Thursday, December 31, 2020
Friday, December 18, 2020
Media headlines have been promoting unrealistic fears of ecosystem collapse due to climate change. Such fears get supported when the International Union for the Conservation of Nature (IUCN) designates some ecosystems as endangered, such as Caribbean Coral Reefs. But reefs are resilient and the human factors threatening individual reefs can be remedied.
The Caribbean reef ecosystem consists of thousands of individual reefs spanning from the east coast of Mexico and Central America to Florida and the Bahamas and south to the coast of Venezuela. Fifteen thousand years ago these reefs did not exist because sea level had fallen by 400 feet during the ice age. Modern reefs became established 8,000 years ago by colonizing newly flooded coastlines.
|Caribbean Coral Reef Boundary|
Based on one IUCN criterion the Caribbean reef ecosystem was designated “Least Concern” due to the widespread occurrence of individual reefs. In contrast, the loss of 59% of total coral cover between 1971 and 2006 prompted the IUCN to designate the reef system as “Endangered”.
Coral cover naturally fluctuates with seaweeds (macro-algae). Coral are killed by hurricanes, disease or bleaching, which allows seaweeds too colonize the vacated space. The seaweed is gradually reduced by algae-eating animals which allows coral to return to their former dominance. Coral usually recover within 15 to 20 years, but recently their recovery has been extremely limited thus reducing coral cover. Unlike the demonized sea urchins that threaten Alaska’s kelp forest, algae-eating urchins are vitally important in maintaining the balance between seaweeds and Caribbean coral. The recent lack of coral recovery is largely attributed to a new disease that devastated urchin populations in the 1980s and minimized the urchins’ consumption of seaweeds.
Caribbean corals had been decimated in the 1980s by the novel White Band disease. However, that disease only affected two coral species from the genus Acropora - staghorn and elkhorn coral. Those species are now considered endangered. Acropora’s evolutionary strategy was to quickly colonize vacated shores produced by natural disturbances like hurricanes. These coral species thus dedicated their energy to rapid growth to out compete the seaweeds. That adaptation allowed staghorn and elkhorn coral to rapidly colonize flooded coasts as sea level recovered from the last Ice Age and dominate modern Caribbean reefs. But that strategy required diverting energy from building stronger reefs or resisting disease.
Because Acropora require shallow habitat they’re vulnerable to storm damage. So, they evolved a reproductive strategy that produced new colonies by cloning new coral from storm damaged fragments. However, cloning reduces genetic diversity which also made them more vulnerable to new diseases.
Mortality from bleaching also reduced coral cover. Bleaching from unusually warm temperatures during summer 2005 and the 1998 El Nino is often highlighted. Surprisingly, fatal cold weather bleaching is rarely mentioned. Yet in January 2010 along the Florida Keys, cold weather killed 11.5 percent of the coral, which was 20 times worse than the 2005 warm weather mortality. Understanding why both warm and cold weather causes bleaching provides insight into how coral have successfully adapted to ever changing climates over the past 220 million years.
Shallow water corals depend on photosynthesizing symbiotic algae (aka symbionts) that provide over 90% of the coral’s energy. However, those corals will remove one symbiont species and acquire a new symbiont that is better adapted to the changing weather conditions. During the winter, colder temperatures and less light reduce photosynthesis. So, coral increase their density of symbiotic algae to counteract reduced productivity. But if it is too cold, the symbionts keep their energy supply for themselves. As a result, coral remove the “freeloaders” causing bleaching. A more productive cold?tolerant symbiont must then be acquired, or the coral die.
In contrast during the summer, more light and higher temperatures produce so much energy, coral reduce their number of symbionts. Because photosynthesis also produces potentially harmful chemical by-products, coral remove symbionts to reduce the production of harmful chemicals. That too causes coral to bleach, and unless a better adapted symbiont is acquired, the coral will die. Despite that mortality risk, research now shows by switching their symbionts, coral can quickly adapt to warmer or cooler climates and enhance the species survival.
