Quantitative food web modeling unravels the importance of the microphytobenthos-meiofauna pathway for a high trophic transfer by meiofauna in soft-bottom intertidal food webs.

Meiofauna are known to have an important role on many ecological processes, although, their role in food web dynamics is often poorly understood, partially as they have been an overlooked and under sampled organism group. Here, we used quantitative food web modeling to evaluate the trophic relationship between meiofauna and their food sources and how meiofauna can mediate the carbon flow to higher trophic levels in five contrasting soft-bottom intertidal habitats (including seagrass beds, mudflats and sandflats). Carbon flow networks were constructed using the linear inverse model-Markov chain Monte Carlo technique, with increased resolution of the meiofauna compartments (i.e. biomass and feeding ecology of the different trophic groups of meiofauna) compared to most previous modeling studies. These models highlighted that the flows between the highly productive microphytobenthos and the meiofauna compartments play an important role in transferring carbon to the higher trophic levels, typically more efficiently so than macrofauna. The pathway from microphytobenthos to meiofauna represented the largest flow in all habitats and resulted in high production of meiofauna independent of habitat. All trophic groups of meiofauna, except for selective deposit feeders, had a very high dependency on microphytobenthos. Selective deposit feeders relied instead on a wider range of food sources, with varying contributions of bacteria, microphytobenthos and sediment organic matter. Ecological network analyses (e.g. cycling, throughput and ascendency) of the modeled systems highlighted the close positive relationship between the food web efficiency and the assimilation of high-quality food sources by primary consumers, e.g. meiofauna and macrofauna. Large proportions of these flows can be attributed to trophic groups of meiofauna. The sensitivity of the network properties to the representation of meiofauna in the models leads to recommending a greater attention in ecological data monitoring and integrating meiofauna into food web models.

Trophic importance of microphytobenthos and bacteria to meiofauna in soft-bottom intertidal habitats: A combined trophic marker approach.

Meiofauna can play an important role in the carbon fluxes of soft-bottom coastal habitats. Investigation of their feeding behavior and trophic position remains challenging due to their small size. In this study, we determine and compare the food sources used by nematodes and benthic copepods by using stable isotope compositions, fatty acid profiles and compound specific isotope analyses of fatty acids in the mudflats, seagrass beds and a sandflat of the Marennes-Oléron Bay, France, and the Sylt-Rømø Bight, Germany. Suspended particulate organic matter was much more 13C-depleted than other food sources and meiofauna, highlighting its poor role in the different studied habitats. The very low proportions of vascular plant fatty acid markers in meiofauna demonstrated that these consumers did not rely on this food source, either fresh or detrital, even in seagrass beds. The combined use of stable isotopes and fatty acids emphasized microphytobenthos and benthic bacteria as the major food sources of nematodes and benthic copepods. Compound specific analyses of a bacteria marker confirmed that bacteria mostly used microphytobenthos as a substrate.

Long-term comparison of a calcium-free phosphate binder and calcium carbonate--phosphorus metabolism and cardiovascular calcification.

BACKGROUND: Calcium carbonate used as a phosphate binder may contribute to cardiovascular calcification. Long-term comparisons of sevelamer, a non-calcium polymeric phosphate binder, and calcium carbonate (CC) are lacking. METHODS: 114 adult hemodialysis patients were randomly assigned to open label sevelamer or CC for 52 weeks. Study efficacy endpoints included changes in serum phosphorus, calcium, calcium-phosphorus product, and lipids. In addition, initial and sequential electron beam computerized tomography scans were performed to assess cardiovascular calcification status and change during follow-up. Safety endpoints were serum biochemistry, blood cell counts and adverse events. RESULTS: Patients receiving sevelamer had a similar reduction in serum phosphorus as patients receiving CC (sevelamer -0.58 +/- 0.68 mmol/l, CC -0.52 +/- 0.50 mmol/l; p = 0.62). Reductions in calcium-phosphorus product were not significantly different (sevelamer -1.4 +/- 1.7 mmol2/l2, CC -0.9 +/- 1.2 mmol2/l2; p = 0.12). CC produced significantly more hypercalcemia (> 2.8 mmol/l in 0% sevelamer and 19% CC patients, p < 0.01) and suppressed intact parathyroid hormone below 150 pg/ml in the majority of patients. Sevelamer patients experienced significant (p < 0.01) reductions in total (-1.2 +/- 0.9 mmol/l, -24%) and LDL cholesterol (-1.2 +/- 0.9 mmol/l, -30%). CC patients had significant increases in coronary artery (median +34%, p < 0.01) and aortic calcification (median +32%, p < 0.01) that were not observed in sevelamer-treated patients. Patients on sevelamer required more grams of binder (sevelamer 5.9 g vs. CC 3.9 g) and experienced more dyspepsia than patients on calcium carbonate. CONCLUSIONS: Sevelamer is an effective phosphate binder that unlike calcium carbonate is not associated with progressive cardiovascular calcification in hemodialysis patients.