Eel grass

[robertj]

I’ve just read the pbo’s largest eel grass planting report.
I just wondered with the wording of ‘we may have lost up to 92% of its eel grass’ the ‘may’ part I find worrying.
have we or haven’t we lost this much or is there no research or records of what areas and to what extent the loss has occurred?

 

[rotrax]

The loss happened in the dim and distant past due to a disease.

Old Harry knows all about this.

In some places it has made a remarkable recovery.

 

[robertj]

So not all doom and gloom then?

 

[Tranona]

Depends on whether you want it to be or not. The doom mongers are happy to guess at their "100%" in the past based on historic observations, but not prepared to recognise observations from people who are still alive about how much of the current 8% is in fact recent growth as the seagrasses recover from a whole range of events that have had a negative impact such as pollution, disease, fishing activity, extreme weather etc. Much easier to blame the current state on rich yachties dropping their anchors in one small corner of the UK coast, where the recovery has actually been dramatic. Interestingly in the few serious scientific investigations, anchoring is never mentioned as something that has a negative impact.

You are right, the word "may" is the clue - that those making such guesses really do not have much of a clue, but their voices dominate the narrative.

 

[Concerto]

These unsupported claims about the loss of eel grass are headline grabbing numbers and the press suck it up. Challenging the conservationist claims will not make headlines, but might get a small mention. At least there seems to be some movement in delaying/stopping the anchor ban in Studland Bay.

 

[westernman]

I remember reading somewhere (no idea if this is true or not) that boat anchors ripping up the eel grass may actually be helping it spread.

 

[Tranona]

Depends on the specific type of seagrass. The type in Studland does indeed recover very quickly after being uprooted, for example each spring after the easterlies have beaten it up in the shallow water and deposited masses on the beach. It reproduces by rhyzomes so fills bare patches adjacent to growing plants. Bit of a stretch though to say that damage by anchors does it good, although as has been demonstrated many times the damage caused by anchors is minimal.

 

[Ian_Rob]

’Zostera marina
Zostera marina has intermediate rates of growth and spread compared to other European seagrasses. Besides the potential for spread derived from the horizontal growth rates of the rhizomes, Zostera marina is able to release large numbers of seeds. At the time of reproduction, eelgrass shoots produce inflorescences which can each develop large numbers of seeds. Reproductive shoots die off following seed set, so that flowering represents a terminal event for eelgrass shoots. Seed production rates in Zostera marina beds reach several thousand per square meter. However, they do not travel far – a few meters at best - from the mother plant after being released, as they are negatively buoyant and sink to the bottom. However, flowering shoots may detach, because of disturbance, and float away, releasing the seeds at considerable distances from the stand where they were produced, which is the mechanism for long-term dispersal available to this species. ‘

How do Seagrasses Grow and Spread? : Núria Marbà (IMEDEA), Carlos M. Duarte (IMEDEA), Ana Alexandra (CCMAR) and Susana Cabaço (CCMAR)

 

[oldharry]

I am off base so cannot quote chapter and verse, but I think two research papers suggested a possibility that disturbance stimulated growth in Zostera marina. Neither researcher followed this up.

 

[Ian_Rob]

It seems to me that the highlighted section is quite important. As I understand it, Duarte et al are amongst the leading authorities on Sea Grass. If the breaking off of inflorescences results in a dissemination of seeds as they suggest, then anchoring may make a positive contribution to the wider proliferation of the species.