Histological features of Rickettsia-like organisms in the European flat oyster (Ostrea edulis L.)

Histopathology of a threatened surf clam, toheroa (Paphies ventricosa) from Aotearoa New Zealand

The toheroa (Paphies ventricosa) is endemic to Aotearoa (New Zealand). Following decades of overfishing in the 1900 s, commercial and recreational fishing of toheroa is now prohibited. For unknown reasons, protective measures in place for over 40 years have not ensured the recovery of toheroa populations. For the first time, a systematic pathology survey was undertaken to provide a baseline of toheroa health in remaining major populations. Using histopathology, parasites and pathologies in a range of tissues are assessed and quantified spatio-temporally. Particular focus is placed on intracellular microcolonies of bacteria (IMCs). Bayesian ordinal logistic regression is used to model IMC infection and several facets of toheroa health. Model outputs show condition to be the most important predictor of IMC intensity in toheroa tissues. The precarious state of many toheroa populations around Aotearoa should warrant greater attention from scientists, conservationists, and regulators. It is hoped that this study will provide some insight into the current health status of a treasured and iconic constituent of several expansive surf beaches in Aotearoa.

Characterisation and distribution of the bacterial genus Endozoicomonas in a threatened surf clam

The toheroa Paphies ventricosa is a large Aotearoa New Zealand (ANZ) endemic surf clam of cultural importance to many Māori, the Indigenous people of ANZ. Extensive commercial and recreational harvesting in the 20th century dramatically reduced populations, leading to the collapse and closure of the fishery. Despite being protected for >40 yr, toheroa have inexplicably failed to recover. In 2017, intracellular microcolonies (IMCs) of bacteria were detected in 'sick' toheroa in northern ANZ. Numerous mass mortality events (MMEs) have recently been recorded in ANZ shellfish, with many events linked by the presence of IMCs resembling Rickettsia-like organisms (RLOs). While similar IMCs have been implicated in MMEs in surf clams elsewhere, the impact of these IMCs on the health or recovery of toheroa is unknown. A critical first step towards understanding the significance of a pathogen in a host population is pathogen identification and characterisation. To begin this process, we examined 16S rRNA gene sequences of the putative IMCs from 4 toheroa populations that showed 97% homology to Endozoicomonas spp. sequences held in GenBank. Phylogenetic analysis identified closely related Endozoicomonas strains from the North and South Island, ANZ, and in situ hybridization, using 16S rRNA gene probes, confirmed the presence of the sequenced IMC gene in the gill and digestive gland tissues of toheroa. Quantitative PCR revealed site-specific and seasonal abundance patterns of Endozoicomonas spp. in toheroa populations. Although implicated in disease outbreaks elsewhere, the role of Endozoicomonas spp. within the ANZ shellfish mortality landscape remains uncertain.