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

 Macroboring organisms are recognised as key agents of reef framework modification and destruction, and while recent studies in the Pacific have improved understanding of spatial variations in macroboring community structure, and rates of macroboring within individual reefs, comparable studies from the Caribbean are largely lacking. This study assesses the distribution of macroboring species and the degree of framework infestation across the reefs at Discovery Bay, north Jamaica. Although individual species of borers exhibit variable distributions across the reef, relative abundances of the main groups of macroborers (sponges, bivalves, worms) illustrate clear distributional trends. Sponges are dominant at fore-reef sites, while sipunculan and polychaete worms are only of importance at back-reef/lagoon and shallow fore-reef sites. Bivalves are locally important within back-reef and lagoon patch reef framework. Average percentages of internal bioerosion (macroboring) vary between sites, but are highest at back-reef and deep fore-reef sites. No systematic pattern of variation occurs within back-reef/lagoon samples, but a significant trend of increased macroboring is recognised with increased water depth on the fore-reef. In addition, significant differences in terms of the susceptibility of individual coral species are recognised. These factors are likely to result in biasing of the fossil record, with variable styles of preservation evident both between sites (i.e. with depth/environment) and within sites (i.e. between coral species). Accepted: 1 June 1998     

Calcium carbonate budgets for two coral reefs affected by different terrestrial runoff regimes, Rio Bueno, Jamaica

A process-based carbonate budget was used to compare carbonate framework production at two reef sites subject to varying degrees of fluvial influence in Rio Bueno, Jamaica. The turbid, central embayment was subjected to high rates of fluvial sediment input, framework accretion was restricted to ≤30 m, and net carbonate production was 1,887 g CaCO₃ m⁻² year⁻¹. Gross carbonate production (GCP) was dominated by scleractinians (97%), particularly by sediment-resistant species, e.g. Diploria strigosa on the reef flat (<2 m). Calcareous encrusters contributed very little carbonate. Total bioerosion removed 265 g CaCO₃ m⁻² year⁻¹ and was dominated by microborers. At the clear-water site, net carbonate production was 1,236 g CaCO₃ m⁻² year⁻¹; the most productive zone was on the fore-reef (10 m). Corals accounted for 82% of GCP, and encrusting organisms 16%. Bioerosion removed 126 g CaCO₃ m⁻² year⁻¹ and was dominated by macroborers. Total fish and urchin grazing was limited throughout (≤20 g CaCO₃ m⁻² year⁻¹). The study demonstrates that: (1) carbonate production and net reef accretion can occur where environmental conditions approach or exceed perceived threshold levels for coral survival; and (2) although live coral cover (and carbonate production rates) were reduced on reef-front sites along the North Jamaican coast, low population densities of grazing fish and echinoids to some extent offset this, thus maintaining positive carbonate budgets.     

Experimental studies of rapid bioerosion of coral reefs in the Galápagos Islands

Experimental carbonate blocks of coral skeleton,Porites lobata (PL), and cathedral limestone (LS) were deployed for 14.8 months at shallow (5–6 m) and deep (11–13m) depths on a severely bioeroded coral reef, Champion Island, Galápagos Islands, Ecuador. Sea urchins (Eucidaris thouarsii) were significantly more abundant at shallow versus deep sites.Porites lobata blocks lost an average of 25.4 kg m^–2yr^–1 (23.71 m^–2yr^–1 or 60.5% decrease yr^–1). Losses did not vary significantly at depths tested. Internal bioeroders excavated an average of 2.6 kg m^–2 yr^–1 (2.41 m^–2 yr^–1 or 0.6% decrease yr^–1), while external bioeroders removed an average of 22.8 kg m^–2 yr^–1). (21.31 m^–2 yr^–1). or 59.9% decrease yr^–1). few encrusting organisms were observed on the PL blocks. Cathedral limestone blocks lost an average of 4.1 kg m^–2 yr^–1). (1.81 m^–2 yr^–1). or 4.6% decrease yr-'), also with no relation to depth. Internal bioeroders excavated an average of 0.6 kg m^–2 yr^–1). (0.31 m^–2 yr^–1). or 0.7% decrease yr^–1). and external bioeroders removed an average of 3.5 kg m^–2 yr^–1). (1.51 m^–2 yr^–1). or 3.9% decrease yr^–1). from the LS blocks. Most (57.6%) encrustation occurred on the bottom of LS blocks, and there was more accretion on block bottoms in deep (61.4 mg cm^–2 yr^–1). versus shallow (35.0 mg cm^–2 yr^–1) sites. External bioerosion reduced the average height of the reef framework by 0.2 cm yr^–1). for hard substrata (represented by LS) and 2.3 cm yr^–1). for soft substrata (represented by PL). The results of this study suggest that coral reef frameworks in the Galápagos Islands are in serious jeopardy. If rates of coral recruitment do not increase, and if rates of bioerosion do not decline, coral reefs in the Galápagos Islands could be eliminated entirely.     

