Add to collection
  • + Create new collection
  • Throughout human existence we have relied on the oceans – for food, as a waste dump, for recreation, for economic opportunities and so on. However, it’s not only our activities in the marine environment that affect life in the sea – it’s also the things we do on land.

    With more than half the world’s population now living within 100 kilometres of the coast, it’s not surprising that our activities are taking their toll. Human impacts have increased along with our rapid population growth, substantial developments in technology and significant changes in land use. Over-fishing, pollution and introduced species are affecting life in the sea – and New Zealand is no exception!

    Threats to marine habitats

    Human actions at sea and on land are putting increasing pressure on the ocean and the species that live there.


    Humans living near the coast have probably always used the ocean as a source of food. However, with advances in fishing equipment, larger ships and new tracking technologies, many fish stocks around the world have reduced significantly. Fish stocks on continental shelf areas are now widely considered to be fully or over exploited. Aside from reducing fish stocks, unsustainable fishing practices can have other negative impacts on the marine environment. For example, some fishing techniques such as dredging and trawling can cause widespread damage to marine habitats and organisms living on the sea floor. These techniques also often capture non-target species (known as bycatch) that are then discarded.

    Rights: Ra Boe, CC BY-SA 2.5

    Commercial fishing boat

    Fishing was probably the first use of the oceans by humans. In the last century, significant increases in commercial fishing have resulted in the over-exploitation of many fish stocks.

    In New Zealand, fisheries are managed by a quota system that sets catch limits for commercially important species and aims at sustainable management of our fish stocks. The Royal Forest and Bird Protection Society (NZ) used to publish the Best Fish Guide to try and encourage us to make more sustainable choices when purchasing seafood. The list evaluated fish stocks and bycatch levels and the fishing methods used.


    Our oceans have long been used as an intentional dumping ground for all sorts of waste including sewage, industrial run-off and chemicals. In more recent times, policy changes in many countries have reflected the view that the ocean does not have an infinite capacity to absorb our waste. However, marine pollution remains a major problem and threatens life in the sea at all levels.

    Rights: Jeff Schmaltz, MOD IS Land Rapid Response Team at NASA GSFC

    Phytoplankton bloom

    This image shows a large phytoplankton bloom that occurred around New Zealand in October 2009. The image was acquired by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA’s Terra satellite.

    Some marine pollution may be accidental, for example, oil spills caused by tanker accidents. Some may be indirect, when pollutants from our communities flow out to sea via stormwater drains and rivers. Some effects may not be immediately obvious, for example, bioaccumulation – the process where levels of toxic chemicals in organisms increase as they eat each other at each successive trophic level in the food web.

    All marine pollution has the potential to seriously damage marine habitats and life in the sea. Scientists are concerned that marine pollution places extra stress on organisms that are already threatened or endangered.


    Eutrophication is the result of a particular type of marine pollution. It is caused by the release of excess nutrients into coastal areas via streams and rivers. These nutrients come from fertilisers used in intensive farming practices on land. Additional nutrients in the sea can lead to excessive phytoplankton growth that results in ‘blooms’. When these large numbers of organisms die, the sharp increase in decomposition of the dead organisms by oxygen-using bacteria depletes oxygen levels. In some cases, this can result in the death by oxygen starvation of large numbers of other organisms such as fish.

    Introduced species

    Since the arrival of humans in New Zealand, introduced species in our terrestrial ecosystems have contributed to a significant loss of biodiversity. Introduced species also present a threat to our marine environment. It is not always easy to monitor or prevent the introduction of unwanted marine organisms, and visiting ships may introduce them accidentally on their hulls, in ballast water or on equipment.

    Not all introduced species will spread or even survive, but once established, they may be difficult or impossible to remove. For example, the Japanese seaweed, wakame Undaria pinnatifida, which probably arrived in 1987, is now widespread. Scientists are still monitoring its impact on our native marine organisms.

    In New Zealand, the Ministry of Primary Industries is responsible for providing border inspectors who manage risks from people, planes, vessels (like ships) and goods coming into the country. They also coordinate responses when new, harmful pests and diseases are detected in our country.

