Nudibranch Puzzle
The resort manager at Loloata Dive Resort in PNG emailed us with a couple of pictures and an interesting description of nudibranch behaviour. For several days, divers at Loloata have seen a large 25-cm Dendrodoris tuberculosa at the Lion Island dive site.
What’s unusual is this — first, the nudibranch has eight commensal emperor shrimps living on it! The most anyone at FiNS Magazine has ever seen up to now is three shrimp on one nudibranch. Eight is simply amazing!
And second, there are two smaller nudibranchs living under it (5 to 7 cm each). They appear to be smaller versions of the bigger nudibranch. From time-to-time, the little ones venture out a bit, then return to the underside of the big sea slug.
We asked FiNS Consultant Clay Bryce what the possible relationship between the large and smaller nudibranchs could be, and whether it’s possible the smaller nudibranchs are offspring of the big one:
“There are quite a few strategy variations as to how nudibranchs develop into crawling slugs from the egg. Some may hatch directly (usually large egg size) from egg to adult shape (also called direct development), others may have a free-swimming laval stage (planktotrophic stage - very small egg size), while others opt for a free swimming, nonfeeding stage that may be only a few minutes long (Lecithotrophic stage).
As to what D. tuberculosa does, I have no idea! I cannot find any reference to it looking after its young. While many a strange thing happens underwater, it’s unlikely that the slug is watching over young. It is more likely an opportunistic event where some smaller slugs or even young D. tuberculosa, if that’s what they are, just happen to be using the larger animal as convenient cover. It could be that all are feeding on the same sponge with the larger animal dominating available space.”
There are just so many things about the ocean we don’t understand. If anyone has any insight into the nudibranch mystery, please let us know.