Global Change Abstracts The Swiss Contribution - SCNAT

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138 Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems Large river floodplains potentially include the full range of freshwater ecosystems from permanently flowing channels to temporary pools and springs. Attempts to restore such complex systems require tools adapted to assess restoration success. In an analysis of invertebrate assemblages in the Rhone River floodplain (France), taxonomic-based indices (rarefied richness and assemblage composition) were compared with functional metrics using trait-based ratios as surrogates of ecosystem processes. Their ability to respond to a gradient of hydrological connectivity was assessed in 7 cut-off channels. The sampling design included 2 sites/channel (upstream and downstream), 4 randomly chosen sampling points (0.5 x 0.5-m quadrats) /site, and 2 sampling seasons (spring and summer). Water physicochemical and habitat variables were recorded when invertebrates were sampled. Environmental variables, including water conductance, (NH 3-N), submerged vegetation cover, diversity of sediment grain size, and organic matter content of the sediment, were used to construct a synthetic variable describing the hydrological connectivity of each site with the main river channel. A quadratic regression of rarefied taxonomic richness and the connectivity gradient was not quite significant, but assemblage composition was strongly related to the gradient. Four of 8 trait-based metrics; were correlated with the connectivity gradient. Values of metrics that are surrogates for top-down control of assemblage structure and habitat stability (based on functional feeding groups) declined along the gradient from disconnected sites to more connected sites. Values of metrics that are surrogates for voltinism and food supply for water- column-feeding fish increased with connectivity. Top-down control and voltinism surrogates suggested a decline in predator-prey relationships and lower habitat stability, respectively, in the more connected sites. Assemblage composition and some of the trait-based metrics were sensitive to a flood that occurred before one of the sampling dates. Some of the traitbased metrics showed potential for explaining floodplain invertebrate assemblages and for monitoring postrestoration conditions in floodplain water bodies. However, the metrics were developed initially for studies of lotic systems and their use in heterogeneous floodplain water bodies will require further investigation, e.g., delineation of reference conditions for trait-based metrics. Journal of the North American Benthological Society, 2007, V26, N4, DEC, pp 779-796. 08.1-266 Bipolar gene flow in deep-sea benthic foraminifera Pawlowski J, Fahrni J, Lecroq B, Longet D, Cornelius N, Excoffier L, Cedhagen T, Gooday A J Switzerland, England, Denmark Biodiversity , Ecology , Marine & Freshwater Biology Despite its often featureless appearance, the deepocean floor includes some of the most diverse habitats on Earth. However, the accurate assessment of global deep-sea diversity is impeded by a paucity of data on the geographical ranges of bottom-dwelling species, particularly at the genetic level. Here, we present molecular evidence for exceptionally wide distribution of benthic foraminifera, which constitute the major part of deep-sea meiofauna. Our analyses of nuclear ribosomal RNA genes revealed high genetic similarity between Arctic and Antarctic populations of three common deep-sea foraminiferal species (Epistominella exigua, Cibicides wuellerstorfi and Oridorsalis umbonatus), separated by distances of up to 17 000 km. Our results contrast with the substantial level of cryptic diversity usually revealed by molecular studies, of shallow- water benthic and planktonic marine organisms. The very broad ranges of the deep-sea foraminifera that we examined support the hypothesis of global distribution of small eukaryotes and suggest that deep-sea biodiversity may be more modest at global scales than present estimates suggest. Molecular Ecology, 2007, V16, N19, OCT, pp 4089-4096. 08.1-267 Earlier onset of the spring phytoplankton bloom in lakes of the temperate zone in a warmer climate Peeters F, Straile D, Lorke A, Livingstone D M Germany, Switzerland Marine & Freshwater Biology , Meteorology & Atmospheric Sciences , Oceanography , Biodiversity Ecology The decoupling of trophic interactions is potentially one of the most severe consequences of climate warming. In lakes and oceans the timing of phytoplankton blooms affects competition within the plankton community as well as foodweb interactions with zooplankton and fish. Using Upper Lake Constance as an example, we present a model-based analysis that predicts that in a future warmer climate, the onset of the spring phytoplankton bloom will occur earlier in the year than it does at present. This is a result of the earlier occurrence of the transition from strong to weak vertical mixing in spring, and of the as-
