The green macroalga Caulerpa lentillifera (sea grapes, green caviar) is a promising source for future nutrition due to its beneficial composition for human consumption. It is cultured in tidal ponds, mainly in Vietnam and the Philippines, and stored for shipment and retail in plastic containers, like polystyrene (PS) and polyethylene terephthalate (PET), exhibiting different properties. This study investigates the influence of irradiances on the physiology of sea grapes under culture and packaging ambience in PET using pulse-amplitude modulated (PAM) fluorometry. Fv/Fm values of C. lentillifera significantly decreased < 0.54 ± 0.06 standard deviation (SD) after 7 days of culture under 100 μmol photons m−2 s−1, but with the potential of recovery. In packaging ambience in the state of desiccation, sea grapes exposed to room irradiances (3 μmol photons m−2 s−1) for 12 days were still physiologically in a good condition (Fv/Fm = 0.70 ± 0.06). However, 12 days under irradiances of 70 μmol photons m−2 s−1 leads to decreased Fv/Fm (0.42 ± 0.11) and a moisture content of 88.2 ± 3.3% of initial. After re-immersion in sea water under room irradiances, Fv/Fm values recovered to a certain degree. In darkness, desiccation was followed by a decrease of Fv/Fm to 0.09 ± 0.19 and moisture content of 49.3 ± 20.2% of initial with no recovery after re-immersion under room irradiances. Results suggest shading of C. lentillifera in pond culture and PET containers as suitable packaging for sea grapes, but a dim light source should be provided during storage.

The resistance of hard corals to warming can be negatively affected by nitrate eutrophication, but related knowledge for soft corals is scarce. We thus investigated the ecophysiological response of the pulsating soft coral Xenia umbellata to different levels of nitrate eutrophication (control = 0.6, medium = 6, high = 37 μM nitrate) in a laboratory experiment, with additional warming (27.7 to 32.8 °C) from days 17 to 37. High nitrate eutrophication enhanced cellular chlorophyll a content of Symbiodiniaceae by 168%, while it reduced gross photosynthesis by 56%. After additional warming, polyp pulsation rate was reduced by 100% in both nitrate eutrophication treatments, and additional polyp loss of 7% d−1 and total fragment mortality of 26% was observed in the high nitrate eutrophication treatment. Warming alone did not affect any of the investigated response parameters. These results suggest that X. umbellata exhibits resistance to warming, which may facilitate ecological dominance over some hard corals as ocean temperatures warm, though a clear negative physiological response occurs when combined with nitrate eutrophication. This study thus confirms the importance of investigating combinations of global and local factors to understand and manage changing coral reefs.

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The clownfish-anemone association exemplifies a symbiosis where both members benefit from nutrient exchange and protection from predators. Clownfish also perform aeration-like behaviour in their host anemones at night, but it is not yet known whether this is stimulated by the onset of hypoxia, and whether both members benefit from O2 replenishment. Oxygen at 3 distances above the sea anemone Entacmaea quadricolor (0.2, 1.2 and 2.2 cm) therefore was measured under 3 light levels (photon flux density = 0, 55 and 110 µmol m−2 s−1), with and without the anemonefish Amphiprion frenatus. Hypoxia (O2 < 50% air saturation) was recorded in the anemone, but only at 0.2 cm away from the anemone surface under dark conditions when A. frenatus was absent. This localised layer of hypoxia was eliminated by the presence of A. frenatus exhibiting aeration-like behaviour. Respirometry revealed that A. frenatus is extremely hypoxia tolerant (S crit = 14.3% at 25 °C), suggesting that aeration behaviour does not provide a major metabolic advantage to clownfish because they do not breathe water at 0.2 cm and are not metabolically constrained by O2 at distances ≥ 1.2 cm. That the aeration behaviour of A. frenatus facilitates only the metabolism of its O2-conforming host reveals a unique aspect of this symbiotic relationship.