Coralline Algal Reef Frameworks

J. geol. Soc. London, Vol. 140, 1983, pp. 365-376, 7 figs.. 1 table. Printed in Northern Ireland.

Coralline algal reef frameworks

D. W. J. Bosence

SUMMARY: Published and unpublished accounts of coralline algal reef frameworks are reviewed. The descriptions are divided into frameworksconstructed from crustose coralline algae andthose constructedfrom branching corallines. Crustoseframeworks are briefly described and illustratedfrom the Miocene of Malta,Recent ‘coralligtne’ from the Mediterranean, Eocene reefs from Spain, Recent algal reefs, of St Croix, U.S. Virgin Is. and algal reefs from Bermuda. Branching frameworks are briefly described and illustrated from the Recent maerl of the NE Atlantic, Recent mud mounds from Florida, Recent algal reefs from St Croix and Recent algal ridges on Pacific reefs. Crustose and branching frameworks show an increase in strength of construction, early submarine cements and macro-borers and a decrease in erodibility from low to high energy environments. The occurrence of genera in coralline frameworks is primarily controlled by their geographic and water-depthranges. The construction of coralline frameworks is seen as the result of competition for living space on shallow marine hard substrates.

Coralline algae and ancestral coralline algae have been layers of greatly thickened crusts with almost unlim- important reef builders since the early Palaeozoic. The ited perithallial growth as in Clathromorphurn (Lebed- ancestral corallines were at their most abundant and nik 1977). More complex frameworks may result from impressive as reef builders during the Carboniferous the bifurcation of crusts followed by leafy overgrowths andPermian. Examples are well known from the and then by fusion on the adjacent crusts. This results Pennsylvanian of Kansas(Wray 1964; Frost 1975). in a more open framework which requires a variety of Coralline algae reached their heyday as reef builders crust divisions and fusions to construct. Bosence & in the Cenozoic and this paper concentrates on the Pedley (1982) and Bosence (1983) describe how frameworks within these reefs. It also reviews existing aMiocene species of Mesophyllum produces leafy accounts of coralline algal reef frameworksand overgrowthsthrough rejuvenation of the perithallial introduces work in progress by the author on a variety meristem to produce a new crust with hypothallus and of frameworks.From this review it is apparent that perithallus (Fig. 1D). Where downward growing crusts little is known about the constructional methods used re-attach onto old crusts additional perithallial tissue by corallines or the possible adaptive significance of welds the crusts together (Fig. lDz). Similarly ‘walls’ the wide range of frameworks. The small scale of perithallial tissue may form between, underand frameworksfound in rhodoliths are notconsidered overlying crusts (Fig. 1D3). here as they have been recently reviewed (Bosence, in Branching frameworkshave not beenstudied in press). detailbut in rhodoliths thenature and density of branching has been shown to be a sensitive indicator of hydraulic conditions(Bosence 1976). Some Framework construction by frameworks have been shown to be constructed from coralline algae both crustose and branching growth, as exemplified by Mesophyllumcommune in the Miocene Coralline Thereare 3 basic morphologiesexhibited by the LimestoneFormation of Malta (see below and coralline algae: (a) laminar crusts made up of a basal Bosence & Pedley 1982). hypothallus, with sub-horizontal filaments of cells, and For convenience of presentation the crustoseand many genera have an upper perithallus of subvertical branching frameworks described may be arranged in a filaments (Fig. 3C), (b) branches arising from crusts seriesfrom those growing in hydraulically quiet which frequently show a central medullary zone with environments to those occurring in exposed areas elongate cells and an outer short celled cortical layer, (Table 1). and (c) articulatingbranches in which uncalcified zones (geniculae) divide calcified segments (Fig. 2C). Crustose frameworks Reef frameworks may only be constructed by crusts andbranches asarticulating branches break up on Coralline algal biostrome, Miocene, Malta death.The simplest crustoseframeworks can result (Fig. 1) froma mosaic of living crusts overgrowing their neighbours(Fig. 4G). These frameworks may vary Crustose frameworks occur at a number of horizons from the superposition of many thin monostromatic as the CrustosePavement facies of this large (20 X layers (Lithoporella, Bosence & Pedley 1982) to fewer 5 km X 16 mthick) biostrome (Bosence & Pedley 1982). 0016-764918310500-0365$02.00 01983 The Geological Society

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 366 D. W. J. Bosence

A P E’ 6

FIG. 1. Crustose pavement; Coralline algal biostrome, Miocene, Malta. A. Crustose Pavement facies with crustose framework and branches arising from crusts. Qala, Gozo. Scale: xi. B. Crustose framework with erosion surfaces (arrows) overlain by rhodoliths (R). II Karraba. Scale: x1/10. C. Weathered and serial sectioned block showing leafy growth of Mesophyllum commune and internal structure (after Bosence & Pedley 1982). Scale: x2. D. 1-6. Sketches illustrating detail of crust divisions and fusions of M. commune in framework construction. Cell rows in hypothallus (semicircles) and perithallial filaments (vertical lines) (after Bosence, in press, b). For details see text. E. Thin section of crusts in biostrome framework, I1 Karraba. Scale: X10.