Coral Growth and Bioerosion of Porites lutea in Response to Large Amplitude Internal Waves

The Similan Islands (Thailand) in the Andaman Sea are exposed to large amplitude internal waves (LAIW), as evidenced by i.a. abrupt fluctuations in temperature of up to 10°C at supertidal frequencies. Although LAIW have been shown to affect coral composition and framework development in shallow waters, the role of LAIW on coral growth is so far unknown. We carried out a long-term transplant experiment with live nubbins and skeleton slabs of the dominating coral Porites lutea to assess the net growth and bioerosion in LAIW-exposed and LAIW-protected waters. Depth-related, seasonal and interannual differences in LAIW-intensities on the exposed western sides of the islands allowed us to separate the effect of LAIW from other possible factors (e.g. monsoon) affecting the corals. Coral growth and bioerosion were inversely related to LAIW intensity, and positively related to coral framework development. Accretion rates of calcareous fouling organisms on the slabs were negligible compared to bioerosion, reflecting the lack of a true carbonate framework on the exposed W faces of the Similan Islands. Our findings show that LAIW may play an important, yet so far overlooked, role in controlling coral growth in tropical waters.     

Comments on coral reef regeneration, bioerosion, biogeography, and chemical ecology: future directions

This paper represents a brief review of three processes operating on coral reefs and the results of studies of a fourth process, and how those results may be applied to the benefit of humankind. The areas are reef regeneration processes; bioerosion; dispersal, recruitment and biogeography of corals; and chemical ecology and natural products chemistry of reef organisms. Possible future directions for research will also be considered in each area. Regarding reef regeneration processes, coral reefs are degrading rapidly on a global scale due to over-fishing, fishing techniques causing habitat destruction, deforestation, mass mortalities of key reef species, nutrient enrichment and sedimentation. Seeding of reefs with the larvae of corals and other key reef organisms, such as echinoids, may help to promote and enhance reef regeneration in the future. Such techniques will be made possible by studies of the embryology, larval ecology, dispersal and recruitment processes, and related local physical oceanographic processes. Regarding bioerosion, both internal and external bioerosion are affected by grazers and predators. Bioerosion is also affected by nutrient enrichment, as shown through correlative studies (Great Barrier Reef) and studies of opportunity (Kaneohe Bay). Ongoing experiments such as ENCORE will help to answer questions about the role of dissolved nutrients in enhancing internal bioerosion. Questions still remain, however, regarding the role of particulates in promoting internal bioerosion and the resultant weakening of and negative growth in the reef framework. Regarding dispersal, recruitment and the biogeography of corals, it is now known that most species of coral reproduce via broadcasting, although there appear to be proportionally more brooders in the Caribbean than in the western Pacific. Differential extinctions in the western Pacific vs. the western Atlantic have contributed to the biogeographic distribution of corals we observe today and the concentric isoclines of species diversity in numerous reef organisms in the western Pacific. The role of reproductive mode in contributing to these patterns is, however, still not understood. Investigations into the roles of different larval longevities and reproductive modes may help us answer questions regarding their differential distribution and the potential effects of major perturbations such as global warming on future distributions. With respect to the chemical ecology of alcyonacean octocorals (soft corals), four functions have been determined thus far for secondary metabolites in this group, anti-predation, anti-competition (allelopathy), anti-fouling, and enhancement of reproductive success. Investigations of alcyonacean reproduction has revealed that it may be necessary for several secondary metabolites to be present simultaneously before a function may be realized or fully manifested. This raises questions regarding the manner in which novel compounds are tested by medical laboratories for bioactivity using a single compound. Simultaneously testing of multiple compounds derived from a single organism may be necessary in the future to reveal potential valuable synergistic bioactivity. Also, some novel secondary metabolites may have other valuable commercial applications, as is the case with the UV-absorbing compounds of corals and other reef organisms found on the Great Barrier Reef. In order to avoid overlooking medically or commercially valuable functions of these compounds, broader testing may be necessary.     

