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1.
Six reef sites were chosen along the west coast of the southern islands of Singapore, at an increasing distance from the densely populated metropolitan area, to study the spatial patterns of coral reef communities on the upper reef slope ( approximately 4m) and the associated environmental conditions. Chronic exposure to high sediment load was the most obvious form of anthropogenic stress. Recruitment rates on ceramic tiles were low (1.4+/-1.0-20+/-14.7 recruits m(-2) yr(-1)) but decreased towards the main island of Singapore as did hard coral cover and coral density. Coral fauna consisted of genera generally found in deeper waters (e.g., fungiids, foliose Oxypora, Leptoseris, and Echinopora) or those well-adapted to turbid waters (e.g., Porites, Pectinia, Leptastrea, Montipora). Light extinction coefficient (K) and % live coral cover (%LCC) showed a strong and inverse curvilinear relationship (%LCC=13.60 *K(-3.40)). Similarly, the rate of sediment deposition (DFSPM) (RR=1.51-0.17 *DFSPM) and water clarity (RR=3.56-2.92 *K) exhibited strong and inverse relationships with recruitment rates (RR). Although measured levels of the downward flux of suspended particulate matter and suspended solids were well within "normal" levels recorded in the literature, it was the proportion of benthic space, generic coral composition, and site history that offered compelling evidence of chronic exposure to increased sediment load. Clearly a reduction in both water clarity and live-coral cover has taken place since monitoring efforts began in the early 1970s, in fact coral cover has more than halved at all sites examined since the 1980s and benthic space was predominantly occupied by dead corals covered with sediment and filamentous algae.  相似文献   

2.
Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities.  相似文献   

3.
Coral community structure is often governed by a suite of processes that are becoming increasingly influenced by land-use changes and related terrestrial discharges. We studied sites along a watershed gradient to examine both the physical environment and the associated biological communities. Transplanted corals showed no differences in growth rates and mortality along the watershed gradient. However, coral cover, coral richness, and coral colony density increased with increasing distance from the mouth of the bay. There was a negative relationship between coral cover and mean suspended solids concentration. Negative relationships were also found between terrigenous sedimentation rates and the richness of adult and juvenile corals. These results have major implications not only for Pacific islands but for all countries with reef systems downstream of rivers. Land development very often leads to increases in river runoff and suspended solids concentrations that reduce coral cover and coral diversity on adjacent reefs.  相似文献   

4.
The coastal zone of the Great Barrier Reef shelf, with an area of 30,000 km(2) and a water volume of 300 km(3), receives an average annual input of sediment on the order of 14-28 Mty(-1)--an estimated two- to fourfold increase since European settlement. There is considerable concern about the impact and ultimate fate of terrestrially-derived nutrients entering the Great Barrier Reef World Heritage Area (GBRWHA). Analysis of current data suggests that microbial communities in coastal waters and in unconsolidated sediments metabolise nutrients equivalent to the entire dissolved and particulate nutrient load debouched from land. River-derived nutrients account for 40-80% of the carbon, 13-30% of the nitrogen, and 2-5% of the phosphorus necessary to support the observed rates of benthic and pelagic mineralisation in Princess Charlotte Bay in the far north, and in Rockingham Bay and Missionary Bay in the central section, of the GBRWHA. Nearly all nitrogen is ultimately returned to the atmosphere via denitrification. There is little net burial of nutrients in subtidal sediments. These budget estimates are based on a sparse data set, but it is clear that marine sources of nutrients (N-fixation by pelagic and benthic cyanobacteria) must be important, but the magnitude of these sources is poorly known and likely to be highly variable in space and time. Data from sediment trap deployments suggest that, despite significant re-suspension, sedimentation fluxes are sufficient to balance benthic mineralisation rates. Most organic material deposited to the benthos appears to be flocculent or colloidal aggregates, perhaps formed via microbial mediation and exudation of extra-cellular material. The geophysical dynamics of the coastal boundary layer plays an important role in concentrating biological and biogeochemical activity within a shallow, narrow coastal zone. Mangroves and tidal flats are small in area, but trap, transform, and store a disproportionate amount of sediment and organic matter within the GBRWHA. The highly efficient use of terrestrially-derived nutrients by benthic and pelagic microbes in the coastal zone helps to explain why coral reefs on the middle and outer shelf have remained relatively unscathed despite a significant increase in sediment delivery.  相似文献   

