Today we learn more about the curious life style of bryozoans from Dr Dennis P. Gordon on Day 2 of the
Bryozoans and Hydroids Workshop.
Do bryozoans have sex? How do they do it? What do they eat? What would eat a bryozoan? And lots more!
Bryozoans are zombies! The feeding zooid has tentacles as well a
stomach to digest food. Nutrients it obtains are passed on to other kinds of
non-feeding zooids in the colony. What is amazing in bryozoans,
the feeding zooid will die after a few weeks usually because its stomach is
all gunked up. After which a new feeding zooid grows within the same
container. This can happen once or 4-5 times.
Here's a closer look at a colony with some live polypides, some dying ones and some in the process of being regenerated.
Bryozoans eat plankton or bacteria. To gather these from the water, bryozoans have tiny 'hairs' or cilia on their tentacles that beat in synchrony. This creates a downward current through the ring of tentacles. Bringing food particles into the mouth in the centre of the ring. But where does the current go after that? Special 'empty' patches are found in the colony where the 'sucked' in water is expelled away from the colony. Somewhat like a sponge with many tiny holes where water is suck into the sponge, after which the water is expelled through larger holes in the sponge.
Some bryozoans have a gizzard, a kind of sac for grinding food. The bryozoan gizzard has tiny teeth that resemble in structure, the bristles of bristleworms!
And now for the exciting details of how the bryozoans have sex. Each animal with tentacles may produce both eggs and sperm. For a long time, no one knew how the sperm was ejected and some thought bryozoans were self-fertilising. Careful study eventually revealed that the sperm emerges through the tip of the hollow tentacles! What emerges from the tentacles is a bundle of sperm and not individual sperm!
Fertilisation takes place internally, so sperm must be sucked into another animal. In some, the fertilised egg is released to develop as free-living larvae among the plankton.
In others, the fertilised egg is squeezed into a specialised zooid that is adjacent to the 'mother' animal. This zooid is called an ovicell and doesn't just protect the egg but also nourishes it through something that acts like a placenta! Bryozoans are good mothers indeed.
Like fastidious ladies, some bryozoan larvae carry bacteria which they squirt around before they settle on a surface. This bacteria produces bryostatin which makes the larvae taste bad to fishes. Byrostatin has also been found to have anti-cancer properties. More in
Marine Moss Reveals Clues To Anti-Cancer Compound Science Daily 11 Mar 2007.
The different zooids in the colony play different roles and have different forms.
Some
zooids are modified into spines which can move about. These can sweep
around to keep the colony clean. In others, like this tiny disc shaped
colony, the spines actually allow the entire colony to creep or right
itself! Like a tiny sand dollar.
Bryozoans have lots of defensive structures and chemicals. Clearly some things find them tasty.
Bryozoans are tiny and there doesn't seem much to snack on. Although
their eggs may be tasty. Still, lots of creatures of all kinds will eat
them. Some drill holes through their containers to get at them.
Dr Dennis showed some slugs that eat bryozoans. They resemble their food perfectly!
In response, bryozoans have all kinds of defences. Some bryozoans will grow spines only if the nudibranch that eats it is present. Others have modified zooids that form huge snapping jaws. These can chomp down on small creatures.
Here's a snapping jaw that has chomped down on a tiny crustacean. The dead crustacean soon rots, and become laden with bacteria which is food the bryozoans! Some zooids may also function to taste the water, alerting feeding zooids to emerge when there's lots of food.
Bryozoans have strange partners. One bryozoan grows on a tiny snail shell and continues to grow to extend the shell and accomodate a hermit crab. Other bryozoans may have stinging hydroids growing on them, which is good as it helps keep off bryozoan predators.
Some bryozoans grow on other marine creatures including sea snakes and horseshoe crabs!
This is just a tiny bit of the fascinating information Dr Dennis shared about bryozoans!
Earlier on, thanks to Cai Yixiong for lugging up my cooler full of bryozoans and hydroids from Changi!
Settling the specimens in the lab, I was a little late for Dr Dennis' tips on how to collect and preserve bryozoans.
Dr Dennis highlights how to prepare bryozoans that are found inside coral rubble. It involves rock cutting tools!
After the lecture, it was time to head up to the lab to have a closer look at the bryozoans.
Dr Dennis kindly draws what we should look for in the microscope!
This bryozoan is so tiny, we couldn't possibly spot it in the field. We
can only find these by checking through material under a microscope.
I realised that this piece of paper listed all the bryozoans Dr
Dennis had identified just during the first day of his visit, many of
them are new records for Singapore! Wow!
Meanwhile in the corridor, Yen-ling was smashing dead corals to see if there were any bryozoans lurking within.
It was great to have a closer look at the
glassy branching bryozoan that I found at Changi earlier today. There are all kinds of other animals on it. It's hard to tell which tentacled animal is the bryozoan and which are hydroids or other beasties.
And here's the bryozoan tentacles. Dr Dennis explains, unlike hydroid tentacles that usually don't move and rely on stingers to catch their prey, bryozoan tentacles are always moving, often flicking the tentacle tips regularly.
Later on, I showed Dr Dennis the photo that
Chay Hoon took of the nudibranchs that live on these bryozoans! We saw these at Punggol but I was too lame to photograph these super tiny creatures.
It was another long tiring day, and another long tiring day tomorrow. We are going to hunt for bryozoans in the mangroves with Dr Dennis! Quite exciting!