Spatial variation in sea urchins, fish predators, and bioerosion rates on coral reefs of Belize

Although sea urchins are critical for controlling macroalgae on heavily fished coral reefs, high densities threaten reefs, as urchins are also prodigous bioeroders. This study examined urchin population characteristics, bioerosion rates, their fish predators (Labridae), and potential competitors (Scaridae) on unprotected reefs and a reef within a marine protected area (MPA) in the lagoonal regions off Belize. Urchin density (<1 m⁻²) and bioerosion rates (∼0.2 kg CaCO₃ m⁻² year⁻¹) were lowest and members of the Labridae were the highest (∼20 fish 200 m⁻³) within the MPA, while several unprotected reefs had higher (∼18–40 m⁻²) urchin densities, lower Labridae abundances (1–3 fish 200 m⁻³), and bioerosion rates ranging from ∼0.3–2.6 kg CaCO₃ m⁻² year⁻¹. Urchin abundances were inversely related to Labridae (wrasses and hogfish) densities; however, on reef ridges, low algal cover (∼15%), small urchin size (∼14 mm), and low proportion of organic material in urchin guts suggested food limitation. Both top–down (predation) and bottom–up factors (food limitation) likely contribute to the control of urchins, predominantly Echinometra viridis, off Belize, thereby potentially diminishing the negative impacts of bioerosion activities by urchins.     

Macrobioerosion in Porites corals in subtropical northern South China Sea: a limiting factor for high-latitude reef framework development

Bioerosion is an important limiting factor in carbonate accretion and reef framework development; however, few studies have quantified the direct impact of macroborers on high-latitude coral communities, which are viewed as potential refuge during a period of global warming. In this study, internal macrobioerosion of Porites corals was examined at Daya Bay, subtropical northern South China Sea. The principal borers were the bivalve Lithophaga spp. and the sponges Cliona spp. and Cliothosa spp. (≥80 %), while sipunculid and polychaete worms and barnacles accounted for small amounts of bioerosion (≤20 %). Porites corals were heavily bioeroded in areas impacted by aquacultural and urban activities (10.34–27.55 %) compared with corals in relatively unpolluted areas (2.18–6.76 %). High levels of bioerosion, especially boring bivalve infestation, significantly weaken the corals and increase their susceptibility to dislodgement and fragmentation in typhoons, limiting accumulation of limestone framework. This study implies that carbonate accretion and reef development for high-latitude coral communities may be limited in future high-CO₂ and eutrophication-stressed environments.     

Coral disease dynamics at a subtropical location, Solitary Islands Marine Park, eastern Australia

Recent observations suggest that a spreading disease is increasingly contributing to hard coral mortality in the Solitary Islands Marine Park, NSW, Australia. This study determined coral disease prevalence and rate-of-spread through individual affected colonies and investigated the effect this epizootic had on coral populations at sites adjacent to South West Solitary Island. Quantitative data were collected between 2002 and 2004 using photographic and video methods, and visual census along radial arc belt transects. Disease similar to the reported white syndrome and white plague was apparent, spreading through hard coral species from the genera Turbinaria, Acropora, Goniastrea, Pocillopora, Stylophora and Porites. Coral disease prevalence varied between survey dates with mean prevalence increasing from 8.55% during March 2003 to 13.58% in June and declining to 7.75% in September and 6.21% during March 2004. There was a significant difference in mean prevalence between the affected species (p<0.001) and an overall difference between survey dates (p=0.001). Additionally, the rate-of-spread of coral disease through coral colonies determined using repeated, seasonal, still photographs followed similar patterns, with disease progression differing between affected species (p=0.004), and between survey dates (p<0.001). Analysis of the video-transects indicated significant difference in disease prevalence over larger spatial scales (100s of m). However, disease frequency did not vary significantly between 2002 and 2003.     

