What happens when a non-native seaweed spreads out to foreign coastlines? It can become invasive and may cause adverse effects on native near shore ecosystems and aquaculture.
The spongy green seaweed Codium fragile subspecies fragile, commonly known as green sea fingers thought to come from the Northwest Pacific, is a non-native seaweed found in both the UK and Norway. It has spread along coastlines in several continents, and may have effects on nearshore ecosystems and aquaculture.
It’s not all bad news
Not all types of green sea fingers are detrimental to foreign coastlines. This subspecies is just one of several within C. fragile species. In contrast to the subspecies fragile, the other seaweeds seem to lack invasive tendencies.
In spite being very similar in appearance, they may look similar to the non-native subspecies. Which is why it’s essential that non-native species can be accurately identified for management and scientific work.
In a study published in the journal Botanica Marina, scientists indicate that commonly-used morphological characters can be unreliable for separating the widespread non-native subspecies from a native subspecies of the green seaweed, Codium fragile
It is critical that the non-native subspecies can be accurately identified for management (monitoring and impact assessments), and scientific work (studies of invasive success).
In Norway, there were thought to be three subspecies: subsp. fragile, subsp. atlanticum, and subsp. scandinavicum. This was however based on morphology, and had not been examined in detail since genetic sequencing became widely available.
A case of mistaken identity
A genetic study based in the British Isles had shown that subsp. scandinavicum was actually subsp. fragile according to the sequence of the Danish type specimen, and that all the subspecies had frequently been misidentified historically.
This cast doubt over the validity of the subspecies identity of Norwegian specimens. The present study was therefore done with three aims: 1) To see when subsp. fragile arrived in Norway, 2) To ascertain which other subspecies are present in Norway, and 3) To assess whether morphological traits commonly used to separate the subspecies are reliable.
Non-natives around longer than previously thought
Genetic sequences of historical herbarium specimens showed that the non-native subspecies, subsp. fragile, had actually been present since at least 1932, not 1946 as previously thought. This ties in well with observations from Norwegian fishermen and scientists who observed a huge increase in the abundance of C. fragile in the 1930s.
Sequences showed that at present, this non-native subspecies is common and may occur in several habitat types. However, the native subsp. atlanticum was also present in mid-Norway, and could co-occur with the subspecies. fragile.
Perhaps most importantly, sequences of herbarium specimens and morphological analysis of collected samples indicated that the morphological characters commonly used to separate these two subspecies can in fact be variable and unreliable.
Read the original article here