Back-reef Zone Research Articles

Linear breakwater reefs of the greater Caribbean: Classification, distribution & morphology.

Geomorphic differences among Caribbean reefs have long been noted. These differences are considered to reflect the presence of reefs in different stages of development, following an incomplete recovery from rapid deglacial sea-level rise. But the possibility that these reflect real developmental differences caused by variation in wind, wave, and climate regime, has never been fully considered. Here, for the first time, we quantify the geomorphology and distribution of Greater Caribbean reefs using satellite images in Google Earth and public-domain bathymetry. To do this, we first standardise their classification based on shallow geomorphology, substrate depth, and physiographic setting, and then count and categorise the total number of reefs. These data show a total of 1023 linear breakwater reefs with a combined length of 2237 km. Of this total length, 80% are fringing reefs, 16% are barriers and 4% are faros and atolls. In terms of categories, there are 16 reef subtypes present, but only 9 are common. Their distribution, however, is not uniform. In particular, flat-subtypes form 60% of breakwater reefs in southern regions, but are less common in northern regions where crest-subtypes dominate (80%). To distinguish the geomorphology of these common reef subtypes, we collect size- and length-related morphometric data from their main reef zones. These data reveal that flat and crest subtypes also have morphometric differences: flat subtypes have well-constrained morphologies with statistically consistent unimodal morphometrics characterised by large back-reef zones, smaller and steeper reef fronts, and more sinuous and persistent crestlines. Crest subtypes, by contrast, have multimodal morphometrics suggesting less consistent morphologies (or unresolved subtypes), and are characterised by crestlines with lower sinuosity, more variable back-reef and reef-front areas, and slopes. These differences in geomorphology and distribution imply that flat- and crest-subtypes are neither successional stages of a single reef type, nor a genetically related sequence of types, but distinct reefal geoforms with different modes of development. In subsequent work we will explore what controls these differences.

The use of artificial substrate units to improve inventories of cryptic crustacean species on Caribbean coral reefs.

Motile cryptofauna inhabiting coral reefs are complex assemblages that utilize the space available among dead coral stands and the surrounding coral rubble substrate. They comprise a group of organisms largely overlooked in biodiversity estimates because they are hard to collect and identify, and their collection causes disturbance that is unsustainable in light of widespread reef degradation. Artificial substrate units (ASUs) provide a better sampling alternative and have the potential to enhance biodiversity estimates. The present study examines the effectiveness of ASUs made with defaunated coral rubble to estimate the diversity of motile cryptic crustaceans in the back-reef zone of the Puerto Morelos Reef National Park, Mexico. Species richness, Simpson’s diversity index, Shannon–Wiener index and the composition of assemblages were compared between ASUs and samples from the surrounding coral rubble substrate. A combined total of 2,740 specimens of 178 different species, belonging to five orders of Crustacea (Amphipoda, Cumacea, Isopoda, Tanaidacea and Decapoda) were collected. Species richness was higher in the surrounding coral rubble and Shannon–Wiener and Simpson indexes were higher in ASUs. Species composition differed between methods, with only 71 species being shared among sampling methods. Decapoda was more speciose in ASUs and Peracarids in the surrounding coral rubble. Combining the use of ASUs with surrounding rubble provided a better inventory of motile cryptic crustacean biodiversity, as 65% of the species were represented by one or two specimens.

Functional consequences of the long-term decline of reef-building corals in the Caribbean: evidence of across-reef functional convergence.

Functional integrity on coral reefs is strongly dependent upon coral cover and coral carbonate production rate being sufficient to maintain three-dimensional reef structures. Increasing environmental and anthropogenic pressures in recent decades have reduced the cover of key reef-building species, producing a shift towards the relative dominance of more stress-tolerant taxa and leading to a reduction in the physical functional integrity. Understanding how changes in coral community composition influence the potential of reefs to maintain their physical reef functioning is a priority for their conservation and management. Here, we evaluate how coral communities have changed in the northern sector of the Mexican Caribbean between 1985 and 2016, and the implications for the maintenance of physical reef functions in the back- and fore-reef zones. We used the cover of coral species to explore changes in four morpho-functional groups, coral community composition, coral community calcification, the reef functional index and the reef carbonate budget. Over a period of 31 years, ecological homogenization occurred between the two reef zones mostly due to a reduction in the cover of framework-building branching (Acropora spp.) and foliose-digitiform (Porites porites and Agaricia tenuifolia) coral species in the back-reef, and a relative increase in non-framework species in the fore-reef (Agaricia agaricites and Porites astreoides). This resulted in a significant decrease in the physical functionality of the back-reef zone. At present, both reef zones have negative carbonate budgets, and thus limited capacity to sustain reef accretion, compromising the existing reef structure and its future capacity to provide habitat and environmental services.

