Population dynamics and life history characteristics of boreal appendicularian species in Conception Bay, Newfoundland, Canada

Choe, Nami (2008) Population dynamics and life history characteristics of boreal appendicularian species in Conception Bay, Newfoundland, Canada. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The primary goal of this study was to investigate the population dynamics and life history traits of boreal appendicularian species in Conception Bay, Newfoundland. Specific questions were; (1) What are the optimum environmental conditions for appendicularian species? (2) What are their generation time, and growth and secondary production rates? (3) How do length-at-age, age-at-maturity and fecundity vary under seasonally fluctuating environmental conditions and how do these demographic parameters relate to population growth rate? In order to study life history and demographic traits of naturally occurring populations of appendicularians, it was necessary to develop an in situ method of age determination. -- The temporal and spatial niche of appendicularian species is defined primarily by temperature and salinity in which Oikopleura vanhoeffeni is a cryophilic, stenothermal and stenohaline species, Fritillaria borealis typica is eurythermal and euryhaline and Oikopleura labradoriensis is mesothermal and mesohaline. Throughout the year, more than 70 % of the individuals of each species were present above 100 m, indicating that a majority of them experienced seasonal variation in abiotic and biotic factors. -- The presence of lipofuscin in the brain tissue, growth rings on the statolith and statolith diameter were explored as age indicators for appendicularians. The results indicated that statolith diameter was a feasible and reliable age indicator. A laboratory study of statolith diameter and somatic growth in O. vanhoeffeni showed that variability in statolith diameter-at-age was substantially lower than that in trunk length-at-age, and that variability in statolith-at-age remained constant with age whereas variability in trunk length-at-age increased with age, suggesting that statolith diameter should be a better in situ indicator of age than body size. Using statolith diameter as a proxy for age, trunk length-at-age of O. vanhoeffeni and O. labradoriensis in Conception Bay varied seasonally depending on food type and concentration, indicating that conventional decomposition of cohorts from trunk length frequency distributions would lead to inaccurate estimation of age structure and thus population growth rates. -- Based on age structures represented by statolith diameter, the generation time of O. vanhoeffeni was one year and that of O. labradoriensis was between 8 months and one year. Somatic growth in both species was exponential, suggesting the absence of food-limitation and that there was no apparent energetic trade-off between growth and reproduction. Somatic growth rate of both species (mass basis) ranged from 0.007 to 0.043 d⁻¹. House production rate far exceeded somatic production in terms of carbon. The annual sum of somatic and house production of both oikopleurid species was equivalent to 49 - 95 % of mesozooplankton production and 3.8 - 7.3 % of primary production in Conception Bay. -- Age-at-maturity of O. vanhoeffeni and O. labradoriensis increased over winter and spring as temperature decreased, while size-at-maturity and potential fecundity increased to a maximum during the spring diatom bloom. The population growth rate of O. vanhoeffeni peaked in spring as age-at-maturity and fecundity increased whereas the population growth rate of O. labradoriensis peaked in the fall when age-at-maturity and fecundity decreased. Thus, O. vanhoeffeni has a life history strategy based upon maximization of clutch size and O. labradoriensis has a life history based upon maximization of population turnover rate. Thus, the appendicularian tunicates appear to have multiple adaptations promoting niche separation including temporal segregation, different optimum temperature and salinity and differing life history adaptations, particularly involving variability in age and size-at-maturity and in individual fecundity.

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