Dictyosphaeria Cavernosa Research Articles

A pyruvylated and sulfated galactan from the green alga Dictyosphaeria cavernosa: Structure, anticoagulant property and inhibitory effect on zebrafish thrombosis

A pyruvylated and sulfated galactan from the green alga Dictyosphaeria cavernosa, designated PSG, was obtained by dilute alkali extraction, ion-exchange and gel filtration chromatography. The backbone of PSG was composed of 3-linked β-d-Galp units with partial sulfation on C-4 and C-6. Pyruvate ketals were linked to O-3 and O-4 of nonreducing terminal β-d-Galp, as well as O-4 and O-6 of 3-linked β-d-Galp. The branches consisting of 6-linked β-d-Galp(4SO4) and β-d-Galp(3,4-Pyr)-(1→ units were located at C-6 of 3-linked β-d-Galp unit. PSG possessed obvious anticoagulant effect in vitro as assessed by the tests of activated partial thromboplastin time and thrombin time. The assay of anticoagulant mechanism showed that PSG promoted thrombin inactivation mediated by heparin cofactor-II and antithrombin-III (ATIII), and could effectively potentiate factor Xa inactivation by ATIII. The antithrombotic activity of PSG in vivo was assessed by phenylhydrazine (PHZ)-induced zebrafish thrombotic model. The results indicated that PSG obviously reduced peripheral erythrocytes aggregation, enhanced cardiac blood flow and improved peripheral platelet circulation, and PSG possessed a marked inhibitory effect on the PHZ-induced zebrafish thrombosis. Thus, PSG is a hopeful anticoagulant and antithrombotic polysaccharide.

A sulfated polysaccharide from Dictyosphaeria cavernosa: Structural characterization and effect on immunosuppressive recovery

A homogeneous sulfated polysaccharide DCS1 was obtained from Dictyosphaeria cavernosa by alkali extraction and chromatography purification. On the basis of chemical and spectroscopic analyses, DCS1 was a novel mannan-type sulfated polysaccharide and had a molecular weight of 15.48 kDa. DCS1 consisted of a main chain of (1 → 4)-α-d-Manp units with partial sulfate substitution at C-2 and branches at C-2/C-6. DCS1 possessed a potent immune-enhancing effect in vitro evaluated by the assays of lymphocytes proliferation and macrophage phagocytosis. The immunomodulatory effect of DCS1 in vivo was further investigated using immunosuppressed mice induced by cyclophosphamide (Cy). The data showed that DCS1 markedly increased the spleen and thymus indexes, and ameliorated the Cy-induced damage to spleen and thymus. Moreover, DCS1 had a significant effect on hematopoietic function recovery, and promoted the secretion of the interleukin-2 and tumor necrosis factor-α. Notably, DCS1 reversed the reduction of CD4+ T cells, improved the disorder of CD4+/CD8+ T cells and enhanced the immune response. The investigation demonstrated that the sulfated polysaccharide DCS1 with novel structure could be a hopeful immunomodulatory agent.

Variable photo-physiological performance of macroalgae and seagrasses from Saya de Malha and Nazareth Banks, Mascarene Plateau

