50% Of The Great Barrier Reef Is Now Dead Or Dying, 93% Is Bleached
The news keeps getting worse for the world’s greatest coral reef system. Fresh on the heels of news that most of the Great Barrier Reef (GBR) has bleached comes the announcement that more than half of the coral in the reef has died this summer. Prospects look grim for most of the rest.
When corals are stressed by disease, pollution, or overheating, they expel their symbiotic microalgae. Microalgae give corals their beautiful colors. Without them, they become bright white in a process known as bleaching. Bleached corals are in danger, but not yet dead. If the source of their stress passes quickly, they can absorb new symbionts – sometimes finding microalgae more resistant to the stressor.
The symbionts are crucial to corals, passing on 90 percent of the energy they trap from sunlight to their host. Without its principal food source, coral is outcompeted by other organisms. If the bleaching event lasts too long, the corals become overgrown by opportunistic species that form the basis of far less productive ecosystems, which can be hard to displace once established. The white corals become a scuzzy brown-green.
Bleached corals are so bright that aerial surveys show 93 percent bleaching. Picking up signs of coral death is harder, but dive teams have been looking at sample locations and are seeing well over 50 percent coral deaths. The extent of the damage varies with how far, and how long, temperatures exceeded normal maxima. Inshore reefs where water has ponded have higher mortalities. Where there are more currents, temperatures have been lower, but even a lot of the outer edge reefs have been very affected. The southern winter will bring relief, but it may come too late to save more than a small fraction of what was once a wonder of the world.
From the tip of Cape York to the Whitsundays, the Great Barrier Reef in the east to the Kimberleys in the west and Sydney Harbor in the south, Australia’s corals are bleaching like never before. This is the worst coral bleaching episode in Australia’s history, with reports of coral dying in places that we thought would be protected from rising temperatures.
Bad as the news is, the reef is not beyond salvation. We will definitely see a degraded reef, however, if the world stops pumping out more CO2, temperatures will stabilize. Corals will be rare, but if we have not wiped them out entirely, they will eventually come back. It is possible to protect small reefs using shade cloth, something that may be viable around tourist resorts, and replanting reefs with coral bred for heat tolerance. The Great Barrier Reef is the size of Italy, so to contemplate replacing corals that have been lost is unrealistic.
BOX JELLYFISH
Box jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their cube-shaped medusae. Some species of box jellyfish produce extremely potent venom: Chironex fleckeri, Carukia barnesi and Malo kingi. Stings from these and a few other species in the class are extremely painful and can be fatal to humans. At least 36 species of box jellyfish were known as of 2007. These are grouped into two orders and seven families.
Anatomy. The medusa form has a squarish, box-like bell. From each of the four lower corners hangs a short stalk which bears one or more long, slender, hollow tentacles. Some species have tentacles that can reach up to 3 m (9.8 ft) in length. Box jellyfish can weigh up to 2 kg. It creates a powerful jet when the bell pulsates and can move up to six meters per minute. In the center of the underside of the bell is a mobile appendage called the manubrium with the mouth.
The box jellyfish’s nervous system is more developed than that of many other jellyfish. A nerve ring around the base of the bell coordinates their pulsing movements. They possess true eyes, complete with retinas, corneas and lenses. Their eyes are set in clusters called rhopalia, located in pockets halfway up the outer, flat surfaces of the bell. Each contains two rhopalial ocelli with lenses, one directed upwards and the other downwards and inwards towards the manubrium. This enables the animal to see specific points of light, as opposed to simply distinguishing between light and dark. Box jellyfish also have twenty ocelli (simple eyes) that do not form images, but detect light and dark; they therefore have a total of twenty-four eyes.
Distribution. The notoriously dangerous species are restricted to the tropical Indo-Pacific region. Various species in tropical and subtropical oceans as far north as California, the Mediterranean Sea, Japan, South Africa and New Zealand.
