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.     

Community structure of stony and soft corals on vertical unplanned artificial reefs in Eilat (Red Sea): comparison to natural reefs

In many reef ecosystems, artificial reefs (AR) have become permanent additions to the area, sustaining well-developed benthic communities. Long-term studies on the development of AR coral communities are scarce, and comparisons with their natural surroundings are limited. The present study describes the stony and soft coral community structure of unplanned vertical AR in Eilat (Red Sea) that have progressed beyond the initial successional phases, and compares these to the adjacent natural reefs (NR). Coral communities were characterized using belt transects, conducted on 34- and 14-year-old unplanned AR, and on two proximate NR. Stony corals were the major component in the NR, while soft corals, mainly Nephtheidae, accounted for up to 90% of the total living coverage in the AR. This was attributed to physical and biological features associated with the ARs vertical orientation, which was absent in the NR, and to the life history traits of these soft corals. Community differences between the two AR were related to structural stability and age. The results suggest that AR may increase local heterogeneity and space availability by adding novel habitats, increasing production and elevating species diversity in the surroundings.Communicated by Biological Editor H.R. Lasker     

Influence of size and spatial competition on the bioactivity of coral reef sponges

Sponges biosynthesize a wealth of secondary metabolites, many with novel structures and strong biological activity. Such compounds may serve multiple ecological roles including anti-predation, anti-fouling functionalities and are implicated in border defense or attack during spatial competition. Relative size of benthic organisms may also play an important role in competitive interactions. To determine if a relationship exists between individual size and bioactive metabolite production in the context of spatial competition, we examined three sponge species with different morphologies: the massive Coscinoderma matthewsi, the club-shaped branching Hyrtios erecta, and the fan-shaped Ianthella basta. Extracts from sponges of various sizes and competitive environments were examined using a cell based bioassay as a proxy of bioactivity. For I. basta, sponge size was correlated with bioactivity; the largest individuals generally being the most bioactive. In contrast, there was no correlation between size and bioactivity for either C. matthewsi or H. erecta. Bioactivity of sponges in this study were however highly variable among individuals, regardless of levels of competition. The prevalence of encroaching organisms was not correlated with sponge size for any of the three sponge species, suggesting that potential bioactivity is not influenced by surrounding competition.     

Cyclone effects on coral reef habitats in New Caledonia (South Pacific)

The impacts of the unusually strong Cyclone Erica (March 2003) on coral reef habitats at a site located on the northwest coast of New Caledonia (South Pacific) were assessed using a 6-year data set (2002–2007). We examined the interannual variations of key variables describing reef habitats (live hard and soft corals, dead corals in place, coral debris, algae and relative proportion of mechanically vulnerable and resistant live hard corals). The cyclone-induced disturbances of habitats differed according to three reef types: patch reefs, barrier reefs far from passes (more than 3 km from the nearest pass) and barrier reefs near passes (less than 3 km from the nearest pass). Short-term mechanical damage was detected on the three-dimensional structure of reef habitats with a notable shift from a community dominated by mechanically vulnerable corals to one dominated by resistant corals on barrier reefs far from passes. The history of habitats and their pre-disturbance characteristics, in link with local hydrodynamics, was found to influence their short-term susceptibility to extreme events such as cyclones. However, the most significant effects appeared in the midterm (within 2 years after the cyclone) as the cover of live hard corals significantly decreased by approximately 45% between 2002 and 2004 on all reef types. The short- and midterm disturbances of coral reef habitats are discussed with regard to published temporal variations in reef fish assemblages, underlining the delayed effects of this cyclonic event on fish as well as benthic habitats. Coral reef habitats and live corals had shown significant patterns of recovery 4 years after the cyclone, followed by similar recovery in fish community, suggesting good resilience in a face of this major natural disturbance in an area under moderate anthropogenic pressure.     

