Kelp forests are a magical world and you do not even have to go to faraway places in the tropics to explore them. What appears to be an ugly algal network on the surface of the sea, hides a huge variety of different species below its canopy. Among its inhabitants are cute sea otters, magnificent whales and mysterious sea horses that seem to have jumped out of a fairy tale. Surprisingly, these ecosystems thrive in temperate to subpolar regions. If you plunge into a kelp forest, you have to be careful to not get tangled up with the up to 45 m long “trees” that provide the space for this extraordinary ecosystem. The “trees” are brown algae, called kelp. If you have wandered along a beach in the temperate or northern regions of the world, you have probably already encountered some brown algae that were washed up on the shore. As a child I was always delighted to take some of this kelp and let the air-filled bubbles blob, which makes a funny noise. Watch the following movie to get a feeling for the magical world of kelp forests:
You can almost watch kelp growing with some species growing up to 45 cm/day. Brown algae are not considered as plants, but they resemble plants a lot. They are also capable of doing photosynthesis, which is the process of taking the CO2, the climate heating causing agent, from the environment, fixing the carbon in form of sugars and releasing harmless oxygen that we also need for breathing. Since a lot of carbon is fixed in the tissue of kelp, kelp forests, similar to tropical rain forests, are considered a very important carbon sink. In addition, the stored sugars attract animals that feed on kelp forests. These are then eaten by larger fish and those again by larger ones. Kelp forests are therefore the base of many coastal food-webs that have important functions all the way to deep oceans. For sure, parts of kelp forests have already ended up on your dish… if it wasn’t for some kind of fish, then it was maybe in a Chinese soup as a vegetable.
Probably you remember Nemo, the clownfish who grew up in and was protected by a sea anemone in the coral reef. Well, kelp forests are similar homes for many small fish in the more temperate and polar regions of the world. In these forests, they are better protected from predators and even from brutal storms.
The home of the leafy sea dragon is endangered
Southern Australia is home to an 8000 km long interconnected kelp-forest system that is called the “Great Southern Reef”. Although not as much known as its northern colourful and shiny “Great Barrier Reef” reef, it is also home to many species that are endemic – that only exist at this one place – among them also the colourful leafy seadragon. This kelp forest alone produces a value of around 1200 US$ per minute which adds up to 600 Million US$ of revenue to the Australian economy per year. Kelp forest can be exploited for livestock food, biofuels or even the production of pharmaceuticals in the near future. Although important on an environmental and economic level, these ecosystems are under enormous threat. If we do not learn to use this ecosystem sustainably, we might never be able to fully exploit the richness of this system. Although global heating leads to the expansion of kelp forest to even more polar regions, overall kelp forests vanish by 2 % per year. In some regions, the disappearance is even at 18 % per year.
What is causing the disappearance of the kelp forests? Let me explain 3 of the most important causes for their disappearance:
- Pollution of the sea with too many nutrients, stemming mostly from a still very ineffective intensive agriculture, leads to the expansion of less ecologically valuable turf algae. Furthermore, the rise of particles and sediments in the sea through pollution leads to less clear water. Then, brown algae aren’t capable of performing photosynthesis efficiently. They become weak, sick and eventually die off.
- Overgrazing of kelp forests by sea urchins. Sea urchins are usually kept in control by predators like sea otters, rock lobsters, different kinds of fish or starfish. Unfortunately, sea otters were almost brought to extinction by humans and still need to recover from that shock. Rock lobster and fish are so overfished by humans that it only leaves starfish to control the rapidly increasing number of sea urchins. Unfortunately, a virus, causing the wasting disease in starfish, decimated the number of starfish. As a result, sea urchins can multiply without control, leading to sea urchin barrens. These are herds of sea urchins that graze off everything that is in their way until everything is eaten up. Some of the urchins move on to graze off the next forest. Some remain and survive in the wasteland they have left for a very long time. Even worse, when sea urchins become hungry they enlarge their jaws and teeth and become able to eat usually unedible material like calcified coralline algae.
