Chromium‐isotope signatures in scleractinian corals from the Rocas Atoll,Tropical South Atlantic

Chromium‐isotope compositions (expressed as δ⁵³Cr) of recent and ancient skeletal and non‐skeletal carbonates are currently explored as a (paleo‐) redox‐proxy for shallow seawater. The idea behind this approach is that biogenic and non‐biogenic carbonates could potentially be used as archives recording the Cr‐isotope composition of seawater in which they formed, and with this contribute to the reconstruction of past paleo‐environmental changes in the marine realm, and potentially to climate changes on land. However, investigations addressing the behavior and uptake mechanism of Cr, and the potential isotope fractionations between seawater and biogenic carbonates are scarce. Here, we present a study of Cr‐isotope variations in three species of corals and contemporary seawater from the Rocas Atoll, NE, Brazil. Cr‐isotope values of the studied coral species (Siderastrea stellata, Porites sp., and Montastrea cavernosa) vary from ?0.5 to +0.33‰ and point to significant isotopic disequilibrium with coexisting seawater characterized by a Cr‐isotope value of +0.92 ± 0.2‰. This isotopic offset requires reduction of hexavalent Cr(VI) in the sequestration process of all the studied coral species. Cr‐isotope values in a profile across an S. stellata colony returned homogeneous, slightly positively fractioned δ⁵³Cr values of +0.07 ± 0.08‰ (n = 8, 2σ), which we interpret to reflect a constant reductive uptake during the 20‐year growth period recorded in this coral. In contrast, samples across a 12‐year growth profile from Porites sp. display rather heterogeneous Cr‐isotope values with δ⁵³Cr varying from ?0.50 to +0.10‰, indicating Cr incorporation under changing redox processes during its growth intervals. We propose a mechanism whereby initial photoreduction of isotopically heavy Cr(VI) to isotopically lighter Cr(III) in the endodermal layer of corals must be followed by efficient and effective re‐oxidation of reduced Cr species to favor subsequent chromate () substitution during the calcifying processes ultimately leading to the formation of the coral skeleton.     

Composition and community structure of the coralline algal reefs from Atol das Rocas, South Atlantic, Brazil

 Coralline-algal frameworks from Atol das Rocas reefs were sampled along windward and leeward transects, and multivariate statistical analysis was used to investigate the composition and community structure of the encrusting community. The following components of the reefs were identified in slabbed and polished reef blocks sampled along each transect: encrusting coralline algae dominated by Porolithon cf. pachydermum, vermetid gastropods, Homotrema rubrum, acervulinid foraminiferans, molluscs, corals, polychaete tubes, clionid sponge borings, polychaete/sipunculid borings, cemented sediments, and growth cavities. Q-mode cluster analysis correctly classified 78% of all windward samples and 69% of all leeward samples, and R-mode separated reef components adapted to high wave energy environments from those adapted to low wave energy. Separate classification and ordination of samples from each transect indicate that seriation breakdown occurs in the windward reef between 25 and 45 m from the reef front. In the leeward reef between 75 and 90 m from the leeward reef front, seriation breakdown was not found to be significant. These results confirm that seriation (zonation) is best developed in the windward reef, as has been documented in coral-dominated reefs. Accepted: 28 February 2000     

Influence of sponge morphology on the composition of the polychaete associated fauna from Rocas Atoll,northeast Brazil

The relationships between the morphology of sponges and variables describing their harbored polychaete fauna were analyzed along Rocas, the only known South Atlantic Atoll, together with the location on host and feeding habits. The identification and quantification of all the associated organisms highlighted the dominance of polychaetes. The adults of the symbiotic species Haplosyllis spongicola were the most dominant sponge endobionts. However, both juveniles and epitokes (reproductive individuals) of H. spongicola were also found, suggesting that this species completes its life cycle inside the host. Polychaete density was significantly greater in lobate sponges than in massive and encrusting forms. Conversely, the highly specific symbiotic mode of life of H. spongicola species seems to play a major role in structuring the composition of the polychaete fauna in relation to sponge morphotypes along Rocas Atoll.     

