Course:EOSC270/2022/Impacts of Human Activity on Kelp Forests in BC

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What is the Problem?

What is kelp?

Kelp is the fastest growing species of marine plants that create extensive, biodiverse and productive ecosystems called kelp forests. The beautiful canopies of these sea forests are made of seaweed “macro-algaes” that attach themselves to rocky substrate through holdfasts and photosynthesize throughout their blades and stem (or stipe).[1]

Kelp forests are found in British Columbia (BC), California, Chile, South Africa and other places that host cold, nutrient-rich, shallow waters. Kelp forests line approximately 25% of the world's coast and create a habitat which fosters life for a tremendous number of invertebrates, fish, crustaceans and other algae species.[1]

Kelp forests are unique in their ability to modify the light, waterflow, pH and sedimentation of their local marine environment. There are over 30 unique species of kelp found globally, with giant kelp (Macrocystis pyrifera) being the most common.[2] 

On a global scale, kelp provides 6 key ecosystem services. Kelp absorbs carbon dioxide, shelters various types of marine life, cleans surrounding waters through filtration, protects fragile shorelines, supports coastal communities and provides the basis of the marine food web by enhancing primary productivity. As a photosynthetic macro-algae, kelp is able to drawdown carbon from the atmosphere and produce oxygen. Kelp along with phytoplankton and other marine plants produce approximately 70% of the planets oxygen. Kelp is also more effective at sequestering and storing carbon dioxide, as it absorbs carbon and sinks to the seafloor at the end of its seasonal lifespan, storing carbon for long periods of time. In the Pacific Ocean, Kelp forests are worth around 900,000 dollars per kilometer per year due to fishing, ecotourism and ocean-climate derived value.[3]

Figure 1. Filbee-dexter, Kelp environments shift from a healthy kelp forest to a sediment-laden turf due to ocean warming and acidification. Kelp is very sensitive and climate change is largely responsible for the reduction of sea forests into algal-populated rocky beds. The various images depict the quality of kelp forest health and their states in response to ocean warming. The 3 categories show the transformation of a healthy kelp forest to a sediment-laden turf through biological drivers such as (c) tropical herbivores, (f) epiphytes smothering kelps, and (i) the invasive bryozoan (Membranipora membranacea) encrusting and weakening kelp fronds. [3]

How are kelp forests threatened?

Kelp loss can be directly attributed to a rise in urchin populations, which eat kelp holdfasts in rocky and temperate environments like BC. Many times, the rise of urchins and decline of top predators are as a result of environmental impacts. In this case, Kelp can recover after years of sea urchin density decline. However, toxic macro-algae called “turf algae” can decimate a kelp forest to the point of no return, by modifying the chemical environment and choking out kelp. Ocean warming and coastal eutrophication perpetuate the growth of turf algae. On a global scale, kelp forests shifting to turf reefs is becoming much more prominent.[3]

Kelp ecosystems are also suffering from ocean warming and acidification. Increased carbon dioxide in the atmosphere creates warmer and more acidic coastal sea water temperatures. This leads to conditions that favor urchin barrens and turf algae. This creates an amplifying feedback loop that slowly decimates kelp populations. Anthropogenic greenhouse gas emissions and inputs into the ocean are decreasing the ability of kelp forests to regenerate themselves and the window for restoration practices on a global scale is slowly closing.[4]

Kelp forests are disappearing

A recent worldwide study has shown that approximately 38% of the world's kelp forests have declined in the last 10 years. The sole species of Kelp within the Salish Sea, Bull Kelp (Nereocystis luetkeana), has been negatively affected by the wide-spread marine heat waves, human disturbances like coastal development and logging, as well as overfishing and acidification in BC waters.[5]

A decrease in the global abundance of kelp species would negatively impact ecosystem services and health by altering the aquatic food-web and consequently leaving lasting oceanic repercussions.Yet despite many threats to its survival, kelp has an incredible ability to rebound quickly and can do so at a local level relatively efficiently with the right conditions for growth. This signifies that kelp can rebound as an ecosystem despite having undergone various stressors. There is hope for the protection, restoration and reimplementation of kelp forests in BC and globally in kelp-rich areas.[6]

What is the impact of this problem?

Impacts of kelp forest loss on marine species

Kelp forests in British Columbia and the Pacific Coast of North America are home to a diversity community of marine species, providing important habitat for foraging and shelter. Zooplankton, decapods, copepods, juvenile salmon, and other forage fishes have been found to occur in higher abundance in kelp forests compared to adjacent open habitat.[7] Additionally, experiments in coastal California found that all seven fish species surveyed declined significantly in abundance following kelp forest removal[8]. By providing important food and shelter for a diversity of species, including a high biomass of lower trophic level species, kelp forests help support a much larger food web. The loss of kelp habitats can cause cascading effects throughout marine ecosystems[9].

