Estimating population features of the anomuran crab Petrolisthes armatus (Porcellanidae) in a remaining and impacted mangrove area of the western Atlantic

Porcellanid crab Pachycheles stevensii parasitized by rhizocephalans Lernaeodiscus spp.: population biology in the northwestern Sea of Japan

We examined the population and reproductive characteristics of the anomuran crab Pachycheles stevensii Stimpson, 1858 (Decapoda: Porcellanidae) heavily infested by 2 rhizocephalans of the genus Lernaeodiscus in the northern part of the species range (Peter the Great Bay, Sea of Japan) in 2020-2021. The prevalence of infestation reached 32.3%, and L. rybakovi proved to be much more numerous than L. kasyanovi. The sex structure of the P. stevensii population was represented by males (38.8%), females (50.6%), and modified specimens (10.6%), which were extremely feminized males. The latter had a broadened abdomen, smaller chelae, shortened gonopod, and 3 additional pairs of female-type pleopods. Thus, the initial sex ratio in the P. stevensii population approximated the expected 1:1, as in most porcellanid crabs. No significant modifications of the secondary sex characters of the female hosts were observed. The size structures of males and females did not significantly differ. P. stevensii produced 1 clutch yr-1. Oviposition and incubation lasted from summer to early fall; recruitment was noted in the fall. There was a correlation between the reproductive cycles of the host and parasites: rhizocephalans with mature externae were found from June-October. A large number of ovigerous female P. stevensii simultaneously carried parasitic externae of L. rybakovi; fecundity was considerably higher in non-infested females.

Brachyuran and anomuran crabs associated with Schizoporella unicornis (Ectoprocta, Cheilostomata) from southeastern Brazil

The main goals of this investigation were to describe the community structure of anomuran and brachyuran crabs inhabiting reefs constituted by colonies of Schizoporella unicornis, and to provide a species importance ranking for this community. Collections were carried out on S. unicornis reefs at two-month intervals from May 2003 to May 2004, in the rocky sublittoral of the southeastern Brazilian coast. Relative abundance and occurrence were used to rank these species in the hierarchy importance. A total of 2,018 individuals were obtained, in 11 families, 22 genera and 31 species. Porcellanidae and Pilumnidae were the most abundant families, comprising respectively almost 60% and 15% of individuals sampled. The species ranking indicated four main groups A, B, C and D, with group A subdivided. Subgroup A1 contained 9 species, including the species of greatest ecological importance for community regarding abundance and occurrence. The great abundance of crabs associated with S. unicornis seems to be the result of its recognized importance during the crab developmental cycle, and as shelter and food for some Decapod species. These observations reveal the importance of conserving the areas occupied by these reef colonies, which appear to be an important environment for maintaining local biodiversity.

Population dynamics of the pea crab Austinixa aidae (Brachyura, Pinnotheridae): a symbiotic of the ghost shrimp Callichirus major (Thalassinidea, Callianassidae) from the southwestern Atlantic

The Pinnotheridae family is one of the most diverse and complex groups of brachyuran crabs, many of them symbionts of a wide variety of invertebrates. The present study describes the population dynamics of the pea crab Austinixa aidae (Righi, 1967), a symbiont associated with the burrows of the ghost shrimp Callichirus major (Say, 1818). Individuals (n = 588) were collected bimonthly from May, 2005 to September, 2006 along a sandy beach in the southwestern Atlantic, state of São Paulo, Brazil. Our data indicated that the population demography of A. aidae was characterized by a bimodal size-frequency distribution (between 2.0 and 4.0 mm and between 8.0 and 9.0 mm CW) that remained similar throughout the study period. Sex ratio does not differ significantly from 1:1 (p > 0.05), which confirms the pattern observed in other symbiontic pinnotherids. Density values (1.72 ± 1.34 ind. • ap.-1) are in agreement with those found for other species of the genus. The mean symbiosis incidence (75.6%) was one of the highest among species of the Pinnotheridae family, but it was the lowest among the three studied species of the genus. Recruitment pattern was annual, beginning in May and peaking in July, in both years, after the peak of ovigerous females in the population (from March to May). Our findings describe ecological and biological aspects of A. aidae similar to those of other species of this genus, even from different geographic localities.