Density and height of Sargassum influence rabbitfish (f. Siganidae) settlement on inshore reef flats of the Great Barrier Reef

Macroalgal beds have been suggested to be an important settlement habitat for a diversity of reef fishes, yet few studies have considered how the composition or structure of macroalgal beds may influence fish settlement. The aim of this study was to investigate how the physical characteristics of Sargassum beds, a common macroalga on inshore coral reefs, influence the abundance of recently-settled rabbitfishes (Siganidae) on Orpheus Island, Great Barrier Reef. The abundance of recently-settled rabbitfish (< 3 cm total length), the density and height of Sargassum thalli, and benthic composition were quantified within replicate 1-m² quadrats across 15 mid-reef flat sites. A total of 419 recently-settled rabbitfish from three species (Siganus doliatus, S. lineatus and S. canaliculatus) were recorded across 150 quadrats (range 0–16 individuals m⁻²), with S. doliatus accounting for the majority (85.2%) of individuals recorded. The abundance of S. doliatus and S. lineatus was greatest at moderate Sargassum densities (ca. 20–30 holdfasts m⁻²) and generally increased with Sargassum height and the cover of ‘other’ macroalgae. These findings demonstrate the potential importance of the physical characteristics of macroalgal beds to the settlement of rabbitfishes on inshore reef flats.

     

Overgrowth of Caribbean octocorals by milleporid hydrocorals

On Caribbean reefs, colonies of the hydrocoral Millepora alcicornis are capable of pursuing and overgrowing arborescent octocorals (Wahle 1980 ). Nearly four decades since these interactions were described, we quantified arborescent octocorals encrusted by Millepora spp. (Linnaeus 1758) on shallow reefs in St. John, U.S. Virgin Islands, and evaluated encrusted colonies for evidence of an origin through pursuit. In 2014, 8% of octocorals (n=1684 colonies) were encrusted by Millepora spp., and in 2015, 12% were encrusted (n=847 colonies). Millepora spp. encrusted colonies of 10 octocoral genera, and in 2014, the most frequently encrusted were Eunicea spp. (40% of encrusted octocorals); in 2015, the most frequently encrusted were Gorgonia spp. (46% of encrusted colonies). In both years, ≥67% of encrusted octocorals were >21 cm from other colonies of Millepora spp.; 7% of octocorals were >1.3 m from colonies of Millepora spp. in 2014; and 16% of octocorals were >2.0 m from colonies of Millepora spp. in 2015. Relative to the ~5% of octocorals encrusted by Millepora spp. in Jamaica in the late 1970s, a high percentage (~9%) of octocorals were encrusted by Millepora spp. in St. John in 2014 and 2015. The large distances from most encrusted octocorals to the nearest colonies of Millepora spp. in St. John are inconsistent with a hypothesized origin through pursuit, contact, and overgrowth (sensu Wahle 1980 ).     

Tropical herbivores provide resilience to a climate‐mediated phase shift on temperate reefs

Climate‐mediated changes to biotic interactions have the potential to fundamentally alter global ecosystems. However, the capacity for novel interactions to drive or maintain transitions in ecosystem states remains unresolved. We examined temperate reefs that recently underwent complete seaweed canopy loss and tested whether a concurrent increase in tropical herbivores could be maintaining the current canopy‐free state. Turf‐grazing herbivorous fishes increased in biomass and diversity, and displayed feeding rates comparable to global coral reefs. Canopy‐browsing herbivores displayed high (~ 10 000 g 100 m^?2) and stable biomass between 2006 and 2013. Tropical browsers had the highest abundance in 2013 and displayed feeding rates approximately three times higher than previously observed on coral reefs. These observations suggest that tropical herbivores are maintaining previously kelp‐dominated temperate reefs in an alternate canopy‐free state by grazing turfs and preventing kelp reestablishment. This remarkable ecosystem highlights the sensitivity of biotic interactions and ecosystem stability to warming and extreme disturbance events.     

