Reef recovery 20 years after the 1982–1983 El Niño massive mortality

For over 20 years the El Niño-Southern Oscillation (ENSO) has caused damage to the coral reefs of the eastern Pacific and other regions. In the mid-1980s scientists estimated that coral cover was reduced by 50–100% in several countries across the region. Almost 20 years (2002) after the 1982–1983 event, we assessed the recovery of the virtually destroyed reefs at Cocos Island (Costa Rica), previously evaluated in 1987 and reported to have less than 4% live coral cover. We observed up to fivefold increase in live coral cover which varied among reefs surveyed in 1987 and 2002. Most new recruits and adults belonged to the main reef building species from pre-1982 ENSO, Porites lobata, suggesting that a disturbance as outstanding as El Niño was not sufficient to change the role or composition of the dominant species, contrary to phase shifts reported for the Caribbean. During the 1990s, new species were observed growing on the reefs. Notably, Leptoseris scabra, considered to be rare in the entire Pacific, was commonly found in the area. Recovery may have begun with the sexual and asexual recruits of the few surviving colonies of P. lobata and Pavona spp. and with long distance transport of larvae from remote reefs. We found an overall 23% live coral cover by 2002 and with one reef above 58% indicating that Cocos Island coral reefs are recovering.     

In situ swimming and settlement behaviour of larvae of an Indo-Pacific coral-reef fish, the coral trout Plectropomus leopardus (Pisces: Serranidae)

Late larvae of the serranid coral trout Plectropomus leopardus (Lacepède), captured in light traps, were released during the day both in open water and adjacent to two reefs, and their behaviour was observed by divers at Lizard Island, northern Great Barrier Reef. Coral trout larvae (n = 110) were present in light-trap catches from 18 November to 3 December 1997, including new moon (30 November). The swimming speed of larvae in open water or when swimming away from reefs was significantly greater (mean 17.9 cm s⁻¹) than the speed of larvae swimming towards or over reefs (mean 7.2 cm s⁻¹). Near reefs, larvae swam at average depths of 2.7 to 4.2 m, avoiding 0 to 2 m. In open water, swimming depth varied with location: larvae >1 km east of Lizard Island swam steeply downward to >20 m in 2 to 4 min; larvae >1 km west oscillated between 2.6 and 13 m; larvae 100 to 200 m east of Lizard Island oscillated between 0.8 and 15 m. Nearly all larvae swam directionally in open water and near reefs. In open water, the average swimming direction of all larvae was towards the island, and 80% (4 of 5) swam directionally (p < 0.05, Rayleigh's test). Larvae swam directionally over the reef while looking for settlement sites. The frequency of behaviours by larvae differed between two reefs of different exposure and morphology. Depending on site, 26 to 32% of larvae released adjacent to reefs swam to open water: of these, some initially swam towards or over the reef before swimming offshore. In some cases, offshore-swimming seemed to be due to the presence of predators, but usually no obvious cause was observed. Depending on the reef, 49 to 64% of the larvae settled. Non-predatory reef residents aggressively approached 19% of settlers. Between 5 and 17% of the larvae were eaten while approaching the reef or attempting to settle, primarily by lizardfishes but also by wrasses, groupers and snappers. A higher percentage of larvae settled in the second week of our study than in the first. Average time to settlement was short (138 s ± 33 SE), but some larvae took up to 15 min to settle. Average settlement depth was 7.5 to 9.9 m, and differed between locations. No settlement took place on reef flats or at depths <4.2 m. Larvae did not appear to be selective about settlement substrate, but settled most frequently on live and dead hard coral. Late-stage larvae of coral trout are capable swimmers with considerable control over speed, depth and direction. Habitat selection, avoidance of predators and settlement seem to rely on vision. Received: 7 July 1998 / Accepted: 26 January 1999     

Field and GIS based post-tsunami assessment of Scleractinian coral cover in the Aerial Bay group of Islands, North Andaman, India

