North Jamaica Research Articles

Fossil Echinoids from the Upper Pliocene Hopegate Formation of North Central Jamaica

The Upper Pliocene Hopegate Formation has been the least attractive limestone unit for paleontological investigation in the Cenozoic of Jamaica due to its extreme lithification and dolomitization, despite the scientific appeal of it being a rare example of a Pliocene raised reef in the Caribbean. Preservation of invertebrate macrofossils is commonly moldic. Hitherto, few named macrofossils from the unit have been published. New and extensive exposures of the Hopegate Formation have become available since 2002 as the main north coast road has been re-engineered in central north Jamaica. Echinoids were previously unknown from this formation, but at least seven taxa are now recognized, namely, Eucidaris tribuloides (Lamarck), Echinometra viridis A. Agassiz, regular echinoids spp. indet., Echinoneus sp. cf. E. cyclostomus Leske, Schizaster sp. cf. S. doederleini (Chesher), Meoma? sp. and Brissus sp. cf. B. unicolor (Leske). The identifiable genera are typical of modern shallow water environments of the Caribbean. With the exception of Meoma? and Brissus, these nominal genera have also been identified from the coeval Bowden Formation, a deeper water deposit with a mixed allochthonous/autochthonous echinoderm fauna. In contrast to the Bowden Formation, which has yielded numerous fragmentary, but well preserved, echinoderm specimens, the Hopegate Formation has yielded only rare, poorly preserved echinoid tests and rarer fragments.

The Influence of Extreme Climate Events on Models of Coral Colony Recruitment and Survival in the Caribbean

Knowledge of coral recruitment patterns helps us understand how reefs react following major disturbances and provides us with an early warning system for predicting future reef health problems. We have reconstructed and interpreted historical and modern-day recruitment patterns, using growth modeling, in order to understand how hurricanes, storms and bleaching events have influenced coral recruitment in the Caribbean. The results indicate that regional hurricane events negatively impact coral recruitment patterns in the Caribbean, from the south in Tobago to more northerly areas in Belize and Jamaica. However, despite multiple large-scale disturbances, corals are still recruiting to marginal reef systems, and to the Mesoamerican Barrier reef off the coast of Belize. While recruitment and initial growth since the Caribbean-wide bleaching event of 2005 has been successful for Colpophylia natans at the sites studied in North Jamaica, medium and large sized colonies of this species have decreased in numbers since the bleaching event at most sites, except where the rugosity is highest, at Dairy Bull reef.

Sustainable Tourism and Management for Coral Reefs: Preserving Diversity and Plurality in a Time of Climate Change

Coral reefs throughout the world are under severe challenges from a variety of anthropogenic and environmental factors. In a period of climate change, where mobility and tourism are under threat, it is useful to demonstrate the value of eco- and research-tourism to individuals and to cultures, and how diversity and pluralism in sustainable environments may be preserved. Here we identify the ways in which organisations use research tourism to benefit ecosystem diversity and conservation, show how an Earthwatch project has produced scientific information on the fringing reefs of North Jamaica, and how a capacity-building programme in Belize developed specific action plans for ecotourism. We discuss how implementation of those plans can help research tourism and preserve ecosystem diversity in times of climate change.

Topography and spatial arrangement of reef-building corals on the fringing reefs of North Jamaica may influence their response to disturbance from bleaching

Knowledge of factors that are important in reef resilience helps us understand how reefs react following major environmental disturbances such as hurricanes and bleaching. Here we test factors that might have influenced Jamaican reef resilience to, and subsequent recovery from, the 2005 bleaching event, and which might help inform management policy for reefs in the future: reef rugosity and contact of corals with macroalgae. In addition, we test in the field, on Dairy Bull reef, whether aggregated Porites astreoides colonies exhibit enhanced growth when exposed to superior competition from Acopora palmata, as has been found by experiment with the Indo-Pacific corals Porites lobata and the superior competitor Porites rus [Idjadi, J.A., Karlson, R.H., 2007. Spatial arrangement of competitors influences coexistence of reef-building corals. Ecology 88, 2449-2454]. There were significant linear relationships between rugosity and the increase in smallest size classes for Sidastrea siderea, Colpophyllia natans, P. astreoides and Agaricia species, and between rugosity and cover of the branching coral Acropora cervicornis. Linear extension rates of A. cervicornis and radial growth rates of P. astreoides were significantly lower (p<0.025; F>6) when in contact with macroalgae. Aggregated colonies of P. astreoides in contact with one another, one of which was in contact with the faster growing competitor A. palmata showed significantly greater growth rates than with just two aggregated P. astreoides colonies alone. These findings suggest that three dimensional topography and complexity is important for reef resilience and viability in the face of environmental stressors such as bleaching. Our findings also support the idea that aggregated spatial arrangements of corals can influence the outcome of interspecific competition and promote species coexistence, important in times of reef recovery after disturbance.

