Climate change, overfishing, overuse, and urbanization threaten the health of corals

conceptual diagram of Kaloko-Honokohau National Historical ParkUnique cultural resources and splendid fish and coral diversity attract many visitors to Kaloko-Honokōhau National Historical Park. These visitors may observe that these corals are not as healthy as they could be. For example, they might see corals damaged by people stepping on them, or they might observe that the clarity of the water is reduced by nutrients and sediments carried from the land to the reef by runoff. These threats and others such as overfishing and climate change are influencing the coral reef ecosystem. Careful monitoring and management is required to help improve coral health.

   Scientists are investigating how groundwater seeps might influence the impacts of climate change in the park 

coast and coral reef at KAHOAlong the coastline of Kaloko-Honokōhau National Historical Park, groundwater seeps into the ocean and creates brackish, or slightly salty water where unique organisms thrive (NPS 2009). How does groundwater reach the ocean? Well, when it rains, some of the rain is absorbed by the ground and travels through the porous volcanic rock as groundwater. Sometimes this groundwater collects to form underground reservoirs of freshwater, or aquifers, and sometimes the groundwater makes its way to the ocean through pores in the rock.

When the groundwater and ocean water meet at the coast, the result is cooler water than the surrounding ocean water. This cooler temperature has made scientists curious about how groundwater seeps might affect rising water temperatures due to climate change. Could this cooling effect from groundwater combat rising ocean temperatures due to climate change at this reef? How will groundwater naturally added to the reef influence bleaching or ocean acidification in this area? Currently, no one knows the answers to these questions. However, scientists at Kaloko-Honokōhau National Historical Park are exploring how groundwater seeps might influence water conditions and coral reef ecosystem in the future. What they discover may help guide the management of coral reefs on Hawaiʻi and other volcanic islands with groundwater seeps.

  Overfishing is putting pressure on coral reefs

boat harbor

Though there is little data about fishing pressure in Kaloko-Honokōhau National Historical Park, scientists have observed some worrying trends in fishing practices and fishing pressure (NPS 2009). Modern fishing practices such as gill netting and scuba spearfishing have the potential increase overfishing in the park (DeVerse et al. 2006) because they remove more fish from the reef than traditional fishing methods. When overfishing occurs, the balance of predators and prey in the coral reef foodweb is upset, and the number and types of organisms living on the reef will change.

Some steps have been taken to counteract overfishing. For example, state law prohibits taking reef fish from Kaloko-Honokōhau National Historical Park for the aquarium trade (DeVerse et al. 2006). For this reason, visitors may see larger reef fish here than on other coral reefs in the area.

Negative impacts from fishing are worsened by activities in a boat harbor next to the park. Fishing charters leaving from this harbor create noise pollution, increase the number of boat collisions with threatened honu (green sea turtles), and some boats cause physical damage to coral reefs when they run aground (DeVerse et al. 2006). In addition, boat maintenance in the harbor adds pollution, heavy metals, and sewage to the water that reduces water quality and coral health (DeVerse et al. 2006).

  Overuse can cause damage to corals

Many people come to Kaloko-Honokōhau National Historical Park to enjoy the cultural and natural sites, and to take the opportunity to explore coral reefs. This is great; however, when large numbers of visitors come to a site and use its resources in a way that damages the resources or reduces the health of the ecosystem, it is called overuse. An example of a problem that can stem from overuse and misuse is stepping on corals while snorkeling, which breaks and damages coral heads. Every coral colony provides habitat for numerous organisms. So, when one coral is damaged, thousands of organisms are made homeless. Scientists at the park have observed that overuse and misuse are damaging coral habitat (NPS 2009).

While exploring coral reefs, it is important to remember to treat all organisms with respect. While visiting coral reefs avoid stepping on coral so they are not damaged. Do not apply sun screen right before going in the water. It will wash off your skin, leave you unprotected, and create a film in the water that hinders corals from absorbing the sunlight they need to live. Leaving trash on the beach or taking pieces of coral home with you also damages coral reefs. Friends of coral reefs leave no trace—after they are gone the reef looks just as it did before their visit.

  Urbanization reduces water clarity by adding nutrients and sediments to coral reefs

algae smothering coral

Urbanization, or the expansion of urban areas and an increase in developed land, illustrates how land-based activities can directly impact marine ecosystems. When new buildings are constructed, dirt and sediment is disturbed. This sediment can be blown on coral reefs by wind or washed onto coral reefs by rain. When the sediment reaches the coral reef, it reduces water clarity by blocking the sunlight that the zooxanthellae in the coral tissue use to make food for themselves and for the coral. With less sunlight, corals have less food and can starve.

More developed lands mean that there are more people in the area using sewage systems and fertilizing lawns. These activities increase the nutrients on the ground that are washed onto coral reefs by rain or brought to coral reefs through groundwater (NPS 2009). When nutrients arrive in the coastal waters, they feed algae and allow them to grow rapidly. They can grow so fast that they smother corals. Currently, efforts to reduce nutrients on coral reefs center on preventing them from entering groundwater in the first place (NPS 2009).

Development also increases the demand for freshwater. For example, golf courses draw precious groundwater from aquifers. This means that there is less water available to the organisms in the park. Lower water levels alter park ecosystems and have a greater effect on native plant species that are sensitive to changes in the natural environment.

More ways to explore corals at Kaloko-Honokōhau National Historical Park

Kaloko-Honokōhau National Historical Park Website
Coral reefs at Kaloko-Honokōhau National Historical Park
Blue soft coral
Climate change monitoring briefs
Coral Reefs in U.S. National Parks