ALBERT

Description: The invertebrate immune system comprises physiological mechanisms, physical barriers and also behavioral responses. It is generally related to the vertebrate innate immune system and widely believed to provide...

Description: In 1956, the shallow-water grouper Cephalopholis argus was introduced from Moorea (French Polynesia), where grouper diversity (14 species) is high, to the Main Hawaiian Islands (MHI), where only 2 rare native deep-water groupers occur. In this non-native environment, the species has flourished and has become the dominant apex predator on many reefs. In the present study, a comparison of non-native populations of C. argus in the MHI with native populations in Moorea showed that mean total length (32.0 vs. 26.9 cm), mass (722 vs. 326 g), growth, and body condition were each significantly elevated in the MHI. In addition, while an ontogenetic shift towards larger prey occurred in both locations, it was faster and more consistent in Moorea than in the MHI. As a result, while small C. argus of comparable size in the 2 locations consumed similar-sized prey, large C. argus in Moorea consumed significantly longer and deeper-bodied prey than their counterparts in the MHI. This pattern was unrelated to the size distributions of available prey and may thus reflect stronger intra- and interspecific competition for small prey in Moorea. Although ecological release in a broader sense (i.e. a combination of predator release, parasite release, and competitive release) may play a role, the most direct explanation for the observed differences between C. argus in native habitats in Moorea (with many competing grouper species) and non-native habitats in the MHI (few competitors) would be competitive release (here used in the sense of benefits resulting from the reduction of interspecific competition).

Description: The maraena whitefish Coregonus maraena is a threatened anadromous species in the North Sea, which in the past was decimated to near extinction. Since the late 1980s, several re-establishment programs have been implemented in rivers draining into the North Sea, but the scientific basis for sustainable conservation measures is often lacking, since little is known about the biology of this species. In this study, otolith microchemistry of fish ranging from 24.6 to 58.4 cm in total length (median 31.3 cm, SD 8.4 cm) was used to characterize the migration behavior of a reintroduced population of maraena whitefish from the River Elbe, Germany. Our analyses revealed the presence of 3 different migration patterns: (1) one-time migration into high-salinity habitat (North Sea) within the first year of life (29.6%), (2) multiple migrations between lowland high-salinity habitats starting in the first year of life (14.8%) and (3) permanent residency within low-salinity habitats, a pattern displayed by the majority (55.6%) of sampled individuals. Not only do these results reveal differential migration behavior, but they also indicate that permanent river residency is common in the River Elbe population of C. maraena. The role of the Elbe as both a feeding and a spawning habitat should thus be considered more explicitly in current conservation measures to support recovery of this species.

Description: The exploitation of marine resources has caused drastic declines of many large predatory fishes. Amongst these, sharks are of major conservation concern due to their high vulnerability to overfishing and their ecological role as top predators. The 2 protected and endangered shark species tope Galeorhinus galeus and smooth hammerhead Sphyrna zygaena use overlapping coastal areas around the globe as essential fish habitats, but data to assess their trophic ecology and niche partitioning are scarce. We provide the first comparative assessment of the trophic ecology, ontogenetic shifts, and niche partitioning of the co-occurring tope and juvenile smooth hammerhead around the Azores Islands, mid-north Atlantic, based on delta 13C, delta 15N, and delta 34S (CNS) stable isotope analysis of muscle tissue of the sharks and their putative prey species. Overall, isotopic niches of both species indicated a reliance on similar resources throughout the sampled sizes (tope: 35-190; smooth hammerhead 54-159 cm total length), with significant ontogenetic shifts. Topes displayed a gradual shift to higher trophic levels and a more generalist diet with increasing size (increasing delta 15N values and isotopic niche volumes, respectively), whereas smooth hammerhead diet shifted towards prey with lower delta 34S at a constant trophic level and a more specialized diet than tope of comparable body size (decreasing delta 34S and constant delta 15N and delta 13C values, respectively). Our results indicate contrasting ontogenetic shifts in delta 13C and delta 34S along with pronounced differences between niche overlap of life stages pointing to intra- and interspecific niche partitioning of habitat and prey.