Wave Action
Wave action is a major stressor to intertidal organisms. Waves breaking onto the shore exert hydrodynamic forces onto the organisms living there.
How does wave action vary?
The power of waves is closely related to their size and frequency, which are determined by geography and weather (in particular wind speed). The distance over which wind blows unimpeded allows the power of the waves to build. The longer the distance wind travels, the greater the potential height of the waves. As an example, an exposed headland on the west coast of Vancouver Island would have greater wave action than a protected bay along an inlet. Wind speed in the open ocean can be categorized by visual observation. Sailors use the descriptive Beaufort scale which ranges from 0 = calm to 12 = hurricane force. The force of the waves as they break onto the shore can be measured as drag force.
Why is wave action biologically important?
Wave action exerts both direct and indirect effects on intertidal organisms (Nybakken & Bertness 2005). Direct mechanical effects include smashing and tearing off of the substratum, which can be detrimental to algae and animals, especially those that need to be fixed to the bottom (algae need to be attached to receive sufficient light for photosynthesis; sessile animals like barnacles secure themselves to surfaces where they can filter food from incoming water and can be close to other barnacles for mating). Motile animals may be inhibited from feeding during storms. Wave action can also move the substrate around (e.g. loose sand or gravel), limiting the establishment of organisms and their access to resources. Indirectly, wave action can extend the upper limit of the intertidal zone by splashing water higher on the shore, allowing some organisms to live higher in wave-exposed areas. It can also reduce the effects of extreme temperatures and desiccation. In severe wave conditions, water-borne debris (e.g. large logs) can damage or remove intertidal organisms
How do animals respond to variation in wave action?
Many intertidal and shallow subtidal organisms have morphological adaptations to withstand wave action (Castro & Huber 2005). Kelp and other seaweeds cement their holdfasts onto rock and are flexible. Barnacles also cement themselves onto the hard substratum and have a low profile that reduces drag forces. Blue mussels secrete strong byssal threads that secure them to rock and each other and have a streamlined shape to reduce drag. Limpets increase their foot area relative to their shell length in wave-exposed locations
Behavioural responses to wave action may include increased suction onto the substratum, withdrawing into shells or tubes, or moving to a sheltered microhabitat such as crevices between rocks. On softer substratum, animals can burrow to escape the force of waves. Aggregating in dense groups (e.g. in mussels) also offer protection from wave shock.
Key search terms: Wave action · Drag force · Morphological adaptations · Behavioural adaptations
References Cited:
Castro P, Huber ME. 2005. Marine Biology. 5th ed. Dubuque: McGraw Hill.
Nybakken JW, Bertness MD. 2005. Marine Biology, an ecological approach. 6th ed. Toronto: Benjamin Cummings.
Note: Any edition of the above books or other marine biology textbook could be useful.
Castro P, Huber ME. 2005. Marine Biology. 5th ed. Dubuque: McGraw Hill.
Nybakken JW, Bertness MD. 2005. Marine Biology, an ecological approach. 6th ed. Toronto: Benjamin Cummings.
Note: Any edition of the above books or other marine biology textbook could be useful.
To learn more:
Brown KM, Quinn JF. 1988. The effect of wave action on growth in three species of intertidal gastropods. Oecologia. 75(3):420–425. https://doi.org/10.1007/BF00376946.
Freeman S, Harrington M, Sharp J. 2014. Biological science. 2nd Canadian ed. Toronto: Pearson.
Wiklund AKE, Malm T, Honkakangas J, Eklund B. 2012. Spring development of hydrolittoral rock shore communities on wave-exposed and sheltered sites in the northern Baltic proper. Oceanologia. 54(1):75 -107.
Note: Any edition of the above book or other biology textbook could be useful.
Brown KM, Quinn JF. 1988. The effect of wave action on growth in three species of intertidal gastropods. Oecologia. 75(3):420–425. https://doi.org/10.1007/BF00376946.
Freeman S, Harrington M, Sharp J. 2014. Biological science. 2nd Canadian ed. Toronto: Pearson.
Wiklund AKE, Malm T, Honkakangas J, Eklund B. 2012. Spring development of hydrolittoral rock shore communities on wave-exposed and sheltered sites in the northern Baltic proper. Oceanologia. 54(1):75 -107.
Note: Any edition of the above book or other biology textbook could be useful.