Abstract Although coral reefs are well developed in the Leeward islands of the Netherlands Antilles, they are poorly developed in the Windward group. Coral communities are common in the Dutch Windward islands, but no structural reefs have been observed. Flat, sandy bottoms there seem to prevent reef development, as is also the case on large parts of the southwest coast of Aruba. The zonation of corals on the reefs, with respect to depth, distance from shore, and conformation to the bottom, resembles that of other Caribbean reefs. Density of living-coral cover ranges in the several zones from nearly zero to almost 100%. Below 20 to 25 m on the forereef slope the corals are areally less abundant than crustose coralline algae. Generic diversity of hermatypic corals is comparable in the Leeward and Windward groups of the Dutch islands, with 24 and 23 genera present, respectively. These numbers are comparable to those of other highly diverse reefs in the Caribbean. The number of species in the Windward group, however, is relatively low. The differences in abundance of coral genera (and species) throughout the Caribbean needs more thorough investigation.

Abstract Abstract The insular shelf off Parguera, Puerto Rico, is 8 to 10 km wide. The shelf break at 20 m depth is a marginal barrier reef. The hard rock surface is covered with massive corals and Acropora cervicornis. The barrier is dissected by numerous narrow channels through which sand is transported over the shelf edge. The upper slope has a 43° gradient where channels are present, and is vertical where channels are absent. Between the shelf edge and the coast, two elongate reef systems divide the shelf into an inner, middle, and outer shelf. The outer shelf, from the marginal barrier to the Margarita – Media Luna line, is covered with a thin veneer of biogenic sands. These are a mixture of recent and relict deposits. The backreef lagoons of the middle and inner shelf are similar, and are characterized by finegrained poorly sorted sediments. The fine material comes from winnowing of the backreef apron and from in-situ bioerosion. Up to 10% of the calcareous fraction is contributed by coccoliths. The backreef apron of Enrique is composed of moderately sorted sands composed of Halimeda, coral, coralline algae, and mollusk fragments. This area is relatively barren, although Thalassia covers part of the area and there is evidence of abundant burrowing activity. In contrast, a large part of the backreef of Media Luna is covered with A. cervicornis thickets. The difference in coral abundance is clearly related to available wave energy. Zonation of the forereef is similar to other Caribbean coral reefs. However, the Lithothamnium ridge found in other reefs is replaced by Millepora. On Enrique, the zones are sharply defined and narrow in depth range, probably because of the low amplitude of available wave action. The zonation on Media Luna is less well defined, but there is a development of spur-and-groove structures. The shelf is at a fairly uniform 20-m depth. Seismic records and bathymetry indicate that the shelf is of structurally controlled subaerial origin with limited modification by post-submergence reef development and sedimentation. The reefs have formed either on sand ridges or on the south limb of a syncline of Cretaceous rocks. Growth of 20 m in approximately 6,000 years gives a rate of 0.3 cm/year for the reefs.

Abstract Abstract The West Flower Garden Bank is located in the northwest part of the Gulf of Mexico at lat. 27°52.6’N, long. 93°49.0’W. It is one of more than 100 knolls that exist on the outer continental shelf between the Mississippi Canyon and Corpus Christi, Texas. The reef has been surveyed and sampled by surface océanographie vessels. It has also been observed and sampled using a submersible. The living reef rises from a depth of 45 m to a crest at 20 m. Its faunal composition places it in the Diploria-Montastrea-Porites zone of typical West Indian reefs. Surrounding the reef, from a depth of about 45 m to 90 m, is a gently sloping sediment apron. The facies that occur on this apron are: (1) coral debris, 45-51 m; (2) algal nodule, 51 -73 m; (3) Amphistegina , 73-91 m; and (4) quartz -planktonic foraminifers, below 91 m. Three dead barrier-reef levels have been found at depths of 56, 91, and 127 m. Behind these reefs are scattered dead patch reefs in various stages of burial by surrounding sediments. The levels of the dead reefs coincide quite well with published sea-level curves. Detritus recovered in a core from the 91-m reef was dated at 19,300 ± 400 years B.P. Pétrographie examination of reef detritus from this level shows that cementation by marine prismatic calcite was followed by freshwater vadose cement. This observation supports Logan’s contention that late Wisconsin sea level stood at approximately —91 m and that there was a rapid withdrawal to —127 m, followed by a transgression to the present level that began about 18,000 years B.P. The last transgression was interrupted by pauses and/or possible reversals.

