ALBERT

Beschreibung: Calcium carbonate minerals produced by marine organisms play a central role in the global carbon cycle and carbonate sedimentation, which influence the climate by regulating atmospheric CO2 levels. Foraminifera are important marine single-celled organisms that have produced calcite shells for over 300 million years. Here, we present new observations promoting our understanding for foraminiferal biocalcification by studying Amphistegina lessonii. We integrated in vivo confocal autofluorescence and dye fluorescence imaging with elemental analysis of the cell supporting the concept that the calcite shells of foraminifera are produced via deposition of intracellularly formed Mg-rich amorphous calcium carbonate (Mg-ACC) particles that transform into a stable mineral phase. This process is likely accompanied by the activity of endosymbiotic microalgae and seawater-derived endocytic vesicles that provide calcification substrates such as DIC, Ca2+, and Mg2+. The final transformation of semi-liquid amorphous nanoparticles into a crystalline shell was associated with Mg2+ liberation.

Beschreibung: 〈jats:p〉Sexually produced juvenile scleractinian corals play a key role in the adaptation process of coral reefs, as they are considered to possess an innate plasticity and thus can adjust to changing environmental parameters within a certain range. In this study we investigated in detail the early life stages of the brooding species 〈jats:italic〉Leptastrea purpurea〈/jats:italic〉 to identify, categorize and visualize the critical steps of the complex transformation process from a swimming coral larva to a sessile coral recruit and later to a coral colony. For that, we performed settlement experiments using previously known cues: cycloprodigiosin (CYPRO) and crustose coralline algae (CCA) as well as novel cues: crude extracts of 〈jats:italic〉Pseudoalteromonas espejiana〈/jats:italic〉 and 〈jats:italic〉P. piscicida〈/jats:italic〉 to identify a general, cue-independent settlement pathway. We monitored the development of 〈jats:italic〉L. purpurea〈/jats:italic〉 over 12 months using bright field and fluorescence microscopy. Also we identified the fluorescence signals of 〈jats:italic〉L. purpurea〈/jats:italic〉 with confocal microscopy at four crucial development steps: (A) swimming larva, (B) metamorphosing larva, (C) coral recruit and (D) adult coral. Our methodological approach allowed us to observe an ontogenetic shift of fluorescence signals which provokes the hypothesis that certain fluorescence patterns might be connected to distinct sequential functions in the early life cycle of scleractinian corals. Our observations showed great similarities to the early development of other brooding and spawning corals, making 〈jats:italic〉L. purpurea〈/jats:italic〉 a prospective candidate to be used as a model organism for coral research. Furthermore, our in-depth picture series provides a robust monitoring reference for coral nurseries or field applications and demonstrates the potential of fluorescence as an indicator to instantly determine the growth stage of a developing coral recruit.〈/jats:p〉

Beschreibung: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉The global degradation of coral reefs is steadily increasing with ongoing climate change. Yet coral larvae settlement, a key mechanism of coral population rejuvenation and recovery, is largely understudied. Here, we show how the lipophilic, settlement-inducing bacterial pigment cycloprodigiosin (CYPRO) is actively harvested and subsequently enriched along the ectoderm of larvae of the scleractinian coral 〈jats:italic〉Leptastrea purpura〈/jats:italic〉. A light-dependent reaction transforms the CYPRO molecules through photolytic decomposition and provides a constant supply of hydrogen peroxide (H〈jats:sub〉2〈/jats:sub〉O〈jats:sub〉2〈/jats:sub〉), leading to attachment on the substrate and metamorphosis into a coral recruit. Micromolar concentrations of H〈jats:sub〉2〈/jats:sub〉O〈jats:sub〉2〈/jats:sub〉 in seawater also resulted in rapid metamorphosis, but without prior larval attachment. We propose that the morphogen CYPRO is responsible for initiating attachment while simultaneously acting as a molecular generator for the comprehensive metamorphosis of pelagic larvae. Ultimately, our approach opens a novel mechanistic dimension to the study of chemical signaling in coral settlement and provides unprecedented insights into the role of infochemicals in cross-kingdom interactions.〈/jats:p〉

Beschreibung: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉The close association between animals and their associated microbiota is usually beneficial for both partners. Here, we used a simple marine model invertebrate, the flatworm 〈jats:italic〉Macrostomum lignano〈/jats:italic〉, to characterize the host-microbiota interaction in detail. This analysis revealed that the different developmental stages each harbor a specific microbiota. Studies with gnotobiotic animals clarified the physiological significance of the microbiota. While no fitness benefits were mediated by the microbiota when food was freely available, animals with microbiota showed significantly increased fitness with a reduced food supply. The microbiota of 〈jats:italic〉M. lignano〈/jats:italic〉 shows circadian rhythmicity, affecting both the total bacterial load and the behavior of specific taxa. Moreover, the presence of the worm influences the composition of the bacterial consortia in the environment. In summary, the 〈jats:italic〉Macrostomum〈/jats:italic〉-microbiota system described here can serve as a general model for host-microbe interactions in marine invertebrates.〈/jats:p〉