Helice Crassa Research Articles

Gill area and ventilation in two mud crabs, Helice crassa Dana (Grapsidae) and Macrophthalmus hirtipes (Jacquinot) (Ocypodidae), in relation to habitat

Helice crassa Dana, 1851 (Grapsidae) which typically constructs burrows in compacted sediments towards high-tide limits and in semi-terrestrial areas, has the same gill formula and weight specific gill platelet number as a second mud crab, Macrophthalmus hirtipes (Jacquinot, 1853) (Ocypodidae), which burrows into waterlogged substrata below mid-tide level. Nevertheless, the gill area of Helice crassa is significantly ( P < 0.05) smaller than that of Macrophthalmus hirtipes, due to a reduction in the area of individual gill platelets, but not to a decrease in gill filament length or fewer platelets per mm of filament. Various structural adaptations ensure that when Helice crassa becomes exposed, water leaving the branchial chambers is recirculated for probable re-oxygenation, together with use in evaporative cooling and food separation by the mouthparts. Macrophthalmus hirtipes cannot maintain prolonged recirculation of branchial water when in air. These observations enable further understanding of the adaptations which allow Helice crassa to occupy high-shore and semi-terrestrial habitats, and why Macrophthalmus hirtipes is restricted to intertidal mud flats that retain surface water upon exposure.

Aerial and aquatic respiration in two mud crabs, Helice crassa Dana (grapsidae) and Macrophthalmus hirtipes (Jacquinot) (ocypodidae), in relation to habitat

1. 1. Weight-specific oxygen uptake by Macrophthalmus hirtipes and Helice crassa was a decreasing function of dry tissue body-weight and generally increased at higher temperatures. 2. 2. Oxygen consumption by small crabs, of each species, was less temperature dependent than for larger individuals. 3. 3. Both species displayed short-term metabolic compensation at temperatures commonly encountered in the field. Such compensation was especially pronounced ( Q 10 values < 1.0) for M. hirtipes. 4. 4. At the temperature of acclimation, in both air and seawater, H. crassa consumed more oxygen than M. hirtipes. Also, relative to M. hirtipes, H. crassa was better able to utilize atmospheric oxygen. 5. 5. Results are discussed in relation to the habitat preferences and characteristic vertical separation of each species.

Habitat preferences of two estuarine burrowing crabs Helice crassa Dana (Grapsidae) and Macrophthalmus hirtipes (Jacquinot) (Ocypodidae)

The horizontal and vertical distributions of two species of endemic, burrowing mud crabs Helice crassa Dana 1851 (Grapsidae) and Macrophthalmus hirtipes (Jacquinot 1853) (Ocypodidae) are described for the Avon-Heathcote Estuary (43°33′S: 172°44′E), Christchurch, New Zealand. Substratum preference is shown to be the most important factor influencing mud crab distribution, but lack of tolerance to salinities below 4‰ is also a significant factor preventing M. hirtipes from occurring at points close to freshwater input. Both species had similar sediment organic content and particle size requirements. Helice crassa was concentrated in well-drained, compacted sediments above mid-tide level, whilst Macrophthalmus hirtipeswas found in waterlogged areas below mid-tide level. This vertical separation is shown not to be caused by differential desiccation tolerances, but by feeding and burrowing adaptations related to these different substrata.

Effect of temperature, season, and stage of life cycle on salinity tolerance of the estuarine crab Helice crassa Dana (Grapsidae)

Survival of juvenile and mature specimens of Helice crassa Dana 1851 (Brachyura: Grapsidae) collected during summer, and of mature crabs collected in winter was measured at various salinity and temperature combinations. Summer crabs were euryhaline and eurythermal, and had low mortality after 7 days in salinities of 3.5–52.5%. at temperatures of 5–30 °C. Mortality was high in all salinities at 35°C and at all temperatures in 0.35%., however, juveniles had longer times to 50% mortality than mature crabs in 0.35%. at temperatures from 10–20 °C. Mature crabs had significantly better survival ( P < 0.05) in 52.5%. at 5, 10, and 30 °C than juveniles. Juveniles showed widest salinity tolerance at temperatures closest to field temperatures at time of collection; lower and higher temperatures reduced the salinity range in which maximum survival was possible. No consistent effect of temperature on salinity tolerance of mature crabs was apparent. Winter crabs had significantly higher survival ( P < 0.05) in 0.35 %. at the three temperatures tested (5, 10, and 20 °C) compared with summer crabs. The salinity tolerance of stage 1 zoeae released from ovigerous female H. crassa maintained in the laboratory was investigated at 20 °C. Larvae were stenohaline, and had 100% mortality within 1 hour's exposure to salinities of 3.5–10.5 %., and within 24 h in 14%.; there was no mortality in 35%. until after 48 h. Combination of wide salinity—temperature tolerances, seasonal acclimatization giving enhanced survival in dilute salinity during winter, and the refuge of a burrow during extreme physico-chemical conditions allows the benthic stages of H. crassa to occupy the most dilute regions of an estuary. In these latter areas, concentration of the vertical distributions of ovigerous females to highest shore levels ensures that larvae are released into salinities within their limited tolerance range.

Influence of salinity on the respiration of an estuarine mud crab, Helice crassa (Grapsidae)

1. 1. The oxygen consumption of the euryhaline mud crab. Helice crassa (Grapsidae), was measured in 150, 100 (33.5 00 0.), 50 and 10% seawater (SW) at 10°C. 2. 2. In all salinities, there was a positive logarithmic relationship between body size (dry weight) and rate of oxygen uptake. 3. 3. Compared with the rate in 100% SW, oxygen uptake was not significantly different in 150% SW, but was significantly lower in 50% SW and significantly elevated in 10% SW ( P < 0.01). 4. 4. The weight exponent “b” (of the equation y = ax b) showed the opposite relationship from oxygen consumption to salinity change, and was highest in 50% SW and lowest in 10% SW.

