Carbon sources supporting benthic mineralization in mangrove and adjacent seagrass sediments (Gazi Bay, Kenya)

The origin of carbon substrates used by in situ sedimentary bacterial communities was investigated in an intertidal mangrove ecosystem and in adjacent seagrass beds in Gazi bay (Kenya) by d13C analysis of bacteria-specific PLFA (phospholipid fatty acids) and bulk organic carbon. Export of mangrove-derived organic matter to the adjacent seagrass-covered bay was evident from sedimentary total organic carbon (TOC) and d13CTOC data. PLFA d13C data indicate that the substrate used by bacterial communities varied strongly and that exported mangrove carbon was a significant source for bacteria in the adjacent seagrass beds. Within the intertidal mangrove forest, bacterial PLFA at the surface layer (0-1cm) typically showed more enriched d13C values than deeper (up to 10cm) sediment layers, suggesting a contribution from microphytobenthos and/or inwelled seagrass material. Under the simplifying assumption that seagrasses and mangroves are the dominant potential end-members, the estimated contribution of mangrove-derived carbon to benthic mineralization in the seagrass beds (16-74%) corresponds fairly well to the estimated contribution of mangrove C to the sedimentary organic matter pool (21-71%) across different seagrass sites. Based on the results of this study and a compilation of literature data, we suggest that trapping of allochtonous C is a common feature in seagrass beds and often represents a significant source of C for sediment bacteria - both in cases where seagrass C dominates the sediment TOC pool and in cases where external inputs are significant. Hence, it is likely that data on community respiration rates systematically overestimate the role of in situ mineralization as a fate of seagrass production

Eten en gegeten worden in het Schelde-estuarium

Like other estuaries, the Schelde estuary is characterized by a diversity of organic matter inputs. These inputs can be classified as ‘autochtonous’, i.e. produced in situ (e.g. phytoplankton and microphytobenthos), or ‘allochtonous’, i.e. transported into the estuary via river and seawater inflow. Together, these organic matter sources form an enormous energy pool, that is utilized by huge numbers of living organisms. The Schelde is a largely heterotrophic estuary, implying that allochtonous sources fuel the majority of the metabolic processes taking place within the system. This is most pronounced in the upstream reaches of the estuary, and is strikingly illustrated in the maximum turbidity zone. All this allochtonous carbon fuels a decomposer food web where bacteria, their protistan grazers, and rotifera and copepods feeding on protists form the link between detritus and the higher trophic levels like shrimps, fish and birds. The high bacterial activity results in oxygen depletion, which in turn causes a relatively species-poor food web. Downstream, the relative importance of autochtonous carbon increases, and an autotrophic, grazer food web develops in addition to the decomposer food web. In the water column, phytoplankton is grazed by copepods, which in turn are food for fish and shrimps. In the benthos, a large variety of algal grazers and detritus feeders exist, forming the basis of complex, interlinked food webs. Inspite of the high concentrations of available carbon and nutrients, much of the consumed sources are constantly being recycled within and between different trophic levels. Unraveling these food webs is often a complex task requiring sophisticated methods such as stable isotope tracer techniques

Expansion of small-scale changes in macrobenthic community inside an offshore wind farm?

The presence of offshore wind farms in the marine environment has some impacts on the macrobenthic community living in the natural sandy sediments. Changes in hydrodynamics, presence of epifaunal coverage along the turbine and fisheries exclusion are expected to be the main causes influencing the macrobenthos. In this study it was investigated whether changes in sediment characteristics and the macrobenthic community occurred inside a wind farm in the Belgian part of the North Sea. Both stations in the close vicinity of the turbines (50 m distance, close samples) and further away (350-500 m distance, far samples) were sampled with a Van Veen grab in autumn 2015

Differences in time until dispersal between cryptic species of a marine nematode species complex

Co-occurrence of closely related species may be achieved in environments with fluctuating dynamics, where competitively inferior species can avoid competition through dispersal. Here we present an experiment in which we compared active dispersal abilities (time until first dispersal, number and gender of dispersive adults, and nematode densities at time of dispersal) in Litoditis marina, a common bacterivorous nematode species complex comprising four often co-occurring cryptic species, Pm I, II, III, and IV, as a function of salinity and food distribution. The experiment was conducted in microcosms consisting of an inoculation plate, connection tube, and dispersal plate. Results show species-specific dispersal abilities with Pm I dispersing almost one week later than Pm III. The number of dispersive adults at time of first dispersal was species-specific, with one dispersive female in Pm I and Pm III and a higher, gender-balanced, number in Pm II and Pm IV. Food distribution affected dispersal: in absence of food in the inoculation plate, all species dispersed after ca four days. When food was available Pm I dispersed later, and at the same time and densities irrespective of food conditions in the dispersal plate (food vs no food), suggesting density-dependent dispersal. Pm III dispersed faster and at a lower population density. Salinity affected dispersal, with slower dispersal at higher salinity. These results suggest that active dispersal in Litoditis marina is common, density-dependent, and with species, gender- and environment-specific dispersal abilities. These differences can lead to differential responses under suboptimal conditions and may help to explain temporary coexistence at local scales

Effects of temperature on the in vitro reproduction of Aphelenchoides rutgersi

L'influence de la température sur la reproduction d'#Aphelenchoides rutgersi en culture axénique a été étudiée. La température optimale de reproduction d'#A. rutgersi est de 28°C. A cette température, une femelle d'#A. rutgersi$pond en moyenne 60 oeufs pendant les 11 jours qui suivent sa maturation; les juvéniles commencent à éclore dès le deuxième jour; 80$ n'augmentent plus. A des températures inférieures à 28°C, les oeufs pondus sont moins nombreux, les éclosions plus tardives, et les durées minimale et moyenne de développement demandent au moins 2 jours de plus. (Résumé d'auteur