The photosynthetic performance of macroalgae and seagrasses related to their body parts, depth and colours from the poorly-studied Saya de Malha and Nazareth Banks on the Mascarene Plateau was investigated in this study. Two seagrass (Thalassodendron ciliatum and Halophila decipiens) and seven macroalgae species (Caulerpa cupressoides, Acrosorium ciliolatum, Dictyosphaeria cavernosa, Halimeda opuntia, Ulva sp., Udotea orientalis and Udotea palmetta) were collected using the five Van Veen grabs attached to the Video-Assisted Multi-Sampler (VAMS) from 29-79 m depths in May during the FAO EAF-Nansen Research Programme 2018. The photosynthetic performance was measured using a Diving-Pulse-Amplitude-Modulated (D-PAM) fluorometer and the parameters included effective quantum yield at photosystem II (PSII) (ΦPSII), relative maximum electron transport rate (rETRm), photosynthetic efficiency (α), photoinhibition (β), saturating light level (Ek), and maximum non-photochemical quenching (NPQmax). All photo-physiological parameters varied significantly in T. ciliatum and C. cupressoides across their body parts. However, variation with seawater depths was not significant for NPQmax and β in the seagrass, and ΦPSII, rETRm and β in the macroalgae. Photo-physiological functioning of the leaf of T. ciliatum was optimal at 40 m. The photosynthetic performance of the frond and stolon of C. cupressoides decreased and remained unchanged, respectively, at 79 m when compared to that at 29 m. The whitish lobes of H. opuntia at 31 m exhibited significantly lower photosynthetic performance, in terms of ΦPSII, rETRm,α and Ek, than the greenish lobes. These findings provide a first insight of seaplant body parts-, depth- and colour-related photo-physiological performance from the Mascarene Plateau.

Recovery of coral cover in records spanning 44 yr for reefs in Kāne‘ohe Bay, Oa‘hu, Hawai‘i

Published and unpublished long-term studies are assembled to examine trends in coral cover and the dependence of change in coral cover on the initial coral cover in Kāne‘ohe Bay over the last 44 yr. Each study showed there had been periods of increase in coral cover in the bay and showed that the rate of change in cover has been inversely dependent on the initial cover at a site. When coral cover is high on upper reef slopes, the fragile structure of reefs in this sheltered bay often collapses, resulting in a decrease in coral cover. The rate of change in coral cover was also inversely dependent on cover in one of the two studies that included analysis of reef-flat corals; the cause of decrease in cover in this habitat is thought to be attributable to particularly low sea levels in Hawai‘i in the late 1990s and 2009–2010. The inverse relationship between initial coral cover and change in cover, and the intersections of the regression lines of these variables with the x-axis at intermediate values of coral cover, is indicative of resilience in this ecosystem over the last 44 yr. In the 1970s, the invasive macroscopic green alga Dictyosphaeria cavernosa covered a high percentage of coral habitat and commonly displaced corals from the reef slope and outer reef flats; the change was cited as an example of a phase shift on a reef. This alga has virtually disappeared from the bay, thus increasing the space available to corals; its disappearance is coincident with the increase in coral cover. Other species of macroalgae, including alien species, have not replaced D. cavernosa as major space competitors. The increase in coral cover and virtual disappearance of D. cavernosa constitute an example of a phase-shift reversal.

Zonation patterns, composition and diversity of macroalgal communities in the eastern coasts of Qeshm Island, Persian Gulf, Iran

This study investigates the spatial and temporal variation of intertidal macroalgae along the eastern coasts of Qeshm Island, Persian Gulf, Iran. Monthly sampling of abundance, biomass, richness and diversity of macroalgae at three intertidal levels was carried out at two different sites during 1 year. The samples were collected every month using quadrats (0.5 × 0.5 m) from October 2012 to September 2013. The species dry weight was applied to examine changes in biomass and assemblage composition of intertidal macroalgae using univariate and multivariate analyses. A total of 42 seaweed species (10 Chlorophyta, 9 Phaeophyceae, and 23 Rhodophyta) were identified. The results confirmed a temporal pattern in the growth of the algal species which also showed a biomass zonation pattern from upper to lower intertidal. The annual mean biomass of macroalgae was highest in winter (29.3 ± 9.8 g dry wt m−2) and the lowest in autumn (17.3 ± 13.5 g dry wt m−2). The annual dominant species by biomass was Padina sp. followed by Padina australis. The most common species in the area, during the sampling period include Ulva intestinalis, Ulva lactuca, Palisada perforata and Padina sp. According to the similarity percentages analysis (SIMPER), the species Ulva intestinalis, Dictyosphaeria cavernosa (Chlorophyta), Padina australis (Phaeophyceae), Champia spp., Centroceras clavulatum and Palisada perforata (Rhodophyta) were responsible for the most dissimilarity of species composition between four seasons during the sampling period. BIOENV analysis indicated that the main environmental factors structuring macroalgal community at the study area were TDS and pH. The simple macroalgae community on the eastern coast of Qeshm Island and absence of slow-growing perennial macroalgae, such as members of the Sargassaceae, known from the lower shore at other intertidal localities along the island’s coast might relate to the predominantly unsuitable sandy-stony substrates unsuitable for their colonization and the unfavourable impact upon them of urbanization.

