The Changing Face of the Ocean Part 1: A Crumbling Foundation

Human actions have radically changed the surface of our world, and I've talked about that a great deal here on Steemit. The surface isn't the only part that's been affected, though- the depths are being changed just as much. Over the course of this series, I'll explore some of the many ways in which we're harming our oceans. First up? Coral reefs.

Part of Australia's Great Barrier Reef. [Image source]

Coral reefs are incredibly complex ecosystems. They take up less than a tenth of one percent of the geographical area of the ocean, and yet one fourth of all marine species are found there. Comparisons to the rainforest are particularly apt. They're the two richest types of ecosystem in biodiversity. They both thrive in surprisingly nutrient rich regions. Both have stunningly complex ecosystem webs that generate far more niches for organisms than are available in less dense ecosystems. Both function in three dimensions more than many other ecosystems. And both are under critical threat from humanity.

To understand the threats coral reefs today face, we should first talk about how coral reefs form. Corals are hard calcarous exoskeletons built by coral polyps. These polyps are Cnidarians- the same phylum that contains sea anemones and jellyfish. Coral polyps breed both sexually and asexually, an extremely effective combination of reproductive strategies. The coral structures themselves are built of calcium carbonate, the raw materials of which the polyps draw from the water around them. Coral polyps have a variety of feeding strategies. Many are filter feeders, using stinging tentacles to capture food. Most corals, however, depend on a symbiotic relationship with photosynthetic unicellular organisms known as zooxanthellae. The corals provide the zooxanthellae a safe place to live in the sun, the zooxanthellae provide the corals with food.

Anatomy of a coral polyp. [Image source]

Corals face a huge number of threats today. First, and most widely publicized, are their two major climate change related threats. The first of these is ocean temperature increases. When the water temperature gets high enough, the coral polyps eject the zooxanthellae living in their flesh. This helps the polyps survive in the short term, but since the zooxanthellae provide the overwhelming majority of their food, it can cause the polyps to starve quickly. As ocean temperatures increase, bleaching events become more and more common. The IPCC considers mass bleaching events to be the single biggest threat to the future of coral reefs. 2016 featured the longest and most severe bleaching episode known.

The second climate change related threat is ocean acidification. Ocean acidification is the sibling of climate change- both are caused by increased CO2 levels in the atmosphere. When it rains, the raindrops pick up CO2 from the atmosphere. They then react with the water to form carbonic acid. This is slowly making the oceans more acidic, when it should be slightly basic. Calcium carbonate, the material coral is made of, is easily soluble in acid. While the ocean has't gotten acidic enough to actively start dissolving coral, it has made it extremely difficult for coral polyps and other shell growing aquatic organisms (clams, for instance) to grow new armor. Ocean acidification also seems to make corals more vulnerable to mass bleaching events.

Coral after a mass bleaching event. [Image source]

Next up we have more direct human damage. Blast fishing is a highly destructive fishing method often used in third world countries. Drop explosives in the water, wait for them to detonate, collect the dead fish that float to the surface. The explosives also wreck the reef. The damage to the reef from a single blast can take 5-10 years to repair itself. Multiple blasts can destroy a section of the reef entirely.

Canal digging and dredging is also extremely harmful to reefs. Since reefs pose a major navigation hazard to ships, canals are often cut straight through the coral. Apart from actively destroying sections of the reef, it acts to divide up the sections of the ecosystem- and shrinking ecosystem size due to barriers (like coral free canals) is a surefire way to reduce its health. Regular dredging of said canals also releases large sediment plumes into the water, which can adversely affect coral reef health.

A healthy coral reef. [Image source]

Overfishing is also harmful to coral reefs. Deep sea trawling involves dragging huge nets across the sea floor. These nets can weigh up to 15 tons, and tend to utterly annihilate deep sea corals. These deep sea corals are primarily filter feeders and don't depend on sunlight to grow. As a consequence of this, they tend to be much slower growing as well, and take much longer to recover. The massive ecological damage of overfishing also harms reefs more indirectly- like any other ecosystem, they're an elaborate web, and damage to one part hurts the rest of it. I'll discuss overfishing more in a later post.

What we do on land is also a huge stressor to corals. Agricultural runoff is threatening coral reefs in a massive way. It causes algal blooms that suck the oxygen out of water as well as directly poisoning reefs. Likewise, heavy metal rich industrial runoff is causing severe damage. One of the most deadly threats from land based runoff is quite surprising: sunscreen. Many common sunscreen formulations are highly toxic to corals, promoting viral infections and contributing to bleaching events. If you're going to the beach, make sure to wear suncreens that contain titanium dioxide or zinc oxide- they're less harmful than many other sunscreens.

More bleached corals. [Image source]

The threats to coral reefs are extreme, but there are actions we can take to protect these delicate ecosystems. Establishing and growing new marine protective reserves and then enforcing and patrolling them is a key step. Being more cautious of our waste products being dumped into the ocean is another. The most important, however, is a course of action that provides direct advantages to in other ways as well: Regulating and limiting our greenhouse gas emissions.

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Bibliography:

The Reef: A Passionate History, by Iain McCalman
The Sixth Extinction, by Elizabeth Kolbert
The Ocean of Life: The Fate of Man and the Sea, by Callum Roberts
https://en.wikipedia.org/wiki/Coral_reef
https://en.wikipedia.org/wiki/Coral
https://en.wikipedia.org/wiki/Zooxanthellae
https://en.wikipedia.org/wiki/Coral_bleaching
https://en.wikipedia.org/wiki/Blast_fishing
https://en.wikipedia.org/wiki/Overfishing