Biology | Ecology and Evolutionary Biology | Marine Biology
Demography of the infaunal polychaete Nephtys incisa was investigated for periods of 1 yr prior to and following disturbance (dredge material disposal) at a site in central Long Island Sound, USA. Infaunal grab samples were taken at 5 stations 200 m to 3 km apart. The demography of populations at each station was based on age-classes spanning juveniles to adults 4 + yr of age. Age-specific survivorship and fecundity were based on changes in mean density of each cohort and a positive correlation between female size and egg production, respectively. Analyses of population matrix models indicated pre-disposal populations had positive population growth rates, despite differences in vital rates among stations. During the second year, population growth rates were reduced by 50%, below population maintenance levels, at each station, primarily due to recruitment failure across the entire study site. Population growth rates were reduced an additional 25% by disturbance at the dump site and next closest station (200 m away) due to decreased worm size and survivorship relative to other stations, and the absence of recolonization by worms > 2 yr of age. Populations of N. incisa appear to experience several demographic 'states', related to periods of potential population growth, decline and recovery from disturbance. Based on analyses of related demographic parameters, there is a concomitant change in the contribution different age-classes make to population growth. During periods of growth 2-yr-old worms make the greatest contribution, older age-classes during declines, while younger age classes become important during recovery from disturbance. These differences result from temporal and spatial fluctuations in recruitment, individual growth and reproductive activity. Responses of long-lived marine infauna to disturbance likely depend on their current demographic state at the time of disturbance (reflecting demographic conditions such as size/age structure) and factors external to the population (e.g. environmental influences on settlement and recruitment or the type of disturbance]. In this case, the disposal of contaminated dredge material had a negative impact on vital rates and potential population growth of N. incisa at and 200 m away from the disposal site, but little or no effect on populations 400 m to 3 km away.
Zajac, Roman and Whitlatch, Robert B., "Natural and Disturbance-Induced Demographic Variation in an Infaunal Polychaete, Nephtys incisa" (1989). Biology and Environmental Science Faculty Publications. 8.
Zajac, R. & Whitlatch, R. (1989). Natural and disturbance-induced demographic variation in an infaunal polychaete, Nephtys incisa. Marine Ecology Progress Series, 57, 89-102.