Reinhold Leinfelder's online reef lecture

Some information on the reef check initiative:

There are a lot of attempts and programs to check the state of modern reefs. These 'checkups' are run by scientists, in part with very sophisticated tools. Although they are most important, the do not easily give an overview of the global state of reefs since reef scientists (especially those with a job) belong to some rare species, and targets can therefore be mostly at a local scale, so comparison between reefs is difficult. This is why an attempt was made to examine as many reef sites each year at the same time with the same methods on a global base. This naturally would involve more scientists than available, so the approach was to train interested recreational divers to join in checking the reefs. The first worldwide reef check action was performed 1997 on occasion of the Interational Year of the Reef (IYOR 1997) which was a global initiative by reef scientists all over the world. Reef check is an initiative where reef researchers cooperate with recreational divers to perform a world wide annual checking of the health state of reefs based on easy-to-learn, simple, but efficient methods, such as counting critical indicator species per square unit, density of coral protection, signs for bleaching or others. As an example I'll present some examples from this first initiative.

In 1997 300 reefs were analised by a team of 750 recreational divers and 100 reef scientists. Testing area per reef was about 800 square metres (wich is about 10% larger than a soccer field). In a first run indicator fish individuals were counted, then scleractinian coral density, after that a 100 metre line transsect in order to analyze the state of coral health.

Some results:

Overfishing:

In 81% of all reefs no lobsters were detected in the testing area. In 179 Indopacific reefs only 25 lobsters were found, from this alone 11 specimens in a single protected reef area in Indonesia (which gives an estimate of the normal density)
The giant grouper was not found in 40% of all reefs; in others only with very few specimens. Two sites in the Maldives and 3 sites in the Red Sea had more than 20 speciments per reef. Both sites were devoid of dynamite and cyanide fishing, showing how a normal population could look like. The Nassau grouper of the Caribbean used to be very widespread. In all Caribbean sites it was detected 12 times, in four of 51 tested reefs.
The impressive Napoleonfish and Barramundi of the Indopacific was formerly were common. In 85% of 179 reefs tested not a single specimen of a Napoleonfish was detected. In a more detailed study, encompassing a reef area of 25 kilometers extension 26 specimens could be detected. Within 125 tested reefs from Asia and Australia only 5 Barramundis were found. Both fish are under strong pressure of cyanide fishing (see below).
Around Hongkong only 2 species from 11 known edible species were discovered, indicating that quite some of these have really died out there.
Sea cucumbers also include indicator species for overfishing, because they are liked to be eaten especially in Asia. Three indicator species were not to be found any more in 41 % of studied Indopacific reefs.
The giant clam Tridacna could be found in about 17 specimens per test area. Sounds ok, but they still have abundances of 150 - 200 shells per test unit in some protected sites. This would more closely correspond to undisturbed population densities.

In relation to overfishing, coral state still seemed to be better (but this was before the great bleaching event of 1998): Coral coverage was, on the average, about 31 %. Caribbean had only 22%. Best spots were found in some (but not all) Red Sea sites.

Reef site examinations were completed with subjectively judging human impact (after having performed all other studies): 45% of reefs showed little influence by humans, but human influence was detectable in all (i.e. 100%) of the studied reef sites, indicating that there is no single pristine reef left on this planet.

This is just an exemplary study. German participation in the first reef check in 1997 was to organize and perform reef checks in the Red Sea and the Maldives, two areas where German recreational divers and tourists are most frequent. For press releases and more information see our reef resource server at www.riffe.de which is the predecessor of the IYOR-reef server (by the way, the German organization team for IYOR 1997 was Reinhold Leinfelder (at that time Stuttgart), Franz Brümmer (Stuttgart), Moshira Hassan (at that time Kiel) and Gert Wörheide (Göttingen). More information on Reef Check, which is an ongoing initiative is found under www.reefcheck.de, a service by Georg Heiß (which also runs on our GeoBio-Center and Palaeontology Munich servers).

