Recolonization of the intertidal and shallow subtidal community following the 2008 eruption of Alaska’s Kasatochi Volcano

the island approximately 400 m offshore to roughly the 20 m isobath. One year following the eruption a reconnaissance survey found the intertidal zone devoid of life. Subtidally, the canopy kelp, as well as limited understory algal species and associated benthic fauna on the hard substratum, were buried by debris from the eruption. The resulting substrate was comprised almost entirely of medium and coarse sands with 10


Introduction
The Aleutian Islands are situated on the northern edge of the so-called "Pacific Ring of Fire", a 40 000-km-long horseshoe-shaped assemblage of continental landmasses and islands bordering the Pacific Ocean basin that contains a large number of active and dormant volcanoes.Of the 27 historically active volcanoes in the Aleutian Islands, nine have had at least one major eruptive event since 1990 (Schaefer et al., 2009).Despite the relatively high frequency of volcanic activity in the Aleutians, the response and subsequent recovery of island ecosystems to volcanic disturbances has been largely unstudied due to the region's isolation.Prior to the Kasatochi eruption, the only ecological studies in the region addressing the effects of volcanic activity on biological systems were done on Bogoslof Island, a remote, highly active volcanic island in the eastern Aleutians.Since emerging from a submarine eruption in 1796, Bogoslof Island has been the site of several avian and marine mammal studies, but no intertidal or subtidal investigations (Merriam, 1910;Byrd et al., 1980;Byrd and Williams, 1994).Bogoslof is similar to the submarine eruption of the Icelandic island of Surtsey, which formed in 1963 (Fridriksson, 1975).
With no confirmed historical eruptions, Kasatochi volcano in the central Aleutian Islands erupted on 7-8 August 2008 and pyroclastic flows and volcanic ash completely covered the island and nearshore marine habitat (Scott et al., 2010;Waythomas et al., 2010a, b).Observations a year following the eruption revealed that virtually all terrestrial and subtidal plant and animal life was eliminated (Drew et al., 2010;Jewett et al., 2010;Sikes and Slowik, 2010;Talbot et al., 2010;Williams et al., 2010).
Nearshore kelp forest habitats provide forage fish with required nursery areas and cover from predation (Bodkin, 1988;Siddon et al., 2008;O'Conner and Anderson, 2010).Prior to the eruption the nearshore zone supported extensive kelp habitat and a complement of nearshore epibenthic foraging birds including cormorants Phalacro-  (Ainley et al., 1981;Kotzerka et al., 2011) and pigeon guillemot Cepphus columba (Drent, 1965;Drew et al., 2010).Although the August 2008 eruption of Kasatochi volcano did not appear to be directly responsible for large numbers of mortalities, based on at-sea surveys conducted in June and July of 2009 (Drew et al., 2010), it buried all nesting habitats on the island as well as the entire nearshore zone that cormorants and pigeon guillemots relied on for foraging.Even if nesting habitat recovered, these species require epibenthic prey associated with productive nearshore habitats to survive.Thus, while we expect the abundance of these species to mirror the recovery of both nesting and prey availability, it will most likely be limited by prey availability.
The reassembly of nearshore ecosystems impacted by catastrophic disturbance has received only limited study despite its importance in defining specific coastal ecosystems and determining their rates of recovery.This paper addresses the recolonization of the intertidal and nearshore community of Kasatochi as well as the effects of this recolonization on nearshore foraging marine birds that occupy highest trophic levels in the system.We documented the recolonization of the intertidal and nearshore communities based on a series of opportunistic visits to the island following the 2008 eruption.Comparisons are also made with the Icelandic submarine volcanic eruption of Surtsey.

Setting
Kasatochi Island (52 • 10.3 N latitude, 175 • 30.6 W longitude), part of the Alaska Maritime National Wildlife Refuge (AMNWR), is located 80 km northeast of Adak, Alaska within the Andreanof Islands in the central Aleutians (Fig. 1).The island lies approximately 19 km north of Atka and Fenimore passes, two of several passes which transition between the North Pacific Ocean and the Bering Sea.Prior to the 2008 eruption Kasatochi was a 5 km 2 island volcano (Waythomas et al., 2010a).The island was somewhat conical, initially covered with vascular plants, and with a small lake in the caldera.Breeding seabirds, in particular auklets Aethia spp., puffins Fratercula spp., and storm-petrels Oceanodroma spp. that nested in crevices in talus slopes and rock piles, dominated the island's vertebrate fauna (Williams et al., 2010).A Steller sea lion Eumetopias jubatus rookery occurred on the northern side of the island with an estimated population of ∼ 1000 animals (J.Williams, AMNWR, personal communication, 2009).Dense beds of canopy dragon kelp Eualaria fistulosa were evident around Kasatochi Island, except along the northern shore, before the 2008 eruption (J.Williams and W. Pepper, AMNWR, personal communication, 2009;B. Webster, personal communication, 2010).The status of understory kelps prior to 2008 is nearly unknown, but presumably similar to nearby islands.The eruption initially increased the island's area about 40 % to 7 km 2 and the diameter about 800 m (Waythomas et al., 2010a, b).The volcanic flows and ash that extended the coastline also buried the kelp beds and associated understory flora and fauna.Since the eruption, the coastline and nearshore community have been subjected to constant erosion and accretion from storms, precipitation, and currents.Due to the logistical challenges posed by studying a remote location with limited access we relied on one or two opportunistic visits per year with variable data collection.