Facies and palaeoecology of Upper Jurassic (Middle Oxfordian) coral reefs in England

Summary This study documents the facies and fauna of Late Jurassic (Middle Oxfordian) coral reefs in England. Sedimentological and palaeoecological analysis of these reefs distinguishes three generic reef types: (1) small reef patches and thickets associated with siliciclastic deposits; (2) small reef patches and thickets associated with siliciclastic-free bioclastic grainstones and packstones; and (3) biostromal units associated with deep water facies. The depositional environments of these reef types are discussed. Two coral assemblages are identified: (1) the microsolenid assemblage; and (2) theThamnasteria, Isastraea, Fungiastraea andThecosmilia assemblage (Thamnasteria assemblage). TheThamnasteria assemblage developed in all shallow water environments in the study area, regardless of local environmental conditions. The fauna is very eurytopic,r-selected and can tolerate significant environmental fluctuations on short temporal scales (sub-seasonal). The main control on the development of the microsolenid assemblage was low light intensity, low background sedimentation rates and low hydrodynamic energy levels.     

Diversity, biomass and distribution pattern of Sargassum beds in the South West lagoon of New Caledonia (South Pacific)

Sargassum (Phaeophyceae, Fucales) is a genus of worldwide distribution recently recognised to proliferate in several regions of the South Pacific. In New Caledonia, species of this genus naturally structure one of the major lagoon habitats but their extent, composition and biomass remain largely unknown. To fill these gaps in our knowledge over large areas, we applied a combination of remote sensing and in situ methods applied to the Neo Caledonian South West Lagoon. Space borne high resolution Landsat (30-m resolution) and Quickbird (2.4-m resolution) images of the Neo Caledonian South West lagoon were used to estimate the spatial extent of the different beds of interest. Species composition was determined for 11 Sargassum beds and seasonal variations were investigated for four representative beds over an 18 month period using quadrats and transects. Relationships between surface cover and biomass were estimated from seasonal field data sets. Finally, four methods requiring variable levels of sampling effort were designed to estimate the total biomass at the scale of each bed, considering (or not) the specific composition, and spatial and temporal variations. Seven Sargassaceae species were identified. Mean surface cover (24.4–51.6%) and total biomass [3.4–1,461.9 t dry matter (DM)] varied widely between beds. Overall, biomass temporal variations were not significantly different, but species-level variations seemed to be bed-specific. The extent of the 11 beds was 9 km²; their total biomass was estimated and compared using each of the four methods, and the most precise method provided an estimate of 2,900 t DM. This study demonstrates a way of characterising Sargassum beds, efficiently and on a large scale, using a combination of remotely sensed and in situ data. These methods should be useful for possible future biomonitoring of Sargassum beds in New Caledonia, and in other areas worldwide.     

Gametogenesis, spawning and fecundity of Platygyra daedalea (Scleractinia) on equatorial reefs in Kenya

The reproductive ecology of the hermaphroditic broadcast spawning scleractinian reef coral Platygyra daedalea was studied on lagoonal reefs in Kenya. While single annual gametogenic cycles occurred in 84% of colonies, biannual gametogenic cycles were recorded in 16% of colonies and these patterns occurred in two morphotypes. In colonies with a single annual cycle, oogenesis occurred for 6–7 months from September to March and spermatogenesis for 5 months from November to March. In biannually spawning colonies, oogenic cycles overlapped for at least 2 months prior to gamete release. The major spawning period occurred in February and March, with minor spawning also occurring in August–October in biannually spawning colonies. Reproductive effort was lower during the minor winter compared to the major summer spawning, with fewer colonies reproducing (12.5–19.2%), not all mesenteries producing oocytes (32.5%) and less than half of the mesenteries with mature oocytes had associated spermaries (48.1%).     

Predation on the urchin Echinometra lucunter (Linnaeus) by migratory shorebirds on a tropical reef flat

Predation on urchins by migratory shorebirds was investigated during tidal exposure of the reef flat at Galeta, Panama. Avian predators, primarily ruddy turnstones Arenaria interpres (Linnaeus) reduced the patchiness of Echinometra lucunter (Linnaeus), the most abundant urchin on the reef flat. No mortality of E. lucunter occurred in quadrats protected from avian predation. No mortality occurred when urchin crowding was increased experimentally in protected areas. Stress-induced mortality could not be determined from the condition of tests alone, since turnstones were capable of removing lantern and internal organs without damage to the test. The importance of shorebird predation in reef communities during aerial exposure can be hard to detect because mortality can occur during brief periods, at night, and without damage to urchin tests.     

