Dinitrogen-Fixing Cyanobacteria in Microbial Mats of Two Shallow Coral Reef Ecosystems

Dinitrogen-fixing organisms in cyanobacterial mats were studied in two shallow coral reef ecosystems: La Reunion Island, southwestern Indian Ocean, Sesoko (Okinawa) Island, and northwestern Pacific Ocean. Rapidly expanding benthic miniblooms, frequently dominated by a single cyanobacterial taxon, were identified by microscopy and molecular tools. In addition, nitrogenase activity by these blooms was measured in situ. Dinitrogen fixation and its contribution to mat primary production were calculated using 15N2 and 13C methods. Dinitrogen-fixing cyanobacteria from mats in La Reunion and Sesoko showed few differences in taxonomic composition. Anabaena sp. among heterocystous and Hydrocoleum majus and Symploca hydnoides among nonheterocystous cyanobacteria occurred in microbial mats of both sites. Oscillatoria bonnemaisonii and Leptolyngbya spp. occurred only in La Reunion, whereas Hydrocoleum coccineum dominated in Sesoko. Other mats dominated by Hydrocoleum lyngbyaceum, Phormidium laysanense, and Trichocoleus tenerrimus occurred at lower frequencies. The 24-h nitrogenase activity, as measured by acetylene reduction, varied between 11 and 324 nmoles C2H2 reduced µg−1 Chl a. The highest values were achieved by heterocystous Anabaena sp. performed mostly during the day. Highest values for nonheterocystous cyanobacteria were achieved by H. coccineum mostly during the night. Daily nitrogen fixation varied from nine (Leptolyngbya) to 238 nmoles N2µg−1 Chl day−1 (H. coccineum). Primary production rates ranged from 1,321 (S. hydnoides) to 9,933 nmoles C µg−1 Chl day−1 (H. coccineum). Dinitrogen fixation satisfied between 5% and 21% of the nitrogen required for primary production.Ocean Development Sub-Committee of France–Japan S&T Cooperation; Mitsubishi cooperation; The Ministry of Education, Science, Sport, and Culture of Japan; Hanse Wissenschaftskolleg; Delmenhorst and Alexander-von-Humboldt Foundation; Bad Godesberg; Germany supported collaborative research on cyanobacterial diversit

LATITUDINAL VARIATION OF THE NUMBER OF MUSCLE FIBRES IN SALPA THOMPSONI (TUNICATA, THALIACEA) IN THE SOUTHERN OCEAN : IMPLICATIONS FOR THE VALIDITY OF THE SPECIES SALPA GERLACHEI (Ninth Symposium on Polar Biology)

The latitudinal variation is of common occurrence in epiplanktonic species with a wide north-south distribution. In Salpidae this phenomenon has been observed in the number of fibres of the body muscles, which is uniform in all tropical-temperate water species. Nevertheless, up to now it has not been observed in species restricted to the Southern Ocean. In this paper we discuss the existence of latitudinal variation in Salpa thompsoni, which is widely distributed and the most abundant salp species in the Southern Ocean. The number of muscle fibres of both aggregate and solitary forms of S. thompsoni showed a maximum at about 56°S and decreased gradually towards the higher latitudes. Body length varied latitudinally the same as the fibre numbers did. In the high latitudes of the Pacific Sector of the Southern Ocean, S. thompsoni is replaced by a sibling species, Salpa gerlachei. These two species differ only biometrically in fibre numbers per muscle band, being less in S. gerlachei. However, a broad overlap in the range of muscle fibre numbers was found between the two species. The present results suggest that these two species are synonymous and S. thompsoni is distributed with a clinal variation from the north to the south

Distribución y ecología de Tunicados pelágicos, (Familia Salpidae), especialmente en el Océano Austral

Fil: Casareto, Beatriz Estela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Salps of the Southern Ocean (Australian Sector) during the 1983-84 summer, with special reference to the species Salpa thompsoni, FOXTON 1961

Studies on salps were carried out on the plankton samples collected by R. V. HAKUHO MARU during the KH-83-4 cruise in the Southern Ocean (Australian Sector) as part of the BIOMASS SIBEX I programme. The geographical distribution of salps showed that widely distributed cosmopolitan species such as Salpa fusiformis, Salpa aspera, Thalia democratica and Pegea confoederata reached their southern limit at the Subtropical Convergence. This boundary represents the northern limit for Salpa thompsoni, the most abundant salp of the Southern Ocean. Ihlea racovitzai was limited to the high latitude Antarctic water. Analysis of stratified samplings performed day and night revealed a pattern of diel vertical migration for Salpa thompsoni, Salpa fusiformis and Ihlea magalhanica. Ihlea racovitzai did not show a clear vertical movement between the day time and the night time. The vertical distribution of Ihlea magalhanica and Ihlea racovitzai appeared to extend deeper than the range determined previously. A pattern of vertical stratification in the size composition and stages of maturity for both aggregate and solitary forms of Salpa thompsoni was observed. Moreover, a comparison of the population at different latitudes revealed different compositions

Chemical and biological characteristics of Albion reef in the South-West of Mauritius Island with special reference to primary production and N2 fixation of benthic substrata

The role of heterotrophic bacteria, pico-cyanobacteria and benthic cyanobacterial mats was assessed in the cycling of organic carbon and nitrogen in the Albion lagoon, Mauritius. Surveys and sampling for biological and chemical parameters were undertaken at three locations along one northern (T1) and one southern (T2) transect perpen- dicular to the shore. Low levels of nutrients showing a typical oligotrophic condition promoted by a rapid water exchange with oceanic waters characterized this lagoon. A general trend in zonation was observed from the shore with seagrass beds followed by sand and rubble, with cyanobacteria forming mats. Coral cover increased towards the reef crest with dominating Porites spp. and Acropora spp. colonies, however coral cover was not higher than 20%. Heavy grazing of pico-plankton was detected in the middle of the lagoon between T1 and T2. In situ incubations on di erent substrata (coral rubble, cyanobacterial mats and surrounding seawater) revealed maximum primary pro- duction and nitrogen xation rates of cyanobacterial mats, with respectively 1-2 and up to 2 orders of magnitude higher levels found than other substrata. This study showed that cyanobacteria mats and coral rubble substrata con- stituted an important source of new nitrogen for the whole lagoon

Marine planktonic ecosystem dynamics in an artificial upwelling area of Japan : Phytoplankton production and biomass fate

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Development of Artificial Reefs Using Environmentally Safe Ceramic Material

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