Sea Urchins – Kina
Sea urchin – Kina Photo: M Francis
Kina are found all around the New Zealand coast in shallow water and down to 15 m. They are the most common of some 70 species of urchins in NZ waters. While kina can reach 15 cm diameter, about 10 cm would be more common for adult urchins. Small kina (1 – 2 cm) are found under rocks and overhangs and can be seen better at night. On the Wellington South Coast kina seem to prefer rocky reef habitats and moderate wave action, and adult urchins may be found attached to brown seaweeds even into the low intertidal zone. Individuals can live up to 20 years.
Kina, (Evechinus chloroticus), is mainly herbivorous, feeding on large brown algae, red algae and encrusting substrate. Looking a little like a hedgehog rolled up in a ball, the spines of kina seem to be impenetrable defences. They are, however, preyed upon by rock lobster, some sea stars and gastropods, and snapper. In the absence of these predators, often through over-fishing of the larger predators, kina can reach large numbers. If kina populations become out of control, kelp forest can be entirely eaten away, leaving bare rocks, also known as Kina Barrens. Thus these urchins can greatly alter or destroy sheltering kelp forests which provide some microhabitat for a large range of small animals, changing the marine environment on a significant scale. Research, especially at the Leigh marine reserve has demonstrated that, with a return of snapper and lobster, kelp forests can flourish again.
Kina barren, Northland Photo: Roger Grace
Kina have a nearly spherical test or shell which protects internal organs. The test carries long and short movable spines and tube feet. On the underside of kina there is a five-sided limy organ called Aristotle’s lantern. This acts as a set of jaws and teeth, grinding up food. They spawn from November to March, and have a free-swimming larval stage that lasts for up to 3 months.
Wellington Harbour is the location for an interesting project that will show light on the role of kina in local sheltered environments. Steve Journee, of the Dive Guys, is project manager for a trial to restore inner harbour biodiversity. Around the Taranaki wharf there are masses of sea life but few algae. The project team found that kina rapidly devoured algae planted in the area, although there was clearly enough nutrients to support plant growth.
Kina existed in numbers but without any threats to the urchins, creating the same imbalance noted at Leigh through overfishing. As more plants were introduced into the area and became established Mr Journee devised an organic method of dealing with the burgeoning kina. The Dominion Post said:
They were moved to patches of Undaria, an invasive seaweed, at a rate of about 100 per dive. When that number had dropped to about 20 per dive, 11-armed star fish, a kina predator, were transported from rocks and piles under the wharf and placed around the weeds in a “defensive” formation to chase the kina away. Steve Journee reported:
“With less kina in the immediate area the weeds are doing well and other natural harbour weeds and algae are also coming back,” he said. “Also the weeds are now being used by juvenile fish and pipefish as safe swimming zones, which is also bringing the short-tailed sting rays closer in to feed, thus creating a balance in the eco system which was the plan in the first place.”
Sources: Te Ara, Wikipedia, and Dominion Post of 13 May 2013
Kina sculptures, Queen’s Wharf, Wellington. Kina without their spines – as they are commonly seen cast up on NZ beaches. Ironically kina are celebrated here close to Steve’s trial work to remove kina for better balance in the inner harbour marine environment. Photo: MH