Long-Term Record of Nutrient Concentrations in Kāne‘ohe Bay, O‘ahu, Hawai‘i, and Its Relevance to Onset and End of a Phase Shift Involving an Indigenous Alga, Dictyosphaeria cavernosa

This study assembles and analyzes published and unpublished data on inorganic nutrient concentrations in the waters of Kāne‘ohe Bay, O‘ahu, Hawai‘i, over the past 48 yr, but particularly over the 34-yr period since elimination of the major point-source of input of nutrients in 1977. As reported in a previous study, in the 1.5-yr period immediately following termination of the point-source input of nutrients (1978–1979), concentrations of PO42−, NO3−+NO2−, and NH4− in the water column declined in all three basins of the bay, followed by improvement in the state of the benthos and planktonic communities. Since 1979, nutrient concentrations have remained low (PO42− Dictyosphaeria cavernosa in the 1960s. Decline in nutrient concentrations beginning in 1977 may ultimately have contributed to the drastic decline in this alga that occurred in 2006. A protracted rainfall that occurred in spring 2006 produced elevated average nutrient concentrations for the year, but nutrient concentrations fell back to pre-2006 concentrations within 1 to 2 months. The record also contains evidence of a decrease of nutrient concentrations in the bay in response to a 4-yr period (1998–2001) of lower than normal rainfall. The response to elimination of the point-source input of nutrients and the responses to a season of exceptional rainfall and years of drought indicate that conditions in the bay’s water column are dependent on both natural events in the bay’s watershed and human activity. Kāne‘ohe Bay is one of a number of marine and aquatic systems whose degradation has been reversed by terminating nutrient addition caused by sewage disposal.

Prophylactic antioxidants and phenolics of seagrass and seaweed species: A seasonal variation study in a Southern Indian Ocean Island, Mauritius

The seasonal variations in the polyphenolic contents and potential antioxidant activities of seven seaweed species ( Padina gymnospora, Gracilaria salicornia, Palisada papillosa, Galaxaura rugosa, Enteromorpha intestinalis, Codium arabicum and Dictyosphaeria cavernosa ) and five seagrass species ( Syringodium isoetifolium, Halodule uninervis, Thalassodendron ciliatum, Halophila ovalis and Halophila stipulacea ) were assessed. In summer, the highest total phenolic content was recorded in the seaweed P. gymnospora and the lowest in G. rugosa . The total phenolic contents in the seagrass species were significantly higher than those observed in the seaweed species during both seasons. The highest flavonoid concentrations (FC) were observed in the seaweed species E. intestinalis in winter and in the seaweed P. gymnospora in summer. All tested species had higher FC in winter. The highest antioxidant activity (assessed using the Ferric ion reducing antioxidant power) was in the seaweed P. gymnospora during summer (FRAP: 9.7 ± 0.3 X10¯³ Fe²+mM/g DW). However, the seaweed P. gymnospora extract and the extracts from all 5 seagrass species had significantly different (p<0.01) antioxidant activities (assessed using the Trolox equivalent antioxidant capacity assay) in winter compared to the summer season. The collective data are indicative of the potential of Mauritian seaweeds and seagrasses as possible sources of secondary metabolites for pharmaceuticals. Further analysis using bio-efficacy models are warranted to justify the phytoceutical capacity of the seaweeds and seagrasses. Keywords : Antioxidant; Total Phenols; Total Flavonoids; FRAP; TEAC; Seagrass; Seaweed; Seasonal variation; Mauritius

Flora da Bahia: Siphonocladaceae

A survey of Siphonocladaceae from Bahia State, Brazil, is presented as a contribution to the knowledge of the chlorophytes from its littoral. Four genera and five species are recognized: Chamaedoris peniculum, Dictyosphaeria cavernosa, D. versluysii, Ernodesmis verticillata and Siphonocladus tropicus. A key for species identification, descriptions, illustrations, comments and maps of distribution in the State are presented.

