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1.
Most of the atolls found worldwide are under microtidal regimes, and their circulation mechanisms are widely documented and well known. Here, we describe the flushing mechanisms of a small-sized mesotidal atoll, based on water-level, wave and current data obtained during two different periods (total of 60 d). Rocas is the only atoll in the South Atlantic Ocean and is built primarily of coralline algae. Two reef passages connect the atoll lagoon to the ocean. Synchronous current profilers were deployed at the two reef passages, one inside and one outside the atoll, to characterize the influence of tides and waves on the circulation. Results showed that wind waves drove a setup on the exposed side of the atoll and that currents were predominately downwind, causing outflow at both reef passages. Waves breaking on the windward side supplied water to the atoll causing the lagoon water level to rise above ocean water level, driving the outflow. However, unlike microtidal atolls, at Rocas Atoll the water level drops significantly below the reef rim during low tides. This causes the reef rim to act as a barrier to water pumping into the lagoon by waves, resulting in periodic activation of the wave pumping mechanism throughout a tidal cycle. As result, inflow occurs in the wider passage during 27% of each tidal cycle, starting at low tides and reversing direction during mid-flood tide when the water level exceeded approximately 1.6 m (while overtopping the atoll’s rim). Our findings show that tides play a direct role in driving circulation on a mesotidal atoll, not only by modulating wave setup but also by determining the duration of wave pumping into the lagoon. 相似文献
2.
A first systematic study of composition, texture, and distribution of modern sediments in two Maldivian atolls reveals the predominance of skeletal carbonates. Fragments of corals, calcareous algae, mollusks, benthic foraminifera, and echinoderms are identified in the grain-size fraction >125 μm. Non-skeletal grains such as cemented fecal pellets and aggregate grains only occur in small percentages. Fragments of skeletal grains, aragonite needles, and nanograins (<1 μm) are found in the grain-size fraction <125 μm. Needles and nanograins are interpreted to be largely of skeletal origin. Five sedimentary facies are distinguished (1–5), for which the Dunham-classification is applied. Fore reef, reef, back reef, as well as lagoonal patch reef and faro areas in both atolls are characterized by the occurrence of coral grainstones (1), which also contain fragments of red coralline algae, the codiacean alga Halimeda, and mollusks. On reef islands, coral-rich sediment is cemented to form intertidal beachrock and supratidal cayrock. Skeletal grains in atoll-interior lagoons are mainly mollusks and foraminifera. The lagoon of Rasdhoo Atoll is covered in the west by mudstones (2), in the center by mollusk packstones (3) and mollusk wackestones (4), and by hard bottoms with corals in the east adjacent to channels through the atoll reef margin. The interior lagoon of Ari Atoll contains mollusk wackestones (4) in the center and mollusk-foraminifer packstones (5). Marginal lagoon areas are characterized by hard bottoms with corals. Facies distribution appears to be an expression of depositional energy, which decreases from the atoll margin towards the center in Ari Atoll, and towards the west in Rasdhoo Atoll. Predominant sediment mineralogies include aragonite and high-magnesium calcite. Mean aragonite content decreases from 90% in coral grainstone to 70–80% in mollusk packstone, mollusk wackestone, and mudstone, and to 50% in mollusk-foraminifer packstone. Stable isotopes of oxygen and carbon in bulk samples range from −3 to −1.5 (δ 18O) and from +0.4 to +3.2 (δ 13C). It is not possible to delineate facies based on O- and C-isotopes. 相似文献
3.
