Coral Reefs Can Look Alive and Still Be Functionally Dead

0:02 A reef can look alive and still be functionally dead. We're gonna talk about how reef complexity really shows the true health of coral reefs and why we are losing that structure and why reefs are really in trouble. We're gonna talk about that on today's episode. And if you care about staying informed on the ocean every weekday, hit that follow button right now so you don't miss tomorrow's story. Here's what happened. There was a... recent study in Thailand that looked at the National Reef Assessment and shows that reefs are losing that structural complexity. You're probably wondering, Andrew, what in the world does that mean? When you look at a coral reef, it's not just flat. It's not just one coral species in a line, and it's just flat all the way across, and you have all these different species.

0:48 A coral reef is made up of a number of different species of corals, whether they're branching, whether they're flat, whether they're like a boulder type. It doesn't matter. It's all these different types and they create this complexity. It's like a 3D model of just different nooks and crannies that species can hide in so that they don't get eaten all the time. They don't get attacked. You see more Aeos feed from there and they hide their regular bodies because they're so long and they come out and they start eating animals. All this complexity really builds into a diverse, structurally ready community. But even though coral cover may still be present in the reef, it doesn't mean that the rugosity, meaning the complexity, is still there and still healthy.

1:34 It could be declining and that's what they're finding. Flattened reefs provide less habitat for fish and invertebrates, as I just mentioned, because of the complexity. And the structural degradation reduces biodiversity and the ecosystem stability. As I mentioned, structure matters for a number of different reasons. You know, you get the structural complexity that supports high fish biomass. So that means the fish can hide, they can grow bigger, and they can grow fatter, essentially. High biomass means you have a lot more species and each and every individual is bigger and thicker because they can grow up to be bigger. You know, they can grow up to adults. They're not just juveniles getting picked off by predators.

2:16 And in a structurally complex reef, they have a lot of places to hide around. I'm not sure if you've ever been diving on a coral reef, but you can see, especially in a very healthy, 3D enabled, structurally complex reef, have branching corals that allow fish to hide. And even if you see them, I can't get my finger in there to grab it. I can't get my hand in there to grab without hurting myself or scratching myself. Imagine a fish like I am a scuba diver, which I wouldn't do anyway. But I, you know, if I'm a scuba diver trying to get a fish, I can scratch my hand. I can scratch like if I'm wearing gloves, I can scratch those gloves because those branching corals are sitting there and they're rugged, they're hard, and so you can get scratched.

2:57 Imagine a fish that's trying to attack another invertebrate or fish that's hiding behind these branched corals. Imagine them getting scratched. That puts them vulnerable to their predators because they're injured. They don't want to get injured. So a lot of these fish and invertebrates end up being protected by the structural complexity of the reef. And I think that's an important aspect to think about. You know, we talk about coral coverage, you know, from a very basic indicator. Not that that's not a good indicator, but we see that from a lot of satellite imagery. We see it from drones. We see it from aerial photography and aerial surveys, even from scuba diving surveys that will tow someone across a reef, you know, in the water. And that person is doing a visual assessment or they're holding a video camera or video cameras being towed.

3:41 It's a very quick survey. And so although certain species might be identified, especially when it comes to fish species or invertebrate species, you're not going to get the full picture of that complexity until you look at that reef. And so when you see a satellite imagery and you measure coral cover as a percentage, so it's like, hey, this area is covered by 80 % coral or 60 % coral or 40 % coral, and you're using that as a health indicator and the only health indicator, that could be a tough thing because as we see more bleaching, as we see more things that are damaging coral reefs, overfishing, algae, overgrowth, that structure is not rebuilding like it used to.

4:23 And that structure takes years and decades to create because these corals that are making the structure, these hard corals, take time to grow. And although there's ways to make them faster through like electrical pulses and things like that, naturally, it's a difficult thing for a species to do, especially if it's getting hit down by storms, which there were more storms because of climate change. If it's not getting enough uh calcium from the uh whole relationship between the zooanthellae, the algae that lives within the corals, providing that bicarbonate so that they can build their skeletal structure and grow their skeletal structure. If we see too high of temperatures, that zooanthellae get exited quickly, expelled out of that coral.