This facies is one of 6 within the biostrome which are epifauna of bryozoans,serpulids, foraminifera, all dominated by corallinealgae. The frameworks brachiopods and gastropods (Bosence & Pedley 1982). reach up to 4.5 m in thickness and cover areas up to Although no examples of similar ancient build-ups are 1km2. Through the frameworkrun erosion surfaces known, the ‘coralligene de plateau’ (Laborel 1961) is overlain by rhodoliths which suggest the structure had considered to be the nearest Recent analogue(see little resistance to turbulence and that the relief of the below). build-up was on a decimetre scale. The framework is open, leafy and constructed mainly by Mesophyllum commune with encrusting Lithoporellamelobesioides ‘Coralligkne biocoenose’, Recent, (Fig. 1 A-C). The detail of framework construction is Mediterranean (Fig. 2) discussed inBosence & Pedley (1982) and Bosence (1983). The crusts build upthe framework by Perks (1967) and Laborel (1961) described coralline foliaceous growth combined with various methods of algal constructions associated with carbonate sands crust fusion, division and upward branch growth (Fig. and gravels in intertidaland shelf areas (down to lD, E). The frame forms about 50% of the build-up 150m) in theMediterranean. The build-ups occur with 10% coralline andother bioclastic debris and from the rocky intertidal (‘trottoir’) to soft substrate 40% micritic matrix. There is a very occasional early shelf areas (corallighe de plateau) from depths of 30 isopachous cement around crusts but the absence of to 150m. Thetrottoirs comprise ledges up to 1m macro-borers and the presence of erosion surfaces in broad in the intertidal and the deepwater coralligknes, the framework suggest that it was not lithified on the have a relief of a few tens of centimetres and cover sea floor. The macro-borers arethought to be thousands of square metres of sea bed. Coralline excluded by the thinness of the crustsand the low growth is reportedto be of 3 main kinds (Laborel density of the framework.Micro-borers include 1961): (1) (‘feuillkte’) A fragile framework of thin sponges and algae. The framework supports a varied dividing crusts of Mesophyllum licherzoides (Fig. 2C),

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 Corallinereef algal frameworks 367

E G

FIG. 2. CoralligPne; Recent, Mediterranean A. Leafy growth and crust bifurcations of Lithophyllum expansurn, Recent, Bay of Naples (coll. W. H. Adey). Scale: X 14. B. Section of coralligtne illustrating inner cemented and bioeroded rock with remnant of crustose frame (inner arrow) and outer veneer of later crusts (arrow). (Coll. H. Zibrowius). Scale: Xl. C. Surface view of leafy bifurcating growth of Mesophyllum lichenoides overgrowing lower crusts and articulating corallines (lower left). Recent, Dorset. Scale: X2. D.Developmental stages of ‘Coralligtne de Plateau’ (after Laborel 1961). (1) accumulation of rhodoliths in carbonate gravel; (2) crusts overgrow and stabilize rhodoliths; (3) continued crust growth to form build-up with internal bioerosion and sedimentation, and (4) collapse following pervasive bioerosion. E. Micrograph of section from B of outer edge of coralligtne indicating bored inner region encrusted by later corallines. (Coll. H. Zibrowius) Mediterranean. Scale: ~40. F. Micrograph from thin section of coralligtne illustrating framework constructed from successive coralline crusts. Recent, Mediterranean (Coll. H. Zibrowius). Scale: ~40. G. Micrograph of section from inner part of coralligtne illustrating borings, internal sediment and remnants of coralline framework. Recent, Mediterranean (COL H. Zibrowius). Scale: X40.

Lithothamniumphilippi and Lithophyllumexpansum this debris is thoroughly cemented by ?aragonite fans (Fig. 2A); (2) (‘fruticuleux’) Thick, densely branching and micrite (Fig. 2B, G). Sections indicate superficial growths of Neogoniolithon mamillosum; (3) (‘concen- crusts of fresh corallines over a substrate of bioeroded trique’)Leafy, concentric growths of Lithophyllum earliercoralline frameworks infilled with cemented expansum. The coralligkne contains a very rich sediment (Fig. 2E,F). Laborel (1961) described the epifauna and flora (Pkrks 1967; Laubier 1966). A large history of these biostromes in the following stages part of these banks (Fig. 2D) consists of bioclastic (Fig. 2D): 1, Accumulation of biogenic sand, gravel and sands and gravels. Specimens of the coralligkne kindly rhodoliths; 2, Stabilization of clasts by encrusting leafy supplied by Dr Zibrowius (Marseilles) indicate that corallines; 3, Continuedcrustose growth producing