5.
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6.
In July 2001, the National Museum of Marine Biology and Aquarium, co-sponsored by the Kenting National Park Headquarters and Taiwan's National Science Council, launched a Long-Term Ecological Research (LTER) program to monitor anthropogenic impacts on the ecosystems of southern Taiwan, specifically the coral reefs of Kenting National Park (KNP), which are facing an increasing amount of anthropogenic pressure. We found that the seawater of the reef flats along Nanwan Bay, Taiwan's southernmost embayment, was polluted by sewage discharge at certain monitoring stations. Furthermore, the consequently higher nutrient and suspended sediment levels had led to algal blooms and sediment smothering of shallow water corals at some sampling sites. Finally, our results show that, in addition to this influx of anthropogenically-derived sewage, increasing tourist numbers are correlated with decreasing shallow water coral cover, highlighting the urgency of a more proactive management plan for KNP's coral reefs.  相似文献   

7.
Successful settlement and recruitment of corals is critical to the resilience of coral reefs. Given that many degraded reefs are dominated by benthic algae, recovery of coral populations after bleaching and other disturbances requires successful settlement amidst benthic algae. Algal turfs often accumulate sediments, sediments are known to inhibit coral settlement, and reefs with high inputs of terrestrial sediments are often dominated by turfs. We investigated the impacts of two algal turf assemblages, and of sediment deposits, on settlement of the coral Acropora millepora (Ehrenberg). Adding sediment reduced coral settlement, but the effects of different algal turfs varied. In one case, algal turfs inhibited coral settlement, whereas the other turf only inhibited settlement when combined with sediments. These results provide the first direct, experimental evidence of effects of filamentous algal turfs on coral settlement, the variability in those effects, and the potential combined effects of algal turfs and trapped sediments.  相似文献   

8.
Cover of the main reef benthic groups, and abundances and taxonomic richness of octocorals were surveyed in the reefs of Hong Kong, and related to spatial and water quality gradients. Nutrient and particle concentrations are high throughout the area, with concentrations declining from the south towards the north-eastern region. Regression tree analyses showed that hard coral cover was most strongly related to water clarity, that macroalgal cover was highest in areas with high wave action and high water clarity, and that crustose coralline algae were negatively related to sedimentation. Octocoral communities (42 species in 23 genera) were dominated by zooxanthellae-free taxa; those few species with zooxanthellae were restricted to reefs with low wave action and high water clarity in the north-eastern region. The water quality gradient spans from conditions that are marginal for zooxanthellate octocorals while still supporting diverse scleractinian communities, towards an estuarine endpoint where zooxanthellate octocorals cease to exist and hard coral communities are reduced to a few resilient colonies. The data suggest that the types, abundances and richness of zooxanthellate octocorals, and the shift from zooxanthellate to azooxanthellate octocoral communities, may act as useful indicators of water clarity in regions where long-term water quality data are unavailable.  相似文献   

9.
Benthic status of 28 near-shore, artisanal, coral reef fishing grounds in the central Philippines was assessed (2000-2002) together with surveys of the seahorse, Hippocampus comes. Our measures of benthic quality and seahorse densities reveal some of the most degraded coral reefs in the world. Abiotic structure dominated the fishing grounds: 69% of the benthos comprised rubble (32%), sand/silt (28%) and dead coral (9%). Predominant biotic structure included live coral (12%) and Sargassum (11%). Rubble cover increased with increasing distance from municipal enforcement centers and coincided with substantial blast fishing in this region of the Philippines. Over 2 years, we measured a significant decrease in benthic 'heterogeneity' and a 16% increase in rubble cover. Poor benthic quality was concomitant with extremely low seahorse densities (524 fish per km(2)). Spatial management, such as marine reserves, may help to minimize habitat damage and to rebuild depleted populations of seahorses and other reef fauna.  相似文献   

