Abstract

Warming can have dramatic effects on plant phenology and reproduction, with important consequences for reproductive output, plant survivorship, or species dispersal. In seagrasses, vegetative growth through clonal expansion is generally the dominant strategy for meadow maintenance, expansion and recovery, with sexual reproduction strongly differing amongst species, being rare for some, and some times associated with disturbance. Even rarer is the occurrence of pseudovivipary, an uncommon phenomenon in the plant realm, which has only been reported twice before in the marine environment as highly localized phenomena associated with environmental stress. Pseudovivipary is an asexual reproduction strategy whereby plantlets replace sexual reproductive structures, leading to the maintenance of the maternal clones. In summer of 2022, the Mediterranean Sea underwent unprecedented warming, and, associated with it, we observed extensive flowering (100% of sites) as well as pseudovivipary across numerous (>85 % of 36 sites) Posidonia oceanica meadows along the Balearic Islands. Our results support the notion that P. oceanica flowering is triggered under high warming but also, and importantly, this is the first time ever that pseudovivipary is reported across so many locations in a marine plant, and the fate of these plantlets is being monitored by assessing development, survivorship and dispersal through time. Considering the negative impacts that warming can have on seagrass ecosystems, the discovery of widespread pseudovivipary is a critical aspect to consider for understanding mechanisms of resilience in seagrasses.

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