Marine and Atmospheric Research

Hobart, Australia

Marine and Atmospheric Research

Hobart, Australia
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Jongma D.N.,Stazione Zoologica Anton Dohrn | Campo D.,Center for Environmental Education | Dattolo E.,Stazione Zoologica Anton Dohrn | D'Esposito D.,Stazione Zoologica Anton Dohrn | And 6 more authors.
Botanica Marina | Year: 2013

On the basis of morphological and molecular studies, we identified the Australian endemic green alga known as Caulerpa distichophylla along the coasts of Sicily (Italy, Mediterranean Sea). The slender Caulerpa previously reported as C. taxifolia from southeastern Turkey (Gulf of Iskenderun) also belongs to C. distichophylla. Morphologically, C. distichophylla clearly differs from C. taxifolia in its slender thallus and the lack of large rhizoidal pillars. However, genetic data do not provide undisputed evidence that the species are distinct. Sequences of the tufA cpDNA gene and of the cp 16S rDNA intron-2 sequences separated the two taxa by only one single nucleotide mutation, whereas ITS rDNA sequences did not clearly distinguish them. The new combination Caulerpa taxifolia var. distichophylla is therefore proposed. Western and eastern Mediterranean populations of C. taxifolia var. distichophylla are probably the result of introduction events from southwestern Australia. Although the vector of primary introductions remains unknown (aquarium trade or shipping), maritime traffic appears to be the most likely vector of secondary dispersal. C. taxifolia var. distichophylla is closely related to C. taxifolia, hence interbreeding with the other C. taxifolia strains in the Mediterranean Sea might be expected to occur. © 2013 by Walter de Gruyter Berlin Boston 2013.

Thompson P.A.,Marine and Atmospheric Research | Thompson P.A.,National Research Flagship | Bonham P.,Marine and Atmospheric Research | Bonham P.,National Research Flagship | And 6 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2011

The composition and dynamics of the phytoplankton communities and hydrographic factors that control them are described for eastern and western Australia with a focus on the Eastern Australian Current (EAC) and Leeuwin Current (LC) between 27.5° and 34.5°S latitude. A total of 1685 samples collected from 1996 to 2010 and analysed for pigments by high performance liquid chromatography (HPLC) showed the average TChla (monovinyl+divinyl chlorophyll a) concentration on the west coast to be 0.28±0.16γgL-1 while it was 0.58±1.4γgL-1 on the east coast. Both coasts showed significant decreases in the proportions of picoplankton and relatively more nanoplankton and microplankton with increasing latitude. On both coasts the phytoplankton biomass (by SeaWiFS) increased with the onset of winter. At higher latitudes (>27.5°S) the southeast coast developed a spring bloom (September) when the mean monthly, surface chlorophyll a (chla) concentration (by SeaWiFS) was 48% greater than on the south west coast. In this southern region (27.5-34.5°S) Synechococcus was the dominant taxon with 60% of the total biomass in the southeast (SE) and 43% in the southwest (SW). Both the SE and SW regions had similar proportions of haptophytes; ~14% of the phytoplankton community. The SW coast had relatively more pelagophytes, prasinophytes, cryptophytes, chlorophytes and less bacillariophytes and dinophytes. These differences in phytoplankton biomass and community composition reflect the differences in seasonality of the 2 major boundary currents, the influence this has on the vertical stability of the water column and the average availability of nutrients in the euphotic zone. Seasonal variation in mixed layer depth and upwelling on the west coast appears to be suppressed by the Leeuwin Current. The long-term depth averaged (0-100m) nitrate concentration on the west coast was only 14% of the average concentration on the east coast. Redfield ratios for NO3:SiO2:PO4 were 6.5:11.9:1 on the east coast and 2.2:16.2:1 on the west coast. Thus new production (nitrate based) on the west coast was likely to be substantially more limited than on the eastcoast. Short term (hourly) rates of vertical mixing were greater on the east coast. The more stable water column on the west coast produced deeper subsurface chlorophyll a maxima with a 25% greater proportion of picoeukaryotes. © 2010 Elsevier Ltd.

Thompson P.A.,Marine and Atmospheric Research | Thompson P.A.,National Research Flagship | Wild-Allen K.,Marine and Atmospheric Research | Wild-Allen K.,National Research Flagship | And 7 more authors.
Progress in Oceanography | Year: 2011

New observations along the continental shelf of Western Australia provide a novel explanation for the established ~60years relationship between Leeuwin Current (LC) strength and greater winter nitrate concentrations at 32°S plus the inter-annual variation in the magnitude of the annual, shelf-scale, phytoplankton bloom. The potential source of dissolved nitrogen to support the annual shelf scale phytoplankton bloom was identified as thin layers of an unprecedented areal extent, nitrate concentration and shallow nature that were observed off the northwest of Australia. We propose that the dissolved inorganic nitrogen (DIN) in these layers enters the LC at depth and then enters the euphotic zone via by three mechanisms: instability that results in a warm core eddy, cooling that deepens the surface mixed layer and shallowing of the thin layer. During the onset of the annual phytoplankton bloom along the west coast of Australia from 22°S to 34°S the poleward flowing LC was clearly evident as a surface intensified ocean boundary current transporting warmer, lower-salinity, greater-silicate waters in a shallow mixed layer rapidly southward. Between 24 and 26°S the core of the LC was present as a 50-100m deep layer over one or more thin layers, 15-50m thick, with high nitrate and low dissolved oxygen (DO). These layers were of lower salinity, cooler water with markedly reduced DO, high nitrate concentrations and distinct nitrate:silicate (NO3:Si(OH)4) nutrient ratios. As the LC flowed south it cooled and deepened thereby entraining the thin layers of high nitrate water into the euphotic zone. The LC also formed large (greater than 100km diameter) warm core eddies with a deep surface mixed layer that also entrained nitrate from these thin layers. In some locations as far south as 32°S the LC was still present with the thin layer of high nitrate intact but now within the euphotic zone. Thus, the available evidence suggests the LC arises under conditions that favour rapid and shallow nitrification. This nitrification fuels a shelf-scale bloom on a downwelling favourable coast. Depending upon the rate of nitrification the source of the particular organic matter may be local or delivered from the tropics via horizontal advection in a subsurface layer of the LC. © 2011 Elsevier Ltd.