Impacts of kelp forest loss on people and traditional practices

Beyond their ecological importance, kelp forests have significance in human life and traditional practices. A decline in kelp can put these practices at risk. In British Columbia and around the world, kelp is harvested for human consumption, and for use in animal feed and agriculture[10]. Kelp is also critical in the harvest of herring roe, an important traditional practice for several First Nations on the British Columbia coast. The Heiltsuk Nation sustains a herring roe fishery on British Columbia’s coast, where they harvest the eggs by collecting the kelp that the eggs have been deposited on[11].

Impacts of kelp forest loss on global climate change

Kelp are photosynthetic organisms. By converting CO₂ to oxygen, they play a role in mitigating climate change. Macroalgae such as kelp are responsible for the removal of 2000 million tons of carbon dioxide each year. Kelp that dies may float offshore and sink to the sea floor, storing solid carbon in the deep sea, where it is unlikely to return to the atmosphere. As kelp forests disappear, this carbon sequestration capacity will decrease[12].

Figure 2. In a classic example of a trophic cascade, a decline in sea otters led to an increase in sea urchins, which led to a decrease in kelp forest cover. This could have further negative consequences on species which rely on kelp forest as habitat, such as fish like salmon. Figure by Liron Gertsman (2022).

Case study: Sea Otter extirpation and kelp forest ecosystems

Historically, Sea Otters were present in numbers along the outer coast of British Columbia, where they were frequently found around kelp forests habitats. However, they experienced substantial hunting pressure due to demand for their extremely dense fur. The last Sea Otter on the coast of Vancouver Island is believed to have been killed in 1929[13]. The consequences of this decline and extirpation were significant. Sea Otters are a natural predator of many benthic species found in and around kelp forests, including the sea urchin. Without their predators, sea urchin populations exploded. Urchins are grazers on kelp, and the increased presence of sea urchins meant that kelp forests were decimated. With reduced availability of kelp forest habitat, this could have adverse impacts on salmon and other marine species which rely on kelp forests for shelter and as foraging habitat, further exacerbating the negative impacts of this trophic cascade. Following the re-introduction of sea otters to the west coast of Vancouver Island in the 1960s and 1970s, kelp forests begun to return to the region. However, there has been a decline in kelp forests in some regions in the last couple decades as environmental conditions have changed in other ways[9].

What is the cause of the problem?

Essentially, the cause of the loss of kelp globally is human activity. There are both indirect and direct impacts as well that affect kelp ecosystems, kelp biomass and their ability to regenerate. Human activities influence the biotic and abiotic factors that regulate the global distribution of giant kelp; inclusive of temperature, nutrient availability and the presence of grazers (such as sea urchins).[14]

Indirect causes  

Anthropogenic activity affects the planet’s highly connected ecosystems. While some activity directly impacts kelp, like over-harvesting of kelp, human activity also has an indirect effect on kelp by affecting the global ecological community. Human activities such as driving or flying attribute to climate change through a chain of events, they indirectly impact kelp. Rising global temperatures alter how ecosystems function and humans are a direct cause for the increase in temperature. Today’s industries and our society of consumption has caused global warming and ocean warming which affects the habitats present. The following sections discuss two instances of indirect causes.

Climate change and ocean warming

Temperature increase has both direct and indirect effects on kelp. Various kelp species such as bull kelp flourish in cool and nutrient rich water hence, climate change and ocean warming do not boost kelp populations by creating warmer conditions.[15] Long periods of warmer weather can reduce spore production which in turn causes kelp to die off by diminishing their capability of reproduction through spores.[15] A more indirect consequence is with an increase in temperature there is an increase in metabolic rates of feeding species and grazing pressure may intensify due to this increase.[16]

Increased herbivory due to overfishing

In some regions such as in the Salish Sea on the West Coast of Canada and the United States, herbivory has increased within kelp ecosystems. Due to overfishing of local populations in the area and removal of predators like sea otters and carnivorous fish, smaller herbivorous species, more specifically kelp grazers such as sea urchins thrive and overfeed on kelp.[15] The absence of predators causes an increase or more stable amount of plant eaters that thrive and eat the kelp.

Direct causes

Equivalently, there is also human activity that directly affects kelp populations such as kelp over-harvesting, marine pollutants and habitat degradation.

