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.

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.

The mating behaviour and reproductive ecology of the big-handed crab Heterozius rotundifrons was studied at Kaikoura between November 1997 and December 1998. H. rotundifrons was found at mean densities of 7.6 per m² (± 1.4) within the middle and low shore levels and varied little between seasons. The variance! mean ratio indicated that males and females aggregated within these shore levels. The sex ratio was significantly female biased during the majority of the year. Allometric growth rates indicated that males and females reached sexual maturity at 11 mm carapace width (CW). In males, spermatozoa production occurred between 9-9.99 mm CW. Ovigerous females were present every month except February. The first broods of the year were produced in March which coincides with a decrease in the female gonado-somatic index (GSI). These broods were incubated for approximately nine months whereas broods produced in August were incubated for only five months. Female brood production appeared to be cyclical, alternating between a winter incubation period and a summer incubation period. The completed cycle takes approximately three years with two broods produced during the cycle. Fecundity increased with female size but egg mortality was quite high (19%). Instantaneous mortality rate increased with increasing brood development. Females mate when recently moulted (soft-shelled). Although females moulted through out the year, in small numbers, there was a peak in female moulting during October and November. The operational sex ratio (OSR) was male biased during all months of the year. Females released an attractant prior to moulting which initiated pre-copulatory mate guarding by the male. Once the female moulted, copulation occurred approximately 6 h later. Copulation lasted for approximately 3 h and was followed by a period of post-copulatory mate guarding. Males increased the duration of post-copulatory mate guarding if another male was present. Large males out competed small males for receptive females. Males used their large cheliped to subdue competitors and to provide protection for the soft female. Mate guarding was shown to reduce cannibalism from other females. Spermatozoa are packaged in spermatophores within the vas deferens of males but are quickly dehisced within the spermathecae (ventral-type) of newly mated females. Last male to copulate probably achieves the highest level of paternity. Postcopulatory mate guarding by the male was found and ejaculates were found in discrete packets within the spermatheca. Sperm competition appeared to be important because large males displaced small males during copulation, males left when a female was still receptive and the females could retain sperm between moults. It is concluded that H. rotundifrons probably has a polygynous mating system in which males compete for soft females (female centered competition)

The mating behaviour and reproductive ecology of the big-handed crab Heterozius rotundifrons was studied at Kaikoura between November 1997 and December 1998. H. rotundifrons was found at mean densities of 7.6 per m² (± 1.4) within the middle and low shore levels and varied little between seasons. The variance! mean ratio indicated that males and females aggregated within these shore levels. The sex ratio was significantly female biased during the majority of the year. Allometric growth rates indicated that males and females reached sexual maturity at 11 mm carapace width (CW). In males, spermatozoa production occurred between 9-9.99 mm CW. Ovigerous females were present every month except February. The first broods of the year were produced in March which coincides with a decrease in the female gonado-somatic index (GSI). These broods were incubated for approximately nine months whereas broods produced in August were incubated for only five months. Female brood production appeared to be cyclical, alternating between a winter incubation period and a summer incubation period. The completed cycle takes approximately three years with two broods produced during the cycle. Fecundity increased with female size but egg mortality was quite high (19%). Instantaneous mortality rate increased with increasing brood development. Females mate when recently moulted (soft-shelled). Although females moulted through out the year, in small numbers, there was a peak in female moulting during October and November. The operational sex ratio (OSR) was male biased during all months of the year. Females released an attractant prior to moulting which initiated pre-copulatory mate guarding by the male. Once the female moulted, copulation occurred approximately 6 h later. Copulation lasted for approximately 3 h and was followed by a period of post-copulatory mate guarding. Males increased the duration of post-copulatory mate guarding if another male was present. Large males out competed small males for receptive females. Males used their large cheliped to subdue competitors and to provide protection for the soft female. Mate guarding was shown to reduce cannibalism from other females. Spermatozoa are packaged in spermatophores within the vas deferens of males but are quickly dehisced within the spermathecae (ventral-type) of newly mated females. Last male to copulate probably achieves the highest level of paternity. Postcopulatory mate guarding by the male was found and ejaculates were found in discrete packets within the spermatheca. Sperm competition appeared to be important because large males displaced small males during copulation, males left when a female was still receptive and the females could retain sperm between moults. It is concluded that H. rotundifrons probably has a polygynous mating system in which males compete for soft females (female centered competition)