A Tale of Plankton and Sewage
Welcome back for another update! Our urban kelp survey is now 100% live. Thanks to you all we BLEW through our first round of images (seriously, over 8000 images in exactly one month!!!) , and we are now ready to start classifying kelp!
Today we’ll briefly talk about our choice for our California site, Los Angeles.
Image Source: Google Earth, accessed 6/12/2020
LA is currently the largest in our study, at least in terms of population/density. It saw its biggest population boom in the early to mid 1900s as both the entertainment and war industries grew. Unfortunately for us, we don’t have satellite data from this time. While we are missing the major population growth spike, Los Angeles continues to be a major metropolitan hub – it is the 2nd most populated city in the United States, and one of the largest worldwide!
The kelp forests in California have a patchy (ha ha…) history that is often closely linked to human activities – If you ask a phycologist about it, you’ll almost certainly hear about the Point Loma and Palos Verdes kelp forests. These two coastal kelp beds are located near San Diego and Los Angeles, respectively, and are infamous for sustaining massive kelp loss in the first half of the 1900s. This was due to a variety of factors, some natural and some human, but it seems that urban sewage discharge was the straw that broke the kelp forests back.
In the case of Point Loma, a broken sewage pipe discharged almost 200 million gallons of sewage into the kelp forest, leading to quick and major kelp loss. Luckily the area quickly recovered after the pipe was repaired – one advantage of kelp’s fast and furious life style is that it can quickly repopulate a large area if environmental conditions are restored! Palos Verdes has had a longer road to recovery, although recent restoration efforts have been successful in recovering many acres of kelp forest.
Discharge from sewer systems is bad for kelp in several ways. The discharge tends to be full of sediments (solid material suspended in the water). This can prevent growing kelp from getting sufficient light or can even completely bury small individuals. Another negative impact associated with these outfalls is nutrient pollution. In some cases, chemicals like ammonia can spike to toxic levels, causing immediate damage.
In other cases, elevated nutrient levels can simply “fertilize” the water. Your first reaction might be to think that this would be good for the kelp, and maybe in a vacuum it would be, but nature isn’t that simple. In this case, the complication comes from phytoplankton, which can compete with kelp for light by forming floating algal mats that block light and shade the seafloor.
Kelp grows quickly, but not as quickly as phytoplankton. When water nutrient levels are elevated (a condition called eutrophication), plankton growth can ramp up into what is called a plankton bloom. That’s a lot of words to say that these algal blooms can have major effects on the ecosystem. This picture might “clear” things up (ecological puns never get old…). These thick green algal blooms are more characteristic of fresh water, but I think this does a good job of illustrating how severe these can be.
Image source: Tim Otten, Oregon State University
The immediate, kelp-relevant effect is a reduction in light at the sea floor. The longer term effects can include reduced oxygen levels in the water, creating uninhabitable “dead zones. This low-oxygen condition is called hypoxia and is a result of rotting phytoplankton. The typical life cycle of a bloom goes something like this:
- Eutrophication event (discharge or runoff causes elevated nutrient levels in the water)
- Algal bloom (opportunistic plankton grow exponentially given high nutrient levels)
- Overgrowth (algal population exceeds available nutrients; growth eventually stops as nutrients are depleted) – Light levels beneath the water’s surface reduced
- Decomposition (algal bloom dies and decomposes. Bacteria associated with decomposition consume oxygen, creating a dead zone) – Hypoxic conditions form, many animals die or leave
Kelps are potentially affected by almost every step of this process. They are shaded out by the initial bloom and then potentially buried in detritus as the plankton decomposes. Many of the animals found in kelp forests are vulnerable to the dead zones caused by algal blooms. Loss of these kelp forest residents can further destabilize the ecosystem.
While the stories of Point Loma and Palos Verdes unfortunately played out mostly outside of Floating Forest’s time window, they serve as clear reminders that human activities can seriously affect kelp forests. Things like sewage discharge and eutrophication are global issues; California may be a high profile example, but is far from the only one. As we continue to explore the effects of urbanization, we will be sure to include as many local factors (such as sewage treatment outfall points) as possible to best understand each of our sites.