An analysis of fish‐habitat associations on disturbed coral reefs: chaetodontid fishes in New Caledonia

A concordance analysis was used to study the simultaneous influence of several environmental data sets on chaetodontid (butterflyfish) distributions. This multivariate and multitable method enabled the correlation of three types of benthic characteristics (mineral substratum, coverage of structural species and large echinoderms) with butterflyfish abundances in two bays of the urban centre of Nouméa (New Caledonia). The first concordance axis was related to a gradient in the coverage of branching corals. This disturbance gradient compared damaged reef areas dominated by long‐spined sea urchins to areas with an extensive coverage of branching corals. The abundance of corallivorous chaetodontids was related to this gradient, supporting the view of corals as a food and shelter source for these fishes. The second concordance axis was interpreted as a gradient of heterogeneity in the coverage of benthic life‐forms. The abundance of omnivorous chaetodontids was related to this gradient. Thus, the concordance axes defined two key components of habitat structure that were related to the entire fish community structure.     

Population recovery of the sea urchin Lytechinus variegatus in a seagrass flat (Araruama Lagoon,Brazil): the role of recruitment in a disturbed environment

Summary

The size, structure, and density of a population of Lytechinus variegatus were recorded from a shallow seagrass bed (Halodule wrightii) at 40-day intervals from April 1994 to April 1995. A local mass mortality was observed in May 1994. The density declined from 0.57±0.10 to 0.06±0.05 ind.m^?2, mean size declined from 37.6±0.49 to 16.2±2.14 mm and maximum size from 75 to 40 mm. Ten months after mortality, the maximum and mean sizes had returned to initialvalues, but density had not (0.10±0.03 ind.m^?2). A second, smaller mass mortality occurred in April 1995. High values of gonad index were recorded before mortality (9.40±5.97) and after population recovery (11.96±5.74). Recruitment was continuous throughout the year, but reached a peak from August to October. This can he related to the patterns of upwelling in the region. Mass mortality is probably an annual event in this population that can be correlated with the occurrence of low tides during daytime in the fell. The population can recover during the summer when low tides occur during the night. The massive input of recruits prevents extinction of the population during the season of high mortality. Population recovery depends on the magnitude of recruitment.     

Cushion star (Culcita schmideliana) preys on coral polyps in Gulf of Mannar,Southeast India

Corallivore animals play vital role in coral reef ecology. Predation on corals by other organisms has not been studied properly in the Indian waters. This study reports the first observation of predation by cushion star (Culcita schmideliana) on coral polyps in Gulf of Mannar (GoM), southeast India. During our regular underwater surveys in GoM, C. schmideliana was found preying on hard coral Acropora formosa and soft coral Sarcophyton sp. at a depth of 3 m in Vilanguchalli patch reef. Though C. schmideliana has been sighted often under water, it has not been observed to predate on corals in GoM before. The area where predation was observed has a major population of hard corals (50.21%) besides seagrasses (8.36%) and soft corals (6.11%). Temperature anomalies and the consequent coral bleaching could be the factors making C. schmideliana prefer coral polyps.     

Correlations between chaetodontid fishes and coral communities of the Gulf of Aqaba (Red Sea)

Synopsis The relationships existing between the chaetodontid fishes and the surrounding coral communities were investigated in the Gulf of Aqaba. Quantitative data were analysed by a correspondence and a cluster analysis. The results demonstrated a similarity in the spatial distribution of both communities. Significant correlations were found between the density of chaetodontid fishes and the diversity of the coral community as well as the substratum coverage by the coral colonies. The density of exclusive coral browsers was also correlated to the abundance of branching colonies. Among the different genera of branching corals, correlations were significant only for the genusAcropora. These results suggested the existence of strong links between coral and chaetodontid fish assemblages.     

