Posts Tagged 'biogeography'

Spring plankton community structure and distribution in the north and south coasts of Sfax (Tunisia) after north coast restoration

The first phase of the Taparura Project aimed at restoring the north coast of Sfax (Tunisia), highly polluted by phosphate industry and uncontrolled phosphogypsum dumping. Before restoration of the north coast of Sfax, we investigated the state of the ecosystem in related coastal waters. To establish the impact of the Taparura Project, we conducted a similar study both after restoration. To discriminate natural changes over time, we extended the study to the south coast of Sfax, submitted to the same industrial pressure but not yet restored. The present study, conducted in May 2010 at 36 stations (18 on each coast, north and south), covered the spatial distribution of the microbial assemblage, nutrients, and abiotic parameters by collecting seawater samples at the surface and the water–sediment interface. Results revealed a striking difference between the two coasts regarding pH, with strong acidification of seawater in the south, likely generated by industrial activity. Suspended matter was higher in the north than in the south. Flow cytometry analysis of ultraphytoplankton (<10 μm) resolved six groups (Prochlorococcus, Synechococcus, nanoeukaryotes and three distinct subgroups within picoeukaryotes). In addition to these autotrophic groups, two unknown groups were characterised on the south coast. Heterotrophic prokaryotes were resolved into three groups, labelled LNA (low nucleic acid content), HNA1 and HNA2 (high nucleic acid content). Prochloroccocus, pico-nano-microphytoplankton, heterotrophic prokaryotes and ciliates were more abundant in the north, whereas Synechococcus and unknown species were more abundant in the south where chl a concentration was also higher. The results show that restoration had positive effects on the microbial assemblage of the north coast; they also highlight the strong acidification still prevalent in the south that may be responsible for the lower development of most phytoplankton groups and the occurrence of unknown species. The case for restoration of the city’s south coast is also reinforced.

Continue reading ‘Spring plankton community structure and distribution in the north and south coasts of Sfax (Tunisia) after north coast restoration’

The benthic foraminiferal community in a naturally CO2-rich coastal habitat of the southwestern Baltic Sea (update)

It is expected that the calcification of foraminifera will be negatively affected by the ongoing acidification of the oceans. Compared to the open oceans, these organisms are subjected to much more adverse carbonate system conditions in coastal and estuarine environments such as the southwestern Baltic Sea, where benthic foraminifera are abundant. This study documents the seasonal changes of carbonate chemistry and the ensuing response of the foraminiferal community with bi-monthly resolution in Flensburg Fjord. In comparison to the surface pCO2, which is close to equilibrium with the atmosphere, we observed large seasonal fluctuations of pCO2 in the bottom and sediment pore waters. The sediment pore water pCO2 was constantly high during the entire year ranging from 1244 to 3324 μatm. Nevertheless, in contrast to the bottom water, sediment pore water was slightly supersaturated with respect to calcite as a consequence of higher alkalinity (AT) for most of the year. Foraminiferal assemblages were dominated by two calcareous species, Ammonia aomoriensis and Elphidium incertum, and the agglutinated Ammotium cassis. The one-year cycle was characterised by seasonal community shifts. Our results revealed that there is no dynamic response of foraminiferal population density and diversity to elevated sediment pore water pCO2. Surprisingly, the fluctuations of sediment pore water undersaturation (Ωcalc) co-vary with the population densities of living Ammonia aomoriensis. Further, we observed that most of the tests of living calcifying foraminifera were intact. Only Ammonia aomorienis showed dissolution and recalcification structures on the tests, especially at undersaturated conditions. Therefore, the benthic community is subjected to high pCO2 and tolerates elevated levels as long as sediment pore water remains supersaturated. Model calculations inferred that increasing atmospheric CO2 concentrations will finally lead to a perennial undersaturation in sediment pore waters. Whereas benthic foraminifera indeed may cope with a high sediment pore water pCO2, the steady undersaturation of sediment pore waters would likely cause a significant higher mortality of the dominating Ammonia aomoriensis. This shift may eventually lead to changes in the benthic foraminiferal communities in Flensburg Fjord, as well as in other regions experiencing naturally undersaturated Ωcalc levels.

