Surveillance of coastal biodiversity through social network monitoring

Knowledge of marine biodiversity is vital for developing appropriate conservation policies. In the current Information Age, data shared by citizens in social networks are a cost-effective alternative to complement on-going marine biodiversity monitoring programs, as well as to understand human interactions with the natural environment from a current perspective. This information can be obtained in a transparent way to the citizen (passive citizen science approach) after sharing relevant content such as: rare catches of recreational fishermen, sightings of invasive species, stranding of cetaceans, sea turtle entanglements, episodes of massive arrival of jellyfish or interactions between organisms, among others. This study has analyzed the content posted on the social networking site X (formerly known as Twitter) from its launch in 2007 to 2022, focusing on those posts that apparently reported a biodiversity observation along the Spanish coast. To avoid an initial bias, generic messages asking "who knows" or if "anyone knows" what they have found were captured, as well as messages stating that they had found something interesting. After retrieving ~11 K tweets with potential information, 597 tweets were finally identified after human validation. Most of the observations (21%) corresponded to gelatinous animals, with observations of fish (11%) and marine mammals (11%) also being frequent. 57% of these tweets were adequately located over the coast, drawing the first coastal biodiversity map in Spain based on this methodology. The results show this technique as a low-cost tool complementary to existing monitoring programs, which allows studying the occurrence as well as the temporal variability of non-indigenous and sensitive species, as well as to alert in case of massive coastal arrivals of jellyfish, or stranding of cetaceans or sea turtles, among others.