A walk in a kelp forest

A walk in a kelp forest

A walk in a kelp forest is the opposite to what you see in a Westcoast rainforest. Recently, himself and I walked through a local forested vale, but could not see the tops of the trees as we looked up to the canopy. However, when you see a bobbing kelp forest from the shore, unless you snorkel or dive, you cannot see what lies below. Also, seasonally, the kelp forest changes just like a terrestrial forest.

a walk in a kelp forest, terrace beach, Ucluelet
Recent snorkel in Terrace Beach, Ucluelet, B.C., in perennial Macrocystis kelp forest

A walk in a kelp forest in the Winter

In the winter, when I gaze from shore out to our local kelp beds, I may see mats of dead kelp, but I seldom see any live blades bobbing on the surface.The kelp blades are not visible because winter storms have pruned them back (1), similar to terrestrial trees in the winter losing their foliage. From January to March, light penetrates to the depths of the ocean and offer growth to other algae and organisms. Winds change and upwell nutrients from the depths (2). By Spring, the wave action lessens, and the kelps grow. Similarly, the same happens on the rainforest floor in the Spring with the growth of wild flowers and shrubbery. Seaweed “shrubs” such as leafy red algae and crusty coralline algae both eek out existences where the kelps do not yet dominate. Their growth is rapid until the kelp forest canopy takes over usually by mid summer (2).

A walk in a kelp forest in the Fall

a walk in a kelp forest, kelp life cycle
Kelp parts and life cycle showing “gin” smelling gametophytes

By fall wind directions change and when the upwelling of nutrients stops (2), the kelp stops growing, weaken and the winter storms shred the thinned blades (2). Their holdfasts also let go, and the surges roll them about (2). Hence, dead kelp float in mats on the surface, wash ashore or more often decay and replenish the ocean floor with nutrients (2). Evenetually, sunlight can again penetrate to lower levels allowing other algae and organisms to grow into the new Spring season. Perennial (Macrocystis) and annual kelp (Nereocystis) release spores that form male and female parts (gametophytes). Eggs and sperm from these parts fertilize one another and form sporophytes. Interestingly, the female gametophyte produces a gin smelling pheromone, lamoxirene, to attract sperm (3). Finally, the sporophytes anchor to the bottom with their holdfasts, and then eventually grow a stipe and blade (2).

Mechanical harvesting of kelp

Kelp grow either at the holdfast or at the blade attachment to the bladder. If the stipe is cut, the kelp will die. Sustainable harvesters should follow the rule: for every stipe cut (20-25%), leave four kelp plants to live (75-80% of the wild stock).  Otherwise, only the blade should be cut leaving at least 1/3 attached to the bladder. About 32 countries harvest wild stock kelp, including Canada (4). Mechanized harvesting techniques that damage the holdfast, such as trawling and vacuum suction, and stipe, such as scoubidou and paddlewheel cutter, require regulation to allow recovery of the wild stocks (5). These techniques not only damage the kelp but also destroy the protective habitat that the kelp forests provide for other living organisms (6).

Ultimately, when left undisturbed, the holdfast of some kelp can survive 10 years for some species and continually regrow into a full kelp each Spring (2)(4). As with the changing of seasons for a terrestrial forest, kelp forests likewise go through their natural life cycles. Therefore, the next time you gaze or swim over a kelp bed, consider the multitude of ecosystems that lie beneath. It’s more than what meets the eye.

References

  1. Fulton-Bennet, K. “Kelp Bed in March”. Seasons in the Sea. 2013. Retrieved on 2018/06/06 from http://seasonsinthesea.com/mar/kelp.shtml
  2. “Kelp Forests”. Project Oceanography. University of Southern Florida. Spring 2002. Retrieved on 2018/06/13 from https://www.marine.usf.edu/pjocean/packets/sp02/sp02u1p4.pdf
  3. Druehl, L. Clarkston, B., (2016). Pacific Seaweeds. 2nd ed. Madeira Park, BC, Canada: Harbour Publishing, p.21-22.
  4. Michéal Mac Monagail, Lynn Cornish, Liam Morrison, Rita Araújo & Alan T. Critchley (2017) “Sustainable harvesting of wild seaweed resources”, European Journal of Phycology, 52:4, 371-390,DOI: 1080/09670262.2017.1365273
  5. “Seaweed Industry in Europe”. Netalgae.eu. 2012. Retreived on 2018/06/10 from http://www.netalgae.eu/uploadedfiles/Filieres_12p_UK.pdf
  6. Kraan, S. “Recent cultivation and applications of marine macroalgae”. Ocean Harvest Technology Ltd., Nov. 2, 2010. Retrieved on 2018/06/10