Stability ofCorynosomapopulations with fluctuating population densities of the seal definitive host

Abstract

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 of more 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 sexually mature 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.

Vertebrate diets derived from trophically transmitted fish parasites in the Bothnian Bay

“…Fish species composition was considered stable over the time period studied (see e.g. Lehtonen et al 1993;Valtonen et al 2004), and food web studies normally integrate data over extended periods. Amundsen et al (2009) assembled information for the Takvatn pelagic web over 21 years.…”

“…Amundsen et al (2009) assembled information for the Takvatn pelagic web over 21 years. Parasites and diets of 109 ringed (Phoca hispida) and 49 grey seals (Halichoerus grypus) were obtained from the senior author's data on alimentary tract contents) from 1977 to 1999 (see Valtonen et al 2004), information on seals' diets being supplemented from the literature for the Baltic Sea (Söderberg 1975;Tormosov and Rezvov 1978;Stenman and Pöyhönen 2005). Diets of bird species were inferred from the literature (Feltham 1990;Fox et al 1990;Kubetzki and Garthe 2003;Gilliland et al 2004;Ross et al 2005;Santoul 2005) and an on-line database (http://bna.birds.cornell.edu/bna).…”

“…Various aspects of the parasite community ecology and transmission have been published elsewhere Valtonen 1990, 1992;Valtonen and Crompton 1990;Valtonen and Julkunen 1995;Valtonen and Gibson 1997;Valtonen et al 1988Valtonen et al , 2001Valtonen et al , 2003Valtonen et al , 2004. The Bothnian Bay is an ecosystem unique to the Baltic Sea in that it is dominated by freshwater Wsh, and this is reXected in the parasite fauna.…”

Age, Sex and Body Condition of Baltic Grey Seals: Are Problem Seals a Random Sample of the Population?

“…Gulf of Bothnia Chubb et al 1995, Valtonen et al 2004, Bergman 2007 How the indicator describes the Baltic marine environment?…”

The occurrence of Echinorhynchus salmonis Muller, 1784 in benthic amphipods in the Baltic Sea

“…However, parasite abundance appeared unrelated to the density of amphipods in the sample, so it is not obvious that there is a tight coupling between amphipod and acanthocephalan populations. Similarly, Valtonen et al (2004) found that the abundance of three seal acanthocephalans in the Bothnian Bay varied little in response to sizeable fluctuations in the intermediate and definitive host populations.…”