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2018.NOV.Issue 1
研究自然
Research Nature
When Two Superheroes in Ecology Unite
An interview on the “Mangroves of Hong Kong, where are they now?” project
Often respectively referred to (jokingly and dearly) as “Ant Man” and “Mangrove Guy”, Dr. Guénard and Dr. Cannicci are experts in their respective fields. A mangrove zoologist and entomologist, what happens when they join forces? Last year in June, the two teachers started their 2-year-long project called “Mangroves of Hong Kong, where are they now?”. The project looks at mangroves from not only a spatial point of view but also a temporal view, to see how mangroves have progressed 2 decades since the last survey. We were lucky to have the opportunity to interview them about their project, to share their experience in the magazine.
Text / Nicole Yu
Interviewers / Hecate Fong, Betty Woo, Nicole Yu
Dr. Stefano Cannicci (left), and Dr. Benoit Guénard (right). Photo by Nicole Yu.
What did we know about Hong Kong’s Mangroves?
The last research project on Mangroves in Hong Kong was conducted 22 years ago, by Dr. Nora Tam from City University. But apart from this, there are few papers on Hong Kong’s mangroves in the past. However, it is not only Hong Kong’s mangroves that have not been largely studied. “All over the world, not just in Hong Kong, the terrestrial part of the fauna in mangroves is really understudied,” says Dr. Cannicci. There is some literature from other parts of the world on ants in mangroves, describing how some ants defend their host trees from caterpillars in Australia, and some iconic species such as the Camponotus anderseni, which live in the anoxic mud of mangroves and are completely submerged during high tide. However, in Hong Kong there is none. “I was seeing something in Sri Lanka, where these caterpillars were destroying a particular tree, just defoliating that species. So we know about that, but we don’t have any scientific publication about that. We know these, we know that this is happening but there is no sound scientific publication, which is a pity” Dr. Cannici shares.
How were the mangroves surveyed?
47 mangrove sites were initially visited, but not all were surveyed in detail in the end for the project. “We try to select what we thought were the more diverse, we had a qualitative assessment on all of them” Dr. Cannicci explained. As some sites were very similar to others or were of low diversity, only some of the sites were chosen on both the east and west of Hong Kong for study, to have an even coverage that had representative results.
For tree density, it was surveyed using the point-centred quarter method, which gives information on the density of the trees. The diameter at breast height (DBH) was on the biomass and canopy size. For crabs, visual survey is used, observing the different holes and trying to catch them by digging up burrows. As for the survey on the insects, there were 3 methods; the Malaise tent, which is a tent used to trap flying insects with the roof directing them to a jar of ethanol, left for two weeks at a time; beating, using a stick to beating the trees so insects fall down onto a 1-meter square white sheet; and bamboo bundles with different sized openings, left outside in the site and collected a few weeks later to see what organisms have colonized it. “For some wasp species, we only collected one specific species of cockroach, others we get only some spiders or only caterpillars. Some, it could be specific types of pollen, things like that.” Dr. Guénard says. “So you can really understand better the ecology of the species, what kind of food, what is their trophic level, In a way, you can get a better picture on the ecological interactions, not just the biodiversity.”
Many new species and much more than that
When asked about their findings so far, the two teachers had no shortage in what to share. “That’s the great part when you work with insects, the question actually is not if there’s anything you could find, but how many you find,” says Dr. Guénard.
In terms of new species, not only were there new species records to add in Hong Kong, but also many new species for science.
There was no shortage of insects in the mangroves to study. In the project, artificial nest traps using bamboo bundles were also used to see what insects would inhabit the area, and the findings were astonishing.
According to Dr. Guénard, such experiments in forests around the world have collection rates of 10 to 20%, but in the project, the collection rate was as high as 40%. “The mangroves, for some reason which I don’t know yet, they are very attractive to a lot of insect groups,” says Dr. Guénard. “Ants, wasps, bees, maybe there's a lack of predator for them there, or maybe it's a good habitat to have a food source, or maybe the canopy conditions.”
Bamboo bundle sample with cells. Photo by Nicole Yu.
Although the project mainly focused on four groups of insects: ants, social wasps, moths, and the beetle family Lampyridae (fireflies), they made some interesting findings with the help of another entomologist, who specializes in Diptera (flies). “We’re providing the samples because we were not planning to do anything on flies originally,” Dr. Guénard shares with a smile. “And we get very excited, and for good reason. I think he was saying this morning that just from the first batch you get 12 new species for Hong Kong, and 12 new species for science entirely. So we definitely have something new for Hong Kong and the world.”
