Grace Day, PhD candidate at Deakin University

Many people have stories about a time when they have seen whales or dolphins in the wild, and it is almost always a memorable experience to cherish. You may have spotted playful dolphins while out on the water in Port Phillip Bay or in the Gippsland Lakes… perhaps you’ve never pondered what unique species these dolphins might be?

Let me introduce you to the critically endangered Burrunan dolphin (Tursiops australis).

The dolphins that live in Victoria’s watery backyard are a unique species, their name, ‘Burrunan’ meaning large sea fish of the porpoise kind in local indigenous languages. Burrunan dolphins are closely related to other bottlenose dolphins; the common bottlenose dolphin (T. truncatus) and the Indo-pacific bottlenose dolphin (T. aduncus). They have unique morphology, having a tri colouration along their side, with a stubby rostrum and a curved dorsal fin (like a common bottlenose dolphin), and are smaller in size (like an Indo-pacific bottlenose dolphin). Yet, they are a unique, distinct species (classified by Dr Kate Robb in 2011).

From baseline population assessments, there are about 120 and 90 resident Burrunan dolphins in Port Phillip Bay and the Gippsland Lakes, respectively. We know from previous studies that they have much smaller breeding population sizes and low genetic diversity. Unfortunately, the Gippsland Lakes population has suffered from two mass mortality events, one in 2006/07 and another that started in 2020 which is ongoing. The mortality events are due to Fresh Water Skin Disease (FWSD), which is brought on when the salinity of the lakes is dramatically reduced. The reduction in salinity is often proceeded by flood/fire events, whereby bushfires reduce the surrounding vegetation, then heavy rainfall flushes into the system. FWSD manifests as ulcerative skin lesions which result in fluid loss, organ failure and are often colonised by secondary infection.

My PhD project investigates the microscopic army that defends Burrunan dolphins from infection and disease. Picture the body as a fortress: outside are invaders, or pathogens lying in wait to breach the defences. The army that protects the fortress is the immune system.

The skin is an integral component of the first line of defence by acting as an impenetrable fortress wall. Hidden within the skin is a brave and loyal force known as the skin microbiome (bacteria, fungi, and archaea), these allies shield the skin surface and act as a sentry network to raise the alert of invasion. Friendly microbes, also known as commensals, do this by outcompeting pathogenic microbes, making a hostile environment for colonisation of pathogens and by alerting skin cells of invasion. A diverse microbiome often is a sign of a healthy microbiome, and one that is out of balance can be disadvantageous for the host. Although research into the microbiome is new and a growing field, it is somewhat novel and in marine mammals. I will characterise the diversity and composition of the skin microbiome in Burrunan dolphins, as a component of the first line of defence.

Should any invaders breach the first line of defence, the second springs to action, with signalling molecules shooting out like arrows from bows, and white blood cells acting as infantry. If the invader’s onslaught should continue, the specialised units of the third line of defence comes into action. This includes antibodies, which are like highly skilled combatants that act with precision and adaptability. To investigate the second and third lines of defence, my project uses next generation DNA sequencing techniques to do population genetic analysis on genes involved in these immune pathways. This project will give an exhaustive insight into the immune repertoire of Burrunan dolphins and ultimately contribute to conservation and management of the species.

Aside from genetics analysis and laboratory work, I’m lucky to spend a lot of time on the Marine Mammal Foundation research vessel, involved in fieldwork wherein we collect biopsies, water quality measures as well as population, acoustic and behavioural data. Visit the Marine Mammal Foundation website (https://www.marinemammal.org.au) for more information about Burrunan dolphins, the research conducted at the foundation, and how you can help in the conservation of such a special and unique species.

Grace Day was awarded a Holsworth Wildlife Research Endowment Grant to support this work.

Image credits: Marine Mammal Foundation