A new record of anemone barrens in the Galápagos

Continuous carpets of the anemone Aiptasia sp. were recorded on vast areas of shallow reef platforms along the eastern shore of Fernandina Island in December 2000 and March 2001. The Aiptasia sp. carpets have replaced diverse assemblages of algae, invertebrates, and fishes that once characterized these platforms. Virtually the only other mega-invertebrate that persists in these areas is the pencil urchin Eucidaris thouarsii. Patches of the alga Padina sp. are occasionally present, although somewhat covered with Aiptasia sp. anemones. Fishes are very low in abundance and diversity. Hence, we describe the anemone-dominated habitat as anemone barrens—the term barrens has been applied previously in many parts of the world to habitats of similarly reduced diversity created by high densities of grazing sea urchins. We define anemone ‘barrens’ as areas of considerably reduced diversity (of species, or biogenic structure, or both) caused by the unchecked spread of a single species or guild, or by an exotic agent of disturbance, or both. Like urchins in urchin barrens, a carpet of anemones might have a high biomass. Anemone barrens might also have moderate levels of primary production due to symbiotic zooxanthellae in Aiptasia anemones (Muller-Parker 1984). Extending the comparison, urchin barrens also have moderate levels of primary production due to algal turfs and microphytobenthos. The upper depth limit of the anemone zone was about 1.5 m, and the greatest depth was 15 m where rock gave way to sand. At Punta Espinosa on the northeastern corner of Fernandina, two of the authors (SAS and TAO) noted that the anemones covered most of the inner part of the bay at depths from 2 to 10 m. While being towed from west to east toward Punta Espinosa and using a diver’s benthic sled to maintain a depth of 5 to 7 m, we observed that the upper depth limit of the barrens deepened as exposure to oceanic swell increased, and that the anemone carpet stopped abruptly about 250 m from Punta Espinosa. Wellington’s (1975) transect B, located about 300 m from Punta Espinosa, was now entirely carpeted with the anemones where previously a macro-algal community of Ulva, Amphiroa, and Codium had covered almost 100% of the reef platform to 10 m depth (Wellington 1975). Surviving specimens of the alga Padina within the barrens were smothered by anemones. The food supply of the large population of marine iguanas on the sheltered side of the peninsula now appears to be limited to a narrow zone of Ulva lobata shallower than 2 m. When did the anemone barrens first appear? Wellington (1975) did not record them in his detailed study of the bottom communities at Punta Espinosa, and he believes that, if present, they must have been rare (G.M. Wellington, pers. comm.). Jaime Penaherrera recalls first seeing anemone patches there in 1995, although he had dived in the area two years previous to that. One of the authors (PCM) has surveyed Punta Mangle and Punta Espinosa annually for sea cucumbers since 1993. She noted in August 1997 that crustose and erect coralline algae had replaced the once dominant Ulva and foliose red algal turf soon after commencement of the El Nino. The once common brown algae, Padina and Hydroclathrus, however, still persisted in smaller patches. The formerly common ophiuroids were uncommon in 1997. In June 1998, Fernando Rivera (pers. comm.) first observed patches of presumably the same anemone at Punta Mangle (at the southeast corner of Fernandina). By February 1999, the anemones were much more conspicuous along that coast and were also observed in Puerto Priscilla (also called Punta Gavilan) between Punta Mangle and Punta Espinosa. In November 1999, PCM recorded that the anemone had spread throughout sheltered areas of Punta Mangle, Puerto Priscilla, and Punta Espinosa and covered much of the bottom from about 1.5 to 10 m depth. She also observed that the amount of loose sediment had also apparently increased at that time. Fernando Rivera (pers. comm.) noted that the anemone had covered some areas that had once contained the algal turfs of the territorial herbivorous damsel fishes Stegastes leucorus beebei and S. arcifrons. On 2 June 1999, Dr. Cleveland Hickman (pers. comm.) found the anemone in great abundance at Punta Espinosa and collected specimens for identification (Fig.1). Dr.

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