The Aerial Bay group of Islands are one of the diverse environments of Andaman & Nicobar Islands, where the coral reefs degraded much due to the natural calamity of tsunami on 26 December 2004. After this event, the entire North Andaman Islands got elevated, which resulted in the exposure of coral reefs during low tide, causing mass mortalities and destructions to this pristine environment. In order to understand the current status, bio-physical monitoring of coral reefs was carried out and compared with classified coral map of pre-tsunami period. A decline from 411.14 to 68.25 hectares (ha) of live coral area was observed in the Aerial Bay group of Islands. The dead corals and other abiotic factors (sand, mud and rubble) were observed to be 317.33 and 25.56 ha respectively, based on comparisons between ground truthed and classified pre-tsunami coral map (2004) processed in ArcGIS®. The detrended correspondence analysis of coral life form categories showed maximum cover of dead coral with algae, in comparison with the live corals. Bray-curtis cluster analysis revealed three different groups of study sites with 60 % similarity based on life-form categories within the coral reef environment.     

Host preference,site fidelity,and homing behavior of the symbiotically luminous cardinalfish,Siphamia tubifer (Perciformes: Apogonidae)

The sea urchin cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), is unusual among coral reef fishes for its use of bioluminescence, produced by symbiotic bacteria, while foraging at night. As a foundation for understanding the relationship between the symbiosis and the ecology of the fish, this study examined the diel behavior, host urchin preference, site fidelity, and homing of S. tubifer in June and July of 2012 and 2013 at reefs near Sesoko Island, Okinawa, Japan (26°38′N, 127°52′E). After foraging, S. tubifer aggregated in groups among the spines of the longspine sea urchin, Diadema setosum, and the banded sea urchin, Echinothrix calamaris. A preference for D. setosum was evident (P < 0.001), especially by larger individuals (>25 mm standard length, P < 0.01), and choice experiments demonstrated the ability of S. tubifer to recognize and orient to a host urchin and to conspecifics. Tagging studies revealed that S. tubifer exhibits daily fidelity to a host urchin; 43–50 and 26–37 % of tagged individuals were associated with the same urchin after 3 and 7 days. Tagged fish also returned to their site of origin after displacement; by day two, 23–43 and 27–33 % of tagged individuals returned from displacement distances of 1 and 2 km. These results suggest that S. tubifer uses various environmental cues for homing and site fidelity; similar behaviors and cues might be used by larvae for recruitment to settlement sites and for the acquisition of luminous symbiotic bacteria.     

Habitat preferences of coral-associated fishes are altered by short-term exposure to elevated CO2

Rising atmospheric carbon dioxide (CO₂) concentrations are causing additional CO₂ to be absorbed by the oceans. Recent studies show that exposure to elevated CO₂ causes olfactory impairment in reef fishes; however, the ecological consequences of this impairment are largely unknown. This study examined the effects of short-term exposure to elevated CO₂ on habitat preferences of coral-dwelling gobies. Adult gobies collected from the reef at Lizard Island (Great Barrier Reef, Australia) were exposed for 4 days to ambient CO₂ (440 μatm) or elevated CO₂ (880 μatm). Habitat preferences were then tested in laboratory and field experiments at ambient conditions. In olfactory preference tests, Paragobiodon xanthosomus displayed a strong preference for odour cues of their sole host coral Seriatopora hystrix; however, this preference was absent in gobies exposed to elevated CO₂. Habitat choice experiments conducted in the field showed that Gobiodon histrio placed on dead coral colonies located preferred live habitat within 24 h; however, gobies exposed to elevated CO₂ associated with both preferred and non-preferred habitats in approximately equal frequency. Preferred habitats are known to confer fitness advantages to coral-dwelling gobies. Consequently, these results suggest that future elevated CO₂ levels might affect the ability of habitat specialist fishes to select favourable habitats.     

