Journal of Fisheries & Livestock Production
Open Access

Although it might be fairer to refer to rainforests as coral reefs on land, coral reefs are frequently referred to as the rainforests of the sea [1]. The importance of coral reefs, like that of rainforests, is not so much in the variety of the corals themselves as it is in the millions of species that dwell mostly or exclusively around them. Veron, for instance, estimates that there are at least 835 species of corals that create reefs, and estimates for the biodiversity of reefs as a whole range from 1 to 9 million.

Coral reefs and contemporary human society do not get along well, unfortunately. The majority of human activities either directly harm corals or harm them inadvertently by negatively affecting interactions with their rivals, predators, viruses, and mutualists [2]. On reefs damaged by human activity, for instance, Edinger and colleagues report losses in coral species diversity ranging from 30 to 60%, with a loss in generic diversity of 25% on two of these reefs in just 15 years. It is therefore challenging to be positive about the health of reefs globally over the short term in light of expanding human populations and economic expansion, even while coordinated measures to safeguard reef ecosystems may halt their steady loss.

Ecological and evolutionary changes on coral reefs, similar to those described for terrestrial and other marine creatures and ecosystems, are inevitable as the globe evolves with increasing human dominance. Coral reefs do benefit from a few things [3]. For instance, many critical reef builders are likely protected from extinction by their widely dispersed larvae and still enormous population levels. Although invasibility may rise with disturbance and the extent to which diversity per se prevents invasions is yet unknown, the variety of coral reef ecosystems may also reduce the likelihood of catastrophic invasions of exotic species [4]. However, it is evident from the fossil record that marine species and ecosystems have their limits, and recent data suggests that these limits may be approached suddenly. For coral reefs, the wider ecological effects of a decline in biodiversity are largely unknown. In fact, we know too little about even the most fundamental physical aspects of climate change that affect reefs.

The particular characteristics of corals and other reef inhabitants that could have an impact on their ecological and evolutionary destiny are the main emphasis of the section below [5]. Since change (and thus a potential glimpse of the future) there has been much larger over the last several decades, the Caribbean is the source of many of the examples. However, the main ideas apply to reefs all around the world.

Broader consequences for biodiversity

It is unknown how much of the richness of healthy coral reef environments-the current homes of the numerous crustaceans, worms, mollusks, bryozoans, and other groups found on reefs-can be sustained by deteriorated reefs and other habitats [6, 7]. Given that the diversity of reef companions is several times greater than that of corals themselves, the following considerations are pertinent: I Are reefs particularly susceptible to environmental change or slow to recover as ecosystems? (ii) Do reef inhabitants have a lower vulnerability than corals themselves? The only reliable information for answering these questions comes from the fossil record of previous extinctions.

Although it is frequently claimed that reef ecosystems are longer to recover and more susceptible to extinction, thorough evaluations are surprisingly rare [8, 9]. Since global change in any direction from the status quo is likely to exacerbate extinction, past extinction events appear to have had a varied range of causes, which is not surprising. This presumably explains why there isn’t a strong prejudice towards tropical habitats in general. Although there isn’t conclusive proof that such ecosystems recover more slowly, it does seem that shallow water, low-nutrient carbonate platforms have been more sensitive than other tropical settings [10]. A small body of evidence also points to the possibility that both the major Oligocene-Miocene extinction and the Cretaceous extinction, which occurred at the end of the Cretaceous period, made photo symbiotic creatures more susceptible to extinction than non-photo symbiotic ones [11]. Since there are no live examples of closely related sister species among the zooxanthellate scleractinian corals on either side of the Isthmus, which are widespread in other groups, corals were also more susceptible to the alterations brought on by the rise of the Isthmus of Panama.

The distributional discrepancies between the groups could be one explanation for this pattern. Many of the creatures that make up coral reefs are not just found there. Of fact, this is also true of corals themselves, which can be seen growing in isolated colonies without forming the intricate, three-dimensional structure that the term “reef” suggests [12]. However, extra reef distributions are probably even more typical among other taxonomic tiers of reef-dwelling organisms. For instance, all fish families regarded as typical of reefs have ranges that extend beyond reefs. In a manner similar to bryozoans, more than 75% of Caribbean species that are linked with reefs can also be found in environments other than reefs [13]. In the event that this turns out to be a common pattern, which seems likely, even the abolition of the majority of coral reef habitats would probably not lead to the extinction of a comparable number of coral reef builders and residents. The above suggests that even the loss of all true reefs would leave many facultative reef associates as survivors, and thus many of the deeper branches of the tree of life intact [14]. There is no taxonomically comprehensive analysis of obligate versus facultative reef associates, but the above suggests that such a loss would leave many facultative reef associates.

