Grapsus tenuicrustatus
Metopograpsus thukuhar
Macromedaeus crassimanus
Unknown xanthid
Leptodius sanguineus
Pilodius areolatus
Plagusia tuberculata
(2 views)
Thalamita danae
Percnon planissimum
Polydectus cupulifer
Petrolisthes coccineus
Calappa gallus
Platypodia eydouxii
(2 views)
Unidentified Majidae
Calcinus elegans
Hawaii’s intertidal

The tidal range–the difference between the high and low tide–in Hawaii is only about 1 m. As a consequence, the intertidal zone is much smaller here than it is in other places. In the Monterey Bay, California, for example, the tidal range is about 2 m; at the Bay of Fundy in Nova Scotia, the range is as much as 17 m. On the Atlantic shore of the Eastern U.S., a low tide can expose kilometers of mudflats, much to the delight of clam diggers. In contrast, many places in the Caribbean like the Canal Zone area of Panama and Curacao, Netherlands Antilles, have a range of less than 0.5 m, which means that a low tide can be completely obliterated by wind waves!

In Hawaii certain locations get regular swells that result in a huge splash zone. In these places, it is wave action, not tidal flux, that dictates where marine organisms can live. The helmet urchin Colobocentrotus atratus and the limpets (opihi) Cellana exarata and C. sandwicensis are characteristic inhabitants of these wave-beaten areas, along with coralline algae in the higher zones and turf algae in the lower zones.

In locations that are relatively protected from waves, Hawaii’s intertidal has predictable faunal assemblages at different tidal heights. This phenomenon is known as intertidal zonation. On Oahu, the best place to view intertidal zonation patterns is Kahana Bay, which has very high abundances of intertidal organisms. There you can find conspicuous bands of sessile (attached) organisms. At the low tide mark, algae dominates; just above this, one finds the mussel Isognomon californicum, above that, the mussel Brachidontes crebristriatus, and above that, the introduced (not native) barnacles Balanus amphitrite and Chthamalus proteus. In and higher than the barnacle band are the pulmonate limpet Siphonaria normalis and the nerite (snail) Nerita picea. Extending higher into the splash zone are various littorine (snail) species and an isopod. This basic pattern holds for other intertidal sites in Hawaii, although the two barnacle species are replaced in many places by the native barnacle Nesochthamalus intertextus.


Hawai`i teachers explore the intertidal in a workshop hosted by the Waipa Foundation & GK-12 Fellows on Kaua`i, May 2003

An overlooked habitat

Life in the intertidal zone is harsh, particularly in tropical locations, where intertidal algae and animals are exposed to high air temperatures during low tides. That, in combination with nutrient poor waters, Hawaii’s relative isolation, and other factors, results in fewer organisms in the intertidal here in contrast to lush intertidal zones elsewhere. Many intertidal inhabitants are small, cryptically colored (blending in with their surroundings) and hiding under rocks or in crevices during day time low tides. In contrast, just a few more steps seaward is the striking coral reef habitat, populated by colorful fish, turtles, and interesting invertebrates such as the red pencil urchin, Heterocentrotus mammillatus, the black-and-white striped wana (a long-spined urchin), Echinothrix calamaris, and various species of Hawaiian lobsters. It’s really no surprise that the intertidal is often overlooked!

In fact, scientists have virtually ignored the intertidal in Hawaii. While various researchers have studied some organisms that happen to live in the intertidal, virtually no scientific work has dealt with the Hawaiian intertidal as a system. This stands in sharp contrast to intertidal systems elsewhere. The intertidal has been the setting for experiments that have lead to the development of many major ideas in ecology, such as Joseph Connell’s demonstration of competitive exclusion of one barnacle species by another (Connell, 1961) and Robert Paine’s demonstration of the ecosystem-changing effects of predation on mussels by a sea star, for which he coined the term keystone species (Paine, 1973).

There are no field guides to Hawaii’s intertidal organisms (the closest is John Hoover’s book, Hawaii’s Sea Creatures, which features both intertidal and subtidal organisms). There are no classes on intertidal ecology offered at the local colleges and universities. Ongoing research on marine invasive (not native, pest) species has been limited to harbor areas and coral reefs. Other conservation initiatives continue to be focused on reef systems and fisheries.

Native Hawaiian culture and the intertidal

Traditionally, native Hawaiians didn’t ignore the intertidal ecosystem. They used many intertidal organisms for food and crafts, and they recognized zonation patterns in the intertidal, which they named based on water movement and the crabs that can be found at different tidal heights. Several intertidal species, including barnacles, are specifically named in the opening lines of the Kumulipo, or creation chant.

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