- Global heating! Due to increasing temperatures in the oceans, either kelp forests simply do not survive because they like colder waters, or invasive tropical species move into a kelp forest and destroy it. Just this year a research group from Australia and Brazil published a finding which is even more upsetting: a marine heatwave along the Australian western coast in 2011, led to a loss of genetic diversity of up to 65 % in kelp forests. Genetic diversity, however, is important for species and ecosystems to be resilient against catastrophes. In every catastrophe, less adapted individuals of a species die, while well adapted ones survive. The traits that make us (or in this case kelp) well adapted to a catastrophe, are encoded in our genome. The impoverishment of genetic diversity can however not be measured by the level of canopy coverage, which is what is mostly studied to see the decline of kelp forests. Therefore, the current status of kelp forests might be much worse than we actually think. If there is any other catastrophe appearing in the near future, it can happen that huge areas of kelp forest die off in a short time because the chance of having a well-adapted individual in a genetically impoverished community is less compared to a richer community.
There are multiple efforts to restore kelp forests and the fight is not yet lost. Luckily, kelp forests are quite dynamic, which is why they can quickly regain their beauty. For kelp forest restoration, two main strategies are used. The first one is “assisted recovery”, where the agent of decline is removed and material is installed that serves as substratum for kelp colonization. This can however be very costly: 2 divers need almost 700 days costing around 1400 US$/day to remove sea urchins in a 1 km2 area if there are 1.5 sea urchins/m2. This is still less compared to average sea urchin barrens. The second restoration effort is called “active restoration”. In this case, kelp from a donor site or a lab-culture are transplanted to a site that needs to be restored. The transplantation needs to be repeated several times until the site becomes autonomous with local recruitment of kelp. Both methods are really cost-intensive and not effective enough to save kelp forests globally. Therefore, your action is needed as well. You are needed to make fishing sustainable and to take measures for decreasing your carbon dioxide footprint.
Unfortunately, buying fish from sustainable sources is more expensive than the fish coming from conventional fishing. This always hurts when you do your groceries. However, when you have to pick, think about the fact that if you pick cheap fish now, in a few years from now, exactly the same type of fish will be so exorbitantly expensive that you would not even think about buying it (if it has not even become extinct). Therefore, you can already pick the expensive variant today and this way happily eat fish also for the years to come. In addition, let’s only pick sea fish for special occasions. This helps saving money that you would need to keep for buying sustainable fish and we value the few fish that are left much more. I think it is horrible to see people eating tuna sandwich on the go in 5 minutes without valuing what they eat. If you are still a very hungry fish eater, you could also pick some local fresh water fish that is not endangered.
These are only a few suggestions to try to alleviate the pressure on our non-fictional magical forests below the sea surface. Please subscribe to my blog or follow me on twitter in order to get more information on the beauty of other vanishing ecosystems or to get further ideas how YOU can make a difference as well.
To continue reading the scientific articles (most relevant resources)
Gurgel CFD, Camacho O, Minne AJP, Wernberg T, Coleman MA. Marine Heatwave Drives Cryptic Loss of Genetic Diversity in Underwater Forests Curr Biol. 2020 Apr 6;30(7):1199-1206.e2. doi: 10.1016/j.cub.2020.01.051
Layton C, Coleman MA, Marzinelli EM, Steinberg PD, Swearer SE, Vergés A, Wernberg T and Johnson CR (2020) Kelp Forest Restoration in Australia. Front. Mar. Sci.7:74. doi: 10.3389/fmars.2020.00074
Thanks also to the RainWater_Gallery for providing the header image for free.
Hallo Nils,
hast du toll geschrieben. Wenn ich es recht verstanden habe, sind die Seetangwälder in allen Meeren, also auch Binnenmeeren unabhängig vom Salzgehalt.
Der Text ist gut verständlich und lässt sich leicht und locker lesen.
Gruß
Papa
Sehr interessant geschriebener Bericht. Wir müssen unsere Umwelt, Meere und Gewässer mit ihren Lebewesen und Pflanzen besser schützen.