New records of marine benthic algae from the Lagon Sud-Ouest of New Caledonia, South Pacific

As part of an ongoing project to substantially increase knowledge of the marine algal flora of the French Pacific territory of New Caledonia, a survey of the Nouméa region was conducted that has resulted in the discovery of 41 previously unrecorded species of macroalgae, including 1 Chlorophyta, 1 Phaeophyceae (Heterokontophyta) and 39 Rhodophyta. Among the biogeographically interesting new records are the green macroalga Rhipilia penicilloides N’Yeurt et Keats (previously endemic to the islands of Fiji some 1000 km east of new Caledonia) and the brown alga Cutleria mollis Allender et Kraft (originally described from Lord Howe Island some 1000 km to the south). The red alga Gloiophloea articulata Weber‐van Bosse, known only from its initial discovery in 1928 from the Mascarene Islands in the western Indian Ocean, is now recorded in the deep‐water channels of the Nouméa region of New Caledonia. The widely distributed Indian Ocean species Corynomorpha prismatica (J. Agardh) J. Agardh has its easternmost distribution record from this area, and Dotyella hawaiiensis (Doty et Wainwright) Womersley et Shepley is recorded for the first time outside its central‐Pacific distribution. These new discoveries represent a 12% increase in the total number of species (377) that are reliably known from New Caledonia.     

New genera of Copepoda (Poecilostomatoida) from the scleractinian coral Psammocora in New Caledonia

Three new monotypic genera of copepods (Poecilostomatoida) are associated with the hermatypic shallow-water coral Psammocora (Stephanaria) logianensis near Noumea, New Caledonia: in the Anchimolgidae, Lipochaetes extrusus (antenna 4-segmented, endopods absent in legs 3 and 4) and Dumbeana undulatipes (antenna 3-segmcntcd, endopod of leg 3 with formula 0 1; 0–2; 1,11,2; leg 4 endopod with 0 1:1); and in the Rhynchomolgidae; Emunoa proknta (leg 4 endopod with 0 1;II, antenna 4-segmented, mandible witli outer pointed process and inner row of spines). Copepoda (primarily Poecilostomatoida and Siphonostomatoida, but also relatively few Cyclopoida and Harpacticoida) are very frequent associates or parasites of Scleractinia. At present 245 species from 48 scleractinian coral genera are known. Species of these copepod associates, their host genera, and localities, described since (and those not included in) previous publications of the author are listed.     

Rebuilding coral reefs: success (and failure) 16 years after low‐cost,low‐tech restoration

Calls for coral reef restoration are increasing amidst continued declines, yet we know little about long‐term outcomes and conditions that lead to successful coral recovery. Here, we report on one of the longest monitoring studies following 16 years of large‐scale, “low‐tech” experimental reef rehabilitation on rubble fields created by chronic blast fishing in Komodo National Park, Indonesia. After blast fishing had stopped, in the absence of rehabilitation, hard coral cover in rubble fields remained about 3% from 1999 to 2016, but on rehabilitation treatments, cover increased from 0% in 2002 to 44.5% (±21.9% SD) in 2016. Coral cover varied among sites and treatments (ranging from <5 to >80% in 2016) in patterns that may reflect current strength and turbidity. Our results demonstrate that low‐tech substrate stabilization can facilitate natural coral recruitment and growth. We conclude that relatively low‐cost methods can deliver sustained rehabilitation of hard coral cover and that long‐term monitoring should be incorporated more widely in restoration activities to inform return on investment.     

Distribution and abundance of the dugong in New Caledonia, southwest Pacific

New Caledonia is at the eastern limit of the dugong's range. In June 2003 standardized dugong aerial survey methodology was used to estimate the abundance and distribution of dugongs in the coastal waters of New Caledonia, resulting in a population estimate of 1,814 ± SE 332. This represents the largest concentration of dugongs in Melanesia and one of the largest populations in the world, outside Australia and the Arabian region. Calves comprised 7.2% of the population. The observed density of dugongs was highest in the center and southern part of the west coast of the island but not significantly different from the density on the north west and north east. In the central west region, sightings were associated with a pass in the barrier reef and up to a third of the on‐survey sightings were outside of the barrier reef. The dugong distribution we observed during June 2003 differs from the reported locations of historical hunts in several respects.     

