Coastal Ecosystems

Colorful fish swimming over just as colorful coral or hiding between the roots of mangrove forests. The coastal ecosystems have long fascinated humans. They are the part of the ocean most people stand a chance to interact with, to see, to explore.

They are also among the most productive, biodiverse, and vulnerable ecosystems on this planet. The coast brings a lot of diversity and different types of ecosystems. Coral reefs, kelp forests, mangroves, estuaries, and the tide pools and beaches themselves all play into the beauty of the coast.

More and more of the coast is getting lost to human development. Coastal development that hardens the shoreline accelerates erosion leads to loss of beaches. During the research for my thesis, I read a paper by Gittmann et al. from 2015 which showed that even then 14% of the US coastlines have already been armored. And hardened shorelines lead to so much less life. Take seawalls, for example. They support 23% less biodiversity and provide homes to 45% fewer organisms than natural shorelines. But they are oh-so-convenient for the humans…


Let’s start with an ecosystem that is often skipped: estuaries, where rivers meet the sea. Estuaries are the regions in the deltas of rivers where freshwater from inland flows into the ocean. Because the waters mix there, the salinity is different from both the ocean and rivers or lakes. The lower salinity there creates living space for species that can’t cope with the high salt-level of the sea or the very low salt levels of the inland rivers.

Okay, technically, there are also estuaries in places like the Great Lakes where river water meets lake water but that’s not the kind of estuary I’m talking about today.

Estuaries are really productive ecosystems with a lot of life. Many species rely on them for feeding, breeding, or as a place to hang out on the way to or from the sea. NOAA goes as far as calling them the nurseries of the sea.

Unfortunately, they are also very delicate ecosystems, as they are so connected. Because we’ve constructed dams, chopped down forest after forest, and soaked our food in pesticides during growing, we’ve changed the composition of river run-off which then messes with the estuaries. Shallow waters are less clear, so less light reaches the bottom.

And we’ve already lost so much wetland. More than 50% of wetlands have been lost globally. Yeah, rates are slowing in Europe and North America but especially Asia is still doing a really good job at fucking with wetlands.

And then we drive container ships through to reach inland harbors and damage the ecosystems more with their hulls, anchors, or by releasing oil into the waters (no matter if on purpose or by accident).

Damn it, this wasn’t supposed to be a tirade on human fuck-ups. So, estuaries.

Mangrove forests

Mangrove forests are one of the ecosystems found in estuaries around the world. One of those ecosystems I can’t wait to see at some point.

Mangrove forests are really fucking important for their ecosystem but also the surrounding coastal populations. They actually lower the pH, so make the ocean less acidic, for the surrounding waters because of how mangroves work. Don’t ask me. I don’t get chemistry. But the magic of mangroves makes the ocean more resilient, something that the ocean urgently needs with all that we throw at it.

I mean, we directly fuck with mangrove forests to make room for our agriculture and living space. We’ve already lost 20-35% of the mangrove forests across the world just in the last half century alone. And, according to a dude called Goldberg who did a study on this in 2020 found that 62% of the mangrove loss between 2000 and 2016 was due to land-use change. Land-use change is a pretty term for humans made room for themselves. In this case, it was mostly for agriculture and aquaculture, so humans, humans, humans.

And this isn’t new. A joint report by the World Bank, the IUCN, and wetland specialists called for urgent wetland protection in 2011. They told the world that degrading wetlands are likely impacting global emissions of carbon dioxide. They pointed to seven deltas that had already released more than 450 million tonnes (500 million tons) of carbon dioxide.

Yeah, let’s just keep going, right?

And mangrove forests are so fucking cool. Above water you will find plenty of birds, but also cool things like the mangrove-tree crab, the proboscis monkey, and even tigers, and below the waves you’ll find a shitton of fish, but also snakes and dugongs, depending on where you are, of course. I definitely hope I get to dive a mangrove forest at some point. Hopefully, we’ll turn the tide before we’ve deforested them all.

Tide pools and mud flats

Until recently, I lived near the Wadden Sea, one of the largest mud flat system of the world. The area is home to millions of shorebirds during their migrations each year and provides a home for many, many species. When I was there last, we were devastated to find almost no birds. It was right after last year’s outbreak of the bird flu in the area, so it wasn’t a surprise but it was still heartbreaking to realize just how many birds were gone.