Coexistence of Low Coral Cover and High Fish Biomass at Farquhar Atoll,Seychelles

We report a reef ecosystem where corals may have lost their role as major reef engineering species but fish biomass and assemblage structure is comparable to unfished reefs elsewhere around the world. This scenario is based on an extensive assessment of the coral reefs of Farquhar Atoll, the most southern of the Seychelles Islands. Coral cover and overall benthic community condition at Farquhar was poor, likely due to a combination of limited habitat, localized upwelling, past coral bleaching, and cyclones. Farquhar Atoll harbors a relatively intact reef fish assemblage with very large biomass (3.2 t ha⁻¹) reflecting natural ecological processes that are not influenced by fishing or other local anthropogenic factors. The most striking feature of the reef fish assemblage is the dominance by large groupers, snappers, and jacks with large (>1 m) potato cod (Epinephelus tukula) and marbled grouper (E. polyphekadion), commonly observed at many locations. Napoleon wrasse (Cheilinus undulatus) and bumphead parrotfish (Bolbometopon muricatum) are listed as endangered and vulnerable, respectively, but were frequently encountered at Farquhar. The high abundance and large sizes of parrotfishes at Farquhar also appears to regulate macroalgal abundance and enhance the dominance of crustose corallines, which are a necessary condition for maintenance of healthy reef communities. Overall fish biomass and biomass of large predators at Farquhar are substantially higher than other areas within the Seychelles, and are some of the highest recorded in the Indian Ocean. Remote islands like Farquhar Atoll with low human populations and limited fishing pressure offer ideal opportunities for understanding whether reefs can be resilient from global threats if local threats are minimized.     

Hydrological Variation and Fish Assemblage Structure in the Middle Wabash River

We assessed the effect of a severe drought in 1999 upon stream morphology and brook trout (Salvelinus fontinalis) populations in seven headwater streams in the Greenbrier and Potomac River watersheds, West Virginia. During the drought, stream discharge was 96% lower than in years of normal precipitation. As a result, habitat availability and quality over all study streams was significantly lower. Riffle area was greatly reduced (?54%) relative to available pool area (?2%). Fine sediment levels (<0.063 mm) significantly increased within spawning substrate (p=0.01). Water temperature and dissolved oxygen were adequate (mean 15.8?°C, >6.0 mg l^?1, respectively) for brook trout survival in all streams during the drought. Brook trout populations were significantly reduced (adult 60%, Young-of-the-year 67%), and individual fish had significantly lower body condition during the drought relative to the post-drought period. Reductions in brook trout density and population condition during, and in the-post drought period, were related to spatially-limited food resources and/or increased fine sediment levels, but not to degraded water quality. Fisheries managers should consider the effect of periodic drought on brook trout populations and consider short-term harvest restrictions to abet recovery after such stochastic events.     

Oyster Reef Restoration in the Northern Gulf of Mexico: Effect of Artificial Substrate and Age on Nekton and Benthic Macroinvertebrate Assemblage Use

In the northern Gulf of Mexico (GOM), reefs built by eastern oysters, Crassostrea virginica, provide critical habitat within shallow estuaries, and recent efforts have focused on restoring reefs to benefit nekton and benthic macroinvertebrates. We compared nekton and benthic macroinvertebrate assemblages at historic, newly created (<5 years) and old (>6 years) shell and rock substrate reefs. Using crab traps, gill‐nets, otter trawls, cast nets, and benthic macroinvertebrate collectors, 20 shallow reefs (<5 m) in the northern GOM were sampled throughout the summer of 2011. We compared nekton and benthic assemblage abundance, diversity and composition across reef types. Except for benthic macroinvertebrate abundance, which was significantly higher on old rock reefs as compared to historic reefs, all reefs were similar to historic reefs, suggesting created reefs provide similar support of nekton and benthic assemblages as historic reefs. To determine refuge value of oyster structure for benthic macroinvertebrates compared to bare bottom, we tested preferences of juvenile crabs across depth and refuge complexity in the presence and absence of adult blue crabs (Callinectes sapidus). Juveniles were more likely to use deep water with predators present only when provided oyster structure. Provision of structural material to support and sustain development of benthic and mobile reef communities may be the most important factor in determining reef value to these assemblages, with biophysical characteristics related to reef location influencing assemblage patterns in areas with structure; if so, appropriately locating created reefs is critical.     

