Showing papers on "Fringing reef published in 1984"

Temporal Variability in the Community Structure of Fish on Coral Patch Reefs and the Relation of Community Structure to Reef Structure

Abstract: Fish assembled on 20 lagoonal patch reefs were censused eight times over 33 mo. Reefs, which ranged in size from 2.71 m2 to 28.35 m2 surface area, supported an average of 128 fish of 21 species at any one time. These were drawn from a total pool of 143 species, and, because of successive recruitments and losses of individual fish, each reef supported many more species during the study than were present at any one census. Structure of the assemblages on each reef, in terms of species number, number of fish, and species composition, varied through time. Mean proportional similarity of assemblages on the same reef was 0.568, z 15% greater than that between assemblages on different reefs (0.422). Structural attributes of reefs, other than size, were of little value in predicting the structure of the fish assemblages formed. The results are compatible with an essentially nonequilibrial view of reef fish communities. This view holds that species recruit to reef sites at varying rates, and independently of each other, while individuals are lost from sites (through death or emigration) also in a way unstructured with respect to the species composition of the resident fauna.

Transport mechanisms and the potential movement of planktonic larvae in the Central Region of the Great Barrier Reef

Abstract: It is suggested that considerable inter-reef dispersal of reef fishes and many benthic invertebrates is likely in the central region of the Great Barrier Reef. Larvae are most abundant in spring-summer when currents on the outer shelf, where most of the coral reefs occur, are almost entirely unidirectional and southeastward (longshore). Net drift on the outer shelf at this time is likely to be greater, but the dispersion smaller, than that nearshore at the same time due to more extensive periodic reversals of water movement in the latter area than the former. Net drift on the outer shelf in winter will be significantly more restricted, but the dispersion greater, than in summer due to extensive periodic reversals of currents in this area during the trade wind (winter) season. These conclusions suggest that reefs within the Central Great Barrier Reef are biologically interconnected and interdependent; a result of considerable significance for management of reefs within the Great Barrier Reef marine park.

Subaerially exposed Holocene coral reef, Enriquillo Valley, Dominican Republic

Abstract: An extremely well-preserved Holocene fringing coral reef occurs at an average elevation of 5 m below sea level around the margins of the central Enriquillo Valley, Dominican Republic. The reef records the latest marine incursion from the east into an 85-km-long, 12-km-wide tectonic depression and appears to represent a unique preservation. Excellent cross sections of the reef exposed in erosional gullies reveal a composition and zonation typical of modern Caribbean reefs that are found in offshore low-energy environments. Radiocarbon age determinations (2) indicate that reef growth coincided with sea-level rise following the last ice age (5,930 + or - 100 to 4,760 + or - 90 yr B.P.). Deltaic deposition and possible vertical movements on active fault scarps dammed the eastern mouth of the valley and created Lago Enriquillo, the level of which was then rapidly lowered by evaporation in an arid climate to produce a saline lake approximately 40 m below sea level. Stratigraphic studies of rocks along the valley edge and data from drill holes in the basin center indicate that there were earlier post-Miocene marine incursions similar to that described here.

Last interglacial reef growth beneath modern reefs in the southern Great Barrier Reef

Abstract: Studies of modem coral reefs have shown that Holocene reef growth is relatively thin, and that in many instances it has developed on an older limestone surface1–4. This surface is commonly associated with leaching and pedogenic processes, indicative of subaerial exposure, and has been termed the solution unconformity5. Investigations into reef growth history have interpreted the pre-Holocene substrate as an older reef surface2–4,6–8 that may or may hot have undergone karst erosion during periods of lower sea level6,9. Uranium-series dating of corals directly below the uppermost solution unconformity at Eniwetok10 and Mururoa11 has shown that previous reef growth, before the Holocene, occurred ∼120 kyr ago. We present here 230Th/234U dates that confirm a last interglacial age for reefal limestones directly beneath the uppermost solution unconformity in the southern Great Barrier Reef.

The Acropora inheritance: A reinterpretation of the development of fringing reefs in Barbados, West Indies

Abstract: The discovery of the widespread occurrence of the remains of the reef coral Acropora palmata within the fabric of the fringing reefs on the west coast of Barbados requires a new interpretation of their Holocene development. Radiocarbon dating of the A. palmata framework suggests that reef construction by this species began as early as 2,300 years B.P. A. palmata probably flourished in Barbados into the present century but has now declined. The present fringing reefs are characterized by a core and base of A. palmata upon which subsequent colonization took place, especially by Montastrea annularis, Porites porites and coralline algae.