Human impact is discussed in section 1.4.2

However, modern reefs also may locally or regionally, sometimes even globally suffer from natural catastrophes or more subtle natural changes. In addition Earth History provides a rich record of examples where reefs have been under threat and even died out for extended time intervals. This latter aspect will be treated in our reef evolution section. (Tip: if you can't wait it, you might see our online presentation 'reefs under stress' (in German)).

We will first discuss some aspects of natural threats and then come to back the human impact on modern reefs.

Studying natural and human hazards is not only important in terms of reef protection and hence, protection of important resources for mankind, but also helpful in determining the boundary limits and stress tolerances of modern reefs. Studying ecosystem boundary limits in ancient reefs and then cross-comparing them with modern reefs is the major method in understanding reef evolution trends as a whole. Only the understanding the evolution of reefs gives us a chance to better understand our present reefs which hopefully allows us to take measures to protect them.

Just one example for that: it can be frequently heard in the media, and even from reef biologists, that reefs may drown because sea-level is rising today. This is wrong: Earth History shows that healthy reefs can cope up with any sea level rise, and might even benefit from it (since ne accomodation space is created), however, under the condition that all other environmental parameters are stable. Sea-level change in an already stressed environment, such as turbid reef settings, or settings with elevated nutrient values, may actually cause the death of such reefs under stress, since their growth capacity was already strongly reduced. Such reefs will drown, loose than even more of their growth capacity due to diminishing light and will actually die. Conclusion: Reefs can save islands or coasts threatened by sea-level rise but only if they are not under man-induced stress.

1.4.1 Natural threats for modern reefs:

Like any other ecosystem, reefs may undergo natural dangers, which even may cause severe damage. However, in general, reefs which were healthy before the hazard has appeared mostly will recover rapidly. This is quite different, if reefs already have suffered from human impact. A natural disaster might then often be the end to such reefs.

Hurricanes and typhoons may cause intense damage in reefs affected by such catastrophic storms. Damages can even affect hundreds of kilometers (although this is rare). However, reefs affected by such storms actually are adapted to them. We will see in the ecology chapter that special ecological faunal associations develop where the abrasive force of hurricanes attacks in a nearly regular manner. Ridges by coralline red algae or communities dominated by tough, encrusting leathery corals are well adapted. Other corals such as the Acroporoids will actually be fractured, transported and redeposited, but guess what: they like it to some extent. Or more scientifically speaking, broken lose branches can easily regenerate and develop into new colonies. So Acropora uses storms as a strategy for expansion. It would be a catastrophy if a hurricane would suddenly affect, say, the Red Sea, because these reefs are not adapted to severe storms.

	##to be included
`Fig.: Fragmented Acropora palmata in a Caribbean coral reef after Hurricane Andrew (1983 ##to be checked). Small inset: large massive coral colony being thrown into lagoonal sea grass area by hurricane.Photograph BobGinsburg`	`Fig: coral island created by storm-deposited Acropora palmata fragments. Near San Andres, Caribbean Photograph: R Leinfelder, 1996`

In general, the recovery potential of reefs after a storm is high, but - here we go again - only if the reef was not damaged or under stress before. In a healthy reef, a severe storm creates new, fresh and hard settling grounds for coral larvae, which otherwise would not have been available. So we could say, a storm may be like a fountain of youth to the reef, giving a new generation a change. If storms wouldn't strike regularly, the fast growing corals would rapidly outcompete the slower ones, causing severe loss of biodiversity. This however, is completely different, if the reef is overfished or to many nutrients are in the waters owing to sewage and agricultural runoff. In this case, soft algae which must have been already a problem in the reef, will immediately overgrow on the new storm created hard surfaces and will deteriorate the state of the reef.

Recovery rates are varying and depend on the damage caused by the reef. Already within a few years, the reef might look just as it did before, and by rules of chance it is unlikely that another hurrican hits the same site of the reef earlier than in another few decades.

