Reef Ramblings

There are reports of extensive warm water coral bleaching in the Andaman Sea.

This is believed to be the worst case of bleaching in Thai waters for 20 years. Coral reefs off Phangnga, Krabi and Phuket, including popular diving sites such as the Similan, Phi Phi and Surin islands have been affected and, according to the Phuket Marine Biological Centre (PMBC), bleaching is likely to extend as far as Satun province, and may worsen if sea temperatures continue to rise. Coral reefs in the Andaman Sea previously suffered severe bleaching in 1991 and 2003.

A bleached coral reef at Koh Aeo in Phuket. PMBC

Bleaching started to occur during April and five percent of the coral reefs so far affected have died. The temperature in the Andaman Sea has been higher than the last two years, staying at around 31-32C, probably because of the late onset of the monsoon over the Bay of Bengal and Andaman Sea. Normally the monsoons arrive during mid-April with the rains bringing a reduction in sea temperature.

The PMBC has been working closely with dive operators, to monitor the coral bleaching situation. The phenomenon is also occurring in the Gulf of Thailand in Rayong province, Somkiat Khokiattiwong, head of the PMBC’s oceanography and environment unit, says Burma and Malaysia could also face the coral bleaching problem in their waters.

The bleached coral reefs may take a long time to recover. The PMBC estimate that coral reefs in shallow waters, depths up to 10m, will take three to four years to recover, whilst deeper reefs will take longer.

The Andaman Sea is one of the Thailand’s most popular diving sites with around 80 sq km of coral reefs. It attracts millions of visitors and divers each year.

For more about the Phuket Marine Biological Center go to the PMBC website.

Tim Hayes

Midland Reefs

May 8, 2010

Over two days, 3 - 4 February 2010, tropical cyclone Oli passed by the west of Tahiti subjecting the islands of Bora Bora, Raiatea-Tahaa, Huahine and Maupiti to waves six to seven meters high accompanied by wind gusting to 170 km/hour. Following this, it was the turn of Tahiti and Moorea followed by the island of Tubuai to undergo the cyclone’s impact, experiencing mean wind speeds of 210 km/hour. This was classed as a severe tropical cyclone, category 4, the second highest storm classification.

Centre National de la Recherché Scientifique, CNRS, the largest governmental research organization in France, has a Coral Observation Department based on Moorea which has been regularly collecting data on coral communities and fish populations in the area. Four days later, after repairing damage to their facilities, they undertook an inventory of the cyclone’s effects after it had passed over two reference sites. Their scientists discovered the extent of the damage to the coral reef, already been made vulnerable by the invasion of a coral predator, was one of almost complete destruction. Their observations revealed that cyclone Oli had flattened the coral population finishing off a reef that was already vulnerable.
The Crown of Thorns Sea Star, Acanthaster planci, notorious for preying on coral, had already nearly wiped out the coral populations on the outer slopes of Moorea. Since the start of an explosion in Acanthaster populations in 2006, the percentages of live coral coverage at 12 meters depth has fallen by around 96 % on the north coast of Moorea, reducing coral cover to roughly 1.0 %. Although this invasion has been a cause for concern, the physical structure of the reefs, particularly the outer slope, the most favourable area for reef growth because of the water’s high level of oxygenation, had been little affected as the skeletons of the dead colonies were still in place, holding out the promise of recovery.

However, once the cyclone had passed, the physical structure of Moorea’s outer slopes, especially the northern side, were found to be seriously and lastingly affected. Comparison of data before and after the cyclone struck reveals a very significant reduction in the relief of the outer slope. The rugosity indices were found to have fallen by 50% at all depths down to 30 meters. Rugosity is an important coral reef parameter that describes the amount of “wrinkling” or roughness of the reef profile. It is an index of substrate complexity. Areas of high complexity are likely to provide more cover for reef fishes and more places of attachment for algae, corals and various sessile invertebrates. A large number of coral colonies previously present were torn off by the wave action and broken up by boulders. The three-dimensional structure of the reef has been badly affected, which may be detrimental to long-term recovery.