In the high Hawaiian Islands, significant accretion due to coral reef growth is limited by wave exposure and sea level. Holocene
coral growth and reef accretion was measured at four stations off Oahu, Hawaii, chosen along a gradient in wave energy from
minimum to maximum exposures. The results show that coral growth of living colonies (linear extension) at optimal depths is
comparable at all stations (7.7–10.1 mm/y), but significant reef accretion occurs only at wave sheltered stations. At wave
sheltered stations in Hanauma Bay and Kaneohe Bay, rates of long term reef accretion are about 2.0 mm/y. At wave exposed stations,
off Mamala Bay and Sunset Beach, reef accretion rates are virtually zero in both shallow (1 m) and deeper (optimal) depths
(12 m). At wave sheltered stations, such as Kaneohe Bay and Hanauma Bay, Holocene reef accretion is on the order of 10–15 m
thick. At wave exposed stations, Holocene accretion is represented by only a thin veneer of living corals resting on antecedent
Pleistocene limestone foundations. Modern coral communities in wave exposed environments undergo constant turnover associated
with mortality and recruitment or re-growth of fragmented colonies and are rarely thicker than a single living colony. Breakage,
scour, and abrasion of living corals during high wave events appears to be the major source of mortality and ultimately limits
accretion to wave sheltered environments. Depth is particularly important as a modulator of wave energy. The lack of coral
reef accretion along shallow open ocean coastlines may explain the absence of mature barrier reefs in the high Hawaiian Islands.
Accepted: 14 May 1998 相似文献
4.
A spectacular mound-like reef formation (126 m in circumference, 10 m high) dominated by highly arched and record-size colonies
of the unattached mushroom coral Halomitra pileus, along with 17 other species of the family Fungiidae, occurs in 31 m of water on the sedimentary lagoon floor of the Great
Astrolabe Reef, Fiji. Core samples show radiocarbon dates which indicate that the formation hypothetically began building
∼4500 y ago, with a calculated mean accretion rate of 2.2 mm ⋅ y -1. The majority of fossil and living material is contributed by H. pileus colonies between 40–70 cm mean diameter, with some individuals up to 1.5 m in diameter. The size, fungiid diversity, and
geological history of the bioherm is unprecedented and represents the first example of a coral reef constructed almost entirely
by Fungiidae.
Accepted: 29 July 1996 相似文献
5.
Christmas (Kiritimati) Island is an unusually large coral atoll, of which a large proportion of the surface is presently
subaerial. Extensive outcrops of in situ branching Acropora corals, together with Porites microatolls, Tridacna, and other shallow marine biota, indicate that the present low-lying area of interconnecting lakes in the island interior
formed as a reticulate lagoon. Radiocarbon dating indicates that these lagoonal reefs flourished between 4500 and 1500 radiocarbon
years BP, and surveying confirms that sea level was 0.5–1.0 m above present at that time, with subaerial exposure resulting
from Late Holocene emergence. Boreholes undertaken for a water resources survey of the island penetrated near-surface Pleistocene
limestones on the northern, southern, and eastern sides of the island. These are highly weathered and fractured, and although
aragonitic clasts are preserved, U-series dating indicates a Middle Pleistocene or older age. At one location flanking the
Bay of Wrecks, an outcrop of limestone, with an erosional notch, 1–2 m above present sea level, yielded a U-series age of
130 ka, and is interpreted as Last Interglacial in age. In contrast to previous interpretations which have suggested that
Christmas Island comprised an atoll superstructure that is entirely Holocene, or the layer-cake interpretation appropriate
for many mid-ocean atolls, Christmas Island appears to have had a form similar to its present in the Middle Pleistocene or
earlier. It has undergone karstification during lowstands. Interglacials, particularly the Last Interglacial and the Holocene,
appear to have resulted in only a minor veneer of coral over older limestone surfaces. Christmas Island is considered characteristic
of an atoll that has not experienced significant subsidence through the Late Quaternary.
Accepted: 15 May 1998 相似文献
6.