Scleractinian coral population size structures and growth rates indicate coral resilience on the fringing reefs of North Jamaica

Coral reefs throughout the world are under severe challenges from many environmental factors. This paper quantifies the size structure of populations and the growth rates of corals from 2000 to 2008 to test whether the Discovery Bay coral colonies showed resilience in the face of multiple acute stressors of hurricanes and bleaching. There was a reduction in numbers of colonies in the smallest size class for all the species at all the sites in 2006, after the mass bleaching of 2005, with subsequent increases for all species at all sites in 2007 and 2008. Radial growth rates (mm yr −1) of non-branching corals and linear extension rates (mm yr −1) of branching corals calculated on an annual basis from 2000–2008 showed few significant differences either spatially or temporally. At Dairy Bull reef, live coral cover increased from 13 ± 5% in 2006 to 20 ± 9% in 2007 and 31 ± 7% in 2008, while live Acropora species increased from 2 ± 2% in 2006 to 10 ± 4% in 2007 and 22 ± 7% in 2008. These studies indicate good levels of coral resilience on the fringing reefs around Discovery Bay in Jamaica.

Bacterial iron oxide reduction in a terrigenous sediment-impacted tropical shallow marine carbonate system, north Jamaica

Discovery Bay, a carbonate-dominated embayment in north Jamaica, has been subject to inputs for 40 years of iron-rich bauxite sediment associated with the local mining and transport of processed bauxite. As such, this site is an ideal natural laboratory to study the records and impacts of iron oxide inputs upon geochemical, diagenetic, and microbial processes in tropical carbonate sediments. Total Fe contents in sites in the bay not receiving bauxite inputs are negligible and porewater Ca 2+, SO 4 2− and Cl − indicate that bacterial sulphate reduction is an important process. In contrast, surface sediments receiving bauxite inputs contain significant total Fe, from 44 μmol/g in shallow (5 m water depth) sites to 110 μmol/g in deeper (20 m water depth) sites. Up-core increases in total Fe record increased temporal inputs into the bay. Within these Fe-rich sediments porewater data shows the presence of Fe II released by bacterial Fe III reduction. There is no direct evidence for significant bacterial sulphate reduction in these sediments. Iron oxides within all bauxite-impacted sediments display a high potential reducibility, from 40% to 80% of the total Fe present as dithionite-extractable Fe III. Experimental analysis of the potential susceptibility to, and rates of, bacterial Fe III reduction, utilising Discovery Bay sediment and Shewanella putrefaciens CN32 (a known Fe III-reducer) has confirmed the high bacterial reducibility of iron oxides within the sediment. Up to 75% of initial dithionite-extractable Fe III in the sediments was reduced over 15 days. The presence of iron oxides within the Discovery Bay shallow marine carbonate systems has markedly altered the chemical diagenetic processes taking place, with a shift from apparent dominance of bacterial sulphate reduction at non-impacted (Fe-poor) sites, to highly significant bacterial Fe III reduction in Fe-rich bauxite-impacted sediments. Given the perceived global increases in terrigenoclastic sediment inputs into tropical carbonate systems as a result of land-use and climate changes, coupled with the documented role that iron oxide reduction plays in nutrient and contaminant cycling in sediment systems, more research into the perturbation of early diagenesis by iron oxide inputs is required.

Distributional patterns and community structure of Caribbean coral reef fishes within a river‐impacted bay

This study examined how riverine inputs, in particular sediment, influenced the community structure and trophic composition of reef fishes within Rio Bueno, north Jamaica. Due to river discharge a distinct gradient of riverine inputs existed across the study sites. Results suggested that riverine inputs (or a factor associated with them) had a structuring effect on fish community structure. Whilst fish communities at all sites were dominated by small individuals (&lt;20 cm), diversity and total biomass were reduced with increased proximity to the river mouth. The abundance of all fishes, but particularly small‐bodied, juvenile and herbivorous fishes was reduced in turbid water when compared to clear‐water sites. Results strongly suggest that fluvial sediment inputs may play an important role in structuring fish assemblages even under intense fishing pressure.