Distribution and environmental control of coral assemblages in northern Safaga Bay (Red Sea, Egypt)

Summary Coral assemblages in northern Safaga Bay, Red Sea, Egypt, are qualitatively described. Nine distinct assemblages were found, which correspond to quantitatively defined community types previously described from the area off Hurghada, northern Red Sea. Their distribution within northern Safaga Bay was mapped. Strong gradient and/or steep relief assemblages were:Acropora assemblage on windward (exposed) reefs,Porites assemblage on leeward (sheltered) reefs,Millepora assemblage on current exposed reefs,Stylophora assemblage on reef flats. Low gradient and/or low relief assemblages were:Acropora dominated coral patches in areas of good circulation to a depth of 15 m,Stylophora/Acropora coral patch assemblages in shallow sheltered environments, faviid carpet in low relief areas between 10 and 25 m which with increasing turbidity turns into a depauperate faviid carpet,Porites carpet in low relief areas between 5 and 15 m with clearest water,Sarcophyton carpet in low relief areas with high suspension load, platy scleractinian assemblage in deeper water (>25 m) with low light intensity. The distribution of coral assemblages depends basically on 1) topography 2) hydrodynamics 3) light and 4) suspension load.     

Trophic structure and productivity of the lagoonal communities of Tikehau atoll (Tuamotu Archipelago,French Polynesia)

Carbon standing stocks and fluxes were studied in the lagoon of Tikehau atoll (Tuamotu archipelago, French Polynesia), from 1983 to 1988.The average POC concentration (0.7–2000 µm) was 203 mg C m^–3. The suspended living carbon (31.6 mg C m^–3) was made up of bacteria (53%), phytoplankton < 5 µm (14.2%), phytoplankton > 5 µm (14.2%), nanozooplankton 5–35 µm (5.7%), microzooplankton 35–200 µm (4.7%) and mesozooplankton 200–2000 µm (7.9%). The microphytobenthos biomass was 480 mg C m^–2.Suspended detritus (84.4% of the total POC) did not originate from the reef flat but from lagoonal primary productions. Their sedimentation exceeded phytobenthos production.It was estimated that 50% of bacterial biomass was adsorbed on particles. the bacterial biomass dominance was explained by the utilisation of 1) DOC excreted by phytoplankton (44–175 mg C m^–2 day ^–1) and zooplankton (50 mg Cm^–2 day^–1)2) organic compounds produced by solar-induced photochemical reactions 3) coral mucus.50% of the phytoplankton biomass belongs to the < 5 µm fraction. This production (440 mg C m^–2 day^–1) exceeded phytobenthos production (250 mg C m^–2 day^–1) when the whole lagoon was considered.The zooplankton > 35 µm ingested 315 mg C m^–2 day^–1, made up of phytoplankton, nanozooplankton and detritus. Its production was 132 mg C m^–2 day^–1.     

