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Kasatochi Island, the subaerial portion of a small volcano in the western Aleutian volcanic arc, erupted on 7–8 August 2008. Pyroclastic flows and surges swept the island repeatedly and buried most of it and the near-shore zone in decimeters to tens of meters of deposits. Several key seabird rookeries in taluses were rendered useless. The eruption lasted for about 24 hours and included two initial explosive pulses and pauses over a 6-hr period that produced ash-poor eruption clouds, a 10-hr period of continuous ash-rich emissions initiated by an explosive pulse and punctuated by two others, and a final 8-hr period of waning ash emissions. The deposits of the eruption include a basal muddy tephra that probably reflects initial eruptions through the shallow crater lake, a sequence of pumiceous and lithic-rich pyroclastic deposits produced by flow, surge, and fall processes during a period of energetic explosive eruption, and a fine-grained upper mantle of pyroclastic-fall and -surge deposits that probably reflects the waning eruptive stage as lake and ground water again gained access to the erupting magma. An eruption with similar impact on the island's environment had not occurred for at least several centuries. Since the 2008 eruption, the volcano has remained quiet other than emission of volcanic gases. Erosion and deposition are rapidly altering slopes and beaches.
Analysis of satellite images of Kasatochi volcano and field studies in 2008 and 2009 have shown that within about one year of the 7–8 August 2008 eruption, significant geomorphic changes associated with surface and coastal erosion have occurred. Gully erosion has removed 300,000 to 600,000 m3 of mostly fine-grained volcanic sediment from the flanks of the volcano and much of this has reached the ocean. Sediment yield estimates from two representative drainage basins on the south and west flanks of the volcano, with drainage areas of 0.7 and 0.5 km2, are about 104 m3 km−2 yr−1 and are comparable to sediment yields documented at other volcanoes affected by recent eruptive activity. Estimates of the retreat of coastal cliffs also made from analysis of satellite images indicate average annual erosion rates of 80 to 140 m yr−1. If such rates persist it could take 3–5 years for wave erosion to reach the pre-eruption coastline, which was extended seaward about 400 m by the accumulation of erupted volcanic material. As of 13 September 2009, the date of the most recent satellite image of the island, the total volume of material eroded by wave action was about 106 m3. We did not investigate the distribution of volcanic sediment in the near shore ocean around Kasatochi Island, but it appears that erosion and sediment dispersal in the nearshore environment will be greatest during large storms when the combination of high waves and rainfall runoff are most likely to coincide.
The 7–8 August 2008 eruption of Kasatochi Island volcano blanketed the island in newly generated pyroclastic deposits and deposited ash into the ocean and onto nearby islands. Concentrations of water soluble Fe, Cu, and Zn determined from a 1:20 deionized water leachate of the ash were sufficient to provide short-term fertilization of the surface ocean. The 2008 pyroclastic deposits were thicker in concavities at bases of steeper slopes and thinner on steep slopes and ridge crests. By summer 2009, secondary erosion had exposed the pre-eruption soils along gulley walls and in gully bottoms on the southern and eastern slopes, respectively. Topographic and microtopographic position altered the depositional patterns of the pyroclastic flows and resulted in pre-eruption soils being buried by as little as 1 m of ash. The different erosion patterns gave rise to three surfaces on which future ecosystems will likely develop: largely pre-eruptive soils; fresh pyroclastic deposits influenced by shallowly buried, pre-eruptive soil; and thick (>1 m) pyroclastic deposits. As expected, the chemical composition differed between the pyroclastic deposits and the pre-eruptive soils. Pre-eruptive soils hold stocks of C and N important for establishing biota that are lacking in the fresh pyroclastic deposits. The pyroclastic deposits are a source for P and K but have negligible nutrient holding capacity, making these elements vulnerable to leaching loss. Consequently, the pre-eruption soils may also represent an important long-term P and K source.
We studied the vegetation of Kasatochi Island, central Aleutian Islands, to provide a general field assessment regarding the survival of plants, lichens, and fungi following a destructive volcanic eruption that occurred in 2008. Plant community data were analyzed using multivariate methods to explore the relationship between pre- and post-eruption plant cover; 5 major vegetation types were identified: Honckenya peploides beach, Festuca rubra cliff shelf, Lupinus nootkatensis–Festuca rubra meadow, Leymus mollis bluff ridge (and beach), and Aleuria aurantia lower slope barrens. Our study provided a very unusual glimpse into the early stages of plant primary succession on a remote island where most of the vegetation was destroyed. Plants that apparently survived the eruption dominated early plant communities. Not surprisingly, the most diverse post-eruption community most closely resembled a widespread pre-eruption type. Microhabitats where early plant communities were found were distinct and apparently crucial in determining plant survival. Comparison with volcanic events in related boreal regions indicated some post-eruption pattern similarities.
