Alessandro TARULLO, TURICCHIA E., ABBIATI M., MIKAC B.,
DESIDERATO A., AIROLDI L., PONTI M.
Dipartimento di Scienze Biologiche, Geologiche e Ambientali (BiGeA) University of
Bologna, Via S. Alberto 163, 48123 Ravenna, Italy
E-mail: alessandro.tarullo2@unibo.it
PORT ENVIRONMENTAL GRADIENTS AND NON-INDIGENOUS
SPECIES
Abstract
Ports are among the main transit points for non-indigenous species around the world. The large
availability of artificial substrates and the reduced water quality usually lead to simplified
benthic communities that offer limited biotic resistance toward non-indigenous species. The aim
of this study is to highlight the role of environmental gradients within ports in favouring the
settlement, permanence, and diffusion of non-indigenous species. The canal-port of Ravenna
(northern Adriatic Sea), which extends for 11 km inland, and the high traffic of commercial
ships, represents an ideal case study. This canal-port generates a water pollution and
confinement gradient, which is reflected in a characteristic substitution of intertidal
assemblages along the concrete quays. The outer harbour and the first stretch of the canal are
characterized by beds of the native mussel, Mytilus galloprovincialis, which assemblages are
rich in native species. Towards the innermost areas of the port, the native mussel is replaced by
the invasive mussel Xenostrobus securis. After a short transition zone characterized by the
coexistence of both species, X. securis monopolizes the substrate accompanied by an increase in
non-indigenous species.
Key-words: Alien species, Marine traffic, Harbour, Mediterranean Sea, Padstow mussel
Introduction
The Ravenna harbour has a main canal-port, called Candiano, where water quality is
affected by urban surface water drainage, civil and industrial wastewater discharges,
and relatively strong tides (up to 80 cm). All these elements generate an evident
environmental gradient by modifying the salinity and pollutant concentration, which are
relevant in the NIS settlement (Airoldi et al., 2015; Lopez-Legentil et al., 2015). The
aim of the study was to analyse how this gradient influences the non-indigenous species
(NIS) abundance along the Candiano canal.
Materials and methods
Samples of intertidal benthic assemblages were taken by scraping the concrete quays of the
Candiano canal at 6 sites over 3 years, from 2016 to 2018, to evaluate the influence of the
environmental gradient. Collected specimens were counted and identified at best possible
taxonomic level. Since the quantity of sample varied with the thickness of the mussel layer,
the abundance of organisms of the different species was standardized and expressed as a
percentage.
Results
Overall, 67 taxa were found, 56 classified at the species level, including 11 NIS
(Zenetos et al., 2017). Among them the most abundant NIS were the barnacle
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
127
DESIDERATO A., AIROLDI L., PONTI M.
Dipartimento di Scienze Biologiche, Geologiche e Ambientali (BiGeA) University of
Bologna, Via S. Alberto 163, 48123 Ravenna, Italy
E-mail: alessandro.tarullo2@unibo.it
PORT ENVIRONMENTAL GRADIENTS AND NON-INDIGENOUS
SPECIES
Abstract
Ports are among the main transit points for non-indigenous species around the world. The large
availability of artificial substrates and the reduced water quality usually lead to simplified
benthic communities that offer limited biotic resistance toward non-indigenous species. The aim
of this study is to highlight the role of environmental gradients within ports in favouring the
settlement, permanence, and diffusion of non-indigenous species. The canal-port of Ravenna
(northern Adriatic Sea), which extends for 11 km inland, and the high traffic of commercial
ships, represents an ideal case study. This canal-port generates a water pollution and
confinement gradient, which is reflected in a characteristic substitution of intertidal
assemblages along the concrete quays. The outer harbour and the first stretch of the canal are
characterized by beds of the native mussel, Mytilus galloprovincialis, which assemblages are
rich in native species. Towards the innermost areas of the port, the native mussel is replaced by
the invasive mussel Xenostrobus securis. After a short transition zone characterized by the
coexistence of both species, X. securis monopolizes the substrate accompanied by an increase in
non-indigenous species.
Key-words: Alien species, Marine traffic, Harbour, Mediterranean Sea, Padstow mussel
Introduction
The Ravenna harbour has a main canal-port, called Candiano, where water quality is
affected by urban surface water drainage, civil and industrial wastewater discharges,
and relatively strong tides (up to 80 cm). All these elements generate an evident
environmental gradient by modifying the salinity and pollutant concentration, which are
relevant in the NIS settlement (Airoldi et al., 2015; Lopez-Legentil et al., 2015). The
aim of the study was to analyse how this gradient influences the non-indigenous species
(NIS) abundance along the Candiano canal.
Materials and methods
Samples of intertidal benthic assemblages were taken by scraping the concrete quays of the
Candiano canal at 6 sites over 3 years, from 2016 to 2018, to evaluate the influence of the
environmental gradient. Collected specimens were counted and identified at best possible
taxonomic level. Since the quantity of sample varied with the thickness of the mussel layer,
the abundance of organisms of the different species was standardized and expressed as a
percentage.
Results
Overall, 67 taxa were found, 56 classified at the species level, including 11 NIS
(Zenetos et al., 2017). Among them the most abundant NIS were the barnacle
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
127