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 368 D. W. J. Bosence

framework of M. lichenoides, L. philippi and L. frameworks of Mesophyllum with subsidary Litho- expansum; 4, Bioerosion on undersurfaces; 5, De- porella and Archaeolithothamnium (Fig. 3A-C). struction by bioerosion which may reduce framework Mesophyllum crustsbifurcate and rejoin to form a to fragments. similar, buttighter, framework thanthat described abovefrom the Miocene of Malta. The leafy framework also contains occasional branches. Com- Corallalgal reefs, Eocene, NE Spain (Fig. 3) monradial fibrous calcite cementsreplace earlier submarine ?aragonite fans growing down from crusts C.Taberner, University of Barcelona, has dis- (cf. St Croix algal ridges detailed below). Borings, covered what may be the earliest examples of coralline post-dating early cements, may completely erode the ridges to coral reefs. Small patchreefs of Porites, framework which is replaced by cementedsediment Goniopora and Acropora occurin a siliciclastic (Fig. 3D). Similar frameworks encrusting Palaeocene shorelinesetting in the Middle Eocene of northern reefs from Yugoslavia wereillustrated by Babic & Catalune. Coralsare overgrown by foliaceous Zupanic (1981).

A B

FIG.3. Corallalgal reefs; Eocene, Spain. A. Micrograph from sectionillustrating crust bifurcations and leafy overgrowth by Mesophyllum forming a framework. Note vertical sections of growth ridges (R) where approaching crusts attempt to overtop each other. Scale: ~50. B. Composite camera lucida drawing of slabs from crustose framework overgrowing corals. Dashed lines outline borings. Scale: X5. C. Detail of Mesophyllum crust with lowerhypothallus with horizontal filaments of cells (h) andan upper perithallus with vertical filaments (p). Arrows indicate early cement (now calcite) as fans under crusts. Scale: X 120. D. Detail of framework and early cements (right) cut by 3 subsequent borings (left). Scale: X50.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 Coralline algal reef frameworks 369

FIG.4. Algal reefs; Recent, St Croix. A. Slabbed section of reef crest illustrating branching frame of Lithophyllurn congesturn and bored areas infilled with internal sediment and cement. Note large Echinornetra borings (e). Scale: x1/6. B. Surface view of reef crest with branching heads of Lirhophyllurn congesturn, uncalcified epiphytes and browsing gastropod (arrow). Most holes are occupied by Echinornetra. Hammer handle 30 cm. C. Micrograph of section near base of reef indicating remnant of branching L. congesturn frame. Sponge borings and interstices infilled with cemented internal sediment. Scale: x50. D. Slabbed section of lower reef crest with framework of cryptic crustose corallines (light), Hornotrerna (dark wavy layers) and vermetids (small dark holes lower part of slab). Noteremnant of L. congesturn frame(arrow) overgrown on side and underside. Scale: X 116. E. Slabbed section near base of front wall of reef with well preserved branching frame of L. congesturn. Note secondary cryptic coralline frame (arrow). Scale: x1/6. F. Sketch section of algal reef (height c. 2 m) indicating reef morphology. Note massive internal erosion of reef and distinctive crest and lip. e = Echinometra borings. G. Micrograph of sectionfrom Slab D illustrating closely superposedcrusts of corallines,vermetids and some debris. Scale: X50.

Cryptic frameworks on algal reefs, St Croix, pachydermum is abundant. Boreholesand sections Recent (Fig. 4) through the reefs (Adey 1975) indicaterapid algal growth keeping pace with rising sea level until the last Algal reefs or boilers which may fuse laterally to 5000 years when the sea level stabilized. Now the reefs form algal ridges are well developed in the Lesser (100 X 40 m across and up to 2 m high) have de- Antilles (Adey & Burke 1975). The reefs develop in veloped lips and overhangs just below low water level exposed areasfrom corallines (Neogoniolithon and (Fig. 4F) and havebeen subjected to pervasive Porolithon) encrusting shallow pavements of Acropora bioerosion, principally by Echinometra and sponges palmata. When built up to the low tide level a rapidly (Fig. 4A-C) (Bosence 1981). Below overhangs and in growing branchingframework of Lithophyllum con- large borings and reef cavities a secondary coralline gestum is constructed(see below) andat heights framework is being constructed which overgrows greaterthan 2Ocm above low water Porolithon previously bored, infilled and cemented frameworks.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 370 D. W. J. Bosence The new cryptic frameworks are superposed crusts of tified fromthe framework: Neogoniolithon sp., Tenarea, the foraminifer Homotrema, Mesophyllum Mesophyllumsyntrophicum andthe squamariacean and Neogoniolithon intergrown with the vermetid Peysonnelia sp. Ginsburg & Schroeder (1973) also Dendropoma (Fig. 4D,G). Surface views of overhangs described extensive bioerosion, internal sedimentation illustratecompetitive overgrowth ina mosaic of and cementation. corallinecursts, vermetids and foraminifera. The Similar boilers were described by Boyd et al. (1963) resultant framework is a dense intergrowth of these from the Yucatan. organisms (Fig. 4G). These frameworks reach thick- nesses of c. 20 cm. Branching frameworks Algal reefs, Recent, Bermuda Maerl, Recent, NE Atlantic (Fig. 5) In a classic studyGinsburg & Schroeder (1973) described the growth and preservation of algal reefs in Loose frameworks constructedfrom branched rhodo- Bermuda. The 8-12 m high cup reefs are constructed liths occur in the Maerl of the NE Atlantic (Bosence mainly by corallinealgae with subsidiary Miflepora, 1980). 10 to30cm high banks are constructed of vermetid gastropodsand foraminifera.Coralline interlocking branched thalli of Lithothamnium coralframeworks are laminar and columnar (‘knob-like’) lioides and Phymatolithon calcareum (Fig. 5A,B). This crusts. Irregular crust growth and columns create small semi-rigid framework covers areas up to 0.5 km2. The pores within what is predominantlydense a individual thalli intergrow andcannot be removed framework. The following corallines have been iden- without breakage. Their rigidity is further enhanced