Benthic Composition of a Healthy Subtropical Reef: Baseline Species-Level Cover,with an Emphasis on Algae,in the Northwestern Hawaiian Islands

The Northwestern Hawaiian Islands (NWHI) are considered to be among the most pristine coral reef ecosystems remaining on the planet. These reefs naturally contain a high percent cover of algal functional groups with relatively low coral abundance and exhibit thriving fish communities dominated by top predators. Despite their highly protected status, these reefs are at risk from both direct and indirect anthropogenic sources. This study provides the first comprehensive data on percent coverage of algae, coral, and non-coral invertebrates at the species level, and investigates spatial diversity patterns across the archipelago to document benthic communities before further environmental changes occur in response to global warming and ocean acidification. Monitoring studies show that non-calcified macroalgae cover a greater percentage of substrate than corals on many high latitude reef sites. Forereef habitats in atoll systems often contain high abundances of the green macroalga Microdictyon setchellianum and the brown macroalga Lobophora variegata, yet these organisms were uncommon in forereefs of non-atoll systems. Species of the brown macroalgal genera Padina, Sargassum, and Stypopodium and the red macroalgal genus Laurencia became increasingly common in the two northernmost atolls of the island chain but were uncommon components of more southerly islands. Conversely, the scleractinian coral Porites lobata was common on forereefs at southern islands but less common at northern islands. Currently accepted paradigms of what constitutes a “healthy” reef may not apply to the subtropical NWHI, and metrics used to gauge reef health (e.g., high coral cover) need to be reevaluated.     

Relative Importance of Coral Cover,Habitat Complexity and Diversity in Determining the Structure of Reef Fish Communities

The structure of coral reef habitat has a pronounced influence on the diversity, composition and abundance of reef-associated fishes. However, the particular features of the habitat that are most critical are not always known. Coral habitats can vary in many characteristics, notably live coral cover, topographic complexity and coral diversity, but the relative effects of these habitat characteristics are often not distinguished. Here, we investigate the strength of the relationships between these habitat features and local fish diversity, abundance and community structure in the lagoon of Lizard Island, Great Barrier Reef. In a spatial comparison using sixty-six 2m² quadrats, fish species richness, total abundance and community structure were examined in relation to a wide range of habitat variables, including topographic complexity, habitat diversity, coral diversity, coral species richness, hard coral cover, branching coral cover and the cover of corymbose corals. Fish species richness and total abundance were strongly associated with coral species richness and cover, but only weakly associated with topographic complexity. Regression tree analysis showed that coral species richness accounted for most of the variation in fish species richness (63.6%), while hard coral cover explained more variation in total fish abundance (17.4%), than any other variable. In contrast, topographic complexity accounted for little spatial variation in reef fish assemblages. In degrading coral reef environments, the potential effects of loss of coral cover and topographic complexity are often emphasized, but these findings suggest that reduced coral biodiversity may ultimately have an equal, or greater, impact on reef-associated fish communities.     

Effects of distinct types of disturbance on seed rain in the Atlantic forest of NE Brazil

In disturbed sites, some groups of seeds might be excluded from the seed rain due to their dispersal modes or seed size, and some groups might be successful as a result of disturbance effects. In the present study, we examined the seed rain in natural treefall gaps and in an area of regenerating forest following an accidental burning, which occurred 4 years before this study. Both of these disturbed areas were compared with nearby forest understorey. The number of seeds, number of species, and proportion of wind-dispersed seeds were compared between these disturbed and undisturbed areas. The treefall gaps have received lower numbers of seeds and species than the nearby understorey, but the number of wind-dispersed seeds did not differ between these areas. The lowest seed number observed in treefall gaps can be attributed to a lower number of animal-dispersed seeds, suggesting that animals may be avoiding treefall gap areas. A higher number of seeds and a lower number of species were observed in the burned area when compared to the adjacent understorey. The high number of small-sized seeds and of wind-dispersed seeds in the burned area was almost surely a consequence of the local production of the pioneer plants established after the burning. In this study, substantial differences were observed in the characteristics of the seed rain at disturbed sites, when compared with undisturbed understorey. However, these two distinct types of disturbance showed quite differing patterns, as treefall gaps received lower number of seeds while the burned area received a higher number of seeds, with a greater proportion of wind-dispersed seeds. The exception was for species richness, which was quite low at both these disturbed sites.     