Nutrient input by seabirds to the forest on a coral island of the Great Barrier Reef

Abstract: The rate of deposition of droppings from WhiteCapped Noddies Anous minutus Boie, the principal seabird nesting and roosting in the trees of Pisonia grandis R. Br. on Heron Island, Great Barrier Reef, was measured 3 times during 1983. Deposition at ground level was extremely variable, partly because much of the material was intercepted by foliage. An average rate of deposition was about 2 g m-2 d-' (dry matter), equivalent to a total input of about 45 tonnes yr-' to the soil under the P. grandis canopy of the island. This represents the transfer of about 1.4 tonnes yr-' of phosphorus from the surrounding waters to the island's soil where P may become stabilised in insoluble form. Coral islands are largely dependent on the surrounding regions of the sea for influx of plant nutrients, mostly deposited by roosting and nesting seabirds. Such nutrients are crucial for the plants on coral cays, which often maintain a stable vegetation, in turn providing suitable habitats and shelter for many bird and other species. Nutrient contents of guano deposits are known for a large number of localities (e.g. Hutchinson, 1950) including some Great Barrier Reef (GBR) islands where phosphate has been mined (cf. Cribb, 1979). However, little is known about the rate of input of plant nutrients by birds to islands of the GBR (cf. Heatwole et al., 1981). This report presents measurements of the input of nitrogen, phosphorus and other elements under the forest of Pisonia grandis R. Br. (Nyctaginaceae), the major plant community on Heron Island (23'27' S, 151'55' E), a coral cay about 16 ha in area. This species is closely associated with colonies of seabirds, having hooked sticky anthocarps leading to dispersal of seeds by birds, and providing nest-sites and nesting material. On Heron Island the most abundant bird nesting and roosting in the P. grandis trees is the White-Capped Noddy Anous rninutus Boie: there were about 70,000 adults in January 1983, and 10,000 young were raised to fledging (K. Hulsman, pers. comm.). On this island Noddies nest principally in P. grandis (cf. Shipway, 1969). Droppings-catchers, polyethylene bags 30 X 45 cm, were pegged out for 2 to 3 d on the ground under closed Pisonia grandis canopy. In January and SepQ Inter-Research/Printed in F. R. Germany tember, 10 bags were set out in a transect at 3 m intervals in the central P. grandis closed-forest (cf. Specht, 1981) to give an unbiased selection of sampling sites. Because this may not have sampled the full range of variation, 10 additional catchers were placed in pairs so that one was in a place heavily contaminated with droppings and the other was in a clean place under the same tree; the 5 trees chosen were widely separated over the island from the edge to the centre and from closed-scrub to closed-forest. The paired catchers were set out in January, May and September. Catchers were visited night and morning to remove leaf litter and debris cast over them by foraging Banded Land-Rails Rallus philippensis L. and burrowing Wedge-Tailed Sheanvaters Puffinus pacificus (Gmelin). No rain fell during any of the periods, and A. minutus was always the principal species in the trees above all catchers. The catch was dried at 50°C, scraped from the bags, and samples were analysed for carbon, hydrogen and nitrogen with a Heraeus CHN-Rapid analyser. Eight of the largest samples were analysed for phosphorus by the molybdenum blue method (Allen, 1974) and for cations by atomic-absorption spectrophotometry. The area covered by P. grandis was measured by tracing round the canopy of every tree on a map from January 1983 air-photographs. The catch (expressed as dry-mass of material d-' m-' of ground area) was abundant at all 3 times of year (Table 1). The material consisted principally of bird droppings, but included some feathers, small pieces of plant material, coral sand and other matter. There was extreme variation between individual catchers. Undoubtedly much material is intercepted by leaves and stems in the canopy of Pisonia grandis, and the density of the foliage as well as number and activity of birds vary from time to time and place to place. Material caught on foliage may b e liberated as flakes during windy conditions or washed to the ground during rain. No attempt was made in this study to estimate 298 Mar. Ecol. Prog. Ser. 19: 297-298, 1984 31 Jan to 30 May to 3 to 5 Sep 3 Feb 1983 2 Jun 1983 1983 Transect (n = 10) 2.2f 1.2 n. d . 1.7k0.8 (Range) (0.002-1 1.6) (0.001-7.0)

A preliminary distributional study of fish larvae near a ribbon coral reef in the Great Barrier Reef

