Explore the science concepts that underpin knowledge and understanding about the interrelationships and food webs in tidal communities.
The New Zealand Ministry of Education’s Building Science Concepts (BSC) series presents sets of interlinking concepts that build stage by stage towards overarching science concepts or big ideas. A big idea shows how a fully developed understanding of the concept might look, but recognises that such an understanding might not be achieved until New Zealand Curriculum level 7 or 8.
This resource is a partial replication of Building Science Concepts Book 22 Tidal Communities: Interdependence and the Effects of Change. The background information on this page, combined with the information in the interactive, covers the science notes provided in the original BSC book. The overarching science concepts (big ideas) and how they may be scaffolded in sequence are illustrated in the interactive below.
Introduction to tidal communities
This resource builds on information from Life between the tides – unpacking more of the details of the interrelationships amongst the beach inhabitants and the potential impacts of changes both natural and human induced. Studying this environment gives students opportunities to explore concepts of:
- the variety and interdependence of living things
- the effects of change, both short term and long term, on an environment
- the relationship between living and non-living elements in an ecosystem1.
Te ao Māori connections
The topic is also a context for incorporating an awareness of values associated with kaimoana2 and kaitiakitanga3. Within te ao Māori4, seashores occur at the border of the realms of Tangaroa5 (god of the sea) and Tāne (god of the forest). Many pūrākau6 are set at this boundary. Similarly, there are many tikanga7 that are observed there and support the survival and management of this area of environmental richness.
Beaches are places of great importance to Māori as sources of food. Each iwi8 has its own particular protocols to observe when visiting coastal sites or gathering any sea-based resources. It is good to arrange for someone from your local iwi to visit to discuss these protocols with students. Introduction of kupu Māori will encourage development of dual perspectives on understanding this environment. Glossary of kupu Māori mō te ara o Hinekirikiri (Māori words associated with the intertidal9 zone) is available in downloadable PDF format.
Feeding relationships in tidal communities
Feeding relationships in any community of living things are complex. Coastal beaches provide a wide variety of habitats10 for living things. These organisms have developed many ways of exploiting their habitats. Each type of beach has its own particular pattern of feeding relationships. Models such as food webs are representations scientists use to illustrate these relationships clearly.
A food web will always start with:
- a producer11 – plants such as rimurimu (seaweed) or pūkohu wai (algae12), which get eaten by
- a kaiota (herbivore13) – such as tungangi (cockles), tuatua or mud lugworms, which get eaten by
- a kaikiko (carnivore) – such as whai (stingrays) and tōrea tai (oystercatchers).
In the tidal community, the most common producers are algae. Seaweeds are one type of algae, but there are many others. Most of these are microscopic and make up meroiti tipu (phytoplankton).
Food webs can also start off with dead plant and algal14 material and the wastes and dead bodies of animals. Detrital food webs are often overlooked, but without them, all the detritus15 would accumulate. Nutrients16 that are locked up inside the detritus are recycled back into the seawater, mud and sand for plants and algae to consume. Detrital food webs follow the pattern of:
- detritus – dead and waste organic matter17 is eaten by
- decomposers – fungi18, bacteria19 and animals such as mud worms and mōwhiti (sandhoppers), which specialise in eating detritus and then go on to be eaten by something else.
Usually any one type of animal can eat a range of foods so there will be multiple pathways showing on the food web. Making a food web in a range of contexts enables students to develop understanding of the concept of food webs as well as mutual dependence that exists in all ecosystems20.
Changing environments
Water and wind are two of the most powerful agents of change in nature. Their actions can be slow and gradual or fast and dramatic. The effects of their actions are readily seen on all beaches. Wave action can move great quantities of sand and shingle and erode away cliffs and rocks. Wind can create or flatten tāhuahua (sand dunes), erode cliffs and rocks and uproot plants.
Storms combine wind and wave action to create extreme turbulence that can scour out rock pools and destroy complex ecosystems. However, these habitats are recolonised within a short time because even the species21 that live in one place on the rocks usually have free-swimming young among the drifting plankton22. The seaweed spores23 arrive and attach to the rock, the mobile young of limpets and barnacles arrive to feed on the seaweeds as they begin to grow, browsing snails follow, shrimps, crabs and the cockabullies arrive and so on until the balance is restored.
Storms inland can also create dramatic changes for the beach. Huge amounts of water can flow down rivers to the sea, carrying vast quantities of silt24 as well as larger organic25 debris, such as branches and trees. In 2019, an old landfill site was breached by a river in flood resulting in tonnes of material being washed up along kilometres of the West Coast of the South Island.
