Reef Ramblings

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

There’s unsettling news this week about a Canadian LFS that seems to have been a victim of sabotage.

The recently opened Indoor Jungle, located at 1285 Kennedy Road, Scarborough, Ontario, is Canada’s largest exotic fish and reptile store.

The storeowners suspect vandalism after hundreds of fish died after bleach or a bleach like substance was poured into the centralised water system. The first indication that something was wrong was when customers alerted store employees to a strong smell of bleach coming from the tanks but by the time they reached the wall of 70 tanks, hundreds of fish were dead or dying.

Fish including small Bamboo Sharks, Queen Angelfish, and Black Lionfish along with hundreds of rare shrimps were among the 700 animals killed, along with corals imported from Australia, Indonesia, Singapore and the Caribbean.

Co-owner Adam Gharavi said he’s certain it wasn’t an equipment malfunction and believes that a chemical was poured into the centralised system servicing 400 tanks holding more than 5,000 fish. He said the vandal, who attacked on Wednesday afternoon, went for the store’s most expensive fish and 200 pieces of rare coral.

“We know whoever did this had some knowledge of how fish tanks work and what the fish need to survive,” Gharavi said. The cost of the incident is estimated to be tens of thousands of dollars.

Inland Jungle is one of about a dozen fish stores along Kennedy Rd. between Steeles Ave. E. and Eglinton Ave. E. Stores have happily coexisted here for years in the knowledge that the more different stores you have in the area, the more people come, to everyone’s benefit.

A Toronto police detective has been assigned to investigate the scene, and on Thursday morning, yellow police tape was seen to close off the wall lined with tanks filled with dead fish.

Tim Hayes

Midland Reefs

©2010

We’ve just created a new Midland Reefs facebook page with the aim of keeping you informed about new products and brief news stories, without cluttering up the pages of Reef Ramblings.

Go to the facebook page to learn about our new products, ask questions about our product range, and to discuss Tim’s articles on Reef Ramblings and in Tropical Fish magazine.

Midland Reefs facebook page.

Tim Hayes

Midland Reefs

©2010