Moult cycle and growth of the crab Halicarcinus planatus (Brachyura, Hymenosomatidae) in the Beagle Channel, southern tip of South America

Abstract

The crab Halicarcinus planatus is the only hymenosomatid crab that inhabits the southern tip of South America and is the only decapod species that reproduces twice a year in the Beagle Channel. In this article, we study the moult cycle in the field (moult frequency, analysis of size frequency distribution) and linked it with growth studied in the laboratory (absolute and per cent growth increment, Hiatt function). Hiatt functions were similar for males and females. Moult frequency was seasonal: in early austral spring and in austral summer. In females, the pubertal moult is the terminal moult, whereas males continue moulting after attaining the size of morphometric maturity. Moult increment was highly variable. The relationship between absolute moult increment and crab size was described by a quadratic function. Per cent growth increment decreased with size, and relationships were different for each sex: linear for females and quadratic for males. Seven and eight modal groups explained the size frequency distributions for females and males from the field, respectively, and revealed the existence of two cohorts of recruits per year. Further modal analysis was mainly hampered by the high variability of size increment that could make any moulting individual fall in its own or one of two following modal groups. The antagonism between growth and reproduction was evident in small males. We hypothesize that the terminal pubertal moult is an advantageous feature that allows females to maximize their investment in reproduction after their terminal moult, which allows this species to have two spawnings per year.

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?

“…The growth pattern among hymenosomatids is variable: some species as Hymenosoma orbiculare Desmarest, 1823 and Elamenopsis lineata A. Milne-Edwards, 1873 have indeterminate growth (Broekhuysen 1955;Lucas 1980), whereas other species, including H. planatus, show determinate growth (Lucas & Hodgkin 1970;Richer de Forges 1977;Lucas 1980;Vinuesa & Ferrari 2008a;Diez & Lovrich 2013). Different traits related to the growth of H. planatus have been studied in the Kerguelen Islands (Richer de Forges 1977), Puerto Deseado (Vinuesa & Ferrari 2008a), Comodoro Rivadavia (Vinuesa et al 2011) and the Beagle Channel (Diez & Lovrich 2013).…”

“…The causes of these variations are unknown. However, an early male dispersal to subtidal cryptic microhabitats has been proposed to explain the deviation in sex ratio (Vinuesa et al 2011;Diez & Lovrich 2013).…”

“…Different traits related to the growth of H. planatus have been studied in the Kerguelen Islands (Richer de Forges 1977), Puerto Deseado (Vinuesa & Ferrari 2008a), Comodoro Rivadavia (Vinuesa et al 2011) and the Beagle Channel (Diez & Lovrich 2013). Different stages in females according to the abdomen morphology have been identified (Vinuesa & Ferrari 2008a): immature (IMM), adolescent (ADO), which refers to the last instar before terminal moult, and mature (MAT).…”

Evolutionary trade-offs in osmotic and ionic regulation and the expression of gill ion transporter genes in high latitude, Neotropical cold clime crabs from the ‘end of the world’

“…Hemolymph Mg 2+ titers in A. albatrossis (21.6 mmol l −1 ) and H. planatus (10.7 mmol l −1 ) are hypo-regulated at very low concentrations compared to most Brachyura (30-50 mmol l −1 ) (Frederich et al 2001). In contrast, the biogeography (Diez et al 2011), distribution and ecology (López-Farrán et al 2021), population dynamics and growth (Diez et al 2013) and thermal and reproductive physiology (Diez et al 2010) of these two sympatric species are well known, and reveal that the abundant populations of both species encountered in the Beagle Channel, Tierra del Fuego, occupy very similar osmotic and thermal niches.…”

The role of nuclear receptor E75 in regulating the molt cycle of Daphnia magna and consequences of its disruption

“…The molt cycle in crustaceans consists of an environmentally entrained infradian rhythm [9]. This rhythm is closely aligned with physiological processes critical to population sustainability such as growth, maturation, and reproduction [10–12]. Adult Daphnia magna shed their exoskeleton (molt) every 3–4 days at 20°C and a 16:8 hour light:dark cycle.…”