Let's explore our amazing underwater life of Hong Kong!
Subvented by the Agriculture, Fisheries and Conservation Department. Any opinions, findings, conclusions or recommendations expressed in this material/ event do not necessarily reflect the views of the Government of the Hong Kong Special Administrative Region.
Does this snail look very colourful to you? Though it may look very attractive, it is indeed one of the most venomous snails and the last snail you may want to touch if you happen to see them on a beach or under the sea. They can stretch out their proboscis, tipped with a harpoon-like tooth at the end, to eject venom into their prey. The venom acts as neurotoxins, and is so strong that even human deaths have been attributed to them. So please make sure you will be aware of it when exploring the Hong Kong shoreline and sea!
𝘏𝘰𝘭𝘰𝘵𝘩𝘶𝘳𝘰𝘪𝘥𝘦𝘢 (𝘔𝘦𝘳𝘵𝘦𝘯𝘴𝘪𝘰𝘵𝘩𝘶𝘳𝘪𝘢) 𝘭𝘦𝘶𝘤𝘰𝘴𝘱𝘪𝘭𝘰𝘵𝘢
Although they may look ordinary to you, they are actually one of the most common sea cucumbers in Hong Kong! They also have a very important role under the sea - maintaining the balance of the nutrient cycle.
When threatened, this sea cucumber discharges a white and sticky substance out of their anus to snare their predators. This substance is known as Cuvierian tubules, which are their internal organs. When they are safe again, these tubules will be regenerated quickly. But one gentle reminder: the regeneration of the Cuvierian tubules is very energy-demanding, so please don’t ever try to trigger this defensive mechanism if you’ve got a chance to see them in the wild!
Long-spined sea urchin have sharp and slender spines, which vary in length. It is characterised by a distinct bright orange ring that looks like an eye! In fact, it is not an eye, but the excretory organ (anal cone) of the sea urchin.
Although their spines seem threatening, they indeed help to support marine biodiversity by providing a safe haven for small shrimps, crabs or fishes! Still, we'd better keep our hands off the sea urchin when we encounter them in the sea. Trust me, you don't wanna feel the pain!
What do you know about the short-spined sea urchin? The deep purple coloured urchin may not look very attractive, but you may have tasted it before you like sashimi! By the way, do you know which part of urchin are you actually eating? The bright yellow-orange edible part of sea urchin is their gonads!
Urchins are typically with a spiny and hard shell, and usually feed on algae. Different types of urchins may not only have distinctive colours, but the length, thickness and even distance between spines may vary too! This urchin featured in the graphic today, is special in a way that it loves to collect little things like stones, shells or algae pieces, to “decorate” itself.
Papuan jellyfish is one of the commonly found jellyfish species in Hong Kong. It is characterised by the pale yellow spots on their semi-transparent bell. Their body is usually observed to be greenish blue to olive green because of the zooxanthellae that live symbiotically within the jellyfish.
Warm reminder: As jellyfish may inject venom into your body when triggered by touch, let's remember to show your respect by not touching them no matter where you meet them!
Are those words on the shell of this cowrie?? Not really! It’s just a complex pattern, which looks like Arabian characters. That’s why it is called Arabian cowrie~ It is a common species in Hong Kong and mainly feeds on algae. It can be found from intertidal to shallow water. Yet, they like to hide in crevices of hard corals or under boulders. So don’t miss the nooks and crannies when you’d like to see one.
Eight-armed starfish is a large-sized starfish, with a diameter up to 30 cm! They always burrow into the sediment with their arms and spines, it might not be that easy to spot them in the sea.
In spite of the name eight-armed starfish, they can have 7 to 9 arms, with 8 arms being the most common. Besides, they are actually active carnivorous animals that hunt and feed on other invertebrates including echinoderms!
Pennant coralfish have two broad black bars on their white body, with a prominent filament extending from their dorsal fin. They feed on plankton and benthic invertebrates, and we may often find them in coral communities or rocky reefs in Hong Kong. They may appear singly, in pairs, or even in small groups!
