Distribution of decapod larvae in the surface layer of an isolated equatorial oceanic archipelago: the cases of benthic Grapsus grapsus (Brachyura: Grapsidae) and pelagic Sergestes edwardsi (Dendrobranchiata: Sergestidae)

Abstract

Two different decapod larval assemblages inhabit the marine environment of Saint Paul's Rocks, differentiating the inlet from the surrounding oceanic waters. Larvae of the crab Grapsus grapsus and of the holopelagic shrimp Sergestes edwardsi are abundant in superficial waters of the archipelago and have previously been shown to be good indicators of the inlet and adjacent oceanic waters, respectively. We investigated the horizontal, diel and temporal distribution of these species at Saint Paul's Rocks. Horizontal surface hauls were conducted from 2003 to 2005, in the inlet and at four increasing distances from the archipelago, in the morning and at night, using a 200-lm mesh net. Larvae of G. grapsus were identified in samples from all expeditions and abundance was found significantly higher at night in the inlet site. Only larvae in the first zoeal stage were found in samples, highlighting the importance of the area for this species reproduction. On the contrary, the distribution of larvae of S. edwardsi was typical of a holopelagic species, which are permanent residents of the water column and spawn in oceanic areas, indicating that the islands are of little influence to them.

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

“…Thus, larvae could be lost in the middle of the ocean or they could eventually reach unusual destinations. Only the first larval stage of Grapsus grapsus is known, but the complete larval development of other grapsid species has been described and the duration of their zoeal phase varies from 30 to 60 days (Brandão et al 2013). Assuming 45 days for the larval plankton phase and using the distance of 2000 km between TR and the equatorial islands, the larvae would need to be transported with an average speed of 0.51 mÁs À1 to survive until settlement and therefore maintain gene flow.…”

“…(Freire et al 2011), suggesting that this population experiences harsh environmental conditions. Furthermore, a recent study suggested the occurrence of retention mechanism limiting Grapsus grapsus larvae dispersal (Brandão et al 2013). According to our results, G. grapsus might reach islands up to 700 km apart (SPSPA, FN and RA) but has a low potential of arriving at more distant islands, due to poor larval survival and occurrence of eddies, vortices and discontinuities of the surface currents.…”

Spatio-temporal variation of planktonic decapods along the leeward coast of the Fernando de Noronha archipelago, Brazil

“…Large neritic larval abundances at coastal stations around oceanic islands are common and may suggest a larval retention (Brandão et al, 2012(Brandão et al, , 2013Landeira et al, 2013) which ensures the maintenance of larvae near their areas of origin (Mcconaugha, 1992;Landeira et al, 2009). …”

“…This effect increases considerably the planktonic biomass in these environments (Doty and Oguri, 1956;Gove et al, 2016). Additional factors are current, eddies and winds, which may lead to retention, depending on their interaction with the local geological features (Brandão et al, 2012(Brandão et al, , 2013Landeira et al, 2013). Previous studies have observed that in more sheltered (leeward) locations of oceanic islands there was a higher abundance of planktonic organisms than at more external (windward) sites of the islands (e.g.…”

“…These factors can influence composition, abundance and diversity of planktonic decapods (Anger, 2001;Strathmann et al, 2002;Gibson, 2003;Landeira et al, 2010). Studies on the larval ecology of Decapoda are essential to the understanding of the marine ecosystems in which they are inserted (Schwamborn et al, 1999;Anger, 2001;Brandão et al, 2012Brandão et al, , 2013. Even so, little effort has been made to assess the distribution and composition of decapod larvae in oceanic island environments in Brazil (Koettker et al, 2010;Brandão et al, 2012Brandão et al, , 2013Marafon-Almeida et al, 2016), specifically for the Fernando de Noronha archipelago (Lira et al, 2014(Lira et al, , 2017(Lira et al, , 2018.…”