Coral-algal relationships, dating back to the age of dinosaurs, have been proven resilient amidst countless climate change events. A study published in the Current Biology journal provides a glimmer of hope that marine reefs could potentially survive the modern era of global warming. It further reveals that these symbiotic relationships are significantly older and more diverse than previously thought.
Understanding Age-old Coral-Algal Relationships
Contrary to past estimates that marked the inception of these partnerships at 50 to 65 million years ago, this study points towards an even longer shared history. Modern corals and their micro-algal partners, popularly known as zooxanthellae, have intertwined existences since the dinosaur era, about 160 million years ago.
Zooxanthellae inhabit the cells of corals, allowing them to harness energy from sunlight and construct massive reef formations. These formations carry immense economic value and offer habitat to myriad marine organisms.
The research team used genetic evidence such as DNA sequences, genome comparisons, and phylogenetic analyses to determine the approximate age of micro-algae’s origin. They also employed traditional morphological techniques – comparing symbionts’ visual characteristics using light and electron microscopy, computer modeling, and other methods. Their findings revealed that the algae family is not only older but also boasts far greater diversity than previously perceived.
Role and Formation of Coral Reefs
Corals are live invertebrate marine animals existing in a symbiotic relationship with microscopic algae, or ‘zooxanthellae.’ Corals shield the algae, which in return feed the coral polyps. The dying corals secrete calcium carbonate forming a hard skeleton that new coral polyps inhabit. Over time, these layers reach the surface, creating table-like structures known as coral reefs.
Favorable Conditions for Coral Growth
Corals thrive in shallow, clean, and warm waters with an average annual ocean temperature of 20-21°C. This confines their range to no more than 30 degrees north and south latitude. Corals also require sufficient sunlight, moderate salinity, calm sea conditions, and waters fed by warm oceanic currents for growth.
Threats to Coral Reefs
The primary threats confronting coral reefs include bleaching, destructive fishing practices, sedimentation, and pollution. Bleaching occurs under abnormal environmental conditions like elevated sea temperatures that cause corals to expel the photosynthetic algae, zooxanthella, thereby draining their color. While the host becomes more susceptible to diseases following algae loss, it can recover if water temperature decreases and the algae can recolonize them.
Destructive fishing practices such as cyanide fishing, blast or dynamite fishing, bottom trawling, and muro-ami pose significant threats to coral reefs, particularly bottom-trawling to cold-water coral reefs.
Sedimentation from erosion caused by construction, mining, logging, and farming increases sediment in rivers, which ends up in the ocean where it can smother corals by depriving them of light necessary for survival. Deforestation of mangrove forests exacerbates the issue by failing to trap large amounts of sediment.
Pollution from urban and industrial waste, sewage, agrochemicals, and oil poisoning are other threats to reefs. Certain pollutants, such as sewage and farming runoff, elevate seawater’s nitrogen level, causing an overgrowth of algae that smothers reefs by obstructing their sunlight.