The distributions and population densities of large benthic foraminifers (LBFs) were investigated on reef flats of the Majuro
Atoll, Marshall Islands. Annual sediment production by foraminifers was estimated based on population density data. Predominant
LBFs were Calcarina and Amphistegina, and the population densities of these foraminifers varied with location and substratum type on reef flats. Both foraminifers
primarily attached to macrophytes, particularly turf-forming algae, and were most abundant on an ocean reef flat (ORF) and
in an inter-island channel near windward, sparsely populated islands. Calcarina density was higher on windward compared to leeward sides of ORFs, whereas Amphistegina density was similar on both sides of ORFs. These foraminifers were more common on the ocean side relative to the lagoon side
of reef flats around a windward reef island, and both were rare or absent in nearshore zones around reef islands and on an
ORF near windward, densely populated islands. Foraminiferal production rates varied with the degree to which habitats were
subject to water motion and human influences. Highly productive sites (>10 3 g CaCO 3 m −2 year −1) included an ORF and an inter-island channel near windward, sparsely populated islands, and a seaward area of a reef flat
with no reef islands. Low-productivity sites (<10 g CaCO 3 m −2 year −1) included generally nearshore zones of lagoonal reef flats, leeward ORFs, and a windward ORF near densely populated islands.
These results suggest that the distribution and production of LBFs were largely influenced by a combination of natural environmental
factors, including water motion, water depth, elevation relative to the lowest tidal level at spring tide, and the distribution
of suitable substratum. The presence of reef islands may limit the distribution and production of foraminifers by altering
water circulation in nearshore environments. Furthermore, increased anthropogenic factors (population and activities) may
adversely affect foraminiferal distribution and production. 相似文献
7.
The role of dissolved free amino acids (DFAA) in nitrogen and energy budgets was investigated for the giant clam, Tridacna maxima, growing under field conditions at One Tree Island, at the southern end of the Great Barrier Reef, Australia. Giant clams
(121.5–143.7 mm in shell length) took up neutral, acidic and basic amino acids. The rates of net uptake of DFAA did not differ
between light and dark, nor for clams growing under normal or slightly enriched ammonium concentrations. Calculations based
on the net uptake concentrations typical of the maximum concentrations of DFAA found in coral reef waters (∼0.1 μM ) revealed
that DFAA could only contribute 0.1% and 1% of the energy and nitrogen demands of giant clams, respectively. These results
suggest that DFAA does not supply significant amounts of energy or nitrogen for giant clams or their symbionts.
Accepted: 7 October 1998 相似文献
8.
Nitrogen (N) and energy (E) requirements were measured in adult Carollia perspicillata which were fed on four experimental diets. Bats ate 1.3–1.8 times their body mass ⋅ day -1 and ingested 1339.5–1941.4 kJ ⋅ kg -0.75 ⋅ day -1. Despite a rapid transit time, dry matter digestibility and metabolizable E coefficient were high (83.3% and 82.4%, respectively),
but true N digestibility was low (67.0%). Mass change was not correlated with E intake, indicating that bats adjusted their
metabolic rate to maintain constant mass. Bats were able to maintain constant mass with digestible E intake as low as 1168.7 kJ ⋅ kg -0.75 ⋅ day -1 or 58.6 kJ ⋅ . Metabolic fecal N and endogenous urinary N losses were 0.87 mg N ⋅ g -1 dry matter intake and 172.5 mg N ⋅ kg -0.75 ⋅ day -1, respectively, and bats required 442 mg N ⋅ kg -0.75 ⋅ day -1 (total nitrogen) or 292.8 mg N ⋅ kg -0.75 ⋅ day -1 (truly digestible nitrogen) for N balance. Based on E and N requirements and digestibilities, it was calculated that non-reproductive
fruit bats were able to meet their N requirements without resorting to folivory and without over-ingesting energy. It was
demonstrated that low metabolic fecal requirements allowed bats to survive on low-N diets.
Accepted: 23 June 1996 相似文献
9.
