  Cultural Ecosystem Services (CES) assessment at large scales is crucial in
marine ecosystems as they reflect key physical and cognitive interactions
between humans and nature. The analysis of social media data with graph theory
is a promising approach to provide global information on users' perceptions for
different marine ecosystems. Fourteen areas were selected to illustrate the use
of graph theory on social media data. The selected areas, known to protect key
recreational, educational and heritage attributes of marine ecosystems, were
investigated to identify variability in users' preferences. Instagram data
(i.e., hashtags associated to photos) was extracted for each area allowing an
in-depth assessment of the CES most appreciated by the users. Hashtags were
analysed using network centrality measures to identify clusters of words,
aspects not normally captured by traditional photo content analysis. The
emergent properties of networks of hashtags were explored to characterise
visitors' preferences (e.g., cultural heritage or nature appreciation),
activities (e.g., diving or hiking), preferred habitats and species (e.g.
forest, beach, penguins), and feelings (e.g., happiness or place identity).
Network analysis on Instagram hashtags allowed delineating the users' discourse
around a natural area, which provides crucial information for effective
management of popular natural spaces for people.
