Egregia menziesii

Egregia menziesii (Turner, 1808) Areschoug, 1876

Link to AlgaeBase: http://www.algaebase.org/search/genus/detail/?genus_id=42098

Type locality: Nootka Sound, Vancouver Island, British Columbia, Canada

Common Name: Feather boa kelp

Taxonomy: Phaeophyceae: Laminariales: Lessoniaceae: Egregia: menziesii

Identification: Egregia menziesii is one of the longest intertidal algae in the Pacific Northwest of North America. This species is characterized by long fronds (more than 2 m in length) that are similar in appearance to feather boas (hence the common name, the feather boa kelp). One individual can have many of these fronds originating at a single holdfast.  Each frond is composed of a single axis – the rachis – which is approximately 1 – 1.5 cm wide, and is covered with many small papillae. Along the edges of each rachis are many smaller lateral blades, which can take the form of being long (approx. 4 cm) and narrow, or being shorter and more spatulate. Among the lateral blades are grape-sized pneumatocysts, occurring irregularly along the entire length of the rachis. At the end of the rachis is a terminal lamina that is slightly wider and thinner than the rachis. Pneumatocysts and lateral blades are also found on the terminal lamina, giving the entire frond a slightly bushy appearance.

Similar to other brown algae, Egregia has a two-phase heteromorphic life history. It alternates between a macroscopic sporophyte (what is visible on the shore) and a microscopic gametophyte. Sporangial tissue can be found on the sporophyte on blades along the entire length of the rachis, but do not have a typical morphology. Therefore, it is usually difficult to discern reproductive blades (sporophylls) from non-reproductive blades.

The oldest specimen for E. menziesii at the Friday Harbor Lab herbarium, collected in 1916 from Kanaka Bay, San Juan Island. Note the central axis (the rachis) with smaller lateral blades along the length of the rachis. Lower on the rachis – toward the holdfast which is not included – smaller rachises are branching off.

The oldest specimen for E. menziesii at the Friday Harbor Lab herbarium, collected in 1916 from Kanaka Bay, San Juan Island. Note the central axis (the rachis) with smaller lateral blades along the length of the rachis. Lower on the rachis – toward the holdfast which is not included – smaller rachises are branching off.

 

Distribution: Egregia is limited to high energy rocky shores in the Northeast Pacific Ocean (the Pacific Northwest of North America). On San Juan Island, Egregia can be found on the west side of the island, with large populations at Cattle Point and Eagle Cove. Overall, E. menziesii ranges from Baja California, Mexico to Vancouver Island, British Columbia, Canada.

Egregia menziesii at Eagle Cove, San Juan Island. One holdfast can produce multiple fronds, each densely covered with lateral blades and pneumatocysts.

Egregia menziesii at Eagle Cove, San Juan Island. One holdfast can produce multiple fronds, each densely covered with lateral blades and pneumatocysts.

Vouchers: The FHL Herbarium has pressed herbarium specimens from several of the west coast, exposed sites on San Juan Island, WA.  The oldest specimen dates to 1916 from Kanaka Bay, but E. menziesii can also be found at sites like Cattle Point, Eagle Cove, Lime Kiln, False Bay, and Mar Vista.

Research notes: E. menziesii is an interesting organism for studies of algal biomechanics because of its ability to grow to extremely long lengths (Fig 3) while persisting on shores with high wave energy. The species is separated into a northern form, typical of that found on San Juan Island, and southern form, found typically south of Point Conception, CA (Blanchette et al. 2002). The northern form may be distinguished from the southern form most easily by the presence of small tubercules, or papillae, along the length of the rachis, whereas the southern form has no – or more sparse– papillae. The morphological differences between the northern and southern forms of E. menziesii are thought to be a plastic response to nutrient availability and the mechanical stimulations from the local flow conditions (Kraemer and Chapman 1991; Blanchette et al. 2002). Although there are no apparent genetic differences between the northern and southern form of E. menziesii, the broad differences in latitudinal distribution may not permit gene flow between populations of each morphotype (Henkel et al. 2007). However, it should be noted that Henkel et al. (2007) only examined the genetic structure of E. menziesii populations in California and Oregon, roughly 1/3 of the latitudinal distribution of the species.

