Between-habitat differences in burrow characteristics and trophic modes in the southwestern Atlantic burrowing crab Chasmagnathus granulata

Abstract

Burrow characteristics, food type, and feeding h a b ~t s of the SW Atlantlc burrowing crab Chasmagnathus grdnulata were compared between ~n d i v ~d u a l s living in mud flats and In Spartinadominated marshes. Burrows were shorter ( X -19.7 cm, SD = 5 8, n = 54) and more dynamlc (entrance displacement: X = 3 2 cm d-l, SD = 1 7, n = 21) in mud flats than In Spartlna-dominated areas (length X = 41 cm, SD = 12, n = 78, no entrance displacement). Sediment turnover rate was much higher in mud flats ( X -5 9 kg m-' d-l) than in Spartlna-dominated areas ( X = 2 4 kg m-' d.'). Burrow shape differed between areas, being straight, near-vert~cal tunnels in the vegetated area, but oblique (average angle to vertical = 60'. SD = 16", n = 110), and having a funnel-shape entrance and a much large]-diameter in mud flats Stomach contents also differed between habitats. Pleces of plants dominated contents in the vegetated area, while sediment (with polychaetes, diatoms, ostracods, and nematodes) d o m ~n a t e d in the mud flats, lndicatlng that crabs are mainly deposit feeders In the mud flats a n d herb~vorous in the Spart~na-dominated areas.