Emna SOUFI-KECHAOU, KOUSSANI W., KHAMASSI F., BEN SOUISSI J.,
ZAOUALI J.
Biodiversity, Biotechnology and Climate Change Laboratory (LR11ES09), University
Tunis El Manar, Tunis, Tunisia
Email: esoufi@gmail.com
SPATIAL EXPANSION OF THE ALIEN INVASIVE BIVALVIA
BRACHIDONTES PHARAONIS AROUND TUNIS SOUTHERN
LAGOON AND ITS ECOLOGICAL AND SOCIO-ECONOMIC
IMPACT
Abstract
Recently mussel beds of the Lessepsian Mytilid Brachidontes pharaonis (Fisher P. 1870), were
observed all around the Tunis Southern lagoon (TSL) located near commercial ports. This study
was carried out in order to collect qualitative and quantitative data about B. pharaonis versus
Mytilus galloprovincialis and to estimate their densities. It also aims to assess the potential of
non-indigenous mussels to spread and colonize new areas. The socio-economic impacts of the
B. pharaonis invasion were identified on the basis of local fishermen interviews. This work
highlights that this invasive species occupied most of rocky shores of the lagoon reaching a
density exceeding 18500 ind.m
-2
. B. pharaonis competes with the native mussel and has
probably displaced it from the lagoon, since no M. galloprovincialis were found, with negative
impacts on the local fishery sistem.
Key-words: Mytilus galloprovincialis, competition, habitat, mapping, fishermen income
Introduction
The Red Sea mussel Brachidontes pharaonis (Fischer, 1870) was one of the first NIS to
invade the Mediterranean Sea in 1869. Since its first occurrence in Tunisia in 2013, B.
pharaonis had spread substantially throughout most of the country with a potential
threat for native species (Sarà & De Pirro, 2011). After the ecological restoration of the
lagoon in 2001, Mytilus galloprovincialis colonized all artificial rocky shores and was
exploited for commercial purpose.
Material and methods
This survey was carried out along the shores of TSL in order to estimate the level of
expansion of B. pharaonis in 20 stations, a distance of 1.5 km, during two field
campaigns in 2022. Percentage of coverage and densities were calculated using a
quadrat (50 x 50 cm). Images of each quadrat were treated by the ENVI software. For
the socio-economic study, 32 face-to-face interviews were conducted with local
fishermen.
Results and discussion
This study highlights the large expansion of B. pharaonis in all the rocky shores of the
lagoon. The extreme densities vary between 300 to 19000 ind.m
-2 with a mean average
of 7400 ind.m
-2 .The highest values of densities were observed near harbours suggesting
a shipping vector of introduction. The size structure of the population of B. pharaonis
revealed that all cohorts (from 2 to 35 mm) were present with a dominance of large
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
125
ZAOUALI J.
Biodiversity, Biotechnology and Climate Change Laboratory (LR11ES09), University
Tunis El Manar, Tunis, Tunisia
Email: esoufi@gmail.com
SPATIAL EXPANSION OF THE ALIEN INVASIVE BIVALVIA
BRACHIDONTES PHARAONIS AROUND TUNIS SOUTHERN
LAGOON AND ITS ECOLOGICAL AND SOCIO-ECONOMIC
IMPACT
Abstract
Recently mussel beds of the Lessepsian Mytilid Brachidontes pharaonis (Fisher P. 1870), were
observed all around the Tunis Southern lagoon (TSL) located near commercial ports. This study
was carried out in order to collect qualitative and quantitative data about B. pharaonis versus
Mytilus galloprovincialis and to estimate their densities. It also aims to assess the potential of
non-indigenous mussels to spread and colonize new areas. The socio-economic impacts of the
B. pharaonis invasion were identified on the basis of local fishermen interviews. This work
highlights that this invasive species occupied most of rocky shores of the lagoon reaching a
density exceeding 18500 ind.m
-2
. B. pharaonis competes with the native mussel and has
probably displaced it from the lagoon, since no M. galloprovincialis were found, with negative
impacts on the local fishery sistem.
Key-words: Mytilus galloprovincialis, competition, habitat, mapping, fishermen income
Introduction
The Red Sea mussel Brachidontes pharaonis (Fischer, 1870) was one of the first NIS to
invade the Mediterranean Sea in 1869. Since its first occurrence in Tunisia in 2013, B.
pharaonis had spread substantially throughout most of the country with a potential
threat for native species (Sarà & De Pirro, 2011). After the ecological restoration of the
lagoon in 2001, Mytilus galloprovincialis colonized all artificial rocky shores and was
exploited for commercial purpose.
Material and methods
This survey was carried out along the shores of TSL in order to estimate the level of
expansion of B. pharaonis in 20 stations, a distance of 1.5 km, during two field
campaigns in 2022. Percentage of coverage and densities were calculated using a
quadrat (50 x 50 cm). Images of each quadrat were treated by the ENVI software. For
the socio-economic study, 32 face-to-face interviews were conducted with local
fishermen.
Results and discussion
This study highlights the large expansion of B. pharaonis in all the rocky shores of the
lagoon. The extreme densities vary between 300 to 19000 ind.m
-2 with a mean average
of 7400 ind.m
-2 .The highest values of densities were observed near harbours suggesting
a shipping vector of introduction. The size structure of the population of B. pharaonis
revealed that all cohorts (from 2 to 35 mm) were present with a dominance of large
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
125