Damage to the reef varies with depth:

• From 0 to 6 meters there’s severe destruction. Most of the scattered live colonies being broken off at the base. The area is now totally covered with fine pale yellow algal matting of an algal bloom and there’s no live coral coverage remaining.
• From 6 to 10 meters although many live, branched colonies are damaged their bases are intact, which means recovery may be possible.
• From 10 to 15 meters the flanks of this area are in a critical state of destruction. The large branched colonies, most of which were already dead following Acanthaster predation but intact before the cyclone, are no longer visible, no algal growth is observed.
• From 15 to 30 meters depth there is an abnormal covering of small coral debris, 5 cm on average.
• The populations of fish, molluscs and sea urchins associated with the reefs have also suffered considerably with many shellfish being seen in a state of decomposition between the surface and a depth of 6 meters.

As to the future of the reef, there seem to be two possibilities:

• Either the algae will increase and continue to dominate the system by overgrowing the substrate, leading to the death of the reef, as has happened to many reefs around the world.
• Or the reef will start from scratch recruiting new assemblages of coral from larval settlement resulting in a reef likely to be different from the pre-existing one regards species present, and bio-diversity.

Given that algae are already encroaching on the remains of the reef, I find the second possibility remote, although one can always hope.

Scientists have been monitoring the resilience of these reefs since the1980s. During this period, the reefs have been suffered seven episodes of massive bleaching (1983, 1987, 1991, 1994, 2002, 2003 and 2007), several cyclones, and two outbreaks of Acanthaster planci, the starfish that preys on coral.

Although in the past these reefs have always recovered, this recent series of stresses, coral bleaching, cyclones, local pollution, and predation gives little cause for optimism. It’s too soon to make an accurate assessment of the impact of the cyclone on other species such as fish, and non-coral invertebrates but changes in their numbers and diversity are to be expected. Data about fish populations is being collected, which in time will provide a clearer picture of the extent of the damage caused by the cyclone. It could take up to ten years before the reefs recover, if they are able to, making long-term monitoring of reefs essential in order to take the measure of the resilience of coral reefs in Polynesia today.

It would appear though that cyclone Oli may have been one cyclone too many for the reefs of some of the Polynesian islands, including Moorea, Tahiti, Raiatea, Tahaa, and Bora-Bora.

Afterword.

This incident serves as an example of the plight of many tropical reefs around the world. If a reef is healthy, say in a MPA not subject to manmade pollution and over fishing, it can weather natural disasters such as a cyclone and recover over time. However, where a reef has been constantly affected by stressors such as pollution unbalanced ecosystem owing to over-fishing, damage from shipping etc, there comes a time when it can no longer recover. It becomes added to the statistics as one of the increasing number of reefs lost over the last 50 years, joining the estimated 19% of the world’s coral reefs already lost and the 35% seriously threatened (Wilkinson, 2008), a process which is continuing with little sign of abatement.

Tim Hayes
Midland Reefs
©2010

A significant bleaching event has been reported from the area of Lord Howe Island. Southern Cross University (SCU) researchers, who have been monitoring the coral reefs off of Lord Howe Island since 1993, have mapped the extent of the bleaching and damage to the corals and will be returning later in the year to assess the rate of recovery.

Above average sea temperatures during early 2010 have led to the first recorded major coral bleaching event here, with water temperatures exceeding 26 - 27 ˚C over the last few months, a couple of degrees higher than the usual summer sea temperature.

Lord Howe Island lies within a marine protected area, the Lord Howe Island Marine Park, and was declared a World Heritage site in 1982. This is a reef of particular importance being the southern-most tropical reef in the world. It features an unusual combination of tropical and temperate marine flora and fauna, including many species living at their distributional limits, reflecting the extreme latitude of coral reef ecosystems.

The diversity of marine life here includes:

· At least 500 species marine fish of which 400 are inshore species and 15 are endemic.

· More than 83 species of corals and 65 species of echinoderms of which 70 per cent are tropical, 24 per cent are temperate and 6 per cent are endemic.

· At least 235 marine benthic algae species of which 12 per cent are endemic

This bleaching event was caused by warm seawater carried south on the East Australian Current, coinciding with the hottest, driest, cloudless January on record. It has been far larger than the minor bleaching that took place during the mass coral bleaching of 1998, which severely damaged coral reefs around the world. Lord Howe Island was relatively unscathed in 1998 with few coral species becoming bleached and most recovering.

Although elevated sea surface temperatures are the main factor in coral bleaching this event seems to have been made more severe by there being little ocean swell during the hot weather, leading to poor water mixing resulting in a hotter lagoon with lower levels of water oxygenation.

Unlike the Great Barrier Reef, Lord Howe Island is relatively isolated from other reefs, this reduces the rate with which recruitment of organisms can occur to replace populations damaged by the event, and as a result, the reef may take decades to recover.