A coral damage index and its application to diving sites in the Egyptian Red Sea

 A coral damage index (CDI) is provided, to screen sites to obtain a perspective on the extent and severity of physical damage to coral. Sites are listed as “hot spots” if in any transect the percent of broken coral colonies (BCC) is greater than or equal to 4% or if the percent cover of coral rubble (CR) is greater than or equal to 3%. To demonstrate its utility, the CDI is applied to a real-life management situation off Hurghada and Safaga, Egypt in the Red Sea. The extent of coral damage covered all four diving sites. Forty percent of all the transects were “hot spots” that required management action. Thirty-one percent of the 16 “hot spot” transects were identified by both broken coral and rubble criteria, 25% by only broken coral criterion and 44% by only coral rubble criterion of the CDI, suggesting that past breakage was responsible for most of the observed damage. Sixty-three percent of the “hot spot” transects were at 4 m depth versus 37% at 8 m depth, suggesting that most of the damage was caused by anchors dragging across the reef in shallow water. The severity of coral damage, reflected by CR, was the greatest at Small Giftun in transect 5 at 4 m depth (333% above the CDI). EI Fanous experienced the most severe degree of broken coral damage (325% above the CDI) at 8 m depth along transect 2. Estimates of the number of dives per year show diving carrying capacities for El Fanous, Gotta Abu Ramada, Ras Abu Soma and Small Giftun being exceeded by large amounts. The CDI can be used globally to; gauge the severity and extent of damage, focus managers on areas that need mooring buoys and associated dive site management programs, and provide a starting point from which to focus more detailed coral reef assessments and restoration programs. Accepted: 30 June 1999     

Damage to the leeward reefs of Curaçao and Bonaire,Netherlands Antilles from a rare storm event: Hurricane Lenny,November 1999

Fringing reefs along the southwestern shores of the Caribbean islands of Curaçao and Bonaire (12°N), located outside the most frequent hurricane tracks, are rarely affected by heavy wave-action and major storms, yet have experienced disturbances such as coral bleaching, coral diseases, and mass mortalities. The last major hurricane to hit these islands occurred over 100 yr ago. In November 1999, Hurricane Lenny took an unusual west-to-east track, bisecting the Caribbean Basin and passing approximately 200 miles north of Curaçao and Bonaire. The leeward shores of both islands were pounded for 24 h by heavy waves (~3–6 m) generated while the storm was centered far to the west. Reef damage surveys at 33 sites conducted between November 1999 to April 2000, following the storm, documented occurrences of toppling, fragmentation, tissue damage, bleaching, and smothering due to the storm. Reefs were severely damaged along westward-facing shores but less impacted where the reef front was tangential to the wave direction or was protected by offshore islands. At the most severely damaged sites, massive coral colonies 2–3-m high (older than 100 yr) were toppled or overturned, smaller corals were broken loose and tumbled across the shallow reef platform and either deposited on the shore or dropped onto the deeper forereef slope. Branching and plating growth forms suffered more damage than massive species and large colonies experienced greater damage than small colonies. Toppled massive corals have a high potential of preserving the event signature even if they survive and continue to grow. Reorientation of large, long-lived coralla may provide a unique indicator of disturbance in a reef system rarely affected by hurricanes. At some locations, wave scouring removed loose sediment to reveal a cemented framework of Acropora cervicornis rubble on the shallow platform above 10-m depth. This rubble was generated in situ, not by storm processes, but rather by an earlier mass mortality of thickets of staghorn coral that covered extensive areas of the shallow platform prior to the incidence of white band disease in the early 1980s.     

Decadal‐scale rates of reef erosion following El Niño‐related mass coral mortality

As the frequency and intensity of coral mortality events increase under climate change, understanding how declines in coral cover may affect the bioerosion of reef frameworks is of increasing importance. Here, we explore decadal‐scale rates of bioerosion of the framework building coral Orbicella annularis by grazing parrotfish following the 1997/1998 El Niño‐related mass mortality event at Long Cay, Belize. Using high‐precision U‐Th dating and CT scan analysis, we quantified in situ rates of external bioerosion over a 13‐year period (1998–2011). Based upon the error‐weighted average U‐Th age of dead O. annularis skeletons, we estimate the average external bioerosion between 1998 and 2011 as 0.92 ± 0.55 cm depth. Empirical observations of herbivore foraging, and a nonlinear numerical response of parrotfish to an increase in food availability, were used to create a model of external bioerosion at Long Cay. Model estimates of external bioerosion were in close agreement with U‐Th estimates (0.85 ± 0.09 cm). The model was then used to quantify how rates of external bioerosion changed across a gradient of coral mortality (i.e., from few corals experiencing mortality following coral bleaching to complete mortality). Our results indicate that external bioerosion is remarkably robust to declines in coral cover, with no significant relationship predicted between the rate of external bioerosion and the proportion of O. annularis that died in the 1998 bleaching event. The outcome was robust because the reduction in grazing intensity that follows coral mortality was compensated for by a positive numerical response of parrotfish to an increase in food availability. Our model estimates further indicate that for an O. annularis‐dominated reef to maintain a positive state of reef accretion, a necessity for sustained ecosystem function, live cover of O. annularis must not drop below a ~5–10% threshold of cover.     