Influence of habitat on grouper abundance in the Florida Keys, U.S.A.

There was a significant inshore to offshore pattern in grouper species composition and density on Florida Keys coral reefs. Red grouper Epinephelus morio and black grouper Mycteroperca bonaci were most abundant on inshore patch reefs. Graysby Cephalopholis cruentata was most abundant on offshore reef types. Density among sites ranged from 0 to 0·43, 0 to 0·26 and 0 to 1·23 100 m⁻² for red grouper, black grouper, and graysby, respectively. Grouper density exhibited no consistency among sites within similar reef types. The densities of red and black grouper were correlated significantly with either physical or biotic habitat parameters. Graysby were observed in microhabitats with whose benthic features differed significantly from the surrounding habitat. This species was observed in high-relief areas with significantly less octocoral species and colony densities. Larger graysby were observed in areas of higher relief and less octocorals than smaller graysby. Habitat was one of several important factors influencing the distribution of groupers among coral reefs types in the Florida Keys.     

The structure of a nearshore fish community of Western Australia: diel patterns and the habitat role of limestone reefs

Synopsis Extensive limestone reefs are a characteristic feature of much of the coastline of Western Australia, and potentially represent a major habitat feature influencing the structure of the coastal fish community. The structure and temporal dynamics of the fish fauna and its relationships to nearshore patch reefs and surrounding habitat near Dongara, Western Australia, were examined using (1) diel gill-netting and (2) quantitative rotenone sampling of enclosed areas of substratum. Long-term and day-to-day variability of the fauna was low. Dominant species of gill-net collections were either associated with reefs or occurred in similar abundances at both reefs and surrounding sand/seagrass flats. The overall abundance, number of species and biomass of netted fishes was higher around reefs. Rotenone collections of the more sedentary species showed a similar pattern, but suggested, however, that a simple reef versus surrounding sand and seagrass habitat comparison is complicated by the canopy-forming seagrass Amphibolis that occurs on reef tops. Time of day had an important effect on overall fish abundance and number of species, with peaks occurring at crepuscular periods. This reflected dusk and dawn activity peaks of a dominant species rather than overlapping activities of many diurnal and nocturnal species. Diel switches between reef-edge habitat and surrounding sand/seagrass flats were uncommon despite expectations (based on literature examples) that patch reefs would function primarily as sheltering habitats and surrounding non-reef areas act as foraging habitat. High catches at reef-edge sites suggest that the majority of fishes forage on or near limestone patch reefs. Fish densities of around 0.8 individuals per m^-2 of bottom on these Western Australian reefs are relatively high in comparison to visual census estimates obtained for temperate reef systems in South Australia and New Zealand, but similar to those obtained using comparable netting methods in temperate Australian seagrass systems.     

Alien algae <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> causes habitat loss for rocky reef fishes in north Patagonia

Since the introduction of Undaria into Nuevo Gulf, Argentina, around 1992, this alien seaweed has now colonized different sites over 700 km of coast, forming dense seasonal forests in waters from 0 to 15 meters in depth. In the spring it is common for plants of Undaria to break away from the substrate and be transported by sea currents. As Undaria gets stuck onto reefs it has the potential to reduce habitat quality for reef fish by physically obstructing refuges. This study aims to assess the impact of Undaria on the abundance of four species of rocky-reef fishes by an observational experiment. Fish abundance on reefs with and without Undaria was estimated by underwater visual census methods. Sites were classified according to their topographical relief, as this was expected to influence the effect of Undaria on the abundance of reef fishes. Fish abundance decreased markedly in low-relief reefs that had been covered by Undaria. In contrast, the drifting Undaria had no effect on the abundance of any of the fish species considered in high-relief reefs, where it tends to cover only the lowest-lying areas, leaving much of the refuges for fish unaffected. In conclusion, the presence of Undaria off the coast of Argentina results in transitory habitat loss for reef fishes inhabiting low-relief reefs during late spring and early summer. Although we do not know how much of a threat this habitat loss represents for the conservation of reef fish populations of northern Patagonia, the documented local impact of Undaria within the gulfs is strong and may affect a number of recreational and commercial activities which are centered on the reefs and their fish assemblages.     

