MARE, FCUL, Polytechnic Institute of Setúbal, Ce3c

The Manila clam (Ruditapes philippinarum) is an invasive species that was introduced in the Tagus
estuary in 2000, where it is intensively harvested, and in the Sado estuary in 2010, where it is less
abundant and less harvested. This invasive species, and its harvesting is recognised for their
environmental and socioeconomic impacts on these ecosystems, however effects on cultural ecosystem
services (ES) and disservices (EDS) are unknown.
This study analysed the perceptions of local users to infer cultural ES and EDS associated to the Manila
clam in the Tagus and Sado estuaries, by conducting i) the characterization of the abundance and
distribution of the Manila clam in each estuary in 2023, to infer the presence of harvesters; and ii) the
analysis of perceptions of local users about this species between 2023 and 2024, derived from opinion-
based surveys.
The Manila clam was more abundant in the Tagus estuary than in the Sado estuary, hence the abundance
of harvesters followed the same pattern. The presence of harvesters depended on the accessibility to the
harvesting areas. Users’ perceptions were more negative in the Tagus estuary, particularly in areas with
higher abundance of the Manila clam, and likely more harvesting. Beach users showed the most
negative perceptions among all users. User group, visit frequency and education level influenced user ́s
perceptions, whereas gender showed no influence. The invasion of the Manila clam in the Tagus and
Sado estuaries affected ES related to human wellbeing and safety, namely water quality, and caused
some EDS, such as accumulation of rubbish in beach areas and a decrease in the population safety. ES
and EDS related to cultural heritage and aesthetic value weren’t affected, possibly due to the abundance
of other similar landscapes around the study area and the traditional nature of clam harvesting in the
estuaries.