Professor Peter Harrison, from SCU’s School of Environmental Science and Management, said that this unusual bleaching event is further evidence that climate change is having a very real impact and that even cooler water, sub-tropical reef systems were not immune to these changes. He also noted that two of the major sites affected by the bleaching were within protected areas of the marine park, and pointed out that research from other tropical reefs showed that areas protected from fishing had better recovery rates from severe coral bleaching episodes.

Marine protected areas are being seen as increasingly important as they can help the recovery of reef systems adversely affected as climate change takes hold and affects the marine environment.

Tim Hayes

Midland Reefs

©2010

In my article, “2010, the International Year of Biodiversity - Clownfishes.” under the section entitled, “Can clownfish adapt to climate change?” there was a mention that one species of clownfish had recently been shown to use soft corals as an alternative habitat, something previously only seen in captivity. This is referenced to Arvedlund, M., and Takemura, A. (2005) Long-term observation in situ of the anemonefish Amphiprion clarkii (Bennett) in association with a soft coral. Coral Reefs 24, 698-698.

Having managed to track this paper down I can now expand on the reference.

Between May 2003 to December 2004, during the course of 37 daytime snorkeling surveys between the hours of 11.00 and 18.00, an adult Amphiprion clarkii was observed at a depth of 1 m, living in the same soft coral, a Lobophytum species of around 90 cms in diameter.

This took place in the Ryukyus Archipelago in southern Japan, at the southernmost local reef of Sesoko Island. This area was seriously affected by the global bleaching event of 1998; in the aftermath of this event several species of host anemones disappeared while the surviving anemone species declined. At the time of the paper, 2005, the anemone population had yet to recover.

Although anemonefishes are known to adopt a wide range of soft corals in captivity, this form of behaviour is almost unknown in the wild.

All 28 known species of anemonefishes have an obligate symbiotic relationship with at least one of ten species of anemones belonging to the families: Actiniidae, Stichodactylidae and Thalassianthidae. There tend to be species specific associations which range from Premnas biaculeatus, Maroon Clownfish, associating with a single species of anemone, Entacmea quadricolor, Bubble-tipped Anemone, to Amphiprion clarkii which has been found in association with all ten species of known host anemone.

From personal observation, the main author of the paper, reports that A. clarkii will often take shelter away from its host anemone when pursued by a potential predator whereas most other anemonefishes, take refuge in their host anemone.  The paper ends by speculating whether the ability of A. clarkii to associate with a wide range of anemones and, as has now been observed, with corals might go some way towards explaining why it’s the most widely distributed species of clownfish.

Other than the fact that Lobophytum species soft corals are amongst the most toxic of corals, something that might deter predation by fishes and aid the coral in competition against other corals, this species appears to offer little in the way of protection for a clownfish. This leads me to further speculate whether A. clarkii is evolving away from its obligate association with host anemones or to question if this is just one fish that has been unfortunate enough to lose its host yet been lucky enough to survive for so long in the absence of an anemone.

More reports of clownfishes, particularly A. clarkii, are required before we can come to any conclusions.

Tim Hayes

Midland Reefs

©2010

The United Nations has declared 2010 to be the International Year of Biodiversity. It is a celebration of life on earth and of the value of biodiversity to our lives. The world is invited to take action in 2010 to safeguard the variety of life on earth: biodiversity

As part of the International Year of Biodiversity (IYOB) the IUCN has published a report presenting 10 new climate change flagship species to demonstrate that it’s not just the Polar Bear that’s in trouble.

These 10 species are as follows:

Staghorn corals

Ringed Seal

Leatherback Turtle

Emperor Penguins

Quiver Trees

Clownfish

Arctic Foxes

Salmon

Koalas

Beluga Whales

One thing that is immediately obvious from the list is that 7 of the species are marine animals. The second thing to strike me about this list is that 2 common aquarium animals are included, most worrying of all is the inclusion of the poster animal of the marine aquarium hobby, the clownfish

In this first of two articles I’m going to look at clownfish, the second article will be concerned with Staghorn corals.

Clownfish and Climate Change

Clownfish, or Anemonefish, belong to the Family Pomacentridae, with their vivid orange and white colouration are one of the most familiar species of tropical marine fishes. This familiarity was boosted by the film ‘Finding Nemo’, which featured the Common Clownfish, Amphiprion ocellaris, a mainstay of the marine aquarium hobby.