Nudibranchs belong to the class Gastropoda and are close relatives to snails. However, they are shell-less, so they have developed different strategies to protect themselves. Many nudibranchs are vibrantly coloured, warning their predators they may not be as tasty as they thought. Another effective defence system is that, they obtain toxic chemicals and derive noxious compounds from the sponges, algae or sea anemones they eat, and use them against their predators later on! To further protect themselves, some nudibranchs even store stinging cells on their back by ingesting the tentacles of jellyfishes, sea anemone, or other stinging animals!
Brownbanded butterflyfish are very distinctive as they have 3 orange-brown vertical bars on their body, as well as a big black spot on the posterior part of the dorsal fin. The attractive butterfly fish is actually one of the most abundant butterfly fish in Hong Kong, and we often find them in shallow boulder areas in Hong Kong. Let’s try to look for them next time when you have a chance to dive into Hong Kong's waters!
Hong Kong pufferfish
Hong Kong pufferfish have lots of irregular white spots on their back, with a whitish to yellow belly. One of the characteristics of pufferfishes is their ability to inflate themselves when threatened and to increase their size dramatically, so it may be rare for you to have seen their ‘usual’ faces as shown in the graphic. Similar to all pufferfish, some body parts of Hong Kong pufferfish contain tetrodotoxin and are highly toxic and lethal if eaten. In Japan, it takes a lot of skill and training to prepare pufferfish safely by removing the poisonous body parts. Chefs also need to take extensive exams before they are legally allowed to serve the dish. If you are given the chance in the future, do you dare to try?
Brain coral (𝘗𝘭𝘢𝘵𝘺𝘨𝘺𝘳𝘢)
Hard corals belong to the subclass Hexacorallia which bear tentacles in multiples of six. They also possess hard calcium carbonate skeleton. 𝘗𝘭𝘢𝘵𝘺𝘨𝘺𝘳𝘢 is one of the most common hard corals in Hong Kong. Their corallites are meandroid, which have fused walls forming valleys, which give them a maze-like or brain-like appearance. 𝘗𝘭𝘢𝘵𝘺𝘨𝘺𝘳𝘢 corals usually form massive colonies, reaching heights of more than 1 meter! Although their growth rate is rather low, they have a special surviving strategy. Under the fierce competition of space, 𝘗𝘭𝘢𝘵𝘺𝘨𝘺𝘳𝘢 corals can attack other corals with their elongated sweeping tentacles! How aggressive!
Staghorn coral (𝘈𝘤𝘳𝘰𝘱𝘰𝘳𝘢)
𝘈𝘤𝘳𝘰𝘱𝘰𝘳𝘢 is also one of the most common hard corals in Hong Kong~ With the common name staghorn coral, I believe it’s not difficult for you to imagine its appearance! Different growth forms of 𝘈𝘤𝘳𝘰𝘱𝘰𝘳𝘢 have been recorded in Hong Kong, including branching and tabular. And actually branching 𝘈𝘤𝘳𝘰𝘱𝘰𝘳𝘢 coral is the fastest-growing species in Hong Kong! The first batch of 𝘈𝘤𝘳𝘰𝘱𝘳𝘰𝘳𝘢 𝘵𝘶𝘮𝘪𝘥𝘢 that was sexually propagated ex-situ by our team is now 7 years old, 14 cm big and is living happily in the sea! With this fast-growing feature, they are able to get space and sunlight more easily. As a result, zooxanthellae, a group of unicellular brown algae which has a symbiotic relationship with hard corals, can effectively carry out photosynthesis and provide food for corals to enhance their growth.
Black corals also belong to the subclass Hexacorallia, but unlike hard corals, the polyps of black corals are not retractable. They seem to be white or yellow in colour, then why are they called black corals? Because they have black axial skeleton! The yellow or white colours that we usually observe are indeed the colours of their polyps on the surface. A variety of growth forms have been discovered in black corals, but only the whip-like and branched form can be found in Hong Kong.
