What happens to marine pest populations when the ocean gets warmer?
On 27 September, NIWA reported that marine heatwave conditions were occurring in the northern and western North Island and the northern South Island, and likely to intensify over summer - a phenomenon that often occurs during La Niña periods.
Warmer waters mean change for our marine ecosystems. We spoke with senior marine biosecurity adviser Dimitri Collella from Auckland Council about what this could mean for marine pest species in the North Island.
“Warmer seas will potentially facilitate range extension of more tropical species and may also stress our cooler water natives or drive them further south,” he says.
It also means those species already here might take advantage of the warmer waters and we could see their numbers increase.
Cr Amy Macdonald of Northland Regional Council with a sample of Asparagopsis taxiformis. Photo / Northland Regional Council
“For example, we are seeing blooms of the sub-tropical red seaweed species Asparagopsis taxiformis, thriving in North Island waters; much further south from its normal range, and exotic Caulerpa, species usually found in tropical waters of the Pacific.
While human mediated spread generally helps pest species travel further and faster, Dimitri explains that oceanic currents and winds drive the movement of tropical water toward New Zealand, providing a vehicle for species to travel on. For example, tropical sea snakes commonly arrive here this way, as can turtles.
Whether they are capable of establishing a population here, depends on whether the conditions are right for them. This includes factors like temperature, habitat, food sources, salinity, nutrients, and light. In the case of the snakes, we know that survival is rare.
However if conditions are right, the species can flourish - especially if their natural predators or grazers which usually keep their numbers in check did not arrive with them.
Mediterranean fanworm is an example of a marine pest species that does not have natural predators/grazers in our waters. Photo / Crispin Middleton, Seacology
“It’s when things get out of balance in the natural ecosystems that we see animals or plants becoming a pest,” says Dimitri. ”This is when an organism might start to negatively impact the environment, by competing for food and space, interfering with human activities, or ruining the natural amenity values of our environment.”
What happens next? That depends, says Dimitri.
“If there are cycles of this, and we go back to normal temperatures, we might see less of these species persisting. They might not be as successful as they have been. However, they might adapt and become naturalised. The marine environment is highly complex, and we are still trying to understand it.’
There are more than 214 marine Non-Indigenous Species (NIS) recorded as being established in New Zealand. Fortunately, only a few of these species are considered to have the potential to cause harm to our marine environment. Learn about some of the species we are most concerned about at our marine pest ID guide.