Sclerochronology – a highly versatile tool for mariculture and reconstruction of life history traits of the queen conch,Strombus gigas(Gastropoda)

Abstract

The queen conch, Strombus gigas, is an important fisheries resource in the Western Tropical Atlantic. In order to maintain harvesting success, improve fisheries management and contribute to mariculture pursuits, a detailed understanding of the life history traits of this species is required. Traditionally, this has been achieved by tedious and time-consuming long-term field observations. This study presents a highly versatile and rapid technique to estimate the timing and rate of shell growth based on sclerochronology. The Belizean S. gigas specimens (N = 2) from the offshore atoll, Glovers Reef, reached their final shell size (maximum shell height: 22.7 and 23.5 cm, respectively; completed formation of the flared lip) after only two years. However, seasonal growth rates varied considerably. Shells grew up to 6 mm d−1 during spring (April-June) and fall (September-November) but only 1 to 2 mm d−1d uring July and August. Furthermore, shell growth ceased between December and March. Fastest shell growth occurred nearly contemporaneously with times of maximum precipitation which probably resulted in increased food availability. Slowest shell growth however, occurred during times of reduced rainfall and reduced riverine runoff, i.e. during times of reduced food supply. Sea-water temperature apparently did not exert a major control on shell growth. Notably, the slow winter growth was marked by a distinct purple-colored growth line in the cross-sectioned flared lip. Formation of a second major growth line (brown) fell together with the main reproduction period (late October/early November). Shell microgrowth patterns potentially represent daily or semidiurnal periods but cannot be used to assign exact calendar dates to each shell portion, because they were not visible across the entire cross-section of the whorl. Also, the protruding spines developed on the outer shell surface do not function as time gauges. The time represented by the shell portion between consecutive spines varies greatly from 1 to 72 days. Sclerochronology can potentially facilitate maricultural strategies and aid in site pre-testing and selection to grow S. gigas.