Abstract Abstract Patch reefs are a significant component of the geologic record; thus an understanding of their modern analogs is important. Coral and foraminiferal communities of 32 randomly selected patch reefs from the lagoon of Glovers Reef Atoll, Belize (formerly British Honduras), were studied. Samples of patch-reef tops, flanks, and adjacent lagoon floor were also examined for quantitative differences in sediment composition and texture. The grain-size distribution and sorting reflect the influences of wave energy and depth on the patch reefs. The uniformity of the sedimentologic patterns from one patch reef to another reflects the uniformity of these environmental parameters in the lagoon. The foraminiferal assemblages, including a Quinquefocu/ina-D \scorb \dae-Archaias-Homotrema reef-top assemblage and a Quinqueloculina-Cribroelphidium-Archaias lagoon-floor assemblage, occur on patch reefs throughout the lagoon. Although the foraminiferal assemblages and the sediment-distribution patterns did not vary significantly from one patch reef to another, there was considerable variation in the coral-algal assemblages. Three “end-member” coral-algal assemblages were recognized: (1) the Montastrea assemblage which tends to have a high degree of faunal zonation and is dominated by the species Montastrea annularis, Acropora cervicornis, A. palmata, and Diploria strigosa; (2) the Acropora assemblage which is less well zoned and is dominated by Acropora cervicornis, A. palmata, and Porites porites; and (3) the A\gae-Porites assemblage which is poorly zoned and is dominated by sparse colonies of Porites porites and Acropora cervicornis. The three assemblages are gradational with each other across the atoll. They change from Montastrea assemblages in the southern portion to Acropora assemblages in the central portion to Algae-Porites assemblages in the northwestern portion of the lagoon. These coral-algal assemblages mimic, in a general way, assemblages recognized on seaward reef slopes, but depth and wave energy, used to explain seaward zonations, cannot explain the distribution of these patch-reef assemblages. No other environmental differences were recognized within the lagoon that could explain these patterns. In fact, the uniform distribution of the foraminiferal assemblages and the similarity of the sedimentologic patterns from one patch reef to another argue against any such differences. An alternative possibility is that the assemblages may reflect different stages of recolonization of a patch reef following some infrequent environmental change that caused the demise of the coral populations. The assemblages may reflect stages in coral-population successions: the Algae- Porites assemblage representing an early colonizing stage, the Acropora assemblage an intermediate stage, and the Montastrea assemblage a later mature stage. If this hypothesis is correct, the environmental change probably occurred most recently, or had its greatest effect, in the northwestern portion of the lagoon which is most distant from channels through the main reef tract. The southeastern portion of the lagoon is closer to channels through the reef; thus this region might be less affected or would return to normal more quickly during a period of environmental stress. However, care must be taken when interpreting fossil coral assemblages. These assemblages may be indicators of different environmental regimes or they may be indicators of environmental predictability within regions of otherwise similar environmental parameters.