Inhibition of dissolution within shallow water carbonate sediments: impacts of terrigenous sediment input on syn‐depositional carbonate diagenesis

AbstractThe early diagenetic chemical dissolution of skeletal carbonates has previously been documented as taking place within bioturbated, shallow water, tropical carbonate sediments. The diagenetic reactions operating within carbonate sediments that fall under the influence of iron‐rich (terrigenous) sediment input are less clearly understood. Such inputs should modify carbonate diagenetic reactions both by minimizing bacterial sulphate reduction in favour of bacterial iron reduction, and by the reaction of any pore‐water sulphide with iron oxides, thereby minimizing sulphide oxidation and associated acidity. To test this hypothesis sediment cores were taken from sites within Discovery Bay (north Jamaica), which exhibit varying levels of Fe‐rich bauxite sediment contamination. At non‐impacted sites sediments are dominated by CaCO3 (up to 99% by weight). Pore waters from the upper few centimetres of cores show evidence for active sulphate reduction (reduced SO4/Cl− ratios) and minor CaCO3 dissolution (increased Ca2+/Cl− ratios). Petrographic observations of carbonate grains (specifically Halimeda and Amphiroa) show clear morphological evidence for dissolution throughout the sediment column. In contrast, at bauxite‐impacted sites, the sediment is composed of up to 15% non‐carbonate and contains up to 6000 μg g−1 Fe. Pore waters show no evidence for sulphate reduction, but marked levels of Fe(II), suggesting that bacterial Fe(III) reduction is active. Carbonate grains show little evidence for dissolution, often exhibiting pristine surface morphologies. Samples from the deeper sections of these cores, which pre‐date bauxite influence, commonly exhibit morphological evidence for dissolution implying that this was a significant process prior to bauxite input. Previous studies have suggested that dissolution, driven by sulphate reduction and sulphide oxidation, can account for the loss of as much as 50% of primary carbonate production in localized platform environments. The finding that chemical dissolution is minor in a terrigenous‐impacted carbonate environment, therefore, has significant implications for carbonate budgets and cycling, and the preservation of carbonate grains in such sediment systems.

Temporal shifts in reef lagoon sediment composition, Discovery Bay, Jamaica

Discovery Bay, north Jamaica, forms a large (1.5 km wide), deep (up to 56 m) embayment that acts as a sink for reef-derived and lagoonal carbonate sediments. Since the mid-1960s, the bay has also provided a sink for inputs of bauxite sediment that are spilled during loading at a boat terminal constructed within Discovery Bay. Bauxite has accumulated across much of the southern section of the bay with surficial sediments presently composed of up to 35 weight% non-carbonate. Cores recovered from sites on the western side of the bay provide a stratigraphic record of this history of bauxite contamination across water depths from 5 to 25 m. The bauxite-influenced upper sediment horizons are clearly visible in each core from the distinctive red–brown colouration of the sediment. These sediments are composed of approximately 10% non-carbonate (bauxite) and have Fe contents of around 2–3000 μg/g (up to 7000 μg/g). The thickness of this upper bauxite-contaminated sequence increases down transect (approximately 18 cm in the shallowest core, to around 47 cm in the deepest core), and in each core overlies a sequence of ‘clean’ lagoon carbonates. These typically are poorly sorted carbonate sands with variable amounts of coral rubble. Down-core data on CaCO 3 and Fe content provide a chemical record of decreasing sediment contamination with depth, with the lower ‘clean’ carbonates composed of only around 2% non-carbonate and <700 μg/g Fe. Down-core sediment-constituent data also indicate significant changes in sediment production at the shallowest sites. At depths of 5 and 10 m, sediment assemblages have shifted from diverse assemblages of coral, mollusc, Amphiroa and Halimeda in the clean lagoon sands, to assemblages dominated by Halimeda and Amphiroa within the surficial sediments. At the deeper sites, no major down-core shifts in sediment constituents occur. These sites thus record a rather complex history of changes in sediment composition and chemistry. Clear shifts in chemistry and stratigraphy occur in all the cores and reflect progressive bauxite contamination in the near-surface horizons. These inputs, however, do not appear to have directly affected carbonate production, since the major constituent changes appear to be a response to more regional declines in coral community and reef status.

