Evidence

(Please see the Latest News section for the latest evidence and discussion, also the Aerial Images section for animated GIF images showing the growth and expansion of the Studland Bay eelgrass beds).

Update Oct 2016:

Underwater Videos show healthy, thriving  eelgrass: Videos taken in inshore areas in Studland Bay in July 2016 with an underwater camera 1.5 m, 5 ft, below the surface, and covering 300 linear metres of seabed, show abundant, dense eelgrass, demonstrating that claims that the eelgrass habitat has been destroyed or badly damaged to be untrue. These videos provide photographic ground-truthing for the aerial images (next item below) and analysis of them supports many of the conclusions drawn in other articles on this website. See Underwater Videos tab, above. Also see Underwater Videos Paper.

Update June 2016:

Animated Graphic shows eelgrass expansion: see the Aerial Images tab above. This is in addition to our historic series of aerial images of Studland Bay covering the years 1972, 1985, 1990, 1997, 2008 and 2011 which may be found here. They show that, far from declining, the eelgrass beds in the Bay have greatly expanded over that period, and gaps in the beds filled in with new growth, although leisure vessels have been anchoring there throughout the period. New growth is moving inshore at a rate of 2 metres a year according to the longer series, and 3.7 metres a year in the recent animated sequence.

Update November 2015:

We have now added a Technical Summaries page which lists and summarises the twenty or so scientific and technical papers and articles published by BORG on this website. The page gives an up to date summary of our evidence relating to boating and conservation issues, including anchoring, eelgrass, seahorses, birds, and invasive marine species. We hope that overview will help people to understand the breadth, depth and strength of our arguments.

Update August 2014:

Still nobody has identified a single credible paper in the worldwide scientific literature which demonstrates anchor damage to eelgrass (Zostera marina). The conservationists can only point to damage to other, more susceptible, species of seagrasses.

Further, a very recent paper on Nordic eelgrass (CHRISTOFFER BOSTRÖM et al 2014,  http://onlinelibrary.wiley.com/doi/10.1002/aqc.2424/pdf) , surveys the status and health of all  the eelgrass in the Nordic countries, up to 2000 sq km of it, in the Baltic and the Norwegian Atlantic coast.  The paper runs to 25 pages and cites 113 references. A word-search of the document showed that the words anchor or anchoring do not occur even once. Anchor damage clearly not an issue there, although leisure boating in the Baltic, and in Sweden and Denmark particularly, is very popular.

A clear picture is emerging to explain why eelgrass can thrive in the presence of anchoring. Firstly it is robust against physical damage – see our article here – and also shows great powers of recovery or resilience – see article here. As gardeners well know, some plants have remarkable powers of regeneration and are very hard to get rid of (convolvulus, nettles, ground elder, dandelions, brambles, to name a few). And lawn grass thrives despite having its leaves mown once a week in season.

Secondly, when we work out how much of the seabed in an anchorage is actually impacted by anchors, it is a surprisingly small proportion, less than 1% in a season. The reason is the area actually impacted by an anchor is fairly small, while the area of the swinging circle of an anchored boat is large. This analysis by BORG, which is an original contribution to the debate, may be found here.

So, a small amount of rapidly recoverable damage applied to a small area of seabed explains the known facts: ongoing expansion of the eelgrass beds despite continuing anchoring by leisure craft. We are trying to drive this message home in appropriate circles.

A 4-page overview covering much of the above, plus other evidence matters, may be found here.(Sept 2014)

Original Evidence Article (2012 plus some updates):

If restrictions are proposed on our activities, and taxpayers’ money spent in the process, then it is only reasonable to expect these proposals to be based on sound evidence, and that the proposals, if implemented, would deliver a more than trivial benefit. BORG has been looking at the justification for the draft MCZ proposals for Studland Bay in particular, and also at the more general situation for eelgrass, which features in many of the proposed MCZ’s.

StudlandBay

We know that boats have been anchoring in Studland Bay for generations, and we know that the eelgrass has not been decreasing, in fact there is now more than ever. About a square kilometre from official figures! So, how can anchoring be reducing the eelgrass cover?

When trying to put this simple argument during discussions, we were told that it was not “scientific” enough. So, a member of BORG with a scientific background looked at the evidence for Studland, and at the relevant published scientific literature in general, and wrote two papers which are published by BORG here and here.

Very briefly, there is as yet (Nov 2012) no solid evidence of any significant extent of damage to the eelgrass in Studland Bay caused by anchoring. Yes, the chains to the fixed mooring buoys do sweep across the seabed as the buoys move with wind and tide and create bare patches of seabed, but this is damage by moorings not anchors. The area of damage is fixed and, as a proportion of the whole eelgrass beds, very small. But this is not anchor damage, although attempts have been made to muddle the two together by writing of “anchor and mooring damage”.

