Length-weight relationship of coral reef-associated fishes from Gulf of Mannar and Palk Bay,Southeast Coast of India

Length-weight relationship parameter was estimated for eight coral reef-associated finfish species from the Gulf of Mannar and Palk Bay, Eastern Indian Ocean. Fish samples were collected from the landings of trawlers with a cod-end mesh size of 25–35 mm, operated at a depth ranging from 50–70 m off Tuticorin, Rameswaram and Thondi coasts on monthly basis between June-2018 and July-2019. Fish specimens were sampled by measuring total length (TL) and total weight (TW) with precision to 0.1 cm and 0.1 g respectively. A new maximum total length was recorded for Canthigaster solandri, Centriscus scutatus and Halichoeres stigmaticus from this study.     

Characterization of archaeal symbionts of sponges from the coral reef ecosystems of the Gulf of Mannar,Southeast coast of India

Sponges accommodate a diverse group of microorganisms with varied metabolic capabilities. The bacterial associates of sponges are widely studied while our understanding of archaeal counterparts is scanty. In the present study, we report the archaeal associates of two sponges, Pseudoceratina purpurea (NCBI barcode: KX454492) and Cinachyra sp. (NCBI barcode: KX454495), found in the coral reef ecosystems of Gulf of Mannar, India. Archaea in the water column was predominated by members of class Halobacteria of Phylum Euryarchaeota (97%) followed by a minor fraction (3%) of Nitrosopumilus sp. of phylum Thaumarchaeota. Interestingly, Thaumarchaeota was identified as the sole archaeal population associated with the two sponges studied, among which Nitrosopumilus sp. occuppied 80 and 100% of the sequences in the clone library of P. purpurea and Cinachyra sp. respectively. Other archaea found in the P. purpurea were Nitrososphaera (10%) and unclassified ones (10%). The study identified Nitrosopumilus sp. as a unique symbiotic archaeon of sponges, P. purpurea and Cinachyra sp. The existence of host driven factors in selecting specific associates from a diverse group of archaea in the environment may need further investigations.     

Tiger cowrie Cypraea tigris feeds on coral-competing sponge Rhabdastrella globostellata in an Acropora dominated reef of Gulf of Mannar,India

Gulf of Mannar (GoM) in the southeast coast of India is known for its coral reefs and reef-associated biodiversity. Corals in GoM were affected to a significant extent by climate change-driven coral bleaching in 2016, and are currently recovering. After the bleaching mortality that corals suffered, the competition for space between corals and sponges is obvious in GoM. Rhabdastrella globostellata is a common marine sponge found overgrowing live coral colonies of the patch reefs in GoM at Pattinamaruthoor in March 2019. Underwater assessment of the reef revealed that 60.06% live coral cover was dominated by Acropora corals (81.91%). Among the acroporans 8.23% of colonies were found overgrown by R. globostellata. During the night dives the tiger cowrie Cypraea tigris was observed to feed on R. globostellata. From this observation the present study infers that C. tigris helps the corals fight these sponges, and concludes that tiger cowries should be protected and promoted to tackle climate change implications.     

Environmental factors influencing urchin spatial distributions on disturbed coral reefs (New Caledonia, South Pacific)

Few works have examined the relative contributions of habitat variables to the distribution of coral reef urchins. In the present study, the spatial distribution of two common urchin species (Diadema setosum and Echinometra mathaei) was studied in the fringing reefs of two urban bays in New Caledonia (South Pacific). Urchins were surveyed at 105 stations with contrasted habitat structure/anthropic disturbance levels; 32 environmental variables (water/sediment characteristics, reef structuring species) were considered. Moderate densities were generally observed at station scale (mean 0.5 individuals m^− 2). The combination of univariate and multivariate techniques highlighted patchy distributions for Diadema as well as Echinometra, with distinct species/habitat associations; environmental gradients occurring within the bays did not seem to influence the species patterns. For Diadema, the spatial variability was better explained by sediment type than by biotic cover; increasing densities occurred across habitats with larger sediment sizes and decreasing coral complexity/macrophytes cover. In contrast, the distribution of E. mathaei exhibited weak relationships with habitat variables. In coral reefs, small-scale heterogeneity may thus be responsible for most of urchins spatial variability.     

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.     

Percent recent mortality (PRM) of stony corals as an ecological indicator of coral reef condition