Radial transects -2009
Six primary transects that radiated from the caldera to the shore of Kasatochi Island were established for terrestrial sampling (Wang et al., 2010).Intertidal sampling occurred on all transects at approximately the +0.5 m tidal height.At each transect, benthic invertebrates were collected from three 0.06 m 2 replicate quadrates by sampling to a depth of 10 cm in soft substrates and scraping the surface on hard substrates.The primary transects were extended into the marine environment where offshore nutrient sampling (Drew et al., 2010) and nearshore (10-20 m water depths) benthic sampling/observations occurred aboard the M/V Ti ĝlax (Fig. 2) (Jewett et al., 2010).quadrat was placed for algal and invertebrate sampling, respectively.The abundance and percent cover of algae and macroinvertebrates were recorded within the 1 m × 1 m (1 m 2 ) quadrat.A diver-operated airlift capped with a 0.5 mm mesh bag was used to collect all invertebrates found within the 25 cm × 25 cm quadrat.
The post-eruption Kasatochi benthic community and sediments were compared to two communities previously sampled from nearby Atka and Amlia islands in 2006 and 2007; sampling methods were comparable (Jewett et al., 2008(Jewett et al., , 2010)).

Diver video -2009
In June and August 2009 video recordings (1-2 min) made by divers from the 10 m transects were intended to provide semi-quantitative information on habitat characteristics and distribution of major algal and macrofauna taxa.To assist with characterizing the habitat, another diver either recorded on a slate or collected representatives of the dominant mature algae and macrofauna from 1 m on either side of the transect (2 × 25 m).Videos, as well as occasional still photos, were taken with a Canon ™ Pow-erShot S80 digital camera.

Remote video -2009, 2012 and 2013
A Splashcam ™ camera was deployed from the M/V Ti ĝlax in August 2009 to characterize the benthic substrate and community at the 20 m depth along the six primary transects.The Splashcam ™ was also deployed from a skiff at 10-20 m depths along

Nearshore marine bird censuses -2003-2013
Prior to the 2008 eruption Kasatochi supported reproductive populations of cormorants Phalacrocorax spp.and pigeon guillemots Cepphus columba.Censuses were used to compare numbers of nearshore foraging marine bird predators, hereafter referred to as nearshore marine birds, before and after the eruption.Censuses were conducted from a 4.5 m skiff approximately 100 m offshore, two observers counted all marine birds on the water or flying within 100 m of either side or 200 m in front of the skiff (resulting in a 200-m-wide survey strip).Observations were geolocated using a GPS and their distributions mapped using GIS software.On-shore nest searches were conducted in June of all years following the eruption (2009)(2010)(2011)(2012)(2013); however, effort varied due to available time, weather, and terrain.

Data analyses
ANOVAs were used for comparisons between water temperatures and years, sediment grain size (percent) and study sites, and amphipod abundance (percent) and sites.All percentages were arcsine transformed prior to the ANOVA testing.Statistical significance was set at p ≤ 0.05.The early state of recovery precluded statistical testing of seabird response in relation to the recovery of their foraging habitat.Instead, we collected and compared census data for nearshore marine birds, compared distributions of nearshore marine birds and kelp habitat, and identified signs of their reproduction.Pre-eruption nearshore marine bird census data provided a baseline for post-eruption comparison.