Global habitat suitability of cold‐water octocorals

Aim Three‐quarters of Octocorallia species are found in deep waters. These cold‐water octocoral colonies can form a major constituent of structurally complex habitats. The global distribution and the habitat requirements of deep‐sea octocorals are poorly understood given the expense and difficulties of sampling at depth. Habitat suitability models are useful tools to extrapolate distributions and provide an understanding of ecological requirements. Here, we present global habitat suitability models and distribution maps for seven suborders of Octocorallia: Alcyoniina, Calcaxonia, Holaxonia, Scleraxonia, Sessiliflorae, Stolonifera and Subselliflorae. Location Global. Methods We use maximum entropy modelling to predict octocoral distribution using a database of 12,508 geolocated octocoral specimens and 32 environmental grids resampled to 30 arc‐second (approximately 1 km²) resolution. Additionally, a meta‐analysis determined habitat preferences and niche overlap between the different suborders of octocorals. Results Suborder Sessiliflorae had the widest potential habitat range, but all records for all suborders implied a habitat preference for continental shelves and margins, particularly the North and West Atlantic and Western Pacific Rim. Temperature, salinity, broad scale slope, productivity, oxygen and calcite saturation state were identified as important factors for determining habitat suitability. Less than 3% of octocoral records were found in waters undersaturated for calcite, but this result is affected by a shallow‐water sampling bias. Main conclusions The logistical difficulties, expense and vast areas associated with deep‐sea sampling leads to a gap in the knowledge of faunal distributions that is difficult to fill without predictive modelling. Global distribution estimates are presented, highlighting many suitable areas which have yet to be studied. We suggest that approximately 17% of oceans are suitable for at least one suborder but 3.5% may be suitable for all seven. This is the first global habitat suitability modelling study on the distribution of octocorals and forms a useful resource for researchers, managers and conservationists.     

Symbiosis and host morphological variation: Symbiodiniaceae photosynthesis in the octocoral Briareum asbestinum at ambient and elevated temperatures

Intra-species morphological variation may occur in sessile organisms, such as corals, living in different habitats. Conversely, the octocoral Briareum asbestinum exhibits both encrusting and upright branching morphologies at the same shallow water habitat, enabling studying physiological differences uncoupled from habitat variation due to depth or reef location. We investigated the mutualism between endosymbiotic dinoflagellate algae, Breviolum spp. (previously clade B Symbiodinium), and these B. asbestinum morphologies at ambient and elevated temperatures. Based on msh1 gene sequences, the host morphologies were genetically similar although they differed in protein content, polyp expansion behavior, and associated Breviolum (B19 for encrusting and B21 for branching B. asbestinum). Due to colony orientation, polyps in encrusting B. asbestinum experienced irradiance levels nearly three times higher than polyps in the branching morph, which probably contributed to the lower photochemical and light absorption efficiencies of the Breviolum in encrusting fragments. The light-limited portion of photosynthesis–irradiance curves and the intracellular chlorophyll concentrations, however, indicated that Breviolum in both morphologies were acclimated to similar internal irradiances. Encrusting B. asbestinum exhibited higher Breviolum density, areal chlorophyll a, and greater photosynthetic rates cm⁻² compared to branching B. asbestinum. Notably, elevated temperature did not cause bleaching in either morphology, as Breviolum and chlorophyll densities did not differ significantly from ambient temperature, although the two morphologies adjusted some of the measured parameters, indicating coping with the stressor. In the face of continued ocean warming, the high thermal tolerance of octocorals may reinforce the shift of Caribbean reefs from scleractinian coral to octocoral dominance.

