Gut microbiome of New Zealand abalone ( <i>Haliotis iris</i> ): a Chatham Islands case study

The New Zealand black-footed abalone, Haliotis iris, holds significant ecological, economic, and cultural value. Abalone from the Chatham Islands fisheries contribute substantially to the national catch, yet populations show marked variability in growth rates. To investigate whether this variability relates to the gut microbiome, sub-adult and adult abalone from four sites were assessed using morphometrics and 16S rRNA gene Illumina MiSeq sequencing. Adult abalone collected from Ascots Beach and Wharekauri were heavier, longer and had larger tissue areas than those from Owenga Harbour and Point Durham, whereas sub-adults showed no size differences. Gut content analysis revealed that fast-growing populations consumed more red algae and less green algae, while brown algae dominated digestion across all sites. Although alpha-diversity did not differ significantly among sites or ages (except at Point Durham), microbial beta-diversity varied significantly by both factors. Core taxa included Psychrilyobacter, Mycoplasma, Vibrio, Propionigenium, unassigned Bacilli, and Blastopirellula. Site- and age-associated microbiome differences may reflect seaweed availability and nutritional quality, warranting further investigation through targeted feeding trials. This study provides a reference baseline for future gut microbiota research on wild H. iris and highlights how algal nutrients and gut-bacteria-mediated digestion may contribute to population-level growth patterns, supporting sustainable fishery management.