This study investigated whether surface hole counts could be used as a reliable estimate of density of the ghost shrimps Trypaea australiensis Dana 1852 and Biffarius arenosus Poore 1975 (Decapoda, Thalassinidea) in south eastern Australia. The relationship between the number of holes and the number of ghost shrimps was explored in two ways. Resin casts were used to document any changes in the number of burrow openings per shrimp burrow over time. Manual suction pumping (bait pumping) within a given mudflat area was used to directly compare the number of holes on the sediment surface with the number of ghost shrimps occupying the corresponding volume of sediment. Resin casting showed that throughout the year, the burrows of T. australiensis consistently had an average of two openings, whereas the burrows of B. arenosus showed much greater variability over time with two to four openings per burrow. Overall, a significant relationship between the number of holes and the number of ghost shrimps (mixed species populations) was found, with 2.1 burrow openings for each ghost shrimp. However, some temporal and spatial variation was seen in this relationship. We suggest that the hole count method may be reliable in estimating ghost shrimp densities with restricted use and site specific validation based on some limitations found in this study.
This study compared the population biology of two co-existing species of ghost shrimps, Trypaea australiensis Dana 1952 and Biffarius arenosus (Poore 1975), over a two year period at Warneet and Crib Point in Western Port, Victoria, south-eastern Australia. Overall, the sex ratio in populations of T. australiensis varied considerably (male and female biases were found at different times) whereas the sex ratio of B. arenosus was generally 1:1 or female biased. A male biased sex ratio was found in the juvenile size class of populations of T. australiensis (both years) and B. arenosus (one year only). Both species reproduced in spring and summer in Western Port and juveniles appeared to recruit into the populations all year round. The embryo and clutch size of T. australiensis females was signifi cantly larger than B. arenosus, and a signifi cant relationship between female body size and clutch size (but not embryo size) was found for both species. Comparisons between this and other population studies of T. australiensis and B. arenosus were made to highlight any latitudinal variation in the reproduction and breeding biology of these species along the eastern coast of Australia.
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