Of course, how could there not be ants involved in the project? 30 ant species were found in the mangroves, which compared to the 150 in terrestrial habitats in Hong Kong doesn’t seem like much, but those species that are found abundant in the mangrove are the ones which are less common in the terrestrial habitat. “You can break a dead branch and you could find a colony of ants living in there. Really mangroves are quite unique in that sense. [...] Maybe it’s because I don’t have the ability to climb on (terrestrial) trees and break all the small branches where they (arboreal ants) actually nest. But when we had the big typhoon, I was actually looking to find some more arbor ants because of all the trees down, it was a perfect opportunity. But I didn’t find many of those species that we find in the mangrove.” This suggests that mangroves are a unique habitat for some ant species, and this intrigued Dr. Guénard. “It’s very hard when you work with ants because you have ants like from the canopy of trees and deep underground. But in the mangrove, you actually don’t have all the ground ants and underground fauna, it’s mostly restricted to species who live on those trees. It’s almost like each of those trees is an island, ” he shares. “That to me was kind of a discovery, in a sense that wow, that’s actually an interesting system to study.[...] I started thinking, if I had to study arbor species and interactions, the mangroves might be a very good habitat to do more experimental work or to just take a different approach.”
On the marine side, the findings were no less interesting, and can even bring forth a breath of relief. According to Dr. Cannicci, most of the mangroves sampled and recorded 20 years ago have expanded, and it’s not only the overall mangrove forest which has thrived. “The rarest of the trees here in Hong Kong which is Heritiera littoralis, we found some population in Tolo harbor that was thought to be done, to be disappeared after the pollution problem of the 60s, so they are back,” says Dr. Cannicci.
However, it’s not all good news. An invasive tree species from Russia was also found, introduced from Deep Bay in Shenzhen, to the northwest of Hong Kong. “Yesterday I was in Southern Lantau, and they were there. Not that many, but two big trees I think about 5 years old, pretty high. It’s a problem it’s expanding. Southern Lantau is not even close to Deep Bay.”
For crabs, there are 6 new records for Hong Kong. What’s surprising is that some of these species have come from the north, as opposed to the trends of moving to higher latitudes due to rising temperatures and climate change. Apart from these records, more was also found about the Haberma tingkok. “We found a new species, as you know, Haberma tingkok. We are starting to find that crab all over, Three Fathoms Cove and things like that. We have something different from what we have, it can be another climbing species from Deep Bay.” Dr. Cannicci says. “We are up to 55 species of crabs from mangroves and adjacent mudflats. Some are very strange, they’re blind crabs, so they dig in the mud, very very strange.”
When talking about the gastropods part of the survey, this was what Dr. Cannicci had to say. “From the gastropod point of view, I would say it’s a mess, it’s still a mess,” he shared. “We are now preparing to do DNA barcoding on about 200 specimens. Because there are new names coming out, but the morphological identification is really difficult. [...] We found a little bit of a problem because DNA extraction of gastropods is not that easy.”
Apart from the ecological findings, the mangroves all had something else in common. “The amount of rubbish in Hong Kong… it’s incredible. I’ve been working in many other areas in the world, it’s really shocking how much rubbish can reach mangroves in Hong Kong. Not even counting the heavy metal pollutants… because you can see them, ok,” a dismayed Dr. Cannicci shares as Dr. Guénard nods gravely, “but the solid rubbish, the things, the shoes, the styrofoam boxes. Styrofoam is everywhere, and they break apart into the small things and they are everywhere in the mangroves, quite shocking.”
What can we take away from this?
When asked about what they would like to tell students, our two teachers shared some important messages. “We went to explore something that most people before were not going to. For that, I had someone to break my comfort zone, and Stefano really pushed me, it was a great opportunity. I wouldn’t have had these interesting findings if I hadn’t come to Hong Kong.” Dr. Guénard shares. “So for the students thinking what could I do in the future, don’t go back to do what people have been doing over and over and over, you know, just find something different because that is where you’re gonna find exciting cool new stuff. I’m preaching for my whole thing, but if you work with insects, usually you will find a lot of cool new stuff, I mean new species with interesting taxonomy, new ecology, new behavior.” “Now I’m searching for crabs in the forest,” Dr. Cannicci adds, “There are 4 or 5 species that I have to really go… the water is there, my crabs are there.” “Just think outside the box” quips Dr. Guénard.
The project definitely took a different approach to mangroves, and saw it in a new light. But what we can learn is not only restricted to the discoveries in the field. “If i can say something that I‘m really proud about this, is that actually in this department, it’s pretty much ‘okay there's the marine people, and there's the terrestrial people’, but that’s not true.” Dr. Cannici says. “It’s not about thinking about a marine group, or a terrestrial group. This is one of the few projects where you break this kind of compartmentalization. You learn a lot working with someone who is doing something different from another point of view.”
So, what’s next?
The project will be completed by the end of May next year, and there's more than just sorting out data for the remaining 9 months. “We are preparing a GIS system, so by the end of the project, we will have a map of Hong Kong, the (mangrove) sites, list of species and everything related to that species.” Dr. Cannicci says. So if you would like to learn more about the “Mangroves of Hong Kong, where are they now?” project, remember to look out for it then.