Impacts of Bauxite Sediment Inputs on a Carbonate-Dominated Embayment, Discovery Bay, Jamaica

Sub-tidal, reef-lagoon surficial sediment samples from Discovery Bay, north Jamaica were analysed in order to quantify the impacts of anthropogenic bauxite inputs on trace metal (Fe, Zn, Mn) levels and sediment characteristics. Contaminant levels exhibit marked spatial variations, but are highest across central and southern parts of the bay and primarily reflect wind blown inputs, modified by subsequent suspended sediment transport. Highest contaminant levels (Fe—13,701 ppm, Mn—237 ppm, Zn—74 ppm) occur immediately adjacent to, and just north-east of, a bauxite loading terminal in the south-west of the bay. Sites of high sediment contamination are negatively correlated with per cent CaCO3 content, indicating the diluting effect of bauxite on the carbonate substrate. At high contamination sites CaCO3 levels are reduced to 63.7% and are in the range of 75–80% across much of the central and southern area of the bay. Magnetic susceptibility level measurements are positively correlated with iron and negatively correlated with CaCO3 content, and indicate the potential for using magnetic susceptibility measurements in metal contaminant tracing studies in carbonate environments. Whilst metal contamination levels are low compared with many clastic-dominated systems, and are currently at levels unlikely to impact the reef biota, the data indicate both the progressive contamination of this previously carbonate-dominated lagoon environment, and the potential for such terrestrial inputs to impact upon sediment characteristics in such restricted settings.

Biological degradation of coral framework in a turbid lagoon environment, Discovery Bay, north Jamaica

The potentially negative effects of increased sedimentation on corals are well documented, whereas, the impacts upon early diagenetic processes, such as bioerosion, remain poorly understood. This study examined macroboring through image analysis of coral slabs from two high sedimentation and turbid reefs, Columbus Park and Red Buoy, within Discovery Bay, north Jamaica. Infestation of coral framework by macroborers was significant at both Columbus Park and Red Buoy for all depth zones sampled: 0–8 m (6.5 versus 8.3%), 8–16 m (11.4 versus 10.7%), and 16–25 m (6.2 versus 18.5%), with only the deepest zone significantly different (P 90%) assemblages in clear-water settings towards a greater relative importance of worms (up to 17.2%) and bivalves (up to 40.5%) with increasing sedimentation. The high infestation levels of the bivalve Lithophaga spp. offset the reduced sponge bioerosion. As a result, macroboring infestation levels are comparable to those reported from adjacent clear-water reef sites. This study indicates that macroboring of coral framework continues under environmental conditions previously inferred to be detrimental to coral growth and survival.

Impacts of light penetration on the bathymetry of reef microboring communities: implications for the development of microendolithic trace assemblages

Sediment samples recovered from three proximate reef environments in north Jamaica, characterised by different light penetration regimes, reveal marked variations in the bathymetric range of sediment microboring communities. In contrast to clear water environments, assemblages developed in turbid water conditions undergo both bathymetric restriction and compression in their range. In clear water sites, the upper photic–lower photic zone transition occurs between depths of 20–30 m. This is marked by a shift from a predominance of cyanobacterial (e.g., Eurygonum nodosum, Scolecia filosa, Fasciculus frutex and Fasciculus dactylus) and chlorophyte (e.g., Rhopalia catenata, Fasciculus grandis, Reticulina elegans and Scolecia botulifera) traces, to assemblages dominated by the traces E. nodosum and S. filosa (cyanobacteria), F. grandis (chlorophyte), Palaeoconchocelis starmarchii (rhodophyte) and Orthogonum fusiferum and Saccomorpha sphaerula (fungi). At sites characterised by intermediate levels of turbidity this same assemblage transition occurs at around 15–20 m depth and at the most turbid site at depths of only 5–10 m. Integration of assemblage data and light readings indicates that this transition occurs where percentages of surface light illumination are reduced to around 10–15%. Compression of the lower photic zone is so extreme at the most turbid site, that microboring assemblages at only 30 m depth show evidence of a transition to an assemblage associated with dysphotic (<1% of surface illumination) conditions. This is dominated by fungal boring traces. Given that microendolithic assemblages have been widely considered to represent useful palaeobathymetric indicators, this study illustrates that it is more accurate to regard assemblages as indicative only of photic zones. The bathymetric range and extent of zones clearly varies significantly as light penetration levels change. Caution is thus needed in the extrapolation of assemblage or ichnocoenosis data to specific bathymetric ranges.