Age and growth. The statoliths, composed of calcium sulfate hemihydrate, exhibit clear sequential incremental layers laid down on a daily basis to estimate growth rates, ages, and age to maturity. A fully grown box jellyfish can measure up to 20 cm (7.9 in) along each box side (or 30 cm (12 in) in diameter), and the tentacles can grow up to 3 m (9.8 ft) in length. Its weight can reach 2 kg. There are about 15 tentacles on each corner. Each tentacle has about 500,000 cnidocytes, containing nematocysts, a harpoon-shaped microscopic mechanism that injects venom into the victim.
Behavior. Box jellyfish display complex visually guided behaviours such as obstacle avoidance and fast directional swimming and have been described as having an active, fish-like behaviour. The box jellyfish actively hunts its prey (small fish), rather than drifting as do true jellyfish.
The venom of cubozoans is distinct from that of scyphozoans, and is used to catch prey (small fish and invertebrates, including prawns and bait fish) and for defence from predators, which include the butterfish, batfish, rabbitfish, crabs (blue swimmer crab) and various species of turtle including the hawksbill sea turtle and flatback sea turtle. It seems that sea turtles are unaffected by the stings because they seem to relish box jellyfish.
Danger to humans. Although the box jellyfish has been called “the world’s most venomous creature”, only a few species in the class have been confirmed to be involved in human deaths, and some species pose no serious threat at all. For example, the sting of Chiropsella bart only results in short-lived itching and mild pain. In Australia, fatalities are most often perpetrated by the largest species of this class of jellyfish, Chironex fleckeri. The venom causes cells to become porous enough to allow potassium leakage, causing hyperkalemia, which can lead to cardiovascular collapse and death as quickly as within 2 to 5 minutes.
In Australia, C. fleckeri has caused at least 64 deaths since the first report in 1883, but even in this species most encounters appear to only result in mild envenoming. Most recent deaths in Australia have been in children, which is linked to their smaller body mass. In parts of the Malay Archipelago, the number of lethal cases is far higher (in the Philippines alone, an estimated 20-40 die annually from Chirodropid stings), likely due to limited access to medical facilities and antivenom, and the fact that many Australian beaches are enclosed in nets and have vinegar placed in prominent positions allowing for rapid first aid. Box jellyfish are known as the “suckerpunch” of the sea not only because their sting is rarely detected until the venom is injected, but also because they are almost transparent.
In northern Australia, the highest risk period for the box jellyfish is between October and May, but stings and specimens have been reported all months of the year. Similarly, the highest risk conditions are those with calm water and a light, onshore breeze. In Hawaii, box jellyfish numbers peak approximately seven to ten days after a full moon, when they come near the shore to spawn.
Treatment of stings. Once a tentacle of the box jellyfish adheres to skin, it pumps nematocysts with venom into the skin, causing the sting and agonizing pain. Flushing with vinegar is used to deactivate undischarged nematocysts to prevent the release of additional venom.
Removal of additional tentacles is usually done with a towel or gloved hand, to prevent secondary stinging. Tentacles can still sting if separated from the bell, or after the creature is dead. Removal of tentacles may cause unfired nematocysts to come into contact with the skin and fire, resulting in a greater degree of envenomation.
Although commonly recommended in folklore and even some papers on sting treatment, there is no scientific evidence that urine, ammonia, meat tenderizer, sodium bicarbonate, boric acid, lemon juice, fresh water, steroid cream, alcohol, cold packs, papaya, or hydrogen peroxide will disable further stinging, and these substances may even hasten the release of venom. Heat packs have been proven for moderate pain relief. Pressure immobilization bandages, methylated spirits, or vodka should never be used for jelly stings. In severe Chironex fleckeri stings cardiac arrest can occur quickly.
Protection during swimming or diving. Wearing pantyhose or full body lycra suits during diving (both by women and men, also under scuba-diving suit) is an effective protection against box jellyfish stings. The pantyhose were formerly thought to work because of the length of the box jellyfish’s stingers (nematocysts), but it is now known to be related to the way the stinger cells work. The stinging cells on a box jellyfish’s tentacles are not triggered by touch, but are instead triggered by the chemicals found on skin.
