Limu: The Good, the Bad, and the Tasty

Whether you enjoy poke, sushi or ice cream—you already eat seaweed and seaweed-derived products. Locally known as limu or ogo, these marine algae are vital to the environment, culturally important, and have serious economic value....
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Celebrating the Cultural and Ecological Importance of Seaweed in 2022 

Whether you enjoy poke, sushi or ice cream—you already eat seaweed and seaweed-derived products. Locally known as limu or ogo, these marine algae are vital to the environment, culturally important, and have serious economic value. By proclaiming 2022 to be the Year of the Limu, Governor Ige has added momentum to efforts by local communities and limu loea (limu masters) to increase awareness of the challenges facing limu and support for the protection and restoration of these important ocean plants.

Celebrating the Cultural and Ecological Importance of Seaweed in 2022. By John Starmer.

The Cultural Importance of Limu

In 2014, Kuaʻāina Ulu ‘Auamo (KUA) partnered with the Ewa Limu Project in an effort to “gather the gatherers.” This initial meeting of 30 traditional limu practitioners from six Hawaiian islands was the start of a growing network that continues to work to reverse the loss of native limu and the loss of associated Hawaiian cultural practices. 

Limu ‘aki ‘aki (Ahnfeltiopsis concinna) can be found on rocky shorelines with good wave action, like this intertidal lava in Kihei. By John Starmer.

Traditionally, limu was the third most important part of the typical Hawaiian diet, right after fish and poi. Limu also is important to lapaʻau (healing) practitioners who use it to treat a wide range of illnesses from cuts and scrapes to digestive problems and more. In addition, Limu serves a spiritual function, as in the example of using limu kala to symbolize closure in the conflict resolution practice of hoʻoponoʻpono. On Maui, groups like Waiheʻe Limu Restoration and Kipahulu ‘Ohana are working to protect the environment necessary to sustain harvests and ecological integrity and maintain limu-associated traditions.

Modern uses for Limu

While you are probably familiar with limu being used as the nori wrapper for sushi (and musubi) and in poke, you may not be as familiar with agar and carageenan -both popular food additives that are produced from algae. These act as thickening agents and texture enhancers. They are common ingredients in ice cream, plant-based milks, toothpaste, processed meats, and much more. As part of the Year of the Limu, KUA, has partnered with UH Sea Grant Program to republish Heather J. Fortner’s 1978 “The Limu Eater-a cookbook of hawaiian seaweed.” Look for it in July of this year.

Possibly limu maneoneo (Laurencia sp.) from the intertidal near Ma’alaea. By John Starmer.

The importance of limu on coral reefs

Although corals get most of the attention in coastal waters, these algae are also fundamental to reef and fish health around the islands. You can think of coral as the trees in a forest, while limu are like the shrubs, grasses, and flowers. Much like a forest system, the trees are important, but far more animals depend on the smaller plants. Limu are the food that most reef herbivores rely on to survive and thrive. Without an abundance of herbivores, prized predatory fish like ‘ulua aukea’, uku, and ‘omilu would not, in turn, have prey to feed on. 

Human effects on limu and coral reefs

With all natural systems, balance is important. There are cycles that can be observed in relation to tides and the seasons. When systems get out of balance, such as when polluted runoff adds excessive nutrients to coastal waters, the natural balance between limu and coral can break down. Unlike forests, algae can, under some conditions, outcompete and smother corals because they grow faster and can “bloom” to cover large areas of reef. Natural blooms tend to be short-lived, in part because herbivores graze down the seaweeds. In cases where too much fertilizer flows into the water or herbivores have been fished down, limu can last long enough to choke out coral.

In the early 2000s, persistent algal blooms in Kahekili Beach, Kaʻanapali pointed to excess nutrients in the water. These nutrients allowed algae, which should have been seasonal, to take over and smother the shallow reefs in this area.The nutrient source was eventually identified as injection well leakage from a nearby sewage treatment plant.

Both the beach rock and green limu pālahalaha (Ulva spp.) are indicators of freshwater flowing to the ocean from the beach of Ho’okipa. By John Starmer.

Another problem for both native limu and coral reefs as a whole is introduced limu species that have become invasive and are harming native coastal habitats. Blooms of hook weed (Hypnea musciformis) have been a nuisance on Maui in the past, washing up in large swaths on beaches. Ecological surveys around Maui have previously identified areas where hook weed was covering up to 80% of the bottom. Gorilla ogo (Graciliaria salicornia) has been enough of a problem on Oahu that there have been efforts to manually remove heavy blooms from affected areas. Both of these non-native nuisance species were escapees from aquaculture projects in the 1970s.

On the whole, limu are an important, even critical component of natural ecosystems on Maui, and they are further eco-culturally important to the Hawaiian people. Limu restoration requires a mix of practices including recovering cultural practices of utilizing limu. Part of this requires ensuring limu populations remain healthy by reducing nutrient and sediment pollution entering limu habitat and maintaining healthy herbivorous fish populations to keep limu in balance with the overall ecosystem. 

In a Department of Land and Natural Resources press release, Division of Aquatic Resources Administrator Brian Neilson noted that “Limu still hold a place of importance in modern Hawai‘i, but many believe it is underutilized and underappreciated in the context of culture, community, commerce, and human health. We want to make a concerted effort, particularly in this ‘Year of the Limu’ to broaden the utilization and appreciation of limu. One of the ways to address the underutilization of limu is to provide communities with more opportunities to harvest limu, for consumption, medicine, or cultural use. We hope to enhance these opportunities through limu restoration projects.” 

Isabella Abbot: Hawaii’s “First Lady of Limu”

When it comes to understanding limu, one pioneering woman has added more to our scientific knowledge of this important plant and its other algae cousins than anyone else, Isabella “Izzy” Abbott (1919 – 2010). Who better to pay tribute to in this Year of the Limu?

Dr. Abbott was the first native Hawaiian woman to receive a PhD in science. She was also the leading expert on Pacific marine algae in general and Hawiian seaweeds in particular. She authored eight books and over 150 publications and is credited with discovering over 200 species of algae. She published two volumes on Hawaiian ethnobotany: Limu: An Ethnobotanical Study of Some Hawaiian Seaweeds (1974) and Lā‘au Hawai‘i (1992), the first comprehensive Hawaiian ethnobotany textbook.

Dr. Abbott was born in Hana on Maui and grew up near Waikiki. She held an undergraduate degree from UH Mānoa, a master’s degree from the University of Michigan, and a Ph.D. from UC Berkeley, all in the field of botany. She became a research associate and taught as a lecturer at Hopkins in 1966 and was promoted to full professor of Biology at Stanford University in 1972. She was the first woman and first person of color to hold this position at Stanford. After her retirement in 1982, she returned to Hawaii and was hired by the University of Hawaii to study ethnobotany.

Learn more & get involved

The Limu Hui: kuahawaii.org/limu-hui/

Year of the Limu Website: express.adobe.com/page/dxoUObuyfak1i/ 

Waiheʻe Limu Restoration: waiheelimu.org

Kipahulu ‘Ohana – Malama I Ke Kai: kipahulu.org/whatwedo/malamaikekai

DLNR Invasive Algae: dlnr.hawaii.gov/ais/invasivealgae

UH Marine Algae of Hawaii: hawaii.edu/reefalgae/default.htm

iNaturalist:

inaturalist.org 

John Starmer

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