10.
Coral recruitment was assessed in highly diverse and economically important Spermonde Archipelago, a reef system subjected to land-based sources of siltation/pollution and destructive fishing, over a period of 2 years. Recruitment on settlement tiles reached up to 705 spat m−2 yr−1 and was strongest in the dry season (July–October), except off-shore, where larvae settled earlier. Pocilloporidae dominated near-shore, while a more diverse community of Acroporidae, Poritidae and others settled in the less polluted mid-shelf and off-shore reefs. Non-coral fouling community appeared to hardly influence initial coral settlement on the tiles, although, this does not necessarily infer low coral post-settlement mortality, which may be enhanced at the near- and off-shore reefs as indicated by increased abundances of potential space competitors on natural substrate. Blast fishing showed no local reduction in coral recruitment and live hard coral cover increased in oligotrophic reefs, indicating potential for coral recovery, if managed effectively.  相似文献   

11.
Reef-associated landforms are coupled to the health of the reef ecosystem which produces the sediment that forms and maintains these landforms. However, this connection can make reef-fronted coastlines sensitive to the impacts of climate change, given that any decline in ecosystem health (e.g. decreasing sediment supply) or changes to physical processes (e.g. sea level rise, increasing wave energy) could drive the sediment budgets of these systems into a net erosive state. Therefore, knowledge of both the sediment sources and transport mechanisms is required to predict the sensitivity of reef-associated landforms to future climate change. Here, we examine the benthic habitat composition, sediment characteristics (composition, texture, and age), and transport mechanisms and pathways to understand the interconnections between coastal morphology and the reef system at Tantabiddi, Ningaloo Reef, Western Australia. Benthic surveys and sediment composition analysis revealed that although live coral accounts for less than 5% of the benthic cover, coral is the dominant sediment constituent (34% on average). Sediment ages (238U/230Th) were mostly found to be thousands of years old, suggesting that the primary sediment source is relic reef material (e.g. Holocene reef framework). Sediment transport across the lagoon was quantified through measurements of ripple migration rates, which were found to be shoreward migrating and responsible for feeding the large shoreline salient in the lee of the reef. The derived sediment fluxes were comparable with previously measured rates of sediment production by bioerosion. These results suggest that sediment budgets of systems dependent on old (>103 years) source materials may be more resilient to climate change as present-day reef health and community composition (i.e. sources of ‘new’ carbonate production) have limited influence on sediment supply. Therefore, the vulnerability of reef-associated landforms in these systems will be dictated by future changes to mechanisms of sediment generation (e.g. bioerosion) and/or physical processes. © 2018 John Wiley & Sons, Ltd.  相似文献   

12.
The Fitzroy estuary (Queensland, Australia) receives large, but highly episodic, river flows from a catchment (144,000 km(2)) which has undergone major land clearing. Large quantities of suspended sediments, and particulate and dissolved organic carbon are delivered. At peak flows, delta(13)C (-21.7+/-0.8 per thousand) and C/N (14.8+/-1.3) of the suspended solids indicate that the particulate organic material entering the estuary is principally soil organic carbon. At the lower beginning flows the particulate organic matter comes from in-stream producers (delta(13)C=-26 per thousand). The DOC load is about 10 times the POC load. Using the inverse method, budgets for POC and DOC were constructed for high and low flows. Under high flows, only a small portion of the POC and DOC load is lost in the estuary. Under dry season (low flow) conditions the estuary is a sink for DOC, but remains a source of POC to the coastal waters.  相似文献   

