Seasonality of larvae of Brachyura and Anomura (Crustacea Decapoda) in the Beagle Channel, Argentina

Abstract

This is the first study in the Beagle Channel that reports the larval seasonal distribution, abundance and duration of the larval stages of Anomura and Brachyura, on the basis of a fortnightly sampling programme. An identification key to the specific level of zoeal stages is included. Between September 1987 and March 1989, 304 plankton samples were taken by means of oblique hauls from the bottom to the sea-surface. Eighty-five percent of the samples were taken shallower than 60 m depth. Decapod larvae occurred only in spring and summer. All but two taxa showed a single cohort of larvae which emerge at the beginning of the spring. A second cohort of Munida spp. and Halicarcinus planatus also occurred during summer. The most abundant taxa were Munida spp. (312 larvae ? 10 m^-3), Peltarion spinosulum (288 larvae ? 10 m^-3),), H. planatus (143 larvae ? 10 m^-3),) and Pagurus spp. (79 larvae ? 10 m-3), which represented 97% of the total larvae collected. Larvae of Pinnotheridae, Eurypodius latreillii, Libidoclaea granaria, and Paralomis granulosa were about an order of magnitude less abundant. Relative abundances of larvae correspond to relative abundances of the respective benthic stages. The absence of certain larval stages or of certain species (Acanthocyclus albatrossis and Lithodes santolla) probably indicates their differential distribution within the Beagle Channel. Particularly, lithodid larvae may have benthic or epibenthic habits.