Stable Laboratory Culture System for the Ctenophore Mnemiopsis leidyi.

Ctenophores are marine organisms attracting significant attention from evolutionary biology, molecular biology, and ecological research. Here, we describe an easy and affordable setup to maintain a stable culture of the ctenophore Mnemiopsis leidyi. The challenging delicacy of the lobate ctenophores can be met by monitoring the water quality, providing the right nutrition, and adapting the handling and tank set-up to their fragile gelatinous body plan. Following this protocol allows stable laboratory lines, a continuous supply of embryos for molecular biological studies, and independence from population responses to environmental fluctuations.

Gephyrocapsa huxleyi (Emiliania huxleyi) as a model system for coccolithophore biology.

Coccolithophores are the most abundant calcifying organisms in modern oceans and are important primary producers in many marine ecosystems. Their ability to generate a cellular covering of calcium carbonate plates (coccoliths) plays a major role in marine biogeochemistry and the global carbon cycle. Coccolithophores also play an important role in sulfur cycling through the production of the climate-active gas dimethyl sulfide. The primary model organism for coccolithophore research is Emiliania huxleyi, now named Gephyrocapsa huxleyi. G. huxleyi has a cosmopolitan distribution, occupying coastal and oceanic environments across the globe, and is the most abundant coccolithophore in modern oceans. Research in G. huxleyi has identified many aspects of coccolithophore biology, from cell biology to ecological interactions. In this perspective, we summarize the key advances made using G. huxleyi and examine the emerging tools for research in this model organism. We discuss the key steps that need to be taken by the research community to advance G. huxleyi as a model organism and the suitability of other species as models for specific aspects of coccolithophore biology.

Mesoscale oceanographic meanders influence protist community function and structure in the southern Indian Ocean.

The interface between the nutrient-rich Southern Ocean and oligotrophic Indian Ocean creates unique environmental conditions that can strongly influence biological processes. We investigated protist communities across a mesoscale meander of the Subtropical Front within the Southern Indian Ocean. 18S V9 rDNA metabarcoding suggests a diverse protist community in which the dinoflagellates and parasitic Syndiniales were abundant. Diversity was highest in frontal waters of the mesoscale meander, with differences in community structure inside and outside the meander. While the overall community was dominated by mixotrophic taxa, the frontal boundary of the meander had increased abundances of heterotrophic taxa, with potential implications for net atmospheric CO2 drawdown. Pulse amplitude modulated (PAM) fluorimetry revealed significant differences in the photophysiology of phytoplankton communities inside and outside the meander. By using single-cell PAM microscopy, we identified physiological differences between dinoflagellate and coccolithophore taxa, which may have contributed to changes in photophysiology observed at community level. Overall, our results demonstrate that frontal areas have a strong impact on the composition of protist communities in the Southern Ocean with important implications for understanding biological processes in this region.

Novel combination coccospheres from Helicosphaera spp indicate complex relationships between species.

Coccolithophores play an important role in global biogeochemical cycling, but many aspects of their ecology remain poorly understood, including their heteromorphic haplo-diplontic life cycle. The presence of combination coccospheres in environmental samples, which represent a transition between the lightly calcified haploid (HOL) and heavily calcified diploid (HET) life phases, provides crucial evidence linking the two life cycle phases of a particular species. Here, we describe combination coccospheres from the Southern Ocean that show a novel association between Helicosphaera hyalina (HET) and Helicosphaera HOL catilliferus type. The ability of Helicosphaera HET and HOL morphospecies to form multiple different combinations indicates a substantial complexity in the relationships between life cycle phases in this group. The findings suggest recent divergence within the Helicosphaera lineage may have resulted in significant inter- and intra-specific variability, with cryptic speciation in one or both life cycle phases contributing to their ability to form multiple HET/HOL associations.