NatureToday | A new tang: blunt reindeer antler

Once again, a seaweed has been found in the Oosterschelde, which has not previously been observed native to the Netherlands (but on land). It concerns stump reindeer antlers (Osmundea hybrida). This species was found near Goese Sas, the same place where finger netted jellyweed (Gelidium spinosum) was found. Blunt reindeer antler is an Atlantic species that has been present south of our country for a long time: from Portugal to the British Isles (from the Channel and north to the Shetland Islands). Tangen is not known north-east of the Netherlands (Helgoland, Denmark and Norway). With this establishment in the Netherlands, the species has managed to expand northwards: it is therefore a so-called climate changer, which has made use of the rising temperatures.

Not into scallops?

Blunt reindeer antler weed immediately caught our attention because quite large plants – 10 centimeters high, 20 centimeters in diameter – were observed in Scalhorus (Patella vulgate) bore mid-tidal grazing zone, the ‘Limpet Zone’ or ‘Shell Horn Zone’. Only a few places in Zeeland manage to graze completely naked in a zone approximately two meters wide. It is of course strange that blunt reindeer antlers are not grazed: perhaps the local shieldhorns do not (yet) recognize this weed as food. Or maybe this seaweed is inedible or unappetizing for some reason. For example, it is known that some seaweeds can produce complex chemicals to prevent damage. The most famous example is vinegar (Desmarestia viridis), which fills its cells with acid with an acidity of less than one. From Osmundeaspecies are known to produce various halogenated compounds (including chlorine and bromine compounds) to prevent grazing by herbivorous crabs and sea urchins. This can therefore also apply to scallops. Other slugs don’t seem to mind the weeds; for example, we looked at and between the seaweed Periwinkle (Littoria littorea) and the Japanese sharphorn (Ocinebrellus inornatus).

Fun fact: It is known from abroad that blunt reindeer antlers can also grow ON the shell of antlers.

Recognize

Blunt reindeer antler is a red tang, although you wouldn’t immediately say so. In the field, the color of the older parts is dark purple-brown, sometimes with a slight red tint. The buds are much lighter in color, almost yellow. During the year the color gradually becomes lighter brown, to yellow under the influence of sunlight and sometimes light green due to endophytic green algae that have settled between the surface cells. It is a fairly firm seaweed that also maintains its structure above water. It adheres (especially) to the shady side of stones with a disk-shaped adhesive base that can be up to 1.5 centimeters in diameter. The seaweed dies out during the summer, the “sticky foot” remains present all year round.

The cartilaginous axes are richly branched, and no distinct main axis can be distinguished. The blunt ends of the small lateral branches are somewhat concave (lowered); in the cavities are bundles of hair. Growth takes place from these cavities. All plants found appeared to produce (asexual) reproductive products: tetrasporangia, capsules with four spores arising from the surface cells. Sexual reproductive products, such as male spermatangia or female cystocarps, have not yet been observed in the Netherlands.

Incidentally, another representative of this genus is known from the Netherlands – on the feet of washed-up shingle weeds: Feathered reindeer antlers (Osmundea pinnatifida). This has much flatter and more regularly sprung shafts and is often reddish purple to purple in color. Unlike the Stubby Reindeer Antler, the Pinnate Reindeer Antler has a creeping, branched adhesive base.

Blunt reindeer antler is a robust red tang with a brown to purplish-brown color, the ends often much lighter, even out of the water.  Right: end of a branch with sunken top and tuft of hair;  in the middle the much redder tetrasporangia

Confirmed by DNA

In the field, the new weed plan made regular visitors to Brittany an instant hit
Osmundea-a kind of thinking, but at first it was still unclear what kind it was. Based on the sunken peaks O. hybrida is seen as the most likely candidate. DNA research carried out by Luna van der Loos from Ghent University has now confirmed this identification.

Call

The first specimens of Stomp reindeer antlers were found on 30 April 2022 on the north side of the old exit from Havenkanaal van Goes (Dykkersted Goese Sas). On 12 July 2022, several specimens were also found 200 meters northwest of it. We are curious how quickly this species spreads through the Oosterschelde and whether it has been observed in more places. We would like to encourage everyone to keep an eye out for Stump reindeer antlers. Location photos are welcome!

Observations

Interested in observing seaweed and animals that live in the intertidal zone on the paved parts of our coast? Then you are very welcome to the ANEMOON Foundation’s LIMP project. You can register and submit observations to this project via the ANEMOON portal. Individual observations are welcome on platforms such as Verdispersingsatlas.nl and Waarneming.nl.

Text: Frank Perk, Luna van der Loos, Mart Karremans & Mick Otten, all ANEMOON Foundation and Beach Work Community; Luna van der Loos also Ghent University
Photos: Mick Otten (main photo: part of a rock completely covered with Stump reindeer antlers (Goese Sas, 30 April 2022); Frank Perk

Leave a Comment