Ecology

Robots are coming to save kelp forests from urchins

Kelp forests around the world have been in trouble. Some reports indicate that the global kelp biomass has been reduced by a 3rd in the last decade. Recently northern California, Australia, and Maine have been hit hard by a population explosion of purple urchins. These urchins graze on seaweeds and can clear entire kelp beds.

What’s causing these urchin booms is unclear, but most signs point to rising ocean temperature. With global temperatures set to rise, these urchin booms may become more frequent.

Some groups have taken it upon themselves to remove urchins from kelp beds, however this takes a lot of manpower and resources, such as, boats and SCUBA equipment. A new startup out of Stanford has designed robots that can go down to 120 feet underwater and collect urchins autonomously. This could be a vital resource in kelp forest defense.

Read more about their project here. (While this article is good at describing the project, we need to note the biological discrepancies. Kelp forests don’t provide 70% of the global oxygen. Kelp forests are important to fisheries, but there are a number of habitats that contribute to global fisheries and to say that kelp forests are the foundation of all fisheries is an overstatement)

Can seaweed combat climate change?

The United Nations Intergovernmental Panel on Climate Change (IPCC) has just released a report on the current state and predictions of anthropogenic climate change as a followup to the Paris Agreement. The Paris Agreement was an international treaty, pending ratification, with the goal of preventing the average global temperature from reaching 1.5 C above pre-industrial levels. The IPCC laid out the global consequences if the 1.5 C threshold is exceeded. The results were not good: sea level rise, ocean acidification, species extinctions, increasing storm frequency and intensity (as we watch hurricane Michael make landfall less than 1 month after hurricane Florence). The IPCC stated that if we can’t develop technology to remove CO2 from the atmosphere these scenarios will come to fruition sooner than previous studies indicated.

The oceans act like a giant CO2 sponge and over 1/3 of anthropogenic CO2 is absorbed into the sea. Increasing CO2 in the ocean causes the water to become more acidic. Ocean acidification has strong negative effects on a number of organisms, especially calcifying or shell building animals. The IPCC is focused on removing CO2 from the atmosphere, but perhaps taking CO2 out of the oceans would also be a key strategy in reducing anthropogenic climate change.

Could seaweeds be used to take CO2 out of the ocean? Like terrestrial plants, algae uses the process of photosynthesis to take up CO2 and release oxygen, locking carbon away in it’s tissues. This idea of decarbonization by algae has been tested by a group in Korea, and they found that they could use natural or constructed kelp beds to take up and store 10 tons of carbon per hectare every year. Another research team made a rough calculation that global macroalgae could pull down up to 268 million tons of carbon per year.

The problem with using macroalgae for carbon storage is that algal tissues will eventually break down and through bacterial decomposition CO2 will be re-released. There have been a few ideas of what to do with all the carbon sequestered in seaweed: some suggest sinking it to the bottom of the ocean while others say to use it as a bio fuel to reduce the use of fossil fuels.

Reducing emissions will go a long way in avoiding many of the doomsday scenarios, but doesn’t address the current and near future ocean acidification issues. While seaweed can’t solve climate change, it will undoubtedly play a major role in curtailing CO2 within the oceans.

Otters and urchins and kelp ... oh my! Does your kelp forest require otters? Maybe not.

It’s sea otter awareness week, and after reading enough posts about how sea otters save kelp forests, we thought it time that we set the record straight.

Sea otters (Enhydra lutris) are commonly thought to be the keystone species in kelp forest ecosystems along the west cost of North America, from the Aleutian Islands to California. The well known paradigm follows the logic that urchins can eat and destroy entire kelp beds, leaving a low diversity/productivity urchin barren. Sea otters are veracious predators of urchins, and when otters are present in a kelp bed, they control urchin populations and prevent barren formation. While sea otters can definitely be effective keystone predators in some systems, the full story is much more complex.

The fur trade in the 1800 nearly caused the extinction of the sea otters. In 1911, otters gained government protection and their populations began to recover. A number of studies showed that the recolonization of sea otters in the Aleutian Islands were able to mitigate urchin barrens (1,2,3). The effect was quick and broad. These systems were clearly dysfunctional in the absence of otters. Subsequently, this idea of top down control became prevalent in scientific circles and an overarching theme applied to all kelp beds. Yet, in California, where otters had been absent for a hundred years, many kelp beds were thriving. Of the 224 kelp beds in southern California in the 1980s, only 10% were classified as urchin barrens (4). How was it that these beds could be doing just fine without otters, while the beds in the Aleutians clearly needed them?

It turns out, that kelp beds in the Aleutians are simple systems and contain few other urchin predators, while the California beds have a number of other species that can fulfill that functional role: the sun star (Pycnopodia helianthoides), sheephead (Semicossyphus pulcher), and the spiny lobster (Panulirus interruptus) (5,6). Urchin barrens do occur in southern California, but generally these are areas (1) subjected to over-fishing of these urchin-eating predators or (2) high levels of pollution, temperature, or other disturbances that directly kill the kelp. Southern California also experiences urchin disease and El Ninos, which can control urchins independent of otters. In fact, its been over one hundred years since an otter swam through the kelp fronds of the worlds largest kelp forest at Point Loma in San Diego, yet this forest remains the global example of a well functioning kelp system.

Food webs within kelp beds are complex and vary in space and time. What is clear, is that kelp forest resilience depends on biodiversity, and over-fishing/ hunting and other disturbances can tip the scales in favor of urchins. This is currently happening in various locations along the Monterey Peninsula, in plan view of a healthy otter population, though this situation probably wont last long. Otters are veracious predators of urchins and can stop or help mitigate urchin population explosions, especially when they are the only form of protection from urchin grazing. Such simple kelp systems, however, are restricted to certain geographic regions (e.g. the Aleutians), whereas other kelp beds (like in California) have a higher diversity of sea otter predators and other forms of urchin control, and don’t require otters for the kelp forest to function properly. But with impending climate change and human impacts on kelp systems, who knows what will happen and those charismatic furry little urchin predators may serve as an insurance policy if all hell breaks loose. Until then, at least they are fun to watch.

  1. Estes and Palmisano 1974

  2. Estes et al. 1978

  3. Estes and Duggins 1995

  4. Foster and Schiel 1988

  5. Watanabe 1984a

  6. Tegner 1980