Halgerda formosa -colour variation [1].

January 7, 2004
From: Yves Coze

Dear Bill
In response to your comments about my latest message here is a composition of all Halgerda we've spotted here in Reunion Island. There were all spotted either in "Cap La Houssaye" or "Abri Cotier" which are two diving spots separated by approx 4 km. Composition of the spot are the same, Rocky area with various sandy and coral area. I've never spotted any halgerda in other diving places in Reunion, but I guess it's more like bad luck !

Nevertheless, Halgerda were mostly spotted on bare basalt area (60%), we spotted a "group" on a red sponge (20%) , sometimes on sandy area (15%)scarcely on coral reef (5%). According to my dive buddy, they can be spotted on these Red sponges at almost every dive. Maybe the Halgerda feed on these sponges ?

While looking at these pictures I noticed something weird. It noticed that most of the sightings happened between end of May to end of August. We reached a "peak" when we spotted approximately 10 Halgerda during à dive. Would you think they have some kind of "seasonal" behaviour ?

I hope all this will help you.
Best regards
Yves Coze

info@rando-reunion.com

Coze, Y., 2004 (Jan 7) Halgerda formosa -colour variation [1].. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11544

Dear Yves,
Thanks for your great collection of photos. As I wanted to keep the images reasonably large I have separated them into a number of separate messages [see message 2, message 3, message 4]. I am sure they are all one species and so show the variability found in Halgerda formosa. As I have often said, extra photos are never a waste. In this case we now have an excellent idea of the variation to be found in this species. I have discussed the variation in a separate message.

Your observations of this species on a red sponge are also of great interest and almost certainly indicate its food sponge. It is most likely that this species has a seasonal cycle. In tropical waters we tend to think that because there aren't the obvious temperature changes associated with the 'seasons' found in temperate climates, that tropical waters don't have changes during the year. Anyone who has spent much time in tropical environments soon realises that there are indeed seasonal changes in the tropics associated with monsoons, wet seasons etc, and althought there is not much published on the topic, many organisms go through annual cycles just like in temperate waters,

Thanks again for this wonderful collection of photos
Bill Rudman

Rudman, W.B., 2004 (Jan 7). Comment on Halgerda formosa -colour variation [1]. by Yves Coze. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11544

Factsheet

Halgerda formosa

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