Large‐scale connectivity of Grapsus grapsus (Decapoda) in the Southwestern Atlantic oceanic islands: integrating genetic and morphometric data

Abstract

The degree of connectivity among island populations can influence their demography and affect their level of genetic differentiation. In this study we investigated genetic and morphometric differences among four populations of Grapsus grapsus (Linnaeus 1758), in Saint Peter and Saint Paul Archipelago (0°55′ N, 29°20′ W), Fernando de Noronha Archipelago (3°50′ S, 32°24′ W), Rocas Atoll (3°50′ S, 33°49′ W) and Trindade Island (20°30′ S, 29°20′ W) from 2003 to 2011. Morphometric results indicated the existence of two distinct groups based on the morphology of their chelae (Trindade Island/Saint Peter and Saint Paul Archipelago versus Fernando de Noronha/Rocas Atoll). In addition, genetic variation in a fragment of the mitochondrial control region revealed substantial differentiation between Trindade and the other islands, with Trindade Island showing only exclusive haplotypes. The congruence of the genetic and morphologic analyses suggests the occurrence of a divergent population in Trindade Island as well as high connectivity among the three remaining equatorial islands. This is the first study to assess the level of morphologic differentiation and genetic connectivity of a species among all four Southwestern Atlantic oceanic islands. Our results provide valuable insight into understanding connectivity through surface ocean currents and suggest that the unstable current system of this area could be responsible for different dispersal patterns. We also suggest that the design of Brazilian marine protected areas should be adjusted to provide stronger protection for Trindade Island as it harbors unique genetic and morphologic variation in G. grapsus.

Genetic diversity and connectivity of Flaccisagitta enflata (Chaetognatha: Sagittidae) in the tropical Atlantic ocean (northeastern Brazil)

“…Similar lineages of the Cephalopoda Octopus insularis were also recorded between the northeastern coast (states of Rio Grande do Norte and Pernambuco) and the same oceanic islands evaluated in this study (SPSPA, FN and RA) [83]. In addition, even semi-terrestrial species as the crabs Johngarthia lagostoma [84] and Grapsus grapsus [85] constitute genetically homogeneous populations between FN and RA; and between SPSPA, FN and RA, respectively. Recently, an individualbased modeling study coupled with a regional hydrodynamic model of the ocean [86] was used to determine the demographic connectivity of reef fishes based on the widespread genus Sparisoma, from oceanic islands and the Brazilian continental shelf between 10˚N and 23˚S.…”

First record of Grapsus grapsus (Linnaeus, 1758) (Brachyura: Decapoda: Grapsidae) in freshwater habitat

“…1A). Trindade Island hosts one unique population of G. grapsus that is genetically distinct from the population of the other three equatorial islands (Teschima et al, 2016). The species has been recorded from the rocky shores of 'Praia das Tartarugas' and 'Pão de Açúcar' since the first scientific expedition to the island (Oliveira, 1951).…”

“…Th e only species recorded in American waters is the sally lightfoot crab Grapsus grapsus (Linnaeus, 1758). In Brazil, G. grapsus is restricted to rocky shores of the oceanic islands of Fernando de Noronha, Rocas' Atoll, St. Paul's Rocks and Trindade (Freire et al, 2011;Teschima et al, 2016). It is also found in the Caribbean, along the tropical Pacific coasts of Central and South America and Galapagos Islands (Teschima et al, 2016).…”

Ocean temperature and density dependence as key drivers of the population dynamics of an intertidal crab at the Brazilian oceanic islands

“…Saint Peter and Saint Paul Archipelago (SPSP), Fernando de Noronha Archipelago (FN), and Rocas Atoll (RA) are equatorial islands with warm sea surface temperature (SST) throughout the year (mean: ~27.5°C), whereas Trindade Island (TRI) (~20° S) exhibits lower SST (mean: 25.3°C) and higher intra‐annual variability (Figures S1 and S2). The SPSP and TRI populations are the most geographically and genetically isolated (Teschima et al, 2016) and most likely maintained by self‐recruitment. Larvae from SPSP and FN possibly reach RA favored by oceanic currents (Freire et al, 2021).…”