B C

FIG.5. Maerl; Recent, NE Atlantic A. Underwater view of surface of Bank facies constructed by branching corallines. Mannin Bay, Ireland. Starfish 15 cm across. B. Detail of branching rhodoliths of Phymatolifhon calcareum (left) and Lithothamnium corallioides (right) with epiphytic algae and sponges. Falmouth Harbour, Cornwall. Scale: X1.1/4. C. Core through Bank facies illustrating branched intergrown rhodoliths with epiphytes (top left) and preservation of branches in uncemented muddy sand matrix. Scale: Xl.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 Coralline algal reef frameworks 371

A R

FIG.6. Mud mounds; Recent, Florida A. Aerial view of windward edge of Tavernier Key illustrating Thalassia covered surrounding sea bed(s), dark Porites zone (p), lighter Neogoniolithon zone (n) and inner Thalassia zone (t). Scale from propeller scour marks 30 to 50 cm across. B. Intergrown clumps of branching Neogoniolifhon at low water spring tide level with surrounding Thalassia and muddy sand and gravel. Scale divisions 1 cm. C. Neogoniolithon overgrowing Porites and forming branching head. Scale: X 1. D. Box core through area in B illustrating in sifu branching framework of Neogoniolifhon and lower bioturbated (b = burrows) sediment of Neogoniolifhon, Halimeda, molluscs and Porifes. Scale: XU6.

by filamentousepiphytes binding the branches Neogoniolithon, Recent mud mounds, Florida together (Fig. SB,C). The frameworkhas anupper Keys (Fig. 6) current-washed zone of live corallines, epiphytes and a diverse andabundant fauna (Bosence 1979). The Recent mud mounds in the back reef area of the depth of this zonedepends on the strength of the Florida reef tract have zones of frame-building bottom currents. Where currents are low a mud and organisms on their windward side (Turmel & Swanson sand matrix is deposited between the algal branches 1976). Anouter (0.3-1.2m deep) zone with a (Fig. SC). There is no early cementation outside the framework of branching Porites is superseded (up to confines of the algal skeletonand no large scale the low watermark) by branching Neogoniolithon bioerosion. The occurrence of the banks is controlled (Fig. 6A). The author’s work on Tavernier Key has by the ecological requirements of the algae which shown that Neogoniolithon encrusts the lower dead result in luxuriant growth in sheltered parts of bays at areas of Porites and then the crusts overgrow the depths of 1-8m. Further S in the Mediterranean the coral. Branches arise from these crusts (Fig. 6C) and banks occur at depths of 30-40 m (Jacquotte 1962). build aframework upto the lower interidal. The