Coral recruitment and juvenile mortality as structuring factors for reef benthic communities in Biscayne National Park, USA

Coral communities of Biscayne National Park (BNP) on offshore linear bank-barrier reefs are depauperate of reef corals and have little topographic relief, while those on lagoonal patch reefs have greater coral cover and species richness despite presumably more stressful environmental regimes closer to shore. We hypothesized that differences in rates of coral recruitment and/or of coral survivorship were responsible for these differences in community structure. These processes were investigated by measuring: (1) juvenile and adult coral densities, and (2) size-frequency distributions of smaller coral size classes, at three pairs of bank- and patch-reefs distributed along the north-south range of coral reefs within the Park. In addition, small quadrats (0.25 m²) were censused for colonies <2 cm in size on three reefs (one offshore and one patch reef in the central park, and one intermediate reef at the southern end), and re-surveyed after 1 year. Density and size frequency data confirmed that large coral colonies were virtually absent from the offshore reefs, but showed that juvenile corals were common and had similar densities to those of adjacent bank and patch reefs. Large coral colonies were more common on inshore patch reefs, suggesting lower survivorship (higher mortality) of small and intermediate sized colonies on the offshore reefs. The more limited small-quadrat data showed similar survivorship rates and initial and final juvenile densities at all three sites, but a higher influx of new recruits to the patch reef site during the single annual study period. We consider the size-frequency data to be a better indicator of juvenile coral dynamics, since it is a more time-integrated measurement and was replicated at more sites. We conclude that lack of recruitment does not appear to explain the impoverished coral communities on offshore bank reefs in BNP. Instead, higher juvenile coral mortality appears to be a dominant factor structuring these communities. Accepted: 9 September 1999     

Parrotfish bioerosion on Egyptian Red Sea reefs

Parrotfishes (family Scaridae) are important agents in marine bioerosion. Here, the feeding ecology of seven species of parrotfishes was studied on Egyptian Red Sea reefs. The most abundant species on both the reef flat and slope was Chlorurus sordidus. In contrast, C. gibbus had the lowest abundance on the reef flat, and Cetoscarus bicolor was the least abundant species on the reef slope. Scarus niger exhibited the highest feeding rate (98.9 bites 5 min^− 1), followed by C. sordidus (76.5 bites 5 min^− 1), whereas the rates for C. bicolor and C. gibbus were low (29.4 and 31.9 bites 5 min^− 1, respectively). The daily feeding patterns of all seven species showed agreement in that activity was relatively constant over the day, with highest values in the early afternoon (1400 h) and a steady decrease until 1800 h. C. sordidus was more similar to S. niger and S. ghobban in showing somewhat higher activities in the morning (0800 h) followed by a slight decrease until noon. The average bite volumes of C. gibbus and C. bicolor were high (0.114 and 0.110 cm³, respectively), whereas S. niger had the lowest average value (0.002 cm³). Based on their feeding intensity, C. gibbus, S. ghobban and C. bicolor have high bioerosion rates on the Egyptian Red Sea reefs. Overall, S. ghobban is the most important bioeroder because it is more abundant than the other two species. All parrotfish species fed on dead coral and hard substrates which are rich in algae, but C. gibbus, C. bicolor and S. ghobban also fed on live coral on both reef zones; C. sordidus avoided live coral. The fresh scars on live coral were bigger than on dead coral because the three large parrotfish (C. gibbus, C. bicolor and S. ghobban) fed mainly on live corals.     