13.
《国际泥沙研究》2019,34(6):591-599
Increasing continental suspended sediment influx to coral reefs is an example of land-sea coupling that requires the identification of sources, magnitude of transport, and controlling processes. In Brazil, a small coastal basin (Macaé River) was identified as a source of suspended sediment to a coral reef on the coast of Cape Armação dos Búzios. Biannual suspended sediment loads were measured at the basin as were fluxes within the estuary and towards the coast during eight tidal cycles. Particle load and yield from this basin were typical of small coastal basins, showing high to moderate slopes and transitional land management. However, the magnitude of the river loads was lower than the sediment transport within the estuary, indicating that the estuary amplifies river fluxes and sustains the transference of suspended sediment alongshore to the coral reef. Nonetheless, the estuary displays both suspended particle retention and export capacity and, therefore, fluxes to the coast and the coral reef occur as episodic events.  相似文献   

14.
South African coral reefs are limited in size but, being marginal, provide a model for the study of many of the stresses to which these valuable systems are being subjected globally. Soft coral cover, comprising relatively few species, exceeds that of scleractinians over much of the reefs. The coral communities nevertheless attain a high biodiversity at this latitude on the East African coast. A long-term monitoring programme was initiated in 1993, entailing temperature logging and image analysis of high resolution photographs of fixed quadrats on representative reef. Sea temperatures rose by 0.15 degrees C p.a. at the site up to 2000 but have subsequently been decreasing by 0.07 degrees C p.a. Insignificant bleaching was encountered in the region during the 1998 El Nino Southern Oscillation (ENSO) event, unlike elsewhere in East Africa, but quantifiable bleaching occurred during an extended period of warming in 2000. Peak temperatures on the South African reefs thus appear to have attained the coral bleaching threshold. While this has resulted in relatively little bleaching thus far, the increased temperatures appear to have had a deleterious effect on coral recruitment success as other anthropogenic influences on the reefs are minimal. Recruitment success diminished remarkably up to 2004 but appears again to be improving. Throughout, the corals have also manifested changes in community structure, involving an increase in hard coral cover and reduction in that of soft corals, resulting in a 5.5% drop in overall coral cover. These "silent" effects of temperature increase do not appear to have been reported elsewhere in the literature.  相似文献   

15.
The 184 m cargo ship Bunga Teratai Satu collided with Sudbury Reef, part of the Great Barrier Reef and remained grounded for 12 days. The ship was re-floated only 3 days prior to the November 2000 mass coral spawning. No cargo or fuel was lost but the impact resulted in significant contamination of the reef with anti-foulant paint containing tributyltin (TBT), copper (Cu) and zinc (Zn). Larvae of the reef-building scleractinian coral Acropora microphthalma were exposed to various concentrations of sediment collected from the grounding site in replicated laboratory experiments. Two experiments were performed, both of which used varying ratios of contaminated and control site sediment in seawater as treatments. In the first experiment, the influence of contaminated sediment on larval competency was examined using metamorphosis bioassays. In the second, the effect of contaminated sediment upon larval recruitment on pre-conditioned terracotta tiles was assessed. In both experiments, sediment containing 8.0 mg kg(-1) TBT, 72 mg kg(-1) Cu and 92 mg kg(-1) Zn significantly inhibited larval settlement and metamorphosis. At this level of contamination larvae survived but contracted to a spherical shape and swimming and searching behaviour ceased. At higher contamination levels, 100% mortality was recorded. These results indicate that the contamination of sediment by anti-fouling paint at Sudbury Reef has the potential to significantly reduce coral recruitment in the immediate vicinity of the site and that this contamination may threaten the recovery of the resident coral community unless the paint is removed.  相似文献   

16.
A recent comprehensive survey covering 125 sites in Hong Kong waters recorded 29 soft coral species in 14 genera, 38 species of gorgonians in 19 genera and six species of black corals in two genera. Environmental variabilities based on water quality data collected by Hong Kong Environmental Protection Department were analyzed using multivariate statistics to find variables that are significantly correlated with coral distribution patterns. Eleven water quality zones with similar environmental variabilities were recognized, which could further be classified into five groups, namely Inner Bay, Outer Bay, Eastern, Western and Southern waters. LINKTREE analysis provided an overall trend indicating the importance of salinity, sediment and nutrient loadings in affecting octocoral and black coral distribution from west to east of Hong Kong waters, and from inner to outer bays. Furthermore, water turbidity and wave exposure could also affect the coral distribution patterns from north, northeast to southern waters.  相似文献   

