Thursday, 12 November 2009
Overfishing has caused the blue crab (Callenectes sapidus) population to dwindle. Thus, human-induced stock enhancement is one of the many practices used to counter the negative effects of overfishing. This study addresses the release and recapture of blue crabs in the megalopal developmental stage. Moreover, this study aims to observe the genetic variation between wild and hatchery crabs. Approximately 280,000 hatchery raised blue crab megalopae were released at the mouth of the Beaufort Inlet, NC. Samples of megalopae were collected further into the estuary at five locations and four consecutive two hour increments. A total of 92 crabs were collected and genotyped using the following markers: the ND2 mitochondrial gene and the 12S ribosomal gene. Out of 92 megalopae, 37 responded to the ND2 primers, while 87 responded to 12S. Samples that responded to the markers were DNA sequenced and analyzed by a UPGMA algorithm to create a phylogenetic tree. Comparing the DNA sequences and the ND2 tree results of the wild-caught crabs to the hatchery broodstock was done to confirm if recapture took place. The 12S tree was used to determine what percentage of the samples were actually Callinectes sapidus and which were Callinectes similis which do not react with the ND2 primers. The results of the trees implicate that none of the 280,000 released megalopae were recaptured. However,a larger than normal genetic diversity among the crabs was noticed with only two sets of two crabs each sharing the same sequence. It's important to note that the genetic diversity in megalopae appears to be much higher than subsequent stages (i.e. juveniles). This level of natural genetic diversity at the megalopal stage also has implications for restocking efforts and may be prohibitively high to recreate in a hatchery setting.
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