Clownfish are found in tropical and subtropical areas of the Pacific and Indian Oceans where they are restricted to shallow waters owing to their mutualistic relationship with a small number of specific anemone species. A host anemone can support a colony of several clownfish consisting of one female, one functional male, and a number of subordinate fishes, all non-functional males.

When the female dies the male turns into a female whilst the largest subordinate fish becomes male. Clownfish lay their eggs close by their host anemone, guarding them until they hatch. On hatching the larvae disperse into the water column where they remain for around 8 to 12 days before settling out as juveniles and seeking a host anemone of their own. As larvae develop, chemical signals allow them to detect suitable host anemone.

Research has shown that the larvae that survive to settle out as juveniles tend to return to the reef where they originated so the majority of the survivors do not disperse very far from their parents’ anemone.

There are 28 species of clownfish described to science; all behave in a similar manner, exhibiting reliance on their obligate association with host anemones for survival.

Captive breeding.

Clownfish have been bred in captivity since the early eighties so we have a lot of information about how different environmental conditions such as temperature and pH affect this species. Although it’s interesting to note that the recent studies from the reef, revealing that reduction in ocean pH levels have an affect on clownfish’s ability to detect the chemical signals necessary for locating an anemone host, answer the question of why captive bred clowns are often slow to adopt an anemone in a reef aquarium.

Why are Clownfish vulnerable to the effects of climate change?

Habitat loss: Coral reefs are in decline owing to increased levels of CO2 in the atmosphere. The current level stands at 387 ppm CO2, higher than 350 ppm that many leading scientists say is the safe upper limit for carbon dioxide in our atmosphere, and the level we need to get back to as early as possible to avoid runaway climate change. If CO2 levels reach 450 ppm, predicted to occur by 2030-2040 at the current rates of increase, reefs will be in terminal decline worldwide from mass bleaching, ocean acidification, and other environmental impacts. Clownfish are dependent on anemones for their survival, which most frequently occur on coral reefs.

A couple of examples: the global coral bleaching event of 1998, led to the complete disappearance of several sea-anemone species used by clownfish in the corals reefs around Sesoko Island, Japan, causing local population declines; and take a look at: Reef Ramblings June/July 2008 to see an earlier article about reduction in clownfish numbers on the Great Barrier Reef.

Disruption of navigation: Decrease in ocean pH levels have been shown to affect a clownfish’s ability to detect the chemical signals that allow them to locate a host anemone. This is known to be a particular problem for juveniles as, if they’re unable to locate a host, they’re at greater risk of predation. Juveniles unable to locate a new anemone face the chance of returning to their parental anemone, increasing the likelihood of inbreeding.

Larval development: As ocean temperatures increase we’d expect to see faster development of larval and juvenile clownfishes. This may bring a reduction in dispersal distance with the result of settlement closer to the parental anemone increasing local competition for recruitment to neighboring host anemones. Again increasing the possibility of inbreeding.

Reproductive behavior: Clownfish, along with many other fish species, only reproduce within a narrow temperature range. This presents the possibility that as temperatures increase that there may be a reduction in breeding activity. A secondary problem that we’re familiar with from captive breeding is that high temperatures can have a deleterious affect on egg development.

It’s also worth noting that in the IUCN report, under the heading of “Other threats”, that the marine aquarium industry is singled out for mention, although it does go on to add that the greatest threat is down to human activities, presumably the usual

Can clownfish adapt to climate change?

Currently this is unknown, most species can usually adapt to changes in environmental conditions as long as these change occur slowly over time. As ocean temperatures continue to increase, clownfish and their associated host anemones may be able to shift their ranges southwards to cooler water. However, neither clownfishes, nor their anemones, are particularly mobile so it’s likely that successful relocation to new, more suitable habitats will be limited.

The concern about more rapid larval development, with its resultant limitation on dispersal, raises the question of inbreeding, the consequences of which are unknown.

A further possibility, but one that seems to me unlikely, is whether clownfishes could adapt to seasonal breeding pattern taking advantage of the cooler seasons.

Interestingly, the IUCN report states the one species of clownfish has recently been shown to use soft corals as an alternative habitat, something previously only seen in captivity. This is referenced to Arvedlund, M., and Takemura, A. (2005) Long-term observation in situ of the anemonefish Amphiprion clarkii (Bennett) in association
with a soft coral. Coral Reefs 24, 698-698.