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 372 D. W. J. Bosence branches within the framework bifurcate and fuse on have massive ridges (15 m broad and up to 60 cm high) toadjacent branches. Adjacent branching heads and groovesand spurs. Algal ridges are dominantly intergrow to form clumps of framework up to 1m’ in windward features and in the intertidal zone take the area (Fig. 6B). Upward growth is halted at low tide full force of waves breaking onthe reef front.The level, resulting in flat topped clumps with subsequent principal algae on ridges are species of Porolithon and growthproceeding laterally as opposed to vertically. Lithophyllum. Therefore the earlier term ‘Lithotham- The framework has a relief of up to 15 cm above the nium (-ion) ridge’ has been dropped. level of the surrounding muddy gravel. However, with Thereare no detailed descriptions of the internal high rates of sedimentation and lowered coralline structures of algal ridges. The available descriptions growth rates at the low water level the corallines may concentrate onexternal morphology of ridges from the get buried. The resultant framework is not strong and Marshall Is. (Taylor 1950; Emery et al. 1954; Ladd et anabundant nestling andboring fauna weakens the al. 1967, 1970; Johnson 1961), Hawaiian Is. (Pollock structure. There is no early cementation of the matrix. 1928; Easton & Olsen 1974; Littler & Doty 1975; Segments of the framework commonly break off and Adey & Boykins, in press) and Raroia (Newall 1954) continue growth shorewards as rhodoliths. The in the Pacific and the Lesser Antilles of the Caribbean framework is not preserved at depth within the mound (Adey & Burke 1975). because of breakage by burrowing crabs and shrimps In the Marshall Is. the ridge consists of pavements (Fig. 6D). and roofed-overgrooves and surge channels. The outer ridge is a honeycomb of cavities and tunnels with a room and pillar structure (Ladd etal. 1967, 1970). Lithophyllum in Recent algal reefs, St Croix The outer part of the ridge supports branching heads (Fig. 4) of Porolithon gardinieri whichmay build up the structure to 25-50 cm above low tide level and up to Recent algal reefs in St Croix have been described 15 m wide. Behind ridges lies a flatter lower pavement under crustose frameworks (above). A major and fast encrusted by Porolithon onkodes. Algal ridge samples algal reef builder is Lithophyllum congestum which has from Enewetok collected by B. Rosen (British branch tip growth rates of up to 8 mm per year Museum, NaturalHistory) contain Porolithon with (Steneck & Adey 1976). The present day upper 4-6 mm thick branches forming adense framework surface of the actively growing reefs in the windward (Fig. 7B). The branches are encrusted by forami- intertidal and shallow subtidal is covered with branch- nifera, vermetids and serpulids and are cemented by a ing heads of this coralline (Fig. 4B). L. congestum has coarse fibrous cement in addition to cemented internal been identified in coresthrough the reefs down to sediment (Fig. 7B). 2.3m (Adey 1975). Slabbedsections through these Studies by Littler & Doty (1975) on the Hawaiian reefs are being studied by the author (Bosence 1981). ridges showed that the ridge front is dominated by P. Branching L. congestum formsa relatively dense gardinieri and Lithophyllum kotschyanum with P. framework in which branches are fused together by onkodes on the ridge crest and flat. They argued that additional Lortical growth.Strength is further en- the corallines are abundant in the intertidal because of hanced by encrusting Tenarea and Homotrema and the the exclusion of other algae by the high surf cementing of wave drivensediment within the conditions, together with adaptations by these algae to framework (Fig. 4A). The branches are attacked by withstand very high levels of illumination (Littler boringepiphytic algae, sponges, Echinometra and 1976). The frondose algae are also excluded from the barnacles. The reefshave a cavernous structure and shallow subtidal by gastropodand echinoid grazing, may be broken during heavy storms. Sections within which the corallines can withstand. This confirms the reef show many generations of boring, sedimenta- earliercomments by van denHoek (1969) that tion and cementation. In spite of the extensive Porolithon growth in the Caribbean is the indirect bioerosion, remnants of the framework can be located result of increased light due to removal of frondose in slabbed sections down to 90 cm below the reef crest algae by heavy surf. (Fig. 4E,G). At reef heights greater than 20 cm above The internal structure of ridges was noted by Taylor mean low water springs L. congestum is succeeded by (1950) and Newall (1954), who found that coralline Porolithon pachyderrnum (Adey 1975) which produces crusts are a veneer overa coral, foraminiferan and crustose and columnar growths up to 5 cm thick in coralline sediment bound together by coralline crusts. Isaacs Reef on St Croix. Incontrast, Pollock (1928) reported widespread crustose frameworks building up Recent and Pleisto- Algal ridges to PaciJic reefs (Fig. 7) cenereefs onOahu. Similarly Ladd et al. (1967, 1970), and Gross et al. (1969) described extensive Algal ridges represent perhaps the most spectacular branching and crustose coralline frameworks. Easton development of corallineframeworks. Many Pacific, & Olsen (1974) described coralline frameworks in the Indian Ocean and Caribbean reefs have been shown to Oahu reefs in cores going back to 7000 B.P.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 Coralline algal reef frameworks 373

FIG.7. Algal ridges; Recent, Pacific Ocean A. Algal ridge, grooves and spurs, Rongelap Atoll (after King, Austin & Taylor, in Wells 1954). B. Section of algal ridge rock from Eniwetok illustrating branching frame of Porolithon gurdinieri with vermetids and cemented internal sediment (coll. B. Rosen). Scale: X2/3.