Potential reversal of a phase shift: the rapid decrease in the cover of the invasive green macroalga Dictyosphaeria cavernosa Forsskål on coral reefs in Kāne‘ohe Bay, Oahu, Hawai‘i

The native green macroalga Dictyosphaeria cavernosa dominated most of the reef slope habitat in Kāne‘ohe Bay, Hawai‘i for 40 years prior to 2006 and had displaced corals from the habitats they created. This has been one of the most oft-cited examples of a phase shift occurring on a coral reef. After decades of relatively constant, high abundance of the alga, percent cover declined dramatically throughout the bay between February and June 2006. The sudden decrease in cover of this alga appears to be the result of an unusually protracted cloudy, rainy period in March 2006, which may have reduced irradiance and caused the alga to lose weight. Corals and red macroalgae living at the same depths and in some of the same habitats were apparently not affected by this 42-day period of rain and overcast skies. Competition between corals and D. cavernosa for space on reef slopes has been virtually eliminated by the death of this alga, but the unstable rubble formations, which remain in much of the area formerly covered by D. cavernosa may not be conducive to rapid increase in cover by the remaining corals or to establishment by coral recruits. Two years later, there was still no recovery of D. cavernosa. This represents a rare example of decline in macroalgal dominance on a reef and a partial reversal, possibly only temporary, of a phase shift.

Introduction to Special Hawai'i Coral Reef Initiative Research Program Volume

Introduction to Special Hawai'i Coral Reef Initiative Research Program Volume Michael Hamnett, Kristine Davidson, William Devick, Lucius Eldredge, Kevin Foster, Jo-Ann Leong, Robert Nishimoto, Francis Oishi, and Celia Smith In 1998, the Hawai'i Coral Reef Initiative Research Program (HCRI-RP) was established to support scientific research and monitoring to enhance the state's capacity to manage its coral reef resources. HCRI-RP is jointly managed by Hawai'i's Department of Land and Natural Resources/Division of Aquatic Resources (DAR) and the University of Hawai'i (UH) through a Management Committee. Currently, the Committee has three representatives from DAR, one from the U.S. Fish and Wildlife Service, two from UH, and one from the Pacific Science Association/Bishop Museum. The papers in this special issue are based on research and monitoring projects supported by HCRI-RP during its first 4 yr (1998-2002). These projects were selected by the Management Committee to provide information to resource managers and contribute to our understanding of coastal processes and threats to the health of coral reef ecosystems. HCRI-RP supported the establishment of a standardized annual coral monitoring protocol allowing for comparison among sites from 1998 to 2002. Commonly known as the Coral Reef Assessment and Monitoring Project (CRAMP), the project's goal was to identify both natural and human factors contributing to the stability, decline, or recovery of Hawai'i's corals. In this volume, Brown et al. describe the development of CRAMP's methodology designed to detect an absolute change of 10% in benthic cover with high statistical power. Using this methodology, Jokiel et al. report on the project's findings, particularly the importance of wave energy, island age, rugosity, and sediment on coral reef community structure. Harvesting for the aquarium trade is one source of fishing pressure in Hawai'i. HCRI-RP sponsored what has come to be known as the West Hawai'i Aquarium Project from 1998 to 2003 to determine the status of aquarium fish populations along the Kona coast of the island of Hawai'i and to assess the effectiveness of nine fish replenishment areas established by the state. Tissot et al. report that there is a significant increase of aquarium fishes in reserves, most likely due to the high recruitment of fish observed in 2001-2002. In 1998-1999, HCRI-RP sponsored a multifaceted project designed to examine the fine-scale processes affecting health and stability of Hawaiian reefs. Part of that project was to determine the feasibility of transplanting herbivorous fishes as a means to control the invasive alga Dictyosphaeria cavernosa. Conklin and Stimson found that fishes did not remain on the reefs to which they were added, despite the addition of large numbers of fishes. The authors speculate that this was due to habitat degradation and the resulting lack of shelter. The remote and vast nature of the northwestern Hawaiian Islands (NWHI) poses unique challenges to researchers and managers. Given the changing federal and state roles within the region, HCRI-RP cosponsored the first Northwestern Hawaiian Islands Reef Assessment and Monitoring Program (NOW-RAMP) and subsequent data analysis in 2000-2002. Preskitt et al. describe a macroscale rapid ecological assessment technique for algal assemblages as a necessary component for monitoring across the region's benthic communities. Maragos et al. report results from rapid coral assessments in the NWHI. Cesar and van Beukering discuss the economic value of Hawai'i's reefs, based on a project funded by HCRI-RP during 2001-2002. Hawai'i's coastal reefs generate an estimated $800 million each year in gross revenues (or, $364 million in added value) for the state's economy. Over 50 yr, reefs surrounding the main Hawaiian Islands will have contributed over $18 billion in added value to the local economy. [End Page 143] As a result of hardening, streams in Hawai'i deliver sediment and nutrients to the nearshore environment in an altered way. Therefore, in 2001-2002, HCRI-RP sponsored Laws and Roth to look at the impact of stream channelization and how to mitigate this degradation. Their results demonstrate that hardened streams have greater downstream delivery of nitrate than nonmodified streams. This is effectively a fast-release fertilizer...