Abstract The deep forereef, a rugged, near-vertical to overhanging cliff, extends from 55 m to approximately 122 m below sea level off Discovery Bay, on the north coast of Jamaica. This cliff is being constructed near its top by a complex, living reef-coral community which extends to approximately 70 m, where it merges with a community dominated by sponges. Active framework construction by sclerosponges, coupled with the lithification of unconsolidated sediment (largely coral and algal debris from above) which is retained by large debris and living sponge “dams,” occurs to depths of approximately 105 m. Below this depth the deep forereef does not appear to be actively accreting seaward. The cliff face consists of a series of irregular, alternating promontories and reentrants. As in shallower reef zones, framework construction and organism diversity are maximized on the promontories, whereas the reentrants are regions of active downslope sediment movement and, near the base of the cliff, of active erosion. The island slope which laps up against the base of the deep forereef either is covered with un-lithified sediment and debris or consists of an unconformity surface of densely cemented debris (reef rock) undergoing intense biologic erosion. Nearly 50 m of densely lithified island slope deposits appears to have been exhumed in one area. Unl”unified reef sediment, which is retained behind various kinds of reef-derived debris, rapidly decreases both in abundance and in grain size downward to 305 m, where pelagic sediment predominates. Below 200 m, rounded limestone blocks as tall as 30 m protrude upward through the island-slope sediment in the axis of a submarine canyon. These limestone blocks are also undergoing intense biologic erosion.

Abstract Abstract Neogene and Holocene volcanism in the Lesser Antillean arc has been explosive in character, and bioherms and carbonate platforms are only slowly established on young volcanic islands owing to the general instability of the pyroclastic shorelines. However, islands inactive for more than several million years begin to develop massive carbonate platforms, and the size and maturity of the eventual platforms depend in large part on the length of the quiescent period. The resulting platforms have been variously subjected to sea-level changes, minor tectonic uplift or subsidence, and, in a few cases, renewed volcanism. Windward Holocene coral reefs up to at least 14 m thick and algal ridges up to 10 m thick are abundant on older island cores or carbonate caps in the eastern Caribbean. The Holocene bioherms are structurally of two types: bench and bank barrier. Bench bioherms are predominantly coral or coralline frameworks throughout, and occur at present depths of less than 6 to 10 m on wave-cut Pleistocene benches or other mound or edge features. They are most abundant on raised or emergent carbonate islands. Bank-barrier reefs formed initially as elongate horseshoe or spit-shaped arcs of carbonate sand and rubble trapped by head corals. They are well developed where extensive carbonate shelfs are found at present depths of 10 to 20 m. The cap facies of bank barriers are coral or coralline frameworks similar to those found in bench bioherms. The deeper layers of these bioherms (greater than 6 to 10 m) are dominated by Montastrea annularis. Acropora cervicornis commonly is present in mid-reef zones but, perhaps because of the common heavy swell, it is not as important a framework builder here as it is in the central and western Caribbean. Above 6 to 10 m, the reef frameworks consist mostly of Acropora palmata, Millepora, or coralline algae, depending on wave energy. High island reefs with turbid coastal waters are characterized by reef crests coated with fleshy algae. Although the crests of some shelf-edge reefs in the Lesser Antilles are emergent and therefore barrier reefs, most shelf edges lie at depths of 15 to 30 m and have little Holocene framework. Extensive shelf-edge barrier or atoll reefs, such as are characteristic of the central Pacific and Australian plates and which occur in the westernmost Caribbean, are not present. In this respect, the Lesser Antillean arc is similar to the seismically active island arcs of plate margins in the Indo-Pacific. The glaciation of Antarctica in Miocene to Pliocene time produced a marked drop of sea level which had the effect of raising all Miocene and older reefs. However, the generally subsiding shelf-edge reefs on islands removed from plate margins resumed Pliocene-Pleistocene building on the older reef structures after a hiatus of several million years. Nonsubsiding shelf-edge reefs were “permanently” raised and new shelf-edge reefs formed against the seaward walls of the original platforms. During the Pleistocene, with interglacial “high” sea levels at intervals of 100,000 to 200,000 years, the reefs of subsiding platforms would have had to build only a few meters at each high stand to remain at their present emergent levels. The stable platforms, developing new shelf-edge reefs, would have their shelf edges built to the average high sea stand of the more numerous inter-stadials (about 25 m below present sea level). We conclude that the reefs of the Lesser Antilles are not “inferior” to Indo-Pacific reefs because of climatic or biotic factors, but rather are typical of reef development in seismic belts where general subsidence is absent.