Clearly, considerable work needs to be undertaken below). The relatively low diversity of open before the structure and environmental significance of frameworks is a reflection of the small number of algal ridges is understood. corallines which are known to grow in this mode. In addition tothe increasedstrength of closely superposed crusts they occur in environments where they Discussion are well cemented by submarinecements (e.g. algal ridges and reefs). Comparison of frameworks Similarly, branching frameworks become more den- Table 1 summarizesinformation onthe coralline sely branched in exposed environments. The shallow frameworks described, and emphasizes the paucity of high energy algal ridges of the Caribbean and Pacific information on many coralline build-ups and the need reefs are also well encrusted andcemented. The for more detailedstudies on the morphology of the absence of large boring organisms from the maerl and framework building corallines and the adaptive signifi- Miocene Crustose Pavement facies is considered to be cance of these structures. The frameworks have been a function of the fineness of the branches and crusts listed in order of increase in hydraulic energy of the combined with an uncemented matrix. Resistance to environment. From thissequence several patterns physical erosion of frameworks also appears to be emerge. Firstly,crustose coralline frameworks from controlled by early cements. The greater evidence of low energy environmentsare characterized by open erosion is in the fragile quietwater uncemented leafy frameworks of a small number of species, and frameworks rather than the cemented coralline thalli thosefrom higher energy environments by dense in exposed environments. closely superposed crusts of several species. Presum- The occurrence of variouscoralline genera in ably this reflects the weakness of such leafy growths frameworks is limited by their depth and geographic despite their considerable competitive advantages (see ranges (Adey 1970; Adey & Boykins, in press). This

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 374 D.W. J. Bosence TABLE1: Summary of characteristics,occurrence and environment of growth of coralline algal frameworks described in text Physical Macro- Early Framework Genera Depth cementsborerserosion Energy Crustose Pavement; Mesophyllum ?50-100 m low/med + 0 0 Miocene, Malta (Lithoporella) “Coralligene”; Mesophyllum Recent. Mediterranean Lithophyllum 0-150 m med - + + Neogoniolithon Lithothamnium Tenarea CoraUalgal reefs; Eocene reefs, Mesophyllum ?shallow ?med + + + Spain Archaeolithothamnium Cryptic frameworks; Tenarea Algal reefs, Recent, Mesophyllum 0-2 m medihigh 0 + + St Croix Lithothamnium Neogoniolithon Algal reefs; Neogoniolithon G12 m medihigh 0 + + Recent, Bermuda Mesophyllum Branching Frameworks Maerl, Recent, Lithothamnium 1-30 m lowimed + 0 0 NE Atlantic Phymatolithon Mud mounds, Recent, Neogoniolithon 0-1 m medilow + 0 0 Florida Algal reefs, Recent, Lithophyllum +0.2-0 m high + + St Croix Algal ridges, Recent, Porolithon +0.6-6 m v. high + + + Pacific Lithophyllum

