03 March 2008
Butterflyfish 'May Face Extinction'
The Chevroned Butterflyfish may be at risk of extinction, scientists have warned.The case of the Chevroned Butterflyfish is a stark example of how human pressure on the world's coral reefs is confronting certain species with 'blind alleys' from which they may be unable to escape, says Dr Morgan Pratchett of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
In a study published in the journal Behavioural Ecology and Sociobiology, Dr Pratchett and Dr Michael Berumen of Woods Hole Oceanographic Institution (USA) warn that the highly specialised nature of the feeding habits of this particular butterflyfish – the distinctively patterned Chaetodon trifascialis - make it an extinction risk as the world’s coral reefs continue to degrade due to human over-exploitation, pollution and climate change.
“The irony is that these butterflyfish are widespread around the world, and you’d have thought their chances of survival were pretty good,” Dr Pratchett said today.
“But they only eat one sort of coral – Acropora hyacinthus – and when that runs out, the fish just disappear from the reef.”
The team found it hard to believe a fish would starve rather than eat a mixed diet, so they tested C. trifascialis in tank trials on a range of different corals. The fish grew well when its favourite coral was available – but when this was removed and other sorts of corals offered, it grew thin, failed to thrive and some died.
“We call these kinds of fish obligate specialists. It means they have a very strong dietary preference for one sort of food, and when that is no longer available, they go into decline. We still don’t have a satisfactory scientific explanation for this, as it seems like rather a risky tactic in evolutionary terms – but it must confer some advantage provided enough of its preferred food is available,” Dr Pratchett says.
The A. hyacinthus coral, which the butterfly fish feeds on, is itself highly vulnerable – to attacks by plagues of crown-of-thorns starfish (thought to be triggered by humans releasing excess nutrients onto the reef as sediment, fertilizer or sewage), to storms and to the coral bleaching caused by the heating of ocean surface waters to 32 degrees or more, which is thought to be linked to global warming.
“Although extremely widespread, the Chevroned butterflyfish may be at considerable risk of extinction following ongoing degradation of coral reefs around the world, because the coral itself is exceptionally vulnerable, Dr Pratchett explains.
“It is estimated that up to 70 per cent of the world’s coral reefs are now badly degraded, which usually involves the loss of this particular coral – and, when it goes, the C. trifascialis also disappear from the reef.
“To make matters worse, butterflyfishes are one of the main families of coral reef fishes being targeted by aquarium collectors. However, the specialized coral-eaters are clearly not suitable for keeping in aquaria - and often die because they cannot obtain their main food source.”
A previous case in which a coral-dependent fish vanished occurred in the case of Gobiodon a specialized coral-dweller known only from one site, Kimbe Bay in Papua New Guinea, which was thought by scientists to have possibly become extinct after its habitat was destroyed.
Researchers consider that such extinctions are likely to occur as part of the global mass extinction of species now taking place, and that marine ecosystems may be particularly vulnerable in that small changes in habitat or water quality can have a big impact on their species.
Dr Pratchett and Dr Berumen say theirs is one of the few studies so far to consider the evolutionary and ecological basis of dietary versatility, and has implications for the fate of specialised feeders throughout the animal kingdom.
More information: ARC Centre of Excellence for Coral Reef Studies
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Labels: medical, research, sealife
21 November 2007
Laser spots decompression sickness
Decompression sickness, it not treated quickly, can cause lasting damage and may even be fatal. Instead of waiting for symptoms to appear, a University of Houston professor is developing a laser-based system that can diagnose decompression sickness in a matter of seconds.Kirill Larin, assistant professor of biomedical engineering and mechanical engineering, is using a $400,000 grant from the U.S. Navy to develop the first optical non-invasive tool to test those most likely to suffer from decompression sickness, such as SCUBA divers, submariners and airplane pilots. Decompression sickness affects those who experience sudden, drastic changes in the air or water pressure surrounding their bodies. It can cause anything from joint pain – known as the bends – to seizure, stroke, coma and, in the most extreme cases, death.
“Most of the time, decompression sickness isn’t addressed until the person starts showing clinical symptoms,” Larin said. “It would be better, of course, to treat the problem before the symptoms appear. That would allow individuals to take the appropriate medical actions to reduce the side effects of decompression sickness.”