Abstract Abstract The model of island-arc sedimentary environments proposed by Dickinson also applies to the Cretaceous volcaniclastic formations of Jamaica. Coarse volcaniclastic units with ash flows, lava flows, agglomerates, and laharic breccias belong to the central facies developed near active volcanic vent centers. Finer grained, bedded volcaniclastic units associated with shales and some limestone units are placed in the dispersal facies, representing distance from or quiescence of vent centers. The Cretaceous succession in central Jamaica contains more units typical of the central facies; westward, the sequence grades mainly into the dispersal facies, indicating increasing distance from the vent centers. Coral-rudist limestones, which occur dominantly in the dispersal facies, are characterized by mainly rudist frameworks associated with four coral assemblages, which either surround, encrust, or are interstitial to rudists. The assemblages are (1) Paracycloseris-Trochoseris-Actinacis assemblage, (2) Multicolumnastrea-Astrocoenia-Actinacis assemblage, (3) Multicolumn-astrea-Actinacis-Dictuophyllia-Dichocoenia assemblage, and (4) Dichocoenia trechmanni assemblage. These coral-rudist limestone units are interpreted as very shallow-water shelf structures, unre-sistant to wave action, which developed at the beginning of transgression or toward the end of regression; these periods alternated with phases of volcanic activity. The complexity, diversity, and abundance of coral-rudist frameworks increased during Cretaceous time, apparently in conjunction with decreasing volcanism and increasing arc-shelf area.

Abstract Abstract Paleoecologic reconstruction of the abundant Cenozoic fossil record of Caribbean reefs is basically dependent on uniformitarian comparisons with the biologic and geologic systems forming modern reefs. Much of the present-day coral-reef food web, however, has no mineralized skeletal parts and therefore has a low preservation potential. Detailed direct methods of reconstructing ancient reef systems must depend largely on analysis of the abundance and distribution of organisms which have hard skeletons. The most useful models for reconstructing the ecology of Caribbean Paleocene-Oligocene reefs are those of the modern Indo-Pacific biotic province, because a substantial part of the Indo-Pacific reef biota descended from lineages which were cosmopolitan during the Paleogene. Because of the mixed cosmopolitan and provincial faunal makeup of early Miocene reef biotas in the Caribbean, uniformitarian comparisons of their ecology with that of modern-day descendants are more complicated than for Paleogene assemblages. Caribbean middle Miocene to Pliocene reef assemblages became increasingly provincial with the extinction of many remnant Paleogene lineages of large forams, the progressive disappearance of cosmopolitan Indo-Pacific lineages of reef-building corals, and the evolution of modern species of mollusks and reef-building corals. Major changes in the ecologic distribution and abundance of key reef biota occurred in the late Neogene and Pleistocene. In order to evaluate effectively how much of ancient reef ecosystems can be reconstructed by comparison with modern reefs, it is necessary to take into account not only the proportion of skeleton-bearing groups at each trophic level, but also the actual importance of each group in terms of standing-crop biomass and contribution to the skeletal record of benthic biota. The potential skeletal record of standing-crop biomass is poorest for benthic plants (producers) in all reef habitats. The proportionate paucity of identifiable skeletal material from the producers is therefore multiplied many times in the resultant accretionary skeletal record because their productivity rates are so much higher than consumers on the reefs. Major conclusions on the ecology of middle Eocene through Pleistocene fossil reefs are: (1) the capacity of Paleogene framework biota to construct and maintain reef structures reached a peak during the Oligocene; (2) reef-framework biota experienced a profound reduction in diversity in the earliest Miocene, with resulting change in the types and abundance of reef structures formed; and (3) the vigor and luxuriance of framework biota appear to have increased throughout the late Miocene and Pliocene.

