Attention was recently drawn to circular hollows on the South Taranaki coast. Kaumātua Potonga Neilson explained that kumara growers made them in the old days to function as hotbeds, to protect their crops from the chilling westerly winds.
Paradoxically, it was those same prevailing westerlies that made it possible to grow kumara further inland up on the volcanic plateau.
For several million years those winds enabled multitudes of sooty shearwaters (hakoko) to carry heavy belly-loads of fish up to their secluded nesting grounds beneath Mt Ruapehu.
In places such as Mangatiti, Ruatiti and Puketiti, they fed their chicks (tītī - so named for their squeak) in hidden burrows (rua) that protected the tītī from predatory birds.
Three million years of seabird droppings had made the soils up here rich in nitrogen, potassium, phosphate, iodine and other essential elements.
For hundreds of years, Uenuku and Ngati Rangi farmers on the Waimarino Plains lived healthy lives because they planted their crops near these nesting grounds, and they also obtained iodine by eating the fledgling tītī, or muttonbirds, that they harvested in autumn.
Some of the iodine from seabird droppings was washed into streams, absorbed by water weeds and moved through food chains up to the eels, enabling people down in the Whanganui and Mangawhero valleys to obtain iodine from sexually mature silver-belly eels.
In the early 1800s, big Norwegian rats arrived with the European whaling boats and wiped out most of the muttonbird nesting grounds on the mainland.
By the early 1900s, thyroid gland disorders arising from iodine deficiency (swollen neck, chronic chills, weak muscles, nerve damage, learning problems, depression, still-births, infertility) were widespread in New Zealand, although these problems quickly vanished when potassium iodide was added to table salt in 1924.
The location of some 22 other ancient seabird nesting grounds in the New Zealand back-country can be traced by such names as Titirangi in Northland, Auckland, Gisborne, Taranaki, Hawke's Bay and Marlborough, Ahititi in Gisborne, Taranaki, Waikato and the Bay of Plenty, as well as Titiroa and Titipua in Southland.
These names indicate the presence of iodine that enabled Māori in those districts to live healthy lives.
However there are no "Titi" place-names at all between Waipawa and Eketahuna. We can presume that the prevailing westerly head-winds prevented heavily-laden seabirds flying from their Pacific Ocean fishing grounds up to the inland plains there.
The resultant lack of iodine had severe consequences for the Ngati Te Whatuāpiti people who settled on the Takapau Plains in the early 1600s.
Their forebears had been forced to move south from the Tūranganui (Gisborne) district 100 previously after their leader murdered two highly gifted twin boys there.
Their medical problems are recorded in the well-known chant "Pinepine te Kura." (tinyurl.com/takapau)
This is an oriori composed sometime about 1720-1750 by Waipawa's medical expert, a tohunga named Ngāpū-o-te-Rangi.
He used this oriori to teach his young son Umurangi how to continue his work of treating the widespread illness and resulting hysteria endemic in the district: people could not walk properly, were weakened, slipping and falling - "I mānene ai i te ara, ka mate kongenge, ka mania, ka paheke" - and they needed to visit a sexual health clinic - "O-kai-ure."
Presumably these symptoms were most pronounced when hot debilitating northerlies blew down from the direction of Gisborne, causing them to blame their disabilities on witchcraft emanating from the vengeful relatives of the murdered twins - "I Tūranga-nui he mata awha, he patu i te tangata kia mate."
The element iodine, and the workings of the thyroid gland, were unknown in Ngāpū's time: it took another 100 years before a Swiss scientist discovered iodine by incinerating sea sponges, and the ash of these sponges was soon being administered to Europeans to cure thyroid gland diseases.
However Ngāpū had correctly diagnosed the true cause of the weaknesses, and his cure was to take his patients eastwards to Ōkaiure, near today's Kairakau Beach, so they could eat groper caught from the offshore reefs there - "I waho o te moana o toka hāpuku."
Ngāpū also taught his son how to dispel the witchcraft hysteria with fire-making rituals and theraputic rebirth role-play.
For a long-term cure, he advised the afflicted to cultivate their kumara the way Taramuru did. This local grower's prized Tukou variety of kumara gave strength due to his uninhibited application of mulch - "Ko Taramuru anake titi kaha mai ra, e popoki noa mai ra i runga te rakau: tērā te tukou."
No doubt the newly-invigorated patients headed back home with loads of dried seaweed on their backs.
If a dig was organised into one of those sunken garden beds along the Taranaki coast, it may possibly unearth remnants of similar "noa" mulch; bones of fish and fragments of kelp perhaps, great sources of iodine and other health-giving minerals.
Nowadays, iodine is added to both table salt and bread, but extra iodine is still needed during pregnancy: the Health Department has warned that pregnant young New Zealand women are often found to be iodine-deficient.
So if your partner or daughter is pregnant, keeping her well-provided with kai moana will help ensure she brings a bonny baby into the world.