Predator Crown-of-Thorns Starfish (Acanthaster planci) Outbreak,Mass Mortality of Corals,and Cascading Effects on Reef Fish and Benthic Communities

Outbreaks of the coral-killing seastar Acanthaster planci are intense disturbances that can decimate coral reefs. These events consist of the emergence of large swarms of the predatory seastar that feed on reef-building corals, often leading to widespread devastation of coral populations. While cyclic occurrences of such outbreaks are reported from many tropical reefs throughout the Indo-Pacific, their causes are hotly debated, and the spatio-temporal dynamics of the outbreaks and impacts to reef communities remain unclear. Based on observations of a recent event around the island of Moorea, French Polynesia, we show that Acanthaster outbreaks are methodic, slow-paced, and diffusive biological disturbances. Acanthaster outbreaks on insular reef systems like Moorea''s appear to originate from restricted areas confined to the ocean-exposed base of reefs. Elevated Acanthaster densities then progressively spread to adjacent and shallower locations by migrations of seastars in aggregative waves that eventually affect the entire reef system. The directional migration across reefs appears to be a search for prey as reef portions affected by dense seastar aggregations are rapidly depleted of living corals and subsequently left behind. Coral decline on impacted reefs occurs by the sequential consumption of species in the order of Acanthaster feeding preferences. Acanthaster outbreaks thus result in predictable alteration of the coral community structure. The outbreak we report here is among the most intense and devastating ever reported. Using a hierarchical, multi-scale approach, we also show how sessile benthic communities and resident coral-feeding fish assemblages were subsequently affected by the decline of corals. By elucidating the processes involved in an Acanthaster outbreak, our study contributes to comprehending this widespread disturbance and should thus benefit targeted management actions for coral reef ecosystems.     

Effects of Small Dams on the Benthic Community of Streams in an Atlantic Forest Area of Southeastern Brazil

We examined the effects of longitudinal discontinuity in small rivers, produced by the construction of small dams, on the macroinvertebrate communities in a biological reserve in southeastern Brazil. Two regulated streams were sampled in the rainy and dry seasons at three sites along the river. One site was upstream of the dam/abstraction and two were below the dam. Our results indicate that there was a difference in the communities between the dry and rainy periods even though water physicochemical parameters of the water were not significantly different. The biotic richness at sites 500 m below the dam were similar to those above the impoundment (control), indicating that the fauna recovered when the discharge values found before water abstraction were reestablished. We concluded that the dam did induce changes in the composition of benthic comunities, especially in the dry period. However, overall, the fauna seemed to be able to persist during periods when the flow was absent. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assemblage of drosophilids (Diptera,Drosophilidae) inhabiting flooded and nonflooded areas in the extreme South of Brazil

Several studies on the potential use of drosophilid assemblages as bioindicator systems have been carried out in the last years. Nevertheless, the successful application of these organisms in these systems requires adequate filling of several knowledge gaps. In this sense, little is known about drosophilid assemblages in wetlands and flooded areas. The present study provides the first survey of drosophilid species inhabiting such environments in the extreme South of Brazil and compares general beta-diversity patterns between assemblages of flooded versus nonflooded areas. The specimens were collected with banana-baited traps, and the assemblages recovered in eight wetlands of the southernmost coast of Brazil were compared to those recovered from seven nonflooded areas of the Pampa and Atlantic Forest biomes. A total of 5028 and 2571 individuals encompassing 27 and 37 species were collected in the flooded and nonflooded areas, respectively. The differential species composition patterns presented between these areas was statistically supported, which seems to be related to the lower beta-diversity presented by swamps, especially in regard to dominance patterns. So, the open and climatically harsher environment provided by wetlands possibly constitutes a hostile environment for the entry and, mainly, for the persistence of several native Drosophilidae species, in contrast to some exotic and more plastic species (as Drosophila simulans and Zaprionus indianus). Since the diversity gradient of flooded areas does not seem to be related to the conservation status of the swamp, our results question the use of Drosophilidae species as bioindicators of environmental disturbance and antropic influence in wetlands.     