Species-specific distribution of intertidal seagrasses along environmental gradients in a tropical estuary (Brunei Bay, Borneo)

Seagrass diversity and distribution in Southeast Asia have been mainly studied in backreef zones but have rarely been studied on intertidal mudflats in estuaries. This research article aims to study seagrass distribution (species diversity, shoot density, and biomass) and morphology (leaf length and leaf number per shoot) on intertidal mudflats in Brunei Bay, Borneo, to understand seagrass responses to water and sediment conditions along the environmental gradient in the estuary. In total, five seagrass species (Cymodocea rotundata, Halodule pinifolia, Halophila ovalis, Halophila minor, and Thalassia hemprichii) were found at five different intertidal sites, and the diversity and biomass were highest at the most upstream site. H. pinifolia was the only species found at all five sites, indicating that this species is the most tolerant of and adaptable to varying water and sediment conditions. H. pinifolia had the highest biomass and longest leaf length at the site with the highest silt and clay percentage (SC%) and organic matter content of sediment, where no other seagrass species were found, suggesting that H. pinifolia could efficiently acquire nutrients without interspecies competition. In contrast, H. ovalis and T. hemprichii were found at the upstream sites and preferred a relatively low SC% in sediment. H. minor was found only at the most downstream site, which had the lowest SC% and is likely to experience the strongest hydrodynamics and receive the least nutrients of all the sites. Based on this study, the seagrass response to environmental gradients in estuaries is proposed to be species-specific, which would have led to the unique seagrass distribution in Brunei Bay.

Coral Reef Degradation Differentially Alters Feeding Ecology of Co-occurring Congeneric Spiny Lobsters

Caribbean coral reefs are undergoing massive degradation, with local increases of macroalgae and reduction of architectural complexity associated with loss of reef-building corals. We explored whether reef degradation affects the feeding ecology of two co-occurring spiny lobsters: Panulirus guttatus, which is an obligate reef-dweller, and Panulirus argus, which uses various benthic habitats including coral reefs. We collected lobsters of both species from the back-reef zones of two large reefs similar in length (~1.5 km) but differing widely in level of degradation, at the Puerto Morelos Reef National Park (Mexico). We measured the carapace length (CL) and weight (W) of lobsters, estimated three condition indices (hepatosomatic index, HI; blood refractive index, BRI; and W/CL ratio), and analyzed their stomach contents and stable isotope values (15N and 13C). All lobsters tested negative for the presence of the virus PaV1, which can affect nutritional condition. Stomach contents yielded 72 animal taxa, mainly mollusks and crustaceans, with an average of 35 taxa per species per reef, but with much overlap. In P. guttatus, CL, HI, BRI, and W/CL did not vary with reef, but mean isotopic values did. The isotopic niche of P. guttatus showed little overlap between reefs, reflecting differences in local carbon sources and underlining the habitat specialization of P. guttatus, which exhibited a higher trophic position on the more degraded reef. Overall, the trophic position of P. guttatus was higher than that of P. argus. In P. argus, none of the variables differed between reefs and the isotopic niche was wide and with great overlap between reefs, reflecting the broader foraging ranges of P. argus compared to P. guttatus. Additional isotopic values from 16 P. argus caught at a depth of 25 m in the fore reef suggest that these larger lobsters forage over different habitats and have a higher trophic position than their smaller conspecifics and congeners from the back reef. The feeding ecology of P. argus appears to be less influenced by coral reef degradation than that of P. guttatus, but our results suggest a buffering effect of omnivory against habitat degradation for both lobster species.