Shoreline geomorphology -2008-2012
Post-eruption satellite images revealed a changing shoreline (Fig. 4).On 17 September 2008, 3.7 weeks following the eruption, a thick accumulation of volcaniclastic deposits had spread seaward of the pre-eruption coastline (image 9 April 2004), increasing the diameter of the island ∼ 0.8 km and resulting in about a 40 % increase in area (Waythomas et al., 2010a).The western shoreline had the greatest offshore expansion, ∼ 0.5 km, while most other sectors spread 0.3-0.4km.Exceptions were the promontories adjacent to Tundering Cove, Whiskey Cove, Sea Lion Spit, and Rye Point, which had little to no offshore extension.Volcanic deposits of predominantly medium and coarse grain sands buried the thick stand of canopy kelp that rimmed most of the island and extended to about 20 m water depths.Also buried were the data logger, located off the east coast in 7-9 m of water, and Shag Rock, about 0.2 km off the pre-eruption southwest shore (Fig. 4).On 18 April 2009, 9.3 months after the eruption, the shorelines along the east, north, and west were reduced 0.05-0.2km, with a few exceptions, from the 17 September 2008 image.In contrast, the southeast, south, and southwest shores expanded 0.15-0.25 km seaward (Fig. 4).By 20 February 2012, 3.6 years post-eruption, the northern shoreline from north of Rye Point to the point north of Oystercatcher Beach had eroded to pre-eruption shoreline proximity.Lesser erosion was evident along the southeast and southwest shores, however, shoreline expansion was evident along the southern shore by as much as 0.1 km, so accretion on this coast grew ∼ 0.5 km from the pre-eruption shore (Fig. 4).

Intertidal community -2009, 2012, and 2013
In 2009 intertidal sampling occurred on Transects (T) 2, 3, and 5  ples a decision was made to not sample the remaining intertidal transects, but to focus on the subtidal sampling.In August 2010, 2011 and 2012 intertidal sampling did not occur because of poor weather.Nevertheless, terrestrial samplers made opportunistic qualitative observations of the intertidal zone where they went ashore at rock-rimed Tundering Cove on the northwest side of the island.In 2010 at approximately +0.4 m tidal height a depauperate intertidal community was observed with a few unidentified barnacles among a thin matt of unidentified diatoms on rocks.In 2011 at a tidal height of approximately +0.4 m this site revealed young ribbon kelp Alaria marginata along with green sea hair Ulva intestinalis and a red seaweed Porphyra sp. in tide pools.Two species of barnacles, Semibalanus cariosus and Balanus glandula, were most numerous, but a few small blue mussels Mytilus trossulus, and limpets were also prevalent.Two size classes of barnacles were apparent, ∼ 4 mm and ∼ 10 mm base diameters.During 2012 in Tundering Cove at a tidal height of approximately the +0.6 m a robust intertidal community with a well-defined barnacle band above a thick band of ribbon kelp and green sea hair in tide pools was revealed.At Tundering Cove in June 2013 a dense band of ribbon kelp and red algae Palmaria hecatensis rimmed the rock wall approximately 1.5 m above the +0.3 m tidal height.

Canopy kelp -2009 and 2012
Limited pre-eruption information on the nearshore marine community at Kasatochi exists.Personnel and scientists who visited Kasatochi from the M/V Ti ĝlax attest that before the 2008 eruption dense beds of canopy-forming dragon kelp Eualaria fistulosa were evident around the island, except along the northern shore where slope and water depth limited offshore kelp (Fig. 5a).Aerial reconnaissance in the spring of 2009 determined that the eruption extended the coastline of the island about 400 m, mainly along the south, southeast and southwest shores, to roughly the 20 m isobath (Scott et al., 2010).This expansion of volcanic material covered the kelp beds and associated benthic community that previously occurred there.Surveys from the M/V Ti ĝlax in August 2009 did not find any canopy kelp along any of the six transects (Jewett et al.,3807 Discussion  A1).However, canopy kelp was visible at the water surface in small patches at three locations, off the east (near T2), northwest (near T5), and southwest sides of the island (Fig. 5b).By August 2012, canopy kelp had expanded considerably, particularly on the western (T4), northwest (T5 & T6), and east (near T2) sides of the island (Figs. 2, 5c; Table A1).No canopy kelp was observed along the southern side, where, prior to the 2008 eruption, the kelp was particularly dense.A reconnaissance visit in June 2013 revealed only three small canopy kelp patches (N, E, and SW), however, maximum kelp length is not attained until fall.

