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Eualaria fistulosa, common name dragon kelp, belongs to the brown algae group.

Taxonomy

The parent of it is Eualaria Areschoug, 1884. Its original name is Alaria fistulosa Postels & Ruprecht, 1840.

Its species name fistulosa is an adjective in Latin, which means fistulate, hollow throughout but closed at ends (Stearn 1973).

Description

The canopy-forming kelp's thallus is brown and characterized by a large branching holdfast (haptera), supporting a 25 cm (10 in) long stipe. Its blade, which can extend up to 25 m (82 ft) in length and 1 m (3.2 ft) in width, features a midrib. The midrib, 2-3 cm (0.8-1.2 in) wide, contains gas-filled chambers (fistulae) that help keep the blade buoyant in the water column. Additionally, reproductive sporophylls develop on the upper part of the stipe.

Dragon Kelp is often found growing alongside Bull Kelp (Nereocystis luetkeana).

Habitat

This rapidly growing plant thrives annually on rocky surfaces, spanning from the low intertidal zone to the subtidal region. It establishes itself in offshore kelp beds within cold environments, ranging from semi-protected to exposed habitats.

Distribution

Aleutian Islands to southern Southeast Alaska; Japan; Russia.

Ecology

Eualaria fistulosa can be found in both foliose algal assemblages and deforested barren areas in the Aleutian Islands,but it is much less abundant in the deforested state. In contrast, sea urchins also occur in both states, but they are considerably more abundant in the deforested state. Sporophylls in barren areas generally had higher phlorotannin content than those in foliose algal assemblages, which shows that phlorotannins under high grazing pressure may protect E. fistulosa and the holdfast communities from being grazed in barren areas.

Individual E. fistulosa sporophytes occurring in the urchin barrens may produce as many as three times more zoospores than individual E. fistulosa sporophytes occurring in the nearby kelp beds, and thus they may contribute disproportionately to the following year’s sporophyte recruitment in both urchin barrens and the adjacent kelp beds.

In Aleutian Islands, E. fistulosa remains abundant in the transition habitats (lack of benthic macroalgae but remaining canopy-forming E. fistulosa and high abundances of sea urchins). It is likely that these E. fistulosa would enhance GPP and perhaps result in positive values of NEP in the mid-water and at the surface in both the kelp forests and transition habitats. However, GPP and Re remain in balance due to deforestation at the benthos. Because of deforestation, both GPP and Re are reduced, resulting in little to no changes in NEP.

Restoring the Eualaria fistulosa forests across the Aleutian Islands would probably need many sea urchins to die off, but that doesn't seem probable right now. One reason could be the scarcity of other urchin predators, such as Pycnopodia helianthoides, which hasn't been common in the central or western Aleutians historically.

Reference section

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