Sedimentary evolution of a coral-, microbialites- and debris-rich Upper Jurassic reef (upper Tithonian, eastern Sardinia, Italy)

This work investigates a portion of a poorly documented upper Tithonian reef (Lower Mt. Bardia Reef, LBR) developed along the northern platform margin of the eastern Sardinia Platform (ESP). The LBR was probably one of the most southerly reefs of the northern Tethys margin, and this study provides the first comprehensive description of facies and internal structure, giving insights for the depositional setting.Detailed compositional and facies analyses of LBR have been carried out in three quarries located in the Orosei Gulf (eastern Sardinia). The main reef components are represented by carbonate (bioclastic) debris, microbialites and microencrusters, and reef-building organisms (mainly corals and stromatoporoids). These components combine in various proportions, forming several facies and facies associations. Ten reef facies (RF), grouped into three main Facies Associations have been identified within the studied reef portion. The distribution and arrangement of facies reveal a sedimentary evolution, evolving from a microframework-dominated reef to a carbonate debris-dominated one, with the internal reef architecture evolving from massive, to patchy, to coarsely stratified and roughly bedded.The reef components and facies indicate that the investigated portion of the LBR corresponds to a shallow back-reef zone, characterized by well-lit and generally low-energy hydrodynamic conditions, possibly developed in back position with respect to a higher-energy zone that was closer to the edge of the platform. In this depositional context, the arrival of large amounts of debris and the evolving internal architecture are interpreted as the result of the infilling process of the back-reef zone due to the progradation of a sand apron, during a long-term regional regressive phase.

Diversity and abundance of conspicuous macrocrustaceans on coral reefs differing in level of degradation.

Coral reefs sustain abundant and diverse macrocrustaceans that perform multiple ecological roles, but coral reefs are undergoing massive degradation that may be driving changes in the species composition and abundance of reef-associated macrocrustaceans. To provide insight into this issue, we used non-destructive visual census techniques to compare the diversity and abundance of conspicuous macrocrustaceans (i.e., those >1 cm and visible without disturbance) between two shallow Caribbean coral reefs similar in size (∼1.5 km in length) and close to each other, but one (“Limones”) characterized by extensive stands of the branching coral Acropora palmata, and the other (“Bonanza”) dominated by macroalgae and relic coral skeletons and rubble (i.e., degraded). We also assessed the structural complexity of each reef and the percent cover of various benthic community components. Given the type of growth of A. palmata, we expected to find a greater structural complexity, a higher cover of live coral, and a lower cover of macroalgae on Limones, and hence a more diverse and abundant macrocrustacean community on this reef compared with Bonanza. Overall, we identified 63 macrocrustacean species (61 Decapoda and two Stomatopoda). Contrary to our expectations, structural complexity did not differ significantly between the back-reef zones of these reefs but varied more broadly on Limones, and the diversity and abundance of macrocrustaceans were higher on Bonanza than on Limones despite live coral cover being higher on Limones and macroalgal cover higher on Bonanza. However, the use of various types of microhabitats by macrocrustaceans differed substantially between reefs. On both reefs, the dominant species were the clinging crab Mithraculus coryphe and the hermit crab Calcinus tibicen, but the former was more abundant on Bonanza and the latter on Limones. M. coryphe occupied a diverse array of microhabitats but mostly coral rubble and relic skeletons, whereas C. tibicen was often, but not always, found associated with colonies of Millepora spp. A small commensal crab of A. palmata, Domecia acanthophora, was far more abundant on Limones, emerging as the main discriminant species between reefs. Our results suggest that local diversity and abundance of reef-associated macrocrustaceans are partially modulated by habitat degradation, the diversity of microhabitat types, and the establishment of different commensal associations rather than by structural complexity alone.

