Bright Before Dark
Kelli Tesh | December 2018
A few years ago I had the opportunity to travel to Mexico. I hoped to be able to experience the vividness of the coral reefs scattered along its coast. Bright, colorful, teeming with life, and resembling the exquisite underwater beauty one could expect to see in a July calendar picture. I wanted to witness the wonders of these mysterious creatures; carnivorous animals, yet plantlike in nature. The beaches of Akumal, Mexico were full of sunburned tourists, dressed in bathing suits with towels slung over their shoulders. My sister and I borrowed some life jackets, slipped those dorky, wide eyed goggles over our eyes, and swam out to a roped off section of the ocean expecting to see fish, coral, sea turtles and manta rays.
I stuck my goggles beneath the water’s surface and saw nothing that resembled the calendar picture scenery I had imagined. Brown, dead coral covered the ocean floor. A few tropical fish made their way across the oceanic desert. I swam a little closer to the ocean floor and managed to catch a glimpse of color. The brightest purple sprang up from the brown, shriveled skeletons. It was a small coral, about four or five inches in height, glowing the brightest shade of purple I had ever seen (I would later find out that the color intensity was the result of fluorescence, a chemical condition certain coral species undergo when they have been bleached and must protect themselves from intense sunlight). Disappointed and confused about coral graveyard, I swam ashore.
It was this tropical, apocalyptic experience that inspired the research for this paper. I felt compelled to share the narrative of coral reefs, specifically the story of a species that may have been found among the remains of the reef I visited. Staghorn coral, Acropora Cervicornis, is one of the most critically endangered species of coral in the Caribbean. It is thought to have evolved in the Paleocene about 55 to 65 million years ago, and had since come to dominate Caribbean reefs within the past 500,000 years. Each colony tends to grow in “thickets” that provide an intricate habitat for marine organisms that seek protection or prey. Staghorn Coral holds the title for one of the fastest growing corals, capable of growing eight inches per year. Each coral grows one to three inch thick antler-like branches that are generally light tan or pale brown in color. The color of the coral, however, largely depends on the pigments of algae that live within the coral tissues, a result from coral-algal mutualisms.
Staghorn Coral are typically found on limestone ridges or hard bottom surfaces, fortifying rubble and stabilizing sediment which protect the coastline from erosion. Staghorn Coral contributes to habitat formation, species interactions, and human livelihoods, who rely on reef habitat as a source of protein. Coral reefs worldwide gain about 172- 375 billion annual economic revenue through ecotourism, fishing, and ornamental harvesting. Consequently, ecotourism, fishing, and ornamental harvesting all pose threats to the health of the coral reefs and risk its sustainability.
Coral reefs are often referred to as “oases” because they tend to thrive in nutrient deficient coastal areas. Corals reproduce both sexually, through sperm and egg releases that correspond with environmental triggers, and asexually, through fragments. Sexual reproduction occurs when coral eggs become fertilized and develop into planktonic larvae. When the larvae settle on the ocean floor it undergoes a metamorphosis, transforming itself into a single, soft bodied polyp. Coral polyps multiply themselves literally from the ground up. They use calcium carbonate to form skeletons around themselves for protection. When coral polyps feel threatened, they will retract into their skeleton much like how turtles retract into their shell. The reason for their survival despite the lack of nutrients is attributed to the mutualism between coral and algae called zooxanthellae. The zooxanthellae live inside the coral’s tissues, capture sunlight to convert into energy, which the then coral use to get nutrients. Another way coral captures nutrients is through tentacles that extend from the polyps. Each tentacle contains an electrifying cell called nematocysts that are used to feed on free floating plankton.
Major threats to Staghorn Coral result from stressors that cause the relationship between coral and zooxanthellae to disband. Corals are temperature sensitive, only cooperating with algae 1-2 degrees Celsius below their upper temperature threshold. As ocean temperatures rise, algae ramps up its photosynthesizing, producing more oxygen within coral tissues. Increased oxygen levels create toxic environments for the coral. For this reason, corals often expel the very mutualism they need to capture nutrients for survival. Since algae pigmentation is what primarily gives coral its color, once they’re expelled, coral appear to be bleached.
Ocean acidification is another anthropogenic effect which negatively affects coral. Corals are reliant on calcium carbonate to form their skeletons for protection, growth, and reproduction. With more carbon dioxide being absorbed by the ocean, more carbonic acid consequently replaces calcium carbonate in coral environments. Carbonic acid dissolves the skeletal protection surrounding the corals and significantly slows down their growth and reproduction rates.
A final threat against coral is its resistance against natural diseases. Just like how humans become sick when under severe levels of stress and environmental pressure, corals experience physiological stress from ocean acidification and warming which leave them vulnerable to disease. The first sighting of coral bleaching was seen in the 1980s, the same time when white band disease wiped out 90-95% of the Staghorn Coral population, officially making it a critically endangered species.
Several efforts have been taken to increase the reproduction of Staghorn Coral, including coral nurseries and fragmentation research. Despite the coral’s success in controlled aquarium environments, once “transplanted” into the coastal nurseries, many of the corals do not develop well enough to increase Staghorn populations. By continuing the “business-as-usual” economic model, which fails to enforce international regulations on anthropogenic CO2 emissions, the human population has failed to respond to the silent cry from coral reefs.
Just like the lone purple coral I saw off the coast of Mexico, Staghorn Coral may never recover from the impacts it has suffered. Instead, many of the coral reefs may emit a final glow of bright color before dying from a rapidly changing environment.