Subtidal community -2009
Jewett et al. ( 2010) reported on the nearshore benthic community at Kasatochi 10 and 12 months following the 2008 eruption.Twelve video recordings (by diver and Splashcam ™ ) and one diver observation made within the 20 m isobath revealed little hard substrate on a largely featureless bottom (Table A1).At 10 m, the surficial substrate was dominated by sand, with gravel and a few partially exposed boulders.At 20 m, sand waves, with coarser sand on the wave crests, were evident on Transects 2 and 5, but fines, i.e., mud and fine sand, were more prevalent on Transects 1, 2, 4 and 6.Soft sediment comprised 100 % of the substrate within most of the 1 m × 1 m sediment quadrats, except along T3 where boulders and cobbles were encountered.Sediment samples collected by divers at 10 m depth on five of the six subtidal transects (T1 not sampled due to rough seas) were predominantly medium and coarse grain sands (0.25-1.0 mm).There was no significant difference in the grain size composition (gravel, sand, mud) at the five sampling sites (ANOVA: df = 4, F = 0.012; p = 0.99).
Benthic organisms (infauna and epifauna) were rarely observed by divers or recorded on videos.Holes in, or mounds on the soft substrate, indicative of macrobenthic invertebrates, and large epifaunal invertebrates were absent from the soft substrate.Divers observed a few live barnacles on T6 and a few juvenile fishes on T2 and T6.One large yellow Irish lord Hemilepidotus jordani was recorded with the Splashcam ™ at 14 m on T3.
Divers found few living representatives of mainly smaller species of algae on secondary transects at 10 m depth.Although no algae were encountered within any of the 1 m × 1 m quadrats, specimens were visible along the transects on scattered boulders partially exposed.Juvenile brown alga of the family Laminariaceae, Saccharina groenlandica (formerly Laminaria bongardiana) and Desmarestia aculeata, dominated on T4.Some fertile S. groenlandica were observed on the video record.Thick diatom mats with occasional filamentous green alga Urospora spp.were on T2 and T5.No sea urchins were observed.At 14-20 m depths along T3, the Splashcam ™ recorded small brown algae of the family Alariaceae, mainly E. fistulosa, with some Cymathaere triplicata, Alaria marginata, and Laminaria longipes, as well as several clumps of S. groenlandica and the red alga Porphyra spp.Some fertile L. longipes were observed.Saccharina groenlandica was also noted at 12 m on T4.Most of the brown algae were young, usually less than 2 m in length.In contrast, no algae were observed at 20 m on Transects 1, 2, 4, 5, and 6.Again, no sea urchins were observed.
Additional features that reflected eruption disturbance included dead barnacles on boulders at 10 m on T4 and T6.Also, on T4 at 12 m, the Splashcam ™ recorded bubbles flowing from the sand at four points during a nearly 3 min drift, indicative of recent burial of volcanic debris with trapped air.Benthic samples were collected at 10 m on five of the six subtidal transects in predominantly medium and coarse sands.A depauperate macrobenthic fauna typified all five sites with average abundance values of 8, 0, 352, 389, and 789 ind.m −2 on Transects 2, 3, 4, 5, and 6, respectively (Jewett et al., 2010).Amphipods were the most abundant organisms, although some polychaetes, cumaceans, and barnacles were found.Amphipods occurred at three sites where they accounted for between 51 and 89 % of the total abundance.Amphipods belonged to six families and there was no significant difference in abundance of the distinct families between the three Because no pre-eruption information on the macrobenthic community at Kasatochi was available for comparison with 2009 data, comparisons were made with data from nearby Atka and Amlia islands (not shown on Fig. 1), in the Andreanof Islands group, with similar depths and soft sediments as sampled at post-eruption Kasatochi.Depths at the two sites were 9 and 14 m, respectively.Although the sediments at these two sites were mostly sands, they were generally finer than at Kasatochi.The faunal abundances at the Atka and Amlia sites were an order of magnitude greater than sites around Kasatochi Island.Furthermore, these sites were mostly dominated by polychaetes, gastropods, and sand dollars, rather than amphipods.These two sites also had evidence of a well-established macrobenthic community, with biotic mounds and holes, and numerous macrobenthic components, like burrowing anemones, polychaetes, hermit crabs, sea urchins, sand dollars, sea stars, and adult and juvenile flatfishes (Jewett et al., 2010).

Subtidal community -2012
Filming on 28 August 2012 with the Splashcam ™ revealed substantial recovery of the benthic environment from observations made in 2009.Large brown algae, mainly dragon kelp Eualaria fistulosa, were present on five of the six transects, i.e., Transects 2, 3, 4, 5, and 6 (Table A1; Fig. 2).The kelp was so dense in places the Splashcam  A1; Fig. 2).Additional evidence of recovery included the presence of feeding pigeon guillemots, young gulls Larus sp. and cormorants amid the dragon kelp canopy at T4, 11 m.Additionally, when the data logger was retrieved on 28 August 2012 (deployed 20 June 2012) from a depth of 9 m near T2 (Fig. 2), a large rock was caught in the anchor.Biota attached to the rock included two juvenile kelp Saccharina sp., a polynoid scale worm, hydroids, bryozoans, barnacles (∼ 10 mm base diameter), and caprellid amphipods.

Subtidal community -2013
On 17 June 2013 Splashcam ™ videos revealed only slight recovery of the benthic environment at a few sites in comparison from 2012 observations.Most sites revealed little or no additional recovery due to recent burial or removal of sand.T4 at 10 m, a site among canopy dragon kelp, had denser dragon kelp and understory kelps S. groenlandica and Alaria marginata, as well as amphipods.T3 at 17 m had more S.
groenlandica.T1 at 22-30 m and T2 at 12 m had germling brown algae.Compared to 2012 water depths remained the same at five study sites (T2 at 12 and 20 m, T5 at 10 m, and T6 at 10 and 20 m), was deeper at four sites (T1 at 22-30 m, T3 at 17.7 and 24.4 m, and T4 at 17 m), and shallower at three sites (T3 at 10 m, T4 at 10 and 20 m) (Table A1; Fig. 2).