Backreef and beach carbonate sediments of the Red Sea, Saudi Arabia: impacts of reef geometry and currents on sediment composition

Three sites in the Red Sea were investigated to assess the variability of composition in Holocene sediments of the backreef environment within 0–2 m of water depth. This is important because composition of the sediment is commonly used to estimate water depth in ancient carbonate rocks. The site located at the King Abdullah Economic City (Saudi Arabia) contains a fringing reef with the reef tract located very close to the beach at the north end, flaring to the south to produce a narrower backreef area compared to the other two sites. This geometry produces a north to south current with a velocity of up to 15 cm s−1, particularly during high onshore winds. The sediments contain predominantly non-skeletal grains, including peloids, coated grains, ooids, and grapestones that form on the bottom. The percentage of coralgal grains in the sediment was significantly lower than at the other two sites studied. Om Al Misk Island and Shoaiba have a much lower-velocity current within the backreef zone and contain predominantly coralgal sediments from the beach to the landward edge of the reef tract. The two locations containing the predominantly coralgal microfacies were statistically similar, but the King Abdullah Economic City site was statistically different despite having a similar water depth profile. Slight differences in reef configuration, including reef orientation and distance from the shore, can produce considerable differences in sediment thickness and composition within the backreef environment, which should induce caution in the interpretation of water depth in ancient carbonate rocks using composition.

Stratigraphy and evolution of emerged Pleistocene reefs at the Red Sea coast of Sudan

Emerged Pleistocene coral reefs constitute a prominent landform along the Red Sea coast of Sudan. They are well exposed with a thickness of up to 12 m and extend over a width of about 3 km parallel to the coastline. Four major reef units that represent different reef zones are distinguished. Unit 1 is located directly at the coastline and is assigned to the rock-reef rim, while unit 2 represents the reef-front zone. Unit 3 is attributed to the reef-flat zone and unit 4 to the back-reef zone. The stratigraphic position and age of the four units respectively the facies zones are based on field relationships and δ18O analysis. Results of δ18O analysis of coral, gastropod and bivalve samples were correlated to previous age dating of correlative reefs in Sudan and other parts of the Red Sea region. Estimation of reef ages was mainly based on δ18O values of the reef-front zone (unit 2) and the observed sedimentary succession of the reefs. δ18O values of two Porites coral samples from the reef-front zone strongly suggest equivalent ages of 120 and 122 ka that correspond to marine isotope stage MIS 5.5. Based on δ18O values and the field relationship to the reef-front zone, ages of reef-flat zone (unit 3) and back-reef zone (unit 4) could be assigned to MIS 9 and MIS 7 respectively. MIS 5.1 is suggested for the reef-rock rim (unit 1). The relationship of the reef zones to individual MIS might be explained by the predominance of a specific zone during a certain stage, while other facies were less well developed and/or later eroded by wave action. The reef unit most distal from the recent coastline formed during interglacial stage MIS 7, while former studies assign this unit to interglacial stage MIS 9. Unique flourishing, high diversity and excellent preservation of corals in the back-reef unit of MIS 7 reflect growth in troughs landward of the oldest reef-flat formed during previous interglacial stage MIS 9.

Community-based, low-tech method of restoring a lost thicket of Acropora corals

Abstract Due to unregulated blast fishing and episodic bleaching events, the back-reef zone near Barangay Lucero in Bolinao, Pangasinan, Philippines, was reduced to a barren area of unconsolidated sand and coral rubble. Anecdotal accounts from local inhabitants, scientific reports, and examination of rubble on the substratum revealed that the area had been dominated by staghorn Acropora corals prior to degradation. With no significant signs of natural recovery, a low-tech restoration method that is both transferable to the community and cost-effective was devised and implemented. Through the help of local inhabitants, 450 fragments of two staghorn coral species (Acropora intermedia and A. pulchra) were transplanted, without using SCUBA equipment, in a total of six 4 × 4 m plots. There were two transplant density treatments: low and high, receiving 25 and 50 fragments of each coral species, respectively. Survivorship and growth of transplants, as well as the assemblage of fishes and macroinvertebrates inside the transplantation and control plots, were monitored periodically for up to 19 months. Transplant survivorship was generally high (68–89%) at the end of the study. There was also an average of a 15-fold increase in ecological volume of the transplants (from 1784.25 ± 162.75 to 26 540.765 ± 4547.25 cm3). Consequently, a significantly higher number of fish and of macroinvertebrates was recorded inside the transplantation plots than in the control plots, indicating signs of restoration success with the reintroduction of the two coral species. Exhibiting significant differences in coral cover, fish biomass and abundance, high-density is more cost-effective than low-density treatment, attaining optimal effects on key reef recovery parameters. The total cost of restoring a thicket of Acropora in a sandy-rubble field using this low-tech rehabilitation method with community participation was estimated to be US$9198.40 ha−1 (US$0.90 m−2), and thus ∼60% cheaper than without community involvement. Community involvement not only reduced the cost of the restoration activity but also provided the community with a sense of ownership and responsibility for their resources, thus ensuring the long-term success of the intervention.