Continue reading ‘The benthic foraminiferal community in a naturally CO2-rich coastal habitat of the southwestern Baltic Sea (update)’

Diel variability in seawater pH relates to calcification and benthic community structure on coral reefs

Community structure and assembly are determined in part by environmental heterogeneity. While reef-building corals respond negatively to warming (i.e. bleaching events) and ocean acidification (OA), the extent of present-day natural variability in pH on shallow reefs and ecological consequences for benthic assemblages is unknown. We documented high resolution temporal patterns in temperature and pH from three reefs in the central Pacific and examined how these data relate to community development and net accretion rates of early successional benthic organisms. These reefs experienced substantial diel fluctuations in temperature (0.78°C) and pH (>0.2) similar to the magnitude of ‘warming’ and ‘acidification’ expected over the next century. Where daily pH within the benthic boundary layer failed to exceed pelagic climatological seasonal lows, net accretion was slower and fleshy, non-calcifying benthic organisms dominated space. Thus, key aspects of coral reef ecosystem structure and function are presently related to natural diurnal variability in pH.

Continue reading ‘Diel variability in seawater pH relates to calcification and benthic community structure on coral reefs’

The benthic foraminiferal community in a naturally CO2-rich coastal habitat in the southwestern Baltic Sea

It is expected that the calcification of foraminifera will be negatively affected by the ongoing acidification of the oceans. Compared to the open oceans, these organisms are subjected to much more adverse carbonate system conditions in coastal and estuarine environments such as the southwestern Baltic Sea, where benthic foraminifera are abundant. This study documents the seasonal changes of carbonate chemistry and the ensuing response of the foraminiferal community with bi-monthly resolution in Flensburg Fjord. In comparison to the surface pCO2, which is close to equilibrium with the atmosphere, we observed large seasonal fluctuations of pCO2 in the bottom and sediment pore waters. The sediment pore water pCO2 was constantly high during the entire year ranging from 1244 to 3324 μatm. Nevertheless, in contrast to the bottom water, sediment pore water was slightly supersaturated with respect to calcite as consequence of higher alkalinity (AT) for the most time of the year. Foraminiferal assemblages were dominated by two calcareous species, Ammonia aomoriensis and Elphidium incertum, and the agglutinated Ammotium cassis. The one year-cycle was characterized by seasonal community shifts. Our results revealed that there is no dynamic response of foraminiferal population density and diversity to elevated sediment pore water pCO2. Surprisingly, the fluctuations of sediment pore water undersaturation (Ωcalc) co-vary with the population densities of living Ammonia aomoriensis. Further, we observed that most of the tests of living calcifying specimens were intact. Only Ammonia aomorienis showed dissolution and recalcification structures on the tests, especially at undersaturated conditions. Therefore, the benthic community is subjected to constantly high pCO2 and tolerates elevated levels as long as sediment pore water remains supersaturated. Model calculations inferred that increasing atmospheric CO2 concentrations will finally lead to a perennial undersaturation in sediment pore waters. Whereas benthic foraminifera indeed may cope with a high sediment pore water pCO2, the steady undersaturation of sediment pore waters would likely cause a significant higher mortality of the dominating Ammonia aomoriensis. This shift may eventually lead to changes in the benthic foraminiferal communities in Flensburg Fjord, as well as in other regions experiencing naturally undersaturated Ωcalc levels.

Continue reading ‘The benthic foraminiferal community in a naturally CO2-rich coastal habitat in the southwestern Baltic Sea’

Review of climate change impacts on marine fish and shellfish around the UK and Ireland

  1. Recent and projected future changes in the temperature and chemistry of marine waters around the UK and Ireland are having, and will in the future have, effects on the phenology, productivity and distribution of marine fish and shellfish. However, the overall consequences are still hard to predict because behaviour, genetic adaptation, habitat dependency and the impacts of fishing on species, result in complex species’ responses that may be only partially explained by simple climate envelope predictions.
  2. There is a broad body of evidence that climatic fluctuations are playing an important role in changing fish distributions and abundances, which is discernible against the background of trends in abundance due to fishing. During warm periods, southern species have tended to become more prominent and northern species less abundant. However, the changes in distribution are often more complicated than might be expected from a simple climate envelope approach, partly due to ocean circulation patterns which create invasion routes for southern water species into the North Sea from the south and from the north via the continental shelf west of Britain and Ireland.
  3. The eventual population-scale impacts of ocean acidification on fish and shellfish are currently very difficult to predict. However, the scant evidence suggests that indirect food web effects arising from the enhanced sensitivity of calcifying planktonic organisms may be important, and the direct effect on fish sensory systems leading to subtle influences on behaviour with possible population-level implications are possible.
  4. In British waters, the lesser sandeel (Ammodytes marinus) is identified as being at particular risk from climate change. Owing to its strict association with coarse sandy sediments it is unable to adapt its distribution to compensate for warming sea temperatures. Sandeels are a key link in the food web, linking primary and zooplankton production to top predators.

Continue reading ‘Review of climate change impacts on marine fish and shellfish around the UK and Ireland’


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