Global Change Abstracts – The Swiss Contribution | Oceans and Fresh Water Systems sociated earlier onset of stratification. According to our simulations a shift in the timing of phytoplankton growth resulting from a consistently warmer climate will exceed that resulting from a single unusually warm year. The numerical simulations are complemented by a statistical analysis of long-term data from Upper Lake Constance which demonstrates that oligotrophication has a negligible effect on the timing of phytoplankton growth in spring and that an early onset of the spring phytoplankton bloom is associated with high air temperatures and low wind speeds. Global Change Biology, 2007, V13, N9, SEP, pp 1898-1909. 08.1-268 Water level fluctuations and dynamics of amphibious plants at Lake Constance: Long-term study and simulation Peintinger M, Prati D, Winkler E Germany, Switzerland Plant Sciences , Modelling , Limnology , Marine & Freshwater Biology Inundations of lakeshores are classical examples of how disturbance can influence community diversity and composition. As the occurrence and intensity of flooding are predicted to change dramatically as a result of climate change, predicting the consequences of such changes has become a major task for community ecology. Here we present abundance data of five species that comprise a species-poor community of high conservation value at lakeshores of Lake Constance over 17 years, during which one of the longest flood periods and the lowest water levels since 1890 occurred. We used simple regression models and increasingly sophisticated Markov chain models plus non-linear parameter estimation to put down abundance changes to direct effects of flooding on population-dynamic parameters and to indirect effects of flooding through modification of interspecific competition. We found a negative effect of flood duration on abundance changes for the non-specialist species Agrostis stolonifera and Phalaris arundinacea, but no effect on Carex acuta. The specialist species, Ranunculus reptans but not Littorella uniflora showed a positive effect of flooding. Data analysis revealed an unambiguous competitive hierarchy with the two graminoid species (C acuta, P. arundinacea) being superior, and the habitat specialists being most sensitive to interspecific competition. We used estimated parameters to project the community dynamics under different flooding regimes. Long-term projection showed that the original community is threatened by two non-specialist species (C acuta 139 and P. arundinacea). Even if this forecast was influenced by various model limitations, it may indicate irreversible changes in soil fertility during the phase of high eutrophication between 1950 and 1980. Our study demonstrated that long-term abundance releves combined with Markov modelling and predictive simulations are an important counterpart to detailed short-term studies. The combination of empirical and theoretical methods elucidates the interaction of biotic and abiotic factors in community change. Perspectives in Plant Ecology Evolution and Systematics, 2007, V8, N4, pp 179-196. 08.1-269 Phytoplankton blooms in the Ross Sea, Antarctica: Interannual variability in magnitude, temporal patterns, and composition Peloquin J A, Smith W O Jr USA, Switzerland Oceanography , Marine & Freshwater Biology The continental shelf of the Ross Sea, Antarctica, is a unique region within the Southern Ocean. Phytoplankton growth is believed to be seasonally limited, first in austral spring by irradiance, and then in summer by biologically available iron. It also is historically known to have taxonomically distinct regimes: the south-central portion is dominated by Phaeocystis antarctica and to the west diatoms are abundant. We measured photochemical yield to interpret the health of the phytoplankton assemblage from 2001-2004 and interfaced these measurements with satellite remote sensing of pigments. The bloom of 2001-2002 was similar in both temporal and spatial distributions to the climatological mean of the Ross Sea, with a peak in biomass being observed in mid-December within the Ross Sea polynyas; F-v/F-m values averaged 0.43. We found high (0.50-0.65) F-v/F-m for most of the seasonal phytoplankton bloom for 2002-2003, suggesting that it was not seasonally iron limited. An unusual, large bloom occurred during 2003-2004, with an initial bloom of P. antarctica during austral spring followed by an extensive diatom bloom in summer that may have been enhanced by an intrusion of modified circumpolar deep water. On the basis of an analysis of the historical SeaWiFS records, accumulation of phytoplankton biomass in February may occur approximately every 2-4 years, potentially being a significant source of carbon on the continental shelf. Journal of Geophysical Research Oceans, 2007, V112, NC8, AUG 23 ARTN: C08013.
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