In river estuaries26, debris can build up and change the course of the river to the sea, leaving what were once tidal mudflats high and dry. The seeds of dry-ground species, carried there by water and wind, may then have the right conditions27 to germinate and grow. In New Zealand, storms can result in the debris from sawmilling operations inland being washed into streams and rivers and thundering downstream, smothering beaches with bark and offcuts.
Changes from people’s activities
Human activities can make big changes to beaches. In urban areas, buildings may encroach on beaches, reducing the range of beach habitats. Mudflats and tidal areas may be drained for subdivision. Run-off28 from streets may be washed out through drains to coastal waters, and sometimes untreated effluent29 from homes and industry is drained into coastal waters.
In rural areas, nutrients from fertilisers and animal wastes can intrude into waterways and from there to the sea. In estuaries, these nutrients encourage the growth of certain plants that can remove the oxygen30 from the water and kill the animal life. Deforestation31 of hillsides inland allows rain to erode the soil, clog the rivers and silt up estuaries and mudflats. People may overharvest shellfish, leaving too few to sustain significant populations32. Vehicles driven on beaches can crush shellfish that live in the wet sand and damage sand dune habitats.
Introduction of competing species, whether accidental or deliberate, may endanger native33 beach species. The introduction of marram grass to stabilise dunes has endangered pīngao, the native sand sedge, which is highly valued by Māori for fine weaving. The South African spider Steatoda capensis (accidentally introduced to New Zealand) has supplanted the native katipō spider (both are poisonous34) on many beaches.
Minimising impacts
People also devise ways of minimising or rectifying the effects that they have on beaches and the tidal communities living there. They exercise their responsibilities of guardianship (kaitiakitanga) by:
- making laws prohibiting vehicles on beaches
- putting in place rāhui35 for fishing and collection of kaimoana
- setting catch limits for fish and shellfish
- fencing off sand dunes
- prohibiting the removal of driftwood
- designating sensitive areas as parks and reserves to protect habitats and their populations of living things – for example, planting pīngao grass to stabilise sand dunes.
Mātauranga connections
If kaitiakitanga is a concept that teachers are foregrounding, it is appropriate to consider scientific data36 but also to take notice of indigenous37 values. One approach to assessing sustainability from a te ao Māori perspective is the use of the online tool the mauriOmeter. The mauri38 of an environment can reflect its health and ability to thrive. This would be similar (but not identical) to considering the ecological balance of an ecosystem with consideration being taken of the biodiversity39, stability of numbers and the passage through a process of natural succession40. An activity such as Estuaries – a Māori perspective supports students to engage with this dynamic41 environment from a te ao Māori perspective.
Alternative conceptions
Students may have alternative conceptions when interpreting the arrows in food web diagrams. They may think the arrow should point from the eater to the eaten – for example, from the bird to its food, the crab. The direction of the arrow in fact represents a transfer of energy. The arrows point from the eaten towards the eater because that is the direction in which the energy provided by the food is flowing.
Students may ignore the role of small species within the tidal community. The tiny creatures that feed on detritus (which may seem to be just rubbish) or the algae and the small invertebrate42 animals that feed on them may seem less important. They may focus instead on larger animals such as birds of fish. This may lead students to think that it is the larger and more attractive animals that are essential and that it doesn’t matter if these smaller organisms die out.
Related content
Learn more about marine food webs:
- Marine food webs – article
- Life in the estuary – article
- Marine ecosystem – interactive
- Build a marine food web – activity
- Beach visits – habitats and food webs – activity
Marine Metre Squared is a New Zealand citizen science43 project that supports communities to monitor their local seashore.
The Hub has curations of resources that support learning about tidal communities:
Biodiversity – estuaries and marine ecosystems is a collection of resources and notes for those teaching in primary school classrooms. You are welcome to copy the collection to your own profile, where you can edit and curate additional resources. Find out more about our easy to use collection tool.
Useful links
Marine organism identification guides
The New Zealand Marine Studies centre at the University of Otago has a downloadable booklet of rocky seashore activities for students
The Assessment Resource Banks (ARBs) also offer a range of levelled activities that are ready for use in the class. Useful searches include tidal zones and beach. You need to be registered to use ARBs.
Acknowledgement
This resource is a partial replication of the New Zealand Ministry of Education’s Building Science Concepts Book 22 Tidal Communities: Interdependence and the Effects of Change.