The reef communities of the Florida coral reef tract play a major role in supporting the regional economy but are threatened by increased exploitation and environmental factors. Coral reef ecosystem services are vital to the economy of SE Florida where revenue and jobs depend on the status of reef resources. Here, we used an extensive, reef monitoring database collected by the Florida Reef Resilience (FRRP, 2003–2011) and the Atlantic and Gulf Rapid Reef Assessment (AGRRA, 1997–2011) programs to evaluate percent recent mortality (PRM) as a robust ecological indicator of coral colony and coral reef status. PRM, the proportion of a coral colony that has experienced recent tissue mortality so that corallite structures in the non-living parts of the coral are still intact and identifiable to species, can be attributed to disturbances taking place within days to a few months preceding the surveys.Based on data from >50,000 colonies from 11 coral species and nearly 1400 sites, we propose a benchmark level of <1% PRM and <5% prevalence of partial mortality for Florida reefs during periods of background, low-stress environmental conditions. PRM levels >1.0% and prevalence levels >5% can be used as early warning indicators of degrading conditions. Average PRM values >2% are indicative of increasingly stressful conditions as those experienced during temperature anomalies and major hurricanes. Finally, PRM values considerably >2% are reflective of significantly stressful conditions and warning signals of potential major coral mortality as evidenced by mean PRM levels of >10% recorded in Florida as a consequence of the 2010 extreme cold-water event. PRM and prevalence values from Florida reefs compared favorably with those recorded in the Caribbean and the Mesoamerican region where a benchmark of 2% for background levels of PRM under low-level, chronic stress was proposed. The status of this indicator can be easily communicated to stakeholders and will benefit managers by providing: (1) a baseline to assess the status of coral populations; and (2) early-warning indicators of unfavorable conditions that may trigger management actions such as temporary closures or the establishment of more permanent protection such as MPAs.     

Effect of Temperature on Germination in Northernmost Populations of Culcita macrocarpa and Woodwardia radicans

Abstract: Spore germination of Culcita macrocarpa C. Presl and Woodwardia radicans (L.) Sm. from nine populations at the northern limit of their distribution, in the northwest Iberian Peninsula, was investigated. In a first experiment, population type and temperature (10, 15, 20, and 25 °C) were both found to affect germination percentage and germination time significantly in both species. There were also significant interactions between the two factors with respect to the percentage germination of C. macrocarpa and the germination time of W. radicans. In C. macrocarpa there was an outstanding increase in germination time at 15 °C and, above all, at 10 °C, whereas in W. radicans the most remarkable result was the existence of two populations with especially low germination percentages. In a second experiment, germination of 20 individuals from each population of W. radicans was compared with similar inter-population differentiation. Although its variability possibly has a genetic basis, these species are able to germinate successfully, and it seems probable that the season in which it occurs depends more on spore release than on thermal conditions in the populations. The effect of temperature on germination in both species does not explain their coastal distribution. Temperature is probably more important in limiting other stages of the life cycle.     

Two new Gammaridean Amphipods (Crustacea) from the Gulf of Mannar,S. India

Summary Two new species of Gammaridean Amphipods are described from the coastal waters of south India. Affinities with related forms are discussed.Zusammenfassung Es werden zwei neue Arten von gammariden Amphipoden aus südindischen Küstengewässern beschrieben, und die Verwandschaft mit ähnlichen Formen wird diskutiert.     

The Vermetidae of the Gulf of Kachchh,western coast of India (Mollusca,Gastropoda)

Coral reefs are often termed underwater wonderlands due to the presence of an incredible biodiversity including numerous invertebrates and vertebrates. Among the dense population of benthic and bottom-dwelling inhabitants of the reef, many significant species remain hidden or neglected by researchers. One such example is the vermetids, a unique group of marine gastropods. The present study attempts for the first time to assess the density and identify preferred reef substrates in the Gulf of Kachchh, state of Gujarat, on the western coast of India. A total of three species of the family Vermetidae were recorded during the study and their substrate preferences identified.     

Coral reef resilience differs among islands within the Gulf of Mannar,southeast India,following successive coral bleaching events

Coral Reefs - We used a 12-yr data set of benthic cover (2005–2017), spanning two bleaching events, to assess changes in benthic cover and coral community composition along 21 islands within...     

Recognition of separate genera within Acropora based on new morphological, reproductive and genetic evidence from Acropora togianensis , and elevation of the subgenus Isopora Studer, 1878 to genus (Scleractinia: Astrocoeniidae; Acroporidae)

Many attempts have been made to recognise divisions within Acropora, the most diverse reef building coral genus on modern reefs, but only subgenera Acropora and Isopora are currently recognised. In this paper, morphological and genetic analyses, and study of reproductive mode and anatomy, demonstrate that an endemic Indonesian species A. (Acropora) togianensis, Wallace, 1997, belongs to Isopora. Despite the presence of a clear central axial corallite (indicating sub-genus Acropora), this species has supplementary axial corallites, broods planula larvae rather than broadcast-spawning for external fertilisation and develops stalked ova: all characters in common with the type species of subgenus Isopora A. (Isopora) palifera and the other species for which such data are available, A. (I.) cuneata and A. (I.) brueggemanni. Phylogenies are based on the protein-coding genes, mitochondrial cytochrome b (cytb) and nuclear histone 2a and 2b (h2ab) also group A. togianensis with these Isoporans. High bootstrapping and Bayesian support in the major lineages of the family Acroporidae demonstrate significant differences between Isopora (including A. togianensis) and Acropora. As the type species of both subgenera, A. (Acropora) muricata (Linneaus 1758) and A. (Isopora) palifera (Lamarck, 1816) are used in these analyses, elevation of Isopora Studer, 1878 to genus is formally proposed.     

