Morphological and physiological differences among alternative morphs of the queen conch (Lobatus gigas) near Calabash Caye, Belize

The queen conch is one of the most valuable marine species in Belize. It also presents a special challenge to regulators, as take limits based on shell dimensions are complicated by the existence of substantial infraspecific variation in shell morphology. While shell length is used to define legal take in Belize, the thickness of the species’ characteristic flared lip is regarded as a better indicator of sexual maturity. Complicating matters, three widely recognized morphs are reported to exhibit qualitatively different relationships between length and lip thickness. “Samba conchs," once suggested to be a different species, have a thicker lip at a given length than the standard queen conch, while “lipless conchs” (also known as “coil conch”), never develop a flared lip, even at extreme shell lengths. Historically, much of the data on variation in queen conch morphology has derived from Bermuda, Florida, and the eastern Caribbean. In an effort to characterize the variation among queen conchs within the Turneffe Atoll Marine Reserve, and determine whether alternative morphs are qualitatively different or merely points along a morphological continuum, we performed a 3-year (2015-2017) study on shell morphology, physiology and distribution. We examined shell length, lip thickness, and gape in 647 conch collected in four sites near Calabash Caye and Blackbird Caye on the eastern edge of Turneffe Atoll. Conch abundance varied greatly by site. Shell length showed weak correlation to lip thickness. Based on the relationship between shell length and lip thickness, and on a 3-dimensional analysis of 150 physical landmarks on the shell, the variation within the species appeared to be continuously distributed, which would undermine the argument for defining distinct morphs. However, using respirometry, we did observe significant differences in mass specific metabolic rate between select samba conchs and standard queen conchs. This longitudinal study on morphological diversity, abundance, and distribution of queen conch morphs creates a foundation for future long-term studies on the conch stock around Calabash Caye. While the shell metrics we measured did not clearly segregate distinct conch morphs, more sophisticated statistical analysis on these data may provide better discrimination, and other traits might clearly distinguish morphs, including previously recognized differences in pigmentation of the mantle tissue. We are currently analyzing the transcriptome for evidence of genetic differentiation among conch morphs, if it exists.Published versio