SF Fig. 2.5. (A) Rapid growth of the macroalga Kappaphycus alvarezii smothers corals and shades them from sunlight.
Image courtesy of State of Hawaiʻi Division of Aquatic Resources
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Weird Science: Invasive Algae
NGSS Crosscutting Concepts
NGSS Disciplinary Core Ideas
Table of Contents
Macroalgae play a crucial role in many aquatic ecosystems. They serve as a habitat in kelp forests and provide food for grazing herbivores on coral reefs. However, macroalgae can also harm other species in their ecosystems under certain conditions. The release of nutrient-rich pollution from storms, sewage, and agricultural can cause large-scale algae blooms. Algae can also grow rapidly and spread if their natural herbivores are missing due to excessive fishing, wildlife diseases, or non-native exotic species.
Although corals have defense mechanisms, they generally grow slowly compared to macroalgae. Invasive algae grow quickly and can form algae mats that are several centimeters thick on top of coral. SF Figure 2.5 shows some examples of invasive macroalgae. Multiple invasive algae species are quickly overtaking coral reefs, smothering them and blocking the sunlight that corals need to survive. Corals provide the dominant habitat in tropical reefs. Thus, when corals die, the diversity of life on reefs is also lost.
SF Fig. 2.5. (B) Gracilaria salicornia is highly invasive in Kāne‘ohe Bay, Island of Oʻahu, Hawaiʻi
Image by Narrissa Spies
Local non-profit organizations and governmental agencies are working together to combat the problem of invasive algae in Kāne‘ohe Bay, Hawai‘i. The Nature Conservancy, in a partnership with the Hawai‘i Department of Land and Natural Resources (DLNR), has developed a pump and underwater vacuum system called the Super Sucker. A pump, located on the Super Sucker barge, creates suction that allows divers to vacuum alien algae from the water onto the barge. The Super Sucker can remove up to 450 kilograms of invasive algae from a reef in a single hour (SF Fig. 2.6 A, B). After sorting on the barge, the algae is bagged and distributed to farmers for fertilizer.
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SF Fig. 2.6. (A) The Super Sucker barge in Kāne‘ohe Bay, Hawai‘i
Image copyright and source
Image courtesy of State of Hawaiʻi Division of Aquatic Resources (DAR)
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SF Fig. 2.6. (B) A diver gently removes alien algae from the reef and uses the Super Sucker vacuum to suck algae from the water.
Image copyright and source
Image courtesy of State of Hawaiʻi Division of Aquatic Resources (DAR)
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SF Fig. 2.6. (C) Students from local community group Nā Pua No‘eau remove invasive algae near the shoreline.
Image copyright and source
Image by Narrissa Spies, Nā Pua No‘eau
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SF Fig. 2.6. (D) Herbivorous collector urchins (Tripneustes gratilla) are placed on reefs to control invasive algae.
Image copyright and source
Image by Narrissa Spies
Following removal of large algae pieces, native collector urchins (Tripneustes gratilla) are placed on the reefs to remove small particles that may have been left behind. The urchins are cultivated at the state of Hawai‘i’s urchin hatchery facility and released as juveniles onto the reefs in Kāne‘ohe Bay. Community groups have also played a large role in controlling shoreline algae. Several non-profit and school groups have organized events where large quantities of algae are removed from the shoreline by hand (SF Fig. 2.6 C, D).
