Studies of Populations of Sea Urchins, "Strongylocentrotus" sp., in Relation to Underground Nuclear Testing at Amchitka Island, Alaska

Barr, Louis

doi:10.2307/1295732

Cited by 3 publications

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“…(All diameters of sea urchins given herein 825 refer to outside test diameter.) Estimations of sizeclass distribution and maximum density of the sea urchin population at Amchitka are from Barr (1971). We measured sea urchin densities at 3-m depth intervals between depths of 3 and 18 m at Bat Island, and at Kirilof Point and Kirilof Rocks on Amchitka (Fig.…”

Section: The Study Areasmentioning

confidence: 99%

Sea Otter Predation and Community Organization in the Western Aleutian Islands, Alaska

Estes¹,

Smith²,

Palmisano³

1978

Ecology

275

148

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Predation by the sea otter (Enhydra lutris) limits epibenthic invertebrates, especially sea urchins (Strongylocentrotus polyacanthus), in turn allowing a luxuriant development of the macroalgal canopy. Where sea otters are abundant, sea urchins are small and scarce in shallow water, and the association of fleshy macroalgae apparently is regulated by competition. Sea urchins are larger and more abundant in deeper water, where they are less accessible to sea otters. Macroalgae are most abundant, and competition in the plant association is severest, near the sublittoral fringe where sea otters can remove sea urchins most efficiently. In deep water, competition among maccroalgae is reduced because the light intensity is lower and grazing by sea urchins increases. On islands where sea otters are absent, sea urchins are abundant, large, and are probably limited by intraspecific competition; and they have eliminated fleshly macroalgae. Available data suggest that the association of Laminaria spp. and Agarum cribrosum contributes most to primary production in nearshore areas of the western Aleutian Islands. Where sea otters are absent and sea urchins have eliminated this plant association, some higher trophic forms also are absent or less abundant than where sea otters are common and the plant association is well developed. Earlier studies of sea otter food suggested that low—density populations of sea otters consume primarily sea urchins and mollusks in the western Aleutian Islands. Later studies of high—density populations showed a wider variety of foods consumed, with fish an important component of the diet. These studies support our observations on the differences in availability of these foods between islands with and without sea otters.

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Section: The Study Areasmentioning

confidence: 99%

Sea Otter Predation and Community Organization in the Western Aleutian Islands, Alaska

Estes¹,

Smith²,

Palmisano³

1978

Ecology

275

148

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“…1). Densities of sea urchins are highly variable at these depths, but range up to 680 m-2 (15). The majority of these sea urchins have test diameters of less than 32 mm (16).…”

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confidence: 99%

Sea Otters: Their Role in Structuring Nearshore Communities

Estes

Palmisano

1974

Science

977

752

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A comparison of western Aleutian Islands with and without sea otter populations shows that this species is important in determining littoral and sublittoral community structure. Sea otters control herbivorous invertebrate populations. Removal of sea otters causes increased herbivory and ultimately results in the destruction of macrophyte associations. The observations suggest that sea otter reestablishment indirectly affects island fauna associated with macrophyte primary productivity.

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“…In the early 1970s sea urchins at Amchitka occurred at a density and size well below those at nearby islands where otters were absent (Estes et al 1978). Data from Barr (1971) and Estes and Duggins (1995) demonstrate further that density and maximum size of sea urchins at Amchitka remained unchanged from the late 1960s through at least 1987. By 1993, however, sea urchin population density had doubled.…”

Section: Discussionmentioning

confidence: 90%

Inter-decadal patterns of population and dietary change in sea otters at Amchitka Island, Alaska

2000

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After having been hunted to near-extinction in the Pacific maritime fur trade, the sea otter population at Amchitka Island, Alaska increased from very low numbers in the early 1900s to near equilibrium density by the 1940s. The population persisted at or near equilibrium through the 1980s, but declined sharply in the 1990s in apparent response to increased killer whale predation. Sea otter diet and foraging behavior were studied at Amchitka from August 1992 to March 1994 and the data compared with similar information obtained during several earlier periods. In contrast with dietary patterns in the 1960s and 1970s, when the sea otter population was at or near equilibrium density and kelp-forest fishes were the dietary mainstay, these fishes were rarely eaten in the 1990s. Benthic invertebrates, particularly sea urchins, dominated the otter's diet from early summer to mid-winter, then decreased in importance during late winter and spring when numerous Pacific smooth lumpsuckers (a large and easily captured oceanic fish) were eaten. The occurrence of spawning lumpsuckers in coastal waters apparently is episodic on a scale of years to decades. The otters' recent dietary shift away from kelp-forest fishes is probably a response to the increased availability of lumpsuckers and sea urchins (both high-preference prey). Additionally, increased urchin densities have reduced kelp beds, thus further reducing the availability of kelp-forest fishes. Our findings suggest that dietary patterns reflect changes in population status and show how an ecosystem normally under top-down control and limited by coastal zone processes can be significantly perturbed by exogenous events.

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Studies of Populations of Sea Urchins, "Strongylocentrotus" sp., in Relation to Underground Nuclear Testing at Amchitka Island, Alaska

Cited by 3 publications

References 0 publications

Sea Otter Predation and Community Organization in the Western Aleutian Islands, Alaska

Sea Otter Predation and Community Organization in the Western Aleutian Islands, Alaska

Sea Otters: Their Role in Structuring Nearshore Communities

Inter-decadal patterns of population and dietary change in sea otters at Amchitka Island, Alaska

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