Any group of living and non-living things interacting with each other can be considered as an ecosystem. Within ecosystems are habitats. A habitat is the natural environment in which an organism or a group of organisms (also called a population) lives. The habitat must supply the needs of organisms, such as food, water, oxygen and minerals. If organisms’ needs are not met, they must either move to a different habitat if they can or die out. Populations within a habitat are constantly competing, preying upon and/or co-operating with others to survive.
Marine habitats are places where populations of marine animals and plants live and interact. The marine environment has a diverse number of habitats that different plants and animals inhabit. Important marine habitats in the Bay of Plenty are found in estuaries, surf beaches, the rocky shore and offshore islands.
An estuary is a partially enclosed body of water that extends inland from the sea. Freshwater from the land mixes with saltwater from the sea. There are a number of estuaries in the Bay of Plenty such as Tauranga Harbour (one of New Zealand’s largest estuaries) and Maketū, Whakatāne and Ōhiwa estuaries.
Estuaries are important productive ecosystems. A number of habitat types are found in and around the Bay of Plenty estuaries – freshwater wetlands, saltmarsh, mangroves, seagrass, sand and mud flats, rocky reefs and tidal channels. The estuaries support abundant and diverse communities of benthic invertebrates. These are organisms (without backbones) that live on or in the seafloor. These invertebrates, including extensive shellfish beds, are an important food source for fish and birds.
The estuaries are nurseries and spawning areas for a number of fish species, including our most popular recreational fish, snapper. They also provide feeding, breeding and roosting sites for wading and coastal birds.
A beach is a platform along the shoreline of the sea. In the beaches of the Bay of Plenty, this consists mostly of sand. The sand is composed of particles of rock or shells and is moved onshore, offshore or alongshore by the forces of waves and currents.
A beach, particularly a surf beach, is an unstable habitat. Plants and animals are exposed to constantly changing and often harsh conditions. One of the main obstacles that surf beach-dwelling organisms face is the lack of stable ground. They need to swim or burrow or they will be swept away. The sand crab, for example, moves backwards – this is ideal for digging down backwards into the sand, leaving only the eyes and antennae out. The antennae unfurl as a wave recedes to strain phytoplankton. The crab’s back legs become paddles, giving it good swimming capabilities should crashing waves dislodge it.
Food is limited under these conditions. Organisms eat algae particles growing in the top few centimetres of the sand or depend on food brought in by the waves.
Surf beaches in the Bay of Plenty include Mount Maunganui, Pāpāmoa, Waihī and Ōhope.
Rocky shore habitats are intertidal, shaped by a combination of waves, tides and the type of rock present (most are volcanic). The seafloor is mostly solid rock. Rocky shores are rich in marine life, providing a vast number of niches for species of fish, marine invertebrates and other marine animals. Life on rocky shores needs to be able to withstand waves, tides (drying out at low tide), salinity and temperature fluctuations due to tidal flow and general stress. On the other hand, waves and tides bring in plankton and organic matter. The nutrient levels and light make the habitat ideal for seaweed and algae growth.
Many creatures living on the rocky shore have developed strong adaptations to survive in this habitat. For example, many produce mucous layers and shells to protect them from drying out at low tide. Other species use shells and adherence to rocks to withhold strong wave action.
An example of a rocky shore habitat in the Bay of Plenty is Mount Maunganui.
Offshore island habitats within the Bay of Plenty are unique. These habitats, such as Astrolabe Reef, White Island (Whakaari) and Mayor Island (Tūhua), lie beyond the coast and are exposed to both warm and cold ocean currents. Their unique location and origin (mostly volcanic) support a rich marine biodiversity. The warm currents attract subtropical marine species, such as the long-finned boarfish and the occasional turtle. The islands have both rocky shore and sandy beach habitats.