A novel approach using the 15N tracer technique and benthic chambers to determine ammonium fluxes at the sediment–water interface and its application in a back-reef zone on Reunion Island (Indian Ocean)

The 15N tracer method and the benthic chamber technique were combined to evaluate NH4+ exchanges at the sediment–water interface. This novel approach consists in measuring NH4+ fluxes during a single in situ incubation in a sample of water enclosed in a benthic chamber placed over the sediment and in a subsample thereof concomitantly incubated in a bottle. Using this combined approach, the influx and efflux of NH4+ across the sediment–water interface can be simultaneously measured along with uptake and regeneration rates of NH4+ in the water column. Details of the experimental protocol and principles behind the calculations of N transport rates are given. We applied this approach to a tropical reef on Reunion Island (Indian Ocean). Experiments were carried out in triplicate at three stations with organic-poor, sandy sediments. At the three stations, the mean flux of NH4+ from the water column to the sediment (29.6–59.2μmolm−2h−1) was much higher than the mean NH4+ uptake rate by phytoplankton (3.0–4.0μmolm−2h−1) indicating that the removal of NH4+ from the water column must be due, for the most part, to uptake by benthic microalgae in the study area. The mean flux of NH4+ from the sediment to the water column (6.7–13.7μmolm−2h−1) was comparable to the mean regeneration rate in the water (7.4–9.9μmolm−2h−1) suggesting that the sediment may constitute a significant N source for phytoplankton in the back-reef zone on Reunion Island.

Blackened bioclasts and bituminous impregnations in the Koněprusy Limestone (Lower Devonian), the Barrandian area, Czech Republic: implications for basin analysis

Carbonate reef talus facies of the Koněprusy Limestone (Pragian, Lower Devonian, Barrandian) locally exhibit widespread impregnation by organic matter resulting in a partial to complete blackening of the limestones. Two contrasting types of impregnation are recognized: blackening of individual carbonate fossils and bioclastic layers within the limestone originated very early during diagenesis. The blackening is due to finely dispersed organic matter and possibly some iron sulphides and clay minerals that selectively adhered to the outer layers of corals, bryozoans, and crinoid fragments, leaving other fossils unaltered. These darkened fossils are similar to black pebbles—i.e., reworked, dark to black limestone clasts and bioclasts that are known to occur exclusively in shallow-water zones of both ancient and modern carbonates. The alteration of fossil fragments may have taken place in very shallow-water environments, possibly those of saline and reducing back-reef lagoons or supratidal-intertidal zones, with organic matter being derived from decayed algae and microbes, or early vascular terrestrial plant material. Following the coloration, the blackened fossils were removed from their original position by waves or storms and transported into relatively deeper-water reef slope settings to form graded, “salt-and-pepper”-colored bioclastic beds. The presence of blackened fossils in the carbonate succession may point to episodic emergence and indicates a vanished vegetated siliciclastic hinterland that may once have existed to the west or south from the present-day erosive edge of the Barrandian Devonian strata. Subvertical veins cutting the Koněprusy Limestone and filled with black solid bitumen and blackened calcite resulted from a subsequent but substantially later diagenetic event, which is a testament of aqueous and petroleum fluid migration through the succession during deeper burial. Microthermometric characteristics of the aqueous inclusions embedded in vein calcite indicate that the veins were precipitated by brines of low to moderate salinity (0.5–9.5 wt% NaCl equiv.) with temperatures in the range of 87–116°C. The bitumen in the veins is epi-impsonite (Rr = 0.70–1.90%), which is interpreted as degraded petroleum residuum that experienced thermal alteration at around 120°C. The AFT modeling combined with fluid inclusion microthermometry and wider geological considerations indicate that the veins originated during the Variscan orogeny, most probably upon deep burial of the Lower Paleozoic strata in Carboniferous time.

