The Problems with Coral Reefs
Martin Moe
In the first two decades, the 60s and 70s, of the six decades of my career as a marine/fisheries biologist and marine aqua culturist in Florida, the coral reefs of the third largest coral reef system located off the Florida southeast coast were spectacular. That changed in 1984. At that time, a plague caused by a bacterium distributed through currents roared through the western mid-Atlantic and directly affected only one species of marine animal. That plague created the greatest, and by that, I mean the most rapid decline of coral reefs in the history of western central Atlantic (Caribbean, Bahamas, and Florida). The result was the loss of 95 to 98 percent of the populations of Diadema antillarum, the long-spined sea urchin, throughout this vast oceanic area in 1983/4. This species of sea urchin is (was) the keystone herbivore on the coral reefs of this part of the western Atlantic. The coral reefs of this vast area that were kept in an ecological balance by the herbivory of Diadema were quickly overgrown by algae.
The decline was slow at first, the reefs in the 60s and 70s were still amazing. Regulations were few, and although some troubling signs were present and efforts were underway to understand and protect the reefs, there were still few regulations beyond protection of commercially valuable fish and invertebrate fishery resources.
The causations of coral reef decline can be attributed to many physical and chemical changes that have affected the broad ecology of these coral reefs, but the short and encompassing major reason for coral reef decline was aptly described by Walt Kelly in the comic strip “Pogo”, when the astute possum he created uttered the phrase “We have seen the enemy, and he is us”. (Walt Kelly, 1972) Even though the details of terrestrial, atmospheric and oceanic decline are examined and explained in hundreds, actually thousands, of scientific and popular communications, three numbers are all that is needed to tell the tale of environmental decline. The estimated numbers of human beings on our Earth in 1927 was 2.0 billion, in 2020 it was 7.8 billion, and for 2050 the estimate is that world population will be 9.7 billion people. These are estimates of course, but the natural ecology and ecosystems of the world are obviously in serious decline trying to support a vast and growing population of just one species, Homo sapiens; and the physical and chemical insults and limitations produced by this species are rapidly closing the door to a good future for Earth and humanity.
Natural events and changes in terrestrial and oceanic ecosystems, excluding giant meteor strikes, are slow and steady over many thousands, even millions, of years. In contrast, the boot prints of humanity on the ecosystems that develop, support, and change the overall, compartmentalized, and interactive ecologies of life on Earth are swift, intense, and usually reach far beyond the human intent of their desired effect.
Many of us are doubtful that humanity will be able to correct the ecological sins of our past in time to reverse the train of ecological disaster that our human expansion and technological development is releasing on our global ecosystems. But we must make our best social, economic, political, and technical efforts to do so. Failure is not an option; it would result in total disaster for humanity.
Coral reefs are often described as the “canary in the coal mine” when decline of oceanic ecosystems are discussed. They are a focus of life in the shallow, most productive areas of our oceans. There are many efforts, many programs, dedicated to preservation of these endangered marine ecosystems. The greatest of these efforts are toward the protection, reproduction, and reestablishment of coral species, the keystones of coral reef ecosystems. Sometimes, though, these efforts focus so strongly on the corals themselves, that preservation and repair of the ecosystems of coral reefs, essential to the existence of these reefs is neglected.
Coral reefs can not be protected unless their entire ecosystems are considered, defined, and protected. We may now be in a position where coral reefs can not be restored to even a shadow of their former glory within a relatively short timeline, say 50 to 100 years. It is still very early in this unprecedented decline of oceanic ecosystems. There are many great problems external to coral reefs that must be corrected. Temperature increase in oceanic waters is part of climate change which must be halted. Every possible effort must be made to reduce and eliminate chemical pollutants in marine waters, because the presence of very small amounts, some obvious and some occult, can affect growth and reproduction of coral reef organisms. Other problems stem from human terrestrial development that encroaches upon coral reef ecosystems, human introduction of alien life that disrupts ecosystems balanced by eons of interactive evolution, anthropogenic introduction of nutrients and bacteria that disrupt and destroy the life and ecology of coral reefs, and occurrence and distribution of various coral diseases that spread trough reefs. These and other negative conditions are not easily corrected. It may be that the best we can do at this time is to protect selected areas that are a part of extensive coral reef ecosystems as “reservoirs” of coral reef life maintained as normal as possible for the extended future.
