Wai'opae pools

Wai'opae pools among basalt bedrock and boulders.

The Big Island has about 6 Marine Life Conservation Districts, marine reserves established by the state of Hawaii that variously protect coastal marine organisms from harvest. A short stretch of coastline containing the Wai’opae pools is the only MLCD on the eastern end of the island. The site is southeast of Hilo, near the town of Kapoho, tucked behind a few coastal residences.

At Wai’opae the dark lava is spread in a wide flat bench that creates a broad area of pools between emergent rocks. Some of the pools are shallow and might be properly considered “tide pools”, but others are deeper and create permanent subtidal habitat. Partly isolated from each other, each pool is a small reef ecosystem.

Purple ember parrotfish, Scarus rubroviolaceus followed by an endemic saddle wrasse, Thalassoma duperrey among convict tangs.

Closeup of coral polyps.

 Saturday I spent several hours exploring five pools, ranging in size, depth and species composition. My son Ben located the first, a deep pool with a few corals and a moderate number of fish located far inshore from the breaking waves off shore.

Later I spent a little time in a round pool not wider than 5 or so few meters across, with black basalt enclosing a cozy aquarium. One side of the pool was shallow, the other deep, but each with a number of brown plate corals. The colonies of this species form rounded shelves against the rocks like shelf fungi that grow on trees or fallen logs in a temperate forest.

The last pool I explored was the largest and had the most obvious active connection to the ocean, indicated by a strong current present at the southeastern end. I was already cold at this point in the afternoon, but I probably ended up staying another hour in this pool. The axis of the pool was like a shallow V-shaped valley, along which I swam back and forth several times. Fish abundance in the pool was remarkable, and included wrasses, butterflyfish, large purple and greenish parrotfish, and a dense school of striped convict fish accompanied by several large black colored fish that swam with their smaller associates. Blue needle fish were common in the surface water, creating a ring around me, but keeping some distance.

Unidentified blenny perched in coral in a shallow pool.

The pools I observed did not have continuous coral cover. In fact, at some had just a few percent cover. Rather, corals appeared as discreet colonies, with bedrock, volcanic rubble, or fuzzy algal turfs occupying the rest of the space. They seemed absent from the shallowest areas, perhaps because these are exposed a low tides. Lobe (Porites sp.), lace, and plate corals were common. In the pools I found few species of larger macroalgae, but notable exceptions were a single siphonous green alga (?Caulerpa sp.) shaped not unlike an immature bunch of green grapes, and dichotomously branched thin blades of an attractive red foliose alga. Larger invertebrates included beautiful slate pencil urchins and two species of holothuroideans (sea cucumbers).

A school of convict fish.

Green siphonous macroalga, perhaps Caulerpa sp.

Plate coral.

Needlefishes swimming near the water surface.

Hawaiian whitespotted toby, Canthigaster jactator.

The common saddle wrasse, Thalassoma duperrey. Many wrasses change sex over
the course of life. This fish is an "early stage" male or female. "Supermales" have a
white vertical mark behind the reddish band.

References

Hoover JP. 2014. Hawai’i’s Fishes. A Guide for Snorkelers and Divers. 2^nd ed. Mutual Publishing, Honolulu.

Krupp D. 2010. Hawaiian Coral Index Page: http://krupp.wcc.hawaii.edu/BIOL200/hawcoral/corindex.htm

Mahaney C, Witte A. 1993. Hawaiian Reef Fish. Blue Kirio Publishing.