Sea star wasting disease pathology in Pisaster ochraceus shows a basal-to-surface process affecting color phenotypes differently.

Sea star wasting disease (SSWD) refers to a suite of poorly described non-specific clinical signs including abnormal posture, epidermal ulceration, and limb autotomy (sloughing) causing mortalities of over 20 species of sea stars and subsequent ecological shifts throughout the northeastern Pacific. While SSWD is widely assumed to be infectious, with environmental conditions facilitating disease progression, few data exist on cellular changes associated with the disease. This is unfortunate, because such observations could inform mechanisms of disease pathogenesis and host susceptibility. Here, we replicated SSWD by exposing captive Pisaster ochraceus to a suite of non-infectious organic substances and show that development of gross lesions is a basal-to-surface process involving inflammation (e.g. infiltration of coelomocytes) of ossicles and mutable collagenous tissue, leading to epidermal ulceration. Affected sea stars also manifest increases in a heretofore undocumented coelomocyte type, spindle cells, that might be a useful marker of inflammation in this species. Finally, compared to purple morphs, orange P. ochraceus developed more severe lesions but survived longer. Longer-lived, and presumably more visible, severely-lesioned orange sea stars could have important demographic implications in terms of detectability of lesioned animals in the wild and measures of apparent prevalence of disease.

Evidence That Microorganisms at the Animal-Water Interface Drive Sea Star Wasting Disease.

Sea star wasting (SSW) disease describes a condition affecting asteroids that resulted in significant Northeastern Pacific population decline following a mass mortality event in 2013. The etiology of SSW is unresolved. We hypothesized that SSW is a sequela of microbial organic matter remineralization near respiratory surfaces, one consequence of which may be limited O2 availability at the animal-water interface. Microbial assemblages inhabiting tissues and at the asteroid-water interface bore signatures of copiotroph proliferation before SSW onset, followed by the appearance of putatively facultative and strictly anaerobic taxa at the time of lesion genesis and as animals died. SSW lesions were induced in Pisaster ochraceus by enrichment with a variety of organic matter (OM) sources. These results together illustrate that depleted O2 conditions at the animal-water interface may be established by heterotrophic microbial activity in response to organic matter loading. SSW was also induced by modestly (∼39%) depleted O2 conditions in aquaria, suggesting that small perturbations in dissolved O2 may exacerbate the condition. SSW susceptibility between species was significantly and positively correlated with surface rugosity, a key determinant of diffusive boundary layer thickness. Tissues of SSW-affected individuals collected in 2013-2014 bore δ15N signatures reflecting anaerobic processes, which suggests that this phenomenon may have affected asteroids during mass mortality at the time. The impacts of enhanced microbial activity and subsequent O2 diffusion limitation may be more pronounced under higher temperatures due to lower O2 solubility, in more rugose asteroid species due to restricted hydrodynamic flow, and in larger specimens due to their lower surface area to volume ratios which affects diffusive respiratory potential.

Distribution and Inferred Evolutionary Characteristics of a Chimeric ssDNA Virus Associated with Intertidal Marine Isopods.

Aquatic invertebrates are common reservoirs of a rapidly expanding group of circular Rep-encoding ssDNA (CRESS-DNA) viruses. This study identified and explored the phylogenetic relationship between novel CRESS-DNA viral genotypes associated with Pacific intertidal isopods Idotea wosnesenskii, Idotea resecata, and Gnorimosphaeroma oregonensis. One genotype associated with I. wosnesenskii, IWaV278, shared sequence similarity and genomic features with Tombusviridae (ssRNA) and Circoviridae (ssDNA) genomes and was putatively assigned to the Cruciviridae clade comprising chimeric viruses. The complete genome of IWaV278 (3478 nt) was computationally completed, validated via Sanger sequencing, and exhibited sequence conservation and codon usage patterns analogous to other members of the Cruciviridae. Viral surveillance (qPCR) indicated that this virus was temporally transient (present in 2015, but not 2017), specific to I. wosnesenskii at a single collection site (Washington, DC, USA), more prevalent among male specimens, and frequently detected within exoskeletal structures. 18S rRNA sequences identified two alveolate protists associated with IWaV278-positive tissues and mechanical epibiont removal of ciliated exoskeletal structures eliminated viral detection, suggesting that the putative host of IWaV278 may be an epibiont of I. wosnesenskii. This investigation provides additional phylogenetic evidence to resolve Cruciviridae evolution and offers insight into the biogeography, specificity, and potential host of a crucivirus genotype.