Climate change and coral reefs: different effects in two high-latitude areas (Arabian Gulf,South Africa)

The findings in this paper show that Arabian Gulf (Abu Dhabi, Dubai, Sharjah) corals have already been measurably affected by climate change and further negative impacts are expected. Corals in South Africa have been only weakly impacted and are expected to persist in this likely refuge. The Arabian Gulf has recently experienced high-frequency recurrences of temperature-related bleaching (1996, 1998, 2002). First evidence may suggest that bleaching patterns in corals changed due to phenotypic adaptation after two strong bleaching events in rapid succession, because Acropora, which during the 1996 and 1998 events always bleached first and suffered heaviest mortality, bleached less than all other corals in 2002 at Sir Abu Nuair and recovered at Jebel Ali and Ras Hasyan. In South Africa, reef corals largely escaped the mass mortalities observed across the tropics in the late 1990s, although bleaching has also increased since 1999. These reefs are protected by local small-scale upwelling events in summer that, if they occur at the right time, keep temperatures below bleaching levels. Both areas, the Arabian Gulf and South Africa, have rich coral faunas but little to no recent reef-framework production. It is possible that many reefs worldwide may have similar dynamics in the future, if the changed climate (recurrence of temperature anomalies, changes in aragonite saturation state, etc.) suppresses sustained reef building at least temporarily. Global climate models predict the possibility of significant environmental changes, including increases in atmospheric temperature, sea-surface temperature (SST), and sea level. Monsoon and El Niño Southeastern Oscillation (ENSO) patterns might change, but climate models are not conclusive. Sea-level rise by up to 0.88 m is expected to be a problem in some low-lying areas, like the southern Arabian Gulf. Ocean aragonite saturation state is predicted to fall throughout the ocean but may not change reef dynamics in the two study areas.     

Dietary partitioning by five sympatric species of stingray (Dasyatidae) on coral reefs

Dietary characteristics and the degree of dietary partitioning by five species of sympatric stingray were assessed using stomach content and sediment analyses within a coral reef lagoon at Ningaloo Reef, Western Australia (the cowtail Pastinachus atrus, blue‐spotted fantail Taeniura lymma, blue‐spotted mask Neotrygon kuhlii, porcupine Urogymnus asperrimus rays and the reticulate whipray Himantura uarnak). A total of 2804 items were recovered from the stomachs of 170 rays and 3215 individual taxa from the environment, which were used in selectivity analyses. Twenty‐four prey taxa were identified from stomach contents and pooled into 10 taxonomic categories for analysis, of which annelids, prawns, brachyurans and bivalves were the most abundant, together accounting for 96% of the diet. Himantura uarnak had the greatest interspecific dissimilarity in diet, consuming a larger proportion of crustaceans, notably penaeids (41% of total diet) than the other four species of rays, all of which had diets dominated by annelids (71–82% of total diet). Crustacean specialization by H. uarnak may exist to maximize resources and reduce competition among sympatric species. The remaining species may partition resources on the basis of space, rather than diet.     

Recurrent disturbances, recovery trajectories, and resilience of coral assemblages on a South Central Pacific reef

Coral reefs are increasingly threatened by various disturbances, and a critical challenge is to determine their ability for resistance and resilience. Coral assemblages in Moorea, French Polynesia, have been impacted by multiple disturbances (one cyclone and four bleaching events between 1991 and 2006). The 1991 disturbances caused large declines in coral cover (~51% to ~22%), and subsequent colonization by turf algae (~16% to ~49%), but this phase-shift from coral to algal dominance has not persisted. Instead, the composition of the coral community changed following the disturbances, notably favoring an increased cover of Porites, reduced cover of Montipora and Pocillopora, and a full return of Acropora; in this form, the reef returned to pre-disturbance coral cover within a decade. Thus, this coral assemblage is characterized by resilience in terms of coral cover, but plasticity in terms of community composition.