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Characterization of Gut Microbial Composition and Diversity of New Zealand Wild Abalone (Haliotis iris) Under Potential Environmental Influences

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Thesis(3.76 MB)

Date

2025

Authors

Guo, Jinchen

Supervisor

Lacap-Bugler, Donnabella
Venter, Leonie
Alfaro, Andrea

Item type

Thesis

Degree name

Doctor of Philosophy

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Publisher

Auckland University of Technology

Abstract

Abalone (Haliotis spp. in Phylum Mollusca) are marine gastropods that have a wide distribution between intertidal and subtidal zones from tropical to subarctic waters in both hemispheres. Abalone are exclusively herbivores grazing on various seaweed in their natural habitats that contribute to maintaining healthy algal reef ecosystems. Additionally, abalone also possess high economic value as a popular shellfish seafood choice in Asia and Pacific Islands. In Aotearoa New Zealand (NZ), Haliotis iris is an endemic abalone species that is both farmed and caught in the wild. Differentiated abalone growth rates among the wild abalone populations are historically documented. While the exact explanations for this growth rate phenomenon are unclear, food digestion and nutrient absorption is one research avenue being looked at due to their energy and nutrient support roles. The gut microbiome (the microorganisms, mostly bacteria, and their genes in the gastrointestinal region of the digestive tract) of abalone plays an essential role in the host’s food digestion. Previous studies on abalone gut microbiomes revealed that abalone gut microbiomes could be mainly influenced by diet and environmental conditions. However, such gut microbiome investigations have only been conducted on farmed stock of H. iris and not on wild populations. Commercial fisheries of wild H. iris contribute substantially to the total abalone production in NZ. Given the differentiated growth rate concern and the significance of the wild abalone populations to NZ’s abalone fisheries, it would be beneficial to evaluate the gut microbiome of wild H. iris and explore how and why the gut microbiomes change. An initial step in evaluating the gut microbiome and the digestion assistance function is to explore the composition and diversity of the gut microbial communities, or “gut microbiota”. The present thesis utilized the amplicon metagenomic sequencing technology to investigate the gut microbiome of wild H. iris populations in Cook Strait and Chatham Islands. The overall thesis goals were to: 1) investigate the gut microbial composition and diversity of wild H. iris populations and 2) investigate some environmental factors that could potentially influence the host’s gut microbiota. This thesis includes an introduction chapter, literature review chapter, three experimental chapters, and a synthesis and conclusion chapter. The literature review (Chapter 2) defines key concepts related to microbiome research, how microbiomes are generally assessed, provides some major influencing factors on abalone gut microbiomes, with an emphasis on dietary and aquatic physical and chemical factors, and pinpoints some suggested future research directions. The experimental chapters (Chapters 3 - 5) utilized Illumina MiSeq sequencing technology to evaluate the gut microbiomes of five wild H. iris populations with a specific focus on the associations of gut microbiome shifts to seaweed diet and over time in NZ. Chapter 3 compared the gut microbial composition and diversity among three abalone digestive regions and the microbiota between abalone’s gut and the surrounding seaweed and sediment in Cook Strait. This revealed that the microbial composition was similar between the foregut (esophageal pouch) and hindgut (intestine), and the microbiomes of the lower section of the digestive tract (foregut and hindgut) were different from that of the buccal cavity of the animals. Moreover, abalone gut microbiome was significantly different from that of the ambient seaweed and sediment samples. In Chapter 4, assessments on the gut microbiota and consumed algal content of four wild abalone populations in the Chatham Islands (CI) revealed differentiated gut microbiota across study sites and between age groups. Moreover, gut content microscopic results also revealed that the observed gut microbiome differences could be related to consumed seaweed type and algal availability. Lastly in Chapter 5, a two-year abalone gut microbiota evaluation on CI was executed and observed that the gut microbiomes of the wild H. iris populations at Ascots Beach and Owenga Harbour changed significantly overtime, with the gut microbial diversity was lower between March-May in 2021 compared to March 2021, November 2021, and April 2022. The observed gut microbiome changes presented in Chapters 4 and 5 could be related to specific seaweed diets and/or oceanographic condition changes over the sampling period, which need to be further investigated through additional field observations and targeted feeding experiments. The present thesis is the first gut microbiota documentation on NZ wild H. iris. The results indicated that seaweed and sediment microbiota by themselves are unlikely to influence the abalone’s gut microbiota. Instead, the gut microbiota of wild H. iris could be potentially affected by consumed seaweed availability and type as well as the changes of oceanographic conditions. Microbiome data collected from wild H. iris digestive tract and the ambient seaweed and sediment in this thesis can be the baseline for future gut microbiome research in NZ. While targeted experiments under controlled conditions need to be further conducted to specifically test the seaweed and environmental parameter hypotheses, seaweed- and oceanography- associated findings from this thesis provide informative predictions on the food digestion efficiency and nutritional and health states of local wild abalone stocks, ultimately influencing the harvesting time and quantity of this iconic species.

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http://hdl.handle.net/10292/20788

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