+, present; 0, absent; -, no data

explains the shallow tropical dominance by Lithophyl- with plants overgrowing or being overgrown by lurn, Neogoniolithon and Porolithon and the temper- neighbours may result in crustose frameworks of ate and deep water tropical occurrence of Mesophyl- closely superposed crusts. Commonly other encrusting lurn, Phymatolithon and Lithothamnium. Thelatter organisms may compete for space on coralline sub- genera will, however, occur in shaded tropical regions strates and will be incorporated into this framework (e.g.cryptic environments, St Croix reefs). The (Fig. 4G). An even more successful form of over- apparently shallow subtropical Eocene Mesophyllurn growth has evolved in a few species of Lithophyllum framework is not understood at this stage. and Mesophyllum which divide and rejoin their crusts to support leafy overgrowths over neighbouring corallines (Figs. 1-3). Overgrowth first shadesand then Adaptive significance of framework creates a cavity in which debris accumulates, thereby building killing the lower crust.This represents the ‘saucer’ The majority of coralline algae can only encrust strategy of Jackson (1979)which is characterized by hard substrates. Living space on hardsubstrates is successful overgrowth of neighbours but at the cost of oftenconsidered tobe the most important limiting a delicate growth form which may be easily broken. resource in this niche (e.g. Jackson 1977). Corallines Examples of such frameworks are given above from can increase their surface area for light and nutrient the Miocene of Malta, the Eocene of Spain and the absorption and reproduction either by marginal crust Recent corallig2ne of the Mediterranean. growth or branch growth. Steneck (1978) showed how Secondly, corallines increasetheir surface area by crustose corallines may competefor space on hard branch growth from crusts. Steneck & Adey (1976) substrates either by growing faster or by ‘overtopping’ considered that this greatly increases surface area, their neighbours. Clear evidence of space competition particularly for reproductionin the ridge-building can beseen in crust overgrowth and growth ridges coralline Lithophyllum congestum. It is commonly which form where adjacent crusts attemptto grow observed that conceptacles occur most frequently on over each other (Fig. 3A). Patchworks of corallines branches as opposed to crusts.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 Co ralline algal Coralline reef frameworks 375 Thereforethe formation of frameworks may be corallines actively overgrow the live coral. viewed as the result of corallines competing for limited The occurrence of corallines onthe windward hard substrate space. intertidal side of reefs suggests that they can withstand. conditions of higher hydraulic and light energy than Corals versus corallines corals. Doty (1974) suggested that high algal ridges may form because of the tolerance of Porolithon to Corals and coralline algae frequently occur in the high light intensity, erosion and the continual pound- same or adjacent habitats and it is reasonable to ask ing by waves. Both Littler & Doty (1975) and van den whatfactors control whether a coral or acoralline Hoek (1969) argued that breaking waves exclude framework is produced in reefs. Somecoralline competition by frondosealgae, thus allowing the frameworks occur outside thedepth and geographic growth of corallines which can withstand the force of range of reefsin temperate latitudes.Bourrouilh surf and the very high illumination. Clearly field (1979) discussed the replacement of corals by coral- experiments are required on thenature of the lines in Miocene/Pliocene platform carbonates of the succession from corals to corallines in the shallow W and SW Pacific. She considered this replacement to subtidal. be caused by a cooling of the climate at this time. Despite this negative correlation many corallines form build-ups in the tropics alongside coralframeworks. ACKNOWLEDGMENTS.I wish tothank colleagues who have One of the closest associations occurs in algal ridges loaned,donated or discussed corallineframeworks from on coralreefs. Adey (1975) described ridges arising around the world: W. H. Adey (National Museum of Natural History, Washington), R. N. Ginsburg (Rosensteil School of fromcoralline growth ondead Acropora stands. In Marine andAtmospheric Sciences, Miami), B. Rosen exposed areas coralline grazers are excluded and the (British Museum, Natural History), C. Taberner (University corallines can accrete to sea level. A similar sequence of Barcelona) andH. Zibrowius(Station de Marine, of corallineovergrowth of corals is reported above Marseilles). I also thankthe Research Committee, Gold- fromTavernier Key, Florida. However,here the smiths’ College and the NERC for field work funds.

References ADEY, W. H. 1970. A revision of the Foslie crustosc Maltese Islands. Palaeogeog. Palaeoclimatol. Palaeoecol. coralline herbarium. K. Norsk. Vid. Selsk. Skr. 1-46. 38, 9-43.

~ 1975. The algal ridges and coral reefs of St Croix: their BOYD, D.W., KORNICKER, L. S. & REZAK, R. 1963. structureand Holocence development. Atoll. res. bull. Coralline algal microatolls near Cozumel Island, Mexico. 187, 1-67. Contrib. Geol. Univ. Wyoming, 2, 105-8. -& BOYKINS, W.T. The crustose coralline algae of the BOURROUILH-LE JAN,G. F. 1979. Les platforms carbonatCes Hawaiian Archipelago. Smithson. Contrib. Mar. Sci. (in de haute Cnergie a rhodolithes et la crise climatique du press). passage Mio-Plioctne dans les donneur Pacific. Bull. - & BURKE,R. 1975. Holocenebioherms (algal ridges Cent. Rech. Explor. Prod. Elf-Aquitaine, 3, 489-95. and bank-barrier reefs) of the eastern Caribbean. Bull. Don, M. S. 1974. Coral reef roles played by free living geol. Soc. Am. 87, 95-109. algae. Proc. 2nd coral reef symp. 1, 27-33. BABIC,L. & ZUPANIC,J. 1981. Various pore types in a EASTON,W. & OLSEN,E. 1974. Radiocarbon profile of Palaeocene reef, Banija, Yugoslavia. In: TOOMEY,D. F. Hanauma reef, Oahu,Hawaii. Proc. 2nd coral reef symp. (ed.).European fossil reef models. Spec.Publ. Soc. 1, 91. econ. Paleontol. Mineral. Tulsa, 30, 473-82. EMERY, T.O., TRACEY, J.I. & LADD, H. S. 1954. Geology BOSENCE, D. W.J. 1976. Ecological studies on two of Bikini & nearbyatolls. 1, Geology. Prof. pap. U.S. unattached corallinealgae from western Ireland. geol. Surv. 260A, 265 pp. Palaeontology, 19, 365-95. FROST,J. G. 1975. Winterset algal bank complex, Pcnnsylva- -1979. Live and dead faunas fromcoralline algal gravels, nian, Eastern Kansas. Bull. Am. Assoc. Petrol. Geol. 59, Co. Galway, Ireland. Palaeontology, 22, 449-78. 265-91. - 1980. Sedimentary facies, models and production rates GINSBERG,R. N. & SCHROEDER,J. 1973. Growth and of coralline algal gravels,western Ireland. Geol. J. 15, submarine fossilisation of algal cup reefs, Bermuda. 91-111. Sedimentology, 20, 275-614. - 1981. Internalstructure of coralline algal ridges, St GROSS,M. G., MILLIMAN,J. D., TRACEY,J. I. & LADD,H. Croix. A preliminary report. (Abstr). Proc. 4th Int. coral S. 1969. Marine geology of Kureand Midway Atolls, reef symp. p. 7. Hawaii: A preliminary report. Pac. Sci. 33, 17-25. -1983. Coralline algae from the coralline algal biostrome, HOEK, c. VAN DEN 1969. Algal vegetation types along the Miocenc, Malta. Palaeontology 26, 147-73. open coasts of Curacao, Netherlands Antilles. Proc. K. - (in press).Description and classification of rhodoliths Ned. Akad. wet. C, 72, 537-77. (rhodoids, rhodolites). In: PERIT, T.(ed.). Coated JACQUOTTE, R. 1962. Etude desfonds de maerl de la Grains, 225-42, Springer Verlag. Mediterranee. Recl.Trav. Stn. mar.Endoume, 26, -& PEDLEY,H. M. 1982. Sedimentology and palaeoecol- 141-235. ogy of aMiocene coralline algal biostromefrom the JOHNSON,J. H. 1961. Fossil algaefrom Eniwetok, Funafuti