Soft corals belong to the subclass Octocorallia, and their polyps have 8 tentacles. Soft corals are different from hard corals as they do not possess calcium carbonate skeleton. Instead, they are soft and contain minute spiny skeletal elements called sclerites. In Hong Kong, we usually find them in deeper areas or areas with strong currents. Their feeding behaviour is also different from hard corals, in that they tend to use their tentacles to filter microorganisms around, including tiny zooplankton or protozoa.
𝘗𝘢𝘷𝘰𝘯𝘢 𝘥𝘦𝘤𝘶𝘴𝘴𝘢𝘵𝘢 is a common hard coral in Hong Kong. They have laminar growth form with vertical upright plates, the plates are perpendicular to each other forming communities. This kind of growth form has allowed them to become good habitats for reef fishes and invertebrates. Besides, they grow well in shallow waters, and one of the largest extensive beds of 𝘗𝘢𝘷𝘰𝘯𝘢 in Hong Kong can be found in Hoi Ha Wan Marine Park. Let’s try to look for them next time when you have a chance to dive there!
Mirror butterflyfish has a yellow body with a black vertical bar crossing through eyes and an obvious black blotch on the dorsal side of the body. It mainly feeds on coral polyps and invertebrates. As it is closely associated with corals, it is considered to be one of the indicator fishes and their presence or absence provides clues to the condition of coral reefs ecosystem. Recently, our team has been so lucky to see them inhabiting our outplanted 𝘈𝘤𝘳𝘰𝘱𝘰𝘳𝘢 coral fragments in Tolo Channel! How encouraging!
Hong Kong grouper
Hong Kong groupers have their body covered with red to orange spots as well as several faint and sometimes visible vertical bars on the sides. Another special feature is the large black spot on the dorsal part. Similar to other groupers, they all start off as female and they are able to switch to male when they become mature or reach a certain size. In the 60s, they were considered to be a common species in Hong Kong, but now have become rare and have been listed as “Endangered” on the IUCN Red List of Threatened Species. If we do not put more effort in conserving them, they may become extinct very soon...
If you are a diver, you may have been told to avoid these moray eels as they are known to be fierce with sharp teeth. Although it keeps its mouth open as if they are ready to bite any second, it’s only because they lack an operculum and thus need this to provide constant circulation of the water towards the gills! Normally, marine organisms rarely attack people unless they are provoked at first. Besides, as top predators in the ocean, moray eels also play an important role in keeping the ecological balance, especially that of the coral communities and reefs.
Many people may mistakenly recognise yellowtail clownfish as the same little fishy character in that popular animated movie, however they are indeed of different clownfish species! If you look at their pattern carefully, you may notice their orange to black body, with 3 white vertical bars. Besides, all clownfish start off as male, but can switch to female when circumstances allow, for example, when the only female present in their group dies or disappears. In that case, the second largest male within the group will switch to female and take over the dominant role in the group. So… you may have already noticed what the movie got wrong. To ensure the survival of the clownfish group, Nemo's father should become its mother instead! How complicated…
Squid are part of the class Cephalopoda, which also includes cuttlefish and octopus. All these animals are carnivorous, and are able to release dark ink as a defence tool. So how can you tell these amazing cephalopods apart? One of the easiest-to-tell features may be their morphology and appearance. While squid is more tube-like, cuttlefish have a stout body. Their internal structure looks quite different too. Squid have a flexible and transparent structure called the pen, where cuttlefish have a broad and yellowish white internal shell called the cuttlebone.
As mentioned in the previous post, squid and cuttlefish both belong to the class Cephalopoda, but they do possess lots of differences! To tell them apart, you may try to gaze into their eyes: squid have round pupils, where cuttlefish pupils are W-shaped. Let’s compare this graphic with the previous post and you should be able to tell the difference! You may also watch it move underwater to differentiate them. While squids are fast-moving predators, cuttlefish are slower and move by undulating membrane-like fins on the sides of their bodies.