Movement by the larger more mobile species of coral reef fish plays a significant role in determining patterns in abundance
and population structure. Fish movement is also relevant to the use and effectiveness of marine reserves in managing fish
populations. Coral trout are large piscivorous serranids supporting major fisheries on the Great Barrier Reef (GBR). This
study reports on the within-reef movement of the common coral trout, Plectropomus leopardus, at Heron Reef, southern GBR, over a twelve month period, investigated by tagging and underwater tracking. Tracking of coral
trout revealed no apparent relationship between the area moved and stage of tide or time of day. However, movement areas were
affected by the size of fish: in spring a linear relationship between fish size and area of movement was measured, but in
summer the largest (male) fish moved over significantly smaller areas than medium-sized fish. Movement of males may be related
to cleaning behaviour and spawning. Fifty nine percent ( n=101) of the tagged fish were resighted over periods of 4–5 months, in “home sites” measuring ∼2000 m 2. Coral trout were not restricted to home sites, but moved on average 2 km along the reef slope; maximum distances of 7–7.5 km
were measured. Coral trout appear to range as mobile, opportunistic predators, but also maintain home sites for access to
shelter and cleaning stations.
Accepted: 1 August 1996 相似文献
10.
Denitrification of a high-strength synthetic wastewater (150 g NO -
3 l -1) was carried out using a wine distillery effluent as an example of an industrial carbon source (22.7 g chemical oxygen demand
l -1). Two configurations were tested: one consisted of an acidogenesis reactor followed by a denitrifying reactor and the other
was a single reactor directly fed with the raw effluents. In both cases, denitrification was achieved at a nitrate load of
9.54 g NO -
3 l -1 day -1 (2.19 g N as NO -
3 l -1 day -1) with good specific reduction rates: 32.6 mg and 35.2 mg N as NO
x
g volatile suspended solids h -1, calculated on a single day, for the two-step and the one-step process respectively. Dissimilatory nitrate reduction to ammonium
did not occur, even in the one-step process.
Received: 26 October 1995/Received revision: 15 February 1996/Accepted: 20 February 1996 相似文献
11.
Amperometric biosensors for naphthalene were developed using either immobilized Sphingomonas sp. B1 or Pseudomonas fluorescens WW4 cells. The microorganisms were immobilized within a polyurethane-based hydrogel, which was used for a microbial biosensor
for the first time. Both strains were shown to be equally suited for the quantification of naphthalene in aqueous solutions.
The biosensors were tested in a flow-through system and a stirred cell (batch method). In both systems a linear response down
to the detection limit was obtained. Measurements in the flow-through system gave sensitivities of up to 1.2 nA mg −1 l −1 and a linear range from 0.03 mg/l to 2.0 mg/l. The response time ( t
95) was 2 min and the sample throughput six per hour; the repeatability was within ±5 %. With the batch method, sensitivities
of between 3 nA mg −1 l −1 and 5 nA mg −1l −1 and a linear range of 0.01–3.0 mg/l were obtained; the response time was between 3 min and 5 min. The sensors reached an
operational lifetime of up to 20 days. The sensitivity of both sensors for naphthalene was, in most cases, more than four
times higher than for various other substrates.
Received: 18 October 1995/Received revision: 22 December 1995/Accepted: 22 January 1996 相似文献
12.
Nocturnal zooplankton assemblages around Taiaro Atoll were sampled over six nights during February 1994. Replicate zooplankton
samples were collected at windward and leeward locations in the enclosed lagoon and adjacent ocean with a metered net (85 cm
diameter, 500 μm mesh) towed for 15 min at 5 m depth. The zooplankton community in the lagoon was very different from that
in the ocean. Oceanic samples contained 50 mostly holoplanktonic taxa (diversity index, H′=2.62; evenness index, J′=0.67).
Lagoonal samples contained 19 mostly meroplanktonic taxa (H′=1.54, J′=0.52) with three taxa (decapod larvae; an ostracod,
Cypridina sp.; a copepod, Acartia fossae) contributing >90% of the individuals. Unlike the ocean, zooplankton distributions in the lagoon were not homogenous; instead
spatial patterns were apparently formed by the interaction between hydrodynamic processes and species-specific behaviour.
