Title

The Effect of Copepod Density On Cannibalism, Survival, Development Rate and Egg Production and the Implications for Population Growth Rate and Demographics of Acartia tonsa Dana (Copepoda: Calanoida)

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Coastal Sciences, Gulf Coast Research Laboratory

First Advisor

Jeffrey M. Lotz

Advisor Department

Coastal Sciences, Gulf Coast Research Laboratory

Abstract

An understanding of the effects of copepod density and cannibalism on the vital rates of copepods (Calanoida) is necessary for developing large-scale intensive cultures of calanoids. The main objective of this dissertation was to identify conditions that maximize the growth rate of a cultured population of Acartia tonsa (Copepoda: Calanoida). The effects of copepod density, phytoplankton density, and gender on cannibalism and the effects of copepod density on survival, development rate, and egg production were determined experimentally. The vital rates determined experimentally were used to form a stage-specific population matrix model that was used to determine the effects of copepod density and cannibalism on population growth, reproductive values and proportions of the instars and the sensitivity of population growth rate to changes in the instar-specific vital rates. Cannibalism was not dependent on the sex ratio. Cannibalism was unaffected by adult density, directly related to naupliar density, and negatively related to phytoplankton density. Cannibalism of nauplii by copepodids increased as the copepodid instar increased and as the naupliar instar decreased. It was unlikely that copepodid stages earlier than C4 were cannibalistic, and that naupliar stages later than 4 or 5 were susceptible to cannibalism. Only the adults could cannibalize naupliar instars higher than N2. Survival and development time were negatively affected by the number of eggs used to start a culture and time. Survival was explained by a linear model that was dependent on time and egg stocking density ( survival = 0.982 - 0.006(day) - 0.045(stocked eggs mL-1 ) ). Median development time of an instar was explained by a linear model that was dependent on egg stocking density (development time = -0.244 + 0.763(copepod instar) + 0.002(stocked eggs mL-1 ) ). Adult survival was explained by a linear model that was dependent on time (Adult survival = 0.978 - 0.003(hour) ). Eggs per capita was explained by a quadratic function dependent on adult density (eggs per capita = 6.1512 (adults mL-1 )2 -19.596 (adults mL-1 ) + 22.785) ). Total eggs was explained by a quadratic function dependent on adult density (eggs L-1 day -1 = -0.0027355(adults L-1 ) 2 +7.125180(adults L-1 ) + 569.8800 ). Population growth rate was higher in populations started with fewer eggs and those without cannibalism. The fraction of adults remaining in the adult instar per unit time had the greatest effect on growth rate, followed by the fraction remaining in N2 and N3. Changes in fecundity had little effect on the population growth. The results of this dissertation support development of an intensive batch culture for A. tonsa that prevents cannibalism by maintaining high levels of phytoplankton and by removing 100% of the eggs produced, optimizes copepod density, increases development times of the second and third naupliar instars, and prolongs the duration of the adult instar.