We are planning to study shrimp species invasion in a bay in Japan. Our primary hypothesis about the method of invasion is through ballast water. However, it could be otherwise. Therefore could you please share your expertise to help us about the procedures, guidelines, methodologies to study marine species invasion. Thank you in advance.
There are very many aspects of species invasions so it would be useful if you could elaborate on what your specific questions are. Are you only interested in how the shrimp arrived in the bay, or are you planning to study some other aspect of the invasion?
Dear Aleksandra Maljkovic: Thank you very much for your interest. My primary objective beside others is to identify the source/method of introduction of Metapenaeopsis sibogae in Japanese waters. This species was reported from Philippines in the past but now is abundant in southern coasts of Japan. So, it is important to identify the source/method first and then could go for further detailed studies. Our hypothesis is, this species is introduced here either by ballast water or by drifting. So, now I need to design my research for studying the method of introduction of this species considering these two as the possible answer. It would be really nice of you if you can suggest me. Thank you in advance.
As far as I can see, this shrimp has been previously reported from Indonesia, New Caledonia, and as you state, the Philippines. As Indonesia and the Philipines trade heavily with Japan, an introduction via shipping is most likely via these routes. The most efficient way to tell where the origin of the shrimp is, is via DNA analysis. If you can pinpoint the geographical source of the introduction using genetic techniques, you can then look at ocean current maps and see whether it is at all possible if they arrived naturally, or whether ballast water from ships is a more likely possibility. A second potential approach, but I think a more difficult one, would be to directly sample ballast water from ships arriving in Japan from potential source countries. Adult shrimp as well as eggs and larvae may be present and could provide irrefutable evidence of a shipping-based introduction.
I agree with Aleksandra. If you want to be sure on the source of origin you have to do this with DNA analysis. Nevertheless, there is possibly more than one source and very likely also several events (many?) when this shrimp arrived in Japan. Ballast water is in many cases of introduction the likely source but I suggest to check ballast water tanks directly. This can be a problem if there are no regulations by law. Otherwise you are dependent on the good will. If you do not check the ballast water, you will always stay with 'the likely source is ...'. Besides ballast water also the fouling matrix on ship hulls is capable to transport invertebrates and even small fish. Drift is dependent on currents and I do not know the currents in this region.
I have limited experience in this area, but it seems as though it would be difficult to demonstrate that shrimp definitely arrived via a specific mechanism. However, you could try to eliminate possibilities. My instinct would be to determine whether the shrimp could survive either method (determine how long the shrimp can survive in ballast tanks vs. open sea water, and how they would need to survive to arrive at the new destination via each method). Ideally, this would be done with progeny in Japan, because it's their ancestors that are in question.
Many crustaceans can be carried in ballast water and this includes shrimp species. However, it is very difficult to ascribe an introduction to a particular species as being due to ballast water as there is no direct evidence. The best result is that you may have reason to deduce a presence from the various activities in the region where it is first found where it is confined and has not expanded its range. One needs to consider all of the possible pathways and their vectors in an area. Should you know the current distribution of the species world-wide (that you can rely on) then this may also aid in identifying a source and perhaps an appropriate vector according to the known trade in your specific area.
You may also read: Ben-Yami, M. and T.Glaser.
The invasion of Saurida undosquamis (Richardson) into the
Levant Basin - an example of biological effect of inter-oceanic
canals. Fish.Bull.(USA), 72 (2):359-373. 1974.
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