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021 376 D. W. J. Bosence and Kita-Daito-Jima. Prof. pap. U.S. geol.Surv. 680A, tion, communities and productivity-ecology of Poro- 22. lithon. J. ecol. 63, 117-29. JACKSON,J.B. C. 1977. Competitionon marine hard NEWALL,N. D. 1954. Reefs and sedimentary processes of substrate:The adaptive significance of solitary and Raroia. Atoll res. bull. 36, 42-58. colonial growth strategies. Amer. natur. 3, 743-6. PEREs, J. M. 1967. The Mediterranean benthos. In: BARNES, - 1979. Morphologicalstrategies of sessile animals. In: H. (ed.). Oceanogr. mar. biol. ann. rev. 5, 449-533. LARWOOD, G. & ROSEN, B. (eds.). Biologyand POLLOCK,J. B. 1928. Fringing and fossil coral reefs of Oahu. Systematics of ColonialOrganisms, 479-85, Academic Bull. Bernice P. Bishop museum, 55, 56. Press. STENECK,R. S. 1978. Factorsinfluencing the distribution of LABOREL,J. 1961. La concrCtionnment algal ‘coralligene’ et crustosecoralline algae (Rhodophyta, Corallinaeae) in son importance geomorphologique enMediterrante. the DamarisottaRiver Estuary, Maine. Thesis, Univ. Rec. Trav. Stn. mar. Endoume, 37, 37-60. Maine, Orono, Ma. (unpubl.). LADD, H., TRACEY,J. I. & GROSS,M. G. 1967. Drilling on - & ADEY,W. 1976. The role of environment in the Midway Atoll, Hawaii. Science, 156, 1088-94. control of morphology of Lithophyllumcongestum, a --, & -1970. Deep drilling on Midway Atoll. Prof. Caribbean algal ridge builder. Bot. mar. 19, 197-215. pap. U.S. geol. Surv. WA, 22 pp. TAYLOR,W. 1950. Plants of Bikini andother northern LAUBIER,L. 1966. La coralligtne des alberes; monographic Marshall Islands. Univ. of Michigan stud., Sci. ser. 18. bioceonitique Annls.Inst. Oceanogr. Monaco, 43, TURMEL,R. J. & SWANSON, R. G.1976. The development of 137-316. Rodriguez Bank, aHolocene mudbank in the Florida LEBEDNIK,P. A. 1977. Post fertilisationdevelopment in reef tract. J. sediment. 46, 497-518. Clathromorphum,Melobesia and Mesophyllum with WELLS,J. W. 1954. Recent corals of the Marshall Islands. comments on the evolution of the Corallinaceae and the Prof. pap. U.S. geol. sruv. 260 I, 385-486. Cryptonemiales (Rhodophyta). Phycologia, 16,379-406. WRAY, J. L. 1964. Archaeolithophyllum, an abundant LITILER, M. M. 1976. Calcification and its roleamong the calcareous alga in limestones of the Lansing Group macroalgae. Micronesica, 12, 27-41. (Pennsylvanian,south-east Kansas). Bull.Kansas geol. - & Don, M. 1975. Ecological componentsstructuring Surv. 170, 1-13. the seaward edges of tropical Pacific reefs: the distribu-

Received 9 March 1982; revised typescript received 10 June 1982. D. W. J. BOSENCE,Department of Geology, Goldsmiths’ College, (University of London),Rachel McMillan Building, CreekRoad, Deptford, London SE8 3BU.

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/140/3/365/4888336/gsjgs.140.3.0365.pdf by guest on 23 September 2021