Stability of Corynosoma populations with fluctuating population densities of the seal definitive host

• Main Authors: E. T. Valtonen, E. Helle, R. Poulin
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2004
• Subjects: Phoca hispida
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.499.620; http://www.otago.ac.nz/parasitegroup/PDF papers/Valtonenetal2004-Para.pdf

In theory there should be a strong coupling between host and parasite population sizes. Here, we investigated population size and structure in 3 species of acanthocephalans, Corynosoma semerme, C. strumosum and C. magdaleni, in ringed seals (Phoca hispida) from the Bothnian Bay over a period ofmore than 20 years. During this period, seal numbers first decreased markedly and then increased steadily; at the same time, a paratenic fish host particularly important for C. strumosum has gradually disappeared from the bay due to decreasing salinity. We found no evidence that the mean abundance of any of the 3 acanthocephalan species changed significantly over time, nor was there any relationship between parasite abundance at any point in time and seal numbers in the corresponding year. Based on the proportion of sexuallymature female worms per infrapopulation, and on relationships between the sex ratio of worms and infrapopulation size, both C. magdaleni and C. semerme appear to be doing well, independently of the population size of their seal definitive hosts. In contrast, perhaps because of the loss of its main paratenic host, C. strumosum appears more at risk in the Bothnian Bay. Our results show that in complex natural systems, there are not necessarily simple, direct links between definitive host population size or density, and parasite population dynamics. Key words: stability, acanthocephalan population, host population, Corynosoma, seals.