     

Coral mortality versus structural collapse as drivers of corallivorous butterflyfish decline

As climate change increasingly threatens biodiversity, identifying specific drivers of species loss as well as the attributes of species most vulnerable to climatic disturbances is a key challenge to ecologists and conservationists. Here we assess the effects of coral loss versus declines in structural complexity on obligate and facultative coral feeding butterflyfishes on coral reefs in the central and western Indian Ocean. In the inner Seychelles, the abundance of the obligate coral feeding group declined markedly in response to live coral mortality (r ² = 0.48), but showed no further decline with respect to erosion of the physical matrix of the reef. Conversely, the facultative feeding group showed no decline in response to live coral loss, reflecting their feeding versatility; however they did decline in response to structural erosion of the reef framework (r ² = 0.26). There were no significant changes in either obligate or facultative corallivore abundances at a reference location (Chagos archipelago), highlighting that butterflyfish populations are stable in the absence of habitat disturbance. While specialised coral dependant fishes are highly vulnerable to coral loss caused by climate-induced coral bleaching, the structural collapse of dead coral colonies may have significant, but more variable, impacts across a wide range of fishes. If conservation and mitigation planning are to be effective, there is a clear need to better understand the mechanisms of reef structural collapse and the dynamics of system recovery following large-scale disturbance.     

Estimating the role of three mesopredatory fishes in coral reef food webs at Ningaloo Reef,Western Australia

Within the complex food webs that occur on coral reefs, mesopredatory fish consume small-bodied prey and transfer accumulated biomass to other trophic levels. We estimated biomass, growth and mortality rates of three common mesopredators from Ningaloo Reef in Western Australia to calculate their annual turnover rates and potential contribution to local trophic dynamics. Biomass estimates of the serranid Epinephelus rivulatus (4.46 ± 0.76 g m⁻²) were an order of magnitude greater than two smaller-bodied mesopredatory fishes, Pseudochromis fuscus (0.10 ± 0.03 g m⁻²) and Parapercis clathrata (0.23 ± 0.31 g m⁻²). Growth parameters generated from a von Bertalanffy growth function fitted to size-at-age data, however, indicated that mortality rates for the three mesopredators were similar and that 32–55 % of fish survived each year. Consequently, interspecific differences in annual turnover rates among E. rivulatus (1.9 g m⁻² yr⁻¹), Pa. clathrata (0.10 g m⁻² yr⁻¹) and Ps. fuscus (0.07 g m⁻² yr⁻¹) were an artefact of differences in local biomass estimates. The rapid turnover estimates for E. rivulatus suggest this species is an important conduit of energy within the isolated patch reef habitat where it is typically found, while Ps. fuscus and Pa. clathrata channel smaller amounts of energy from specific habitats in the Ningaloo lagoon. Apparent differences in habitat, diet and turnover rates of the three species examined provide an insight into the different roles these species play in coral reef food webs and suggest that life-history traits allow for variability in the local and spatial contribution of these species at Ningaloo Reef. Moreover, calculating turnover rates of a broader suite of fish species from a range of trophic groups will help better define the role of fishes in coral reef trophic dynamics.

     

The genetic identity of dinoflagellate symbionts in Caribbean octocorals

Many cnidarians (e.g., corals, octocorals, sea anemones) maintain a symbiosis with dinoflagellates (zooxanthellae). Zooxanthellae are grouped into clades, with studies focusing on scleractinian corals. We characterized zooxanthellae in 35 species of Caribbean octocorals. Most Caribbean octocoral species (88.6%) hosted clade B zooxanthellae, 8.6% hosted clade C, and one species (2.9%) hosted clades B and C. Erythropodium caribaeorum harbored clade C and a unique RFLP pattern, which, when sequenced, fell within clade C. Five octocoral species displayed no zooxanthella cladal variation with depth. Nine of the ten octocoral species sampled throughout the Caribbean exhibited no regional zooxanthella cladal differences. The exception, Briareum asbestinum, had some colonies from the Dry Tortugas exhibiting the E. caribaeorum RFLP pattern while elsewhere hosting clade B. In the Caribbean, octocorals show more symbiont specificity at the cladal level than scleractinian corals. Both octocorals and scleractinian corals, however, exhibited taxonomic affinity between zooxanthella clade and host suborder.Communicated by R.C. Carpenter     