Larin’s optical device can locate microbubbles of nitrogen gas in blood and tissues, which can restrict the flow of blood throughout the body and cause harm. Larin is developing the tool, which works much like an ultrasound machine, with Dr. Bruce Butler of the UT Health Science Center in Houston. Instead of getting readings using sound waves, however, Larin’s system uses light waves in the form of lasers that bounce back when they encounter resistance, thereby providing a high-resolution image.
The Navy could eventually use this technology on all divers or pilots returning to the surface. By shining the laser on one of these individuals, it would provide an image that would reveal the presence of any microbubbles in the blood or tissue – all in a matter of seconds. If microbubbles are found, then medical steps, such as time in a decompression chamber, could be taken before the symptoms appear.
An early version of the tool has been able to locate microbubbles as small as six micrometers, or six thousandths of a millimeter. Most microbubbles are between five and 15 micrometers, about the size of a red blood cell.
With continued research, everyone from highly trained naval divers and pilots, to astronauts and recreational SCUBA divers could benefit.
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Labels: decompression sickness, medical, research
16 October 2007
Researchers pronounce diving with asthma "safe"
In a new study, Israeli researchers reviewed the scientific literature to evaluate the risks asthmatics take when diving.
They found that although there is some indication that asthmatics may be at an increased risk of pulmonary barotrauma (burst lung), the risk seems to be small.
Thus, under the right circumstances, they concluded that patients with asthma can safely dive without any apparent increased risk of an asthma-related event. They added that decisions on whether or not diving is hazardous must be made on an individual basis and be founded upon an informed decision shared by both patient and physician.
Journal Reference: Sade K et al. [Asthma and scuba diving: can...[PMID: 17476937]
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22 August 2007
New Scale Developed to Diagnose Decompression Sickness
There are currently no universally accepted diagnostic criteria for the diagnosis of decompression sickness. The new SANDHOG (SAN Diego Diving and Hyperbaric Organizations) criteria uses a point scale and entrance level for the diagnosis of decompression sickness. Once the entrance criterion has been met, points are awarded based upon the diver's symptoms and their time of onset.
The point system and time limits were determined based upon US Navy and Royal Canadian diving reports.
On validating the SANDHOG criteria against a database of diving related injuries, the researchers found that the specificity of the SANDHOG criteria to be good, and concluded that the SANDHOG criteria are a useful tool for the diagnosis of decompression sicknes.
Journal Reference: Undersea Hyperb Med. 2007 May-Jun;34(3):199-210.
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Labels: decompression sickness, medical
05 June 2007
Decompression sickness causes lasting poor health
A team from Haukeland University Hospital in Norway investigated the impact of decompression sickness and diving exposure on the health of Norwegian divers who previously worked in the North Sea.
They questioned 230 ex-divers on their diving education and history of decompression sickness. They also gave them a questionnaire to fill in to assess their health status, called the SF-36 questionnaire. This measures eight properties: physical functioning, social functioning, role limitations due to physical problems, role limitations due to emotional problems, mental health, energy/vitality, pain and general health perception.
All the questionnaire scores were significantly reduced compared with Norwegian norms. Further reduced scores were seen among divers who reported previous decompression sickness compared to those without decompression sickness. There was a decreasing trend in scores related to number of days in saturation and maximal depth. However, the impact of saturation diving was present only in divers who had experienced decompression sickness.
The researchers concluded that having had decompression sickness during a diving career contributes significantly to a reduction in all health aspects, and neurological decompression sickness has the most pronounced impact. Cumulative diving exposure, including days in saturation, and maximal depth also contributed to poorer health.
Journal reference: Occupational Medicine, doi:10.1093/occmed/kqm032
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Labels: decompression sickness, medical, research
22 February 2007
Diving Several Times a Day Damages the Ear
Due to the condition known as middle ear squeeze, scuba diving has become one of the main causes of barotrauma. Barotrauma typically occurs to air spaces within a body when that body moves to or from a higher pressure environment.