- ecosystem: An interacting system including the biological, physical, and chemical relationships between a community of organisms and the environment they live in.
- kaimoana: Māori word for seafood.
- kaitiakitanga: A Māori term that encompasses ideas about care and guardianship of the sea, sky and land – the environment. Kaitiaki refers to those who carry out kaitiakitanga such as tangata whenua (people of the land).
- te ao Māori: Māori world view (belief system), which provides a Māori epistemology (study of knowledge) of source, origin, knowledge, and application.
- Tangaroa : The Māori name for the atua or deity of the sea.
- pūrākau: Traditional narrative, story.
- tikanga: Māori customs and traditions that have been handed down from the ancestors.
- iwi: Māori tribe or large community, often consisting of several hapū (clans) bound together by common ancestors.
- intertidal: Marine habitats that are above the water at low tide and below the water at high tide.
- habitat: The natural environment in which an organism lives.
- producer: An organism that makes its own food from inorganic matter.
- algae: A large, diverse group of photosynthetic eukaryotic organisms. Algae have no stems or leaves and grow in water or on damp surfaces.
- herbivores: An animal that only eats plants, compared to carnivores, which only eat meat, or omnivores, which eat plants and meat.
- algae: A large, diverse group of photosynthetic eukaryotic organisms. Algae have no stems or leaves and grow in water or on damp surfaces.
- detritus: In biology, particulate matter from dead organisms.
- nutrient: A substance that provides nourishment for growth or metabolism.
- organic matter: The decomposed remains of living organisms and their waste products.
- fungi: The Fungi are a kingdom separate from plants and animals. Like animals, a fungus (or fungi – plural) is an organism that cannot make its own food. It can be multicellular such as mushrooms and moulds, or unicellular such as yeasts. Fungi may be decomposers, parasites, or mutualists (helping plants to grow).
- bacteria: (Singular: bacterium) Single-celled microorganisms that have no nucleus.
- ecosystem: An interacting system including the biological, physical, and chemical relationships between a community of organisms and the environment they live in.
- species: (Abbreviation sp. or spp.) A division used in the Linnean system of classification or taxonomy. A group of living organisms that can interbreed to produce viable offspring.
- plankton: A group of marine organisms including single-celled and multi-celled organisms.
- spores: Small reproductive structures that can grow into a new individual. Produced by ferns, fungi, and some algae and protozoans. In bacteria, spores are different – they form in some bacteria in unfavourable conditions, protecting the bacteria from environmental harm.
- silt: A granular material of a size somewhere between sand and clay. Its mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in water. It may also exist at the bottom of a water body.
- organic: 1. Molecules that contain carbon and that have a biological origin. 2. Grown using natural processes with nutrients from natural sources.
- estuary: A partially enclosed body of water where freshwater mixes with saltwater from the sea.
- condition: An existing state or situation; a mode or state of being.
- run-off: Water carried away from land to streams and rivers.
- effluent: The outflowing of water from a system – often refers to the discharge of sewage, but can also be natural, for example, the outflowing of a river to the sea. Agricultural effluent refers to the treated and untreated wastewater collected during the management of livestock.
- oxygen: A non-metal – symbol O, atomic number 8. Oxygen is a gas found in the air. It is needed for aerobic cellular respiration in cells.
- deforestation: Deforestation is the long-term or permanent loss of forest cover when trees are removed to clear land for another use.
- population: In biology, a population is a group of organisms of a species that live in the same place at a same time and that can interbreed.
- native: A species that lives naturally in a country, as opposed to species that have been introduced by the activity of humans.
- poisonous: Capable of harming or killing by or as if by poison. A poisonous organism only delivers its toxins when eaten, touched or inhaled.
- rāhui: A Māori word meaning to restrict access to or use of an area or resource by unauthorised persons.
- data: The unprocessed information we analyse to gain knowledge.
- indigenous: Originating and living or occurring naturally in an area or environment. People who are the original inhabitants of an area, or their descendants.
- mauri: Life force or spiritual essence of a person, place or thing.
- biodiversity: The range of species found in a particular region. The more species that exist (the higher the biodiversity), the more likely it is that an ecosystem will survive episodes of change.
- ecological succession: The change in the types of species living in a specific area over time.
- dynamic: In science, a process or system characterised by constant change.
- invertebrates: An animal without a backbone, for example butterflies, worms, snails, insects, spiders and aquatic species such as crabs and jellyfish.
- citizen science: Citizen volunteers participate in scientific projects and work in partnership with scientists to answer scientific questions.