Validating the identity of Paramoeba invadens, the causative agent of recurrent mass mortality of sea urchins in Nova Scotia, Canada

Abstract

Green sea urchins Strongylocentrotus droebachiensis along the coast of Nova Scotia, Canada, suffer mass mortalities from infection by the pathogenic amoeba Paramoeba invadens Jones, 1985. It has been speculated that P. invadens could be a form of Neoparamoeba pema quidensis, a species associated with disease in S. droebachiensis and lobsters in the northeast USA. During a disease outbreak in fall 2011, we isolated amoebae from moribund urchins collected from 4 locations along ~200 km of coastline. In laboratory infection trials, we found that timing and rate of morbidity corresponded to that of similar experiments conducted in the early 1980s, when P. invadens was first identified. All isolates had a similar size and morphology to the original description, including an absence of microscales. Sequences of nuclear SSU rDNA show that disease was caused by one 'species' of amoeba across the range sampled. Phylogenetic analyses prove that P. invadens is not conspecific with N. pemaquidensis, but is a distinct species most closely related to N. branchiphila, a suspected pathogen of sea urchins Diadema aff. antillarum in the Canary Islands, Spain. Morphology and closest phylogenetic affinities suggest that P. invadens would be assignable to the genus Neoparamoeba; however, nuclear SSU rDNA trees show that Neoparamoeba and Paramoeba are phylogenetically inseparable. Therefore, we treat Neoparamoeba as a junior synonym of Paramoeba, with P. invadens retaining that name, and N. pemaquidensis and N. aestuarina reverting to their original names (P. pemaquidensis and P. aestuarina), and with new combinations for N. branchiphila Dykova et al., 2005, and N. perurans Young et al., 2007, namely P. branchiphila comb. nov. and P. perurans comb. nov

Sea urchin Diadema africanum mass mortality in the subtropical eastern Atlantic: role of waterborne bacteria in a warming ocean

“…Therefore, those authors argued that Neoparamoeba branchiphila (which has recently been sug gested as Paramoeba branchi phila comb. nov. based on evidence from analysis of SSU rDNA; Feehan et al 2013) either caused the observed disease in D. africanum or contributed to it. Considering this previous information, our study supports the hypothesis that the amoeba N. branchiphila may play an opportunistic role, given that experimental injection of V. alginolyticus caused disease symptoms in D. afri ca n um.…”

Sea urchin barrens as alternative stable states of collapsed kelp ecosystems

“…Disease outbreaks in Nova Scotia have been linked to storm activity and warm water temperatures and are becoming increasingly more frequent (Scheibling & Lauzon-Guay 2010, Scheibling et al in press). Con sequently, kelp beds currently dominate much of the Nova Scotian coast, although barrens exist locally along headlands off central Nova Scotia and the southwestern shore (Feehan et al 2013). …”

Novel Circular Single-Stranded DNA Viruses among an Asteroid, Echinoid and Holothurian (Phylum: Echinodermata)

“…For many of these disease events, a causative pathogen remains undescribed which severely limits the study of the ecology and evolution of infectious diseases of these animals. Of the cases in which a pathogenic agent has been identified or statistically associated with a disease, bacteria and eukaryotic parasites (amoebozoa) are the most well described [5,6]. To date, no fungi have been found associated with echinoderm disease and viruses have only recently been explored as potential pathogens [7].…”