ABOUT MARINE LIFE- Threats

Coral reefs in Hawaii are home to over 5,000 species of marine plants and animals and add millions of dollars in revenue to the economy. However they are impacted by human activities on land and in the ocean. Human use must be balanced with ecosystem needs in order to conserve these important ocean ecosystems.









It is estimated that fish abundance in Hawaii has declined by 75% since 1900 due to overfishing. This is the practice of harvesting marine life at an unsustainable rate, ie at a rate that cannot be replenished naturally through growth and reproduction. This decline in fish numbers has been attributed to wasteful fishing practices, habitat destruction due to coastal development which decreases the available habitat for fishes, and an increased human population and therefore demand for fish and better technology for catching fish. Populations of the deep-sea red snappers onaga, or ula`ula koa`e (Etelis coruscans) and the ehu, or ula`ula (Etelis carbunculus), part of the bottom fishery, have declined steadily since the early 1950’s with a large decrease in the last decade. In 2000 about 84% of the onaga landings were immature. Taking immature fish out of the ocean reduces their chance of reproduction (Source: DAR). There are a number of marine resource management areas in Hawaii that serve to manage fish populations and protect marine life. See Management.

Hawaii is a popular holiday destination. In 20 years there has been a 66% growth in visitors and more than 80% of present visitors engage in ocean recreation activities. The marine environment is therefore vulnerable to direct human impact such as reef trampling, touching, anchor damage, turtle harassment, overcrowded beaches and recreational water craft disturbances. These direct human activities not only impact the reef but may also affect important habitat such as spawning, feeding and nursery areas. The greatest damage to corals is often in high use shallow areas or shoreline entry points. Education and an understanding about the reef ecosystem is needed to make sure we can enjoy the reef without impacting it.

Coastal development for agriculture and residential purposes has altered the natural habitat. Land has been cleared to construct housing developments, harbors and marinas along the coasts. Development can cause sediment runoff into adjacent reefs, which smothers corals by reducing the light they need to survive. Sediment can also carry pesticides, petroleum residue and other contaminants into the ocean. Development can also alter the natural habitat which can cause a reduction in fish breeding areas and alter the natural water flow and run-off causing erosion. Agriculture and overgrazing by feral animals all contribute to erosion leading to increased sedimentation on the reef.

Invasive species are plants and animals not native to a region that are introduced accidentally or intentionally and become successful in their new environment, dominating ecosystems and out-competing native species. Hawaii’s marine life has evolved in isolation, resulting in a high number of reef species being endemic and found nowhere else in the world. This makes Hawaii’s marine environment particularly susceptible to the effect of introduced or alien species. There are a number of invasive algae species that were intentionally introduced in Hawaii for aquaculture or arrived on the bottom of shipping barges that have since become established in certain areas on some islands in Hawaii. These are known to spread and compete with native algae species and smother coral. Reporting the presence of these species is essential to prevent their further spread. See the ReefWatchers Field Guide to Alien and Native Hawaiian Marine Algae.

Nutrification occurs when reefs are exposed to large amounts of nutrient loading. Nutrification can be caused by sewage systems in the area or run off from golf courses or agricultural lands that use fertilizers. This decreases water quality and encourages the proliferation of algae which compete with corals, in turn affecting other reef organisms. See Homeowners Guide for tips on how to maintain a healthy waste disposal system.

Human debris such as fishing nets or plastics can cause the entrapment and strangulation of marine wildlife. Entanglement causes wounds that could lead to infections and limits mobility to find food or escape from predators. Marine animals can ingest debris which can lead to malnutrition or starvation, damage the digestive tract or block air passages. Fishing gear can break or smother coral. Since corals provide food and shelter to other reef organisms, this leads to habitat destruction. Marine debris also serves as a transport mechanism for alien species and can ruin the beauty of our beaches. Marine debris is difficult to manage as it can come from local sources as well as thousands of miles away.

Marine environments are also subject to more natural stress such as torrential rainstorms and flash flooding where nutrients, sediments and debris get carried onto the reef. This problem is made worse by human development and habitat destruction. In places like Puako there can also be large swells and direct wave impact on the reef.

See Guidelines for how to make sure you are minimising your impact on the reef in Puako.

Photographs: Robert Shallenberger and Andrew Walsh.

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