The marine environment of Hong Kong comprises of a vast diversity of marine lives. In order to enrich public’s understanding on the rich marine biodiversity in Hong Kong as well as to promote the message of marine conservation in the society, the Agriculture, Fisheries and Conservation Department organises the Hong Kong Marine Biodiversity Roving Exhibition at five venues between June and December 2018. Through interactive panels and games, display of marine lives models and photo and video galleries etc, this roving exhibition aims to introduce to the public the unique marine environment of Hong Kong, fun facts of some interesting marine species as well as various conservation measures implemented by Agriculture, Fisheries and Conservation Department.
The giant clam Tridacna gigas which can grow to 120 in width and 200 kg in weight is one of a group of clams called giant clams – the Tridacnids. Although T. gigas is the biggest of them, there are others which are still pretty huge by clam standards. One of these giant clam species, the Maxima clam Tridacna maxima, used to occur in Hong Kong. It grows to about 40 cm width, though typically is only around 20 cm in width. But consult the IUCN records for this clam species and you will see that although it occurs throughout the tropical and sub-topical waters of the Indian and western Pacific Oceans, the entry for Hong Kong sadly reads ‘regionally extinct’. When did that happen? Why did they vanish? These are the questions I wanted to find answers to.
When did it go ‘regionally extinct’?
The first entry I could find for the Maxima clam being regionally extinct in Hong Kong is 1983. Unfortunately that’s about all I could find. But at it has been gone from Hong Kong since at least 1983. Unless of course it has returned….its a slow-growing animal but has a very wide dispersal through free-floating larvae that live in the plankton – that’s why it occurs over such a wide geographical area spanning nearly a quarter of the planet! So theoretically, if conditions are right (see more below) and larvae are swept over Hong Kong or are purposely introduced by humans, the Maxima clam could reestablish itself in Hong Kong. So the next question is why did it go extinct in Hong Kong in the first place?
What happened to the Maxima clam in Hong Kong?
Apart from the fact that the Maxima clam lived on coral reefs in Hong Kong waters, I can not find any more details of how big the population was, which exact areas in inhabited (obviously coral reefs, so that narrows it to Eastern and Southern Hong Kong waters) or whether it was harvested locally. It is however clear that Hong Kong used to be a big regional market for giant clam species in Asia. Giant clams were and still are a delicacy in Asia (mostly the meat big abductor muscle) and the shell was used for decoration (though not extensively). Even the UN Food and Agriculture Organization has no useful fisheries statistics for Tridacnids. So there is no information on how many – if any – were harvested from Hong Kong waters before they disappeared. The maxima clam like all clams is a filter feeder which suck in water, filters out and swallows edible particles and then ejects the water out again. As such it is quite vulnerable to toxic substances in the water. In addition, it harbors symbiotic microscopic algae called zooxanthellae (zoo-oh-zan-the-lay) in its tissue. These absorb the clams waste products like CO2 and photosynthesize turning them into sugars in the presence of sunlight and giving off oxygen for the clam.
When open, the bright blue, green or brown mantle of the clam is exposed and obscures the edges of the shell which have prominent distinctive furrows. The attractive colours of the mantle are the result of pigment cells, with a crystalline structure inside. These are thought to protect the clam from the effects of intense sunlight, or to bundle light to enhance photosynthesis of the zooxanthellae.
This is essentially what corals do, too, which is why they share the same habitat – coral reefs. And like most reef corals the maxima clam also gets most of its nutrients from its zooxanthellae . Coral reefs suffer enormous damage from smothering by sediment that washes into the sea from rivers and rainfall and from clouding of the water and smothering by excessive algal blooms. Both of these were and still are to some extent big problems for Hong Kong waters, whereas in the past this was not the case. Algal blooms and sediment runoff increased a lot as a result of the increase in human population in Hong Kong and as a result of rapid industrialization and the associated water pollution. This combined with harvesting seems to be the most likely reason for the disappearance of the Maxima clam from Hong Kong waters before 1983.
Will there ever be giant clams in Hong Kong again?
I hope so. Like I said earlier, if conditions are right, any of the wide-ranging planktonic larvae of the clam that stray into Hong Kong waters could settle and grow to adulthood. Failing that humans could also try to establish them by attaching cultured juveniles to appropriate spots on reefs – but this is more complicated and costly, although Singapore has attempted this with initial success using another giant clam species Tridacna squamosa. But the main criteria is suitable conditions for a population to establish and grow – in other words we need clean seas again. Hong Kong has improved a lot on this front up until very recently, when the increased coastal development in southern China started to create a lot of water pollution which somewhat diminishes the results. There is still a long way to go. But I would say that divers should keep an eye out. In fact, the ReefCheck 2015 recorder forms even have a section for giant clams (Tridacna sp.), so its not just me that is hopeful! You never know. you could be diving some coral reef in Sai Kung, Tung Ping Chau, Hoi Ha Wan or the Ninepin Islands and come across a maxima clam. It might be an old dead one stuck in a reef with just the wavy outline of the two shell valves (probably) or it could have the fat, bright blue or green mantle of a live clam – in which case 1) hooray for Hong Kong and 2) please report your finding to the AFCD and Reef Check!
Sea spiders? Sounds like a B-movie horror story: ‘Sharkrantula”, maybe? Not at all. Sea spiders is the common name for pycnogonids (pik-noh-go-nids) which are a type of marine arthropod (joint-legged animal) which includes crustaceans like crabs, lobsters, shrimp and prawns, but also insects. But pycnos have actually got more in common with horseshoe crabs and spiders in terms of anatomy, so the name sea spiders is not too far from the truth.
