The August 2008 eruption of Kasatochi Volcano, Alaska, buried Kasatochi Island in pyroclastic material, creating a new surface for re-establishment and succession of the island ecosystem. Since 2009, researchers have collected data to measure recovery of the island's terrestrial heterotrophic biota. Specific goals included quantifying the eruption's magnitude of impact on populations of key groups of organisms, measuring the subsequent population recovery and community assembly over time, and identifying the factors that limit or promote the early establishment and recovery of the island's terrestrial biota. The disturbance impact on soil microbes, terrestrial arthropods, and seabirds was predicted to be large, given the extent of disturbance; the recovery extent was predicted to be limited by the availability of suitable habitat and food sources for each group of organisms, and promoted by the survival of or dispersal of successful colonists to initiate population growth and community assembly. Annual surveys of birds, arthropods and soil microbes were conducted (2009-2016) using standard protocols and standardized transects for each group: visual surveys both offshore and onshore for birds; hand and sweepnet surveys for arthropods; surface soil collection followed by 16S rRNA gene and ITS copy number quantification and sequencing for soil bacteria and fungi.
While the eruption's impact on terrestrial biota was large, a surprisingly high resilience was observed for certain groups. Five years post-eruption, the observed species richness of passerines, shorebirds, insects, spiders and centipedes was still depleted relative to pre-eruption levels (19±3 arthropod species < estimated 100 pre-eruption; 1±1 land bird species < 8 pre-eruption (mean±SD)), while observed richness of seabirds, raptors and soil microbes had recovered to levels at or approaching reference conditions (14 seabird and 2 raptor species, equal to pre-eruption; 5200±1000 ≤ 6800±760 bacterial taxa). Despite the high richness observed in these groups, seabird nesting success was near zero until 2011, and population sizes of soil bacteria were orders of magnitude lower in post-eruptive than reference soils (108±107 < 1010±109 bacterial gene copies). Most arthropods observed post-eruption were small soil-dwelling taxa, or found on detritus along the shoreline. In sum, survivorship of the largest and smallest heterotrophs (birds, small arthropods, microbes), via refuge in unimpacted open-ocean or deeper-soil habitats, appears to have supported early recovery of species richness but not necessarily of thriving populations. The legacy species influence on succession at Kasatochi Island is clear, but recovery of terrestrial food webs is still limited by availability of plant-derived resources.