Diversity and relative abundance of corals, octocorals and sponges at Jaragua National Park, Dominican Republic

The Jaragua National Park is located in a remote area to the SW coast of the Dominican Republic. Fishing and mining are the major human activities. The main reef formations of the Park include: (a) long bank reefs (spur and groove) growing as bands over the platform and running in a SW-NW direction at 12-25 m depth, (b) well developed, deep, fringing reefs at the platform edge (drop-off) areas which could extend from 10 to 45 m depth, and (c) small patch reefs and poorly developed coral-octocoral-sponge-algal communities in shallow platforms near shore, rocky bottoms, and over the submerged walls of the uplifted reef. Nine reef localities were surveyed between Cabo Beata and Bahia Honda using Scuba diving to inventory the diversity and relative abundance of scleractinian corals, octocorals and sponges. Fringing reefs were surveyed starting at the bottom (30 m) and swimming in a zig-zag pattern (50 m on each side) to shallower areas. Bank reefs were surveyed by swimming in zig-zag across the spur-groove formation along 500 m. Sponges were the most diverse group with 83 species in 50 genera followed by the scleractinian corals with 56 species in 26 genera and the octocorals with 47 species in 15 genera. New records included eight coral species, 29 octocoral species and 59 sponges. The diversity, species composition and abundance of particular groups varied across the different localities. Northern reefs within the park and the Los Frailes Island offshore had the highest live cover, relative abundance and diversity for the three groups. In general, the Jaragua National Park had the highest diversity of corals, octocorals and sponges reported for the Dominican Republic and rank amongst the highest reported for the northern Caribbean. It is recommended that the area be protected and that fishing activities be regulated or eliminated altogether.     

Macroalgal herbivory on recovering versus degrading coral reefs

Macroalgal-feeding fishes are considered to be a key functional group on coral reefs due to their role in preventing phase shifts from coral to macroalgal dominance, and potentially reversing the shift should it occur. However, assessments of macroalgal herbivory using bioassay experiments are primarily from systems with relatively high coral cover. This raises the question of whether continued functionality can be ensured in degraded systems. It is clearly important to determine whether the species that remove macroalgae on coral-dominated reefs will still be present and performing significant algal removal on macroalgal-dominated reefs. We compared the identity and effectiveness of macroalgal-feeding fishes on reefs in two conditions post-disturbance—those regenerating with high live coral cover (20–46 %) and those degrading with high macroalgal cover (57–82 %). Using filmed Sargassum bioassays, we found significantly different Sargassum biomass loss between the two conditions; mean assay weight loss due to herbivory was 27.9 ± 4.9 % on coral-dominated reefs and 2.2 ± 1.1 % on reefs with high macroalgal cover. However, once standardised for the availability of macroalgae on the reefs, the rates of removal were similar between the two reef conditions (4.8 ± 4.1 g m^?2 h^?1 on coral-dominated and 5.3 ± 2.1 g m^?2 h^?1 on macroalgal-dominated reefs). Interestingly, the Sargassum-assay consumer assemblages differed between reef conditions; nominally grazing herbivores, Siganus puelloides and Chlorurus sordidus, and the browser, Siganus sutor, dominated feeding on high coral cover reefs, whereas browsing herbivores, Naso elegans, Naso unicornis, and Leptoscarus vaigiensis, prevailed on macroalgal-dominated reefs. It appeared that macroalgal density in the surrounding habitat had a strong influence on the species driving the process of macroalgal removal. This suggests that although the function of macroalgal removal may continue, the species responsible may change with context, differing between systems that are regenerating versus degrading.     