There are even more advantages for the reef than just prodiving new substrates and redistributing acroporids. Storms can manage the following:

sweep reef surfaces clean. This is especially important in calm water reefs, e.g. in slightly deeper or well protected waters. Bioerosion might cause a lot of mud-sized particles which infil reef cavities but also tend to remain on the surfaces. Sweeping this material to the open sea or to the lagoons helps stabilizing reef growth, Reef organisms then will preferrably grow on such surfaces, which is an autofeedback mechanisms for pronounced upwards reef growth.
Truly severe hurricanes can throw huge blocks of reef rocks into the lagoon, where they can act as a substrate for nucleation of patch reef growth. Alternatively, huge reef blocks may tumble down into the sand and mud dominated fore reef where again they may be the nucleus for - in this case deeper - growth of patch reefs.
Reefs can pile up a lot of rubble behind the main reef crest which reinforces the reef barrier and may also result in island formation, a most welcome side effect for man. Just another paradise island might just have been created....

Epidemic deadly infection of diademid sea urchins. These frequent sea urchins were severely under pressure in the early 80s, where in the Caribbean there was a mass death occurrence. The impact on reefs was large: Overfishing prior to this event was largely compensated by a more rapid expansion of diademid echinoids which are efficient herbivorous grazers. After the mass death Caribbean reefs strongly deteriorated, since soft algae and weeds were not sufficiently browsed on. Even nowadays diademid populations are still not normalized in most places of the Caribbean.

Acanthaster planci, the crown-of-thorns-starfish: The crown-of-thorn starfish (german: Dornenkronenseestern) which is widespread in the Indopacific feeds on coral polyps and tends to appear in mass occurrences. The starfish population can rapidly devastate an entire reef, but under normal conditions also tends to dissappear by itself. Although far from being fully understood it seems that these mass occurrences appear as natural cycles and largely control themselves. Once starting to become more frequent, larvae of the starfish tend to dominate over coral larvae so that a next generation of starfish has more specimens than the pervious one. On the other hand more starfish larvae also mean more heterotrophic food for the coral polyps which in turn might cause a shift towards stabilizing the coral community. Nevertheless a climax may be reached where starfishes dominate until there is no more food available since the reef corals are mostly gone. Since reefs tend to have a lot of major gaps, larvae of the starfish do not so easily reach the next reef. The devastated reef now is a perfect settlement for new coral larvae and the abraded reef area might rapidly recover. This all is true however, only for otherwise intact reefs. Unfortunately, starfish larvae seem to be more resistant to eutrophication and other pollution than coral larvae, so in polluted reefs, the starfish has a selective advantage, reaching climax stages more often. It is also discussed whether collecting the beautiful Triton gastropod shells supports crown-of-thorn starfish development. Triton feeds on this starfish. Actually Triton is mostly gone. On the other hand, a Triton specimen can eat only one starfish per day, at the most. Their controlling capacity might be of important for low-density populations of crown-of-thorn starfish, but they could not help once mass occurrences of the starfish take place. So the crown-of-thorn-starfish problem appears to have become a major problem only by human impact.

Other reef eroding organisms: There are many coral eating or coral abrading animals such as porcupinefishes or parrotfishes. They are, however, an important part in the ecosystem, helping to maintain ecological balance. They are in no way a threat to reefs.

Similarly, the bleaching problem also appears to be a combined problem. It certainly is a natural threat occuring whenever water temperatures peak, but the problem appears to be largely increased by anthropogenic rise of global temperatures. We will treat bleaching in more detail in the human impact section.


`Fig.: Black Band Desease. Green: healthy coral; black: infected area; white: dead coral. The desease will spread into the green healthy coral area. Photograph Hanna & Wells`	`Fig: White Band Desease. Not yet fully understood, this desease might represent a viral infection. Photograph: Hanna & Wells`