Bayesian Network Analysis reveals resilience of the jellyfish Aurelia aurita to an Irish Sea regime shift

Robust time-series of direct observations of jellyfish abundance are not available for many ecosystems, leaving it difficult to determine changes in jellyfish abundance, the possible causes (e.g. climate change) or the consequences (e.g. trophic cascades). We sought an indirect ecological route to reconstruct jellyfish abundance in the Irish Sea: since zooplankton are jellyfish prey, historic variability in zooplankton communities may provide proxies for jellyfish abundance. We determined the Bayesian ecological network of jellyfish–zooplankton dependencies using jellyfish- and zooplankton-abundance data obtained using nets during a 2-week cruise to the Irish Sea in 2008. This network revealed that Aurelia aurita abundance was dependent on zooplankton groups Warm Temperate and Temperate Oceanic as defined by previous zooplankton ecology work. We then determined historic zooplankton networks across the Irish Sea from abundance data from Continuous Plankton Recorder surveys conducted between 1970 and 2000. Transposing the 2008 spatial dependencies onto the historic networks revealed that Aurelia abundance was more strongly dependent over time on sea surface temperature than on the zooplankton community. The generalist predatory abilities of Aurelia may have insulated this jellyfish over the 1985 regime shift when zooplankton composition in the Irish Sea changed abruptly, and also help explain its globally widespread distribution.

Marmara Denizi’nde Deniz Salyası/Müsilajı Oluşturan Sebepler

Jelimsi canlılar veya denizanaları yüksek düzeyde bozulmuş sistemlerin göstergeleri olarak kabul edilmesine rağmen, organik madde ve mikro planktonun filtrasyonundan trofik seviyenin üst segmentlerine kadar önemli rol oynadıklarından, pelajik sistemin anahtar türleridir. Genel olarak ani ve aşırı artışları, ötrafikasyonu, kıyı dolgusu, avcılık gibi yerel ekosistem dengelerinin ani bozulması yanı sıra, iklim değişikliğine bağlı olarak tür dağılımının genişlemesi ve üreme potansiyelinin artışı ile de ilişkilendirilmektedir. Yerli olmayan jelimsi türlerin bozulmuş ekosistemlere kazara girmesi, aşırı çoğalarak ciddi sonuçlara neden olabilir. Bunu 2007’de Liriope tetraphylla türlerinin oluşturduğu ekosistem hasarı ile gördük. Günümüzde pelajik sistemin tekrar çökmesinde ise yerler türler rol oynamıştır. Yerli türlerin aşırı artışlarında rol oynayan ana etken küçük pelajik üzerindeki aşırı avcılık baskısı ve besin bolluğudur. 2018’de kaydedilen aşırı avcılığın ardından, Marmara Denizi’nde önce Salpa kolonileri ardında Rhizostoma pulmo ve Aurelia aurita türlerinde aşırı artışlar, fitoplankton ve zooplankton yoğunluğunda ise belirgin düşüş gözleniyor. Sonuç olarak, plankton üstünden beslenen balık türleri tür çekilince yerini yine plankton üstünde beslenen jelimsi canlılar alıyor. Kasım aralık ayında balıkçıların salya dedikleri oluşum başlıyor ve ardından yoğun nanoplankton çoğalması izleniyor. Böylece Marmara Denizi pelajik sistem besin akışı tamamen değişiyor. Yapılan aylık gözlemlemelerde musilaj oluşumunu tetikleyen sistemin ortamdaki jelimsi canlıların artışı ile kuvvetli ilişkisi vardır.

Shorter, warmer winters may inhibit production of ephyrae in a population of the moon jellyfish Aurelia aurita

Scyphozoan jellyfish blooms display high interannual variability in terms of timing of appearance and size of the bloom. To understand the causes of this variability, the conditions experienced by the polyps prior to the production of ephyrae in the spring were examined. Polyps reared from planula larvae of Aurelia aurita medusae collected from southern England (50°49′58.8; − 1°05′36.9) were incubated under orthogonal combinations of temperature (4, 7, 10 °C) and duration (2, 4, 6, 8 weeks), representing the range of winter conditions in that region, before experiencing an increase to 13 °C. Timing and success of strobilation were recorded. No significant production of ephyrae was observed in any of the 2- and 4-week incubations, or in any 10 °C incubation. Time to first ephyra release decreased with longer winter incubations, and more ephyrae were produced following longer and colder winter simulations. This experiment indicates that A. aurita requires a minimum period of cooler temperatures to strobilate, and contradicts claims that jellyfish populations will be more prevalent in warming oceans, specifically in the context of warmer winter conditions. Such investigations on population-specific ontogeny highlights the need to examine each life stage separately as well as in the context of its environment.

The Native Microbiome is Crucial for Offspring Generation and Fitness of Aurelia Aurita

ABSTRACT All multicellular organisms are associated with microbial communities, ultimately forming a metaorganism. Several studies conducted on well-established model organisms point to immunological, metabolic, and behavioral benefits of the associated microbiota for the host. Consequently, a microbiome can influence the physiology of a host; moreover, microbial community shifts can affect host health and fitness. The present study aimed to evaluate the significance and functional role of the native microbiota for life cycle transitions and fitness of the cnidarian moon jellyfish Aurelia aurita. A comprehensive host fitness experiment was conducted studying the polyp life stage and integrating 12 combinations of treatments with microbiota modification (sterile conditions, foreign food bacteria, and potential pathogens). Asexual reproduction, e.g., generation of daughter polyps, and the formation and release of ephyrae were highly affected in the absence of the native microbiota, ultimately resulting in a halt of strobilation and ephyra release. Assessment of further fitness traits showed that health, growth, and feeding rate were decreased in the absence and upon community changes of the native microbiota, e.g., when challenged with selected bacteria. Moreover, changes in microbial community patterns were detected by 16S rRNA amplicon sequencing during the course of the experiment. This demonstrated that six operational taxonomic units (OTUs) significantly correlated and explained up to 97% of fitness data variability, strongly supporting the association of impaired fitness with the absence/presence of specific bacteria. Conclusively, our study provides new insights into the importance and function of the microbiome for asexual reproduction, health, and fitness of the basal metazoan A. aurita. IMPORTANCE All multicellular organisms are associated with a diverse and specific community of microorganisms; consequently, the microbiome is of fundamental importance for health and fitness of the multicellular host. However, studies on microbiome contribution to host fitness are in their infancy, in particular, for less well-established hosts such as the moon jellyfish Aurelia aurita. Here, we studied the impact of the native microbiome on the asexual reproduction and on further fitness traits (health, growth, and feeding) of the basal metazoan due to induced changes in its microbiome. We observed significant impact on all fitness traits analyzed, in particular, in the absence of the protective microbial shield and when challenged with marine potentially pathogenic bacterial isolates. Notable is the identified crucial importance of the native microbiome for the generation of offspring, consequently affecting life cycle decisions. Thus, we conclude that the microbiome is essential for the maintenance of a healthy metaorganism.