Growth and maturity of the spider crab Halicarcinus planatus (Brachyura: Hymenosomatidae) females in the southwestern Atlantic Ocean. Can these parameters be influenced by the population sex ratio?

Abstract

The Halicarcinus planatus populations of the southwestern Atlantic Ocean show a highly variable sex ratio and a large size overlapping between females in the last immature instar (ADO) and mature (MAT) females. We hypothesized that these facts are related and that female impregnation has a central role in this relation. Non-impregnated ADO females delay maturity and would continue to grow, leading to size overlapping. This scenario is most probable in populations with a scarcity of males and could affect the growth, maturity and population structure. The sex ratio and female size distribution of several populations of the southwestern Atlantic Ocean were analysed. Growth and maturity were studied in two populations with different sex ratios (Camarones, a population with males, and Rada Tilly, a population where no males were found). Size overlapping was not related to the population sex ratio. Size overlapping was due to a variable moult increment and, to a lesser extent, to delayed maturity. Females mated before terminal moult in both populations. However, in Camarones, physiological maturity was not related to impregnation, while in Rada Tilly, vitellogenic oocytes were observed only in impregnated females. Also, differences in the number of spermatophores in female spermathecae were related to the sex ratio. Our results showed that the morphological maturity pattern of females was not influenced by the population sex ratio. However, physiological maturity was related to female impregnation and sex ratio. Also, the variation in the number of spermatophores suggests differences in the mating system related to the sex ratio. ARTICLE HISTORY

Dispersal models alert on the risk of non‐native species introduction by Ballast water in protected areas from the Western Antarctic Peninsula

“…In February 2010, a living and mature female of the brachyuran crab Halicarcinus planatus (Fabricius, 1775) was reported in shallow, subtidal waters of Deception Island (Western Antarctic Peninsula) (Aronson et al, 2015) (Figure 3). Halicarcinus planatus is usually distributed in shallow water areas of southern South America and along coastal areas of some sub‐Antarctic Islands (Falkland, Marion, Crozet, Kerguelen and Macquary islands) (Aronson et al, 2015; Boschi et al, 1969; Richer de Forges, 1977; Varisco et al, 2016). This little crab (shell diameter from 15 to 20 mm, Figure 3) is an opportunistic feeder (Boschi et al, 1969) that is commonly found sheltered below intertidal and subtidal rocks (Richer de Forges, 1977; Vinuesa & Ferrari, 2008).…”

Is the southern crab Halicarcinus planatus (Fabricius, 1775) the next invader of Antarctica?

“…Previous to this record, Stebbing (1914) reported this species in Macdougal Bay, South Orkney Islands; however, the reliability of this occurrence has been questioned, considering its circum‐Subantarctic distribution (Aronson et al, 2015; Diez & Lovrich, 2010; Thatje & Arntz, 2004; Yaldwyn, 1965). Halicarcinus planatus is the only hymenosomatid crab that inhabits shallow waters (Garth, 1958; Varisco et al, 2016) of southern South America and the Subantarctic Falkland/Malvinas, Marion, Crozet, Kerguelen and Macquarie islands (Aronson et al, 2015; Boschi et al, 1969; Griffiths et al, 2013; Melrose, 1975; Richer De Forges, 1977). This small crab (carapace width up to 15 and 20 mm for female and male, respectively, in Punta Arenas; Figure 1) is an opportunistic feeder (Boschi et al, 1969) commonly found sheltered under rocks in the intertidal and subtidal zones, in between holdfasts of the giant kelp Macrocystis pyrifera or sheltered in hydrozoans and mussel colonies (Chuang & Ng, 1994; Richer De Forges, 1977; Vinuesa & Ferrari, 2008).…”