A November 2015 expedition to the remote, subtropical Kermadec Islands doubled the area’s number of known sponge species, with a sponges taxonomist on the team for the first time. That was exciting to see, says Auckland War Memorial Museum’s Tom Trnski, the expedition leader. But often the really interesting part, he tells us, is how species distribution fits together – and may change – in this isolated patch of ocean at the northern end of New Zealand’s Exclusive Economic Zone.
Are the Kermadecs rich in new species?
It had been considered a species poor region but we’re beginning to realise that was because of a lack of sampling. It actually has high levels of endemism in some groups such as algae, crustaceans, invertebrates or sponges.
The sponges are a strange group. They have a skeleton of sorts but it’s made up of tiny little spicules. Some of the sponges we came across had so few of those that as soon you scraped it off the rock it turned into a wet blob. That was unusual, but until they take it back to the lab we don’t what it is. It’s the first time a sponge taxonomist has visited and prior to this expedition nine species were recorded, and he collected seventeen. It was great watching the sponge expert coming up from a dive and getting very excited by an unexpected colour or texture. I do that when I see a new fish. It actually doesn’t matter whether it’s a species that is known or whether it’s something totally new, it feeds information into how the Kermadecs fit into the broader biogeographic region.
How do the Kermadecs Islands fit in? They’re pretty isolated aren’t they?
Yes, and endemism emerges from isolation. One species that is a bit of a puzzle is a type of damselfish which is currently only known from Kermadecs and Easter Island / Rapanui. We’re just getting enough samples to determine if they are the same species. I’ve done a lot of sampling just north of the Kermadecs and they’re not found at any of those locations. So the question is how one species of fish can occur on opposite sides of the Pacific Ocean, but not in between. The South Pacific Gyre is a potential mechanism for connection. But the larval stage is only two to three weeks so they wouldn’t get across the Pacific across that time. If they turn out to be different species – which I suspect they are – they must have been isolated from each other for a very long time.
Are you seeing the effects of climate change in the Kermadecs?
What we expect to see are a lot more tropical species arriving. An aim of our last trip was to gather more species for genetic analysis. What we’re trying to determine is how closely related the Kermadecs are with places to the north, such as Tonga. One interesting example is the crown-of-thorns seastar which occurs on coral reefs all through the Indian and Pacific oceans. The Kermadecs aren’t quite warm enough for true coral reefs and yet we found crown-of-thorns seastars in some of the highest densities ever recorded, feeding off the limited coral that is there. We wanted to know whether the larvae have actually been dispersed over a long distance. We confirmed that isn’t the case – they are self-recruiting. But what was a surprise was that we expected they would have come from further west, dispersing from the dominant current – a branch of the East Australia Current. But instead they seem to derive from the north. I’ve collected samples of other sea urchins from Tonga and Nuie to use to model this dispersal. What it’s going to help us understand is how things are going to change and what the risks are for New Zealand.
What tropical species pose a risk to New Zealand?
One of the things we were looking for in this last trip was a particular type of toxic algae. We had collected samples in 2011 but the species couldn’t be determined. So we collected more samples last year. Microscopic examination has now confirmed that they are toxic dinoflagellates. What happens in many Pacific Islands is that the toxin accumulates in fish and then those particular fish are toxic to humans. In the Cook Islands we visited an atoll where the major source of income is parrot fish because it doesn’t have the toxin, whereas the neighbouring atolls do.
No one is allowed to eat fish from within the Kermadecs so no one has become sick from them. But it’s possible that dinoflagallate could become quite abundant in northern New Zealand as well. There are a lot of algae species that this dinoflagellate could live on. Obviously there aren’t parrot fish in New Zealand but there are other fish that feed on algae, such as butterfish. A lot of spear fishers catch butterfish. So that is one future risk that may need to be managed, although there are a lot of ‘ifs’ on the way.
Is the new Kermadec Ocean Sanctuary going to help marine biodiversity?
The current Kermadec marine reserve goes out to 12 nautical miles, and actually all my research has focused on shallow species within that area. The new ocean sanctuary will protect some species migrating between islands. There is a kahawai that only occurs in the Kermadec Islands and northern New Zealand. Having a larger protected area also has advantages from a compliance point of view, and particularly for larger species. Bigger species tend to move around a lot and migrate –like whales, tuna, or turtles. The ocean sanctuary will offer protection to those species while they are within it. And there are now a series of these big ocean sanctuaries dispersed around the Pacific Ocean, including Hawaii, Pitcairn Island and the Cook Islands.
But the unfortunate thing is that, while New Zealand now has a huge zone of marine protection, the protection tends to be focused on remote offshore islands. The areas where these big reserves now exist are in very low demand for commercial and recreational fishing. A bigger challenge for New Zealand is to develop a representative system of marine reserves that encompass all habitats, environments and species. What has tended to drive marine reserves on the mainland is picturesque places that people like. And then overcoming resistance to marine reserves by marine users is difficult, because they only see the negative outcomes. But the most recent research shows that marine reserves provide double the benefit to fish stocks compared to other areas. What that means is you could have a reserve that covers 30 percent of an area and still have no loss of fish to catch.
The top image is a Fukui cardinalfish from the Kermadec Islands, collected in 2011 and now confirmed as a new species record for the islands. Photocredit: Dr Malcolm Francis, NIWA.
Dr Tom Trnski was one of the authors of a recent Royal Society of New Zealand report, National Taxonomic Collections in New Zealand.
These interviews are supported by the Royal Society of New Zealand, which promotes, invests in and celebrates excellence in people and ideas, for the benefit of all New Zealanders.