Amani CHAFFAI, RJIBA BAHRI W., GHANEM R., BEN SOUISSI J.
Biodiversity, Biotechnology and Climate Change Laboratory (LR11ES09), University
of Tunis El Manar, Faculty of Sciences of Tunis, Tunisia.
E-mail: chaffaiamani@yahoo.fr
DECORATING BEHAVIOR OF THE INVASIVE CRAB LIBINIA
DUBIA H. MILNE EDWARDS, 1834 IN TUNISIAN WATERS
Abstract
Invasive species display the ability to thrive and establish populations while adapting to a host
of novel pressures in new environments. In this context, spider crabs often decorate themselves
to hide and protect against predators. This behavior is considered a kind of camouflage and
operates either by avoiding detection (pre-detection defense) or by reducing recognition or
consumption when the animal is already detected (post-detection defense). In this study, we
evaluated the decoration behavior of 4469 specimens Libinia dubia collected from the Gulf of
Gabès from January 2015 to December 2016. The sample comprises 2189 juveniles (1658
males and 531 females), and 2280 adults (616 males and 1664 females). In both sexes, juvenile
crabs engaged more in decoration, and attached various materials to hooked setae on their
carapaces such as algae, Magnoliophyta, sponges, Bryozoa and other organisms. They showed
a marked self-decorating behavior with higher level of carapace coverage compared to adults.
Moreover, we recorded a variation in the body covering pattern between the two sexes.
Decorative materials were more commonly distributed on male carapaces. In general, L. dubia
juvenile use fragments of algae and Magnoliophyta to decorate their carapaces rather than
other organisms. Decorating behavior was proportional to the carapace width increase,
rendering crabs less vulnerable to predators, thus reducing their need for decoration.
Behavioral changes exhibited by L. dubia resulted as “sexually dimorphic ontogenetic shifts”,
that is, decorative behavior shifts depending on the crab’s age and gender.
Key-words: Brachyura, Tunisian marine waters, NIS, Camouflage, Geographic comparison.
Introduction
The Western Atlantic native spider crab L. dubia H. Milne Edwards, 1834 has only been
observed in southern Tunisian coasts since its occurrence in the Mediterranean Sea in
1997 (Enzenross & Enzenross, 2000). Here, we report the decorating behavior of L.
dubia in order to investigate possible difference modalities and geographic variation in
masking behavior between the native and invasive populations.
Material and methods
Sampling was conducted monthly over two years (2015-2016) where 4469 crabs were
caught from the Gulf of Gabès (Tunisia), sexed and classified into juveniles or adults.
For each specimen, the Carapace Width (CW, 0.01 mm) was measured and the
percentage of coverage was assessed.
Results
Overall, L. dubia presented a clear preference for algae and seagrass as decorative
materials (Fig. 1). Juveniles engaged more in decoration compared to adults. Moreover,
camouflage materials were more abundant in male carapaces with higher mean %
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
85
Biodiversity, Biotechnology and Climate Change Laboratory (LR11ES09), University
of Tunis El Manar, Faculty of Sciences of Tunis, Tunisia.
E-mail: chaffaiamani@yahoo.fr
DECORATING BEHAVIOR OF THE INVASIVE CRAB LIBINIA
DUBIA H. MILNE EDWARDS, 1834 IN TUNISIAN WATERS
Abstract
Invasive species display the ability to thrive and establish populations while adapting to a host
of novel pressures in new environments. In this context, spider crabs often decorate themselves
to hide and protect against predators. This behavior is considered a kind of camouflage and
operates either by avoiding detection (pre-detection defense) or by reducing recognition or
consumption when the animal is already detected (post-detection defense). In this study, we
evaluated the decoration behavior of 4469 specimens Libinia dubia collected from the Gulf of
Gabès from January 2015 to December 2016. The sample comprises 2189 juveniles (1658
males and 531 females), and 2280 adults (616 males and 1664 females). In both sexes, juvenile
crabs engaged more in decoration, and attached various materials to hooked setae on their
carapaces such as algae, Magnoliophyta, sponges, Bryozoa and other organisms. They showed
a marked self-decorating behavior with higher level of carapace coverage compared to adults.
Moreover, we recorded a variation in the body covering pattern between the two sexes.
Decorative materials were more commonly distributed on male carapaces. In general, L. dubia
juvenile use fragments of algae and Magnoliophyta to decorate their carapaces rather than
other organisms. Decorating behavior was proportional to the carapace width increase,
rendering crabs less vulnerable to predators, thus reducing their need for decoration.
Behavioral changes exhibited by L. dubia resulted as “sexually dimorphic ontogenetic shifts”,
that is, decorative behavior shifts depending on the crab’s age and gender.
Key-words: Brachyura, Tunisian marine waters, NIS, Camouflage, Geographic comparison.
Introduction
The Western Atlantic native spider crab L. dubia H. Milne Edwards, 1834 has only been
observed in southern Tunisian coasts since its occurrence in the Mediterranean Sea in
1997 (Enzenross & Enzenross, 2000). Here, we report the decorating behavior of L.
dubia in order to investigate possible difference modalities and geographic variation in
masking behavior between the native and invasive populations.
Material and methods
Sampling was conducted monthly over two years (2015-2016) where 4469 crabs were
caught from the Gulf of Gabès (Tunisia), sexed and classified into juveniles or adults.
For each specimen, the Carapace Width (CW, 0.01 mm) was measured and the
percentage of coverage was assessed.
Results
Overall, L. dubia presented a clear preference for algae and seagrass as decorative
materials (Fig. 1). Juveniles engaged more in decoration compared to adults. Moreover,
camouflage materials were more abundant in male carapaces with higher mean %
2nd Mediterranean Symposium on the Non-Indigenous Species (Genoa, Italy, 22-23 September 2022)
85