Successive reef depositional events along the Marquesas foreslopes (French Polynesia) since 26 ka

Bathymetric surveys of submarine platforms and terraces of the tropical Marquesas archipelago (French Polynesia), coupled with sedimentological and paleoecological analyses and radiometric dating of dredged rocks, reveal the occurrence of several distinct intervals of reef deposition during the last deglacial sea-level rise (i.e. the last 26,000 yr or 26 ky). Five facies related to reef, shallow-water and deeper depositional zones have been identified, on the basis of their respective biological assemblages. Facies 1, 2 and 3 consist of in situ scleractinian corals (mainly Porites) associated with thick crusts of coralline algae species, Hydrolithon onkodes, H. reinboldii, Lithophyllum pustulatum group, and widespread vermetids and victoriellinid foraminifers. These assemblages are typical of high-energy, shallow-water reef settings (i.e. upper forereef, reef crest and outer reef flat, and inner reef flat respectively). Facies 4 is characterized by the prevalence of Halimeda plates, mixed with debris of Amphiroa and Amphistegina spp.; these algae generally inhabit the inner parts of the reef flat and backreef zones but also the relatively protected, deeper parts of outer reef slopes. Facies 5 is composed of large broken mollusc shells (oysters), embedded in fine-grained sediments with significant numbers of deep-living coralline algae Mesophyllum sp., and planktonic foraminifers. Locally, mollusc shells are covered with microbialite crusts. The replacement of shallower assemblages by deeper ones is interpreted as an upward-deepening sequence. Identification of morphological and biological features combined with coral dating provide evidence of 4 reef generations (RG) between 26 and 9 ka, now ranging from 138 to 58 m in depth: 1) RG 0 from 26 to 19 ka in the 125–115 m depth interval; 2) RG 1 from 18 to 15 ka between 110 and 95 m; 3) RG 2 from 14 to 11.5 ka between 80 and 68 m; and 4) RG 3 younger than 11.5 ka, at around 55 to 60 m. The first three units exhibit clear zonation, from upper reef slope to reef flat. Their development was probably interrupted by abrupt rises in sea-level and/or drastic climate changes. Such a scenario is similar to observations reported in Barbados and Hawai'i where rapid rises in sea-level, interpreted as reflecting major melting events of continental ice, caused the drowning of reefs. The younger unit refers to coral banks similar to those in modern Marquesas environments. The replacement of typical coral reefs by coral banks may reflect an increase El Niño-Southern Oscillation (ENSO) frequency and intensity inimical to reef development in the last 12 ka.

Feeding ecology of the three juvenile phases of the spiny lobster Panulirus argus in a tropical reef lagoon

The three juvenile phases of the spiny lobster Panulirus argus (algal phase: 5–15 mm carapace length, CL; postalgal phase: 15–45 mm CL, and subadults: 45–80 mm CL) occur in the reef lagoon at Puerto Morelos, Mexico. The algal phase abounds in this lagoon, which is covered by extensive seagrass–algal meadows, but the density of postalgal and subadult juveniles is low, owing to the scarcity of crevice-type shelters suitable for these phases. The feeding ecology of the three juvenile phases was investigated to examine whether spatial or temporal differences in food intake, diet composition, or nutritional condition occurred among phases and could partially account for the low abundance of the larger juveniles. Juveniles were collected by divers at night, from January to November 1995, throughout the mid-lagoon and back-reef zones. Percent stomach fullness, relative weight of the digestive gland (RWDG, an index of nutritional condition), percent frequency of occurrence and percent volume of food categories in the diet were compared between sexes, juvenile phases, molt stages (postmolt, intermolt, premolt), seasons, and sampling zones (mid-lagoon and back-reef zones). Significant differences in stomach fullness occurred only among molt stages, mainly because postmolt individuals had emptier stomachs. The main food categories in all juvenile phases were crustaceans (mostly hermit crabs and brachyurans) and gastropods, but the food spectrum was wide, including many other animal taxa as well as plant matter. In June 1995, the epibenthic macrofauna was sampled in five sites in the lagoon that differed in their amount of vegetation. The most abundant taxa in all sites were decapods and gastropods, but density and diversity measures showed that the distribution of these potential prey taxa for juvenile P. argus was rather patchy. Diet overlap in juvenile lobsters was high between sexes, juvenile phases, sampling zones, seasons, and molting stages, indicating that all juveniles fed on the same general food categories throughout time. The only factor that affected the RWDG was the juvenile phase. RWDG was significantly lower in subadults than in algal and postalgal phases, suggesting a poorer nutritional condition in the largest juveniles. This may be related to the scarcity of suitable shelters for large juveniles throughout the lagoon, which may preclude subadults from exploiting food resources in areas of the lagoon where shelter is limited.

