Kai's journey from rock pools to fish schools

On a cold autumn morning, Kai Paijmans dons his wetsuit in the carpark of Bushrangers Bay in Shellharbour and lugs his diving gear down the stairs to the water's edge. Armed with a specialised stereoscopic camera, he's on the hunt for a specific species of fish - the Indo-Pacific sergeant (Abudefduf vaigiensis).

For the University of Wollongong PhD student, beneath the surface is where he's in his element. Kai has amassed hours of footage over countless dives in an effort to analyse aspects of the behaviour of this fish, and how this will be impacted by climate change.

Like many who pursue marine science as a career, Kai has always been enamoured with the ocean. When asked why he chose this path, he simply replies that a childhood by the sea "was inspiration enough".

Growing up on the Far South Coast of NSW, Kai remembers being fascinated by the plants and animals that surrounded him, taking every chance he could to explore the coastal and marine ecosystems of his home.

"I remember fishing with my dad," Kai says. "He tells me that on one camping trip I wouldn't sleep from excitement after we caught a big Australian Salmon from the rocks. I also have distinct memories of encountering big stingrays when snorkelling as a kid, probably etched into my mind because of how scary they seemed."

_{UOW PhD student Kai Paijmans at the beach.}

These experiences in Kai's early childhood opened his eyes to the magic of the underwater world, and it wasn't long before he picked up surfing, scuba diving, spearfishing, and anything else that could get him in and around the ocean.

For Kai, there wasn't a definitive moment when he decided marine science was his future. It was simply a logical progression from his time spent observing marine creatures when he was younger, an extension of those activities that allowed him to spend his days in the water. Studying ecology could satisfy his need to be around the ocean, while also fueling his desire to gain a better understanding of how and why marine animals do what they do.

"I started undergrad at UOW with no real expectations about my path," Kai says. "I really enjoy learning and I think that researching marine ecosystems is a fantastic way of interacting with them and appreciating how amazing they are."

_{UOW PhD student Kai Paijmans, who studies marine life, explores underwater.}

Once it came time to complete his honours, Kai could be found among the jagged crags and bouldered gullies of the rocky shore, peering into rock pools to study their residents. While overlooked by many in favour of sprawling reefs or tall kelp forests, rock pools are one of the most captivating marine ecosystems. Existing in the space between high and low tide, these little portals of life provide important habitat for many marine animals that cannot be found anywhere else, and are crucial to the overall health of the ocean.

"Rockpools are a fantastic marine ecosystem to study because they're small and easy to access, with no boats required," Kai says. "They provide a natural laboratory where ecosystem function can be easily investigated as they come in many different shapes and sizes, which allows researchers to understand how different habitats shape marine communities."

Using rock pools as his study system provided a great opportunity for Kai to foster his interest in behavioural ecology - the study of how and why animals interact with each other. Kai had many questions about the social lives of the fish in these rock pools, and he was finally able to answer some of them.

"I wanted to understand how so many different species can live together in such a small space," Kai says. "Two different fish species that compete aggressively for space can happily coexist in the same pool by simply using different micro-habitats. One species (the Eastern Jumping Blenny) prefers vertical crevices and overhangs, while another (the Cocos Frillgoby) prefers to hide under pebbles at the bottom of the pool."

_{A colourful bed of seaweed, taken underwater.}

Following his honours, Kai was hooked on behavioural ecology and knew this was the field of research for him.

"I find behavioural ecology particularly interesting because it's a really handy tool which we can use to gain an in-depth understanding of broader ecosystem function," Kai says. "By investigating why a given fish species behaves in a certain way, we can identify key aspects of the environment driving that behaviour and how it influences other organisms."

Under the supervision of Dr Marian Wong, Kai took what he learned during his time among the rock pools and brought his skills to the open ocean.

"My PhD research is on fish social behaviour and how it influences climate change-driven species redistributions.

"The marine region of South Eastern Australia is an ocean warming 'hot spot', meaning it is predicted to experience some of the most dramatic climate change-driven increases in ocean temperature of anywhere on earth. One consequence of this warming is the movement of tropical fish species from the tropical north to the temperate south."

_{The octopus tetricus, also known as the common Sydney octopus.}

As these tropical species move south they mix and mingle with local species, forming social groups called 'shoals'. By recording the interactions between these species in the wild and in lab experiments, Kai is investigating how easily the tropical species 'fit in' with the shoals of local fish, and it turns out they're doing pretty well. Mixed-species shoaling is providing the tropical fish with protection from predators through "safety in numbers", and the tropical and temperate fishes are even working together when searching for food.

Kai's motivation for undertaking this research is clear - to contribute to the understanding of how climate change is going to alter the animals in our ecosystem, and how we can best prepare for these ecological shifts.

"How an animal behaves can have a profound influence on how capable it is of adapting to a changing climate. Social animals are often more adaptable to change because of social learning, which allows individuals to learn quickly based on the experiences of others," Kai says. "What I think is important to understand is that climate change is going to mean ecosystems - both on land and in the ocean - will be different from what they are now."

_{Starfish cling to an underwater rock formation.}

Although Kai is only at the beginning of his journey, his research has already made ripples in the scientific community, and has seen him present findings around Australia and internationally. Most recently, Kai presented his PhD research at the Species on the Move 2019 conference, held in South Africa.

"The focus of the conference was on climate change-driven redistributions of plants and animals, both on land and in the oceans - and the trip was supported by UOW's Global Challenges.

"I've been to a bunch of other cool places as part of my research including Heron and One Tree Island on the Great Barrier Reef, Exmouth, and Ningaloo Reef."

While Kai's research has taken him to some amazing locations, he's forever bound to the Far South Coast - "This region contains one of the most beautiful coastlines on earth" - something that keeps him inspired to conserve and protect his own home for the future.

"My motivation comes from a desire to continue learning, and sharing our amazing local marine environment with as broad an audience as possible," Kai says.

"I want to continue doing research and learning about fish behaviour, and I would like to do this in combination with community engagement and teaching because I think the most important aspect of marine conservation and management is appreciating what we have right on our doorstep."

_{A school of fish.}