Wild West Coast

New Zealand Herald, Volume LXXVI, Issue 23275, 18 February 1939, Page 10 (Supplement)

Wild West Coast

By A.G, STEVENSON

IN company with several people interested in marine biology I recently spent a day on the rocky shore at Motutara, just south of the Muriwai Beach. As luck would have it, the sea was exceptionally calm and the tide went out a very long way, so that we were able to explore a large area not usually accessible. With its sandy bays, rocky points, deep pools and extensive flat rock platforms, this part of the West Coast offers a great variety of conditions, and in consequence supports a wide range of marine life.

Conditions are very severe, however, due to the perpetual pounding of the surf, and we find that only the most rugged and hardy life forms survive. On the East Coast, with its many sheltered bays and estuaries, there is quite a different state of affairs. Under the much milder conditions soft-bodied creatures abound, while shells are more fragile and usually brighter in colour. But on the shores of the Tasman nearly all the shells are heavy and solid and, in common with the starfish and other animals, capable of adhering very tightly to the rocks. The same applies to the seaweeds. Compared with the East Coast, very few kinds are to be found here, but they are interesting nevertheless. The most outstanding seaweed on the West Coast is the bull-kelp or Durviliea, kno\yn to the Maori as rimu rapa and sometimes roasted by him for medicinal purposes. This kelp lives at or below extreme low-water mark and is seldom uncovered by the tide for more than the briefest intervals. Fast to Rocks

On our recent excursion we were lucky to be able to walk about among the kelp, which had been left high and dry by the low tide. It attaches itself to the rocks by means of a disc-shaped holdfast about the size of a soup plate,

and from this spring flat, ribbon-like streamers several yards long. These are composed of cellular tissue and are quite buoyant, so that when the tide covers them they float up and down, backwards and forwards in the surge. The streamers are tough like leather and the holdfast is attached to the rocks so secure]}' that nothing short of a hatchet will dislodge it. Still, we often find kelp detached by heavy seas and cast up on the beach, proof of the mighty force of the breakers. A noticeable feature of the life on any rocky shore is that it arranges itself in definite bands with reference to the tide-marks. Some organisms can withstand long periods of exposure to 6un and air, while others must bo immersed nearly all the time. Consequently, they naturally gravitate to the level at which the most suitable conditions obtain. At Motutara this banding or zoning of life is very evident even to the unpractised eye, and the lines of demarcation between contiguous zones are quite distinct. Not Young Mussels

The uppermost band is the strip at extreme high-water mark, visited # by the tide, or perhaps only tho spray, for a very short period each day. In this zone live only the creatures hardy enough to withstand long periods of blazing sun or drying wind. Barnacles,

Marine Life at MurivOai

two kinds of periwinkle and a few small limpets just about complete the list. Directly below this there is a very distinct band of black, mussel-like shellfish which crowd together so thickly as to quite obscure the rocks to which thev adhere. Contrary to popular belief", these are not young mussels, but a small related species, Volsella neozelanicus, which seldom exceed about an inch in length. But the Volsella zone is quite narrow and ceases suddenly, giving place to the first seaweed band. This seaweed is quite small and covers the rocks with a dark-green feathery growth three or four inches long. Below this again is the mussel zone. The West Coast mussels are not very large, but numbers are legion. Within well-defined limits, they crowd thickly over every available rock surface, forming a band only a few feet wide on vertical faces, but spreading out into wide fields on the flat platforms. This area, which is uncovered for a relatively short period _ each day, abounds with life. Sprawling -over the mussels and feeding on them, we find large numbers of the orange-coloured starfish. Stichaster australis, with ten to twelve arms, and sometimes attaining over a foot in diameter. Secure under the thick coating of mussels uves a variety of smalt creatures, shellfish, crabs and marine worms, whose presence would not be suspected by the casual observer. Red Colour Explained The lowest zone to which we have access is that of the kelp, at extreme low-water mark. The predominating colour here is red, and indeed the rocks and many of'the shellfish adhering to them look as if they have been given a liberal coating of red paint. This colour is really duo to an encrusting growth of Melobesia and Lithothamnion, two minute seaweeds belonging to the family CoraLlinaceae. On the rocks, among the kelp holdfasts are found the Chitons, or coat of mail shells, so-called from the fact that their oval shells are made up of eight transverse strips surrounded by a | leathery girdle, sometimes like the

armour worn by the knights of old. In appearance the Chitons somewhat resemble the common slater or woodlouse, and we saw many specimens several inches in length. The largest species, Eudoxochiton nobilis, was there in numbers on this particular day, as also was Guildingia obtecta, a somewhat smaller species usually ranging from two to three inches in length. Time Well Spent

Another species, always common at low tide, is Sypharochiton sinclairii, a prettily marked shell whose girdle is covered with small scales instead of hairs.

Owing to the extent and variety of formation of this particular piece of coastline, it is impossible in one day to investigate more than a few of its interesting features. Work is necessarily restricted to the comparatively brief period of low tide, and at any one spot we will find enough to interest us for many hours. The only way to obtain an accurate idea of the fauna and flora of the whole area is to make a number of visits, specialising each time on one small section. This is, of course, not practicable for everybody, but I can assure those really interested in marine lire that a single visit to any one spot will well repay the time spent.