Macroboring of Pleistocene Coral Communities, Falmouth Formation, Jamaica

Abstract Coral samples recovered from the Falmouth Formation in north Jamaica, an emergent Pleistocene (Sangamonian) fringing reef complex, contain a wide range of boring morphologies belonging to the ichnogenera Entobia (7 (+1?) ichnospecies), Gastrochaenolites (2 ichnospecies), Maeandropolydora and Trypanites. Sampling from four distinct shallow-water reef biofacies permitted quantification of spatial variations in boring community composition and degree of substrate infestation. Coral samples from back-reef/lagoon facies (mostly coral rubble) are characterized by diverse assemblages of borers, dominated by both sponge and “worm” borings, but with bivalve borings locally important. By contrast, shallow fore-reef facies are dominated by sponge borings, with “worm” borings locally important and bivalve borings rare or absent. Highest rates of substrate infestation (expressed as a % of framework removed by borers) occur within lagoon/back-reef samples. Although facies constraints (especially the absence of...

Factors Controlling Sediment Preservation on a North Jamaican Fringing Reef: A Process-Based Approach to Microfacies Analysis

ABSTRACT Compositional characteristics of limestones are fundamental to the interpretation of depositional environments, with an assumption that preserved grain assemblages preserve sufficient evidence of initial sediment input to enable delineation of environments. It is acknowledged, however, that a range of early diagenetic processes (including encrustation, fragmentation, abrasion, microboring, dissolution, cementation, and recrystallization) may influence grain preservation potential, and thus bias the composition of resultant grain assemblages. This study examines the effects and relative importance of a range of early diagenetic processes across a fringing reef at Discovery Bay, north Jamaica. Physical processes (abrasion and fragmentation) are most important at shallow fore-reef sites, whilst back-reef sites are dominated by biochemical processes, including microboring, recrystallization, biofilm-related calcification, and dissolution. Grain susceptibility to each process is highly variable and influenced by mineralogy and skeletal structure. Coral fragments, for example, are most susceptible to the effects of microboring, whereas Halimeda plates are most susceptible to dissolution. Extensive alteration of grain assemblages is predicted within the back-reef, where dissolution of coral and Halimeda occurs because of intense microboring and pore-water undersaturation. Fore-reef assemblages, by contrast, remain relatively unaltered. Results have implications both for improved ecological interpretation of carbonate sedimentary sequences and for understanding of how and why carbonate microfacies develop.

Biofilm‐related calcification, sediment trapping and constructive micrite envelopes: a criterion for the recognition of ancient grass‐bed environments?

Micrite envelopes are a common feature in carbonate sediments and are typically associated with the micrite filling of borings produced by microendolithic organisms. These are referred to as ‘destructive micrite envelopes’ and have long been recognized as reflecting an important early diagenetic process. Recent analysis of sediments collected from back‐reef environments at Discovery Bay, north Jamaica, however, has demonstrated ‘envelope’ formation on the surfaces of carbonate grains, clearly distinct from the micrite filling of microborings. Such constructive envelopes occur almost exclusively in sediments from grass‐bed environments and are always intimately associated with ‘biofilms’ comprising abundant mucilage, cyanobacteria, bacteria and diatoms. It is suggested that these envelopes represent a product of both biologically mediated micrite precipitation (occurring within the biofilm mucilage and around the biofilm components, i.e. cyanobacteria and diatoms) and associated trapping of carbonate mud and fine‐grained sediment. Their recognition only within grass‐bed sediments may enable their use as a diagnostic feature of grass‐bed environments or vegetation‐stabilized substrates in the rock record.

