Posidonia fruits arrive earlier than expected!
02/28/2023 Posidonia oceanica is a marine plant unique in the Mediterranean Sea. It forms underwater meadows on our coasts and provides important benefits: they contribute to fisheries, keep waters clean, and act as a carbon sink, among others. Unfortunately, this species is not immune to the impacts of human activities, nor does it escape climate change. The extreme marine heat wave last summer, which brought the Mediterranean to temperatures between 4 and 5 ºC higher than usual, was associated with an abundant flowering of Posidonia in many parts of the Spanish Mediterranean coast. Now, this February, Posidonia fruits, also called “sea olives”, are starting to be seing. It is unusually early, since they usually show up in spring. The abundant flowering and the advance in the formation of fruits could indicate that the warming of the sea has altered the reproduction patterns of Posidonia. To better understand this phenomenon, you can contribute to research by sending observations of Posidonia oceanica fruits to the Seagrass in Reproduction project. HOW TO COLLABORATE? If you are in an area with Posidonia oceanica, look for its fruits! Download and use this guide to better quantify them. Upload your observations to the project Seagrass in Reproduction . If you are in Mallorca, notify their presence to as soon as possible! The scientific team will take the fruits to analyze them in the laboratory with greater precision. We encourage you to collaborate! The reproduction of Posidonia oceanica Although this marine plant can reproduce sexually with flowers and fruits (as terrestrial plants commonly do), this sexual reproduction is generally rare, and the colonization of the substratum is carried out mainly by vegetative growth (asexual reproduction), thanks to the growth and expansion of the rhizomes, that is, the underground stems. However, nowadays it is more common to observe the flowering of Posidonia. In the last decades, episodes of massive blooming have been observed related to water warming, especially with “marine heat waves” events. The flowers that reproduce successfully create fruits, known as "sea olives", which detach and float when ripe, allowing the species to expand to other possibly more favorable areas. Also, as a result of sexual reproduction, the formation of fruits increases the genetic diversity of populations, which favors the adaptation of the species to new environmental conditions. Therefore, the activation of sexual reproduction associated with marine heat waves is interpreted as a response to environmental stress, and may serve to increase the chances of success of the species. The effect of marine heat waves In summer of 2022, the Mediterranean Sea experienced the most severe marine heat wave experienced since 2003, with some parts of the Western Mediterranean experiencing temperatures up to 5ºC higher than usual. Taking into account the intensity of the latest marine heat wave and the flowering observed, the arrival of abundant fruits could be the expected outcome. However, it is still uncertain if this stress can cause other effects, such as changing the maturation patterns of the fruits, or reducing reproductive success. Thus, in order to understand the consequences that warming may have on this iconic Mediterranean species, it is very important to be able to quantify these patterns of fruit production. Citizen collaboration is essential for this, because, as the fruits float, many times they reach the sandbanks of the beaches, where they are very easy to observe. In fact, in Mallorca they have already begun to observe important arrivals of fruits, when the most common thing is to observe them in spring. Thus, it could be that warming has altered the reproduction patterns of Posidonia, and citizen collaboration is necessary to investigate it.