Abstract Abstract That coralgal reefs recover readily from natural disasters is widely known. Storm destruction even embodies aspects of self-rejuvenation and/or extension of the colony, rather like forest fires. Such natural catastrophes do not affect reefs in ways from which they cannot recover; man affects things differently. Reefs are abundant on Venezuelan islands, but are limited to local favorable sites on the Caribbean coast. The increase of wealth and travel since World War II has inadvertently resulted in damage to some reefs at Chichiriviche. The small fringing reef there has changed, in a decade, from a healthy reef with a normal complement of fish to a dull and mostly dead mass under turbid water. The reef is rimmed by dead Acropora palmata in growth position; the A. cervicornis and massive corals are partly dead. Soft algae and bryozoans drape most surfaces and the bottom is coated with mud of loose organic floccules and fine mineral sediment. Udotea is uncommon and apparently decadent. Halimeda and Penicilius are more abundant, but are partly dead and heavily coated with the pervasive floccules. Similar conditions prevail on the southwest side of Cayo de Los Muertos and on the patch reefs in Bah’a Chichiriviche. This damage is due to increase in human and industrial wastes, consequent upon a new public water supply built in 1963. The developed terrain is of highly permeable quartz or skeletal sand, and is less than 2 m in elevation. Both residential and small industrial sources add locally insupportable amounts of particulate and soluble organic wastes by dumping, drainage, or sewage. A cement company dumps its waste, trash from visiting ships, and the rinse from its kiln into the bay.

Abstract Abstract As many as 500 species of sponges are estimated to occur in Caribbean reef habitats down to a depth of 120 m. Fully 90% of these belong to the Class Demospongiae,the rest are species of the Classes Calcarea and Sclerospongiae. The scarcity of siliceous sponge spicules in reef sediments may be related to the slow growth rate of many reef sponges as well as the rapid dissolution of spicules in the unsaturated waters above reefs. Excavating sponges of three families play a role in the erosional remodeling of reefs, and the particles excavated from calcareous skeletons and rocks by these sponges may make up as much as 30% of the sediments of reef environments. The massive aragonitic skeletons of sclerosponges contribute to the primary framework of the deep forereef and help strengthen and build out the walls of caves, tunnels, and crevices in shallower reef environments.

Abstract Abstract Coral colony survival depends greatly on the ability of their skeletal structures to minimize destruction caused by waves and currents. Hydrodynamic theory has been used to calculate the mechanical stresses operating on coral structures from currents, nonbreaking waves, and breakers. These calculations suggest two adaptive strategies are available to corals for minimizing hydraulically induced stress: (1) reduction in branch size and transformation of the corallum to massive hemispherical or encrusting form, and (2) development of oriented branched colonies. Strategy 1 is characteristic of Pocillopora, Montipora, Acropora, and the hydrozoan Millepora. Strategy 2 is characteristic of Acropora, particularly A. palmata. Measurement of hydraulic conditions and colony morphology for A. palmata from Isaac Bay reef, St. Croix, supports our theoretical predictions regarding (1) distribution of branch azimuths; (2) angles of attack of branches, (3) colony eccentricity and alignment relative to flow, and (4) variation in branch shape and size. Hydraulically satisfactory morphology probably develops by a combination of a tropistic polypary growth response to prevalent flow conditions and a hydraulic selection process that destroys branches and colonies unsuited for the ambient hydraulic conditions.

