Burukovsky R.N., Sudnik S.A. 2024. Size composition, reproductive characteristics and food composition in crabs Seulocia vittata (Ortman, 1858) and Lyphira perplexa Galil, 2009 (Decapoda: Brachyura: Leucosiidae) from Nha Trang Bay (South Vietnam) // Arthropoda Selecta. Vol.33. No.1: 87–96 [in English].
Kaliningrad State Technical University, Sovietsky pr., 1, Kaliningrad 236022 Russia. E-mail: burukovsky@klgtu.ru ; svetlana.sudnik@klgtu.ru
doi: 10.15298/arthsel.33.1.08
ABSTRACT. Data on the size composition, reproductive parameters and food composition of two widespread Indo-Westpacific crabs from the family Leucosiidae (Crustacea: Decapoda: Brachiura) were described: Seulotia vittata (244 specimens, carapace length 29.5–43.3 mm and body weight 1.80–5.72 g) and Lyphira perplexa (318 specimens, respectively 26.7–40.9 mm and 1.50–6.42 g). Crabs were collected in Nha Trang Bay (South Vietnam) in February 2007. They were found on sandy and silty bottom of the sublittoral at depths from 7 to 85 m. Juveniles were not found; the sex ratio (male to female) was close to one to one in S. vittata and 1.7 : 1 in L. perplexa. Both among males and females of both species were predominated specimens with similar carapace width (CW, near 18–22 mm). The size at first maturity of males was 19–20 mm CW in S. vittata and 21–24 mm CW in L. perplexa; in both species females this trait could not be determined: all of them were maturing or ripe.
The main reproductive features of both species in Nha Trang Bay were quite similar. February was the time of their active spawning: egg-bearing specimens predominated; there were up to 40–55% of almost mature and pre-spawning females many. In S. vittata, fecundity was up to 3014 eggs with size of newly laid eggs 0.220 ± 0.01 × 0.245 ± 0.02 mm; in L. perplexa — 3282 eggs with size 0.230 ± 0.01 × 0.259 ± 0.02 mm; egg volume was 0.005–0.006 mm3. In females of both species, there is a possibility of repeated spawning event in given reproductive period. Slightly larger fecundity and larger egg size in L. perplexa may contribute to its more successful reproduction in Nha Trang Bay, active dispersal and some numerical dominance.
Judging by the contents of the stomachs, both species can be tentatively attributed to predator-gatherers or even attacking predators. In both species, decapod crustaceans play a significant role in food: in S. vittata these were peneid shrimps and Stomatopoda, i.e. bury and burrowing animals, and in L. perplexa — some kind of crab (possibly epibenthic). In S. vittata, bivalves (mainly infauna representatives) were present among the eaten mollusks, and in L. perplexa, epibenthous gastropods, as well as plant remains. At this level of knowledge of the composition of the food of these two species, it can be assumed that both of them are predators-benthophages that do not neglect necrophagy, but S. vittata is also a detritophagus that feeds mainly on infauna, and L. perplexa is rather an epibentophagus. Due to these crabs probably do not compete with each other.
KEY WORDS: Seulotia vittata, Lyphira perplexa, Nha Trang Bay, sizes, reproductive biology, fecundity, oocytes, eggs, food composition, benthic predators.