A geological perspective on the degradation and conservation of western Atlantic coral reefs

Continuing coral‐reef degradation in the western Atlantic is resulting in loss of ecological and geologic functions of reefs. With the goal of assisting resource managers and stewards of reefs in setting and measuring progress toward realistic goals for coral‐reef conservation and restoration, we examined reef degradation in this region from a geological perspective. The importance of ecosystem services provided by coral reefs—as breakwaters that dissipate wave energy and protect shorelines and as providers of habitat for innumerable species—cannot be overstated. However, the few coral species responsible for reef building in the western Atlantic during the last approximately 1.5 million years are not thriving in the 21st century. These species are highly sensitive to abrupt temperature extremes, prone to disease infection, and have low sexual reproductive potential. Their vulnerability and the low functional redundancy of branching corals have led to the low resilience of western Atlantic reef ecosystems. The decrease in live coral cover over the last 50 years highlights the need for study of relict (senescent) reefs, which, from the perspective of coastline protection and habitat structure, may be just as important to conserve as the living coral veneer. Research is needed to characterize the geological processes of bioerosion, reef cementation, and sediment transport as they relate to modern‐day changes in reef elevation. For example, although parrotfish remove nuisance macroalgae, possibly promoting coral recruitment, they will not save Atlantic reefs from geological degradation. In fact, these fish are quickly nibbling away significant quantities of Holocene reef framework. The question of how different biota covering dead reefs affect framework resistance to biological and physical erosion needs to be addressed. Monitoring and managing reefs with respect to physical resilience, in addition to ecological resilience, could optimize the expenditure of resources in conserving Atlantic reefs and the services they provide.     

Sedentary or mobile? Variability in space and depth use of an exploited coral reef fish

Movement of fishes defines the distribution and abundance of populations and occurs on a range of spatial and temporal scales. To successfully parameterise assessments and design management strategies for exploited fish populations, knowledge and consideration of their movement patterns are essential. Since the efficacy of management approaches vary depending on the sedentary or mobile nature of the target species, presence, space use and depth utilisation were examined to understand the movement patterns of redthroat emperor Lethrinus miniatus. Sixty individuals were monitored for up to 12 months in an acoustic array comprising three coral reefs, and variation in space use and movement patterns was observed among 26 individuals. Half of the individuals were recorded only in proximity of one receiver along the reef edge, while the other half were detected at multiple receivers and used horizontal areas of approximately 4 km². Periods of non-detection and lower detection frequency at night (χ ₁ ²  = 342.157, P < 0.001) indicated individuals may move away from the monitored reef edge to the adjacent sandy habitat, but most movements outside the array remain unknown. Long-distance movement was recorded for one individual, recaptured ~160 km from the release location. Generally, no trends in depth use were apparent, L. miniatus inhabited a variety of depths, which were not related to individual size or time of day, yet some effect of month was evident. Variation in movement among adult L. miniatus indicates that while some individuals undergo broader-scale movement, spatial closures that cover individual reefs (>4 km²) could provide protection from fishing for the proportion of the population that displayed high site fidelity and moderate-sized activity spaces (over a period of up to 12 months).     

Spatial and temporal variation in coral recruitment on the Great Barrier Reef: Implications for dispersal hypotheses

Over 15 000 coral recruits were counted on settlement plates from three mid-shelf reefs and six fringing reefs in the northern section of the Great Barrier Reef during two summers (1986 and 1987) and one winter (1987). The density of coral recruits on some settlement plates from a fringing reef was up to 4.88 cm^–2, the highest value ever reported. Mean density of recruits was greater on fringing reefs (81.1 recruits/settlement plate) than on mid-shelf reefs (15.6 recruits/settlement plate), but there was greater spatial variation in abundance of recruits between the fringing reef sites. Other differences between the mid-shelf reefs and the fringing reefs were that different taxa were dominant, and that settlement orientation differed, with mid-shelf recruits settling preferentially on horizontally oriented surfaces and fringingreef recruits preferring vertical surfaces. Of the three midshelf reefs, Green Island reef recorded the highest recruitment rate for each of the two summers, despite having a depauperate adult coral population following predation by the asteroidAcanthaster planci. This suggests that coral larvae frequently travel between reefs. In contrast with an earlier study, there was no consistent difference in abundance of recruits between forereef and backreef locations. Overall, the results indicated great spatial variation in the availability of coral larvae, both on the scale of whole reefs and within-reef habitats.     