LIGHT AND ELECTRON MICROSCOPIC OBSERVATIONS OF PREFERENTIAL DESTRUCTION OF CHLOROPLAST AND MITOCHONDRIAL DNA AT EARLY MALE GAMETOGENESIS OF THE ANISOGAMOUS GREEN ALGADERBESIA TENUISSIMA(CHLOROPHYTA)1

Gametogenesis in male and female gametophytes was studied by light microscopy and EM in the dioecious multinucleate green algaDerbesia tenuissima(Moris &amp; De Notaris) P. Crouan &amp; H. Crouan, where male and female gametes differ in size. Gametogenesis was divided into five stages: 32 h (stage 1), 24 h (stage 2), 16 h (stage 3), 8 h (stage 4), and 0.5 h (stage 5) before gamete release. At stage 1, the first sign of gametogenesis observed was the aggregation of gametophyte protoplasm to form putative gametangia. At stage 2, gametangia were separated from the vegetative protoplasm of gametophytes. Morphological changes of nuclei and organelles occurred at this early stage of male gametogenesis, and organelle DNA degenerated. At stage 3, male organelle DNA had completely degenerated, whereas in female gametangia, organelle DNA continued to exist in both chloroplasts and mitochondria. Gametogenesis was almost completed at stage 4 and fully at stage 5. Small male gametes had a DNA‐containing nucleus and a large mitochondrion and one or several degenerated chloroplasts. The mitochondria and plastids were devoid of DNA. The large female gametes had a nucleus and multiple organelles, all of which contained their own DNA. Thus, degeneration of chloroplast DNA along with morphological changes of organelles occurred at male gametogenesis in anisogamous green algae (BryopsisandD. tenuissima), in contrast with previous studies in isogamous green algae (Chlamydomonas,Acetabularia caliculus, andDictyosphaeria cavernosa) in which degeneration of chloroplast DNA occurred after zygote formation.

