Story: Coastal shoreline
Page 4 – Rock pools and boulder shores
Rock pools and surge channels are good places to observe life in the low-tide zone. At first glance, animals may be difficult to detect, for many are camouflaged, or hide under rocks and in crevices. The most mobile are small fish, of which there are at least 40 species. Cockabullies or common triplefins (Forsterygion lapillum) swim about in search of any small animal to eat. The nearly transparent shrimp (Palaemon affinis) is also a fast mover when it detects a scrap of food.
Found crawling about the sides and bottom of the pool are whelks (Cominella species), common predators of other shellfish. A whelk shell has a distinctive spindle shape, but appearances can be deceptive. Empty shells are a favoured home for kāunga, the hermit crab (Pagarus novaezelandiae), and a rapidly moving whelk shell signifies crab ownership. Other crabs commonly found in this habitat include the purple shore crab (Leptograpsus variegatus) and the smaller rock crab (Hemigrapsus edwardsii).
Encrusting or attached animals live in rock pools and the lower tidal zone. Red sea anemones (Isactinia tenebrosa) survive out of water as a blob of jelly. But once the tide is in they become killers, eating any small animal that passes within reach of their deadly stinging tentacles. Filter-feeding worms live more peaceably in lime tubes attached to rocks or seaweed fronds. They trap their food in a crown of fine filaments.
Two species that are now uncommon in accessible rock pools and reefs are the edible abalone pāua (Haliotis australis) and kina, the sea urchin (Evechinus chloroticus). Both have suffered from over-harvesting and poaching.
A traditional use of pāua shell was as inlay for eyes in Māori carvings – the iridescent colours have a life-like quality. The pāua eyes are called mata-a-ruru (eyes of the owl) and signify that the carved being is all-seeing and all-wise.
Shores of gravel and small stone are the harshest areas of the coast. Few organisms survive the constant grinding action of stone upon stone as waves surge up the beach. Water drains rapidly from coarse sediments and the tops of stones become too hot and dry for most plants and animals.
Several native lizards favour the upper level of stony beaches for basking, and hunt through tidal drift for small insects and crustaceans. They slither under stones or into crevices if disturbed.
Around mid-shore where the tides reach each day, crabs, snails and limpets occupy shaded undersides of large boulders and feed on encrusting seaweeds and algal slimes growing on the sides and bottoms of the rocks. Beaches composed of large and less mobile stones and boulders support a similar assemblage of animals to that of the rocky shore.