Ecological controls on stromatolite development in a modern reef environment: A test of the ecological refuge paradigm

Paleontological and neontological studies suggest that stromatolite development may be limited to environments where ecological processes such as colonization (recruitment), growth, competition, and predation (herbivory) are low. We quantitatively tested this “ecological refuge paradigm” at a unique stromatolite-reef complex at Stocking Island, Bahamas where three contiguous zones grade in dominance from stromatolites in the back reef to a macroalgal turf in the reef flat to reef building corals and coralline algae and reef fishes in the fore reef. At two independent transects along this gradient, we quantified the distribution and abundance of the dominant organisms and measured the rates of the above-listed ecological processes and determined survival and growth of stromatolite, turf, and coralline algae transplanted to each of the three zones. We also measured both the sediment dynamics and temperature profiles along this gradient to determine if these may be controlling the ecological processes. Stromatolites dominate the back reef zone where species diversity (especially among eukaryotes) and associated ecological pressures were low. Measured rates of colonization from calcified (i.e., coralline) and noncalcified macroalgae and filamentous turf algae were lowest in the back reef (i.e., <5% substrate colonization/y) and highest in the fore reef (95% substrate colonization/y). This suggests that competition for space was lowest in the stromatolite zone. Growth and survival rates of transplanted coralline algae were low in both the back reef (3 mm/y and 20–40% annual survival rates) and reef flat (<2 mm/y, 0% surviving) and highest in the fore reef (about 10 mm/y, 80% surviving). Foraging activity from all fishes was lowest in the back reef (total 0.4 bites/m2/h) and reef flat (0 bites/m2/h) and highest in fore reef (900–2200 bites/m2/h, mostly from omnivorous wrasses). Herbivory from all potential sources was below detectable levels in the stromatolite zone and was highest in the fore reef. The ecological refuge found in the back reef stromatolite zone resulted primarily from periodic sediment inundation. Most eukaryotic reef-dwelling organisms cannot persist under as much as 700 mm of sediment for periods up to 100 days. Although the reef flat suffered both desiccation and thermal stress (averaging more than 5°C greater daily temperature fluctuation than the fore reef), natural and transplanted eukaryotic turf algae thrived there. Although transplanted stromatolites survived best in the back reef (about 80% of the original transplant surviving/y), they also persisted in the fore reef (about 40% surviving per year). Therefore,Schizothrix-dominated stromatolites can persist in fore reef environments but because of the presence of other organisms and associated ecological pressures, their laminated microbial-produced structure is lost or obscured. While the sediment and the organisms necessary for stromatolite formation exist in this and probably in other modern reef environments, their reef-building contribution will be low except in unusual habitats where abiotic stresses maintain an ecological refuge.

