New Zealand intertidal zones

• Category: Marine and Oceanic Biomes.
• Geographic Location: New Zealand.
• Summary: A contrast between upwelling and non-upwelling regimes exerts great biological variation in intertidal community structures of this biome.

Southern Hemisphere latitudes similar to New Zealand’s are comparable to those located close to the Pacific Northwest region of the Northern Hemisphere. For these biogeographic regions, the taxonomic composition of rocky intertidal flora and fauna is quite similar, despite differing almost completely at the generic level. New Zealand’s rocky shores and harbor intertidal communities are similar to those of other temperate rocky coasts. Barnacles dominate high zones, mussels dominate middle zones, and a mixture of algae, sessile invertebrates, and bare space rules the low zones. Processes such as predation and competition on New Zealand’s shores are comparable to those in Europe, North America, South America, and Australia.

The climate in New Zealand ranges from semiarid in Central Otago, to very wet in areas west of the Southern Alps. Rainfall in these areas ranges from approximately 12 inches (300 millimeters) to 314 inches (8,000 millimeters). In the summer, temperatures are generally 77 degrees F (25 degrees C) across most of the country and may rise to 86 degrees F (30 degrees C) in the east. In the winter, temperatures fall between 50 and 59 degrees F (10 and 15 degrees C) on the North Island and between 41 and 50 degrees F (5 and 10 degrees C) on the South Island.

North Island Biodiversity

On the North Island, a narrow band of the brown barnacle (Chamaesipho brunnea), sometimes accompanied by a broader band of the black stubbly lichen (Lichina confinis), is found near the high-tide level. Between high- and mid-tide levels is the column barnacle (Chamaesipho columna), accompanied by a few Pacific oysters (Crassostrea gigas) and green seasonal sea lettuce (Ulva lactuca). Frequent ornate limpets (Cellana ornata) graze microalgae on the rocks at all levels and are joined between mid- and low-tide levels by golden limpets (Cellana radians) and the snakeskin chiton (Sypharochiton pelliserpentis).

Predation determines composition in the low zone and the distribution of the dominant sessile animals. Several studies have shown that whelk predation prevented the establishment of persistent populations of barnacles such as C. brunnea and Epopella plicata. Comparably, the distribution of the New Zealand green-lipped mussel (Perna canaliculus) was determined by the predation of a keystone sea star (Pisaster ochraceus). The selective feeding of a species of sea star found in the South Pacific Ocean called the reef starfish (Stichaster) prevents this competitive filter feeder from monopolizing the lower intertidal region, thus allowing the coexistence of numerous inferior invertebrates and seaweeds.

South Island Biodiversity

On the South Island, rocky shores on the east coast are nearly solidly covered by the Chamaesipho columna and Epopella plicata in the high zone and covered by the mussels. Mytilus galloprovincialis and Perna canaliculus, and the red coralline alga Corallina officinalis in the mid-and low-zones. On the shore, a canopy of the brown algae Durvillaea willana and D. antarctica are dominant.

Lepsiella scobina is the most common whelk, occurring only in the middle and high zones. The whelks Thais orbita and Haustrum haustrorum, along with sea stars Coscinasterias calamaria and Patiriella regularis, are common in the mid and low zones.

Zonation for the rocky shores on the west coast has dense populations of the barnacle Chamaesipho columna in the high zone and dense populations of the mussels. Mytilus galloprovincialis and Xenostrobus pulex in the mid zone. Mussels are scarce in the low zone, and primary space is dominated by algal turfs (upper low zone), crustose and foliose red algae (lower low zone, mostly Gigartina decipiens and G. clavifera), and bare space. Qualitative observations indicate that sea snails Lepsiella and Thais are rare on the west coast, but similar in size to the east coast animals. The sea star Stichaster australis is abundant.

On the east coast, whelks and oystercatchers are top predators, with Lepsiella feeding exclusively on barnacles, mussels, oysters, limpets, snails, and tubeworms. On the west coast, the diet of Stichaster australis is very similar to that observed on the North Island. Stichaster is considered a generalized predator, consuming mussels, barnacles, whelks, and other gastropods. Although similar biota occur on both sides of the island, the sea star Stichaster australis is far more abundant on the west coast. Stichaster australis thrives in rocky intertidal zones with strong wave action, common on New Zealand’s west coast, where upwelling currents provide abundant food sources like plankton. In contrast, the calmer East Coast waters lack the energy levels needed for the species’ optimal feeding and reproduction.

Near-Shore Biodiversity

Near-shore oceanographic conditions vary from coast to coast and seem to offer contrasting environments. For the west coast, the eastward-flowing Tasman Current splits into the northeasterly flowing Westland and Southland currents. The Westland Current flow is enhanced periodically by northeastward winds, which in turn are influenced by the orographic effect of the Southern Alps, creating upwelling-favorable conditions.

During strong northward winds, surface waters move westward offshore, drawing nutrient-rich water from the deep to the surface along the west coast, eventually leading to phytoplankton blooms. An evident consequence of this west coast upwelling is relatively high concentrations of chlorophyll at shallow inshore depths.

To the contrary, with predominantly southwesterly winds, the east coast of the South Island generally is a downwelling ecosystem. Some upwelling can occur when northerly winds bring deep nutrient-rich waters into the intertidal zones.

Several studies have shown that bottom-up processes (recruitment, mussel growth, nutrients, and chlorophyll a concentration) and top-down processes (predation and grazing) appear to be greater on the west coast, creating the differences in community structure.

Environmental Issues

The intertidal zone is a carefully balanced environment of extremes, with creatures adapted to the harsh conditions. As such, the environment is sensitive to variations in water temperature, tides, winds, and currents. The rising temperatures due to climate change could lead to enhanced trematode infections, among other stressors, and possible local extinctions of intertidal animals.

New Zealand’s intertidal zones face significant challenges in the twenty-first century due to ocean acidification, rising seas, and warming waters. Ocean acidification, driven by increased carbon dioxide absorption, hampers the growth of calcium carbonate-based species like plankton, mollusks, and crustaceans, disrupting the marine food web. Coastal erosion and rising sea levels are creating a “habitat squeeze,” threatening the survival of coastal ecosystems as they are pinched between the ocean and developed land. Warmer waters and shifting currents may reduce ocean productivity and alter the abundance of prey species, such as krill and plankton, which are key components of the food chain. Additionally, these warmer conditions may enable invasive species and marine diseases to spread, which would further destabilize indigenous ecosystems.

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