Aspects of the ecology, growth and dispersal behaviour of Heterozius rotundifrons A. Milne Edwards, 1867 (Brachyura: belliidae)
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
H.rotundifrons A. Milne Edwards, 1867, the big-handed crab, belongs to the Belliidae and is the only crab representative of this family in New Zealand. It lives in the intertidal zone. The megalopae undergo 13-16 moults to become fully mature at a size of 11-13mm CWo These mature crabs live up to a maximum of 19 years and attain a size of 23-25mm CW (24-26 instars). The laboratory growth curve of H.rotundifrons is asymptotic and there is no terminal ecdysis. Growth is similar between the sexes up to maturity but decreases more in males after puberty thus exhibiting an "anomalous" pattern. Average weight gain after ecdysis was found to be same for both sexes and independent of size (approx. 18%). Environmental and physical factors which normally affect growth have no profound effect on H.rotundifrons. However, moult frequency was found to be increased by removal of eyestalks or when crabs were maintained in constant darkness. Starvation and limb removal considerably reduced the moult increment. Alpha ecdysone concentration increased to a peak 40 days before ecdys is and returned to base 1eve1s at moulting. Moulting is seasonal having a high peak in mid-summer and a smaller peak in April-May. A field study of dispersal showed that short-range movements (5.06m), within the intertidal zone, are common for H.rotundifrons (n=212). Many crabs left their refuge between low tides and their movements were independent of one another. Neither home range nor long dispersal movement (>21m) have been observed in H.rotundifrons. Diet of H.rotundifrons comprised algae (60.7%), crustaceans (19.6%), sand & unidentified materials (11.7%), sponges & worms (5.7%), and molluscs (2.3%). Although brown algae were always the single dominant food item, diet composition varied seasonally. The majority of the population at Kaikoura (602(M):858(F)) consisted of pre-pubertal males and females and fewer post-pubertal males were found than post-pubertal females, a reflection of slower male growth and suggesting higher male mortality.