Climate-induced changes in bottom-up and top-down processes independently alter a marine ecosystem

Climate change has complex structural impacts on coastal ecosystems. Global warming is linked to a widespread decline in body size, whereas increased flood frequency can amplify nutrient enrichment through enhanced run-off. Altered population body-size structure represents a disruption in top-down control, whereas eutrophication embodies a change in bottom-up forcing. These processes are typically studied in isolation and little is known about their potential interactive effects. Here, we present the results of an in situ experiment examining the combined effects of top-down and bottom-up forces on the structure of a coastal marine community. Reduced average body mass of the top predator (the shore crab, Carcinus maenas) and nutrient enrichment combined additively to alter mean community body mass. Nutrient enrichment increased species richness and overall density of organisms. Reduced top-predator body mass increased community biomass. Additionally, we found evidence for an allometrically induced trophic cascade. Here, the reduction in top-predator body mass enabled greater biomass of intermediate fish predators within the mesocosms. This, in turn, suppressed key micrograzers, which led to an overall increase in microalgal biomass. This response highlights the possibility for climate-induced trophic cascades, driven by altered size structure of populations, rather than species extinction.     

Calcium‐dependent behavioural responses to acute copper exposure in Oncorhynchus mykiss

Using rainbow trout Oncorhynchus mykiss, the present study demonstrated that: (1) calcium (Ca) increased the range of copper (Cu) concentrations that O. mykiss avoided; (2) Ca conserved the maintenance of pre‐exposure swimming activity during inescapable acute (10 min) Cu exposure. Data showed that when presented with a choice of Cu‐contaminated water (ranging from 0 to 454 µg Cu l^?1) and uncontaminated water in a choice tank, O. mykiss acclimated and tested at low Ca concentration (3 mg Ca l^?1) avoided the 10 µg Cu l^?1 only. By contrast, O. mykiss acclimated and tested at high Ca concentration (158 mg Ca l^?1) avoided all the Cu concentrations ≥37 µg l^?1. The Cu avoidance was connected with increased spontaneous swimming speed in the Cu‐contaminated water. When subjected to inescapable Cu exposure (35 µg Cu l^?1), O. mykiss acclimated and tested at low Ca concentration reduced their spontaneous swimming speed, whereas no response was observed in O. mykiss acclimated and tested at high Ca concentration. Collectively, the data support the conclusion that in O. mykiss the behavioural responses to acute Cu exposure are Ca‐dependent.     

The red alga Bonnemaisonia asparagoides regulates epiphytic bacterial abundance and community composition by chemical defence

Ecological research on algal-derived metabolites with antimicrobial activity has recently received increased attention and is no longer only aimed at identifying novel natural compounds with potential use in applied perspectives. Despite this progress, few studies have so far demonstrated ecologically relevant antimicrobial roles of algal metabolites, and even fewer have utilized molecular tools to investigate the effects of these metabolites on the natural community composition of bacteria. In this study, we investigated whether the red alga Bonnemaisonia asparagoides is chemically defended against bacterial colonization of its surface by extracting surface-associated secondary metabolites and testing their antibacterial effects. Furthermore, we compared the associated bacterial abundance and community composition between B. asparagoides and two coexisting macroalgae. Surface extracts tested at natural concentrations had broad-spectrum effects on the growth of ecologically relevant bacteria, and consistent with this antibacterial activity, natural populations of B. asparagoides had significantly lower densities of epibacteria compared with the coexisting algae. Terminal restriction fragment length polymorphism analysis further showed that B. asparagoides harboured surface-associated bacteria with a community composition that was significantly different from those on coexisting macroalgae. Altogether, these findings demonstrate that B. asparagoides produces surface-bound antibacterial compounds with a significant impact on the abundance and composition of the associated bacterial community.     

Investigations on cephalosporin C adsorption kinetics and equilibria

Summary The kinetics and equilibria of cephalosporin C adsorption on different commercial adsorbents were investigated. Adsorption isotherms could be analysed according to the Brunauer, Emmett and Teller theory. For the interpretation of adsorption kinetics it was necessary to develop a more complex model comprising both a rapid and a slower step. An integrated approach combining kinetics and equilibria allowed for simulation of the experimental data and can be used as a basis for predicting technical approaches such as fluidized-bed technology.Dedicated to Professor F. Wagner on the occasion of his 60th birthdayOffprint requests to: K. Buchholz