Hello,
I have been passed this photo of a small crustacean (Malacostraca?) eating planted mangrove seedlings (Rhizophora) in central coastal Vietnam. They are girdling the seedlings, which then fail.
My knowledge does seem to be limited to: oh, looks like a sea louse (!), so I am asking the question.
The situation is somewhat brackish evidently, due to fluvial influence at that part of the estuary, and there is no herbivory in more saline water plantings.
The picture isn't great, but hopefully enough. I do not expect there are easy solutions to the pest problem in mass reforestation efforts!
(Planted seedlings do seem to be generally more susceptible to herbivory and I do think, without visiting the site, that the mangrove species selection may be wrong here, but that is another topic!).
Is it this guy? https://www.sms.si.edu/irlspec/Sphaeroma_terebrans.htm
This is a isopod may be PhD. Socorro Madrigal of the Universidad del Mar, Mexico is expert in these groups. Her mail is [email protected] or ms_garcia_m @hotmail.com writing
Thanks for the answers...certainly S. terebrans looks like it and fits its ecology, Julian, and that is a great site for comprehensive info. I wonder if it is native to Vietnam...
I will send the picture to Dr Madrigal for conformation.
Perhaps the 'plague' numbers are an artefact of the planting in favourable situations for the isopod, and potentially unfavourable situations for Rhzophora (including the likely attempt to plant in mud subject to flooding too deep and too long, as is typical). Last year there were unusually long and deep floods, which might have stressed
The seasonal flooding season in central Vietnam was unusually severe last year which might have weakened the seedlings.
If it is that species (or related), it looks like it has an ubiquitous distribution, amongst Rhizophora stands at least. I know when I have worked with guys replanting mangroves in Kenya (Gazi Bay), they used 'nurseries' which would be much drier and pretty well at the highest tide mark (Gazi is fully marine I think), in order to establish the seedlings, then transplant to the fully inundated areas. They did reasonably well, but there were so many factors at play its hard to know why some failed and others didn't (I was doing fish, they were doing the tree ecology...). Maybe Rhizophora have narrow habitat requirements for mangroves?
Yes, there is debate about nurseries for the Rhizophoraceae, especially Rhizophora because the 'propagule' (viviparous seedling) is so easy to direct plant. The VN experience in reforesting after the US defoliation in Rung Sat (Can Gio now) and Ca Mau and continuing now in farmers planting in aquaculture areas was/is direct sowing. So easy.
Generally nursery culture is a waste BUT perhaps not in this case if the advanced seedlings are more resistant if grown on in a nursery. An avenue to try, although substitution of the first planted species in affected areas to Avicennia or Sonneratia might be better!?
Gazi Bay is more saline I think, both being pretty open to the ocean and not having the same intensity of wet season, where everything turns fresh as here, even out to sea at the mouths of the rivers!
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