No abstract

Ocean warming (OW), ocean acidification (OA) and their interaction with local drivers, e.g., copper pollution, may negatively affect macroalgae and their microscopic life stages. We evaluated meiospore development of the kelps Macrocystis pyrifera and Undaria pinnatifida exposed to a factorial combination of current and 2100-predicted temperature (12 and 16 °C, respectively), pH (8.16 and 7.65, respectively), and two copper levels (no-added-copper and species-specific germination Cu-EC50). Meiospore germination for both species declined by 5–18% under OA and ambient temperature/OA conditions, irrespective of copper exposure. Germling growth rate declined by >40%·day−1, and gametophyte development was inhibited under Cu-EC50 exposure, compared to the no-added-copper treatment, irrespective of pH and temperature. Following the removal of copper and 9-day recovery under respective pH and temperature treatments, germling growth rates increased by 8–18%·day−1. The exception was U. pinnatifida under OW/OA, where growth rate remained at 10%·day−1 before and after copper exposure. Copper-binding ligand concentrations were higher in copper-exposed cultures of both species, suggesting that ligands may act as a defence mechanism of kelp early life stages against copper toxicity. Our study demonstrated that copper pollution is more important than global climate drivers in controlling meiospore development in kelps as it disrupts the completion of their life cycle.

No abstract

For the cold-water corals (CWC), living in the deep and dark ocean, heterotrophs are the key microbiome partners of the host. The role of the CWC microbiome and the type of association to the host remain however poorly known. In this paper we tested whether diet shapes the composition of the bacterial community associated to the two most common cold water coral species: L. pertusa and M. oculata. We demonstrate that a large portion of the corals" bacterial community represents a food influenced microbiome. The differences between diets were seen in terms of beta diversity, richness, individual OTU dynamics and coral metabolisms (energy reserves). The microbiomes remained, however, species-specific independently of the diet, which suggest that the niche offered to the microbes by the host also shapes community composition. This study, which is the first to test the effect of diet on coral microbiomes, casts a new light on coral microbial ecology by showing that the coral specific bacterial communities should also be considered as a food influenced microbiome. This result is important and will certainly inspire further research on CWC but also on tropical coral microbiomes.