Comprehensive Description

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Comprehensive Description

Until recently, this species was known as Alaria fistulosa (Lane et al. 2007; Wynne 2009). This canopy-forming kelp of the northeastern Pacific is brown with a large branching holdfast, a stipe 25 cm long, and a blade with a midrib up to 25 m long and 1 m wide. The midrib is 2 to 3 cm wide with gas-filled chambers (fistulae) that hold the blade in the water column. Reproductive sporophylls develop on the upper portion of the stipe. This fast growing annual occurs on rock from the low intertidal to subtidal and forms offshore kelp beds in cold, semi-protected to exposed habitats. (

In southeast Alaska, the floating kelps Eualaria fistulosa and Nereocystis luetkeana have been commercially harvested since 1992 by the Alaska Kelp Company, which processes them for use as a plant fertilizer supplement (Stekoll et al. 2006).

Lane et al. (2007) used mitochondrial DNA, the nuclear internal transcribed spacer (ITS) of the ribosomal cistron, and the plastid Rubisco operon spacer (rbcSp) to undertake a phylogenetic analysis of the taxa then included in Alaria. They concluded that A. fistulosa was so clearly distinct that it warranted placement in a new genus (they erected the genus Druehlia for this purpose, but Wynne 2009 determined that Eualaria was already available and therefore should be given priority). They noted that the genetic distinctiveness of this species is consistent with a range of other data. According to Lane et al., this is the most morphologically distinct "Alaria" based on the air bladders within the midrib of the blade, which allows the blade to float to the surface of the sea. A number of other characters also separate this species from Alaria species, including its large, complex conical holdfast (the attachment of the thallus to the substrate); its wide, flattened rachis (where sporophylls are produced), which in section has distinctly raised margins (as does the midrib); and its larger size. Its fistulose midrib is unique among all the genera of the Alariaceae and makes its ecology and ability to disperse distinct from that of Alaria species. Ecologically, Alaria species are found in the intertidal or shallow subtidal waters, often in a distinct band just above the Laminaria/Saccharina band. Eualaria fistulosa is the only species in the genus that is a true denizen of the subtidal environment, where it forms extensive offshore floating kelp beds. (Lane et al. 2007 and references therein)


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© Shapiro, Leo

Source: EOL Rapid Response Team


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