On 11 June 2008 the first author spent 10.66 h on Kasatochi Island and collected 396 terrestrial arthropod specimens estimated to represent a minimum of 58 species. Among these are included the first Alaskan records of the fly genus Lestremia and the ghost moth Sthenopis quadriguttatus (Grote). Also found were a new species of salpingid beetle in the genus Aegialites and sawfly in the genus Pseudodineura. On 10 and 12 August 2009, one year after an eruption that buried the island in ash, the first author spent 15 h sampling terrestrial arthropods. Specimens were also collected on 12–14 June 2009 by other team members. An estimated 17 post-eruption species were documented by the collection of 210 specimens. Evidence of breeding was seen in 4–9 species. Pitfall traps run from 14 June to 10 August 2009 flooded, capturing no arthropods. Fallout collectors representing 1 m2, run during the same period, had four flies and no seeds. The majority of species recovered post-eruption were probably survivors or their offspring, some of which had commenced breeding on rotting kelp and bird carcasses. Of significance as the first post-eruption evidence of multi-trophic level interaction, a fly predator on kelp flies, Scathophaga, and an ichneumonid endoparasite of flies, Phygadeuon, were also present. No phytophagous or fungivorous species were found. Supporting the heterotrophs-first hypothesis of Hodkinson et al. (2002), the current terrestrial ecosystem of Kasatochi is necromass-based rather than plant-based.
Kasatochi Island, home to a rich community of largely marine-dependent fauna, erupted with little warning on 7–8 August 2008 and buried the island under up to 30 m of tephra. We visited the island during the summer of 2009 to examine the effects of the eruption on local wildlife. The abundance of sea lions and many seabird species in 2009 was comparable to pre-eruption estimates, suggesting that adult mortality was low for these species. In contrast, shorebirds and passerines formerly breeding on the island were not observed in 2009 and probably perished in the eruption. The largest direct effect of the eruption to individual animals was probably mortality of chicks, with an estimated total 20,000–40,000 young birds lost. Indirect effects on wildlife consisted of loss of foraging habitat for species that relied on former terrestrial, intertidal, or nearshore-subtidal habitat and the near-total destruction of all former nesting habitats for most species. Although several species attempted to breed in 2009, all except Steller's sea lions failed due to lack of suitable breeding sites. The recovery of wildlife at Kasatochi will depend on erosion of the tephra layer blanketing the island to re-expose former breeding habitat.
A description is presented of the nearshore benthic community of Kasatochi Island 10–12 months after a catastrophic volcanic eruption in 2008. The eruption extended the coastline of the island approximately 400 m offshore, mainly along the south, southeast, and southwest shores, to roughly the 20 m isobath. Existing canopy kelp of Eualaria (Alaria) fistulosa, as well as limited understory algal species and associated fauna (e.g., urchin barrens) on the hard substratum were apparently buried following the eruption. Samples and observations revealed the substrate around the island in 2009 was comprised almost entirely of medium and coarse sands with a depauperate benthic community, dominated by opportunistic pontogeneiid amphipods. Comparisons of habitat and biological communities with other nearby Aleutian Islands, as well as with the Icelandic volcanic island of Surtsey, confirm dramatic reductions in flora and fauna consistent with an early stage of recovery from a large-scale disturbance event.
Kasatochi volcano, an island volcano in the Aleutian chain, erupted on 7–8 August 2008. The resulting ash and pyroclastic flows blanketed the island, covering terrestrial habitats. We surveyed the marine environment surrounding Kasatochi Island in June and July of 2009 to document changes in abundance or distribution of nutrients, fish, and marine birds near the island when compared to patterns observed on earlier surveys conducted in 1996 and 2003. Analysis of SeaWiFS satellite imagery indicated that a large chlorophyll-a anomaly may have been the result of ash fertilization during the eruption. We found no evidence of continuing marine fertilization from terrestrial runoff 10 months after the eruption. At-sea surveys in June 2009 established that the most common species of seabirds at Kasatochi prior to the eruption, namely crested auklets (Aethia cristatella) and least auklets (Aethia pusilla) had returned to Kasatochi in relatively high numbers. Densities from more extensive surveys in July 2009 were compared with pre-eruption densities around Kasatochi and neighboring Ulak and Koniuji islands, but we found no evidence of an eruption effect. Crested and least auklet populations were not significantly reduced by the initial explosion and they returned to attempt breeding in 2009, even though nesting habitat had been rendered unusable. Maps of pre- and post-eruption seabird distribution anomalies indicated considerable variation, but we found no evidence that observed distributions were affected by the 2008 eruption.