Physiognomic-structural characterization of dry- and humid-forest fragments (Atlantic Coastal Forest) in Pernambuco State,NE Brazil

Although both dry- and humid-forests have been intensively studied, their physiognomic and structural differences have not yet been well characterized. The present work seeks to identify the physiognomic and structural differences between fragments of humid- and dry-forests in the state of Pernambuco, Brazil. The humid-forest fragment was located in the municipality of São Vicente Férrer (7°37′ S × 35°28′ W) and the dry-forest fragment in the municipality of Aliança (7°38′ S × 35°14′ W). Fifty 10 × 20 m plots were delimited in each area and all individual living plants with a diameter at breast height (DBH) ≥5 cm were included. It was observed that the total density (1,390 ind ha^?1) and total basal area (29.9 m² ha^?1) were greater in the humid-forest than the dry-forest (649 ind ha^?1 and 18.7 m² ha^?1, respectively). Individual plants in the humid-forest tended to be taller, while those in the dry-forest had generally larger diameters. There were also differences in the most structurally important families as, for example, Clusiaceae, Moraceae, Myristicaceae, and Sapotaceae in the humid-forest and Sterculiaceae, Fabaceae, Bignoniaceae, and Moraceae in the dry-forest. Physiognomic differences were also observed in the different forest layers, as the group of species composing the canopy of the dry-forest are dominated by deciduous species, while many of the species in the understory are evergreen. In the humid-forest, both the understory and canopy are predominantly composed of evergreen species. The examination of the phytosociological parameters of average height and species richness allowed us to identify physiognomic differences between humid and dry forests in Pernambuco State. The present study demonstrated that dry forests are not simply floristic/structural subsets of humid forests, and that there is a great need to establish conservation areas to protect these important but spatially restricted forests within the Atlantic coastal domain.     

Embryos of common thresher shark Alopias vulpinus in southern Brazil, South Atlantic Ocean

Eight embryonic thresher sharks Alopias vulpinus (53·9–124 cm total length) were collected from two females caught by commercial longline off southern Brazil in September and November 2004. Morphometric measurements are provided.     

Studies on Biodiversity in the Plankton, Benthos, and Fish Communities, and the Ecosystems of Fresh Water Bodies Differing in Productivity

The species diversity of phyto- and zooplankton, benthic animals, and ichthyofauna was studied in continental water bodies that differ in type, geographic location, size, and productivity. The results showed that the number of species in the communities of aquatic organisms and in ecosystems depends on the area and volume of the water body and the level of plankton primary production. Corresponding relationships can be approximated by the equations of exponential and polymodal functions. The species number and biomass per unit area or volume proved to decrease as the area or volume of the water body increased. The greatest number of heterotrophic species was observed in water bodies whose primary production approached 1400 kcal/m² per year. It is proposed that the number of aquatic species in a body of water depends on the total area of the latter and the area of individual territories occupied by the representatives of certain species.     

Coral Reefs at the Northernmost Tip of Borneo: An Assessment of Scleractinian Species Richness Patterns and Benthic Reef Assemblages