MARINE ALGAE ASSOCIATED WITH CARIBBEAN ROCKY SHORES, QUINTANA ROO, MEXICO

Albert, E. M. &amp; Lehman, R. L.Center for Coastal Studies, Texas A&amp;M University‐Corpus Christi, Corpus Christi, TX 78412 USARocky shores located on the east coast of the Yucatan Peninsula are typically high‐energy habitats associated with fringing or barrier reef systems. They are phytokarstic (iron‐shore) consisting of fossiliferous limestone that is composed of stony coral skeletons. This study compares the macroalgae from three rocky shores located on the east coast of the Yucatan Peninsula, Quintana Roo, Mexico. Fifteen 0.25m2 quadrates were randomly placed in the intertidal and subtidal zones and evaluated for dominant algal cover. In addition, fifteen 0.25 m2 quadrates of standing stock material was randomly collected and used to characterize algal composition, species richness, abundance, and biomass. A voucher collection including herbarium mounts and preserved specimens were prepared for all species encountered. Thirty‐five species were identified representing three divisions: Rhodophyta, Chlorophyta, and Phaeophyta. Rhodophyta had the highest species richness with a total of fifteen taxa identified. Phaeophyta had the lowest species richness with seven taxa but dominated algal coverage at two of the three sites. Chlorophyta was represented by thirteen species. Species common to all points were represented by Digenia simplex, Laurencia poiteaui, Laurencia sp., Polysiphonia sp., Microdictyon marinum, Halimeda opuntia, Dictyosphaeria cavernosa, Padina sanctae‐crucis, and Turbinaria tricostata.

Effects of herbivory, nutrient levels, and introduced algae on the distribution and abundance of the invasive macroalga Dictyosphaeria cavernosa in Kaneohe Bay, Hawaii

Since the 1960s, and possibly earlier, the macroalga Dictyosphaeria cavernosa has overgrown and displaced corals on reef slopes and outer reef flats in Kaneohe Bay, Oahu. This shift in reef community composition is generally attributed to nutrient enrichment resulting from sewage discharge. Following the diversion of most of the sewage effluent in 1977–1978, it was expected that D. cavernosa growth would become nutrient-limited and its abundance would consequently decline, but the alga remains abundant in much of the bay. One explanation for its persistence is that nutrients are once again high enough to support the alga's growth. An alternative explanation is that there has been a reduction in grazing intensity in the bay. In this study we resurveyed the distribution and abundance of D. cavernosa at 120 reef slope sites originally surveyed in 1969. We conducted additional surveys to estimate the biomass of herbivores and the areal coverage of D. cavernosa and other macroalgae on reef slopes and flats. Field experiments were used to determine spatial and temporal patterns of grazing intensity on and growth rates of D. cavernosa and the introduced macroalga Acanthophora spicifera. Laboratory experiments were used to examine preferences among herbivores for some of the most abundant macroalgae on Kaneohe Bay reefs. Twenty years after sewage diversion, D. cavernosa cover on reef slopes has decreased substantially in southern Kaneohe Bay, the site of most of the historical sewage discharge. D. cavernosa cover has changed less in other regions, remaining high in the central bay and low in the north bay. D. cavernosa thalli protected by grazer exclusion cages sustained positive growth rates on reef slopes and flats throughout the bay. Reduced nutrient concentrations may have caused a reduction in D. cavernosa growth rates, and a consequent reduction in D. cavernosa abundance in the south bay shortly after sewage diversion. Measurements of grazing intensity and surveys of herbivorous fish abundance suggest that the continued abundance of D. cavernosa is the result of a reduction in grazing intensity. Reduced grazing intensity on D. cavernosa may in turn be the result of a historical reduction in herbivore biomass or the establishment of several introduced macroalgae on reef flats. The introduced species are preferred by herbivorous fishes over D. cavernosa, as indicated by preference tests. The hypothesis that reduced grazing pressure on D. cavernosa is related to the establishment of introduced species is supported by the observation that D. cavernosa cover is highest on reef slopes where the cover of preferred introduced macroalgae on the adjacent outer reef flat is also high. Conversely, D. cavernosa cover is low or zero on reef slopes where the cover of introduced macroalgae on the adjacent reef flat is low or zero

Nitrogen efflux from the sediments of a subtropical bay and the potential contribution to macroalgal nutrient requirements.

