The life cycle of the pteropod Limacina helicina in Rivers Inlet (British Columbia, Canada)

• Main Author: Wang, Kang
• Format: Thesis
• Language: English
• Published: University of British Columbia 2014
• Subjects: British Columbia; Canada; Limacina helicina
• Online Access: http://hdl.handle.net/2429/46485

The life cycle of Limacina helicina has been continuously debated within the literature. We believe the current lack of consensus regarding fundamental aspects of its life cycle (e.g. seasonal times of spawning, seasonal development of the population size structure, as well as the life cycle longevity) is primarily due to using datasets of low temporal resolution. Using fort-nightly data, two population cohorts were identified using the mixdist statistical package and tracked for more than 400 days, throughout 2008 to 2010. From this, a life cycle longevity of 1.2--1.5 years was estimated for L. helicina in Rivers Inlet. Throughout the seasons, the population size structure showed a continually high presence of the smaller size-groups suggesting continuous spawning, however, based on total densities of > 600 ind.m^-³, the late spring was put forward as the period of peak spawning. Continuous spawning was confirmed with the use of daily data. Identification of a summer peak spawning established late spring and summer as two periods of enhanced spawning, although continuous spawning occurred throughout the season (in a limited fashion). Short-term periods of significant growth were observed prior to peak spawning in late spring and summer. This was not directly coupled with chlorophyll concentrations, possibly due to the time lag between periods of high chlorophyll biomass and zooplankton response. Attempts were made to estimate the instantaneous mortality of L. helicina, and the seasonal changes experienced from spring to summer. Our estimates were complicated by a combination of 1.) inherent patchiness of L. helicina, 2.) advection, and 3.) merged recruits. Generally, there were no cases of significant mortality throughout the seasons however, short term mortality was observed after peak spawning. It is plausible that the smallest size-groups of L. helicina experiences the highest mortality after peak spawning. Our findings show that in Rivers Inlet, L. helicina has a life cycle spanning 1--1.5 years with spring and summer peak spawning activities. The spring cohort is likely spawned by the summer cohort from the previous year. It utilizes the spring phytoplankton bloom to reach sexual maturity and spawn the summer cohort.