Effect of temperatury, season, and stage of life cycle on salinity tolerance of the estuarine crab Helice crassa Dana (Grapsidae) : Jones, M.B., 1981 J. expl mar. Biol. Ecol., 52(2/3): 271–282

Effect of temperatury, season, and stage of life cycle on salinity tolerance of the estuarine crab Helice crassa Dana (Grapsidae) : Jones, M.B., 1981 J. expl mar. Biol. Ecol., 52(2/3): 271–282

Reproductive ecology of the estuarine burrowing mud crab Helice crassa (Grapsidae)

The reproductive cycle and population biology of the endemic, burrowing mud crab Helice crassa Dana, 1851 (Brachyura, Grapsidae) in the Avon-Heathcote Estuary (44°33′S, 172°44′E), Christchurch, New Zealand, was studied from April 1975 to December 1976. Juvenile crabs (≤4 mm carapace width) were present throughout the year, but were most numerous from February to April. Males of all sizes (4.1–18.0 mm carapace width) were significantly (tested by χ 2 ) more abundant than females and the overall sex ratio was 1.48♂♂: 1♀. Maximum carapace widths were 17.7 mm for male crabs, 15.8 mm for non-ovigerous females and 15.1 mm for ovigerous females. Ovigerous females occurred from August/September to March with maximum numbers present in November. Peaks of egg production were found in October and January. Egg volume at oviposition was constant throughout a breeding period; however, eggs from August–November 1975 ( volume=0.0099 μl±0.0032) had a significantly larger volume ( t =3.68, P <0.01 for 45 D.F.) than those from September–December 1976 ( volume=0.0074 μl±0.0021). Eggs did not increase in volume during development and had no measurable mortality. Egg numbers were not affected by season and were related to female carapace width according to the equation y =−13931.8+1890.8 x ( r 2 =0.886). These findings are compared with studies on the reproduction of this species from marine habitats elsewhere in New Zealand, and are considered with respect to the influence of latitude and environment on the breeding biology of H. crassa .

Reproduction, Growth and Distribution of the Grapsid Crab Helice Crassa (Dana, 1851) in the Southern Part of New Zealand

Une population libre du crabe Grapside Helice crassa (Dana, 1851) a ete echantillonnee chaque mois, les crabes etant deterres sur une etroite section, suivant la pente de la plage. Ce crabe vit typiquement dans des terriers a la limite superieure de la zone intertidale, mais il est plus concentre dans la partie haute de la plage pendant l'hiver, de mai a octobre, que pendant l'ete. Les crabes de chaque echantillon ont ete divises en cinq categories: les petits, les juveniles, les mâles adultes, les femelles adultes non ovigeres et les femelles ovigeres. Les femelles ovigeres et les petits etaient distribues de la meme facon que les autres crabes. Les petits et les juveniles ont ete trouves pendant toute l'annee mais en plus grand nombre dans les mois d'ete. Les femelles ovigeres etaient presentes dans la nature pendant six mois, de septembre a fevrier. Des individus marques ont ete conserves en laboratoire pendant des periodes atteignant 17 mois et, dans ces conditions, il y avait des femelles ovigeres entre juillet et mars, c'est-a-dire pendant 9 mois. L'accouplement s'est produit quand les femelles avaient une carapace dure et a ete observe en laboratoire entre juin et janvier. La duree d'incubation en laboratoire etait de 35 jours, en moyenne, mais variait entre 22 et 53 jours. Le temps d'incubation diminuait pendant la saison de reproduction (r = 0.88, P<0.001) et etait en correlation avec la temperature moyenne de l'eau (r = -0.78, p<0.001). La plupart des crabes adultes ont mue deux fois par an, au commencement et a la fin de l'ete.

The composition of the blood of the grapsid crab, Helice crassa Dana

The ability of the grapsid crab, Helice crassa Dana, to regulate the ionic concentration of its blood in adverse salinities has been investigated. The significance of these data is compared with those for other grapsid crabs and other Crustacea.

Life‐history studies on New Zealand Brachyura

Summary Pre‐zoea and first stage zoea larvae of the New Zealand grapsid crabs Leptograpsus variegatus (Fabricius), Planes marinus Rathbun, Hemigrapsus crenulatus (H. Milne Edwards), H. edwardsi (Hilgendorf), Cyclograpsus lavauxi H. Milne Edwards, C. insularum Campbell and Griffin, Helice crassa Dana, and Plagusia chabrus (Linnaeus) are described, and a key is given for their separation. On the basis of larval characters known grapsid zoeae fall into four groups, and these support the arrangement of adult genera into subfamilies except for a division among larvae of the subfamilies Varuninae and Sesarminae. The four groups are defined in a key and this arrangement is compared with an earlier system of larval classification. Grapsid zoeae show close affinities with those of genera in the families Ocypodidae and Gecarcinidae. Except Hemigrapsus edwardsi which breeds in late autumn and winter, all New Zealand species breed during late spring or summer. Where Cyclograpsus lavauxi and the recently rediscovered C. insularum occur together, their breeding periods do not coincide. All species have five zoeal stages and a megalopa larva, and planktonic larval life may last up to seven weeks. The length of larval life is apparently unrelated to the absence of grapsid crabs (or to the presence of certain other species) in the Chatham Islands.