Abstract: Fish larvae from horizontal plankton tows along a single transect near outer ribbon reefs of the Great Barrier Reef in spring 1979 and summer 1980 had persistent distributional patterns. Larvae were identified to family and divided into young (preflexion) and old (postflexion) larvae, thus giving 28 taxa abundant enough for analysis. Non-uniform larval distributions were found for 81% of the 16 reef fish taxa with non-pelagic eggs, but for only 17% of the six reef fish taxa with pelagic eggs. Most differences in larval concentration were between the lagoonal and seaward sides of the reef. Only tripterygiid larvae had highest concentration just seaward of the reef, while larvae of 12 reef and three oceanic fish taxa occurred in highest concentrations on the lagoonal side of the reef. In five taxa of reef fishes, higher larval concentrations were found in the lagoonal backreef compared with the mid-lagoon habitat; but the reverse was not found in any taxon. Eleven taxa had indeterminate distributions, (i.e. no difference in concentration between stations). Mechanisms responsible for the distribution remain unknown, but we suggest that the view which considers fish larvae to be passively-drifting particles is unjustified without more information on larval behaviour.

Computer simultion of the reef zonation at Discovery Bay, Jamaica: Hurricane disruption and long-term physical oceanographic controls

Abstract: A computer model (COREEF) designed to simulate the growth of Caribbean coral reefs has been tested for its ability to reconstruct the storm-induced and the established zonation patterns on the West Reef at Discovery Bay, Jamaica. Hindcast waves for nine positions of Hurricane Allen were routed across the reef, and the disruptions to the coralgal and sediment zones were calculated for each position. The predicted maximum and intermediate stage damages closely matched the actual destruction produced by this and other smaller storms. Despite their severity, hurricanes probably have minimal long-term effect on the established zonation of this reef, because their return period is generally less than the recovery period of the reef. Additional simulation experiments indicate that a composite of the wave conditions at Discovery Bay maintain the established reef zonation and that winter storm conditions produce the maximum bottom velocities that the coralgal framework can withstand without disruption.

Holocene reef sequences and geochemistry, Britomart Reef, central Great Barrier Reef, Australia

Abstract: Holocene reef development was investigated by coring on Britomart Reef, a mid-shelf reef, 23 km long and 8 km wide situated 120 km north of Townsville in the central Great Barrier Reef (GBR). Two holes were drilled, Britomart 1 on a lagoon patch reef, and Britomart 2 on the windward reef crest. The Holocene reef (25·5 m) is the thickest yet recorded in the GBR and overlies an uneven substrate of weathered Pleistocene limestone. Mineralogical and geochemical analyses show that magnesian calcite and aragonite were converted to low Mg-calcite below the Holocene-Pleistocene disconformity. Corals above the interface have 7500–8500 ppm Sr, but 1650–1500 ppm just below it, decreasing to 400–800 ppm downwards. The intermediate Sr values could be due to partial replacement of aragonite by calcite or higher original Sr content in the corals. Three units are recognized in the Holocene: (1) coral boundstone unit, (2) coral framestone unit, and (3) coral rudstone unit. The coral boundstone unit forms the top 5 m of both cores and is algal-bound coral rubble similar to the present reef top. The coral framestone unit is composed of massive head corals Diploastrea heliopora and Porites sp., and is currently forming in patch reefs situated in the lagoon and along the reef front. The coral rudstone unit comprises coral rudstone and floatstone with unabraded, and unbound, coral clasts in muddy matrix. This matrix may be up to 30% sponge chips. Radiocarbon dating indicates the reef grew more rapidly under the lagoon than under the reef front from 7000 to 5000 yr BP. The rate of reef growth matched existing estimates of sea-level rise, but lagged approximately 1000 years (5–10 m) behind it. Most of the reef mass accumulated between 8500 and 5000 yr BP as a mound of debris, perhaps stabilized by seagrasses or algae. Accretion of the reef top in a windward direction between 5000 and 3000 yr BP created the present, steep reef-front profile.

Initial observations of the zooplankton microdistribution on the fringing coral reef at Aqaba (Jordan)