Nearshore Foraging Birds -2003-2013
Following the eruption cormorants Phalacrocorax spp., though never observed in large numbers around the island, became rare (Fig. 6).Although post-eruption sampling was limited to a single June census, the most recent (June 2013) had the highest count of cormorants since the eruption.To date there is no evidence that cormorants are breeding on the island.Pigeon guillemots Cepphus columba showed a different pattern than the cormorants.Relatively common prior to the eruption, the first post-eruption count of pigeon guillemots in June 2009 was the highest recorded.The census numbers then dropped in the two subsequent counts (2012 and 2013) to the lowest numbers recorded (Fig. 7).A single pigeon guillemot nest was discovered on the east side of the island in 2010, and evidence of successful fledging was noted in August 2011 (1 juvenile) and 2012 (2 juveniles) on the west side of the island.

Discussion
Although no pre-eruption intertidal investigations occurred on Kasatochi Island, the intertidal community there was presumably similar to that of other islands in the central Aleutians.Lebednik and Palmasino (1977) and O'Clair (1977) provided extensive descriptions of the intertidal communities around Amchitka Island.Algae that dominated the littoral zone of 0 to +0.8 m tidal height included Rockweed Fucus distichus, the Saccharina (Hedophyllum sessile) zone that contained six associations (Saccharina, Ulva, Analipus, Corallina, Halosaccion, and Iridaea), and Alaria.The sublittoral zone (0 to −3 m) was dominated by Laminaria spp., but primarily L. longipes (Lebednik and Palmasino, 1977).O'Clair (1977) listed over 365 invertebrate species in the littoral and sublittoral zone and identified three invertebrate communities according to their dominant macrophytes, the Laminaria community, the Alaria-Saccharina community, and the Halosaccion-Fucus community.The invertebrates in these communities were mostly inconspicuous.
Intertidal sampling was initiated at Kasatochi in 2009, but because of the new and unstable shoreline no life was found.The intertidal zone for most of the island has been largely in transition since the eruption, with shorelines alternating in accretion and erosion (see Fig. 4), similar to an active island volcano in Italy (Romagnoli et al., 2006).
In hindsight, it would have been better to establish quantitative intertidal monitoring only on the areas dominated by hard substrates, like Tundering Cove.But, this would have required deviating from sampling on the six transects.The only intertidal data available (qualitative) was limited to a few opportunistic photographs at Tundering Cove.These photographs from +0.3 to +0.6 m tidal height on rock substrate transitioned from a few barnacles among diatom matts in August 2010, to young ribbon kelp Alaria marginata, green sea hair Ulva intestinalis, a red seaweed Porphyra sp., barnacles Semibalanus cariosus and Balanus glandula, and small blue mussels Mytilus trossulus in August 2011, to a well-defined barnacle band above a thick band of ribbon kelp and green sea hair in tide pools in August 2012, to a dense band of ribbon kelp and red alga Palmaria hecatensis in June 2013.We anticipated the intertidal community on hard substrate will continue to increase in diversity and stabilize within a few years, as demonstrated on the submarine volcano Surtsey (Jónsson and Gunnarsson, 1982).But, the community on shorelines composed of soft substrates will not occur until land and coastal erosion equilibrates.
Following nearly a century of sea otter range expansion and population growth, sea otter numbers began to decline about 1990 across the Aleutian Islands (Doroff et al., 2003), generally causing an ecosystem phase shift from a kelp-dominated to an urchin-dominated subtidal community (Estes et al., 2004).While today the Aleutians are generally in an urchin-dominated state (i.e., urchin barren) (Estes et al., 2010), canopy kelp beds, primarily the annuals Eualaria fistulosa and Nereocystis luetkeana, as well as numerous species of understory algal species, e.g., the annual Cymathaere triplicata, and the perennials Saccharina groenlandica, Laminaria spp., Agarum spp., andThalasiophyllum clathrus, still occur in some areas of the archipelago (Konar and Estes, 2003;Lindeberg and Lindstrom, 2010;Dasher et al., 2012).
Alaska Maritime National Wildlife Refuge personnel obtained information on the kelp community of Kasatochi Island prior to the eruption from surface observations while aboard the M/V Ti ĝlax.This vessel makes annual sojourns to the island, as well as elsewhere in the Aleutians.Refuge personnel maintained that in years leading up to the 2008 eruption dense beds of canopy-forming dragon kelp E. fistulosa, were prevalent around Kasatochi, except along the northern shore where deep waters limit the canopy nants of the once robust Eualaria fistulosa community that surrounded most of the island.This kelp can attain lengths up to 25 m (O'Clair and Lindstrom, 2000), and it is likely that some portions of the kelp community were not completely buried, especially along the outer margin of the Eualaria zone.While video recordings approximately a year after the eruption further underscored the near complete elimination of kelps, it did reveal isolated kelp remnants.Recordings at 12 locations along transects revealed relatively small (< 2 m) algal plants at a few locations where the top of boulders were protruding through the soft substrate.The kelp E. fistulosa mainly dominated at 14 m on T3 and Saccharina groenlandica dominated at 10-12 m on T4.That some fertile S. groenlandica was observed indicates some understory kelps survived the eruption.