Coral frameworks revisited–reefs and coral carpets in the northern Red Sea

 Coral communities were investigated in the northern Red Sea, in the Gulfs of Suez and Aqaba, for their framework building potential. Five types of coral frameworks were differentiated: Acropora reef framework, Porites reef framework, Porites carpet, faviid carpet, and Stylophora carpet. Two non-framework community types were found: the Stylophora-Acropora community, and soft coral communities. Reef frameworks show a clear ecological zonation along depth and hydrodynamic exposure gradients, with clear indicator communities for each zone. By definition, coral carpets build a framework but lack distinct zonation patterns since they grow only in areas without pronounced gradients. In the northern Red Sea they show a gradual change with depth from Porites to faviid dominance. A Stylophora carpet is restricted to shallow water in the northern Gulf of Suez. Although growth rates of carpets may be somewhat less than those of reefs, the carbonate accumulation is considered to be higher in carpet areas due to their significantly higher areal extension. In addition, reefs and carpets have different sediment retention characteristics – the carpet retains, the reef exports. The in situ fossilization potential of coral carpets is expected to be higher than that of reef frameworks. Accepted: 25 May 1999     

Bioerosion experiments at Lizard Island,Great Barrier Reef

The rates at which dead coral substrates are modified by bioerosional processes were determined by exposing recently killed corals for up to four years in a variety of reef environments at Lizard Island (northern Great Barrier Reef). Grazers were the major croding agents of these coral substrates and exhibited differences between sites that varied between sampling periods. Subtidal reef slopes and lagoon environments of water depths < 20 m were subjected to higher average rates of grazing erosion (0.30–1.96 kg/m²/y) than shallow depths less than 1 m (0.07–0.26 kg/m²/y). A deep site at 20 m experienced low average rates of grazing (0.08–0.29 kg/m²/y). Boring rates by worms (polychaetes and sipunculans), sponges and molluscs were relatively low and varied between sites, but increased with length of sampling period as larger borers succeeded the initial colonizing small polychaete worms. We hypothesize from these experiments that the extent of boring in reef substrates will be influenced by the interaction between the succession of the boring community and the rate at which the substrate is destroyed by grazing. We suggest that the level of grazing modifies the successional pattern of borers by removing the surface substrate and continually exposing bare substrate that can be colonized by early boring colonists. Thus, constant high levels of grazing may maintain the boring community at an early successional stage and prevent the development of a mature boring community. In order to establish large borer populations, reef substrates must be protected from extensive grazing bioerosion. This interaction of grazing and boring has important implications for the way dead coral is preserved in different reef environments.     

Foraminiferal assemblage and reef check census in coral reef health monitoring of East Brazilian margin

Human activity is changing environmental conditions on a global scale. Among the ecosystems that are affected by human activities, coral reefs are among the most prominent. In Brazil, the coral reefs of the Corumbau Marine Extractive Reserve (CMER) and Abrolhos National Marine Park (ANMP) in Bahia state have some of the highest coral cover in the South Atlantic Ocean. Hard coral cover, algal cover, and foraminiferal population distribution patterns were used to assess the coral reef benthic environments, and define a background that can be used in worldwide comparisons in future studies. To compare these two monitoring approaches in different coral reef environments, relative frequency data for occurrence of hard coral and algal cover, using point-intercept transects as proposed by the Reef Check protocol, and foraminiferal samples were collected from Corumbau (nearshore) and Abrolhos (offshore) in April 2005. The foraminiferal assemblage was evaluated using the FORAM index (FI — Foraminifera in Reef Assessment and Monitoring), which provides a numeric diagnosis of suitability of benthic habitat to support calcifying organisms that host algal symbionts, originally developed for Caribbean reef areas. Coral cover in the surveyed areas, both in Corumbau and in Abrolhos, ranged from 13% to 37%, while high foraminiferal diversities (H') were found in all stations. Dominance of symbiont-bearing taxa of Amphistegina lessonii and Archaias angulatus only occurred at two shallow stations, Mato Verde and Siriba, both in Abrolhos, where FI > 4.00. Stations located in Corumbau and Abrolhos had FI values < 4.00. Q-mode cluster analysis showed that foraminifers have specific preferences for physical conditions, especially hydrodynamics and light availability, which influence the FI index. Although coral cover in these areas can be considered good by regional standards, foraminifer analysis showed that the benthic system was unfavorable for symbiont-bearing foraminiferal species at most stations. This discrepancy reveals that the FI must be used with caution in areas other than the northwestern Atlantic and Caribbean where it was developed, and that some coral species can thrive in muddier conditions than can most symbiont-bearing foraminifers.     

