Host starvation and in hospite degradation of algal symbionts shape the heat stress response of the Cassiopea-Symbiodiniaceae symbiosis.

Background: Global warming is causing large-scale disruption of cnidarian-Symbiodiniaceae symbioses fundamental to major marine ecosystems, such as coral reefs. However, the mechanisms by which heat stress perturbs these symbiotic partnerships remain poorly understood. In this context, the upside-down jellyfish Cassiopea has emerged as a powerful experimental model system.

Symbiotic nutrient exchange enhances the long-term survival of cassiosomes, the autonomous stinging-cell structures of .

Medusae of the widely distributed upside-down jellyfish release autonomous, mobile stinging structures. These so-called cassiosomes play a role in predator defense and prey capture, and are major contributors to "contactless" stinging incidents in (sub-)tropical shallow waters. While the presence of endosymbiotic dinoflagellates in cassiosomes has previously been observed, their potential contribution to the metabolism and long-term survival of cassiosomes is unknown.

Assessment of temperature optimum signatures of corals at both latitudinal extremes of the Red Sea.

Rising ocean temperatures are pushing reef-building corals beyond their temperature optima ( ), resulting in reduced physiological performances and increased risk of bleaching. Identifying refugia with thermally resistant corals and understanding their thermal adaptation strategy is therefore urgent to guide conservation actions. The Gulf of Aqaba (GoA, northern Red Sea) is considered a climate refuge, hosting corals that may originate from populations selected for thermal resistance in the warmer waters of the Gulf of Tadjoura (GoT, entrance to the Red Sea and 2000 km south of the GoA).

Elevated temperatures reduce the resilience of the Red Sea branching coral stylophora pistillata to copper pollution.

Copper (Cu) is a common marine pollutant of coastal environments and can cause severe impacts on coral organisms. To date, only a few studies assessed the effects of Cu contamination in combination with elevated seawater temperatures on corals. Furthermore, experiments focusing on coral recovery during a depuration phase, and under thermal stress, are lacking.

Contrasting heat stress response patterns of coral holobionts across the Red Sea suggest distinct mechanisms of thermal tolerance.

Corals from the northern Red Sea, in particular the Gulf of Aqaba (GoA), have exceptionally high bleaching thresholds approaching >5℃ above their maximum monthly mean (MMM) temperatures. These elevated thresholds are thought to be due to historical selection, as corals passed through the warmer Southern Red Sea during recolonization from the Arabian Sea. To test this hypothesis, we determined thermal tolerance thresholds of GoA versus central Red Sea (CRS) Stylophora pistillata corals using multi-temperature acute thermal stress assays to determine thermal thresholds.

Fast and pervasive transcriptomic resilience and acclimation of extremely heat-tolerant coral holobionts from the northern Red Sea.

Corals from the northern Red Sea and Gulf of Aqaba exhibit extreme thermal tolerance. To examine the underlying gene expression dynamics, we exposed from the Gulf of Aqaba to short-term (hours) and long-term (weeks) heat stress with peak seawater temperatures ranging from their maximum monthly mean of 27 °C (baseline) to 29.5 °C, 32 °C, and 34.

Recovery assessment of the branching coral Stylophora pistillata following copper contamination and depuration.

Most contemporary coral reefs live under both global (e.g. warming and acidification) and local (e.

A method to disentangle and quantify host anabolic turnover in photosymbiotic holobionts with subcellular resolution.

A wide range of organisms host photosynthesizing symbionts. In these animals the metabolic exchange between host and symbionts has prevented in situ host anabolic turnover to be studied without the confounding effect of translocated photosynthates. Using the symbiotic coral Stylophora pistillata as a model organism and [1-C]-pyruvate and [2,3-C]-pyruvate in different incubation conditions (light, light + DCMU, and darkness), we employed NanoSIMS isotopic imaging to quantify host anabolism, with and without translocated metabolites from their photosynthesizing dinoflagellate symbionts.