Kelli Tesh | December 2018
A few years ago I had the opportunity to travel to Mexico. I hoped to be able to experience the vividness of the coral reefs scattered along its coast. Bright, colorful, teeming with life, and resembling the exquisite underwater beauty one could expect to see in a July calendar picture. I wanted to witness the wonders of these mysterious creatures; carnivorous animals, yet plantlike in nature. The beaches of Akumal, Mexico were full of sunburned tourists, dressed in bathing suits with towels slung over their shoulders. My sister and I borrowed some life jackets, slipped those dorky, wide eyed goggles over our eyes, and swam out to a roped off section of the ocean expecting to see fish, coral, sea turtles and manta rays.
I stuck my goggles beneath the water’s surface and saw nothing that resembled the calendar picture scenery I had imagined. Brown, dead coral covered the ocean floor. A few tropical fish made their way across the oceanic desert. I swam a little closer to the ocean floor and managed to catch a glimpse of color. The brightest purple sprang up from the brown, shriveled skeletons. It was a small coral, about four or five inches in height, glowing the brightest shade of purple I had ever seen (I would later find out that the color intensity was the result of fluorescence, a chemical condition certain coral species undergo when they have been bleached and must protect themselves from intense sunlight). Disappointed and confused about coral graveyard, I swam ashore.
It was this tropical, apocalyptic experience that inspired the research for this paper. I felt compelled to share the narrative of coral reefs, specifically the story of a species that may have been found among the remains of the reef I visited. Staghorn coral, Acropora Cervicornis, is one of the most critically endangered species of coral in the Caribbean. It is thought to have evolved in the Paleocene about 55 to 65 million years ago, and had since come to dominate Caribbean reefs within the past 500,000 years. Each colony tends to grow in “thickets” that provide an intricate habitat for marine organisms that seek protection or prey. Staghorn Coral holds the title for one of the fastest growing corals, capable of growing eight inches per year. Each coral grows one to three inch thick antler-like branches that are generally light tan or pale brown in color. The color of the coral, however, largely depends on the pigments of algae that live within the coral tissues, a result from coral-algal mutualisms.
Staghorn Coral are typically found on limestone ridges or hard bottom surfaces, fortifying rubble and stabilizing sediment which protect the coastline from erosion. Staghorn Coral contributes to habitat formation, species interactions, and human livelihoods, who rely on reef habitat as a source of protein. Coral reefs worldwide gain about 172- 375 billion annual economic revenue through ecotourism, fishing, and ornamental harvesting. Consequently, ecotourism, fishing, and ornamental harvesting all pose threats to the health of the coral reefs and risk its sustainability.
Coral reefs are often referred to as “oases” because they tend to thrive in nutrient deficient coastal areas. Corals reproduce both sexually, through sperm and egg releases that correspond with environmental triggers, and asexually, through fragments. Sexual reproduction occurs when coral eggs become fertilized and develop into planktonic larvae. When the larvae settle on the ocean floor it undergoes a metamorphosis, transforming itself into a single, soft bodied polyp. Coral polyps multiply themselves literally from the ground up. They use calcium carbonate to form skeletons around themselves for protection. When coral polyps feel threatened, they will retract into their skeleton much like how turtles retract into their shell. The reason for their survival despite the lack of nutrients is attributed to the mutualism between coral and algae called zooxanthellae. The zooxanthellae live inside the coral’s tissues, capture sunlight to convert into energy, which the then coral use to get nutrients. Another way coral captures nutrients is through tentacles that extend from the polyps. Each tentacle contains an electrifying cell called nematocysts that are used to feed on free floating plankton.
Major threats to Staghorn Coral result from stressors that cause the relationship between coral and zooxanthellae to disband. Corals are temperature sensitive, only cooperating with algae 1-2 degrees Celsius below their upper temperature threshold. As ocean temperatures rise, algae ramps up its photosynthesizing, producing more oxygen within coral tissues. Increased oxygen levels create toxic environments for the coral. For this reason, corals often expel the very mutualism they need to capture nutrients for survival. Since algae pigmentation is what primarily gives coral its color, once they’re expelled, coral appear to be bleached.
Ocean acidification is another anthropogenic effect which negatively affects coral. Corals are reliant on calcium carbonate to form their skeletons for protection, growth, and reproduction. With more carbon dioxide being absorbed by the ocean, more carbonic acid consequently replaces calcium carbonate in coral environments. Carbonic acid dissolves the skeletal protection surrounding the corals and significantly slows down their growth and reproduction rates.
A final threat against coral is its resistance against natural diseases. Just like how humans become sick when under severe levels of stress and environmental pressure, corals experience physiological stress from ocean acidification and warming which leave them vulnerable to disease. The first sighting of coral bleaching was seen in the 1980s, the same time when white band disease wiped out 90-95% of the Staghorn Coral population, officially making it a critically endangered species.
Several efforts have been taken to increase the reproduction of Staghorn Coral, including coral nurseries and fragmentation research. Despite the coral’s success in controlled aquarium environments, once “transplanted” into the coastal nurseries, many of the corals do not develop well enough to increase Staghorn populations. By continuing the “business-as-usual” economic model, which fails to enforce international regulations on anthropogenic CO2 emissions, the human population has failed to respond to the silent cry from coral reefs.
Just like the lone purple coral I saw off the coast of Mexico, Staghorn Coral may never recover from the impacts it has suffered. Instead, many of the coral reefs may emit a final glow of bright color before dying from a rapidly changing environment.