Of course, historical extinctions linked to alterations akin to those anticipated for the next century serve as the best predictors of the future. Unfortunately, we don’t have a lot of information to help us [15]. Mass extinctions have been extensively researched, but because they happened in the distant past, the organisms involved had different evolutionary affinities from the ones whose reactions we are trying to predict. Furthermore, although ongoing anthropogenic extinctions are concerning, they do not even come close to matching the magnitude of these cataclysmic occurrences [16]. If they did, Homo sapiens would have far more to be concerned about than the survival of coral reefs. The Oligocene-Miocene and Pliocene-Pleistocene extinctions and their respective cooling episodes rather than global warming are the most pertinent similarities. Nitrification, global warming, and the extinction of top predators not to mention the introduction of novel harmful chemicals is factors that have never before occurred in the last 65 million years [17]. The fact that many of the reef creatures that survived and thrived during the most recent biological upheavals are now suffering the most may not come as a surprise. It’s impossible to predict who will win this time, but we might not be too pleased with the results.

Conclusion

Given all the unknowns, qualitative analogies can be a valuable addition to quantitative assessments. I’ll end with the idea of the “straw that broke the camel’s back” for this reason. Ecological collapse is not “caused” by a single straw; rather, it is impossible to predict based on how the camel reacts to earlier straws. However, once ecological collapse has taken place, the camel does not stand back up when the final straw is withdrawn. Coral reefs’ recent history implies that collapse is not inconceivable and that, in fact, we might be closer to a global collapse than we think. Furthermore, due to the detrimental synergistic effects between many forms of stressors, the weight of the straws is probably multiplicative rather than additive. Like crippled camels, damaged coral reefs offer significantly fewer services and can be extremely expensive to rehabilitate. Emp Reefs have come and gone and come again over the history of life, making them more likely than camels to rebound on their own. However, this is likely to be a very gradual process, and we might not be around to see true reefs when they do return.

1. Davidson OG (1998) The Enchanted Braid (Wiley, New York, 1998).

Google Scholar

2. Reaka-Kudla ML, Wilson DE, Wilson EO (1997) Biodiversity II: Understanding and Protecting Our Biological Resources. Joseph Henry Press 83–108.

Google Scholar , Crossref, Indexed at

3. Wilkinson CR (1999) Global and local threats to coral reef functioning and existence: review and predictions. Mar Freshwater Res 50: 867–878.

Google Scholar , Crossref

4. Vermeij GJ (1991) When Biotas Meet: Understanding Biotic Interchange. Science 253: 1099–1104.

Google Scholar , Crossref, Indexed at

5. Knowlton N (1992) Thresholds and Multiple Stable States in Coral Reef Community Dynamics. Am Zool 32: 674–682.

Google Scholar , Crossref

6. Chapin FS, Zavaleta ES, Eviner VT, Naylor RL, Vitousek PM, et al. (2000) Consequences of changing biodiversity. Nature (London) 405: 234–242.

Google Scholar , Crossref, Indexed at

7. Levitan DR, Petersen C (1995) Sperm limitation in the sea. Trends Ecol Evol 10: 228–231.

Google Scholar , Crossref, Indexed at

8. Courchamp F, Clutton-Brock T, Grenfell B (1999) Inverse density dependence and the Allee effect. Trends Ecol Evol 14: 405–410.

Google Scholar , Crossref, Indexed at

9. Carlon DB (1999) The evolution of mating systems in tropical reef corals. Trends Ecol Evol 14: 491–495.

Google Scholar , Crossref, Indexed at

10. Oliver J, Babcock R (1992) Aspects of the Fertilization Ecology of Broadcast Spawning Corals: Sperm Dilution Effects and in situ Measurements of Fertilization. Biol Bull 183: 409–417.

Google Scholar , Crossref, Indexed at

11. Omori M, Fukami H, Kobinata H, Hatta M (2001) Significant drop of fertilization of Acropora corals in 1999: An after-effect of heavy coral bleaching?  Limnol Oceanogr in press.

Google Scholar , Crossref, Indexed at

12. Guzmán HM, Holst I (1993) Effects of chronic oil-sediment pollution on the reproduction of the Caribbean reef coral Siderastrea siderea. Mar Pollut Bull 26: 276–282.

Google Scholar , Crossref, Indexed at

13. Soong K (1993) Colony size as a species character in massive reef corals. Coral Reefs 12: 77–83.

Google Scholar , Crossref

14. Smith LD, Hughes TP (1999) An experimental assessment of survival, re-attachment and fecundity of coral fragments. J Exp Mar Biol Ecol 235: 147–164.

Google Scholar , Crossref

15. Heyward AJ, Babcock RC (1986) Self-and cross-fertilization in scleractinian corals. Mar Biol (Berlin) 90: 191–195.

Google Scholar , Crossref, Indexed at

16. Hatta M, Fukami H, Wang W, Omori M, Shimoike K, et al. (1999) Reproductive and genetic evidence for a reticulate evolutionary history of mass-spawning corals. Mol Biol Evol 16: 1607–1613.

Google Scholar , Crossref, Indexed at

17. Carlon DB, Olson RR (1993) Larval dispersal distance as an explanation for adult spatial pattern in two Caribbean reef corals. J Exp Mar Biol Ecol 173: 247–263.

Google Scholar , Crossref