Science is addressing global societal challenges, and due to limitations in research financing,
scientists are turning to the public at large to jointly tackle specific environmental issues. Citizens
are therefore increasingly involved in monitoring programs, appointed as citizen scientists with
potential to delivering key data at near to no cost to address environmental challenges, therein
fostering scientific knowledge and advising policy- and decision-makers. One of the first and
most successful examples of marine citizen science in the Mediterranean is represented by the
integrative and collaborative implementation of several jellyfish-spotting campaigns in Italy, Spain,
Malta, and Tunisia starting in 2009. Altogether, in terms of time coverage, geographic extent, and
number of citizen records, these represent the most effective marine citizen science campaigns thus far
implemented in the Mediterranean Sea. Here, we analyzed a collective database merging records over
the above four countries, featuring more than 100,000 records containing almost 25,000 observations
of jellyfish specimens collected over a period of 3 to 7 years (from 2009 to 2015) by citizen scientists
participating in any of the national citizen science programs included in this analysis. Such a wide
citizen science exercise demonstrates a valuable and cost-effective tool to understanding ecological
drivers of jellyfish proliferation over the Western and Central Mediterranean basins, as well as a
powerful contribution to developing tailored adaptation and management strategies; mitigating
jellyfish impacts on human activities in coastal zones; and supporting implementation of marine
spatial planning, Blue Growth, and conservation strategies.