化学污染物对珊瑚礁生态系统的影响研究进展

化学污染物是影响珊瑚礁生态系统健康的重要因素之一。近年来,中国沿海地区农业活动、城市工业化以及旅游业发展迅速,珊瑚礁区的环境污染问题日趋严重。珊瑚礁生态系统长期处于化学污染物的联合毒性作用下,生态风险日益增加,已受到国内外研究者的广泛关注。本文综述了该领域的重要研究进展,并从个体、细胞和分子水平重点介绍了化学污染物对珊瑚的影响,主要包括:(1)珊瑚礁对重金属和多环芳烃有明显的富集作用,可以作为该海域化学污染物污染水平的外在反映;(2)化学污染物对珊瑚幼体的影响程度比成体大;(3)抗氧化酶和特定的功能基因可被用作生物标记物(biomarker)来监测珊瑚礁生态系统的健康状况。最后,本文对我国珊瑚礁生态系统未来的研究方向进行了展望,建议在典型的珊瑚礁海域进行长期的生态学监测,并结合室内毒理学实验,筛选出敏感的生物标志物,评价珊瑚礁生态系统可能存在的生态风险,为今后珊瑚礁生态系统的保护和管理提供科学依据。     

Coral-spawn slicks in the Great Barrier Reef: preliminary observations

Aerial surveys and surface samples in the spring of 1985, showed that slicks of coral eggs and embryos (coral spawn) formed in large numbers within and between reefs in the Central Great Barrier Reef Region. Coral-spawn slicks appeared on the days immediately following the annual mass multispecific spawning of reef corals. They were white or pink in colour, and were often highly elongate in form extending up to 5 km in length, and 10 m in width. Over 99% of each slick sampled during the surveys consisted of dead eggs, embryos and their breakdown products, which formed dense, highly viscous patches readily recognizable during aerial surveys. Despite the low proportion of live material, the slicks contained high concentrations of live embryos (15 to 230 per litre) which were over two orders of magnitude greater than concentrations in adjacent water masses. The distinctive colour, shape and texture of the coral-spawn slicks generally distinguished them from slicks formed by blooms of the blue-green alga Oscillatoria erythraea, which also occur commonly in the region. Many of the slicks were closely associated with surface oceanographic features, such as fronts between water parcels, and wakes and eddies behind reefs. Although more detailed sampling and surveys are required, these results suggest that it may be possible to track the movements of coral embryos and larvae directly for the first one or two days following mass spawning, and indirectly thereafter by monitoring other surface features.     

Fine-scale distribution of larval fishes: patterns and processes adjacent to coral reefs in Kaneohe Bay,Hawaii

Plankton samples were taken from January to June 1987 in Kaneohe Bay, Oahu, Hawaiian Islands, with a free-fall plankton net, to investigate the fine-scale distribution of larval fishes around coral reefs. Daytime samples indicated that the postflexion larvae of two gobiids (Psilogobius mainlandi and an unidentified species) were significantly more abundant at stations immediately adjacent to reefs (near-reef) than at stations in open water off the reef (off-reef). These postflexion gobiid larvae appeared to be capable of resisting advection and dispersal while remaining in the water column near suitable adult habitats. The larvae of Foa brachygramma (Apogonidae) and Encrasicholina purpurea (Engraulidae) were significantly more abundant at off-reef stations than at near-reef stations. Nighttime samples indicated that the gobiid larvae depend on visual cues to remain near the reef. The horizontal distributions of F. brachygramma and E. purpurea larvae appeared to be related to their vertical positioning. These data suggest that typical ichthyoplankton surveys which do not sample close to adult fish habitats would greatly underestimate the abundances of larvae such as the gobiids.     

Temporal and spatial variability in coral recruitment on two Indonesian coral reefs: consistently lower recruitment to a degraded reef

Corals are the primary reef-building organisms, therefore it is key to understand their recruitment patterns for effective reef management. Coral recruitment rates and juvenile coral abundance were recorded in the Wakatobi National Marine Park, Indonesia, on two reefs (Sampela and Hoga) with different levels of environmental degradation (12.5 vs. 44 % coral cover with high and low sedimentation rates, respectively) to examine consistencies in recruitment patterns between years and seasons. Recruitment was measured on multiple panels at two sites on each reef (6–7 m depth) and cleared areas of natural reef. Although coral recruitment was twofold higher in 2008–2009 than in 2007–2008, and seasonal differences were identified, consistent significant differences in recruitment rates were found between the two reefs even though they are separated by only ~1.5 km. Recruitment rates and juvenile abundance were lower on the more degraded reef. These patterns are likely a consequence of differential pre- and post-settlement mortality as a result of the high sedimentation rates and degraded conditions and possibly reduced larval supply.     