Accepted: 28 August 1997 相似文献
13.
Kikai-jima in the central Ryukyu Islands of Japan is fringed by exposed terraces of Holocene reefs, which formed as a result
of periodic local tectonic uplift associated with subduction/collision. The terraces form four topographically distinct features
(TI-IV) around the island and represent reefs that grew to sea level at 9000–6065 y BP, 6065–3390 y BP, 3790–2630 y BP, and
2870 to 1550 y BP. The modern reef terrace has been growing since approximately 1550 y BP. The reef terraces were uplifted
sequentially around 6050 y BP (4 m), 3390–3790 y BP (2.5 m), 2630–2870 y BP (1 m) and 1550 y BP (2.5 m). Five sites were studied
to define reef development in response to periodic relative sea level fall and different stillstand recovery periods. Thirty
coral genera and 70 species were recorded from four distinct shallow reef flat to upper reef slope and one deeper reef slope
coral assemblage. Significant lateral variations in total coral abundance, genera number, diversity, and the coverage density
of Acropora spp. and Faviids occur both within and between the terraces. Stratigraphically, drill core and outcrop data recorded shallowing
upward sequences characterised by tabulate Acropora spp. overlying massive Porites sp. and Faviids. The biological variations may represent growth strategies responding to initial colonisation, episodic perturbation
(relative sea level fall) and differing recovery times during stillstands, and indicate a reef ecosystem stable and strong
enough to recover after substantial perturbations. However, this study suggests that relatively small geological changes have
had substantial biological effects, and modelling indicates that such changes would have been more profound had a third factor,
such as substrate angle, varied more dramatically. In such a case, the drowning growth strategy exhibited in the drill core
transect may have been more prevalent, and reefs would be struggling to grow around Kikai-jima today.
Accepted: 27 May 1998 相似文献
14.
The fully enclosed Taiaro lagoon is hypersaline (42.5 psu) and non-tidal; constant salinity and water level result from strong
evaporation balanced by low percolation through the lagoon floor. Seawater can flow over the atoll rim during exceptionally
high seas and may then replenish lagoonal communities with propagules of oceanic origin. The distinctive water chemistry of
the lagoon suggests a possible way of identifying these immigrants. We established this potential by analysing stable isotopes
of carbon and oxygen in the recent growth layers of otoliths of two adult reef fishes, Chaetodon ulietensis and Acanthurus triostegus, collected from both sides of the atoll rim. Fish from the two locations were discriminated by their isotopic signatures,
suggesting that analysis of the microchemical signatures deposited during the larval development could be used in future work
to determine which individuals and species complete their life-cycles in this unusual lagoon.
Accepted: 28 August 1997 相似文献
15.
The biofiltration of dimethyl sulphide (Me 2S) and other volatile sulphur compounds results in the accumulation of the metabolite sulphuric acid in the carrier material.
Regeneration of an acidified (pH 4.7), Hyphomicrobium-MS3-inoculated compost biofilter degrading Me 2S was not possible by trickling tap water (days 0–28) or a KH 2PO 4/K 2HPO 4 buffer solution (1.26 g PO 3-
4 l -1, pH 7) (days 29–47) over the bioreactor at a superficial liquid flow rate of 34 lm -2 day -1. Since the protons produced displaced nutrient cations (Na +, K +, Ca 2+, Mg 2+, NH +
4) from the cation-exchange sites on the compost material, 95% of the SO 2-
4 was leached as the corresponding sulphate salts and not as sulphuric acid. Concomitantly, the pH of the compost material
decreased from 4.7 to 3.9 over the 47 days rinsing period. Moreover, the rinsing procedure resulted in the leaching of essential
microbial nutrients from the compost material, such as NH +
4 (22.3% wash-out over the 47-day rinsing period) and PO 3-
4 (39.3% washout over the 28-day tap-water rinsing period). However, mixing limestone powder into the Me 2S-degrading compost biofilter was a successful approach to controlling the pH in the optimal range for the inoculum Hyphomicrobium MS3 (pH 6–7). A stoichiometric neutralisation reaction (molar ratio CaCO 3/H 2SO 4=1.1) was observed between the CaCO 3 added and the metabolite of the Me 2S degradation, while high elimination capacities (above 100 g Me 2S m -3 day -1) were obtained over a prolonged (more than 100 days) period.
