Behavioural and metabolic adaptations of marine isopods to the rafting life style

Rafting on floating objects is a common dispersal mechanism for many marine invertebrates. In order to identify adaptations to the rafting life style, we compared behavioural and metabolic characteristics of two isopods, the obligate rafter Idotea metallica and the facultative rafter Idotea baltica. In laboratory experiments, I. metallica showed low locomotive activity and a tight association to the substratum. Idotea baltica, in contrast, was more active with more frequent excursions in the surrounding water column. Oxygen consumption rates were similar in both species. Idotea metallica fed on zooplankton making this species widely independent of autochthonous food resources of the raft. Feeding rates and digestive enzyme activities were low in I. metallica. Reduced egestion rates may indicate slow gut passage and, thus, efficient resorption of nutrients. Efficient food utilization and the ability to accumulate high amounts of storage products, i.e. lipids, indicate a possible adaptation of I. metallica to low food availability or starvation. The feeding behaviour of I. baltica, in contrast, was more herbivorous and appeared wasteful and inefficient. Low lipid contents in I. baltica also indicate poor storage reserves. Thus, I. baltica requires a permanent access to food.     

Dietary effects on multi-element composition of European eel (<Emphasis Type="Italic">Anguilla anguilla</Emphasis>) otoliths

Otolith microchemistry is widely used as a tool to track individual migration pathways of diadromous fish under the assumption that the elemental composition of fish otoliths is directly influenced by the physicochemical properties of the surrounding water. Nevertheless, several endogenous factors are reported to affect element incorporation into fish otoliths and might lead to misinterpretations of migration studies. This study experimentally examined the influence of eight different diets on the microchemical composition of European eel (Anguilla anguilla) otoliths using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Seven natural prey types and one artificial diet were fed during 8 weeks in freshwater circuits. Results show for the first time that food has no significant influence on the incorporation of Na, Sr, Ba, Mg, Mn, Cu and Y into European eel otoliths. This indicates that the incorporation of elements usually chosen for migration studies is not affected by diet and that individual feeding behaviour of A. anguilla will not lead to any misinterpretation of migration pathways.     

Annoyance due to aircraft noise has increased over the years—Results of the HYENA study

In the HYENA study (HYpertension and Exposure to Noise near Airports) noise annoyances due to aircraft and road traffic noise were assessed in subjects that lived in the vicinity of 6 major European airports using the 11-point ICBEN scale (International Commission on Biological Effects of Noise). A distinction was made between the annoyance during the day and during the night. L_den and L_night were considered as indicators of noise exposure. Pooled data analyses showed clear exposure–response relationships between the noise level and the noise annoyance for both exposures. The exposure–response curves for road noise were congruent with the EU standard curves used for predicting the number of highly noise annoyed subjects in European communities. Annoyance ratings due to aircraft noise, however, were higher than predicted by the EU standard curves. The data supports other findings suggesting that the people's attitude towards aircraft noise has changed over the years, and that the EU standard curve for aircraft noise should be modified.     

Differences in resource utilization and behaviour between coexisting <Emphasis Type="Italic">Jassa</Emphasis> species (Crustacea,Amphipoda)

Species of the genus Jassa are an important element of marine fouling communities, several species often co-occurring on a wide range of hard substrates. At Helgoland (North Sea, German Bight), the cosmopolitan J. marmorata occurs associated with the NW European species J. falcata and J. herdmani. Field and laboratory experiments revealed some ecological differences among species which may facilitate their coexistence. Test panels in the field were instantly colonized by the complete spectrum of resident Jassa species, but J. marmorata proved clearly superior to its congeners in rapidly colonizing new habitats. Further differences among species relate to microhabitat selection (differential use of peripheral and central parts of algal thalli) and the behavioural response to mechanical disturbance.     

Potential impact of climate warming on the recruitment of an economically and ecologically important species, the European lobster (Homarus gammarus) at Helgoland, North Sea

A laboratory-based study was performed to assess the impact of climate warming on the recruitment of the endangered population of the European lobster (Homarus gammarus) at Helgoland (North Sea, German Bight). Egg-bearing females collected in situ just after spawning in late summer were subjected to various seasonal temperature regimes. Regimes with elevated temperatures (mild winters) resulted in a strong seasonal forward shift of larval hatching. Hatching took place at significantly lower temperatures than under regimes with normal winters. Experiments on larval development across a range of constant temperatures showed that no successful larval development occurred at temperatures below 14°C. Larval survival increased from 9% at 14°C to 80% at 22°C, while duration of larval development decreased correspondingly from 26 to 13 days. We hypothesize that an ongoing warming of the North Sea will strongly affect the recruitment success of the Helgoland lobster, mainly resulting from a decoupling of the seasonal peak appearance of larvae from optimal external conditions (temperature, food availability) for larval development.