Sunday, December 22, 2013

Ask an Expert: Seaweed Harvesting in BC


I've heard that wrack seaweed is being harvested in BC. Is this something we should be worried about?  Submitted by Elizabeth K.

Answer (by Tom Carefoot)

Yes, most definitely we should be worried. But, first, let's define what 'wrack' is. You may have heard the expression 'going to wrack and ruin', where 'wrack' in old times referred to the wreck of a ship on the shore, then later referred to cast up seaweed (see photo 1).  Nowadays, of course, the expression refers to falling into a state of destruction and decay.  When the word is applied to seaweed it is sometimes just a quaint way to refer to all stranded seaweeds, but may also be used to refer to certain species of brown kelps such as the Atlantic coast brown alga Ascophyllum nodosum.

Photo by Ian Birtwell.

So why do the harvesters want to harvest wrack seaweed? The harvested seaweeds can be processed for their content of commercially useful substances, including alginates, agar, and carrageenans, depending upon the type of seaweed.  In a seaweed, the carbohydrates mentioned are involved in structural support, while in commerce they are used as various thickening or gelling agents in face creams and other cosmetics, toothpaste, ice cream, and pharmaceuticals. For many biologists, including me, the term 'wrack' assumes a certain amount of drying, up to and including even the most crinkly sun-dried seaweed that one finds higher up on the shore. Less water, of course, means less expense for the harvesters to gather, load and transport the wrack for processing. One important wrack harvesting species in BC, Mazaella japonica, is a red algae with a particularly high content of carrageenan.   It is also a non-native species with an aggressive, over-growing presence.

Photo by Ian Birtwell.

The most recent harvesting of wrack in British Columbia that I know of, and that has created a fair bit of controversy, occurred in 2012/2013 in the Deep Bay/Browser area around Parksville, and is ongoing.  The BC Ministry of Agriculture granted 5 licenses, each for 1000 tonnes of Mazaella japonica wrack to be removed from 21km of shoreline in 2012, and two more licenses in 2013 each for 300 tonnes.  It seems that only 300 tonnes in total were harvested in 2012, with the data not yet in for 2013.  The harvesters are allowed to use vehicles on the beach to cart and load the seaweed (see photo 3), but there appears to be little or no on-site monitoring of number and size of these vehicles.  In face of growing opposition from local citizens, environmental groups, First Nations peoples, and scientists (ref. cited below), the granting of smaller-scale licenses suggests that the Ministry of Agriculture may be tentatively applying the brakes, at least for now. 

Photo by Pamela Smythe & The Comox Valley Echo.

 Photo by Ian Birtwell.

So, what’s the issue?  Does harvesting of wrack have important ecological consequences?  The answer is “yes”, for several reasons. The main concern relates to possible negative effects on inshore fisheries. There are several species of fishes, such as Pacific sand-lance, herring, and surf smelt, that use these same beaches on which to spawn.  Of serious concern in this regard is the physical damage done to the shore by harvesting machinery and raking. 

Sandy beaches are not desolate wastelands that can tolerate being disrupted in this way.  Sand lances, for example, preferentially spawn in intertidal sand/gravel areas, sometimes quite high on the shore.  In the absence of physical protection and shading provided by wrack, the eggs are more vulnerable to drying and being eaten by bird and fish predators.  Additionally, in the above-tide or strand area itself (where wrack eventually ends up), there exist many species of worms, amphipods, isopods, beetles, and so on.  These live in and among the seaweeds, and in burrows in the sand beneath them, and many of them, but most notably the amphipods (beach-hoppers), feed directly on the seaweeds (see photos 4 and 5).  These crustaceans feed and breed, and often become so numerous that that the sand and seaweeds can hardly be seen for their bodies. Whole kelp plants can be consumed in just a few days.  As the seaweeds diminish in volume and/or move about in high wave-swash these arthropods are found and eaten by fishes and birds.  Fine particles and pieces of seaweed find their way back into the intertidal and subtidal regions where they are consumed by a host of suspension- and deposit-feeding crustaceans, worms, and sea urchins, and by numerous omnivorous and herbivorous invertebrates.  Wrack, therefore, is a living entity on the beach, and plays a vital role as a steady, predictable, and necessary conduit of energy and nutrients from the ocean to the land and back again.

Photo by Maryjo Adams.

Photo by Ingrid Taylar.

For several species of semiterrestrial arthropods, wrack in its dried form is actually preferred as food over fresh seaweeds.  In the summer of 1998 at the Bamfield Marine Science Centre, a group of 6 international scientists, including myself, hosted by NSERC Canada and the participating scientists’ home countries of England and Germany, investigated the biology of the sea-slater isopod Ligia pallasii (see photo 6) and two amphipod species Megalorchestia californiana and Orchestia traskiana.  Among other things, we discovered that these consumers actually prefer the wrack form of stranded seaweeds, probably owing to the fact that, in their dried state, wrack provides about 50% more energy and nutrients “per mouthful” than would be available from a diet of fresh seaweeds.

  Photo by Tom Carefoot.

To some, wrack is just old rotting seaweed from which to derive profit.  In reality, wrack is a valuable component of the sea/land interface, essential for the livelihoods of many invertebrates that require it as food, and of many species of fishes and birds that eat these invertebrates and/or use the wrack to help them survive and lay their eggs.  Best to leave it be. 

Learn more about amphipod use of wrack seaweeds as food. Visit a Snail's Odyssey.  


Birtwell, I. K., R. C. de Graaf, D. E. Hay, and G. R. Peterson. 2013.  Seaweed harvesting on the east coast of Vancouver Island, BC:  a biological review. Unpublished report. 28 pp.   

Thanks to Mike Hawkes, Department of Botany, University of British Columbia for seaweed identifications.

Tom Carefoot, Marine Biologist

Department of Zoology

University of British Columbia

Tom Carefoot is Professor Emeritus with the University of British Columbia Department of Zoology and a marine ecology expert. He is a frequent contributor to E-Fauna BC and provides introductory notes for marine invertebrates. E-Fauna BC is cross-linked to his marine invertebrates web site, A Snails Odyssey.

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