Evaluating different methods to determine a cause for reproductive failure in Lobatus gigas.

Queen conch (Lobatus gigas) have been experiencing low reproduction rates throughout their distribution. Imposex female conchs have been observed with male verges in the British Virgin Islands and have been linked to areas of high boating activity. While in the Florida Keys, reduced reproduction has been linked to Lobatus gigas located in nearshore habitats. This literature review will evaluate the most effective method to determine a cause for reproductive failure in Lobatus gigas. In the British Virgin Islands, Cassander Titley-O’Neal analyzed imposex females and performed a butylin analysis on the digestive glands and food resources within the habitat the conch were collected. Titley-O’Neal recognized imposex morphology in Lobatus gigas and collected samples based on these features in areas of high boating activity, using reproductively normal conch from areas of low boating activity as reference. Gabriel Delgado compared the gonadal tissue and cerebral ganglia cell diameter and density of non-imposex queen conch offshore and nearshore in the Florida Keys. In the La Parguera area of Puerto Rico, Shawna E. Reed compared the gonads of imposex females to normal female conch gonads. Low concentrations of Tributyltin (TBT) in the turtle grass and marine algae samples taken by Titley-O’Neal, suggested food source is not enough uptake of TBT to cause imposex in Lobatus gigas. The presence of TBT was found in both male and female digestive glands, and in all sites, except one reference site, Anegada, but was highest in boating active sites. Concentration of Tributyltin was observed to be higher in male conch compared to females of the same area. The nearshore male and female queen conch of the Florida Keys were found to have less than 50% developed gametogenic tissue resulting in more than half being sexually inactive. The offshore population were observed to be highly reproductive with over 50% developed oogenic tissue in females and over 75% spermatogenic tissue in males. Delgado concluded that there appears to be abnormalities in the cerebral ganglion (c.g. responsible for hormone production) and deficiencies in the gonads of nearshore conch, both associated with reproduction. Given there was no environmental samples taken, there is no confirmed environmental or physical source for the cause of the abnormality in nearshore conch, other than the closer geographic proximity to anthropogenic factors. Reed compared imposex gonads to the gonads of normal reproducing females and determined no difference in sexual tissue. Imposex females demonstrated no male-like behavior. One imposex female was collected near an egg mass and had emptied signet cells, indicating successful reproduction. After evaluating each method, it appears abnormalities in cerebral ganglia, and deficiencies in gonads have been more successful in providing reason for reproductive failure in Lobatus gigas, compared to looking at masculinized females. Imposex has not yet been proven to have a negative effect on conch reproduction other than hypothesized issues regarding eggs masses as of present. Further study in the spawning of normal and imposex queen conch, with specific attention to their egg masses and habits, can potentially link imposex to failing reproduction among aggregations. Butlytin analysis on the gonads of queen conch may determine a link between Tributyltin concentration and delay in gametogenic tissues. Further research in water quality and sediment sampling to detect TBT in habitats of Lobatus gigas spawning.