The coral reefs at the northernmost tip of Sabah, Borneo will be established under a marine protected area: the Tun Mustapha Park (TMP) by the end of 2015. This area is a passage where the Sulu Sea meets the South China Sea and it is situated at the border of the area of maximum marine biodiversity, the Coral Triangle. The TMP includes fringing and patch reefs established on a relatively shallow sea floor. Surveys were carried out to examine features of the coral reefs in terms of scleractinian species richness, and benthic reef assemblages following the Reef Check substrate categories, with emphasis on hard coral cover. Variation in scleractinian diversity was based on the species composition of coral families Fungiidae (n = 39), Agariciidae (n = 30) and Euphylliidae (n = 15). The number of coral species was highest at reefs with a larger depth gradient i.e. at the periphery of the study area and in the deep South Banggi Channel. Average live hard coral cover across the sites was 49%. Only 7% of the examined reefs had > 75% hard coral cover, while the majority of the reef sites were rated fair (51%) and good (38%). Sites with low coral cover and high rubble fragments are evidence of blast fishing, although the observed damage appeared old. Depth was a dominant factor in influencing the coral species composition and benthic reef communities in the TMP. Besides filling in the information gaps regarding species richness and benthic cover for reef areas that were previously without any data, the results of this study together with information that is already available on the coral reefs of TMP will be used to make informed decisions on zoning plans for conservation priorities in the proposed park.     

Comparative Environmental Assessment in the Studies of Benthic Diatom,Macroinvertebrate, and Fish Communities

Community response to environmental gradients operating at hierarchical scales was assessed in studies of benthic diatoms, macroinvertebrates and fish from 44 stream sites in the New York City watershed. Hierarchical cluster analysis (TWINSPAN) of diatoms and fish partitioned the study sites into four groups, i.e., acid streams, reservoir outlets and wetland streams, large eutrophic streams, and small eutrophic streams; macroinvertebrate TWINSPAN distinguished an additional group of silty eutrophic streams. The correspondence among the three assemblage TWINSPAN groupings was moderate, ranging from 51 to 57%. The similarity across the four major group types was the highest among large eutrophic stream and acid stream assemblages, and the lowest among small eutrophic stream assemblages. Stepwise discriminant function analysis revealed that environmental factors discriminated most effectively the diatom grouping and least effectively the fish grouping. The best environmental predictors for diatom and macroinvertebrate grouping were conductance and percent surface water, while population density was most powerful in separating the fish groups. Carbaryl was the only pesticide that correlated with macroinvertebrate grouping. Partial redundancy analyses suggested a differential dependence of freshwater communities on the scale of the environmental factors to which they respond. The role of small‐scale habitat and habitatland cover/land use interaction steadily increased across the diatom, macroinvertebrate, and fish assemblages, whereas the effect of large‐scale land cover/land use declined.     

Effects of Pressure and Temperature on the Catalytic and Regulatory Properties of Muscle Pyruvate Kinase from an Off-Shore Benthic Fish

SYNOPSIS. Muscle pyruvate kinase from an abyssal Coryphaenoidesspecies occurs as a single electrophoretic form with an isoelectricpoint of about pH 6.0. Maximum catalytic rates are dramaticallyreduced by pressure. For catalysis at 3°C, the volume changeof activation, V*, is about 44 cm³/mole (calculated between14.7 and 8000 psi). The value ot V* decreases at higher temperaturesbut is pH independent. The activation energy for rattail musclepyruvate kinase at 14.7 psi is about 13 Kcal/mole and doublesat 12,000 psi. Mg²⁺ saturation kinetics involve positive site-siteinteractions. Hill plots yield n values of about 2.4 and K_avalues of about 2 mM (at 3°C), and these constants are pressureindependent. The K_m values for ADP increase slightly with pressure.PEP saturation curves are complex: at high PEP concentrations,the n values are about 2–2.5, while at low PEP levels,values for the Hill constant are about 1.0. The Hill constantlor PEP is not affected by pressure, but the apparent K_m increasessomewhat with pressure. FDP dramatically activates rattail musclepyruvate kinase (500% activation with 0.1 mM FDP) by (1) reducingthe K_mPEP, (2) increasing the maximum velocity, and (3) overridingnegative ATP modulation of the enzyme. The latter control featureis strictly dependent upon pressure and is not observed at lowpressure. In the presence of FDP, the K_m for PEP decreases athigh pressures, in this way counteracting the inhibitory effectsof pressure. Under low concentrations of substrates, pyruvatekinase activity is probably determined by its kinetic propertiesand not by energy-volume relationships.