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Trophic connectivity between intertidal and offshore food webs in Mirs Bay, China

Ning Jiajia, Du Feiyan, Wang Xuehui, Wang Lianggen, Li Yafang

Oceanologia

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2019

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No. 61 (2)

208--217

EN

Trophic interactions are common worldwide, both within and between ecosystems. This study elucidated the trophic connectivity between intertidal and offshore zone, in Mirs Bay, China. The contributions of offshore suspended particulate organic matter (SPOM), intertidal macroalgae and epiphytes to consumer biomass were assessed, and the trophic pathways were identified through the use of stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) of basal sources and consumers. Mean δ13C values of basal sources had a wide range (-19.6‰ to -11.8‰) and were generally well separated in Mirs Bay. The average δ13C of consumers in Mirs Bay ranged from -19.2‰ to -11.8‰, reflecting a carbon source integrated from different primary producer signals. IsoSource model solutions indicated consumers assimilated organic carbon from a mixture of basal sources. Offshore SPOM carbon was the primary carbon source supporting most consumers in both intertidal and offshore zones. Intertidal macroalgae and epiphytes also accounted for a large fraction for some consumers. δ15N data indicated 5 trophic levels in Mirs Bay. Intertidal consumers, except for Capitulum mitella, had a TP (trophic position) between 2 and 3, and mainly included filter-feeders and grazers. In contrast, almost all offshore consumers had a TP of between 3 and 4 except for filter-feeders (zooplankton), planktivores (Clupanodon punctatus and Sardinella aurita) and piscivores (Gymnura japonica). The basal sources fueled consumer through two trophic pathways, each of which involved organisms of both intertidal and offshore zones, implying trophic connectivity between them in the Mirs Bay ecosystem.

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The use of stable isotope analyses in freshwater ecology: Current awareness

Grey Jonathan

Polish Journal of Ecology

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2006

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Vol. 54, nr 4

563-584

EN

Ecological research using stable isotopes has progressed rapidly during the last 20 years and although more studies are including the addition of isotopically labelled compounds at tracer levels, the overwhelming majority rely on measurements of natural abundance ratios. Access to isotope ratio mass spectrometry has increased, spurred on by awareness of the techniques and increasing demand, and consequently cost of sample analysis has dropped. Today stable isotopes of carbon ([13]C/[12]C), nitrogen ([15]N/[14]N), sulphur ([34]S/[32]S), oxygen ([18]O/[16]O), and hydrogen ([2]H/[1]H) can be determined routinely. Perhaps one of the most appealing attributes of isotopic signatures is their potential use to find patterns and determine mechanisms across a range of scales from the molecular level through to characterizing whole food webs, reconstructing palaeoenvironments, tracing nutrient fluxes between ecosystems and identifying subsidies, or migrations of organisms. Ecologists from every discipline who are unlikely to have been trained as isotope chemists have added stable isotope analysis (SIA) to their "toolbox", but often increasing use leads to increasing abuse. The usefulness of SIA arises from predictable physical and enzymatic-based discrimination between biological and non-biological materials leading to different isotopic compositions. Without some ecological understanding of these, interpretation of isotope-derived data can often be flawed. Here, I explore how SIA recently has been used for research in aquatic ecology, reviewing how some of these techniques have allowed elucidation of key processes in aquatic systems such as the contribution of allochthony to lake food webs, and discuss the "state of the art". Included are some thoughts on where our knowledge in aquatic ecology remains deficient and how continued development and future application of SIA and interdisciplinary methodologies may be applied.

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Daphnia: model herbivore, predator and prey

Lampert Winfried

Polish Journal of Ecology

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2006

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Vol. 54, nr 4

607-620

EN

In the past 30 years, Daphnia has become a model organism in aquatic ecology. I review the changing concepts and paradigms in plankton ecology as reflected in the work on Daphnia. The availability of radiotracers favoured a new physiological approach that resulted in better energetic models and more reliable estimates of filtering rates. This led to deeper insights into the role of herbivore grazing on phytoplankton and microbial communities, and nutrient recycling. It provided a conceptual basis for general hypotheses on predictable seasonal successions (e.g. the PEG model). On the other hand, increasing knowledge about selective predation on zooplankton triggered population dynamic models and gave explanations for changing community structures. The Size-Efficiency-Hypothesis generated a framework for studies on trade-offs between competitive ability and susceptibility to predation. Daphnia was now in the centre of interaction-based concepts, being predator and prey at the same time. It was the backbone of practical applications of the theory in food-web manipulations. When ultimate factors came into the focus, Daphnia played an important role in explaining striking phenomena like diel vertical migration and cyclomorphosis. Its central position in food-webs, the unique propagation mode, easy cultivation and accessibility by molecular genetic methods made it a favourite object for studies in evolutionary ecology, concerning local adaptation, evolution of defences and life histories, induced phenotypic change, and genetic diversity. The large advantage of Daphnia over other biological model organisms is that its importance in pelagic freshwater systems is undoubtedly known. Hence there is a direct way of applying the results to ecological systems.