The absence of hard substrate is apparently the major factor limiting kelp recolonization around Kasatochi Island.Studies in temperate systems have shown that algal communities can recover to previous densities within one year of denuding (Foster, 1975;Bertness et al., 2004).In situations where algal communities are buried, recovery is entirely dependent upon the rate of sediment erosion.There is no information on the depth of the overlaying subtidal fines, the erosion rate of subtidal fines by ocean currents, and the erosion rate of terrestrial fines on Kasatochi (from land to sea).Little information exists on currents around Kasatochi or through the closest passes, Fenimore and Atka, but net northerly current speeds through Seguam Pass (east of Kasatochi) and Tanaga Pass (west of Kasatochi) are moderate (20-25 cm s −1 ) (Stabeno et al., 2005).
Current velocities necessary to erode medium and coarse sands (0.25-1.0 mm) are about 20 cm s −1 and greater (Hjulström, 1939).Thus, if currents, especially the tidallydriven ones, are > 20 cm s −1 around Kasatochi it may not be long before they erode the subtidal fines down to hard substratum.This would result in increased hard substrate in the nearshore environment that would enable a diverse algal community to become established again.
Another important component of the subtidal community that presumably was buried by the eruption was the long-lived and slow-growing red crustose coralline algae (Frantz et al., 2005;Halfar et al., 2007).In the Aleutian Islands, red crustose coralline algae (Clathromorphum nereostratum and Lithothamnion spp.) are widespread in the low intertidal and shallow subtidal regions, and cover most available hard substrates (Chenelot et al., 2011).Crustose coralline algae were observed at one location near Kasatochi in 2002, as noted above, and it is thought to have been pervasive in the nearshore zone based on observations made during Aleutian surveys in 2006-07 (Chenelot et al., 2011;Dasher et al., 2012).Subtidal habitats dominated by crustose coralline algae are often associated with sea urchin-barren grounds and regarded as supporting limited invertebrate communities, especially compared to the adjacent kelp forests.Despite the desolate appearance of crustose habitats, the interstitial spaces of the crustose environments support faunal communities as diverse and abundant as those found in rich kelp forests (Chenelot et al., 2011).Thus, the loss of this habitat is viewed as significant as the loss of the foliose algal community.It is unknown how long it will take for this crustose community to recover when suitable hard substrate is re-exposed by erosion.
Subtidally around Kasatochi, the newly deposited sand substrate was largely devoid of life, since video recordings revealed only barnacles (T6 at 10 m) and no mounds or holes formed by infauna.The dominant macrofaunal species present were motile crustaceans, such as amphipods, that presumably moved into the devastated area from outer unaffected regions.This is in contrast to the Atka and Amlia sites with similar depth and substrate (Jewett, unpublished).Sand communities in the latter region were well established and showed no effects of physical or biological disturbance.They were characterized by high macrobenthic diversity and abundance with dominant faunal components (i.e., polychaetes, gastropods, sand dollars) less motile or sessile than the amphipods found at Kasatochi.Numerous investigators have found amphipods among the first opportunistic species on soft substrates following disturbances (e.g., Oliver et al., 1980;VanBlaricom, 1982;Oliver and Slattery, 1985;Jewett et al., 1999).VanBlaricom (1982) discovered that shallow sand sites disturbed by digging rays were characterized by low macroinvertebrate abundance, but four families of tube-dwelling and burrowing amphipods dominated.Benthic amphipods (13 genera including tube-dwelling corophiids and burrowing oedicerotids) were among the dominant early colonizing taxa at sandy locations subjected to placer gold mining in Norton Sound, Alaska (Jewett et al., 1999).Little is known about the life history of the amphipods in the family Pontogeneiidae that dominated near Kasatochi, but this family is reported to be a nestler (Yu et al., 2002) and a free surface dweller that feeds as a herbivore, surface detritivore, and carnivore (Biernbaum, 1979).Diatom films or mats were pervasive in the nearshore zone around Kasatochi, and the pontogeneiid amphipods appear to have been the first grazers to utilize this algal resource (Jewett et al., 2010).