Satellite observation of Keppel Islands (Great Barrier Reef) 2002 coral bleaching using IKONOS data

An examination of IKONOS satellite imagery of the Keppel Islands (Great Barrier Reef) acquired before and during a coral bleaching event indicates that severe bleaching of reefs can be detected as an increase in brightness in the band 1 (blue) and band 2 (green) IKONOS spectral bands (4-m resolution). The bleaching was not detected in band 3 (red), band 4 (near-infrared), or in the 1-m panchromatic band data. A total of 0.74 km² of bleached coral was identified, with detection occurring in waters as deep as 15 m. The procedure requires that one of the scenes be radiometrically normalized to match the reference scene prior to image differencing. A relative radiometric normalization was used in this case because variable cloud cover present in the image acquired during the bleaching event prevented reliable modeling of atmospheric effects. The success at coral bleaching detection at Keppel Islands represents both a best-case and a cloud-challenged scenario. It was a best-case scenario in that coral cover was extensive (70–90% live coral cover, mostly acroporids) and the bleaching level was extreme (92–95% of coral cover white bleached). It was a cloud-challenged scenario in terms of having extensive and highly variable cloud cover present in the image acquired during the bleaching event. Color difference images reveal extensive areas of bleached coral at sites away from our study area, indicating that this platform and methodology may be a valuable tool for mapping high coral cover areas during bleaching events. Additional studies and technique refinements would be required to test the detection limits of bleaching with IKONOS imagery or to develop a spectrally based bleaching detection index.An erratum to this article can be found at     

Removal of bacteria and nutrient dynamics within the coral reef framework of Curaçao (Netherlands Antilles)

The authors studied removal rates of bacteria and the regeneration of inorganic nutrients in coral reef cavities in the reef slope of Curaçao, Netherlands Antilles. We found that in cavities the hard substratum surface area (=ca 68% of cavity surface area) is 65% covered with sessile filter feeders. The cryptic cavity surface area exceeds the projected surface area of the reef by 1.5–8 times. Consequently, the organisms living in these cryptic habitats have potentially a large impact on pico- and nano-plankton densities and are important in reef water nutrient dynamics. We closed cavities (±70 l volume, 15 m depth) in seven experiments to study changes in bacterial densities and dissolved inorganic nutrients (DIN, DIP, and silicate) over time. Water samples were taken from the middle of the cavity at 5-min intervals, for 30 min, and analyzed for heterotrophic bacterial abundance and nutrient concentrations. After closure, bacterial abundance dropped rapidly. Of the initial bacterial concentration in the cavities, 50–60% had disappeared after 30 min, an average disappearance rate of 1.43×10⁴ bacteria ml^–1 min^–1 (0.62 mg C l^–1 d^–1; or 30.1 mg C m^–2 cavity surface area d^–1). NO_x concentrations increased significantly during the time of closure. Efflux rates varied between 1.02–9.77 mmol m^–2 cavity surface area d^–1. NH₄⁺ and PO₄^3– concentrations were variable and did not show a consistent change over time in the experiments. Comparison of bacterial organic nitrogen disappearance rates and DIN (NO_x+NH₄⁺) release rates suggests that on average only 30–40% of additional sources of N besides bacteria were required to balance the nitrogen budget. This highlights the importance of heterotrophic bacterioplankton as food for cryptic filter feeders on coral reefs. Silicate concentrations significantly decreased after closure with 0.50 mmol m^–2 cavity surface area d^–1, suggesting the net deposition of SiO₄^2– in spicules of cryptic filter feeding sponges. We conclude that coral reef cavities are a major sink for heterotrophic bacteria, a sink for dissolved silicon (DSi), and a source for NO_x. That reef cavities are a source for NO_x suggests strong remineralization and nitrification in cavities with a potential role for sponge-symbiotic microbial nitrification.Communicated by K.S. Sealey