Berghia norvegica rediscovered

Berghia norvegica nudibranch

The Berghia norvegica nudibranch was described back in 1939, but it has never been seen until we rediscovered it at the Nudibranch Safari in March 2012. See images and video here!


The first image of the newly rediscovered Berghia norvegica with eggs. Shot at Gulen Dive Resort, March 2012.


Posted on May 3, 2012
In December 2010, this strange nudibranch turned up at the house reef at Gulen Dive Resort on a dive with fellow underwater photographer Bjørnar Nygård.

We had never seen anything like it, and were both puzzled by its appearance. Further dives turned up a few more specimens in January 2011, but we were still unable to identify it.

We were hoping that the expert team of experienced nudibranch spotters present at the Nudibranch Safari in March 2011 could help us determine what species it was - but this time we could not find it.

The plot thickens

When the strange nudibranch was spotted again in April 2011 a specimen was collected and shipped to scientists Jussi Evertsen and Torkild Bakken of the Norwegian University of Science and Technology (NTNU) for further study.

They have been running a nudibranch identification program since 1997, mapping and DNA barcoding the species found along the Norwegian coast.

After the initial study of the collected specimen, they soon suspected we might have found a Berghia norvegica, a species described by Swedish zoologist Nils H. Odhner from two locations in the Trondheim fjord in 1939. It had never been seen since.

The radula holds the key

Unfortunately, the scientists needed more material to work with in order to make a positive identification. Anticipation was running high before the Nudibranch Safari 2012 - would we be able to find it again?

A pair of Berghia norvegica with eggs, found underneath a rock. Note the tiny, egg-eating nudibranch Favorinus blianus in the foreground - probably looking for a meal.

They did not have to worry: Several more nudibranchs turned up during the Nudibranch Safari, and on-site study reinforced the belief that Berghia norvegica was the most likely suspect.

Several specimens were brought by the scientists back to their lab in Trondheim, where they scrutinized the radula - a small, calcareous tooth that molluscs use to feed.

Image gallery - please click for larger images:

Looking at the radula under microscope is one of the few ways to distinguish one species of nudibranch from another. DNA barcoding is of course even more effective - but old recordings like this one does for obvious reasons have no DNA to compare with.

Their conclusion after comparing the radula to Nils Odhner's original description was that the collected specimens were indeed Berghia norvegica - documented for the first time since 1939.

Significant rhinophores

Berghia norvegica is a rather large aeolid species, measuring up to at least 30 millimetres. It is bright orange in colour with white-tipped fringes (cerata) on its back, and it has long oral and head tentacles (rhinophores). According to Jussi Evertsen, the rhinophores are significant:

- One of the important characters are the rhinophores with large tubercles. Other important characters is the round shape of the cerata and arrangement of the cerata into arches, he says.

The knobbly head tentacles was one of the things that had us puzzled in the first place - we had never seen anything quite like it.

Jussi Evertsen explains that the only other nudibranch in Norwegian waters that could resemble the Berghia norvegica is Flabellina nobilis, which also has tuberculated rhinophores:

- The pigmentation and ceratal arrangement is however quite different, and luckily the radula is distinguishable from the Aeolidiidae, he concludes.

Worldwide, there are just nine species in the genus Berghia, mainly found in European and Caribbean waters. They are closely related to the Aeolidia and Aeolidiella genuses.

The Berghia norvegica was under close scrutiny at the Nudibranch Safari at Gulen Dive Resort in March 2012. Still, a positive identification could not be made until the radula was examined undeer microscope some time later.

Shady behaviour

Berghia norvegica is a burrowing species, and seems to prefer areas with moderate to strong current where the rock and gravel size allows it to hide in the substrate.

This might indicate that the distribution is limited only to habitats meeting its specific demands, although it is now proved to not occur only in one geographic location.

When observing the Berghia norvegica, it was evident that it does not like to be out in the open: As soon as it was exposed it moved with surprising speed and determination towards safety under a rock or empty seashell, as can be observed in this video:

All the specimens we found at the Nudibranch Safari were buried in the substrate, although we did observe a few exposed animals in December 2010 and January 2011.

We also found numerous egg spirals believed to belong to the Berghia, also located underneath rocks. They were sometimes under attack from Favorinus blianus, but although it is still unclear what the Berghia feeds upon they seemed to have no interest in the eggs.

On several occations we have observed a quite noticeable 'pout' like the one displayed by Flabellina species when attacking a hydroid, and one observation suggests that Berghia may feed on small polyps such as Gonactinia prolifera. Further observations are however necessary to confirm the food source.

Join the Nudibranch Safari

For spotting nudibranchs in Norway, there is no better place than the house reef at Gulen Dive Resort. In the spring there are nudibranchs everywhere! So far more than 50 species have been recorded - more than any other location in Norway.

If you want to see the Berghia norvegica for yourself, the Nudibranch Safari is a good place to start. Sign up for next year's most beautiful adventure!

» Click here to read more about the Nudibranch Safari

The scientists have also written about the rediscovered Berghia norvegica on their blog (Norwegian only):

» Click here to visit Nudibranchia.no








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Christian Skauge
Etterstadsletta 4 G
N-0660 Oslo, Norway


   

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