Since no post-eruption information on eruption effects or recolonization of nearshore communities on other Aleutian volcanic islands are available, comparisons are made between this study and the volcanic island of Surtsey, off the coast of Iceland.During the ∼ 3.5 year volcanic eruption of Surtsey (1963Surtsey ( -1967)), the cinder cone built up from a water depth of 120 m and eventually covered an area of 6.5 km 2 , of which 2.8 km 2 were above water to a height of 172 m (Fridriksson, 1975(Fridriksson, , 2006)).Smaller satellite volcanoes were added to the submarine base of the Surtsey structure.During the later period of volcanic activity ash flowed down and destroyed all benthic organisms on the sea floor.Ash reached as far out as 1.8 km off the island, where a thin layer of ash was deposited over a layer of mud.The immediate effects of the eruption on the temperature and nutrient composition of seawater were negligible and there was no effect on salinity.
One element of the algal community around Kasatochi bears resemblance to the first stages of algal settlement around Surtsey.Pioneers of the marine benthic algae that colonized Surtsey 21 months after the island emerged in 1963 were composed only of diatoms Navicula mollis and Nitzschia bilobata and one species of filamentous green alga Urospora penicilliformis (Jónsson, 1967).We also found the first algae colonizers off Kasatochi 10-12 months after the eruption to be unidentified diatoms, mixed with Urospora spp., along with young brown (Alariaceae) algae, Eualaria fistulosa and Saccharina spp., and red alga Porphyra spp.It was not until nearly three years after Surtsey emerged did any brown algae (Alariaceae) appear (Jónsson, 1968) for red algae (Porphyra spp.) (Jónsson, 1970).The number of benthic algae discovered growing on Surtsey three and four years later were 17 and 27 species, respectively.By 1971, seven years after Surtsey's first eruption, about 40 benthic algal species were found (Jónsson and Gunnarsson, 1982).
As for the first observed benthic marine fauna around Surtsey (autumn 1967), at least 12 taxa were found in the littoral zone that was dominated by lamellibranch bivalves and barnacles (Sigurdsson, 1968).Subtidally to 20 m depths divers found at least 21 taxa that were dominated by juvenile bivalves, principally Mytilus edulis and Anomia squamula around the 20 m depth zone (Sigurdsson, 1968).Three amphipod species were found near 20 m, but not identified or quantified.Presumably amphipods at Kasatochi were opportunists derived from the remnants of the kelp bed within and/or immediately outside the devastated area.No such kelp was available at the newly formed Surtsey for three years (Jónsson, 1968).
Prior to the 2008 eruption, Kasatochi Island provided extensive nesting habitat for a range of marine birds, including those associated with shallow nearshore habitats (Drew et al., 2010).Nearshore censuses of epibenthic foraging marine birds, i.e., cormorants and pigeon guillemots, before and after the 2008 eruption suggest that these birds have persisted, though in lower numbers, on and around the island since the eruption.We speculate that the high number of pigeon guillemots observed during the June of 2009 census may have been due to a combination of fidelity to the island for nesting and a lack of nesting sites in that first year post-eruption.Given the short foraging range of nesting pigeon guillemot (Gaston and Jones, 1998), the discovery of a pigeon guillemot nest in 2010 and the sighting of fledged young in 2011 and 2012 suggest that shallow epibenthic prey have recovered around Kasatochi to levels sufficient to support a limited reproductive population.On Surtsey, black guillemots Cepphus grylle were observed nesting three years after the cessation of volcanic activity (Peterson, 2009).Given the short foraging range of nesting Cepphus spp.(Gaston and Jones, 1998;Ronconi and St. Clair, 2002) it appears that their shallow epibenthic prey recovered or developed rapidly around Kasatochi and Surtsey respectively, to levels sufficient to support a limited reproductive population.
In conclusion, the 2008 eruption of Kasatochi Island resulted in catastrophic change to marine habitats and the near complete loss of biological communities surrounding the Island with a few relict species surviving.Biological legacies, which result from organisms that survive a disturbance, can favor deterministic processes in community assembly and improve predictions of successional trajectories (Walker et al., 2013).The rocky reef habitats that presumably were dominated by sea urchins and canopy kelp prior to the eruption were replaced by a new substrate of medium and coarse sands dominated by benthic amphipods.There is sound evidence that the erosion process is continuing, as demonstrated by greater depths at some stations and the emergence of boulders.These changes have led to greater understory and canopy algal colonization, and increases in benthic fauna that have begun to affect higher trophic levels, i.e., marine birds, the top predators in this ecosystem.
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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Benthic samples were collected by divers at 10 m depths along secondary transects 3803 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | perpendicular to primary transects (Fig. 3); underwater videos were recorded at 10-20 m depths.Sampling occurred 12-15 June and 10-12 August 2009.Details of the diver sampling methodology are presented in Jewett et al. (2008, 2010) and a sampling layout is shown in Fig. 3.At each sampling point, a set of 3 nested quadrats (1 m × 1 m, 50 cm × 50 cm, and 25 cm × 25 cm in size) were placed on the offshore side of the transect.Within each 1 m 2 quadrat, a 50 cm×50 cm (0.25 m 2 ) and a 25 cm×25 cm (0.06 m 2 )