Importance of macroalgal fields as coral reef fish nursery habitat in north-west Australia

Macroalgal fields are a feature of the shallow tropical benthos, yet their importance for coral reef fish population dynamics remains poorly understood. The abundance of fish recruits was recorded using underwater visual census at six macroalgal and 11 coral reef sites in the Montebello and Barrow Islands. Surveys identified 6,935 individual recruit fish from 105 species, 54 genera and 20 families. Of these, 1,401 recruits from 48 species, 31 genera and 14 families were observed in macroalgal sites. Sixteen of the 105 recruit species (15.2 %) were observed exclusively at macroalgal sites. Forty-two (87.5 %) of these species have been observed as adults on adjacent coral reefs. Species composition of fish recruits differed significantly between the two habitats. Corallivore, small omnivore and zooplanktivore recruits had significantly higher numbers in the coral sites, while the results clearly demonstrate that juveniles, within the genera Lethrinus and Choerodon, as well as large algal croppers, are predominantly found at macroalgal (74–100 %) rather than coral-dominated sites. High-canopy macroalgae cover was positively correlated with abundance of these taxa, particularly Lethrinids (r ² = 0.40). This study is the first to highlight the important attributes of tropical macroalgal fields and suggests that they have a similar role to seagrass meadows as essential juvenile habitat, thus warranting greater attention in conservation planning and ecological studies.     

The relationship between lunar periodicity and activity of fish-parasitic gnathiid isopods in the Caribbean

Gnathiid isopod larvae are members of the marine demersal zooplankton community and are common ectoparasites of coral reef fishes, emerging from the substratum, mostly at night and crepuscular periods to feed on fish blood. Given that the activity of many marine organisms is often linked to changes in the phase of the moon, we examined the relationship between lunar phase and activity in gnathiid isopods on Caribbean reefs. We employed two sampling methods to quantify gnathiid activity: (1) Emergence traps set on reefs over a 24 h period; and (2) live fish placed in cages on reefs and retrieved during night and dawn peaks in gnathiid activity. These were compared during discrete phases as well as a continuous metric, the lunar “angle”, and an estimate of ambient light availability (luminance). Lunar phase and angle varied in their statistical effect on gnathiid activity patterns by sampling method and/or year. Luminance had a significant but inconsistent effect on measures of gnathiid activity. Our results suggest that changes in the lunar cycle are not a strong predictor of gnathiid activity at our shallow reef study sites.     

Porites and the Phoenix effect: unprecedented recovery after a mass coral bleaching event at Rangiroa Atoll,French Polynesia

The 1997/1998 El Niño Southern Oscillation (ENSO) was the most severe coral bleaching event in recent history, resulting in the loss of 16 % of the world’s coral reefs. Mortality was particularly severe in French Polynesia, where unprecedented mortality of massive Porites was observed in lagoonal sites of Rangiroa Atoll. To assess the recovery of massive Porites 15 years later, we resurveyed the size structure and extent of partial mortality of massive Porites at Tivaru (Rangiroa). Surveys revealed an abundance of massive Porites colonies rising from the shallow lagoonal floor. Colony width averaged 2.65 m, reaching a maximum of 7.1 m (estimated age of ~391 ± 107 years old). The relative cover of recently dead skeleton within quadrats declined from 42.8 % in 1998 to zero in 2013, yet the relative cover of old dead skeleton increased only marginally from 22.1 % in 1998 to 26.1 % in 2013. At a colony level, the proportion of Porites dominated by living tissue increased from 34.9 % in 1998 to 73.9 % in 2013, indicating rapid recovery of recent dead skeleton to living tissue rather than transitioning to old dead skeleton. Such rapid post-bleaching recovery is unprecedented in massive Porites and resulted from remarkable self-regeneration termed the ‘Phoenix effect’, whereby remnant cryptic patches of tissue that survived the 1997/1998 ENSO event regenerated and rapidly overgrew adjacent dead skeleton. Contrary to our earlier predictions, not only are large massive Porites relatively resistant to stress, they appear to have a remarkable capacity for recovery even after severe partial mortality.     

