Differing responses of red abalone (Haliotis rufescens) and white abalone (H. sorenseni) to infection with phage-associated Candidatus Xenohaliotis californiensis

Abstract

The Rickettsiales-like prokaryote and causative agent of Withering Syndrome (WS)—Candidatus Xenohaliotis californiensis (Ca. Xc)—decimated black abalone populations along the Pacific coast of North America. White abalone—Haliotis sorenseni—are also susceptible to WS and have become nearly extinct in the wild due to overfishing in the 1970s. Candidatus Xenohaliotis californiensis proliferates within epithelial cells of the abalone gastrointestinal tract and causes clinical signs of starvation. In 2012, evidence of a putative bacteriophage associated with Ca. Xc in red abalone—Haliotis rufescens—was described. Recently, histologic examination of animals with Ca. Xc infection in California abalone populations universally appear to have the phage-containing inclusions. In this study, we investigated the current virulence of Ca. Xc in red abalone and white abalone at different environmental temperatures. Using a comparative experimental design, we observed differences over time between the two abalone species in mortality, body condition, and bacterial load by quantitative real time PCR (qPCR). By day 251, all white abalone exposed to the current variant of Ca. Xc held in the warm water (18.5 °C) treatment died, while red abalone exposed to the same conditions had a mortality rate of only 10%, despite a relatively heavy bacterial burden as determined by qPCR of posterior esophagus tissue and histological assessment at the termination of the experiment. These data support the current status of Ca. Xc as less virulent in red abalone, and may provide correlative evidence of a protective phage interaction. However, white abalone appear to remain highly susceptible to this disease. These findings have important implications for implementation of a white abalone recovery program, particularly with respect to the thermal regimes of locations where captively-reared individuals will be outplanted.

The role of diversity in mediating microbiota structural and functional responses in two sympatric species of abalone under stressed withering syndrome conditions

“…Adult abalone are considered ecosystem engineers, as they graze macro-and microalgae and thus maintain open habitats that may be exploited by other organisms [2][3][4]. Moreover, these gastropods support valuable sheries in many countries worldwide [5][6][7]. The peninsula of Baja California harbors seven exploitable abalone species [8], although the harvest is focused almost entirely on the blue abalone Haliotis fulgens (HF) and the yellow abalone Haliotis corrugata (HC) [8,9].…”

“…In recent decades, the main disease contributing to the decline of wild Mexican abalone populations has been withering syndrome (WS), a chronic and fatal disease that has been responsible for moderate and massive mortality events [10,11]. Notably, the degree of susceptibility and occurrence of this disease varies among abalone species and the causes of WS remain poorly understood [1,3,7].…”

Population genetic and genomic approaches for the management of the blackfoot paua, Haliotis iris Gmelin 1791, within the genus context

“…Mortality of abalone can be caused by predation, especially in the juvenile phase, from invertebrates (e.g., octopus and echinoderms) and vertebrates (e.g., fishes, sea otters and marine birds) (Tissot, 1988;Shepherd, 1973;Douros, 1987 ;Shepherd, 1990;Aspe et al, 2019) and by susceptibility to virus-and bacterial diseases (Vater et al, 2018;Corbeil, 2020;Matsuyama et al, 2021).…”