17.
This paper presents initial results from a study of factors that inhibit or enhance hard coral recovery in rubble fields created by blast fishing in Komodo National Park and Bunaken National Park, Indonesia. Within nine sites monitored since 1998, there was no significant natural recovery. Levels of potential source coral larvae were assessed with settlement tiles in the rubble fields and in nearby high coral cover sites. Rubble movement was measured and shown to be detrimental to small scleractinians, especially in high current areas. In shallow water (2-6 m deep), rubble is often overgrown by soft corals and corallimorpharians, which inhibit hard coral survival. There is increased scleractinian recruitment in quadrats cleared of soft coral, and Acropora nubbins transplanted into soft coral fields suffer greater mortality than those transplanted above the soft coral canopy. Gaining an understanding of the prognosis for coral recovery is essential not only in order to assess the long-term impacts of blast fishing, but also to improve management decisions about protection of intact reefs and potential restoration of damaged areas.  相似文献   

18.
Coral reef fish communities in the Seychelles are highly diverse and remain less affected by the direct impacts of human activities than those on many other coral reefs in the Indian Ocean. These factors make them highly suitable for a detailed survey of the impacts of the 1998 mass coral mortality, which devastated the coral faunas of the region. Using underwater visual census (UVC) techniques. fish communities were sampled in three localities in the southern Seychelles and one locality in the northern (granitic) Seychelles. Initial surveys were undertaken from the latter site in 1997. Surveys were undertaken at all sites during the coral bleaching episode in 1998 prior to any major changes in the reef fish communities. Repeat surveys were undertaken in 1999 one year after the coral mortality. Over 250 fish species were sampled from 35 families. Results suggest that changes in the overall fish community structures are not great, despite massive changes in the benthic cover. Significant changes have been observed in a number of individual species. These include those most heavily dependent on live coral cover for shelter or sustenance. Future potential changes are discussed, and potential management interventions are considered.  相似文献   

19.
A management proposal aims to partly remove a WWII military causeway at Palmyra Atoll to improve lagoon water circulation and alleviate sedimentation stress on the southeast backreef, an area of high coral cover and diversity. This action could result in a shift in sedimentation across reef sites. To provide management advice, we quantified the proximate environmental factors driving scleractinian coral cover and community patterns at Palmyra. The proportion of fine sedimentation was the optimal predictor of coral cover and changes in community structure, explaining 23.7% and 24.7% of the variation between sites, respectively. Scleractinian coral cover was negatively correlated with increases in fine sedimentation. Removing the causeway could negatively affect the Montipora corals that dominate the western reef terrace, as this genus was negatively correlated with levels of fine sedimentation. The tolerance limits of corals, and sediment re-distribution patterns, should be determined prior to complete removal of the causeway.  相似文献   

20.
The accelerating deterioration of the coral reefs of Eilat has raised debate over the exact causes and how they affect the reefs. The hypothesis of the present study was that a low recruitment rate of reef-building coral species may play an important role in the decline of the Eilat reefs. Our goal was to assess spatial and temporal recruitment patterns in Eilat, focusing on examining the possible impact of human activities. The results of coral recruitment to 10 series of ceramic tiles on metal racks, revealed very low overall recruitment relative to other geographical regions. In addition, we found that recruitment rates and recruit survival were lowest at sites closest to the major eutrophication sources in Eilat. The low recruitment rates may be chronically too low to compensate for the elevated coral mortality rates of recent years. The significant differences between the present study and a similar study carried out during the same period using a different method, emphasize the crucial need for a standardized method for recruitment assessment in coral reefs worldwide.  相似文献   

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