Abstract Abstract Observations off Bonaire, Netherlands Antilles, support the recent contention that Caribbean reefs are occasionally subjected to low-water emergence and are therefore more similar to reefs of the Indo-Pacific than previously believed. Off Bonaire, some incipient reef flats and the shallow floor between the flats and shore are sporadically awash for extended periods of time. Most of the corals (representatives of over 20% of ail known Caribbean species) that inhabit the emergent biotopes appear to be able to endure subaerial exposure without severely deleterious effects. However, destruction of Montastrea annularis either results directly from exposure or, more probably, is initiated by it. Bonaire’s shallow-water reefs are of three types. The type that occurs in turbulent water is composed almost entirely of Acropora palmata and is therefore similar to the typical, shallow-water reefs of the Caribbean. The two types that are found in calm water differ considerably in species composition from typical Caribbean reefs and differ from one another as a consequence of whether they undergo or escape emergence. Calm-water reefs that are constantly immersed consist almost exclusively of nearly continuous colonies of Montastrea annularis. Those that are intermittently emergent are the result of a succession of heterogeneous corals. Construction of the reefs of varied corals was begun by abundant large colonies of M. annularis, but most of these colonies were killed when they attained sizes at which their summits were subaerially exposed during exceptionally low stands of the sea. Following the decline of the M. annularis colonies and erosion of their coralla by boring organisms, construction of the reef framework was continued by an extraordinarily diverse coral assemblage. Framework building has been culminated upward by the establishment of exposure-tolerant corals and other cnidarians, but the diverse assemblage is maintained on the reef flanks and deeper portions of the flats. The diversity of the corals (32 of the 48 species found off Bonaire) that are involved in the formation of the sometimes emergent reefs is unusual in shallow water in the Caribbean; such diversity is usually associated only with much deeper reef zones. Because Montastrea annularis has been shown to be dominant over most of the corals of the unusually diverse, shallow-water reef assemblage in the extracoelenteric-digestion hierarchy (i.e., a “pecking order” in which representatives of subordinate coral species are consumed and thereby eliminated from competition for reef space by those that are more aggressive), the diversity of the assemblage is attributed to the initial decimation and continued control by emergence of the once prolific colonies of this coral.

Abstract Within the Caribbean region, Montastrea annularis is considered to be a major contribu¬tor to framework construction in both modern and fossil coral reefs. The species forms large colo¬nies over a wide depth range, which in places may extend to as much as 100 m. Growth-rate data for this hermatypic scleractinian are of considerable interest, as, for example, in establishing maxi¬mum limits for reef development over long periods of time. Also of interest are the effects of environmental parameters such as water temperature, depth, and light on growth rate. Growth-rate values for Montastrea reported in the literature span a remarkably wide range, with nearly an order of magnitude separating maximum and minimum measurements of annual increment in colony height. Long-term monitoring studies, in which the dimensions of a given colony are repeatedly measured, are not only time consuming and costly, but also require that the specimens be handled during the measuring process. Skeletal X-radiography, a new method for determining coral growth, has several important advantages over conventional techniques. From annual density-variation bands in the carbonate skeleton, it is possible to obtain a wealth of quantitative growth data from corals that have lived in their natural reef environment undisturbed by human experimentation. Many years of growth are recorded in a single colony. X-radiographs were taken of 59 specimens of M. annularis and M. cavernosa from five Caribbean sites (Jamaica, Barbados, Key West, Belize, and Panama). Although there is considerable variability in annual growth increment from one colony to another within a population consisting of one species—at one depth and at one reef location—the linear increase in height (measured along the axis of maximum growth) for M. annularis in water less than 3 m deep falls within the range 3 to 12 mm/year. These rates are generally lower than those reported by others, but they are comparable with values determined for another faviid coral, Platygyra, in the Indo-Pacific. The results also indicate that M. cavernosa grows more slowly than M. annularis under similar environmental conditions. Observed growth rates for shallow-water M. annularis are highest at Belize, lowest at Key West, and intermediate at Barbados and Jamaica. A plot of mean growth rate versus mean annual water temperature at these localities provides a preliminary estimate of the temperature dependence of growth rate: 0.94 mm/year/°C. The result is similar to that for the Indo-Pacific coral Platygyra (0.9 mm/year/°C) which has been studied over the temperature range 23.9 to 29.3°C. It is increasingly evident that,because of the individual variability in growth rates exhibited by corals in their natural habitats, further investigation of the factors that control coral growth will necessitate statistical analysis of large quantities of data. For this purpose, X-ray examination of the skeleton is ideally suited. Seasonal density banding, further¬more, appears to be well preserved in coral fossils, thereby making possible the study of coral development in ancient reefs; examples include M. annularis (original aragonite) from elevated Pleistocene reefs of Barbados, and an unidentified faviid coral (recrystallized to calcite) of Miocene age from Saipan.