ALBERT

Description: We quantify the long-term predictability of global mean daily temperature data by means of the Rényi entropy of second order K2. We are interested in the yearly amplitude fluctuations of the temperature. Hence, the data are low-pass filtered. The obtained oscillatory signal has a more or less constant frequency, depending on the geographical coordinates, but its amplitude fluctuates irregularly. Our estimate of K2 quantifies the complexity of these amplitude fluctuations. We compare the results obtained for the CRU data set (interpolated measured temperature in the years 1901-2003 with 0.5° resolution, Mitchell et al., 2005)with the ones obtained for the temperature data from a coupled ocean-atmosphere global circulation model (AOGCM, calculated at DKRZ). Furthermore, we compare the results obtained by means of K2 with the linear variance of the temperature data.

Description: Macroalgae can defend themselves against generalist and specialist herbivores via morphological and/or chemical traits. Herein we examined the defensive responses (via relative palatability) of two brown (Lessonia nigrescens, Glossophora kunthii) and two red algae (Grateloupia doryphora, Chondracanthus chamissoi) from the northern-central coast of Chile against selected generalist meso-herbivores. Two laboratory experiments were conducted to investigate whether (i) algae can respond generally to grazing pressure of meso-herbivores (amphipods, isopods and juvenile sea urchins) and whether (ii) these algal responses were inducible. In order to examine palatability and thus effectiveness of responses, feeding assays were run after each experiment using fresh algal pieces and artificial agar-based food. Lessonia nigrescens responded to amphipods but not to sea urchins, and G. kunthii showed inducible response against one species of amphipods. Grateloupia doryphora did not respond against any of the tested grazers, whereas C. chamissoi responded against one species of amphipods and the tested isopod. Our results indicate variable responses of macroalgae against selected generalist meso-herbivores and evidence of an inducible defense in the brown alga G. kunthii.

Description: Rafting of marine and terrestrial organisms has been reported from a variety of substrata and from all major oceans of the world. Herein we present information on common rafting organisms and on ecological interactions during rafting voyages. An extensive literature review revealed a total of 1206 organisms, for which rafting was confirmed or inferred based on distributional or genetic evidence. Rafting organisms comprised cyanobacteria, algae, protists, invertebrates from most marine but also terrestrial phyla, and even a few terrestrial vertebrates. Marine hydrozoans, bryozoans, crustaceans and gastropods were the most common taxa that had been observed rafting. All major feeding types were represented among rafters, being dominated by grazing/boring and suspension-feeding organisms, which occurred on all floating substrata. Besides these principal trophic groups, predators/scavengers and detritus-feeders were also reported. Motility of rafting organisms was highest on macroalgae and lowest on abiotic substrata such as plastics and volcanic pumice. Important trends were revealed for the reproductive biology of rafting organisms. A high proportion of clonal organisms (Cnidaria and Bryozoa) featured asexual reproduction, often in combination with sexual reproduction. Almost all rafting organisms have internal fertilisation, which may be due to the fact that gamete concentrations in the rafting environment are too low for successful fertilisation of external fertilisers. Following fertilisation, many rafting organisms incubate their offspring in/on their body or deposit embryos in egg masses on rafts. Local recruitment, where offspring settle in the immediate vicinity of parents, is considered an important advantage for establishing persistent local populations on a raft, or in new habitats. Some organisms are obligate rafters, spending their entire life cycle on a raft, but the large majority of reported rafters are considered facultative rafters. These organisms typically live in benthic (or terrestrial) habitats, but may become dispersed while being confined to a floating item. Substratum characteristics (complexity, surface, size) have important effects on the composition of the rafting community. While at sea, ecological interactions (facilitation, competition, predation) contribute to the community succession on rafts. Organisms capable to compete for and exploit resources on a raft (space and food) will be able to persist throughout community succession. The duration of rafting voyages is closely related to rafting distances, which may cover various geographical scales. In chronological order, three features of an organism gain in importance during rafting, these being ability to (1) hold onto floating items, (2) establish and compete successfully, and (3) develop persistent local populations during a long voyage. Small organisms that do not feed on their floating substratum and with asexual reproduction or direct development combine all these features, and appear to be most suited for long-distance dispersal on rafts and successful colonisation after reaching new habitats. All available evidence suggests that rafting is an important process for the population dynamics of many organisms and that it also has had and continues to have a strong influence on coastal biodiversity.

Description: Epipelagic transport (or rafting) was introduced as a dispersal mechanism for marine species. Rafting is the passive dispersal of organisms on objects floating at the sea surface. It is particularly important for species that lack a natural capacity for efficient dispersal such as species without extended planktonic larval development. The requirements rafting organisms have to cope with during their epipelagic journey were briefly discussed. The capabilities of holding on to a floating object, obtaining food, reproducing during the journey, and persisting in competition with other rafting species are decisive for the success of an organism in being dispersed via rafting.Historical changes in rafting opportunities have increased the importance of rafting as dispersal mechanism significantly. Naturally occurring rafts such as floating macroalgae, wood and pumice have become supplemented over the last decades by a dramatically increasing abundance of anthropogenic objects such as plastics and floating tar balls. Especially the advent of plastics in the marine environment was revolutionary for the efficiency of rafting. High densities of plastic objects in the worlds oceans have increased the frequency of rafting events. Due to their high resistance against natural degradation these objects allow for a transport of associated rafters over large distances. Consequently, the probability of introductions of non-indigenous species via rafting has increased significantly.The potential of rafting to introduce alien species has been demonstrated by examples of several non-indigenous peracarid species that were collected from floating objects in the North Sea. These species were of southern origin indicating that the severe temperature regime of the North Sea was responsible for their former absence from that region. However, a substantial increase in mean winter water temperatures observed since the 1990s probably allowed for a successful colonization. Furthermore, strong westerly winds in the North Atlantic region as a consequence of a consistently positive North Atlantic Oscillation Index probably favored the introduction of rafting species into the North Sea.These examples demonstrate that increasing rafting opportunities together with changing environmental conditions as they are expected from global climate change provide a powerful combination that potentially leads to range expansions of marine species.The North Sea is considered to be one of the best investigated marine areas in the world. However, in contrast to other regions such as the Mediterranean no information exist about the amount of flotsam of both natural and anthropogenic origin in that region. The monitoring of floating objects and associated rafters is highly recommended. Early observations of species introductions might help to evaluate and forecast consequences for native communities and to develop efficient management strategies.