Giovanni SCRIBANO, ROS M., MARCHINI A.
Department of Earth and Environmental Sciences, University of Pavia, Italy
E-mail: giovanni.scribano01@universitadipavia.it
POPULATION DYNAMICS OF THE PACIFIC SPECIES
PARANTHURA JAPONICA (CRUSTACEA: ISOPODA) IN A
MEDITERRANEAN SITE
Abstract
Our knowledge of marine Non-Indigenous Species (NIS) biology and ecology suffers from several
gaps, including data on their most basic life history traits. Determining the characteristics of
successful invaders, identifying the traits directly or indirectly related to invasiveness, while
predicting the profiles that are more likely to cause future invasions, remain major goals in
marine invasion biology. The present study aims to fill the knowledge gap related to the biology
and ecology of the Pacific isopod Paranthura japonica Richardson, 1909 in a newly invaded site,
Marina di Ragusa (Sicily) touristic harbour, focusing on: (I) its population dynamics, (II)
gathering biological and ecological data on this species, and (III) testing the effectiveness of an
Artificial Substrate Unit for this type of investigations. Our study took place from December 2017
to December 2018; we collected three artificial sponges every two weeks, after they had been
deployed underwater and kept there for two months. Sex class, length, number of eggs per female
and egg developmental stage were registered for more than 1400 individuals collected throughout
the year. We conclude that P. japonica, native to the cold Okhotsk Sea, has well adapted to the
warm Mediterranean conditions. Its population has been found well-established and persistent
throughout the year, while its numeric positive response to increasing temperature was one of our
most surprising findings. In fact, reproductive events occur throughout the year, but peak during
summer. Finally, we show that nylon bath sponges represent an efficient artificial substrate for
obtaining quantitative samples of peracarid crustaceans.
Key-words: Alien species, bioinvasion, population dynamics, Isopod, artificial substrate units
Introduction
The pacific isopod Paranthura japonica Richardson, 1909 currently represents one of
the most common alien species in Mediterranean marinas (Ulman et al., 2019);
however, very little is known about its biological and ecological traits. In fact, besides
taxonomic descriptions and notes on its geographic distribution, the only additional
knowledge regards its habitat preferences and feeding strategy, common to other
members of the family Paranthuridae. Other traits, especially those related to life cycle,
have never been investigated so far. The poor knowledge regarding this species is to be
attributed to the difficulties in spotting specimens in the wild and collecting
standardised, quantitative data. Therefore, studying the biology and ecology of the nonindigenous P. japonica requires appropriate and specific methods. The present study
addresses the aforementioned problems and aims to study the population dynamics of
this species in a newly invaded site.
Materials and methods
The study occurred in Marina di Ragusa (southern Sicily), a tourist port in the Central
Mediterranean Sea. Its fouling community had already been studied in 2016 by Ulman
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
121
Department of Earth and Environmental Sciences, University of Pavia, Italy
E-mail: giovanni.scribano01@universitadipavia.it
POPULATION DYNAMICS OF THE PACIFIC SPECIES
PARANTHURA JAPONICA (CRUSTACEA: ISOPODA) IN A
MEDITERRANEAN SITE
Abstract
Our knowledge of marine Non-Indigenous Species (NIS) biology and ecology suffers from several
gaps, including data on their most basic life history traits. Determining the characteristics of
successful invaders, identifying the traits directly or indirectly related to invasiveness, while
predicting the profiles that are more likely to cause future invasions, remain major goals in
marine invasion biology. The present study aims to fill the knowledge gap related to the biology
and ecology of the Pacific isopod Paranthura japonica Richardson, 1909 in a newly invaded site,
Marina di Ragusa (Sicily) touristic harbour, focusing on: (I) its population dynamics, (II)
gathering biological and ecological data on this species, and (III) testing the effectiveness of an
Artificial Substrate Unit for this type of investigations. Our study took place from December 2017
to December 2018; we collected three artificial sponges every two weeks, after they had been
deployed underwater and kept there for two months. Sex class, length, number of eggs per female
and egg developmental stage were registered for more than 1400 individuals collected throughout
the year. We conclude that P. japonica, native to the cold Okhotsk Sea, has well adapted to the
warm Mediterranean conditions. Its population has been found well-established and persistent
throughout the year, while its numeric positive response to increasing temperature was one of our
most surprising findings. In fact, reproductive events occur throughout the year, but peak during
summer. Finally, we show that nylon bath sponges represent an efficient artificial substrate for
obtaining quantitative samples of peracarid crustaceans.
Key-words: Alien species, bioinvasion, population dynamics, Isopod, artificial substrate units
Introduction
The pacific isopod Paranthura japonica Richardson, 1909 currently represents one of
the most common alien species in Mediterranean marinas (Ulman et al., 2019);
however, very little is known about its biological and ecological traits. In fact, besides
taxonomic descriptions and notes on its geographic distribution, the only additional
knowledge regards its habitat preferences and feeding strategy, common to other
members of the family Paranthuridae. Other traits, especially those related to life cycle,
have never been investigated so far. The poor knowledge regarding this species is to be
attributed to the difficulties in spotting specimens in the wild and collecting
standardised, quantitative data. Therefore, studying the biology and ecology of the nonindigenous P. japonica requires appropriate and specific methods. The present study
addresses the aforementioned problems and aims to study the population dynamics of
this species in a newly invaded site.
Materials and methods
The study occurred in Marina di Ragusa (southern Sicily), a tourist port in the Central
Mediterranean Sea. Its fouling community had already been studied in 2016 by Ulman
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
121