Kasatochi Island is a small volcanic island in the central Aleutian Islands that erupted on 7 August 2008. An interdisciplinary team visited the island and its vicinity in the summer of 2009 to describe the immediate consequences of the eruptions on terrestrial, coastal, and benthic communities. The initial effects of the eruptions on soils, oceanic waters, benthic terrain, terrestrial plants, land birds, shore birds, nesting sea birds, arthropods, marine algae, and marine invertebrates were described. This overview summarizes the conventional understanding of mechanisms that drive the reassembly of devastated ecosystems and shows how studies of Kasatochi Island may enhance our understanding of succession. The presence of residual soils and low mortality among sea birds will hasten early recovery, but significant erosion (removal of tephra and marine sediments) must occur to permit a return to a fully functional ecosystem. Long-distance dispersal over seawater will be needed to replenish the plant communities. While scavenger arthropods survived, dispersal will be needed to generate complete insect communities. Land birds were killed and their habitats destroyed, so their re-colonization awaits vegetation development. Ecosystem recovery will be facilitated by allochthonous inputs of nutrients and by plant establishment. Monitoring how the biota returns to a new equilibrium and comparisons to adjacent islands will allow tests of assembly and biogeographic theory and further our understanding of terrestrial-marine interactions. The study of Kasatochi Island's recovery will produce a valuable story of ecosystem reassembly.
Tundra soils contain large amounts of organic carbon (C) that might become available to microbial decomposition as soils warm. To elucidate the C sources currently sustaining CO2 emissions from striped tundra soils (soil respiration) in Northwest Greenland, we studied the seasonal pattern and radiocarbon (14C) signature of soil respiration and of CO2 within the pore space, respired from roots and non-root–associated microbes, and of bulk soil organic matter.
Old C pools are present in the topsoil of both barren ridges (1000–5000 yrs) and vegetated troughs (modern to 600 yrs). Before leaf-out, soil respiration was depleted in 14C relative to atmospheric CO2, root and microbial respiration within the topsoil, demonstrating a substantial contribution of C fixed before 1950. As the growing season progressed, the contribution of older C pools decreased, but remained apparent in the soil respiration from ridges and in pore space CO2. Soil respiration from troughs became dominated by recently fixed C.
As the active layer deepens with permafrost thaw, buried C may become an increasingly larger component of soil respiration. Detecting microbial decomposition of older C pools requires continuous monitoring of soil and microbial respiration and better constraints on soil C pools.
Variability in the vascular plant species composition of four stages of primary succession was investigated on 39 glacier forelands in the Jotunheim and Jostedalsbreen regions of south-central Norway. The relative frequencies of species were recorded in the pioneer zone adjacent to the glacier snout, in vegetation on terrain ages of c. 70 years and c. 250 years, and in mature vegetation outside the foreland (approximately 10,000 years since deglaciation). Sørensen dissimilarity, non-metric multidimensional scaling, and cluster analysis were used to compare the relative variability in species composition of these four stages and to identify patterns of succession within four altitudinal belts. Indicator species analysis identified characteristic species within each stage. Variation partitioning was used to quantify the relative influence of altitude and continentality on species composition.
Variability increased between pioneer and later successional stages at all but the highest altitudes, which showed no significant difference in variability between stages. The results suggest that up to an altitude of around 1600 m succession on glacier forelands follows a divergent trajectory: above this altitude little successional change occurs. Rate of successional change also varies with altitude: below about 1000 m, in the sub-alpine belt, the transition from pioneer vegetation to birch woodland occurs within 70 years; above about 1600 m in the high-alpine belt, herbaceous pioneer vegetation can persist indefinitely; at intermediate altitudes, the dwarf-shrub and snowbed vegetation types of the low- and mid-alpine belts develop within c. 250 years. The explanatory power of altitude and continentality on compositional variation and the relative importance of altitude increased with successional stage.
In subarctic Sweden, recent decadal colonization and expansion of aspen (Populus tremula L.) were recorded. Over the past 100 years, aspen became c. 16 times more abundant, mainly as a result of increased sexual regeneration. Moreover, aspen now reach tree-size (>2 m) at the alpine treeline, an ecotone that has been dominated by mountain birch (Betula pubescens ssp. czerepanovii) for at least the past 4000 years. We found that sexual regeneration in aspen probably occurred seven times or more within the last century. Whereas sexual regeneration occurred during moist years following a year with an exceptionally high June–July temperature, asexual regeneration was favored by warm and dry summers. Disturbance to the birch forest by cyclic moth population outbreaks was critical in aspen establishment in the subalpine area. At the treeline, aspen colonization was less determined by these moth outbreaks, and was mainly restricted by summer temperature. If summer warming persists, aspen spread may continue in subarctic Sweden, particularly at the treeline. However, changing disturbance regimes, future herbivore population dynamics and the responses of aspen's competitors birch and pine to a changing climate may result in different outcomes.