Kelp and the Big City
If you’ve read through our “about section” or seen our blog in the past, you’ll know that kelp is threatened by climate change. This is perhaps the main reason why we are so interested in kelp in the first place, and so far Floating Forests has allowed us to build some of the most complete kelp forest datasets around. Soon we will be adding a new set of images to the project, this time examining a few key, high-risk locations with a fine-toothed comb. We’re interested in how coastal construction or development might impact kelp forests – it’s time to take our kelp research to the city! We will be taking a close look at kelp forests in California, Chile, Argentina, Australia, and New Zealand.
While global climate change is extremely important, there is great value in examining smaller scales as well. In fact, studies such as this one have shown that kelp forests are strongly affected by local conditions! As you might expect, changes to these local environmental conditions can have significant effects on the local wildlife.
We call changes that affect the environment “drivers”. For example, a construction project could “drive” environmental change by releasing sand and dirt (which are collectively referred to as “sediments”) into the water. When two different drivers interact and affect each other, we refer to them as “synergistic”. Occasionally they can create especially favorable conditions, but often one exacerbates the negative effects of the other, so we call these “synergistic stressors”.
One way to think about this is to say that one driver can amplify the effects of another. For example: a marine ecosystem might be able to handle a 2° Celsius increase in average temperature without collapsing. Separately, it also might be able to handle the effects of a large construction project. However, the effects of both at the same time could prove catastrophic: organisms already stressed by warming might not be able to cope with disturbances caused by the construction, and most importantly, things might get bad much more quickly than we might expect.
Because an emoji is worth a thousand words:
This example is one of the many that play out across an ever-developing world. One consistent trend over the last several decades has been a large increase in coastal population. To say this more plainly – more people than ever before live near the coast. As coastal cities grow, constant expansion is needed in order to keep up with the population. This conversion of land from natural to urban terrain is known as “urbanization” and brings with it a host of environmental impacts – some of which are potentially harmful for kelp forests.
By digging into the satellite record, we can get an idea of how kelp forests in urban areas have changed over the last few decades in response to this trend of development. What’s really exciting about this opportunity is that with the power of citizen science we can cover a lot of ground: we want to compare cities across the globe in order to build a better understanding of how kelp in different places is affected by human activities. We expect there to be many interesting differences between these locations – it would probably be more surprising to learn that kelp in Australia was acting exactly like kelp in Chile!
Stay tuned as we prep for the launch of this exciting phase of Floating Forests – details about our study sites and more about the connections between urbanization and kelp coming soon!
Kelp On The Edge!
With the Falklands classifications wrapping up, it’s time to move on to our next phase of global kelp mapping – kelp on the edge! Giant kelp is a cold water species – warm nutrient poor water is a definite no. Their range extends towards the equator wherever they are found until they hit a wall of warm water. There they shall stop, and no further.
But what about when that wall – that range edge – starts heating up? That’s when you’ve got…
We’ve witnessed a variety of other kelps die back when things got to hot, and our own Jorge Assis has shown some projected major range shifts of kelps in the future.
With the data from Floating Forests, one question we want to ask is, how have kelps on the edge been faring? Over the past 35 years, have we seen kelps on warm water range edges dwindling? Have any of those populations blinked out? Have the ranges of giant kelp actually been on the move?
The great thing about this project is the simplicity of the question. Rather than circling kelp beds (although we’ll get there), we want to begin just by looking at range edges of giant kelp around the planet and the area up to 500km away and ask you just to note, do you see any kelp? Yes or no? That’s it!
We’re also putting kelp on the edge into the Zooniverse app where you can swipe right for kelp! click here for the iPhone app or here for android!
The first set of images is up – from Baja California using Landsat 7 and 8. L4 and L5 imagery will come in the next few days, and more of Baja and then New Zealand next week.
So what are you waiting for! Pull out your phones and get swiping! (or click here.
Also… the music we can’t get out of our heads
There’s somethin’ wrong with the kelp today
I don’t know what it is
Something’s you’ll see with our eyes
We’re classifyin’ things in a different way
With swipe fast left or right
The data will surprise
Kelp’s livin’ on the edge!
Floating Forests 
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