It’s not known if other species of clownfish could adopt other host species, nor whether such associations would have the same value as the present association with anemones.

What can we do?

Whilst climate change does not mean extinction, some species will be able to adapt whilst others will perish. The question is which species will survive and which will perish? Worsening climate change effects are inevitable, even if all CO2 emissions ceased today, because of the lag-effects of the greenhouse gasses already emitted.

It’s up to all of us, along with our governments, to commit to targets to reduce emissions at the earliest opportunity if, we want to slow the pace of climate change and give clownfishes and other species a chance to survive.

If you are a reefkeeper, try to raise awareness of the destructive affects of climate change to the marine environment by using the familiar clownfish as an example of what may be lost.

You can download the IUCN report here: Species and Climate Change

Tim Hayes

Midland Reefs

©2010

Although we tend to associate coral bleaching with elevated water temperatures, it may not be as widely known that it can also occur when water temperatures drop below the low limit of coral survivability, 15 ˚Celsius. Bleaching occurs when a coral undergoes stress and loses or expels its zooxanthellae, or symbiotic algae, with prolonged stress resulting in coral death.

Cold-water Bleaching on the Reef.

The recent sustained low water temperatures in South Florida and the Florida Keys have triggered severe coral bleaching and coral fatalities. Temperatures in some areas of the Florida Keys National Marine Sanctuary have dropped to as low as 11 ˚Celsius for several days, well below average for the time of year. This is the first time that cold-water bleaching and die-off has occurred in Florida since the late 1970s.

“The Keys have not seen a cold-water bleaching event like this since the winter of 1977-78, when acres of staghorn coral perished,” said Dr. Billy Causey, southeast regional director of NOAA’s Office of National Marine Sanctuaries. “But today we are better prepared to document and assess the impacts of stress thanks to numerous partners.”

Over the next two weeks, teams of science divers from federal and state agencies, non-governmental and academic organizations, will be surveying the reefs to assess and monitor mortality and changes in coral health.

“If there is any ‘good news’ it’s that reef managers and scientists are able to quickly respond to this event and are in a good position to learn more about how reefs will rebound following such a rare occurrence,” said Chris Bergh, director of The Nature Conservancy’s Coastal and Marine Resilience Program.

Usually the Florida Reef Resilience team carries out surveys following warm-water bleaching events. Activating the team now will provide valuable insights on what happens to corals when they get too cold. Monitoring needs to be implemented as quickly as possible, because macro-algae and cyanobacteria quickly invade or overgrow dead coral making identification of recently deceased corals difficult.

Reports so far indicate that all species have been equally affected by the cold, though more will be known when the results of the survey are in. It seems that offshore reefs have fared better than inshore and mid-channel reefs.

The coral reefs of the Florida Keys are part of a unique and diverse ecosystem that forms the third largest barrier reef in the world. Reef-related expenditures generate more than $4.4 billion annually in southeast Florida and reef recreation supports more than 70,000 jobs.

Cold-water Bleaching in the Aquarium.

Cold-water bleaching can also occur in the reef aquarium. During the very cold weather of December 2009 - January 2010, I experienced this phenomenon in one of the Midland Reefs research tanks. Interestingly it was a half a dozen or so Entacmaea quadricolor, Bubble-tipped anemones, that were affected rather than any of the stony corals in the system.

The problem was caused, as you might have guessed, by a couple of defective heaters. These had been running since the system had been set-up so were in the region of 8 years old, As an aside, I’ve noticed numerous equipment failures in the fish house over the last year so I’m now minded to change many items of equipment, heaters, ballasts, pumps, etc. once they reach the 6 year mark. After all, no item of equipment is going to last forever, especially non-serviceable items such as ballasts, ignitors, and heaters.

So far the anemones are remaining in good health, they’re feeding well and producing nematocysts but there’s not yet any sign of recruitment of new strains of zooxanthellae.

I feel an experiment coming on to ascertain whether the anemones can use the strains of zooxanthellae present in the corals that they share the system with. I’ll try removing half of the bleached anemones to a system containing unbleached specimens of the same species and then compare the two systems for signs of zooxanthellae recruitment.

And in the meantime, whilst I’m awaiting results of the experiment, it’s time to search the science for more information regarding zooxanthellae and which organisms that they choose to inhabit.

Tim Hayes

Midland Reefs

©2010