Abstract: Diurnal and nocturnal zooplankton was sampled simultaneously at the surface and at 35 m depth on the outer slope of the fringing reef off the Jordanian coast in the Guff of Aqaba, Red Sea, over a period of 8 d during July 1982. Complementary surface sampling was carried out above the reef and in the open sea in the morning and afternoon for a period of 5 d. Five groups of organisms were classified according to changes in their vertical distribution in the water column which is analyzed and discussed. Zooplankters of the first group appear to be positively phototactic (Calanus robustior, Mecynocera clausi, Oithona helgolandica, Corycella rostrata). Those of the second group also seem to be positively phototactic, but only as regards average and low light (moonlight) intensities (Nannocalanus minor, Acartia negligens, Sagitta enflata, S. hexaptera, Thalia democratica, Oikopleura fusiformis, O. longicauda). The zooplankton of the third group displays a negative phototaxis (Oithona nana, calyptopis and furcilia euphausiid stages, pelecypods and other mollusc veligers). Species exhibiting uncertain behaviour or caught in low numbers and exhibiting no particular distribution are relegated to the fourth and the fifth groups. The horizontal microdistribution of the zooplankton community is not easily discernible: certain neritic or oceanic affinities can be identified, however, by comparing the WP2 standard net surface samples collected above the reef with those from the open sea. The importance of zooplankton communities is emphasized, and the necessity of elucidating the temporal and spatial migrations and exchanges between reef and planktonic organisms in order to gain more insight into their trophic relationship with the reef system.

Skeletal extension of Acropora formosa at a fringing reef in the Andaman Sea

Abstract: A growth study of Acropora formosa (Dana) was conducted in situ at a fringing reef in front of Phuket Marine Biological Center, the Andaman Sea, southern Thailand Monthly extensions of branches tagged with wire were measured in addition to sunshine, rainfall, settlement of sediment, turbidity, salinity, and temperature The average extension of coral branches was 8 cm in 344 days Growth was found to be approximately two times faster during the dry northeast monsoon compared with the wet southwest monsoon Factors which can cause the observed pattern of growth are discussed

The ecological research on coral reefs of the Red Sea

Abstract: Klunzinger (1872) characterised the zonation of the coral reef near Al-Qusayr, Egypt with the help of indicator species. He identified a Stylophora -zone among other zones and established the first biophysiographic zonation of a coral reef which is, in many respects, still valid today. Since then, ecological research work on coral reefs has developed to its present understanding of one of the most complicated and densely populated ecosystems on Earth. Much biological and ecological work has been done on the coral reefs along the Red Sea coasts. This is not surrising, because the Red Sea is the coral sea closest to Europe and has attracted the interest of European investigators for over 200 years. With few exceptions, this interest has been concentrated on a limited number of coastal sites: Jeddah, Al-Qunfudhah, Al-Luhayyah and Al-Mukha along the east coast, and Assab, Mesewa, Al-Qusayr and As-Suways along the west coast. Although the early coral reef workers were primarily interested in collecting animals, they also made some informal observations on the habitats of the species they collected. However, full ecological statements were rare — with the exception of those of Klunzinger (1872). Research centres have been established and active programmes continue on the Sudanese coast at Dungunab (since 1907), Sawakin and Bur Sudan (since 1963 when the first ecological investigations on Bur Sudan coral reefs occured (Mergner, 1967), and in 1974 and 1976 respectively the biological stations at Sawakin and Bur Sudan were established), on the Egyptian coast at Al-Ghardaga (since 1930), on the Sinai coast at Eilat (since 1968) and on the Jordan coast at Al-Aqabah (since 1972). New research centres continue to open, such as aong the east coast at Jeddah. The special interest of the ecology of Red Sea coral reefs is that it encompasses a broad range of problems: the influence of abiotic factors on the community structure, distribution and species diversity of corals and the biophysiographic zonation of coral reefs, the interspecific and intergeneric competition of corals and other sessile animals and algae within the reef, the qualitative and quantitative analysis off the coral assemblages of different reef zones and the ecology of several important reef animal groups (sponges, molluscs, echinoderms, fishes, etc.). Closely connected with these problems is an interest in the behaviour of reef animals, and finally reef ecologists cannot ignore the urgency of the problems associated with the pollution and conservation of coral reefs in the Red Sea.

Photographic survey of a coral reef flat

Abstract: In recent years, an increasing number of field scientists have adopted photographic and photogrammetric techniques for the capture and analysis of their ohservations. A description of a technique of “through-water” photography applied to an ecological survey of coral types on the reef flat around Heron Island is presented. This technique allowed 1500 square metres to be photographed per day. Mosaics were prepared to aid spatial analyses which will permit investigations of the density and diversity of the coral types and assist the evaluation of “balance of nature” theories.

Coral Reef Islands and Their Problems

Abstract: Small islands and in particular those more or less dependant on their reefs as a resource were often selfcontained units, maintaining a fragile equilibrium in which even small changes could and nave wrought fatal disturbances. ~he pressures of the modern world have endangered these vulnerable units economically, socially and biologically. In all instances the "'popul a t i on factor~ has played an important role. Coral reef islands appear to be more susceptible to the side effects of rapidly growing modernization than other types of islands. No clear answer or solution to this problem can be given but recognition of the threats to them may bring the remedies closer.