Ahn J.,Seoul National University | Brook E.J.,Oregon State University | Mitchell L.,Oregon State University | Rosen J.,Oregon State University | And 4 more authors.
Global Biogeochemical Cycles | Year: 2012

We report a decadally resolved record of atmospheric CO2 concentration for the last 1000 years, obtained from the West Antarctic Ice Sheet (WAIS) Divide shallow ice core. The most prominent feature of the pre-industrial period is a rapid ∼7 ppm decrease of CO2 in a span of ∼20-50 years at ∼1600 A.D. This observation confirms the timing of an abrupt atmospheric CO2 decrease of ∼10 ppm observed for that time period in the Law Dome ice core CO2 records, but the true magnitude of the decrease remains unclear. Atmospheric CO2 variations over the time period 1000-1800 A.D. are statistically correlated with northern hemispheric climate and tropical Indo-Pacific sea surface temperature. However, the exact relationship between CO2 and climate remains elusive due to regional climate variations and/or uneven geographical data density of paleoclimate records. We observe small differences of 0 ∼ 2% (0 ∼ 6 ppm) among the high-precision CO2 records from the Law Dome, EPICA Dronning Maud Land and WAIS Divide Antarctic ice cores. However, those records share common trends of CO2 change on centennial to multicentennial time scales, and clearly show that atmospheric CO2 has been increasing above preindustrial levels since ∼1850 A.D. Copyright 2012 by the American Geophysical Union.

Olds A.D.,Griffith University | Olds A.D.,University of The Sunshine Coast | Connolly R.M.,Griffith University | Pitt K.A.,Griffith University | And 11 more authors.
Global Ecology and Biogeography | Year: 2016

Aim: Connectivity structures populations, communities and ecosystems in the sea. The extent of connectivity is, therefore, predicted to also influence the outcomes of conservation initiatives, such as marine reserves. Here we review the published evidence about how important seascape connectivity (i.e. landscape connectivity in the sea) is for marine conservation outcomes. Location: Global. Methods: We analysed the global literature on the effects of seascape connectivity on reserve performance. Results: In the majority of cases, greater seascape connectivity inside reserves translates into better conservation outcomes (i.e. enhanced productivity and diversity). Research on reserve performance is, however, most often conducted separately from research on connectivity, resulting in few studies (<5% of all studies of seascape connectivity) that have quantified how connectivity modifies reserve effects on populations, assemblages or ecosystem functioning in seascapes. Nevertheless, evidence for positive effects of connectivity on reserve performance is geographically widespread, encompassing studies in the Caribbean Sea, Florida Keys and western Pacific Ocean. Main conclusions: Given that research rarely connects the effects of connectivity and reserves, our thesis is that stronger linkages between landscape ecology and marine spatial planning are likely to improve conservation outcomes in the sea. The key science challenge is to identify the full range of ecological functions that are modulated by connectivity and the spatial scale over which these functions enhance conservation outcomes. © 2016 John Wiley & Sons Ltd.

McCreless E.E.,University of California at Santa Cruz | Huff D.D.,Point Adams Research Station | Croll D.A.,University of California at Santa Cruz | Tershy B.R.,University of California at Santa Cruz | And 5 more authors.
Nature Communications | Year: 2016

Invasive mammals on islands pose severe, ongoing threats to global biodiversity. However, the severity of threats from different mammals, and the role of interacting biotic and abiotic factors in driving extinctions, remain poorly understood at a global scale. Here we model global extirpation patterns for island populations of threatened and extinct vertebrates. Extirpations are driven by interacting factors including invasive rats, cats, pigs, mustelids and mongooses, native species taxonomic class and volancy, island size, precipitation and human presence. We show that controlling or eradicating the relevant invasive mammals could prevent 41-75% of predicted future extirpations. The magnitude of benefits varies across species and environments; for example, managing invasive mammals on small, dry islands could halve the extirpation risk for highly threatened birds and mammals, while doing so on large, wet islands may have little benefit. Our results provide quantitative estimates of conservation benefits and, when combined with costs in a return-on-investment framework, can guide efficient conservation strategies.

Tanimoto J.,Kyushu University | Brede M.,Marine and Atmospheric Research | Yamauchi A.,Kyushu University
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

We propose a network reciprocity model in which an agent probabilistically adopts learning or teaching strategies. In the learning adaptation mechanism, an agent may copy a neighbor's strategy through Fermi pairwise comparison. The teaching adaptation mechanism involves an agent imposing its strategy on a neighbor. Our simulations reveal that the reciprocity is significantly affected by the frequency with which learning and teaching agents coexist in a network and by the structure of the network itself. © 2012 American Physical Society.

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