What is the non-local impact of a large-scale destruction of coral reefs?

Question

I'm reading today that the "bleaching" of coral reefs is progressing with unanticipated speed. Bleaching is occurring at a scale which was previously believed to be decades in the future.

Bleached corals, according to the article in the New York Times¹, have shed their symbiotic algae in order to protect themselves from toxins the algae produce when the water temperature rises above a certain threshold. If cooler temperatures are not restored quickly, the corals will die. This has happened with many affected reefs in the past and seems likely with the latest wave of bleaching too, given the apparent long-term increase in global water temperatures.

Even if the article does not say so directly it appears to me a distinct possibility that most coral reefs will simply disappear from the planet within just a few decades.

What impact will the disappearing of the coral reefs have on the oceans and the life in them, and ultimately on the whole planet? We know that reefs are the core of a complex and rich ecosystem. Which plants and animals outside the immediately affected areas depend on it? Are there migratory species who lose the reefs as a seasonal base? Which food chains will be interrupted, or over-provided? Do coral reefs have other functions like filtering, causing or reducing turbulence, influencing currents? Have there been studies or simulations which try to assess the global consequences?

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[Edit]: I know the question is very broad. I'd be happy about answers to just one aspect. Specifically I'm interested in effects which are not obvious and/or have not been broadly publicized. Links to scientific publications would be awesome. Maybe somebody is working in the field, or knows somebody?

For example, affecting migratory species (fish or birds) may have unexpected consequences in otherwise unrelated parts of the world, similar to the effect of disappearing wetlands on migratory birds.

I also think it's possible that non-reef fish which are important food sources directly or indirectly depend on coral reefs. Are there specific examples?

I'm less interested in answers concerning species just living around the reef because cause and effect (though significant) are obvious.

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_{¹Which refers to the original study in this nature article.}

Answer 1

Disclaimer: the question is too broad and speculative to some extent, and thus less likely to get complete answer (at least in a single post).

As is already known, thousands (or millions) of species are dependent on coral reefs for their survival and are likely to get extinct (unless they adapt) because of destruction of coral reefs. A short list includes fishes, turtles, sharks, eels, crabs, shrimps, urchins, sponges, algae, and so on¹. Now, telling which of them will be immediately affected will be largely speculation, yet the first 5 species to lose the race, as per a speculation, are²:

1. Butterfly Fish: Species of fish that are obligate corallivores, such as many butterfly fishes (Chaetodontidae), feed exclusively on coral polyps. Obviously, survival would not look good for these fish if their food source disappeared. Like parrotfish, butterflyfish assist in keeping algae from smothering corals.

   

2. Spiny Lobsters: Spiny lobsters rely on coral reefs for protection, especially during their vulnerable molting episodes. These lobsters have a significant role in maintaining a balanced ecosystem. Like sea otters, spiny lobsters are predators of sea urchins, which feed on kelp forests and can destroy them if populations are not predator-controlled. Kelp is important for many reasons, including those listed on OGP’s kelp recipes.

   

3. Whales (and dolphins): Many scientific studies have substantiated that dolphins and whales have extreme emotional intelligence. Sadly, their intellect won’t be enough to help these animals if coral reefs are destroyed. Dolphins and most whales (cetaceans) are predatory animals and they are all carnivorous. It’s a fish eat fish world and many fish survive by consuming fish that rely on coral reef habitats. Every species lost will affect another…and another…and many others. So, these come under the indirect adverse effects of coral depletion, since they themselves don't rely on corals.

   

4. Whale Sharks: Whale sharks are an important indicator of marine productivity and have a role in the conservation of other marine organisms. Although there has not been adequate research to understand why whale sharks are dependent on coral reefs, it has been shown that decreases in whale shark populations in the late 1980’s and early 1990’s may have been linked to increased rates of coral destruction.

   

5. Hawksbill Sea Turtles: Although all sea turtles would be affected by the loss of corals, Hawksbill sea turtles have become critically endangered species and are highly dependent on coral reefs for their food sources, mainly consisting of sponges. Sea turtles play significant roles in their ecosystems in that they help with nutrient cycling from ocean to land, maintaining healthy sea grass beds, and balancing food webs.

   

Coral reef fishes are in general rather sedentary and territoriality and home range behavior patterns are highly developed. However, many species migrate, often relatively long distances compared to body size and often with spectacular precision. Migrations in reef fishes may be associated with³:

1. Life history: movements of planktonic larval stages to reefs or movements of juveniles from nursery areas to reefs

2. Seasons: precisely timed spawning aggregations drawing fishes to particular locations from wide areas of the reef

3. Diel patterns: movements to and from feeding or resting areas associated with dawn and dusk.

Another species, which is to be affected, though not immediately, by destruction of corals, is humans(!). As per experts⁴, coral depletion will bring threat to not only income and economic stability, but also to survival by causing depletion of food and increased risk of coastal disasters, which are likely to kill millions.

Coral reefs also serve many purposes, a few of which are⁵:

• protect coastlines from the damaging effects of wave action and tropical storms

• provide habitats and shelter for many marine organisms

• are the source of nitrogen and other essential nutrients for marine food chains

• assist in carbon and nitrogen fixing

• help with nutrient recycling.

Finally, I suppose most of the species will be affected because of depletion of source of food rather than more-than-sufficient amount of something. Also, I was unable to find any simulations of the global consequences of destruction of coral reefs. I hope this much would help!

EDIT: I did some online research, and found lack of research about this topic. But I found a paper regarding relationship between seagrass, mangroves and coral reefs⁶ regarding life cycle of migratory fishes. From the same:

Coral reefs showed the highest mean fish species richness and were dominated by adult fish, while juvenile fish characterized seagrass beds and mangrove sites...Our results suggest that connectivity of seagrass, mangrove, and coral reef sites at a species and site levels, should be taken into consideration when implementing policy and conservation practices.

It becomes evident from this research that depletion of coral reefs would certainly affect life cycles of these fishes, which include Scarus iseri (Striped Parrotfish) and Lutjanus apodus (Schoolmaster Snapper), which will, in turn, affect biodiversity in seagrass beds and mangroves, leading to further break in food chain in more diverse areas.

Some researches have also suggested that seabirds might also be on a high rank in this list. Seabirds survive by eating fishes, and studies have shown that increasing water temperatures halt their growth while higher sea levels cause them problems in nesting. Now, it has also been suggested that due to coral bleaching, many fish species which live on corals might either die or move to other places, because of which seabirds could also face survival crisis⁷.

Another point regarding your demand I'm interested in effects which are not obvious and/or have not been broadly publicized, specifically not been broadly publicized, is that it has now become difficult to find such papers. This topic (climate change) has become so much publicized now that all related papers get attention immediately. So, it is quite difficult to find environmental research papers about climate change which hasn't gained much attention. Yet, I'll keeping on adding more research papers as I find some more.