Figure 3. Stressors impacting nearshore kelp forest ecosystems. Figure art by Su Kim [18]

In British Columbia, the harvesting industry is monitored and said to be sustainably run but there is uncertainty in commercial harvesting since it is minimally tracked and relies on self reported statistics to monitor sustainable intake. Harvesting is seen to be sustainable and not the main cause of the loss of kelp in the ocean in British Columbia (according to Ocean Wise assessments) - this may vary in other regions. Harvesting kelp remains an issue because kelp continues to be endangered and harvesting may interfere with restoration since kelp is vulnerable to many other factors.[17]

Another direct cause found in the Salish Sea region is the development of the coast surrounding kelp forests. It was found that contaminants from sewage and pollutants including metals and chemicals (ex: petrochemicals from fossil fuel extraction) limited kelp primary production.[18]

Given the impact, what are the solutions?

Kelp restoration

One potential solution to saving kelp forests is by actively restoring kelp. Scientists from the Pacific Northwest conducted a study on bull kelp (Nereocystis luetkeana) that was transplanted to two islands off the coast of Washington, San Juan Island and Saddlebag Island. Original results were not very promising, as only 28% of the transplanted bull kelp survived while the study took place. A methodical error was made when transplanting the bull kelp that severely impacted the survival rate. However, although the mortality rate was high, all the bull kelp that survived until sexual maturity propogated nearby habitats and remained in the area for months afterwards.[19]

In Australia, scientists implemented Operation Crayweed, where they planted mature Phyllospora comosa plants along the coast of Sydney. Around 70% of the transplanted crayweed survived and went on to reproduce six months after they were planted. At one site, the resulting generation of crayweed that arose from the transplanted crayweed were present in numbers ten times larger than crayweed that had not been interfered with.[20]

Interestingly, the bull kelp transplanted to San Juan and Saddlebag Island was juvenile and grown in a lab[19] while the crayweed in Sydney was mature and taken from a nearby local habitat.[20]

Figure 4. Turnbull, J. (2016). Crayweed restoration, South Bondi #marineexplorer [photo].

The downsides to active restoration efforts such as Operation Crayweed is that they are very costly and require a lot of human labour. The cost of restoration was estimated to be $46,250 USD per hectare, which doesn’t include the ongoing site supervision or overall conducting of the project.[21] With costs being so high, it is difficult to justify them to government agencies. However, scientists at Operation Crayweed engaged the local Sydney community through videos, art installations, and other forms of media and were able to crowdsource over $20,000 AUD within just a few days of promoting the project.[20] Crowdfunding may be a tool that other scientists around the world can use to help secure public support and project funding.

Marine Protected Areas (MPAs)

The implementation of no-take Marine Protected Areas (MPA) is another possible solution to the decimation of kelp forests as well as other related problems such as overfishing, marine pollution, and habitat disturbance. In Tasmania, kelp forests were disappearing in connection to the overfishing of lobsters (primarily Jasus edwardsii) and resulting overabundance of urchins (Centrostephanus rodgersii). Through video observation, scientists discovered that the lobsters were the main predator of the urchins, and that larger, older lobsters were the most successful hunters. These lobsters were being targeted by commercial and recreational fisheries and studies found a direct link between the overfishing of lobsters and the decreasing biomass of kelp forests. The implementation of a no-take MPA in eastern Tasmania allowed lobster populations in the MPA to slowly rebound and kelp forests to increase.[22] Similar results were observed in the Channel Islands of California, where the California spiny lobster (Panulirus interruptus) and the California sheephead fish (Semicossyphus pulcher) were being overharvested. In the location the MPA was established, lobsters and sheephead increased in abundance and the area was transformed from an urchin barren into a kelp forest.[23]

A regulated no-take MPA might be the solution to the disappearing kelp forests off the coast of British Columbia.

Genetic engineering, the future?

A novel approach to saving declining kelp forests is the use of genetic modification. Since there are many direct and indirect causes to this problem, a variety of solutions must be explored to find what works best for each unique ecosystem.

Scientists have proposed engineering kelp to be more resistant to heat, pollution, and disease as well as modifying its flavours to be less appealing to herbivores. Scientists are also exploring the possibility of enriching agricultural crops with the Omega 3 fatty acids that are naturally found in seafood.[24] The thought process behind this idea is to provide a nutritional alternative to seafood and hopefully reduce the demand for wild-caught fish and shellfish. The intended result is to leave more shellfish available to keep the main grazers of kelp, sea urchins, in check.[24] Another possibility is genetically modifying sea urchin embryos to control their populations.[24] Scientists have successfully used CRISPR, a gene editing tool, to disrupt genes controlling growth in sea urchin embryos.[25] In areas with rapidly expanding urchin populations, scientists may consider modifying urchin genomes to decrease reproduction or embryonic survival rates.

Although bioengineering is not without its downsides, its applications appear to be endless. If kelp forests are not positively responding to other human interventions, and pollution and ocean warming continue rapidly, bioengineering may be the next step in trying to save kelp forests. Eventually, it may just be our only option of saving these vital ecosystems.[24]


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