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Ellyn Tong
Hawai'i Audubon Society

Species abundance and diversity were sampled using the Reef Environmental Education Foundation (REEF) survey method for reefs at Kure Atoll and Pearl and Hermes Atoll. These surveys involved snorkelers recording the relative abundance they observed of reef fish species while swimming in a random pattern, taking care to not swim over the same area twice. REEF fish surveys can also involve diving, but the educators did not have that option on this particular trip. For the most part, the survey sites were no deeper than 20 feet.

A chart of Kure Atoll with the thirteen REEF fish survey sites plotted. Click on the chart to see a larger, high-resolution version. (Photo: NOAA)

Thirteen sites were surveyed in and around Kure Atoll and three at Pearl and Hermes Atoll. The Kure sites were chosen so all corners of the atoll are represented with nine surveys on the inside reef and four on the outside reef. Differing habitats were targeted. The north shore outside reef site, however, was not attainable to give a full representation of all areas on Kure Atoll. The three Pearl and Hermes Atoll sites were chosen to represent shallow reef and a deep-channel environment.

This colorful fish called a spectacled parrotfish or uhu 'ahu'ula (Scarus perspicillatus) is also an endemic species that was one of the top ten most commonly seen species in the Northwestern Hawaiian Islands. (Photo: Claire Johnson, NOAA)

The numbers of different species at each site differed from between 35-65 species, representing 34 families of fish. The three sites with fewer than 40 species counted were shallow water, protected sites. The top ten most common species by number were represented by six families and included the Pacific Gregory (Stegastes fasciolatus), threadfin butterflyfish (Chaetodon auriga), spectacled parrotfish (Scarus perspicillatus), convict tang (Acanthurus triostegus), whitebar surgeonfish (Acanthurus leucopareius), bluespine unicornfish (Naso lituratus), blacktail wrasse (Thalassoma ballieui), Hawaiian cleaner wrasse (Labroides phthirophagus), Hawaiian hogfish (Bodianus bilunulatus), saddle wrasse (Thalassoma duperrey), and sea chub sp. Half of the most common species are also endemic species, and the three species found at every site include Pacific gregory, blacktail wrasse, and the saddle wrasse. The two wrasses found at every site, the blacktail wrasse and the saddle wrasse are endemic species.

The yellowstrip coris (Coris flavovittata) is another endemic species commonly found in the Northwestern Hawaiian Islands. (Photo: Claire Johnson, NOAA)

The percent incidence of endemism was calculated for each site for number of fishes surveyed. Fish that are endemic are those species that are thought to have evolved in the Hawaiian Islands and are found for the most part in the Hawaiian Islands. Some of Hawaii’s endemic species are also found at Johnston Atoll. Though 25% of the list of fish on our species list were endemic, seven of the sites showed 40% or higher rates of endemism by number of fishes counted. This means that the endemic species have proportionally more representatives than their non-endemic counterparts. Endemics may therefore be better suited, having evolved certain life history characteristics to more efficiently live on Hawaiian reefs. Typically island endemics are small bodied and have restricted geographic ranges.

Most of the sites with high levels of endemism occur on the inside reef that faces the north. These sites had close to or exceeded 40% endemism by number. An explanation of this endemism may be that these environments with coral heads interspersed with sandy bottoms, provide suitable habitat for butterflyfishes and wrasses, two families of fishes that have higher numbers of endemic representatives than other families. For example, wrasses constitute over half of all endemics counted and need sandy bottoms to burrow in when they sleep at night.  Butterflyfishes often sleep in holes and in spaces between many types of coral.

A juvenile, endemic multiband or pebbled butterflyfish (Chaetodon multicinctus) has found the perfect home in this coral head. (Photo: Claire Johnson, NOAA)

Recruitment may be an important factor favoring endemics, as endemic species may have evolved reproduction and dispersal patterns more attuned for the Northwestern Hawaiian Islands than non-endemics. Ocean currents and the timing of the availability of food for larvae may make the difference between which species witnesses more recruits and which does not. On average for most coral reef fish, only one out of 250,000 eggs reaches adulthood. Most of the mortality occurs during the larval stage, with half of the larvae succumbing to predators, and the other half starving due to lack of suitable food (Leggett and Deblois, 1994).

The endemic blacktail or old woman wrasse, hinalea luahine (Thalassoma ballieui) was one of three species found on every single snorkel site in the Northwestern Hawaiian Islands. (Photo: Claire Johnson, NOAA)

Outside reef sites had lower rates of endemism, and this may be a result of those sites being more exposed to top carnivores and having fewer niches for recruitment of juveniles and typically smaller bodied endemic species. Some of these outside reef environments experience large wave events every year that may exceed over twenty feet. While the waves are this large, few species of fish would find this environment suitable. Transient species, like smaller surgeonfishes and chub would be more suited to this environment than butterflyfishes and wrasses, which often develop territories that they keep and defend for many years. There are no endemic surgeonfish and chub in Hawaiian waters (Hoover, 1993).

The South/Southeast sheltered reef showed a high rate of endemism (75-84%), and this may be due to a somewhat strong surge current and lack of non-endemic schools of chub, convict tangs, whitebar surgeonfish, and goatfishes that may not have been able to swim effectively against the surge current. There were several species of wrasse, many of them tiny juveniles, which are typically small bodied and quick, able to swim against the current.

The Potter's angelfish is an endemic species commonly found in the main Hawaiian Islands, yet only found on a handful of the REEF fish survey sites in the Northwestern Hawaiian Islands. (Photo: Claire Johnson, NOAA)

In a paper by Drs. Edward DeMartini and Alan Friedlander, Spatial Patterns of endemism in shallow water reef fish populations of the Northwestern Hawaiian Islands, they showed through scientific surveys an increasing incidence of endemism with increasing latitude. The four northernmost Hawaiian Islands were observed to have the highest rates of endemism that reached in some parts 52% by number. They surveyed 59 stations by snorkel and scuba. They were better trained and had the advantage of using scuba that may have resulted in higher reports of endemism than what we experienced.  Most endemics are small bodied and a diver on scuba is more likely to get an accurate count by carefully looking under ledges and in holes for the smaller fishes, than a snorkeler.

One Hawaiian endemic not seen in REEF fish surveys was the Hawaiian grouper, Hapuu (Epinephelus quernus). A larger species, reaching 32 inches or more, it does not follow the general rule for small endemics. It is a member of the grouper family, a family whose members classically take many years to reach adulthood, spawn in aggregations, and change their sex. Though it is part of the bottomfish fishery, unfortunately very little is known about the life history of this fish.

The Hawaiian Islands are the most remote island chain on Earth. This isolation has supported the evolution of many marine fish species that exist nowhere else on earth. Through REEF fish surveys the education team were able to realize the unique abundance of these species on two atolls’ remote reefs. Preservation of the Northwestern Hawaiian Islands as havens for endemics is important for their survival and our knowledge and appreciation of how special and unique the Hawaiian Island archipelago truly is.

References

Hoover, John P. 1993. Hawaii’s Fishes: A Guide for Snorkelers, Divers and Aquarists. Mutual Publishing.

Leggett, W.C. and E. Deblois. 1994. Recruitment in Marine Fishes: Is it Regulated by Starvation and Predation in the Egg and Larval Stages? Netherlands Journal of Sea Research 32 (2): 119-134.

Special thanks to the Kure Atoll, State Wildlife Refuge and the Hawaiian Islands National Wildlife Refuge, U.S. Fish and Wildlife Service, Department of Interior.