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mrbheagney
09-01-2008, 15:42
I am a Marine Biologist as well as a diver and that's why I felt this kind of place was really missing from the discussion boards. Working in the industry I often come across people who say they have had a boring dive and that really grinds my gears, especially since I am always working in the tropics. I see every dive I go on as a classroom lesson in the University of Marine Biology. my teachers are the animals that I observe, their behaviour and their interaction with each other and their environment. I like to learn something new on every dive I go on and it is always possible - especially in the tropics with so much going on. Although there is usually some life in any given body of water, especially your bath tub. Just to ID a particular fish I have never seen before or observe something interesting like a Trumpetfish Shadowing a larger Grouper to sneak up on unsuspecting prey. Just a few months ago I inspected the underside of a large sea cucumber in search of small shrimps and I found a beautifully patterned little crab. Feeling threatened by my camera it rushed directly to the anus of its much larger host and held on for dear life. I try to imagine how the sea cucumber must have been feeling about these little clamps on it's bottom. I have attached a picture of the aforementioned ass bandit in his luxurious hideout for your enjoyment. The underwater world really is an amazing place if you try hard to look that little bit closer. Understanding the world beneath the waves makes it a much more enjoyable place. I will keep this thread updated with more animal stories as I come across them. Thanks for creating this discussion area Larry. Thanks for looking too.

DevilDiver
09-01-2008, 18:16
I am a Marine Biologist as well as a diver and that's why I felt this kind of place was really missing from the discussion boards. Working in the industry I often come across people who say they have had a boring dive and that really grinds my gears, especially since I am always working in the tropics. I see every dive I go on as a classroom lesson in the University of Marine Biology. my teachers are the animals that I observe, their behaviour and their interaction with each other and their environment. I like to learn something new on every dive I go on and it is always possible - especially in the tropics with so much going on. Although there is usually some life in any given body of water, especially your bath tub. Just to ID a particular fish I have never seen before or observe something interesting like a Trumpetfish Shadowing a larger Grouper to sneak up on unsuspecting prey. Just a few months ago I inspected the underside of a large sea cucumber in search of small shrimps and I found a beautifully patterned little crab. Feeling threatened by my camera it rushed directly to the anus of its much larger host and held on for dear life. I try to imagine how the sea cucumber must have been feeling about these little clamps on it's bottom. I have attached a picture of the aforementioned ass bandit in his luxurious hideout for your enjoyment. The underwater world really is an amazing place if you try hard to look that little bit closer. Understanding the world beneath the waves makes it a much more enjoyable place. I will keep this thread updated with more animal stories as I come across them. Thanks for creating this discussion area Larry. Thanks for looking too.

Nice...
So, what kind of crab is this? I looks like a clinging crab of some kind but I am not fimilar with the pattern.

:smiley20:

drako
09-01-2008, 18:30
Nice...
So, what kind of crab is this? I looks like a clinging crab of some kind but I am not fimilar with the pattern.


Looks like a porcelain crab. Really cool crabs, they are filter feeders. When I had a tank setup I had two or three of em. Really cool to watch.

mrbheagney
09-01-2008, 19:54
I also believe it to be a Porcelain Crab of sorts but I have not been able to formally identify it as yet. As for feeding I would speculate that it feeds on orgainic matter from the detritus adhering to the cucumbers body and possibly on secretions form the cucumber itself. It may filter feed but my preliminary finding are contrary to this assertion as the crab is always underneath the cucumber where filter feeding would be difficult because of limited water passage. I have not observed the symbiosis at night, it would be interesting to see if the crab then moved up onto the body for filter feeding. Considering the accuracy of its camouflage these two are a nice example of co-evolution and as such they most likely derive benefit from each other which would class the relationship as mutualistic, although is difficult to see the benefit for the cucumber. It may be feasable to assume the crab cleans it host in return for transport as cover. The other side of the argument is that the crab simply hitches a ride saving energy as it host travels distances otherwise impossible for such a small animal, jumping on and off as desired to feed. Beautiful little critter anyway. If anyone wants to view these crabs just find a big cucumber abd turn it over briefly for a look. Please remember to respect marine life and be gentle with the cucumber, replacing it back on its belly when you are done. Thanks

warscout2
09-01-2008, 20:02
that is a great picture how big would you say that crab is? would it be smaller then say a dime?

sidneydiver
09-01-2008, 21:44
Thank you for suggesting this topic. I am far from being a marine biologist but I am so interested in the life that I see while I'm diving and in learning to ID more life and learn about the behaviours.

drako
09-01-2008, 23:45
First and foremost THANK YOU! I did not even take into account the whole situation. I would agree with you that it is feeding from the detritus. Was this the first time you saw this fella hitch hiking on the sea cucumber?
When I have observed the porcelain crabs, they do infact filter feed at night. How exciting man, I have only been able to observe them in captivity! I think the crab is also referred to as an "anemone" crab in some circles. Although I would like to think that there is a symbiotic relationship my basic understanding of them would have me incline in the second argument. Although they are pretty non-aggressive animals.
:smiley32: It would be great to have more discussions. I was only a student in Marine Bio for a few years. Should of kept on going with it:smiley13:

mrbheagney
09-02-2008, 16:04
Being unfamiliar with american currency I am not sure about the size of a dime but the animal was probably about 1 cm at the widest point of it's carapace. Really tiny actually.

mrbheagney
09-02-2008, 16:25
First and foremost THANK YOU! I did not even take into account the whole situation. I would agree with you that it is feeding from the detritus. Was this the first time you saw this fella hitch hiking on the sea cucumber?
When I have observed the porcelain crabs, they do infact filter feed at night. How exciting man, I have only been able to observe them in captivity! I think the crab is also referred to as an "anemone" crab in some circles. Although I would like to think that there is a symbiotic relationship my basic understanding of them would have me incline in the second argument. Although they are pretty non-aggressive animals.
:smiley32: It would be great to have more discussions. I was only a student in Marine Bio for a few years. Should of kept on going with it:smiley13:

I have observed this crab on several occassions on the Holothuria fuscopunctata sea cucumber and I can find it quite easily at one particular dive site in Ha'apai, Tonga. I have actually begun to recognise one particular individual cucumber that always has it's crab aboard. I also see the Porcelain Anemone crabs you mention and have attached another pic of that one (in new thread to keep threads specific). They seem to be always associated with the short tentacle anemones of the family Stichodactylidae. It is interesting to note that the Chelicera (claws) are much more flattened in the anemone crabs than they are in the cucumber crab. This crab may belong to a different family than the Porcelain crabs. The carapace and eye position are very similar though so I don't know. Can you simplay buy these animals in a store????

CompuDude
09-03-2008, 11:53
Fascinating. :)

I love the tropics, but one nice thing about our nutrient-rich, low-vis, cold waters, is the abundance of smaller life... you just have to slow down to look.

Wide Angle photography gets all the covers, but it's all about Macro for me. :D

mrbheagney
09-03-2008, 12:18
Yeah, I agree totally. I have seen most of the big stuff and I now get much more excited discovering the critters. The macro photos are a bit less technical too which is helpful considering my skill level.