Received: 1 December 1995/Received revision: 26 April 1995 Accepted: 29 April 1996 相似文献
16.
Henderson Island, in the Pitcairn Group, preserves a Pleistocene atoll physiography with the rim of the raised reef structure, supporting spur and groove topography, enclosing a central lagoon. Excellent preservation of coral reef communities occurs along the ancient atoll rim and within the central lagoon. The previously interpreted depositional nature of the fossil atoll structure is herein corroborated with geomorphologic and stratigraphic evidence from previously un-visited portions of the island. Stratigraphic and lateral facies relationships indicate a physiographic zonation which includes spur and grooves, outer reef flat, lagoon margin, and an interior lagoon with patch reefs. The in situ occurrence and zonation of reef coral communities around the periphery and within the interior of the island appear to reflect the original physiography of the atoll lagoon, with the most pronounced reef development on the SE side of the original atoll. Stratigraphic units which comprise the raised atoll lagoon structure represent different time intervals, so the atoll lagoon structure formed during various sea level fluctuations. The modern atolls of the Pitcairn Group, Oeno and Ducie, provide some comparisons (similarities and differences) with the fossil lagoon on top of Henderson Island. 相似文献
17.
Ophiocoma scolopendrina exhibits a distinctive pattern of feeding activity on intertidal reef platforms off Kenya. With the first wave of the flooding tide, dense aggregations of these ophiuroids (up to 320 m −2) engage in a 1–2 min burst of surface-film feeding, vigorously sweeping the air-water interface and associated sea foam with the ventral surface of 2–4 arms. Suspension feeding (with arms extended in the water column) is the primary feeding mode throughout the rest of the tidal cycle (involving 25–65% of the population at a time), while bottom feeding (with arms extended along the substratum) is infrequent (<10%). Field experiments showed that surface-film feeding is regulated by water depth and can be triggered by suspended particles. This feeding mode appears to be an adaptation to the intertidal habitat, enabling the ophiuroids to exploit a nutrient-rich surface film during a temporal refuge (low tide) from fish predation. Dense populations of O. scolopendrina may represent an important trophic link between producers of particulate organic material and higher-level consumers in coral reef environments.Tara Oak and Robert E. Scheibling contributed equally to this paper. The order of authorship is alphabetical 相似文献
18.
The zooplankton of the under-shelf-ice ecosystem at White Island (78 °10′ S, 167 °30′ E), McMurdo Sound, Antarctica was investigated during December 1976 and January 1977. The water column was sampled through
a hole in the McMurdo Ice Shelf over a water depth of 67 m. Seawater temperatures under the ice shelf ranged from −1.91 to
1.96 °C. Dissolved oxygen levels ranged from 5.0–6.05 ml l -1 in early December to 4.65–4.8 ml l -1 in late January. Current speeds of up to 0.13 m s -1 were recorded at a depth of 50 m and a predominantly northward flow was detected. Light levels under the shelf ice were low
with less than 1% of the incident light being transmitted to a depth of 3 m. No chlorophyll a was detected within the water column throughout the investigation. Mean zooplankton biomass values in the water column ranged
from 12 to 447 mg wet weight m -3 and were similar to values recorded elsewhere from Antarctic inshore waters, but were very much higher than those recorded
from under seasonal sea ice in McMurdo Sound. Thirty-two zooplankton species were recorded including 1 ostracod, 21 copepods
(10 calanoids, 3 cyclopoids and 8 harpacticoids), 4 amphipods, 2 euphausiids, a chaetognath and 3 pteropods. Larvae of polychaetes
and fish were found on some occasions. The species composition in general was similar to that recorded from McMurdo Sound
and other Antarctic inshore localities. Among the Copepoda, however, there were a number of species, especially among the
Harpacticoidea, that have not been found previously in McMurdo Sound and the Ross Sea, but that are known to be associated
with ice in other localities in Antarctica. Two recently described species are known only from White Island. They were present
in the water column but were most abundant in the surface water of the tide crack where they were the most abundant zooplankters.
