H. Milne Edwards, 1837) (Brachyura, Grapsoidea) from a Temperate Estuary in the Eastern South Pacific

INCIDENCE PATTERNS OF LIMB AUTOTOMY IN THE ESTUARINE CRAB, HEMIGRAPSUS CRENULATUS (H. MILNE EDWARDS, 1837) (BRACHYURA, GRAPSOIDEA) FROM A TEMPERATE ESTUARY IN THE EASTERN SOUTH PACIFIC

RAMIRO RIQUELME-BUGUEÑO1) Center for Oceanographic Research in the Eastern South Paciﬁc (FONDAP-COPAS), Research Program 3, Marine Biology Station, University of Concepción, P.O. Box 42, Dichato, Concepción, Chile

ABSTRACT

The first quantitative report about limb autotomy in decapods that inhabit the southeastern Pacific Ocean is here presented. The study analysed samples coming from the south of the Gulf of Arauco, central Chile, of a population of the estuarine crab, Hemigrapsus crenulatus in the course of one year. The number and type of limb lost were registered for each sex. Fifty-two percent of the males and 47% of the females presented at least one limb lost for all samples analysed. Limb types more frequently autotomized were the chelipeds of the males (32%) and the fifth pereiopods of the females (24%). These results indicate that this phenomenon recurs in the population, probably as a consequence of threats from predators or from intraspecific interactions (e.g., cannibalism).

RESUMEN

Se presenta por primera vez información cuantitativa sobre autotomía de apéndices en decápodos habitantes del Océano Pacíﬁco Sur Oriental. Se analizaron muestras de una población del cangrejo estuarino Hemigrapsus crenulatus por un periodo de un año, provenientes del Golfo de Arauco, Chile central. Se registró el número y tipo de apéndice autotomizado en ambos sexos. El 52% de los machos y el 47% de las hembras presentaron al menos un apéndice autotomizado para el total de las muestras analizadas. El tipo de apéndice más autotomizado correspondió a los quelípodos en los machos (32%) y al quinto pereíopodo en las hembras (24%). Los resultados indican que este fenómeno es frecuente en la población, probablemente como una respuesta a las amenazas de depredadores o interacciones intraespecíﬁcas (por ej. canibalismo).

1) e-mail: [email protected] © Koninklijke Brill NV, Leiden, 2006 Crustaceana 79 (8): 925-932 Also available online: www.brill.nl/cr 926 RAMIRO RIQUELME-BUGUEÑO

INTRODUCTION Autotomy is the loss of a part of the body of an animal at a predetermined fracture plane, which is followed by a high-speed scarring process (Wood & Wood, 1932), that frequently is a response to a predator’s attack (Arnold, 1988). Consequently, the immediate benefit of autotomy is basic survival in the face of a predator (Robinson et al., 1970; Smith, 1990) and the avoidance of contracting an infection in the case of a damaged limb (McVean & Findlay, 1979). However, it also has its costs, such as decreasing the speed of growth (Kuris & Mager, 1975; Smith, 1990), limiting feeding rate (Juanes & Hartwick, 1990; Smith & Hines, 1991), reducing locomotive efficiency (Smith, 1990), and affecting the ability to compete for a mate or a refuge (Smith, 1990). In fact, autotomy can be particularly important in aquatic environments, because soluble chemical cues can alert predators about the existence of an injured animal or a potential prey (Zimmer-Faust, 1989; Ferner et al., 2005). According to Juanes & Smith (1995), the phenomenon of autotomy is of substantial significance in decapods, because the loss of different types and numbers of limbs can alter the physical status and, probably, the decision-making process of an animal. The patterns of lesions within a species may provide evidence of how selective factors influence an animal’s behaviour and life history. If the cost of the limbs lost is significant, and the frequency of autotomy in a population is high, this phenomenon could have profound effects on the population and the ecological community at a higher level. The incidence of autotomy is the percentage of a population’s individuals that have lost limbs (appendages). Extensive literature exists on limb autotomy and regeneration in brachyurans crabs (reviewed in Juanes & Smith, 1995). However, in the south-eastern Pacific (∼15◦-45◦S) there is no background on this phenomenon in populations of brachyurans decapods, in particular for estuarine and intertidal crabs. The estuarine crab, Hemigrapsus crenulatus (H. Milne Edwards, 1837) (Brachy- ura, Grapsoidea, Varunidae) inhabits the eastern South Pacific and is distributed in the Chilean territory from Arica (∼18◦S) to the Estrecho de Magallanes (∼53◦S) and also inhabits the coast of New Zealand (Retamal, 2000). This report gives the first account of the phenomenon of autotomy in brachyuran Decapoda in the southeastern Pacific Ocean.

MATERIAL AND METHODS The study was carried out in the estuary formed by the outlet of the rivers Tubul and Raqui, located in the south of the Gulf of Arauco (37◦14S73◦27W;