Studying fossil reefs, scientists determined that Caribbean corals had been declining decades before widespread bleaching and disease outbreaks occurred. Growing human populations cleared the land for farms, sugarcane and banana plantations. Resulting soil runoff reduced water clarity required for efficient photosynthesis. Increased sewage also reduced clarity and introduced pathogens. Those stressors made coral more susceptible to subsequent bleaching and disease. Soil runoff also added nutrients that tipped the ecological balance to favor seaweed growth, while overfishing removed seaweed?eating fish that once restricted seaweed dominance.
We can, and are controlling soil runoff and treating sewage. Fishing regulations are restoring the ecosystem that had balanced seaweeds and coral. And with those protections, naturally resilient coral will steadily recover.
Thursday, December 3, 2020
Over the past few years the media, such as the NY Times, have hyped a coming apocalypse and an existential crisis as ecosystems collapse. Inside Climate News, one of the more egregious fear mongers suggests “Global Warming Could Collapse Whole Ecosystems, Maybe Within 10 Years”. In contrast, most scientists agree ecosystems are very complex and still not well understood. By understanding each ecosystem’s unique pressures from humans, other organisms and natural climate change, perhaps we can make ecosystems more resilient and prevent the alleged "crises".
The International Union for the Conservation of Nature (IUCN), the foremost scientific organization evaluating threats to species and ecosystems, has created the “Red List of Ecosystems” that provides assessments that characterize threats to individual ecosystems. To date, only one ecosystem has collapsed, central Asia’s Aral Sea. It’s the world’s fourth largest inland water body. Landlocked, its fate is determined by the balance between inflowing water and evaporation. But 2000 years of irrigation has disrupted that balance. Between 1950 and 2007, irrigation nearly quadrupled causing the Aral Sea to largely dry up, eliminating most of its species. The Aral Sea has been sacrificed in order to feed a growing population. However most other ecosystems have a more optimistic future.
The first IUCN Endangered ecosystem I’ll examine in a series of articles is Alaska’s giant kelp forests. The fate of kelp forests is largely determined by the interactions between urchins, otters, humans and killer whales. Hungry kelp-eating urchins can quickly convert a kelp forest into an urchin barren stripped of kelp. However, urchins are regulated by their primary predator, sea otters. Before Alaska’s fur trade began in the mid 1700s, otter populations and kelp forests flourished. One hundred and fifty years later overhunting exterminated or reduced all otter populations, urchins proliferated and kelp forests declined. Alarmed, a 1911 international treaty forbade hunting otters. To further their recovery, otters were re-introduced to islands where they had been eliminated. With improved human stewardship, otters rebounded to their pre-hunting abundance by 1980. With fewer urchins, kelp forests flourished again. But then killer whales began overhunting otters.
FIg 1. Extent of Alaska's kelp forests: From the Aleutian Islands in the west to southeastern Alaska.
Each killer whale population has a specialized feeding strategy. Some strictly eat fish while others feed on marine mammals. Some congregate around Alaska’s eastern Aleutian Islands near Unimak pass to prey upon migrating gray whale calves. In the 1980s some killer whales began reducing Steller sea lion and harbor seal populations along Alaska’s Aleutian Islands. An autopsy of one killer whale revealed 14 research tags originally attached to endangered Steller sea lions. As seal and sea lion populations declined, killer whales increased their intake of otters, which allowed urchins to again multiply.
Mostly due to killer whale predation, otter populations declined by 50% to 80% and kelp forests declined by 50% between 1980 and 2000 Those declines prompted the designation of kelp forests as Endangered and possibly Critically Endangered. However more recent surveys evoke hope. Along the coast of Alaska from the peninsula south, otter populations have been steadily increasing at a rate of 12-14% a year and there kelp forests dominate. However depleted otter populations throughout Alaska’s Aleutian Islands still remain at 50% of their 1980 abundance. There, with fewer otters sea urchin barrens became more common.
Although these biological interactions control ecosystem shifts between kelp forests and urchin barrens, climate factors play a role, and in a most positive way. Otters are limited by ice. In places like Glacier Bay where ice has retreated, otter habitat is expanding. Likewise, kelp benefit from less sun-blocking ice while greater concentrations of carbon dioxide enhance photosynthesis and promote more growth. Life is good.
published in Battle Born Media What's Natural column
Jim Steele is Director emeritus of San Francisco State’s Sierra Nevada Field Campus, authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism, and member of the CO2 Coalition