Abstract
The sulphur-rich and acidic vent waters of a shallow hydrothermal vent field next to Kueishan Island in Taiwan provide a specific and generally toxic environment. Among only a few aquatic organisms able to survive there, the grapsoid crab Xenograpsus testudinatus is the dominant species with a high population density in the vent area. Here we study the gender-specific distribution, morphological traits, and relationship of wet weight vs. carapace width of this crab. A total of 1120 individuals including 831 male and 289 female (included 15 ovigerous) were examined during August and September in 2011 and May and September in 2012. Except in August 2011, there are no significant differences in the distribution of X. testudinatus in the hydrothermal vent area from the vent spout during most months. Among crabs, the weight of male (6.87 ± 2.90 g) was significantly heavier than that of females (4.17 ± 1.25 g) (p < 0.001, Student’s t-test). As for the wet weight of crabs, significant differences were noted in both the length of chela and the width of carapace between males and females. Sexual dimorphism of X. testudinatus is evident in three morphological traits. Pearson’s correlation showed a significant and positive correlation (p < 0.001) of wet weight, width of carapace and length of chela of the two sexes. Ovigerous crabs (shortest carapace width: 1.93 cm) were present in the specimen collected from August 2011 and May 2012. The ovigerous crabs were not found in the samples collected from September in both years 2011 and 2012, indicating that reproduction may have ceased during the period of sampling. The present results suggested that the reproductive period of X. testudinatus was before September. The distribution pattern and sexual dimorphism of X. testudinatus provided a better understanding of the idiobiology of this dominant metazoan in the hydrothermal vent area.
Highlights
Submarine hydrothermal vents are called shallow if their depth is above 200 meters in the range of the euphotic zone at many places worldwide
The present in situ study showed that there is no significant difference in the distribution of X. testudinatus in the hydrothermal vent area from the vent spout in most months
The present study found that X. testudinatus in the hydrothermal vent area had a clear pattern of sexual dimorphism by developing larger chelipeds in males, which is similar to fiddler crabs (Uca spp.) [43,51,56], and another hydrothermal vent crab M. distinguendus [13]
Summary
Submarine hydrothermal vents are called shallow if their depth is above 200 meters in the range of the euphotic zone at many places worldwide. If their location in a depth range deeper than 200 meters in the aphotic zone is called deep sea hydrothermal vent. There is a small volcanic island located at the northeastern coast off of Taiwan [3], named Kueishan Island ( called as Kueishantao, Gueishan Island or Turtle Island). This island originated from volcanic eruptions about 7000 ± 700 years ago [4]. Seabed temperature reveals that the heat flow at offshore Kueishan Island was about 700–1284 mW/m2, the highest record up to 2500 mW/m2 [7]
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