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.     

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%).     

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.     

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.     

Accumulation of Heavy Metals in Some Marine Fisheries Resources Collected from Gulf of Mannar Marine Biosphere Reserve,Southeast Coast of India

Concentrations of toxic metals viz. mercury (Hg), cadmium (Cd) and lead (Pb) were evaluated in four species of fishes (Sardinella longiceps, Selaroides leptolepis, Epinephelus quoyanus and Lethrinus lentjan), one species of shrimp (Penaeus semisulcatus) and one species of crab (Portunus sanguinolentus) sampled from Thoothukudi, Keelakarai and Veerapandian pattinam of Gulf of Mannar, Southeast coast of India. Results revealed accumulation of these metals in the following order Hg > Cd > Pb. Hg concentration was found to be higher in Po. sanguinolentus followed by E. quoyanus, Pe. semisulcatus and L. lentjan however, the same was absent in Sa. longiceps and Se. leptolepis. Cd concentration was recorded in decreasing order in Po. sanguinolentus > Pe. semisulcatus > L. lentjen > E. quoyanus > Sa. longiceps > Se. leptolepis. Pb was detectable only in four species. Results of One-way ANOVA revealed significant variations (p < 0.05) in accumulation of Cd in Sa. longiceps, Se. leptolepis and Pe. semisulcatus and Hg in E. quoyanus, L. lentjan and Po. sanguinolentus. Variations noted in Pb were not statistically significant throughout.     

Direct measurements of carbon and carbonate export from a coral reef ecosystem (Moorea Island , French Polynesia)

The export of carbon and carbonate from coral reefs was investigated through a multidisciplinary investigation of the hydrological, geochemical, sedimentological and biological features of Tiahura reef on the northwestern coast of Moorea Island (French Polynesia). The hydrology of the fore-reef is characterised by prevailing longshore western currents and a strong thermocline. As revealed by turbidity structures (benthic and intermediate nepheloid layers) and by the amount of particles collected by near-bottom sediment traps, horizontal and downslope advections of particles dominate over offshore vertical transport. The exported material is rich in carbonate (ca. 80%) and poor in organic matter (ca. 4%). Sedimentation rates at 430 m depth, i.e. definitive export, reached 209.6 mg m^-2 d^-1 (dry weight). Estimates of carbon and carbonates export for Tiahura reef also reported here represent respectively 47% and 21% of the organic and inorganic carbon produced within the reef.     

Comparative morphometry,biochemical and elemental composition of three marine sponges (Petrosiidae) from Gulf of Mannar,India

Abstract

Three marine sponges Neopetrosia similis, Xestospongia testudinaria and Petrosia nigricans from the Gulf of Mannar, Southeast coast of India were compared based on their morphometric parameters and their biochemical and elemental composition. These sponges showed differences inspicule : protein (spongin) ratio of 5:1, 11:1 and 13:1, respectively. Xestospongia testudinaria possessed the longest oxeae, 3.05 times than P. nigricans and 1.47 times than N. similis. Spectral analysis revealed that the spicules of these sponges are mostly composed of O (>50%) and Si (29–45%), whereas Al and Ca (4–5%) were additionally detected only in the spicules of P. nigricans. In contrast, the percentage elemental composition in pinacodermal sections was significantly different as O and Si were the maximum (23–50%); followed by Cl and Al as moderate (1–17%); and Na, S, Fe and Ca in minor quantities (0.2–6%). Cluster analysis and traditional taxonomic arrangements show that X. testudinaria and N. similis have a close relationship whereas P. nigricans was hypothesized to be their sister group. The present findings could be the key for identifying sponges in situ as well as determining whether sponges could be used to assess pollution in the sea.     

Bathymetry,water optical properties,and benthic classification of coral reefs using hyperspectral remote sensing imagery

The complexity and heterogeneity of shallow coastal waters over small spatial scales provides a challenging environment for mapping and monitoring benthic habitats using remote sensing imagery. Additionally, changes in coral reef community structure are occurring on unprecedented temporal scales that require large-scale synoptic coverage and monitoring of coral reefs. A variety of sensors and analyses have been employed for monitoring coral reefs: this study applied a spectrum-matching and look-up-table methodology to the analysis of hyperspectral imagery of a shallow coral reef in the Bahamas. In unconstrained retrievals the retrieved bathymetry was on average within 5% of that measured acoustically, and 92% of pixels had retrieved depths within 25% of the acoustic depth. Retrieved absorption coefficients had less than 20% errors observed at blue wavelengths. The reef scale benthic classification derived by analysis of the imagery was consistent with the percent cover of specific coral reef habitat classes obtained by conventional line transects over the reef, and the inversions were robust as the results were similar when the benthic classification retrieval was constrained by measurements of bathymetry or water column optical properties. These results support the use of calibrated hyperspectral imagery for the rapid determination of bathymetry, water optical properties, and the classification of important habitat classes common to coral reefs.