Sedimentary Organic Carbon and Nitrogen Sequestration Across a Vertical Gradient on a Temperate Wetland Seascape Including Salt Marshes,Seagrass Meadows and Rhizophytic Macroalgae Beds

Coastal wetlands are key in regulating coastal carbon and nitrogen dynamics and contribute significantly to climate change mitigation and anthropogenic nutrient reduction. We investigated organic carbon (OC) and total nitrogen (TN) stocks and burial rates at four adjacent vegetated coastal habitats across the seascape elevation gradient of Cádiz Bay (South Spain), including one species of salt marsh, two of seagrasses, and a macroalgae. OC and TN stocks in the upper 1 m sediment layer were higher at the subtidal seagrass Cymodocea nodosa (72.3 Mg OC ha⁻¹, 8.6 Mg TN ha⁻¹) followed by the upper intertidal salt marsh Sporobolus maritimus (66.5 Mg OC ha⁻¹, 5.9 Mg TN ha⁻¹), the subtidal rhizophytic macroalgae Caulerpa prolifera (62.2 Mg OC ha⁻¹, 7.2 Mg TN ha⁻¹), and the lower intertidal seagrass Zostera noltei (52.8 Mg OC ha⁻¹, 5.2 Mg TN ha⁻¹). The sedimentation rates increased from lower to higher elevation, from the intertidal salt marsh (0.24 g cm⁻² y⁻¹) to the subtidal macroalgae (0.12 g cm⁻² y⁻¹). The organic carbon burial rate was highest at the intertidal salt marsh (91 ± 31 g OC m⁻² y⁻¹), followed by the intertidal seagrass, (44 ± 15 g OC m⁻² y⁻¹), the subtidal seagrass (39 ± 6 g OC m⁻² y⁻¹), and the subtidal macroalgae (28 ± 4 g OC m⁻² y⁻¹). Total nitrogen burial rates were similar among the three lower vegetation types, ranging from 5 ± 2 to 3 ± 1 g TN m⁻² y⁻¹, and peaked at S. maritimus salt marsh with 7 ± 1 g TN m⁻² y⁻¹. The contribution of allochthonous sources to the sedimentary organic matter decreased with elevation, from 72% in C. prolifera to 33% at S. maritimus. Our results highlight the need of using habitat-specific OC and TN stocks and burial rates to improve our ability to predict OC and TN sequestration capacity of vegetated coastal habitats at the seascape level. We also demonstrated that the stocks and burial rates in C. prolifera habitats were within the range of well-accepted blue carbon ecosystems such as seagrass meadows and salt marshes.

     

Intertidal territoriality and time-budget of the surgeonfish, Acanthurus lineatus, in American Samoa

Synopsis The herbivorous surgeonfish Acanthurus lineatus aggressively maintained feeding territories in the surf zone of the outer reef flat in American Samoa. Intertidal territories were re-established each morning, as well as after displacement by low tides or rough surf. Day-to-day site fidelity of recognizable individuals was high: 99.9% return rate per day for adults (15–20 cm), 99.6% for juveniles (8–13 cm), and 97.2% for recruits (2.5–5 cm). Fish fed on turf algae primarily in the afternoon (80% of available time), and spent 10% of their time on active territorial defense and 2–13% of their time on forays from their territory. On average, a fish defended its territory 1900 times daily and took 17 000 bites (= 7400 bites m^–2 d^–1), but rough surf reduced feeding by 60% and defense by 75%. High territorial defense requirements significantly reduced feeding rates. Although the distribution and behavior of this species in Samoa was in large part similar to that reported for it elsewhere (Australia, Indian Ocean), there were notable differences: in Samoa A. lineatus densities within colonies were greater (0.4 fish m^–2), territory size was smaller (2.3 m²), and defense rate against intruders was greater (2.5 attacks min^–1). These differences in Samoa may be related to their smaller body size, greater abundance or increased food supply caused by hurricane damage to reefs which has enhanced the algal turfs that A. lineatus feeds upon.     

Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities

Cleaning behaviour is deemed a mutualism, however the benefit of cleaning interactions to client individuals is unknown. Furthermore, mechanisms that may shift fish community structure in the presence of cleaning organisms are unclear. Here we show that on patch reefs (61–285 m²) which had all cleaner wrasse Labroides dimidiatus (Labridae) experimentally removed (1–5 adults reef⁻¹) and which were then maintained cleaner-fish free over 8.5 years, individuals of two site-attached (resident) client damselfishes (Pomacentridae) were smaller compared to those on control reefs. Furthermore, resident fishes were 37% less abundant and 23% less species rich per reef, compared to control reefs. Such changes in site-attached fish may reflect lower fish growth rates and/or survivorship. Additionally, juveniles of visitors (fish likely to move between reefs) were 65% less abundant on removal reefs suggesting cleaners may also affect recruitment. This may, in part, explain the 23% lower abundance and 33% lower species richness of visitor fishes, and 66% lower abundance of visitor herbivores (Acanthuridae) on removal reefs that we also observed. This is the first study to demonstrate a benefit of cleaning behaviour to client individuals, in the form of increased size, and to elucidate potential mechanisms leading to community-wide effects on the fish population. Many of the fish groups affected may also indirectly affect other reef organisms, thus further impacting the reef community. The large-scale effect of the presence of the relatively small and uncommon fish, Labroides dimidiadus, on other fishes is unparalleled on coral reefs.     

Structure and injuries of octocoral communities (Octocorallia: Alcyonacea) of Ecological Reserve Siboney-Juticí, Santiago de Cuba, Cuba

In the spur-and-groove reefs of the Ecological Reserve Siboney-Juticí (Southeast Cuba) octocorals are one of the predominant components of the sessile fauna. Main objectives of the present paper are characterizing the composition, structure and conservation status of the octocoral communities and assessing on the prevailing environmental conditions in the study area. For data collection, six sampling sites were located every 2-3 km ranging from 12 m to 17 m depth along the spur-and-groove reefs. In each site, 22-26 lm2 quadrants were zigzag arranged every 2 m. The density of colonies was determined per site. The severity degree and predictability of environmental conditions were inferred by using the Heterogeneity and Equitability indexes, respectively. Hydrodynamic stress and the Comparative Pollution Index were also assessed. Current affectations of the octocoral communities were also determined and classified into four main categories: mechanical damage, diseases, predation and invertebrate and macroalgae overgrowth. As a result, 25 species represented by 752 colonies were recorded and Eunicea flexuosa and Gorgonia ventalina were the most abundant. The occurrence of Eunicea succinea forma succinea constituted the first report for Eastern Cuba. Site densities ranged from 3.58 +/- 1.84 to 7.58 +/- 2.16 colonies/m2 and considered from moderate to low. The biggest densities were reported at both sides of the San Juan River mouth. Despite of the composition and structure of the octocoral communities, low to high hydrodynamic stress and low and moderate levels of contamination were inferred, it is likely that these indexes could have been overestimated due to the sensitivity of the indicator species to other factors such as sedimentation. The environmental conditions were mostly favorable and stable. In general, the number of dead colonies was low and mostly caused by the detachment of the substrate and overgrowth of Millepora alcicornis. Injuries were mainly brought about by mechanical damage, followed by coenenchyme loss, predation by Cyphoma gibbosum and macroalgae overgrowth. On the other hand, negative effects by Hermodice carunculata predation, bleaching, Red Band and Black Band Disease were not observed. Among sampled species, G. ventalina colonies were the most severely damaged within the community. As a whole, octocoral communities of spur-and-groove reefs in the Ecological Reserve Siboney-Juticí showed a good conservation status.     