5:09 And so a coral reef can go bleach over time and then that... structure doesn't grow and it can get knocked down through storms and if it's not constantly growing, if it's not healthy, then that can uh be a detriment to the whole coral reef health. And so you get less diversity of species, you get less resiliency, which because that's what diversity provides. And then that doesn't support a healthy reef. That predator-prey balance just goes out of whack because once the predators pick off all the prey, then the predators are going to leave. and then there's nothing there to stabilize the overgrowth of algae or there's nothing there to kind of prop up and keep uh species from eating coral.

5:52 There's a lot of things that go on within a coral reef. You have algae overgrowth that can happen at any point in time depending on the right nutrients and phosphate levels and the right sunlight levels and the right heat. You can get a huge algal bloom on a reef and it can grow on these corals. And these corals will get smothered because light won't penetrate the coral skeleton to get to the zooanthellae. And then usually what you have is you have these species that will eat the algae off the coral and keep the coral, like keep the algae down so you keep the coral intact. But if all those species are picked off by predators because they can't hide in the coral, those corals are vulnerable. You're get less of those species, the predators are gonna go and then you're not gonna have anything to maintain, you know, this coral.

6:33 That's just one example of what happens on a coral reef. It's not the only thing that will... deter a coral or be detrimental to a coral reef, but it helps it helps a lot and there's a lot of debate within coral reef science about what is better, you know, like the algae eaters or the coral eaters and all these kind of things, but you know, it really goes to looking at how we can maintain these reefs in a healthy thing looking at one indicator and I've been a scientist that works with indicators a lot and oftentimes just working with one indicator is not the right indicator to use or it doesn't really speak to overall health. It speaks to one aspect of health. And I'm not saying the scientific community is working off one indicator.

7:14 What this story tells us is that we as citizens, as people who listen to uh health of corals, when we're looking at corals, we have to know that complexity is a big part of reef health and not just coral cover. Right? Because that's what a lot of times, know, journals or uh... articles on the on the internet will kinda give will be like all there's more coral cover here but if it's just flat that is not necessarily saying is going to be healthy Now, if this is the kind of stuff, you know, the clear ocean breakdown that you find helpful, please make sure you're following the show. New episodes are dropping every weekday morning at 5 a.m. Eastern. It's something that I'm looking forward to doing and I want you to be a part of it.

7:57 So as I said before, flattened reefs weaken coral like coastal storm protection, right? Like if we don't have, I'm going start that over. So flattened reefs not only stop corals from growing and is really bad for coral reef health in general, but it's also weak in storm protection. Coral reefs are, because of their structure, as waves come over the coral reef, the wave energy, that force of that energy dissipates. It gets lower and lower and lower, and once it reaches the shore, you're fine. So for instance, when the tsunami in 2004 hit the Indian Ocean, and the coastal parts of the Indian Ocean, those areas that had intact coral reefs, intact mangroves, intact sea grasses did better in terms of less damage and less mortality of people than areas that were degradated.

8:50 Unfortunately, that's just what happened. So keeping the complexity of the reefs make better storm protection, coastal storm protection. And then of course, if you have a flattened reef, fisheries productivity declines with habitat loss. And then of course coral percentage alone is not reliable ecosystem, and it's not a reliable ecosystem metric. So reefs can look alive and still be ecologically diminished. That's the point of this story, of this episode, of this podcast. You know, it's one of those things where we look, we may look, and people who are not around coral reefs all the if you're diving or snorkeling on a coral reef, and you're going from above, say you're snorkeling, and you're...

9:33 maybe 10 or 20 feet above a coral reef. know, obviously people can dive down and look at the complexity there. Those free divers, those amazing people who can hold their breath for a lot longer and go down. Unfortunately, I'm not trained as one of them. But when you look at it from the top and you see just the coral cover, you could be like, actually, this is pretty cool. Like, it looks pretty healthy. And it might indicate a part of health. The coral cover still is important. But the fact that we can't go down and see whether it's three dimensional, whether we see the branching corals, whether we see the stony corals that are like in a boulder or that are flat and that provides those hiding spots for those corals or for those species that are helping those corals, those fish species, those invertebrate species like the shrimp, the worms, the crabs, all those things that that make corals really beautiful and diverse.

10:20 If you don't have that complexity in those hiding spots, those nooks and crannies, you don't have a full time healthy reef. And that is going to degrade faster and easier. than it would if it was three-dimensional. So flat reef will be a lot more vulnerable than a 3D complex reef. So that's why I want to get over on this episode. I think it's really important that you know that. And if you want more focused up ocean updates, five days a week, hit follow now and I will see you tomorrow. Happy conservation.