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Paper | Discussion Paper | Discussion Paper | Discussion Paper | the same transects in June 2009, August 2012 and June 2013.Video segments 2-13 min in duration were recorded on a DVD while the ship or skiff drifted over the site.

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™ often tangled in the kelp.Although coarse sand still dominated, boulders, the substrate for kelp attachment, were considerably more prevalent than in 2009.Furthermore, several of the transect site depths were about 1-5 m deeper in 2012 than in 2009, suggesting the erosion of fine substrate occurred.No sites were shallower.Other observed biota included diatoms and light green algae (T1 at 21 m), red algae (T2 at 10 m), brown alga Saccharina groenlandica (T3 at 14 m), barnacles (T6 at 10 m), and three small Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | flatfishes (one Pacific halibut Hippoglossus stenolepis and two unidentified) (Table

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Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |(J.Williams and W. Pepper, AMNWR, personal communication, 2009).Additionally, robust canopy kelp was visible around most of the island 19 July 2008, 18 days prior to the eruption on 7 August(B.Webster, personal communication, 2010).Pre-eruption information of subtidal community is from two dives from the M/V Ti ĝlax that were made on 3 September 2002 along the east side of Kasatochi (R.Lauth,     NOAA, personal communication, 2009).The first dive (52 • 10.250 N 175 • 29.395 W) was approximately 200 m north of our 2009 Transect 2, 10 m site (Fig. 2).On the first dive, at a depth of ∼ 9 m, video recording revealed a dense canopy of E. fistu-losa at the surface.At this depth, where the temperature data logger was retrieved, the hard substrate was covered by E. fistulosa and dense understory of the brown alga Cymathaere triplicata.On the second dive, ∼ 200 m WNW of the data logger position, divers descended a wall to 25 m. Brown algae Agarum turneri and Saccha-rina groenlandica were present along the upper portion of the wall.Algae deeper than ∼ 20 m were the green alga Codium ritteri and encrusting red coralline algae, Clathromorphum nereostratum and Lithothamnion spp.The wall and the floor at the base of the wall were completely covered with sessile organisms such as sponges, sea anemones, gorgonian corals (e.g., Paragorgia spp.), hydroids, bryozoans, rock jingles Pododesmus macrochisma, barnacles, and tunicates.Mobile epifauna consisted of a scale crab Placetron wosnessenskii, sea stars (Henricia spp.and Solaster sp.), brittle stars, and sea urchins Strongylocentrotus polyacanthus.Numerous black Se-bastes melanops or dusky rockfish S. ciliatus were noted along the dive, especially below 20 m.Based on widespread changes in benthic community structure in recent years (Estes et al., 2010), it is difficult to predict what the more widespread subtidal community at Kasatochi looked like just prior to the eruption.Nevertheless, whatever dominated the nearshore community around Kasatochi prior to the eruption was mostly destroyed by the 2008 eruption.Extension of the shoreline to 400 m offshore to a pre-eruption depth of ∼ 20 m buried the algal community with mainly medium and coarse sands.In all likelihood, the three small patches of canopy kelp observed in August 2009 were the only sea surface rem-Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper |

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Fig. 1 .Fig. 2 .Fig. 2 .Fig. 3 .
Fig. 1.Location of Kasatochi Island in the central Aleutian Islands of Alaska.Also shown are nearby islands and extent of ash fall from the 7-8 August 2008 eruption.

Fig. 4 .
Fig. 4. Satellite image of Kasatochi Island 3.6 years following the August 2008 eruption.Shorelines of pre-eruption, 3.7 weeks and 9.3 months post-eruption are also shown.3833

Fig. 5 .
Fig. 5. Generalized distributions of canopy kelp (mainly dragon kelp Eualaria fistulosa) by ob-servations around Kasatochi Island.(a) Pre-eruption distribution on a satellite image taken 9 April 2004.(b) Distribution one year (10-12 August 2009) after the eruption on a satellite image taken 18 April 2009.Yellow lines denote pre-eruption boundary of 9 April 2004.(c) Distribution four years (28 August 2012) after the eruption on a satellite image taken 20 February 2012.Yellow lines denote pre-eruption boundary of 9 April 2004.Blue line denotes shoreline of 18 April 2009.

Table A1 .
Comparison of observations at six nearshore transects off Kasatochi Island, June and August 2009, August 2012 and June 2013 (see Fig.2).