The concentration of dissolved inorganic nitrogen (DIN) in the porewaters of shallow-water tropical marine sediments can be as high as 50-100 µM, at sediment depths of shallow as 20 cm. These concentrations are at least two-orders of magnitude greater than the DIN concentration in the overlying water. High porewater concentrations, and the resulting concentration gradient, result in substantial efflux of DIN from the sediments to the water column. This sediment-derived DIN may be an important nutrient source for benthic algae. In Kaneohe Bay, Hawaii, a mean ammonium efflux rate of 490 µmolm(-2)day(-1) and a mean nitrate+nitrite efflux rate of 123 µmolm(-2)day(-1) were measured on reef slopes in the habitat occupied by benthic algae. It has been demonstrated that this nutrient source is essential for the growth of at least one abundant alga, Dictyosphaeria cavernosa, and possibly others. The DIN concentrations in Kaneohe Bay sediment porewaters, and the rates of DIN efflux from those sediments, are greater than porewater concentrations and efflux rates reported for other, more pristine tropical sites. The rate of sedimentation of particulate nitrogen is similar to rates reported from other tropical lagoons, and about twice as high as the efflux rate of total dissolved nitrogen. Given the present low nutrient concentrations in the water column of the Bay, these results support the view that nutrient efflux from the benthos is in part responsible for the persistence of D. cavernosa on these reefs. It is possible that efflux of DIN from sediments may be responsible for sustained benthic algal productivity in similar habitats on other tropical reefs.

Spectral discrimination of coral reef benthic communities

Effective identification and mapping of coral reef benthic communities using high-spatial and -spectral resolution digital imaging spectrometry requires that the different communities are distinguishable by their spectral reflectance characteristics. In Kaneohe Bay, Oahu, Hawaii, USA, we collected in situ a total of 247 spectral reflectances of three coral species (Montipora capitata, Porites compressa, Porites lobata), five algal species (Dictyosphaeria cavernosa, Gracilaria salicornia, Halimeda sp., Porolithon sp., Sargassum echinocarpum) and three sand benthic communities (fine-grained carbonate sand, sand mixed with coral rubble, coral rubble). Major reflectance features were identified by peaks in fourth derivative reflectance spectra of coral (at 573, 604, 652, 675 nm), algae (at 556, 601, 649 nm) and sand (at 416, 448, 585, 652, 696 nm). Stepwise wavelength selection and linear discriminant function analysis revealed that spectral separation of the communities is possible with as few as four non-contiguous wavebands. These linear discriminant functions were applied to an airborne hyperspectral image of a patch reef in Kaneohe Bay. The results demonstrate the ability of spectral reflectance characteristics, determined in situ, to discriminate the three basic benthic community types: coral, algae and sand.

Temperature responses of macroalgae from the tropical island Hainan (P.R. China)

