A dead finless porpoise (Neophocaena phocaenoides) was found in Discovery Bay on Sunday afternoon, the fourth dead marine mammal discovered in four days after the bodies of three dolphins were discovered on Thursday.
It was found in the water and handed over to the Ocean Park Conservation Foundation for an autopsy. The OPCFHK said that the porpoise was a 1.55 metre long female and the body had reached the fourth stage of decomposition. Its cause of death has yet to be determined.
On Thursday, the bodies of three Chinese white dolphins (Sousa chinensis) were found – one entangled in fishing wire near Lido Beach in Sham Tseng, one in waters near Lamma Island and another in Fan Kwai Tong off Lantau Island.
The Hong Kong Dolphin Conservation Society (HKDCS) estimate that there has been a decline since 2014, when 61 dolphins were estimated to be in Hong Kong waters.
It appears that shortly after the first sighting of a short-finned pilot in Hong Kong (see post from January 14th), we now have the first stranding of a dead short-finned pilot whale. Ocean Park’s Cetacean Stranding Response Team investigated an adult female short-finned pilot whale stranding case today at Cheung Sha Lan, Discovery Bay. It’s 365cm long and as the carcass was severely decomposed, the cause of death cannot be determined. The Team and a veterinarian have done a necropsy on site. The preliminary findings show:
• A 12cm superficial wound was found near the fluke, though it unclear if this is pre-mortem or post-mortem
• A thin blubber layer of 1.5cm (mean blubber layer thickness of adult female short-finned pilot whale is 1.91cm), indicating that the dolphin was relatively thin and weak
The team sent the head, flippers and dorsal fin to Hong Kong Veterinary Imaging Centre for Computed Tomography (CT) scanning, and collected tissue samples for further testing.
Many people asked if this short-finned pilot whale is the same one people sighted at Tsim Sha Tsui on January 13. The dorsal fins on cetaceans have unique characteristics that allow identification of individuals, but since the dolphin’s dorsal fin was severely decomposed, no identification can be made as yet. Yet, as short-finned pilot whales are rare in Hong Kong, and the length of the carcass is similar to the estimated length of the pilot whale sighted in Tsim Sha Tsui (about 3 meter), the possibility can not be ruled out that they are the same individual.
In case you are wondering how this white carcass could have come from a black short-finned pilot whale: this often happens to decomposing whales and dolphins. I once saw a 0.5 m Finless porpoise washed up dead at the Cape D’Aguilar Marine Reserve. Normally Finless Porpoises are black, but the carcass was also white.
This week red tides have been reported all across the western half of Hong Kong including Discovery Bay, Peng Chau, Mui Wo, East and West Lamma Channel. The culprit was once again the plankton species Noctiluca scintillans – neither fully plant not fully animal. It’s a single-called organism from a group called dinoflagellates. They consist of a bubble-shaped cell with two whips called flagella – that propel them through the water.
Though Noctiluca eats other plankton it doesn’t always kill what it eats: sometimes it leaves algae intact and stores it in little bubbles in its body (cell) where the algae make sugars that leak out and feed Noctiluca while the waste produced by Noctiluca feeds the photosynthesis of the preyed on algae – a process known to most as symbiosis and also found in tropical corals. However Noctiluca can also just eat the algae. Why and how it decides to eat or farm the algae is not really clear.
Noctiluca is a well known and non-toxic local red tide species and its occurrence is not necessarily a sign of pollution, but entirely natural. What is perhaps not natural is the size of the bloom, though. This could well point to agricultural fertiliser run-off and sewage effluent particularly from the fast growing population of the Pearl River Delta (PRD).
Images of the recent red tide at Lantau
Noctiluca has however a redeeming feature – bioluminescence! That beautiful sea sparkle of iridescent blue that night divers in the tropics often sea or beach goers see in the breaking waves at night. So blood-red tides on the one side and beautiful sea sparkle on the other, Noctiluca is the Jekyll and Hyde of HK’s marine environment.
Long exposure image of a Noctiluca scintillans patch (cm via WikiCommons):
If you would like to know more about Actual toxic red tides in Hong Kong here is a little TV news documentary from 2013 I found on YouTube:
Here are some images of some pretty right red tide patches. But what on earth is it that makes the water go red like this and is it dangerous?
Red tide is the collective name for phytoplankton blooms that tend to colour the water. Phytoplankton is made up of microscopic plants that drift through the sea. When conditions are right (mostly when there is nutrient-rich water and a stable water column) some species of these micro-algae form red tides. Depending on the pigments, the massive growth of algal cells may turn the water into pink, red, brown, reddish-brown, deep green or other colours.
Red tides are a relatively common sight in Hong Kong with 20-30 reports a year. The immediate reaction from most people is to think that they are the result of some terrible pollution. In fact the phytoplankton species are perfectly natural and normally occur in Hong Kong waters, but under certain conditions they can grow faster and form patches on the sea surface which we call ‘blooms’. Phytoplankton blooms by different species occur all over the world and are often seen by satellites with colour sensors.