Macroborers within coral framework at Discovery Bay, north Jamaica: species distribution and abundance, and effects on coral preservation

Macroboring organisms are recognised as key agents of reef framework modification and destruction, and while recent studies in the Pacific have improved understanding of spatial variations in macroboring community structure, and rates of macroboring within individual reefs, comparable studies from the Caribbean are largely lacking. This study assesses the distribution of macroboring species and the degree of framework infestation across the reefs at Discovery Bay, north Jamaica. Although individual species of borers exhibit variable distributions across the reef, relative abundances of the main groups of macroborers (sponges, bivalves, worms) illustrate clear distributional trends. Sponges are dominant at fore-reef sites, while sipunculan and polychaete worms are only of importance at back-reef/lagoon and shallow fore-reef sites. Bivalves are locally important within back-reef and lagoon patch reef framework. Average percentages of internal bioerosion (macroboring) vary between sites, but are highest at back-reef and deep fore-reef sites. No systematic pattern of variation occurs within back-reef/lagoon samples, but a significant trend of increased macroboring is recognised with increased water depth on the fore-reef. In addition, significant differences in terms of the susceptibility of individual coral species are recognised. These factors are likely to result in biasing of the fossil record, with variable styles of preservation evident both between sites (i.e. with depth/environment) and within sites (i.e. between coral species).

Grain susceptibility to the effects of microboring: implications for the preservation of skeletal carbonates

The boring activity of microendolithic organisms such as cyanobacteria, chlorophytes, rhodophytes and fungi, represents a major destructive process affecting sediment preservation within reef environments. This study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north Jamaica, correlating to the upper (&lt;18 m depth) and lower (&gt;18 m depth) photic zones. The upper photic zone assemblage is dominated by cyanobacteria and chlorophytes, whilst rhodophytes and fungi become more abundant with increasing water depth. Most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types. The highest degree of grain infestation occurs within shallow, low‐energy back‐reef environments and the most susceptible grains (at all sites) are corals, molluscs and foraminifera. Coralline algae, Halimeda and echinoid fragments are rarely heavily infested. High rates of infestation at back‐reef sites result in rapid diminution of the most susceptible grains, especially coral, which are either underrepresented, or contribute only to the finer sediment fractions, in the subsurface. Fore‐reef grain assemblages undergo relatively little alteration. Microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains. The impact of microboring upon back‐reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments.

Disarticulated Echinoid Ossicles in Paleoecology and Taphonomy: The Last Interglacial Falmouth Formation of Jamaica

Echinoids from the last interglacial (=Sangamon; ca. 125,000 years old) Falmouth Formation fo north Jamaica, a raised reef plaeoenvironment, are almost invariably preserved as disarticulated skeletal ossicles. Comparison of over 11,000 of these ossicles with extant shallow-water echnoids from the island has enabled half of the living genera to be recognized from the Pleistocene raised reef. The paleoecological distribution of these ossicles is in good agreement with the ecological distribution of these taxa within reeefs at the present day, and supports the reconstruction of the Falmouth Formation reef ecosystem based on sedimentological and coral data

Dynamic hydrology and diagenesis of a submerged Pleistocene fringing reef, Discovery Bay, Jamaica

In the Discovery Bay area of north Jamaica, a Pleistocene fringing reef grew and was subsequently planed off as sea level rose to and fell from a highstand approximately 5 to 10 m below modern sea level between 132,000 and 147,000 yrs BP. Dynamic movement of seawater through the reef today, evidenced by flow of water in and out of open core holes, has caused precipitation of cements which overprint previous diagenetic fabrics in certain zones. In the reef-flat and distal fore-reef facies, where porosity is diffuse, modern water movement is slow and has had little effect on pre-existing diagenetic fabrics, which are dominantly vadose in texture. In facies with conduit porosity, as in the reef crest and proximal portions of the shallow fore-reef, seawater is channelized and high flow rates have resulted in the precipitation of substantial amounts of Holocene sparry high-magnesian calcite cements (15–18 mol% MgCO 3) up to 250 μm thick, resulting in incorporation of significant amounts of 14C in the Pleistocene rocks. Smaller Mg-calcite crystals, having lower magnesium content, are characteristic of zones with diffuse porosity. The dynamic marine system apparently also favors the precipitation of dolomite. In zones of diffuse porosity, water motion within the reef results in the slow movement out of the man-made conduits. In zones of conduit porosity, such as in facies having highly localized permeability, water is sucked into open core holes in accordance with Bernoulli's Principle. It is not known to what depths such channelized flow occurs. Data from a recording current meter demonstrate that the driving force responsible for the dynamic hydrology has a strong tidal component. The tidal component is augmented by wind-driven waves and is probably superimposed on another, unidentified, current which contributes to the flow of water in the reef at all tidal stages.

The Self‐Thinning Rule: Another Interpretation of Weller's Results

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