SUMMARYThe temperature tolerances of 24 tropical macroalgae collected on Hainan Island (P.R. China) were investigated. For some isolates, growth response curves were also determined. The upper survival temperatures (USTs, 32–37°C) of these tropical west Pacific strains are similiar to those of tropical Atlantic species. With regard to their lower survival temperatures (LSTs) the species investigated show high variations: 12 species have LSTs between 16 and 7°C (Hypnea musciformis (Wulfen) Lamx. var esperi J, Ag., Centroceras clavulatum (C. Ag) Mont., Falkenbergia hillebrandii (Bornet) Falkenberg, Gelidiopsis intricata (Ag.) Vickers, Halymenia maculata J. Ag., Hypnea cenomyce J. Ag., Hypnea spinella (C. Ag.) Kütz., Gracilaria changii (Xia et Abott) Abott, Chang et Xia, Dictyopteris repens (Okam.) Boerg., Laurencia cartilaginea Yamada, Gelidium pusillum (Stackh.) Le Jol., Laurencia sp.). Their LSTs and temperature requirements for growth (range: 15–30 °C, optimum: 25–30 °C) are mostly similar to those of tropical west Atlantic and amphi‐Atlantic (sub)tropical macroalgae as well as to tropical isolates of species with an Atlantic tropical to warm‐temperate distribution. The remaining 12 species have LSTs between 6 and 1 °C (Ulva conglobata Kjellm., Ulva fasciata Delile, Padina boryana Thivy, Dictyosphaeria cavernosa (Forssk.) Boerg., Boodlea composita (Harv.) Brand, Boergesenia forbesii (Harv.) Feldm., Cladophora vagabunda (L.) van den Hoek, Enteromorpha compressa (L,) Grev., Enteromorpha intestinalis (L.) Link, Gracilaria tenuistipitata Chang et Xia, var liui Chang et Xia, Monostroma nitidum Wittr. and Valonia aegagropila C. Ag.). Their LSTs are mostly similar to those of Atlantic macroalgae with a tropical to (warm‐) temperate distribution. The results are discussed with respect to the factors which may have triggered the development of the temperature requirements of the various species.

Fatty acid composition of twelve algae from the coastal zones of Qatar.

Fatty acid compositions of twelve algal species from two different classes were determined. Three Chlorophyta species (Acetabularia calyculus, Cladophora sericoides and Dictyosphaeria cavernosa) and nine Phaeophyta species (Colpomenia sinuosa, Cystoseria trinodis, Dictyota cervicornis, Hormophysa triquetra, Padina gymnospora, Sargassum binderi, S. boveanum, S. denticulatum and S. heteromorpha) were investigated. Thirty-four fatty acids were identified. Myristic, palmitic, oleic, linoleic, eicosodienic and lignoceric acids were predominant in all examined algal species. Branched saturated fatty acids were also found in all investigated species except Cladophora sericoides.

Effects of water velocity on NH4 and PO4 uptake and nutrient-limited growth in the macroalga Dictyosphaeria cavernosa

Effects of water velocity on NH4 and PO4 uptake and nutrient-limited growth in the macroalga Dictyosphaeria cavernosa

Seasonal growth of the coral reef macroalga Dictyosphaeria cavernosa (Forskål) Børgesen and the effects of nutrient availability, temperature and herbivory on growth rate

The green alga Dictyosphaeria cavernosa (Forskål) Børgesen competes with corals for space on the slopes of patch and fringing reefs in Kane'ohe Bay, O'ahu, Hawai'i. Macroscopic algae rarely occur on pristine coral reef slopes, but are increasingly common at sites of anthropogenic nutrient input and overfishing. A field study of D. cavernosa growth rates indicated that, in the absence of grazing, an annual cycle occurs with maximum growth rates in fall and minimum growth rates in spring. This pattern corresponded more closely to annual changes in water temperature than to annual changes in irradiance or water column nutrient concentrations, yet laboratory experiments showed that growth rates do not vary with temperature within the annual range for Kane'ohe Bay reef habitats. Enrichment experiments conducted in outdoor laboratory tanks supplied with running seawater indicated that D. cavernosa growth is nitrogen-limited at nutrient levels measured in Kane'ohe Bay. Inorganic nitrogen and phosphorus levels are significantly higher in enclosed spaces or chambers created by the growth of D. cavernosa thalli than in the adjacent water column. It is hypothesized that nutrient regeneration from sediments beneath thalli, and/or excretion by animals inhabiting these chambers contribute to the elevated nutrient levels. Nutrient regeneration rates appear to be temperature dependent, and seasonal changes in nutrient availability beneath thalli may explain the annual growth pattern observed in D. cavernosa.

Nitrogen-limited growth in the coral reef chlorophyte Dictyosphaeria cavernosa, and the effect of exposure to sediment-derived nitrogen on growth

Nitrogen-limited growth in the coral reef chlorophyte Dictyosphaeria cavernosa, and the effect of exposure to sediment-derived nitrogen on growth