Some red tides produce natural toxins, and can cause depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms (HAB). The most conspicuous effects of these kinds of red tides are the deaths of marine and coastal species of fish, birds, marine mammals, and other organisms. This happens either as a direct effect of the toxins produced or because of oxygen depletion (known as hypoxia) which happens when the algae die and bacteria consume all the oxygen in decomposing the dead algae.
Only some species involved in red tides however are toxin-producing and cause fish kills. The bioluminescing species Noctiluca scintillanswhich I wrote about in an earlier post, is not toxic but still can cause red tides.
For Hong Kong this is an economic concern because of the many fish farms and aquaculture areas. When a toxic red tide drifts into a fish farming zone only early warning will help the farmers avoid large economic losses from fish kills by temporarily evacuating their fish cages or transferring their fish to tanks.
The Agriculture, Fisheries & Conservation Department (AFCD) of Hong Kong runs a red tide monitoring network which relies partly on fish farmers and members of the public. The AFCD follows up reports by taking samples from the red tides and identifying the contributing species under the microscope to determine the risk to aquaculturists and the public. The majority of the reports are caused by non-toxic species. If you would like to know more about the network, the AFCD now has a fantatsitc app for iPhone and Android (pictured below) with weekly updates and the functionality to report red tide sightings (which I proudly did today) with this new app, including submitting pictures. (I would also recommend some of the other Hong Kong apps for marine enthusiasts out there: HK Geopark, Wetland Park, Reef Check, Red Tide Information Network and the WWF Seafood Guide).
The AFCD started to record the occurrences of red tide since 1975. From 1975 to 2013, a total of 875 red tide incidents were recorded in Hong Kong waters. Amongst these incidents, only 27 were associated with fish kills.
77 algal species have formed red tides in Hong Kong, but majority of them are harmless. 19 of these species are considered harmful or toxic. Amongst these harmful/toxic algal species, only 5 of them caused fish kills and the other two caused contamination of shellfish by toxin in Hong Kong. The red tide associated fish kill events were mostly recorded in the 80’s and early 90’s.
So are there dangers to human health? If a red tide is identified as a harmful algal bloom (HAB) – then, yes, there is a risk:
The consumption of shellfish (e.g. mussels, clams) is one of the most common ways for algal toxins to impact human health. Each species has it’s own toxin so the health effects they cause are also varied. One example is Ciguatera fish poisoning. This type of fish poisoning is caused by eating fish that contain toxins produced by a the marine microalgae Gambierdiscus toxicus, which has been recorded in Hong Kong waters. Barracuda, black grouper,blackfin snapper, king mackerel, groupers and any large predatory fish can carryciguatoxins. People who haveciguatera may experience nausea, vomiting, and neurologic symptoms such as tingling fingers or toes. They also may find that cold things feel hot and hot things feel cold.Ciguatera has no cure. Symptoms usually go away in days or weeks but can last for years. People who haveciguateracan be treated for their symptoms. In Hong Kong with its rapacious appetite for seafood, ciguatera fish poisoning occurs quite frequently. For example, in 2004 it made up 7.9% of all food poisoning cases recorded that year. In June 2013, fourteen men and five women, aged 23 to 71, fell ill with ciguatera poisoning after eating coral reef fish at a restaurant in Sok Kwu Wan (Lamma Island). The fish in this case actually came from the Pratas/Dongsha Islands out in the South China Sea. Ciguatoxin’s is very stable, so cooking, drying or refrigerating fish will not destroy the poison. There is also no effective way to test fish for ciguatoxin, yet. If you want to play it safe avoid large predatory fish like tuna, grouper and others alltogether (they are mostly overfished already, especially blue-fin tuna, so you would be doing the planet a big favor).
So eating shellfish or fish which has been exposed to HABs is the main danger to humans. There are instances of skin irritations and breathing difficulties after direct human exposure to HABs but these are rarer and not as well understood. So to be absolutely safe, I would advise you to avoid contact with red tides – no swimming in, diving under or touching them!
Flesh-eating disease – or necrotizing fasciitis as its known medically – is fast, nasty and often fatal. The fact that you can get it from contact with seawater makes it even more scary! Should we not swim in the sea anymore? Avoid all seafood? Stay away from beaches, boats and wet markets? These are the sort of questions raised recently. This thread from concerned residents on the Discovery Bay Forum is a good example.
But hold on a minute! The case discussed in the forum actually turned out to have nothing at all do with beaches, seawater, shellfish fish or anything else marine. A common Streptococcus bacteria which lives all around us on our bodies and in our guts was the cause of that infection.
So don’t panic! It’s a fascinating topic, and I want to look at the facts and the data first and then bring things into perspective with a look at the history of marine flesh-eating disease in Hong kong. What exactly is the danger? How worried should we be?
What is flesh-eating disease?
It is a serious bacterial infection of the soft tissue. The bacteria don’t actually eat flesh but the toxins they release while multiplying kill off living cells around them. This can cause death within 12 and 24 hours and about 20 to 30 percent of cases are fatal.