The distribution of molluscan assemblages and their postmortem fate on coral reefs in the Gulf of Aqaba (northern Red Sea)

Molluscan assemblages were studied on fringing reefs (reef flats, Millepora-fringing reefs, fringing reefs with massive corals) and fore-reef hard substrata (coral patches, coral carpets and small patch reefs) in the Gulf of Aqaba at water depths ranging from the intertidal to 26 m. A total of 1,665 molluscan individuals from 51 taxa was counted on 44 transects, which covered 220 m2 at eight diving sites. The most important molluscs in the assemblage were the parasitic gastropod Coralliophila neritoidea, the encrusting gastropod Dendropoma maxima and the coral-associated bivalve Pedum spondyloideum. The dead assemblage, in contrast, was dominated by encrusting bivalves (Ostreoidea, Chamoidea, Spondylidae) and the coral-predating gastropod Drupella cornus. Distinct molluscan assemblages inhabit each of the three fringing reef-habitats and most of the important depth-related community changes occurred within the uppermost 5 m. In contrast, the three deeper fore-reef habitats are characterized by a more uniform molluscan composition. Molluscan assemblages were more dependent on substrata and their coral associations than on water depth. Comparisons with other published studies indicate that reefoidal hard substrata in the northern Red Sea are largely characterized by similar species-abundance patterns. The minor differences to other Red Sea studies probably reflect the northern, isolated position of the Gulf of Aqaba, the lack of certain molluscan habitats, and the differential impact of anthropogenic influences. Strong differences between living and dead assemblages in Aqaba are similar to those observed in other regions and are due to distinct biases in the dead assemblage. Molluscs closely associated with living corals (mostly bivalves and Dendropoma) can easily be overgrown after death and are thus undetectable in visual censuses. Some gastropod taxa are preferentially transported into surrounding soft-substrata postmortem or redistributed by hermit crabs. Such complex relationships between ecology and taphonomy are crucial in evaluating the quality of the molluscan fossil record in coral reef environments. The comparison of our results with literature data documents an increase in coral predators during the last two decades in the northern Red Sea. Due to the greater mollusc biodiversity in the shallower Aqaba reef habitats, damage to this coral reef zone would have the greatest impact on the overall mollusc community.     

Recreational diving impacts and the use of pre-dive briefings as a management strategy on Florida coral reefs

Ecotourism often is promoted as an ecologically sustainable activity, but some ecotourism activities negatively impact coastal ecosystems. Impacts of intensive diving tourism on coral reefs remain poorly understood, especially in the Florida Keys. We determined patterns of recreational dive frequency, diver behaviour, and coral damage on reefs near Key Largo, and assessed how pre-dive briefings and other factors affect these damage rates. Recreational divers contacted live stony corals ~ 18 times per scuba dive; most contacts deposited sediment onto corals, but also caused abrasion to coral tissues and fracture of coral skeletons. Divers who received pre-dive ecological briefings caused significantly less coral damage than those who did not, and divers with cameras and/or gloves caused the most damage. The proportion of damaged corals increased significantly with the estimated rate of recreational diving on each reef, and the percent cover of live corals decreased. We conclude that current rates of recreational diving in Key Largo are unsustainable, resulting in damage to >80 % of coral colonies and reduction of live coral cover to <11 % at heavily-dived sites. We recommend that dive tour operators administer pre-dive ecological briefings to all recreational divers, provide extra briefings to camera and glove users, and employ underwater dive guides who intervene when divers inadvertently damage live stony corals. This study provides a scientific basis to support management of intensive ecotourism on Florida coral reefs.     