Effects of habitat on the settlement and post-settlement success of the ocean surgeonfish Acanthurus bahianus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 161:51-59 (1997) - doi:10.3354/meps161051 Effects of habitat on the settlement and post-settlement success of the ocean surgeonfish Acanthurus bahianus Andrea Risk* Department of Biological Sciences, University of Windsor, Windsor, Ontario, Canada N9B 3P4 *E-mail: sale@server.uwindsor.ca Local population dynamics of fishes on coral reefs are dependent on processes affecting the settlement of pelagic larvae and the subsequent persistence of these new settlers. The ability of larvae to choose favourable places to settle in terms of persistence may make the dynamics of certain populations predictable at the reef scale, and cause patterns of recruitment to differ from those of larval supply. I collected data on settlement, recruitment and persistence of the ocean surgeonfish Acanthurus bahianus in different physiographic zones of the Tague Bay reef, on the island of St. Croix, U.S. Virgin Islands. There was significantly higher settlement and recruitment to the back-reef zone than to the fore-reef zone or seagrass zones at the bases of the back-reef and fore-reef, suggesting that larvae select settlement sites and do not necessarily settle to the first reef zone encountered. On the back-reef, settlers used pavement more than any other type of substratum, and the post-settlement persistence of settlers and recruits was highest on pavement when compared to these other substrata. These results suggest that patterns of ocean surgeonfish settlement are affected by reef-based processes, and that selection for certain zones and substrata occurs. Subsequent modification of these initial settlement patterns by increased persistence in preferred habitats adds predictability to patterns of recruitment, resulting in larval supply alone being an insufficient explanation of the distribution and abundance of ocean surgeonfish populations at this scale. Coral reef fish · Caribbean · Otoliths · Habitat selection · Recruitment · Growth · Persistence Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 161. Publication date: December 31, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)

Dynamics of fish communities on Reunion fringing reefs, Indian Ocean. I. Patterns of spatial distribution

This work describes the distribution of fish communitites, including species richness, abundance of individuals and trophic structures on the four main fringing reefs of Reunion Island. Patterns are quantified on several spatial scales: an intra-reef scale and an interreefs scale which includes within-reefs, between-reefs, and between-reefs and zones scales. The total ichthyofauna (217 species) is structured into three main communities — back-reef, inner reef flat and outer reef flat communities — which are influenced by the wave exposure and topographic relief. These communities are organized in a spatial continuum rather than into three totally separate communities. Herbivorous (mainly acanthurids) and omnivorous fishes (mainly pomacentrids) are the most numerous on the inner and outer reef flats. Diurnal carnivorous (mainly mullids) and herbivorous fishes (mainly schooling juveniles) are the dominant fishes in the back-reef zones. The low abundance of carnivorous fishes on the reef flat, irrespective of diet, is most likely due to alterations of benthic communities (e.g. coral damage, increase in algae populations) as a result of anthropogenic activities. The ichthyofauna of each of the four reefs is organized into the same three fish communities. There is a north-south gradient of decreasing distribution of species and abundance of individuals in these communities. However, fish communities are more clearly separated on the northern reefs compared with those of the southern reefs. This pattern is probably due to differences in coral vitality, habitat complexity and width of the reefs. Hydrodynamic conditions, more pronounced in the south of the island, might also lead to a higher flux of recruitment of fish larvae on the northern reefs.

Disturbance impact on reef fish communities in Reunion Island (Indian Ocean)

Coral reefs in Reunion Island are subjected to eutrophication due mainly to anthropogenic activities following urbanisation of the watershed. This study assesses the impact of consequent coral reef degradation on fish communities. A quantitative study on fish communities was conducted on two sectors (undisturbed and disturbed) of a fringing reef. Data were collected using visual census techniques. The ichthyofauna is structured into three main communities (back reef, inner reef and outer reef). No significant difference was found between the undisturbed and disturbed sectors for the outer reef flat communities. Reef perturbation was found to affect fish abundance mainly on the back reef zone. In the undisturbed back reef zone, the overall fish abundance was almost double that in the disturbed one. The fish communities of the former showed higher homogeneity than the latter. Perturbation of the behaviour of the most abundant fish populations of the back reef zone is discussed with respect to their ecological preferences. Species may also be affected by disturbance, owing to their changing habitat and food availability.

Diagenetic history of a submerged Pleistocene Jamaican fringing reef

In the Discovery Bay area of northern Jamaica, a fringing reef grew and was subsequently planed off as sea level rose to and fell from a highstand between about 132,000 and 147,000 y B.P. Depositional facies encountered in cores consist of back reef, reef flat, reef crest, and shallow fore-reef zones, and many appear to have a storm-modified fabric analogous to the modern fringing reef. Eustatic changes in sea level resulted in 3 periods of marine submergence, and two periods of emergence in a meteoric vadose regime.