The Wadden Sea is a protected area and a World Heritage Site but a lot of commercial interests still act right around the national park and it definitely doesn’t help that multiple countries have to manage things, because the Wadden Sea spans Danish, German, and Dutch coastlines.

Mudflats are the most endangered habitat in Central Europe. In Germany, where I currently live, 60% of the mudflat species are listed as endangered on the German Red List. There are restoration efforts and scientists are doing studies to help with them, but we are still doing a lot of damage. Add lovely factors like the bird flu, and you’ve got a recipe for disaster.

When they are intact, mudflats create a habitat for diverse species from birds to crabs to fish. Flatfish are a highlight for me whenever I get to see one. They just look so goofy with both eyes on one side of the head, lying on their sides. But I will also never tire of searching to little pools of salty water for crabs and snails of all sizes.

A similar and yet completely different ecosystem are the tide pools. There are tide pools in the mud flats–like the pools I just mentioned–but the water flows away more easily in mudflats. On rocky shores, tide pools are more prevalent, as water stays in the rocky pools until the next tide covers them.

Species living in these pool are specially adapted to deal with the high temperatures of a tide pool in summer heat, and the lack of water movement during low tides. Some species have gone to quite some lengths like the Epaulette shark which can shut off quite a few organs to save oxygen when in a pinch and essentially walks on land to get back to the ocean.

When we were in California, we’d often find sea stars in the tide pools, but also a lot of crabs and snails, and little tiny fishies. Tide pools are an adventure, and we should make sure children can still get excited by all they can find in them in the future. Nature is the best education, and I believe we all have a right to experience it.

Coral reefs

One of the ecosystems underwater that everyone keeps talking about (and yet, it often feels like no one is listening) are coral reefs. I won’t spend much time on them, because there are plenty of really good documentaries on them like Chasing Coral which was originally a Netflix thing but is now on Youtube, too.

I also won’t bore you by telling you that coral reefs are dying left, right, and center. You’ve all heard of coral bleaching, warming sea temperatures, and how urgently we need to act.

Coral reefs are fascinating and one of my favorite ecosystems on this planet. I loved diving between stony corals in California, above fields of mostly white and beige corals around Hawaii, and I soak up documentaries on corals like a sponge–which also live on coral reefs, of course.

Coral reefs are also one of the most fragile, as they depend on the corals which are vulnerable as fuck to changes in the ocean. When they feel threatened, they throw out their little microbe friends. Corals rely on two ways of eating: food they eat themselves as a communal organism and energy provided by photosynthetic friends they’ve invited into the fold. Deep-sea corals are little different, as we’ve seen in the episode on the deep-sea benthos, of course.

Without corals, fish and crabs, snails and shrimp, and all the other little friends can’t hide, sharks and eels can’t forage for those very friends between the corals, and everything just falls apart. It’s a beautiful ecosystem that we urgently need.

So, maybe, let’s save nemo, shall we?

Kelp forests

And then there are the kelp forest. Kelp forests are at the very top of my list. I love kelp forests. I love seeing sea lions playing with the kelp, swimming between the broad blades. I loved being surrounded by fish in kelp forests around the Channel Islands. And I loved diving the CROP reserve in New Zealand, a shallow protected area with a thriving ecosystem.

And it’s that very ecosystem that gives me hope. While urchin barrens, so areas where urchins have eaten up the kelp because the kelp is fragile in the hotter waters or there aren’t enough otters to eat the urchins, are taking over everywhere, there are still pockets of protected kelp forests that show us it can be better.

The CROP reserve was one of the first marine protected areas worldwide. With protection, they turned the area from slimy rocks into a flourishing kelp forest that now acts as a baseline for studies everywhere.

The reserve shows that protecting nature can benefit everyone. Fishers benefit from the spill-over of larvae and adults leaving the park. Locals benefit from a great diving site and a pretty look from the beach. And nature benefits from protection because she gets a chance to take a breath, to recover, to restore.

If only, we let her.



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