Several different bacteria can cause it. The most common cause is group A Streptococcus, which lives in people’s throats or on their skin. The man in Discovery Bay who recently died actually contracted a type of Streptococcus. But other bacteria can also cause it, including some which naturally live in your guts, on your skin, in marine sediment and seawater, soil, decaying plants and other places. One type called methicillin-restistant Staphylococcus aureus – best known from the news as MRSA – has also become important in the last 10 years because it is resistant to almost all antibiotics and is a major problem in hospitals. And it doesn’t have to be one type of bacteria that causes flesh-eating disease, they can also act together in what is known as Type II or polymicrobial necrotizing fasciitis.
So you can’t avoid these bacteria as they are everywhere in the environment. However, to cause an infection with flesh-eating disease they need a way into your body, because skin will not let them in, but an open wound will give them a chance to grow. Even once inside, your immune system is a great defence, as long as the bacteria do not enter your bloodstream directly. The majority of reported cases are in people who for several possible reasons have a weakened immune system: e.g. underlying illness, chronic diseases, tumours, diabetes, alcoholism or immuno-surpressing drugs and these cases are most likely to be fatal if the infection enters the blood stream. In fact one of the test of Vibrio vulnificus involves injecting the bacteria into the blood stream of mice to see if they die….sometimes science is a bit grim…but still, it saves lives.
Most but not all of the cases reported in Hong Kong recently were all caused by a marine bacteria Vibrio vulnificus, a relative of the bacteria that causes cholera (Vibrio cholerae).
What is the danger from Vibrio vulnificus?
The bacterium is everywhere, both geographically and in a variety of environments, although it occurs in relatively low numbers. It is naturally present in warm seawater and is not linked to pollution, although some studies have found higher numbers of this bacteria in tar balls (e.g. washed up tar balls from the Deep-water Horizon Oil spill), which attract many kinds of bacteria. It likes brackish (mixed fresh and seawater) and so is more common in estuaries and near river mouths. Because it likes warm water, it is more common in the summer months. Infection occurs through open wounds or through eating raw or undercooked shellfish or fish, but is not transmissible between persons. Anyone can be affected by wound infections, but persons with underlying medical conditions, especially liver disease, are at increased risk of blood stream infection and serious complications.
Vibrio vulnificus infections happen worldwide: the US, Japan, Southern Europe etc. In Taiwan, an annual number of 13-26 cases were reported during 1996-2000. The incubation period is usually 12 to 72 hours and the symptoms are intense pain, redness, swelling and rapidly developing tissue destruction usually associated with some form of wound. In persons with underlying medical conditions, especially liver disease, it can cause bloodstream infections with fever, chills, decreased blood pressure, blistering skin lesions and even death in severe cases. In healthy persons, it can cause diarrhoea, vomiting and abdominal pain. Sometimes, the swelling starts at the site of minor injury such as a small cut or bruise, but in other cases there is no obvious source of infection. Bloodstream infections in persons with liver disease are fatal about 50% of the time.
The infection is treated with antibiotics to kill the bacteria as soon as possible, but patients may also need surgery to cut away infected dead tissue or amputate the affected limb. Other than that, those who recover suffer no long-term consequences.
What is the dangerous it in Hong Kong?
In the last 7 years (since May 2005), there have been 51 reported cases of Vibrio vulnificus infections in Hong Kong – 37 Men and 14 women – an average of about 7 cases a year. To put this into perspective, in 2011 there were 6 reported cases of leprosy and in 2010 there were 124 reported snake bites in Hong Kong.
Infections occur predominantly in the summer months from May to October when the water is warm and conditions are right. Isolated cases also appear in colder months, but this could simply be because fish or shellfish is often kept in warmer tanks or because fresh seafood is now globally traded and flown around the world and imported from warmer regions.
Although the fatality rate is high at 27%, with 32% for men and 14% for women. The average age of infected persons was 66 for men and 71 for women.
From about July 2011 the Department of Health also reported if cases had underlying illnesses, and this shows that at least 53% of cases had underlying illness (3% did not have underlying illness and for the remaining cases the Centre for Health Protection’s press releases did not have enough information). I have compiled the data as a spreadsheet which you can download for free by clicking this link.
So basically, if you are older and/or weakened by illness or chronic disease you are at risk if you suffer a wound from handling seafood or have an open wound that comes into contact with uncooked seafood or seawater. Otherwise, there is no need to worry yourself greatly.
You should of course follow the CHP’s advice on prevention, which is more or less common-sensical:
* Avoid foot/leg contact with dirty water when visiting wet market;
* Avoid exposure of open wounds or broken skin to seawater or salty water;
* Wounds should be thoroughly cleaned and properly covered; and
* Wear thick rubber gloves when handling raw shellfish.
* You should seek medical advice promptly if you develop symptoms and signs of infection such as increasing redness, pain and swelling.
As V. vulnificus is so fond of warm brackish water, consider this: climate change is a leading cause of warming seas around the world, as well as of increased freshwater run-off from more erratic and heavier rain storms caused by the higher evaporation of seawater. This means that one of the effects of climate change could be an increase in infections, because the ideal conditions for V. vulnificus are becoming more widespread. There is a very direct and personal reason to cut your carbon foot-print, especially if you like shellfish and beach holidays…