These identified, protected, and managed reservoirs of coral reef life would be preserved as small ecosystems that will function as research stations and genetic banks for future ecosystem expansion. Such a program will also allow experimentation in the best possible environmental conditions with genotypes that can be selected for survival characteristics in changing environments such as increasing temperatures. If we can stem the progress of coral reef decline in at least a few natural areas, we can keep the basic ecological structure of coral reefs reasonably intact for rejuvenation and expansion in a better world. One of the most important aspects in the creation and maintenance of restored coral reef reservoirs would be the addition and maintenance of the ecological function of herbivory.
Observations on coral reefs in the Florida Keys commonly reported that where Diadema urchins were present, coral cover was considerably greater and algae cover much lower than on reefs with little or no presence of these urchins. It was important to analyze and document the effects of Diadema herbivory. I was part of a study done for the Florida Keys National Marine Sanctuary in 2001/2003 in the Upper Florida Keys. This study restored pre plague populations of Diadema (about one per square meter), to two isolated coral patch reefs and maintained that population for one year. Two similar patch reefs in the general area were identified as control reefs without additions of juvenile Diadema urchin populations.
The ecology of these reefs was analyzed in great detail including presence and growth of corals and algae by the NOAA National Undersea Research Center (NURC). This was done before placement of Diadema on the experimental reefs at a density of 1 per square meter, and then again one year later. The analysis of reef ecology was extensive and highly detailed. As was expected, the presence of corals increased and algae cover declined greatly on the experimental reefs with the enhanced presence of the herbivorous urchins, and the opposite occurred on the control reefs. From the ecological analysis…
“The magnitude of change in percent coral cover on the experimental sites (9.8% to 15.3%) was +5.5% absolute and +56% relative. Coral cover on the control patch reefs declined from 9.1% to 6.8%, representing a –2.4% absolute change and –26% relative change during the study.” And “The coverage of brown foliose algae, primarily represented by Dictyota spp., greatly declined on experimental patch reefs (Figure 5), especially at experimental site #1, where coverage decreased from 11% to 1.8%. Overall, the coverage of brown foliose algae on experimental sites decreased from 10% to 5.1%, representing a –4.9% absolute decline and –48.7% relative decline. In contrast, control sites either exhibited no change or an increase in coverage of brown foliose algae (Table 9).” The complete text of the two papers on the results of the project is available online.
The next step in the prospect to return herbivory to Florida Keys reefs was to restore Diadema urchins in ecologically functional numbers and maintain their populations on the reefs by adding urchins as needed. It was not possible to do this through translocation of urchins since they had not rebounded from the great plague and their numbers were still minimal. The obvious answer was to develop the technology for spawning and rearing the larvae through metamorphosis in a land-based laboratory/hatchery. This was not an easy undertaking because they were difficult to spawn and no technology had been developed for mass rearing of this species. I took this task upon myself and built a small aquaculture laboratory in my house on Lower Matecumbe Key in the Florida Keys. It took many years and great effort, but I was successful in developing a basically functional technology for the spawning and larvae rearing of large numbers of Diadema antillarum. I could not continue into the next step of the project, resolution of the remaining problems and consistent production of large numbers of larvae for experimental placement on coral reefs. The project has been picked up by the Center for Conservation of the Florida Aquarium that is beginning to supply juveniles to institutions in Miami and the Florida Keys. A book describing this work with Diadema is currently in publication by Ricordea Publishing from Miami, Florida.
In closing, it is possible to return the function of herbivory to the coral reefs of the western mid Atlantic. It will be done.