The author holding a single frond of E. menziesii at Eagle Cove, San Juan Island, WA. Fronds typically reach lengths exceeding 2 m.

The author holding a single frond of E. menziesii at Eagle Cove, San Juan Island, WA. Fronds typically reach lengths exceeding 2 m.

Egregia menziesii is also an important organism on rocky shores because it can shape local patterns of biodiversity and species richness. Neighboring algae, or even neighboring animals, can be dislodged from the substratum as the fronds whip back and forth under the force of water flow and crashing waves (Hughes 2010). The ‘scouring potential’ of E. menziesii is a function of the stiffness and strength of the fronds, which can vary significantly within a population (Demes et al. 2013). The northern form of E. menziesii, which is present on San Juan Island, is stronger than its southern counterparts (Kraemer and Chapman 1991; Blanchette et al. 2002), and thus represents a relatively strong source of disturbance on the shores of the San Juan Island, potentially dislodging smaller or more fragile organisms in the ‘sweeping vicinity’ of E. menziesii (Hughes 2010).

Despite the ability for each frond to grow to considerable lengths on wave-exposed shores, growing too long can cause the whole organism to be dislodged from the substratum, or for the entire frond to be broken from the holdfast. This risk of damage arises due to the increased drag forces – a hydrodynamic force acting in the direction of flow – that accompanies an increase in the geometric area exposed to the direction of flow. The increase in drag can cause excessive tensile forces in the basal section of each frond, which may exceed the stipe’s strength and result in a broken frond (Friedland and Denny 1995). Damage that E. menziesii sustains from scouring the substratum can eventually degrade the terminal lamina and intercalary meristem, preventing further growth of the broken frond and prompting growth of other fronds from the stipe (Black 1976; Demes et al. 2013). Similar to the abrasion-induced pruning, fronds can also be damaged by grazers degrading more proximal areas of a frond (Black 1976), giving multiple avenues that may help each E. menziesii increase its biomass in ‘bushiness’ rather than length. This increased biomass could increase reproductive fitness, as sporophylls can be develop at any length along each frond (Abbott and Hollenberg 1976). Despite these general ‘rules’ of how the northern form of E. menziesii performs on high energy rocky shores, slight environmentally-induced variation in morphology can be found among the different sites of the outer coast of San Juan Island as the alga responds to more specific regimes of hydrodynamic stress, grazing damage, and competition for resources.

 References:

Abbott, I. A., and G. J. Hollenberg. 1976. Marine Algae of California. Stanford University Press.

Black, R. 1976. The effects of grazing by the limpet, Acmaea insessa, on the kelp, Egregia laevigata, in the intertidal zone. Ecology 57: 265-277.

Blanchette, C. A., B. G. Miner, and S. D. Gaines. 2002. Geographic variability in form, size and survival of Egregia menziesii around Point Conception, California. Mar. Ecol.-Prog. Ser. 239: 69-82.

Demes, K. W., J. N. Pruitt, C. D. G. Harley, and E. Carrington. 2013. Survival of the weakest: increased frond mechanical strength in a wave-swept kelp inhibits self-pruning and increases whole-plant mortality. Funct. Ecol. 27: 439-445.

Friedland, M. T., and M. W. Denny. 1995. Surviving hydrodynamic forces in a wave-swept environment: Consequences of morphology in the feather boa kelp, Egregia menziesii (Turner). J. Exp. Mar. Biol. Ecol. 190: 109-133.

Henkel, S. K., G. E. Hofmann, and A. C. Whitmer. 2007. Morphological and genetic variation in Egregia menziesii over a latitudinal gradient. Bot. Marina 50: 159-170.

Hughes, B. B. 2010. Variable effects of a kelp foundation species on rocky intertidal diversity and species interactions in central California. J. Exp. Mar. Biol. Ecol. 393: 90-99.

Kraemer, G. P., and D. J. Chapman. 1991. Biomechanics and alginic acid composition during hydrodynamic adaptation by Egregia menziesii (Phaeophyta) juveniles. J. Phycol. 27: 47-53.

 

Author: Nicholas Burnett is a graduate student in the Department of Integrative Biology at the University of California – Berkeley.