Milner 1994

Milner AM. 1994. Colonization and succession of invertebrate communities in a new stream in Glacier Bay National Park, Alaska. Freshwater Biology 32: 387-400.

This author describes long term monitoring of colonization and succession in a stream recently formed from a retreating glacier in south-eastern Alaska. The glacier filled its bay around 1700 AD, and has been retreating since, forming new streams and lakes, and novel habitats similar to what is thought to have occurred across northern North America and Eurasia at the end of the last ice age. There are few previous studies of stream systems that completely lack an upstream source of drift-colonizing organisms; this author describes this work as unique regarding its long time frame (12 years), spatial extent (kilometres), and primary succession characteristics.

Of the possible routes for colonization of the study stream by invertebrates, only aerial oviposition is possible as the other routes rely on suitable habitat upstream or downstream of the study site. The study site is bounded by the ocean below, and a new proglacial lake and associated ice field above. The first organisms present in the stream were chironomids, of species known to be exceptionally tolerant of cold water (~2°C). Species richness increased through the study period, with the addition of one species of Ephemeroptera, one species of Plecoptera, and a turnover in chironomid species and relative abundances.

A portion of the discussion section describes the distinction between fugitive species, good dispersers but poor competitors with habitat refugia in extreme environments, and opportunistic species, good dispersers that are also good competitors in their local microhabitats, maintained by disturbance. The first few chironomid species found in the stream are considered fugitive species because their population abundances were severely reduced in later years as other species, including a predatory stonefly, became established. A later portion discusses deterministic and stochastic processes in succession, arguing that water temperature and flow characteristics have been strong deterministic drivers of this stream system, in contrast to the strong role argued for stochastic processes (‘first come first served’) in other, more temperate streams studied by other authors.

The distinctions between fugitives and opportunists, and between stochastic and deterministic, would not be possible without species-level identification of chironomid larvae. Several species are described as Genus sp. A or similar, but nonetheless the ability to discriminate between closely related species with different ecological characteristics is clearly applied, allowing levels of analysis not normally seen in stream-succession studies.

This paper is part of a special issue of the journal Freshwater Biology, devoted to alpine and polar freshwater environments, and seems to be slightly lower in scientific rigour compared to normal papers in this journal. Many of the citations in this paper are of the author’s own previous unpublished data, and key blocks of data such as particular field collection seasons, have already been described in previous publications; this paper apparently serves primarily to integrate across the long time frame of repeated sampling.