First report of the invasive swimming crab Charybdis hellerii (A. Milne - Edwards, 1867) (Decapoda, Portunidae) near the Great Amazon Reef System, Amapá, Brazil

. In this paper, we report for the first time the occurrence of the swimming crab Charybdis hellerii (A. Milne - Edwards, 1867) on the continental shelf of Amapá State. Four specimens were collected as bycatch fauna during industrial fishing operations targeting the southern brown shrimp. The specimens have been deposited in the Carcinological Collection of the Centro Nacional de Pesquisa e Conservação da Biodiversidade Marinha do Norte — ICMBio/CEPNOR. The occurrence fills a knowledge gap about the distribution of the species in the northern Brazilian coast since the species was recorded in French Guyana and in the northern to southeastern regions of Brazil.


Introduction
The establishment of exotic species in marine waters has advanced at an accelerated rate. These invasions are the consequence of anthropic actions such as maritime transport, the opening of channels connecting seas and oceans, the release of exotic biodiversity into the environment and abiotic modifications of ecosystems caused by climate change (Dahl & Patterson III, 2013, Phillips & Kotrschal, 2021. The Great Amazon Reef System (GARS; see Francini-Filho et al., 2018) had its existence indicated by Collette and Rützler (1977) and confirmed by Moura et al. (2016). The GARS is composed of great complexity and diversity of habitats (Francini-Filho et al., 2018).
Currently, in tropical waters, one of the main bioinvasive agents in coastal marine environments is the swimming crab Charybdis hellerii (A. Milne-Edwards, 1867), which belongs to the family Portunidae Rafinesque, 1815 (Wee & Ng, 1995). Charybdis hellerii is native from warm waters of the Indo-Pacific and widely distributed in the Red Sea, Somalia, South Africa, Madagascar, Persian Gulf, India, Philippines, Indonesia, China, Japan, Australia and Hawaii , Tavares & Amouroux, 2003.
This species was first identified in Brazil in 1996 in the states of Alagoas, Bahia and Rio de Janeiro (Calado, 1996, Carqueija & Gouvêa, 1996, Tavares & Mendonça-Júnior, 1996, be-ing subsequently reported in coastal regions from the north to the south of the country. Based on that, the present study aims to fill a gap in the knowledge of the distribution of C. hellerii in Amapá state, confirming the invasion of the species in the northernmost region of the Brazilian coast.

Material & Methods
The specimens of C. hellerii were collected by scientific observers under the supervision of the Centro Nacional de Pesquisa e Conservação da Biodiversidade Marinha do Norte (ICMBio/CEPNOR) in the industrial fisheries targeting the southern brown shrimp in the northern Brazilian coast (Amapá State), between the depths of 20 and 90 m ( Figure 1). On board, the specimens of C. hellerii were photographed, measured in Carapace Length (CL) and Carapace Width (CW) with a caliper (0.01 mm), packaged in suitable containers and stored in a cold chamber.

Discussion
The first occurrence of C. hellerii on the northern Brazilian coast was reported 10 years ago by Bentes et al. (2013), but the species occurrence in French Guiana was reported in 2003 by Tavares & Amouroux (2003). So, the occurrence reported here, in the State of Amapá, fills a gap in knowledge about the distribution of the species on the Brazilian coast.
The bioinvasion of C. hellerii is considered an example of successful introduction of a marine exotic species in the Atlantic Ocean (Tavares & Amouroux, 2003). Although it was recorded in Brazil only in the 1990s, C. hellerii was captured for the first time in Ilha Grande, State of Rio de Janeiro, in 1965 (Tavares & Rössener, 2019).  (Dineen et al., 2001), a period longer than needed to cross the Atlantic Ocean in ballast water of ships or larval transport via coastal currents. According to Negri et al. (2018) the Mediterranean Sea represented the main origin of the Western Atlantic populations.
For the coastal Brazilian States, there is no occurrence record of C. hellerii in Paraíba, Sergipe and Rio Grande do Sul. As there is no abiotic or biotic barrier explaining the nonestablishment of this species in these States, we believe it is already present at these coastal states, except in Rio Grande do Sul, where lower water temperatures may limit its southern distribution.
The specimens caught presented carapace color varying from greenish to brown/ reddish, with a mottled pattern (Figure 2). These phenotypic variations are observed in other Brachyura and it may be related to camouflage in the micro-habitat, reducing predation effects. As observed by Watanabe et al. (2015), color may also vary with size or sexual maturation stage.
Southern brown shrimp [(Penaeus subtilis (Pérez-Farfante, 1967) and Penaeus brasiliensis (Latreille, 1817)] fishing is performed at the Brazilian northern coast between the depths of 20 and 90 m, using bottom trawl. This fishing activity is harmful to the aquatic environment because there is a diverse bycatch fauna associated with the fishery, whose removal disrupts the local marine communities. This may favor the establishment of opportunistic species such as the invasive swimming crab C. hellerii.
The report of C. hellerii in Amapá confirms the northernmost occurrence in Brazil of this swimming crab and its adaptability to different ecosystems, once we find variations in climate and physicochemical conditions of the water masses along the coastal zones, as observed in the Amazon River discharges.
This invasive swimming crab is well established in estuaries and shallow intertidal rocky shores (Sant'Anna et al., 2012. The record of its occurrence near the GARS, at depths of 30 to 50 meters, contributes to the understanding of the extent of its invasion and resulting impacts.
An example of the impact of alien species on other species is food competition. In the case of the diet of C. hellerii, it is similar to that of other native crabs which feed on crustaceans, molluscs, polychaetes and algae, among Revista  First report of the invasive swimming crab Charybdis hellerii near the GARS, Amapá, BR others .
Considering this and other impacts generated, it is essential to carry out efforts to monitor and control alien species, especially in priority environments for conservation such as GARS.