Interestingly, while the scientific literature has many papers on damage to eelgrass (Zostera marina) from various causes, there seem to be very few papers indeed which describe damage by anchoring, suggesting it is not generally an issue.

Update: our views have been upheld by the results of the Seastar Survey, a detailed 2-year study commissioned by The Crown Estate, which administers the seabed, and Natural England, which concludes “There is therefore no consistent evidence of boat anchoring impacting the seagrass habitat at Studland Bay.”  See Latest News for more information.

Update: How much of the sea bed actually does get impacted by anchors? We have done some analyses, and the answer is surprisingly little – in the worst case of nearly continuous close-packed anchoring, perhaps 1 to 1.5% in a boating season. Our report may be found here and we hope it will prove useful in establishing the true picture of anchoring and eelgrass.

Seahorses at Studland

It has been said that because seahorses are found in the eelgrass at Studland,  then the eelgrass is their habitat and must be conserved. But after decades of anchoring, there are still extensive meadows of eelgrass.  A substantial decline in eelgrass due to anchoring is just not going to happen. (There are however other threats to eelgrass, see below).

Would a modest eelgrass decline, if this occurred for whatever reason, affect the seahorse population?  The answer is very probably no. The numbers of seahorses are small, they are not limited by the extent (nearly 1 sq km) of habitat available. In 2011, only eleven individuals were seen at Studland, down from a maximum of 40 a few years back (reference here ). In 2012 just nine, yet this was a year with fewer boats visiting because of the awful summer. There had been no decline in eelgrass, and the Executive Director of the Seahorse Trust, Neil Garrick-Maidment, suggested factors like temperature and plankton levels might have been responsible for the decline in seahorses in 2011 (same reference). Note: see Latest News: in 2012, just 9 individuals seen.

The cited article gives an interesting overview of seahorses at Studland, and while BORG do not agree with all Garrick-Maidment’s views, we do respect the valuable work he has done to promote the study and understanding of seahorses.

Our argument that the seahorse population is probably not sensitive to modest changes in eelgrass extent, and the other arguments in respect of Studland, are developed more fully in the Studland-evidence paper.

Eelgrass issues

Because eelgrass (a seagrass, Latin name Zostera marina) grows in areas often suitable for anchoring, it has become an issue in a number of possible Marine Conservation Zones. Borg has therefore published a second technical paper which reviews the scientific literature. It considers Zostera marina’s  conservation status, life cycle, causes of damage, and potential for recovery from short-term damage. There is also an appendix which reviews and questions the evidence presented in the paper “The impacts of anchoring and mooring in seagrass, Studland Bay, Dorset, UK” by Collins et al (2010) which has been used in support of conservation measures there. A summary of the BORG paper follows, and the paper itself may be found here.

 Summary:

 “Concerns have been raised about possible damage to Eelgrass (Zostera marina) from anchoring by leisure vessels. Eelgrass is on the IUCN Redlist, in the category of Least Concern, and not in a threatened category. It is widely distributed in the northern hemisphere. There appear to be few or no reports of significant anchor damage to eelgrass in the scientific literature. A brief review of published reports of mortality and recovery of eelgrass from various causes showed a distinction between damage from long-acting (over a year) threats, which can cause serious and long-lasting declines, and short-acting threats which can be followed by rapid recolonisation. Four studies of short-acting damage found substantial or complete regrowth from seedlings in a year or less. A study in which all shoots and rhizomes were raked out from 2m square plots (4 sq m)  found rapid growth initiation and full recovery in two years by rhizome growth from the adjacent undisturbed eelgrass bed. It is argued that damage from anchoring , which is a short-acting event, might be repaired by regrowth from seed or by rhizome spread, and these mechanisms can account for the lack of reports of eelgrass damage from anchoring.

 An appendix to the review considers published evidence relating to eelgrass re-colonisation in Studland Bay, contained in a report by Collins et al.”

 It is worth quoting from the IUCN Red List on eelgrass:

“This species is widespread, circumglobal in the Northern hemisphere. There have been documented localized declines in parts of the range, but not sufficient to warrant placement in a threatened category. Zostera marina is listed as Least Concern.”

–  and- “Zostera marina is widespread and circumglobal in northern latitudes, found throughout the north Atlantic and north Pacific and in the Mediterranean and Black Seas. Zostera marina extends into the Arctic in Alaska, Canada, Greenland, and northern Europe and to the tropics in Baja California, Mexico.”

So, while it has been declining (1.4% a year) on a global basis, it is not a rare and endangered species.

Aerial Images of the eelgrass beds

There is further evidence on the Aerial Images page.