The Travel Medicine and Infectious Disease study by the Universidade de Sao Paulo used 19 experienced divers. These divers undertook four dives per day on five consecutive days. Their eardrums were examined by creating variations of air pressure in the ear canal. The researchers found repeated dives caused damage to the eardrum and within the middle ear. However, when there was a surface interval of 11 hours between dives the damage did not occur
The scientists suggest that extending surface intervals may offer protection against middle ear barotrauma in recreational scuba diving.
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07 December 2006
Breath-Hold Divers Get Decompression Sickness Too
Normally associated with SCUBA diving, decompression sickness (DCS) is also be a risk for repetitive breath-hold diving. This was put forward as early as 1965 but is still not widely acknowledged.
A new study in the Research in Sports Medicine journal compared four groups of breath-hold divers: (1) Japanese and Korean amas and other divers from the Pacific area, (2) instructors at naval training facilities, (3) spear fishers, and (4) free-dive athletes. While the number of amas is likely decreasing, and Scandinavian Navy training facilities recorded only a few accidents, the number of spear fishers suffering accidents is on the rise, in particular during championships or using scooters. A number of free-diving athletes, training for or participating in competitions, are increasingly accident prone as the world record gets deeper and deeper.
The researchers - JD Schipke, E Gams, and O Kallweit of the University Hospital Duesseldorf - report some 90 cases in which DCS occurred after repetitive breath-hold dives. They suggest that breath-hold divers and their advisors and physicians be made aware of the possibility of DCS and of the appropriate therapeutic measures to be taken when DCS is suspected. Because the risk of suffering from DCS increases depending on depth, bottom time, rate of ascent and duration of surface intervals, some approaches to assess the risks are presented. Regrettably, none of these approaches is widely accepted. They propose the development of easily manageable algorithms for the prevention of avoidable accidents.
Journal Reference: Res Sports Med, 2006; 14(3): 163-78.
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30 November 2006
Nitric Oxide Reduces Bubble Formation in Divers
In their experiments, the researchers from the University of Split and the Norwegian University of Science and Technology gave 16 experienced divers 0.4 mg of Nitroglycerine by oral spray 30 minutes before a dive. They found this significantly reduced bubble formation.
Nitroglycerine, best known as an explosive, is converted to nitric oxide in the body. One of the effects of Nitric oxide is to widen the blood vessels.
The divers were split into two groups. One group dived to 30 m in seawater for 30 minutes and exercised during the dive. The other group performed simulated dives to 18 m for 80 minutes in a hyperbaric chamber and remained sedentary. Each group performed two dives, the first acting as a control with no nitroglycerine administered. The open-water dive resulted in significantly more bubbles than the dry dive, but both sets of divers benefitted from the nitric oxide donor.
Journal Reference: The FASEB Journal. 2006;20:A1249.
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30 September 2005
Diving And Subaquatic Medicine
New edition of the advanced text on clinical diving medicine. Now in it's fourth edition, Diving and Subaquatic Medicine remains the leading text on diving medicine. This completely revised edition covers the newly described diseases of diving medicine, the modern types of diving and diving equipment, free and indigenous diving, as well as updating the previous edition's coverage of established diving disorders. Each medical disorder is discussed from an historical, aetiological, clinical, pathological, preventative and therapeutic perspective in the accessible but informative style that has made the previous editions so popular.
The principal disciplines addressed are diving medicine, occupational medicine and aquatic medicine. Those new to the text will soon find it a must for the personal bookshelf.
More info: http://www.Amazon.co.uk/exec/obidos/asin/034080629X/1286
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Labels: medical
09 September 2005
Insurers won't cover £20,000 Medical Fees for Bent Diver
Anthony Allen, 68, from Shirley, Solihull, West Midlands, has had treatment since he got the bends on 8 August.
More info: http://news.bbc.co.uk/1/hi/england/west_midlands/4204696.stm
Labels: medical
Exercise during decompression stop reduces bubbles in blood
| Decompression sickness is initiated by the formation of gas bubbles in tissue and blood, if the divers return to surface pressure too fast. The effect of exercise before, during, and after dive on bubble formation is still controversial. A new study finds that a mild underwater swimming during a 3-min decompression period reduces post-dive gas bubble formation. More info: http://highwire.stanford.edu/cgi/medline/pmid;16118578 |