Energy flow to two abundant consumers in a subtropical oyster reef food web

Oyster reefs are among the most threatened coastal habitat types, but still provide critical habitat and food resources for many estuarine species. The structure of oyster reef food webs is an important framework from which to examine the role of these reefs in supporting high densities of associated fishes. We identified major trophic pathways to two abundant consumers, gray snapper (Lutjanus griseus) and crested goby (Lophogobius cyprinoides), from a subtropical oyster reef using stomach content and stable isotope analysis. The diet of gray snapper was dominated by crabs, with shrimp and fishes also important. Juvenile gray snapper fed almost entirely on oyster reef-associated prey items, while subadults fed on both oyster reef- and mangrove-associated prey. Based on trophic guilds of the gray snapper prey, as well as relative δ¹³C values, microphytobenthos is the most likely basal resource pool supporting gray snapper production on oyster reefs. Crested goby had omnivorous diets dominated by bivalves, small crabs, detritus, and algae, and thus were able to take advantage of prey relying on production from sestonic, as well as microphytobenthos, source pools. In this way, crested goby represent a critical link of sestonic production to higher trophic levels. These results highlight major trophic pathways supporting secondary production in oyster reef habitat, thereby elucidating the feeding relationships that render oyster reef critical habitat for many ecologically and economically important fish species.     

Mapping and biomass estimation of the invasive brown algae<Emphasis Type="Italic"> Turbinaria ornata</Emphasis> (Turner) J. Agardh and<Emphasis Type="Italic"> Sargassum mangarevense</Emphasis> (Grunow) Setchell on heterogeneous Tahitian coral reefs using 4-meter resolution IKONOS satellite data

Turbinaria ornata and Sargassum mangarevense (Halophyte, Sargassaceae) are two Fucales that have strong biotechnological potential for the cosmetic industries. To plan for the harvesting of these two species on Tahiti (French Polynesia, South Pacific Ocean) reefs, their total biomass is estimated for three morphologically different reefs using a combination of field data and three 4-m resolution IKONOS satellite images. Fieldwork provided mean algal cover for each of the main habitats of the reefs and a ubiquitous relationship linking percent cover and biomass. Images were used to map the spatial extent of the habitats. Image classification resulted in an overall habitat map accuracy of 70%. For the three reefs, the total biomass was 153,565 ± 73,441, 561,718 ± 192,956, and 215,203 ± 75,012 tons of dry matter, which yielded a mean areal biomass of 0.173 ± 0.083 kg.m^–2, 0.133 ± 0.046 kg.m^–2, and 0.193 ± 0.067 kg.m^–2 (dry matter). The different total and areal biomass reflect different reef structures and the abundance of suitable substratum for algal settlement. Images reveal the spatial distribution of the algae, mostly located on the outer edges (crest and dense back-reef) of the reefs. Since percent cover data were collected during the cool season when algal densities are at their highest, the computed biomasses are maxima.     

The effectiveness of different meso-scale rugosity metrics for predicting intra-habitat variation in coral-reef fish assemblages

Habitat structure is frequently an important variable affecting species’ abundances and diversity, and identifying the key aspects and spatial scales of habitat complexity is critical for understanding the ecology and conservation of a range of communities. Many coral-reef fishes are intimately linked with benthic habitat structure, and previous research has demonstrated rugosity as an important predictive variable of assemblage parameters. However, these studies typically consider rugosity at small scales, amalgamate multiple habitat features, or are semi-quantitative. This study considers meso-scale rugosity (within 51 plots of 25 m² on a Belizean forereef) generated by varying coral densities, heights, and complexities. Seven rugosity metrics were calculated for each plot, and were regressed against each of 11 fish assemblage parameters. Intra-habitat variability of each fish parameter was significantly positively or curvilinearly correlated to at least one metric of meso-scale rugosity, but the metric generating the strongest correlation varied. The abundance of small fishes, and consequently most of the assemblage statistics (e.g., total fish abundance and diversity) were best predicted by the number of tall (>50 cm) corals. The abundance of damselfishes, parrotfish biomass, the abundances of medium-sized and large fishes, and total fish biomass were curvilinearly related to mean coral height. The abundances of wrasses and surgeonfishes were most strongly correlated with the number of corals within a plot. Because coral-generated meso-scale rugosity is an important factor influencing intra-habitat variation in fishes, it should be explicitly considered when investigating fish-habitat relationships and predicting the impacts of coral mortality on ecosystem processes and services.