The tide crack, which probably is an extension of the under-ice habitat, is apparently a significant nursery area for amphipods
and copepod species.
Received: 23 November 1994/Accepted 7 May 1995 相似文献
19.
A vertically integrated numerical model of wind-driven circulation at One Tree Reef is presented. The model is the numerical model SURGE developed originally to study tropical cyclone surge. Current data collected in the reef lagoon and over the reef flats is used to test the model's applicability. The reef topography has been modelled explicitly, rather than using an assumed reef shape, with a grid spacing of 150 m. The model corresponds well to the measured current behaviour. The greatest drawback to use of the model is that, at low tide, currents reverse with depth due to lagoon enclosure and a depth integrated model cannot produce water velocity depth profiles. The model can be used to predict current behaviour in strong wind conditions, such as during a cyclone, and to estimate net flows into and out of the lagoon. 相似文献
20.
The oceanography around Mauritius (in the Western Indian Ocean) remains largely unstudied, hence there is an acute scarcity
of marine environmental data for management purposes. Rigorous water depth and current measurements were made on a system
of grids inside Le Morne lagoon (in the south western part of Mauritius) in March–April 2000 to generate semi-quantitative
models of general flow pattern in the form of contour maps using SURFER 6 computer programme. A simultaneous survey on composition
of bottom cover was conducted to examine possible relationships with current speed. A separate investigation recorded surface
and bottom currents prevailing amongst various habitat types to demonstrate the nature of the resulting damping effect on
surface current speed. Significant correlations generated from data analysis were discussed as a basis for real biophysical
relationships. Some of the limitations in the current analysis and some of the seemingly contradictory results are acknowledged
and addressed in the light of the general assumption that the structure of the lagoon is conditioned by current speeds. Much
stronger current speeds just outside the reef (e.g. >0.5 m s −1) than inside the lagoon (e.g. <0.32 m s −1) indicated a substantial slow-down of water current by the reef barrier. Inshore bottom currents were weaker than at the
surface and current speed correlated well with water depth. Bottom and surface current directions were generally similar,
i.e. going northward during flood tide and southward during ebb. The lagoon would be classified as ‘restricted’, exhibiting
well-defined tidal circulation, which is modified by wind forcing. Dense fields of branching Acropora corals slowed down surface current speed by as much as 87%, but the relationship between current speed and bottom cover appears
to be variable, depending on the specific location within the lagoon under consideration. The contour plots of the flow pattern
model generated reasonably high qualitative modelling of spatial current speed pattern in the lagoon, with stronger currents
generally along the reef areas, at the reef passes and in the deeper zones. However, these plots did not match closely those
displaying distribution of bottom cover, thus confirming results obtained from pair-wise correlation tests, namely the lack
of a significant relationship between current speed and bottom cover. Most of the correlations would appear to represent biological
relationships, with different types of communities enabling or excluding other types. Thus, the biophysical structure of the
lagoon would be driven a priori by the distribution and abundance of corals rather than current speeds, which contradicts the above hypothesis. Recurrent
natural hazards subject the benthic communities to a state of ‘perpetual knock-down and recovery’. Recovery, however, can
be seriously impaired by the chronic ongoing degradation of the coastal marine environment of Mauritius. An urgent review
of its coastal zone management and protection strategy would be desirable for the island. 相似文献
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