    Nature of science

    Scientific research sometimes uncovers environmental problems that are linked to human lifestyles. This research shows that the way we live needs to be balanced with environmental needs, which sometimes puts scientists in a difficult position in defending their work.

    Ocean acidification

    There is evidence to suggest that human activities have caused the amount of carbon dioxide in our atmosphere to rise dramatically. This impacts on the marine environment as the world’s oceans currently absorb as much as one-third of all CO2 emissions in our atmosphere. This absorption of CO2 causes the pH to decrease, resulting in the seawater becoming more acidic.

    Our role in ocean acidification

    In this video, Associate Professor Abby Smith, from the University of Otago, talks about what we can do to help reduce ocean acidification.

    Scientists have long understood that an increase in carbon dioxide in the atmosphere will result in higher levels of dissolved CO2 in seawater. However, a relatively recent discovery is that even small changes in water pH can have big impacts on marine biology. Ocean acidification is a worldwide issue, but as CO2 is more soluble in colder water, it is of particular concern in New Zealand’s temperate oceans.

    It is difficult to predict the overall impact on the marine ecosystem but many scientists fear that ocean acidification has the potential to decrease marine biodiversity on a very large scale.

    New Zealanders are aware that old ways of managing our seas are in need of a rethink. The Sustainable Seas National Science Challenge is tasked with helping New Zealand enhance the value of our marine resources while ensuring they are safeguarded for future generations.

    Related content

    Explore the timeline to look at some of the historical aspects of fisheries in New Zealand.

    Overfishing is an ongoing environmental issue in our oceans. This article answers the question: how do you locate ships that have gone ‘dark’ and are fishing illegally?

    The Rena disaster impacted the habitat of many species, read how marine life adapts to habitats and how it deals with stress caused by human impacts.

    Waitā is a whetū in the Matariki cluster connected to the oceans and marine environments. He reminds us that the mauri of the people is closely connected to the mauri of the moana.

    Raʻui: Giving it back to the gods is a Connected article that takes a Pacific worldview and describes how the people of the Cook Islands have attempted to manage and protect their marine resources with the re-introduction of the tradition of ra‘ui.

    Use these articles below to investigate how we measure human impacts on the marine environment?

    Activity ideas

    In Introducing biodiversity, students make models of a marine ecosystem and then explore ways humans might impact on that ecosystem.

    After watching the video Our role in ocean acidification, explore why egg shells are dissolving and can you get a fisherman and a conservationist to agree?

    Changes on the beach is a cross-curricular activity that explores natural and human-induced changes to beach environments.

    Citizen science

    Using online citizen science opportunities as a way to deepen student learning and engagement is easier than you think. Have a look at this example, Adrift, looking at marine microbes drifting continually in our ocean systems. Read about these schools’ citizen science projects in the Connected articles Down the drain and Sea science.

    Useful links

    Visit the Department of Conservation’s website to find out more about marine reserves and other efforts being made to protect life in the sea.

    In this recording, Marine reserves, part of Te Papa’s Science Express programme, hear biologist Jonathan Gardner discuss marine reserves around the world – their importance as ecosystems, and the competing interests that threaten or help protect them.

    The OECD commissioned the report 2023 Agency in the Anthropocene. This easy to read report, co-authored by Dr Chris Eames at the University of Waikato, explains the competencies youth need to address local and global challenges in this Anthropocene epoch of human influences on the planet.

    This classroom module for marine biosecurity is designed for years 5-8 to help them understand the role they play in protecting our coastlines. It is provided in both Google Docs and as printable PDFs so that it's easy for teachers to use. Part 3 uses the Marine Metre Squared project.

    The Marine Stewardship Council is an international non-profit organisation that aims to protect oceans and safeguard fish stocks. It has a system for labelling sustainable seafood for consumers. Some critics argue the system is ‘greenwashing’, take a look at the Greenpeace article Understanding the true price of fish. Do either of the articles align with the 2017 Best Fish guide by the New Zealand Forest and Bird? If you were buying seafood, how would you decide on what species are sustainable?

      Published 8 October 2009, Updated 13 April 2015 Referencing Hub articles
          Go to full glossary
          Download all