are reported herein for the 
first time from a Subantarctic South Pacific sea- 
mount (?bank) (54?49'S, 129?48'W, 549-915 m) and 
from two ChUean fjords (48?09'S, 74?36'W, 821 m, 
8.3?C and 51?52'S, 73?41'W, 636 m, 10?C). 
The South Pacific and Chilean records have not been 
verified by observation or seismic profile but are 
strongly indicated by the abundance of typical 
framework coral species and the diversity of the 
associated fauna. 
Environmental limitations imposed on all deep- 
water coral banks are: 1) location on a hard 
substrate usually below the general depth of her- 
matypic reef-building activity, 2) association with 
vigorous current activity and nutrient supply, such 
as in an area of upwelling, the axis of a current or 
gyre, or at the mouth of a fjord which is receiving a 
rapid exchange of nutrient-rich water, and 3) cool 
water temperatures. The South Pacific structure is 
suspected to be in an area of current divergence and 
therefore of upweUing. Houtman (1967) has shown 
that such a divergence occurs between the Suban- 
tetfctic and Subtropical Convergence Zones on the 
New Zealand Plateau and a similar divergence may 
also occur between the closely spaced convergences 
in the vicinity of the Subantarctic seamount coral 
structure. 
The framework structure of deep-water banks is 
produced by one or only a few species of corals so 
the total coral diversity is usually low. These 
framework-building scleractinian species are slight- 
ly different for the coral banks of each geographic 
eu-ea.Some cosmopolitan species.such as Desmophy- 
Hum cristagalli and Solenosmilia variabilis, are pre- 
sent on most banks, whereas other framework 
species are endemic to particular ocean basins. The 
Subantarctic South Pacific structure is dominated 
by Solenosmilia variabilis, usually a minor compo- 
nent of other coral banks. The Chilean coral struc- 
ture appears to be based on pseudocolonial 
Desmophyllum cristagalli, a large, robust solitary 
Figure 2. Distribution of known deep-water ahermatypic coral banks. Numbers refer to structures given in Table 1. 
generalized for North Atlantic. Isotherms for the southern hemisphere should be shifted upward. Depth and latitude of 
individual coral structures are plotted as generalized rectangular ranges. In most cases, the "corners" of the rectangles 
can be ignored, favoring a closer correspondence to the isotherms (see Squires 1963). 
614 CAIRNS AND STANLEY 
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616 CAIRNS AND STANLEY 
species which attaches to individuals of the same 
species, forming long pseudocolonial chains. 
In contrast to the relatively low coral diversity in 
a deep-water bank, the total faunistic diversity is 
usually high. Burdon-Jones and Tambs-Lyche 
(1960) recorded 300 species from a Norwegian bank, 
and 32 benthic invertebrate groups representing 13 
phyla were collected from the Subantarctic South 
Pacific structure. Obviously then, intricate ecologic 
relationships exist and high predation pressures can 
be expected. As a possible consequence of this high 
predation pressure, one South Pacific stylasterine 
hydrocoral has developed freely hinged opercula to 
protect its gastrozooids (Cairns, in press). 
FOSSIL DEEP WATER CORAL BANKS 
Unlike Holocene examples, fossil counterparts of 
deep-water scleractinian banks are extremely rare. 
Only eight occurrences from Triassic to Tertiary age 
are known for the world (Fig. 2, Table 1). Some of 
these appear strikingly similar to better-known 
Holocene banks and thickets. 
The oldest suspected examples are of Triassic age 
and are known from western North America (Stan- 
ley 1979a) and Europe (Zankl 1971). These were con- 
structed by some of the earliest scleractinians and 
occur as thin, biostromal to biohermal carbonate 
masses. They developed on hard substrates in 
basinal settings, usually on molluscan shell debris. 
Examples in Europe bordered shallow-water car- 
bonate banks. They were constructed primarily by 
Thecosmilia, a branching colonial, framework- 
building coral similar to Lophelia in growth form. 
A small Cretaceous thicket was reported from the 
western interior of the United States (Coates and 
Kauffman 1973). Its framework was produced by 
Archohelia, a colonial branching coral closely 
related to Oculina, a genus known to produce aher- 
matypic banks off Florida (Table 1). 
Examples representing relatively shallow banks 
and thickets at higher latitudes come from the Early 
Tertiary of Greenland and Denmark (Floris 1972, 
1979). They are constructed by slender, branching 
species of Oculina and DendrophylUa. as well as 
other corals, producing distinctive mounds in out- 
crop. 
Finally, Late Tertiary banks constructed by 
Lophelia were reported from two localities in New 
Zealand by Squires (1964). These are directly com- 
parable to Holocene examples in composition and 
shape (Table 1). 
The first scleractinian corals of the Triassic did 
not build reefs or contribute extensively to reef 
Umestone (Wells 1956, Newell 1978). It has been 
suggested that most, if not all, of these early sclerac- 
tinians were ahermatypic, with many of the same 
species living in shallow as well as occasionally 
deeper water environments (Stanley 1979b). 
Changes in diversity patterns and the appearance of 
true reefs later in the Mesozoic suggest that abun- 
dant hermatypic corals may not have existed until 
some time after the Triassic. This was a major turn- 
ing point in the evolution of scleractinian corals as 
well as shallow and deep-water reef-like structures. 
