Glossary Terms
Shoreline intertidal communities span the area between the mean high water line and lowest spring tide level. In Hawai‘i, this zone is typically narrow due to a small tidal range of approximately one meter (three feet). It includes tide pools, which are pools of water isolated from the rest of the ocean during low tide. The splash zone, which gets occasional splash from waves and salt spray from wind, is often considered to be part of the intertidal zone, even though it is above the high tide line.
Yokohama Bay rocky intertidal zone.
Source: CZM Hawai‘iTypical habitats of the Hawaiian intertidal zone include volcanic rock, hao trees, mud, sand, and seagrass (Coyne and others 2003). These habitats occur in different levels of exposure to wave energy from highly exposed rocky shores to areas sheltered from waves. Mud habitat is usually associated with river discharge and areas sheltered from high-energy waves. With the exception of the Wai‘anae boat harbor, mud bottom is rare along the Wai‘anae coast. Sand and uncolonized volcanic rock habitats are associated with areas exposed to currents or wave energy, both common along the Wai‘anae coast. Seagrass, typically Halophila hawaiiensis, colonizes sand, mud, or hard-bottom substrate.
Life in the intertidal zone is harsh. The tide rises and falls, alternately drenching and drying out the animals and plants. Wave shock, the powerful force of crashing waves, tears at the structures and underpinnings of the residents. Temperature can change rapidly as cold water hits warm shells, or as the sun shines directly on newly exposed organisms. The intense sunlight of the tropics exposes marine life to ultraviolet radiation and bakes the rocks on which these organisms cling. Too much fresh water can shock the intertidal marine life during storms (Garrison 1999). These extreme conditions, in combination with nutrient-poor waters, Hawai‘i's relative isolation, and other factors, result in fewer organisms in the intertidal zone here in contrast to lush intertidal zones elsewhere. Many intertidal inhabitants are small and cryptically colored (blending in with their surroundings), and hide under rocks or in crevices during daytime low tides.
Zonation is apparent on this piling, with barnacles reaching the highest mark, followed by mussels and turf algae. Intertidal zonation is much more pronounced in sheltered habitats.
Source: C. ZabinIn locations that are relatively protected from waves, Hawai‘i's intertidal zone has predictable species distributions at different tidal heights. This phenomenon is known as intertidal zonation (Zabin 2003). At the low tide mark, turf algae dominates; just above that is the mussel, Isognomon californicum; above that, the mussel, Brachidontes crebristriatus; and above that, the introduced (non-native) barnacles, Balanus amphitrite and Chthamalus proteus.
This basic pattern changes on exposed coasts as stronger wave action causes heavy overlap between zones. Many places along the Wai‘anae coast get regular swells that result in a huge splash zone. In these places, wave action, not tidal flux, dictates where marine organisms can live. Species composition also changes, as the two non-native barnacle species have not displaced the native barnacle Nesochthamalus intertextus in the wave-beaten coasts of Wai‘anae (Zabin 2003).
Mā‘ili Point zonation pattern consists of littorine snails (Littoraria pintado and Nodilittornia hawaiensis), Nerita picea, and the limpet (Siphonaria normalis) at and near the high tide mark (Preskitt 2002). Coralline algae are also found in this zone. The crab (Grapsus tenuicrustatus) and the urchin (Colobocentrotus atratus) are common intertidal species that can move in and out of this high intertidal zone.
The limpets (opihi; Cellana exarata and C. sandwicensis) cling to this reef in the middle zone of these wave-beaten areas. Turf algae are the base of the lower zone, providing food, shelter, and substrate for a biologically diverse ecosystem. Common species include the algae, Padina japonica, the urchins, Echinometra mathaei and E. oblonga, the sea cucumbers, Actinopyga maritiana and Holothuria cinerascens, the algae such as Turbinaria ornata, and some Sargassum, all growing in a vibrant complex environment.
A cluster of the endemic littorine snails, Nodilittorina hawaiensis, in the high intertidal zone.
Source: C. ZabinTide pools and reefs are often created by the vermetid tube snail (Dendropoma gregaria). The hermit crab (Calcinus seurati) clings to the algae (Hinksia breviarticulata) in the high-zone tide pools, while the anemone (Aiptasia pulchella) occurs in the mid-tide pools (Zabin 2003).
Turf algae are the foundation of the most productive habitat on coral reefs. They are made up of a variety of algal species, cyanobacteria, diatoms, detritus (decomposing material), and micrograzers. The algal species here are two to five centimeters (0.78 to 2 inches) tall. They act as anchors for the other species, and retain moisture and provide shade for the entire community. The detritus and nitrogen-fixing cyanobacteria contribute additional nutrients to this otherwise nutrient-limited community. Diversity in turf algal communities can be either high, including as many as 100 different species, or low, with monospecific stands separated by the previously discussed zonation. Factors determining the diversity of species include availability of substrate and wave energy.
"Besides fishing, we would go to the beach to pick limu that we would bring home for the family to eat. There were all kinds of limu and we were taught the different kinds that were especially ono to eat."
– Lydia Hilapo Sharpe, born in Wai‘anae in 1907
Native Hawaiians recognized zonation patterns in the intertidal zone, which they named based on water movement and the crabs that can be found at different tidal heights. They used many intertidal organisms in cultural ceremonies and for food and crafts. Collecting limu (seaweed) during low tide was a communal daily event for native Hawaiian women for centuries and continues today by a few people. Several intertidal species, including barnacles, are specifically named in the opening lines of the Kumulipo, or creation chant.
Coyne, M.S., T.A. Battista, M. Anderson, J. Waddell, W. Smith, P. Jokiel, M.S. Kendell, and M.E. Monaco. 2003. Benthic Habitats of the Main Hawaiian Islands [NOAA Technical Memorandum NOS NCCOS CCMA 152]. http://biogeo.nos.noaa.gov/projects/mapping/pacific/
Garrison, T. 1999. Oceanography: an Invitation to Marine Science (3rd Edition). Wadsworth Publishing Co. Belmont, California.
Preskitt, L. 2002. Intertidal Turf Algae Poster. Hawaii Coral Reef Initiative Research Program. http://www.hawaii.edu/ssri/hcri/rp/brochure-09.htm
Zabin, C. 2003. Hawaii Intertidal Project. University of Hawaii and the Education Laboratory School. http://intertidalhawaii.org/index.html
Waianae Coast Culture and Arts Society. 1986. Ka Poe Kahiko O Waianae: Oral Histories of the Waianae Coast of Oahu. Topgallant Publishing Company, Limited. Honolulu, HI.
