New Zealand intertidal zones
New Zealand's intertidal zones are diverse ecosystems located along its rocky shores, exhibiting rich biodiversity similar to other temperate coasts around the world. These zones are characterized by distinct ecological layers: barnacles are prevalent in the high intertidal areas, followed by mussels in the mid-tide zones, and various algal species and invertebrates in the lower zones. Biodiversity varies between the North and South Islands, with each hosting unique species and competitive dynamics, influenced by factors such as predation and environmental conditions. The intertidal ecosystems are sensitive to climatic changes, which pose threats such as rising temperatures and ocean acidification, potentially disrupting the balance of these habitats. The oceanic currents and coastal geography also play a critical role in shaping the biological communities present in these zones. Overall, New Zealand's intertidal zones demonstrate a complex interplay of species and environmental factors, making them vital areas for ecological research and conservation.
New Zealand Intertidal Zones
Category: Marine and Oceanic Biomes.
Geographic Location: New Zealand.
Summary: A contrast between upwelling and nonupwelling regimes exerts great biota variation in intertidal community structures of this biome.
Southern Hemisphere latitudes similar to New Zealand’s are comparable to those located close to Oregon in the Pacific Northwest region of the Northern Hemisphere. For both biogeographic regions, the taxonomic composition of rocky intertidal flora and fauna are quite similar, despite differing almost completely at the generic level. The rocky shores of New Zealand harbor intertidal communities that 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 rule the low zones. Processes such as predation and competition on New Zealand shores are comparable to those in Europe, North America, South America, and Australia.
The climate in New Zealand ranges from semiarid in central Otago, with rainfall of approximately 12 inches (300 millimeters), to very wet—with up to 314 inches (8,000 millimeters) in areas west of the southern Alps. In the summer, temperatures are generally 77 degrees F (25 degrees C) over most of the country, and may rise to 86 degrees F (30 degrees C) in the east. In the winter, temperatures are 50–59 degrees F (10–15 degrees C) in the North Island, and 41–50 degrees F (5–10 decrees C) in 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 (Ulvalactuca). 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 canaliculusis) was determined by the predation of the keystone sea star (Pisaster ochraceus). The selective feeding of 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 have nearly solid covers of the Chamaesipho columna and Epopella plicata in the high zone, and 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 Durvillea willanar 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 have 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 oyster-catchers 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 the one 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.
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 because of climate change could lead to enhanced trematode infections, among other stressors, and possible local extinctions of intertidal animals. Acidification of the oceans likely will also have an effect on wildlife.
Bibliography
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Grace, Roger V. “Zonation of Sublittoral Rocky Bottom Marine Life and its Changes From the Outer to the Inner Hauraki Gulf, North Eastern New Zealand.” Tane 29 (1983).
Jellison, Brittany M., et al. "Low-pH Seawater Alters Indirect Interactions in Rocky-Shore Tidepools." Ecology and Evolution, vol. 12, no. 2, 2022. DOI: 10.1002/ece3.8607. Accessed 30 Aug. 2022.
Menge, Bruce A. “Top-Down and Bottom-Up Community Regulation in Marine Rocky Intertidal Habitats.” Journal of Experimental Marine Biology and Ecology 250 (2000).
Morton, John E. and Michael C. Miller. The New Zealand Sea Shore. London: Collins, 1968 and 2009.
Wood, Spencer A., et al. “Organismal Traits are More Important Than Environment for Species Interactions in the Intertidal Zone.” Ecology Letters 13 (2010).