Besides the advent of shallow-water reef building 
on a large scale, the impact of this event was the 
sharp differentiation of corals along two ecologic 
lines. Most hermatypic reef corals today are colonial 
while the majority of ahermatypes are soUtary. A 
clear differentiation became apparent in the 
Jurassic with the evolution of the deep-water 
caryophylliids. During their evolution, ahermatypic 
corals have been subjected to intense and long-term 
competitive pressures by their faster-growing her- 
matypic counterparts, relegating most ahermatypes 
to deep-water environments. It may be difficult 
therefore, to make direct comparisons in size and 
growth forms between ahermatypes of ancient 
deep water banks and those of the Holocene. Still, 
however, there are many colonial ahermatypic 
corals, including those which construct deep-water 
banks, that are difficult to distinguish from her- 
matypic species on morphologic lines alone. 
PROBLEMS OF RECOGNITION 
AND INTERPRETATION 
A major question that arises is why there are not 
more examples of deep-water coral banks in the rock 
record. There is some evidence of the existence of 
deep water scleractinian structures as far back as 
the early Mesozoic and, considering the abundance 
and wide distribution of these features along the 
margins of continents today, one would expect them 
to be much more common than the spotty 
geographic and stratigraphic distributions reflected 
in Figure 2. We suspect that they may very well be 
more common and that the problem may be primari- 
ly one of recognition and interpretation. 
As was pointed out by Teichert (1958), if pre- 
served in a stratigraphic sequence, many of the 
Holocene deep water coral banks and thickets could 
easily be misinterpreted as tropical, shallow-water 
structures. Especially significant in Holocene ex- 
amples is the extent of framework and debris pro- 
duced by scleractinian corals and the abundance 
and high diversity of the preservable organisms. 
Such relationships are not those normally 
associated with deeper water deposits and it is con- 
ceivable that many ancient occurrences go 
undetected simply because they are misinterpreted. 
This may stem from the type of circular reasoning 
that unilaterally associates colonial coral reef struc- 
AHERMATYPIC CORAL BANKS 6^7 
tures with tropical, shallow-water settings. Caution 
is urged in the designation of shallow-water en- 
vironments based simply on the presence of corals 
or reef structures. 
CRITERIA FOR RECOGNITION OF ANCIENT 
DEEP-WATER CORAL BANKS. 
Some criteria have already been proposed by 
Teichert (1958) to aid in the recognition of ancient 
deep water coral banks, including: 1) absence or 
paucity of algae, 2) lack of extensive, laterally con- 
tiguous shallow-water facies, 3) breakdown of coral 
framework predominantly by bioerosion rather than 
wave erosion (Wilbur 1976, Wilson 1979), 4) low 
diversity of the coral fauna, 5) an admixture of open 
ocean (planktonic) and deep-water constituents 
together with coral faunas, 6) occurrences at high 
paleolatitudes. and 7) lenticular or mound-like 
shapes and geometries. It is apparent that aher- 
matypic corals produce reef-like banks of different 
compositions in a variety of latitudes, physical set- 
tings, and depths, including some overlap with 
shallow-water reefs (Fig. 1, Table 10) so that no 
single criterion can serve to interpret a deposit as a 
deep-water bank. 
Other criteria that may be helpful include the suc- 
cessional development in composition and shape of 
the banks as outlined by Squires (1964) and Wilson 
(1979), which appears to be different from shallow 
reef succession. 
Designation of the corals from a bank as aher- 
matypic solely on the basis of external morphology 
may be difficult, as has been expressed by Rosen 
(1977), but possibilities for indirect inferences may 
come from studies of colony integration (Coates and 
OUver 1973). Also, if the fossil corals are still 
preserved in original aragonite, the use of stable 
isotopes of oxygen and carbon may help to dis- 
tinguish ahermatypic corals (Weber 1973). How- 
ever, because of the instability of aragonite, this 
method is useful only under exceptional instances of 
preservation and therefore not widely applicable to 
fossil occurrences (Scherer 1977). 
SUMMARY 
Today, with continued exploration of the sea, 
Holocene deep water ahermatypic coral banks are 
becoming increasingly well known. They occur in a 
variety of physical and biological settings and, in 
some cases, growth of coral framework produces 
structures of impressive size. Such extensive, 
porous carbonate banks are frequently aligned 
along the edge of continents, and these may have 
potential as hydrocarbon reservoirs. Their value as 
rich fishing grounds is also known, and some are a 
source of precious corals (i.e., CoralUum, an- 
tipatharians, gold and bamboo corals) (Center for 
Natural Areas 1979). Recent discoveries of banks on 
Pacific seamounts and guyots show that these 
banks may act as staging areas for the migration 
and dispersal of the coral larvae. 
The general paucity of ancient examples, which 
nevertheless extend back to the Triassic, leads us to 
suspect that many occurrences in the rock record 
may go undectected. This could be because of their 
close resemblance to shallow-water counterparts 
and the circular reasoning frequently attached to 
the occurrence of coral-rich deposits as being solely 
from shallow-water habitats. Increasing awareness 
of deep-water Holocene banks and the apphcation of 
multiple criteria can aid in the recognition of ancient 
deep-water examples. 
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