Changes in epizoic crustacean infestations during cetacean die-offs: the mass mortality of Mediterranean striped dolphins Stenella coeruleoalba revisited

Abstract

In the summer and autumn of 1990, a cetacean morbillivirus caused a massive epizootic mortality of striped dolphins Stenella coeruleoalba in the western Mediterranean. Previous circumstantial evidence suggested that the disease could also have increased host susceptibility to infestations with epizoic crustaceans. In this study we provide strong evidence supporting this hypothesis. We examined striped dolphins stranded along the Mediterranean central coast of Spain from 1981Spain from to 2004, and recorded data on prevalence, intensity of infestation, size and reproductive status of 2 sessile crustacean species specific to cetaceans, the phoront cirriped Xenobalanus globicipitis and the mesoparasitic copepod Pennella balaenopterae. Compared with the pre-epizootic (n = 12) and post-epizootic (n = 62) dolphin samples, the following changes were noted in the dolphins stranded during the epizootic (n = 62): (1) the prevalence of both X. globicipitis and P. balaenopterae increased; (2) the intensity of X. globicipitis and P. balaenopterae infestations did not increase; indeed, it was even slightly lower than in the other periods, as was their degree of aggregation; (3) individuals of both species were smaller, and a higher proportion were non-gravid; (4) the 2 species tended to co-occur in the same dolphins, but their numbers did not co-vary. These patterns strongly suggest that, during the epizootic, there was a short-term increase in the probability of infestation of these 2 species because of the sudden rise in the population of susceptible hosts; the growth of the new recruits was limited by the early death of dolphins. The high susceptibility was likely related to the immunosuppressive effects of viral infection and the abnormally heavy loads of polychlorinated biphenyls found in sick dolphins; the level of inbreeding was also higher in dolphins from the 'epizootic' sample. Epizoic crustaceans could be suitable indicators of health in cetacean populations. KEY WORDS: Cetacean · Morbillivirus · Epidemics · Mass mortality · Epibiont · Parasite · Susceptibility Resale or republication not permitted without written consent of the publisherDis Aquat Org 67: [239][240][241][242][243][244][245][246][247] 2005 ease provokes immunological depression that leads to secondary opportunistic infections, or activation of latent infections, of a variety of bacteria, fungi and protozoons (Domingo et al. 1992, Duignan et al. 1996. One of the most prominent clinical signs of the striped dolphins affected by the CeMV was the occurrence of apparently abnormal burdens of some epizoites (Aznar et al. 1994). In particular, a phoront barnacle specific to cetaceans, Xenobalanus globicipitis, was more frequently found during the epizootic period than in previous years. Also, many individuals were young, suggesting recent infestation events. We speculated that these patterns might have resulted from an increase of host susceptibility due to the CeMV disease (Aznar et al. 1994). However, the evidence at that time was circu...

Emerging infectious diseases in cetaceans worldwide and the possible role of environmental stressors

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