The occur in seas all over the world from tropical reefs to frozen polar seas and from shallow water to depths of over 7,000 m. Most are tiny although some deep-sea species can grow to 90 cm. Pycnogonids have extremely reduced bodies in which the abdomen has almost disappeared, while the legs are long and clawed. Muscles are in some cases reduced to a single cell! They can even breathe and absorb food through their skin. As you can imagine their dietary needs are therefore very small. And yet they are predators that prey on corals and worms. The head has a long proboscis with an unusual mouth at the end and several simple eyes on a tube-like stalk. The head also has a pair of claws and a pair of attachments on which the eggs can be carried. All in all, it can be very hard to tell just which end of a pycnogonid is the head!
You might think so what? Spiders are creepy and yucky and iffy. But marine biologists love pycnos – they are just so strange and fascinating biologically.
But what has all this got to do with Chinese takeaways And taxonomical jokes?
Earlier this year I received the sad news that the head of the department I used to work in the Natural History Museum in London passed away. Roger Bamber (tribute by Dr. Tammy Horton) was a legend of a man and also an expert on pycnogonids – a pycnogonid taxonomist. Unlike the more familiar taxidermist (who stuffs and preserves dead animals), a taxonomist is an expert on the certain groups of animals or plants and decides what is and is not a new species – but come to think of it and they also work with dead animals and need to preserve them…sometimes they stuff them too…but its much more complex and tricky, I promise. There is a difference honestly!
Anyway, one of Hong Kong’s pycnos (there at least 6 species locally) was discovered by Roger. Tanystylum sinoabductus was identified in Hong Kong’s only marine reserve at Cape D’Aguilar where the Swire Institute of Marine Science is located. (Note: a marine reserve, unlike a marine park, does not allow any sort of anchorage or fishing, so its is completely protected – except for water pollution of course.) This particular pycno was found in exposed mussel beds. But at only roughly 1/2 a mm in size you will only see it with a magnifying glass and only recognize it under a microscope.
And now the for long awaited joke: the species is part of the genus Tanystylum, but the specific (species) name that Roger chose – sinoabductus -is the taxonomical joke. Sino in latin means chinese (duh!), and abductus – if you have not already guessed it – means ‘taken away’, thus sinoabductus is the “Chinese takeaway’. OMG, I hear you say. What an unfunny joke! You have to understand there is not much opportunity for humor in science (except in the pub after the work) and marine biologists spend a long time in the lab staring down a microscope or hours pouring data on a computer and reading and writing scientific papers any chance to get away with even a bit of humor is appreciated!
And just in case anybody in this era of social justice warriors and political correctness thinks that this species name could be racist: the other reason for the name is that the type species – that is the 1 animal that was selected as typical of the species and which represents the ‘gold standard’ for that species – now resides in the National Museum of Wales in Cardiff, UK. Thus this Chinese sea spider species was in fact ‘taken away’ to a noted museum for that group of animal (which is standard practice as well, so no accusations of kidnapping or robbery please!).
More than 25 local marine biologists have been awarded a grant that will enable them to study the marine biodiversity and ecology of the Tolo Harbour and channel.
Tolo Harbor is a semi-enclosed body of water in the northeast of Hong Kong linked to the sea only by the narrow Tolo Channel. The Tolo Channel and Harbor were infamous in the 1980’s for terrible water pollution, fould smells and red tides. A rapid expansion of urban areas on the firnge of Tolo Harbor with direct, untreated sewage discharges into the Harbor caused large scale eutrophication. The sewage outfalls provided nutrients feeding massive algal blooms which subsequently died and their decomposition by microorganisms used up so much oxygen that the water and sediment became anoxic, killing fish and many other marine organism (again feeding oxygen demand form decomposition) and causing foul smelling water. The problem was made much worse because Tolo Harbor is not very well flushed with new oxygenated water from the sea. It was eventually improved by providing proper modern sewage treatment and recognizing the particular vulnerablility of the area to eutrophication.
The HK$4.3 million will benefit the Joint University Consortium for Biodiversity, Ecology and Conservation of Marine Ecosystems and comes via the Environment and Conservation Fund (ECF). The ECF was established by the government in 1994 as part of its long-term commitment to environmental protection and conservation and received an injection of $5 billion in 2013, to serve as seed money generating an annual investment returns to support green projects and activities. The ECF has so far funded over 4,290 educational, research, and other projects and activities in relation to environmental and conservation matters.
Despite the funding being delayed for about two years, the proposal was approved last month and the 18-month project will commence later this year. The first stage of the two-phase study is aimed at finding the current ecological status of the area as well as the economic value of marine resources. The team will establish a comprehensive species database of the area. Kevin Ho King-yan, a senior research assistant at the School of Biological Sciences at the University of Hong Kong, said the proposal was aired at least two rounds of interviews, possibly because of the large amount of money required.
“Usually, project funding proposals to the conservation fund average around the hundred thousand mark, but this time it is in the millions,” he said. The announcement comes after an international conference, jointly organized by the Swire Institute of Marine Science and the University of Hong Kong School of Biological Sciences, kicked off at HKU yesterday.
More than 280 participants from 26 countries have come together for the four-day conference to discuss issues such as coastal development and marine conservation. More than 20 marine scientists from overseas and the mainland are attending. Organizing committee chairman Kenneth Leung Mei-yee said experts from across the globe need to work together to map out a plan to protect marine biodiversity. “We need experts from all different sectors to join hands together to uncover what we have and how we can protect them and how we can make sustainable use of these resources,” Leung said.
Note: The Hoi Ha Wan marine park – noted for its corals – is located at the seaward mouth of the Tolo Channel.
Source: The Standard 2nd June 2015