Possible effects of water pollution on the community structure of Red Sea corals

The community structure and species diversity of hermatypic corals was studied during 1969–1973, in two reef flats in the northern Gulf of Eilat, Red Sea: the reef flat of the nature reserve at Eilat, which is chronically polluted by oil and minerals, and a control reef, located 5 km further south, which is free from oil pollution. In 1969, the nature reserve and the control reef had similar coral community structure. In September, 1970, both reefs suffered approximately 90% mortality of corals, as a result of an unexpected and extremely low tide. In 1973 the control reef was “blooming” with a highly diverse coral community, while almost no signs of coral recolonization have been observed at the nature reserve, and it is significantly lower in diversity. It is suggested that phosphate eutrophication and chronic oil pollution are the major man-made disturbances that interfere with coral colonization of the reef flat at the nature reserve. Although no direct evidence is provided that oil damages hermatypic corals, the data strongly suggest that chronic oil spills prevent normal settlement and/or development of coral larvae. It is possible that chronic oil, pollution results in either one or a combination of the following: (1) damage to the reproductive system of corals; (2) decreased viability of coral larvae; (3) changes in some physical properties of the reef flat which interfere with normal settlement of coral larvae.     

The 1998 bleaching event and its aftermath on a coral reef in Belize

Widespread thermal anomalies in 1997-1998, due primarily to regional effects of the El Niño-Southern Oscillation and possibly augmented by global warming, caused severe coral bleaching worldwide. Corals in all habitats along the Belizean barrier reef bleached as a result of elevated sea temperatures in the summer and fall of 1998, and in fore-reef habitats of the outer barrier reef and offshore platforms they showed signs of recovery in 1999. In contrast, coral populations on reefs in the central shelf lagoon died off catastrophically. Based on an analysis of reef cores, this was the first bleaching-induced mass coral mortality in the central lagoon in at least the last 3,000 years. Satellite data for the Channel Cay reef complex, the most intensively studied of the lagoonal reefs, revealed a prolonged period of elevated sea-surface temperatures (SSTs) in the late summer and early fall of 1998. From 18 September to 1 October 1998, anomalies around this reef averaged +2.2°C, peaking at 4.0°C above the local HotSpot threshold. In situ temperature records from a nearby site corroborated the observation that the late summer and early fall of 1998 were extraordinarily warm compared to other years. The lettuce coral, Agaricia tenuifolia, which was the dominant occupant of space on reef slopes in the central lagoon, was nearly eradicated at Channel Cay between October 1998 and January 1999. Although the loss of Ag. tenuifolia opened extensive areas of carbonate substrate for colonization, coral cover remained extremely low and coral recruitment was depressed through March 2001. High densities of the sea urchin Echinometra viridis kept the cover of fleshy and filamentous macroalgae to low levels, but the cover of an encrusting sponge, Chondrilla cf. nucula, increased. Further increases in sponge cover will impede the recovery of Ag. tenuifolia and other coral species by decreasing the availability of substrate for recruitment and growth. If coral populations are depressed on a long-term basis, the vertical accretion of skeletal carbonates at Channel Cay will slow or cease over the coming decades, a time during which global-warming scenarios predict accelerated sea-level rise.     

Resource use by five sympatric parrotfishes in the San Blas Archipelago,Panama

Resource use by five sympatric species of parrotfish was quantified in the San Blas Archipelago of the Republic of Panama from March to August 1987. Detailed observations of parrotfishes on patch reefs and surrounding seagrass beds showed that they partition resources with respect to habitat, food and size, but not time. Although parrotfishes shared resources, the proportions of each resource used differed significantly among species. Scarus iserti (Bloch) scraped filamentous microalgae that grew from eroded coral pavement on lower slopes of patch reefs and in halos, the area of sparse vegetation surrounding reefs. Sparisoma viride (Bonnaterre) foraged on upper slopes of patch reefs where they mostly took bites from dead coral and associated algae. S. aurofrenatum (Cuvier and Valenciennes) had the broadest diet, which consisted mostly of seagrasses and macro- and microalgae that were attached to dead coral on lower reef slopes and in halos. Although S. chrysopterum (Bloch and Schneider) commonly occurred on patch reefs, it primarily foraged in seagrass beds that surround them. S. rubripinne (Cuvier and Valenciennes) was distributed most widely, ranging from seagrass beds to reef crests, where it took bites from seagrasses, dead coral and macroalgae. Juveniles of all species occurred on lower slopes or in halos where they scraped filamentous microalgae from coral pavement. As they matured, parrotfishes moved into other habitats changing access to different types of food. All of these parrotfishes fed throughout the daytime, and resource use did not differ between morning and afternoon.