Can you eat mussels straight from the beach?

Richard Prideaux looks at the dangers from eating wild and foraged mussels

When you teach people about foraging and ‘wild food’ you often run the risk of sounding negative or over-cautious about the potential hazards that come from eating shellfish, or fungi,or whatever else it is that you are solemnly warning people about. I do this with good reason – people are paying to attend on of our North Wales foraging courses to learn more about the subject, and I have a duty of care towards them as an instructor, and just as a (mostly?) decent human being. That said – there IS a difference between laying out the potential risks and telling somebody that they shouldn’t/can’t do something.

One of the areas where this is most apparent is in the realm of coastal foraging, and particularly the business of finding, gathering and eating edible mussels (usually Mytilus edulis). It’s one of the most anticipated section of the entry-level coastal foraging courses – the moment where I start talking about the culinary wonders of this grey bivalve. It starts off well, discussing byssal threads and the ethical issues of harvesting mussels (minimum landing sizes and so on) but as soon as I start to discuss the potential dangers the mood changes and the once-confident mussel foragers look increasingly alarmed.

So, what are the dangers of eating wild mussels?

The first thing we need to get out of the way here is that there is an element of risk involved in eating EVERYTHING. That’s food from supermarkets, served to you in restaurants, grown in your own back garden or picked from the soil or plucked from a rock somewhere on the Snowdonia coastline. Improper handling, preparation and sometimes just bad luck all have a role to play and we can never guarantee that our food is ‘safe’. There are a few very good reasons why wild shellfish, and particularly bivalves, have a reputation for potentially being ‘dodgy’.

There are several interesting and diverting ways in which they can nobble you:

  • Paralytic (PSP), Amnesiac (ASP), Neurotoxic (NSP) and Diarrhoetic (DSP) Shellfish Poisoning
  • Viruses (particularly Norovirus, aka the Winter Vomiting Virus)
  • Bacteria (such as E Coli)
  • Parasites (lovely things like Cryptosporidium parvum)
  • Heavy metal and chemical contamination
  • Allergies and other physiological disagreements

Blimey. Why would you even bother eating foraged mussels?

The really scary ones above are the various Shellfish Poisonings. They are caused by algal blooms, which can develop in both salt and freshwater. As mussels feed by filtering nutrients from seawater they can also accumulate the toxins from any algal blooms that have developed in the water around them. Paralytic Shellfish Poisoning (PSP) is the one that tends to get most of the attention when discussing the hazards of eating mussels, and it’s not just human foragers that need to be careful – there have been several cases of dogs dying or becoming ill from eating dead crustaceans or shellfish contaminated in this way.

The two methods relied upon in commercial supply (see below for more detailed explanations)  – depuration and cooking – remove some of these contaminants and organisams, but not all. Depuration does not work well with viruses and some algal toxins, and cooking only kills bacteria, viruses and parasites.

mussel foraging uk

So what about the ones in shops and restaurants?

An excellent question, and one that does need some explanation.

There are plenty of areas along the British coast that are famed for their mussels, and you can find these locally-sourced delicacies on the menus of most of the restaurants nearby (and often further afield too). They are indeed ‘grown’ in the sea, in the same waters where you might be foraging for them yourself. They are often farmed on ropes, being carefully selected for size and health and harvested in a sustainable way – in waters that are regularly checked for cleanliness and contamination.

Water that is graded as being suitable for ‘immediate human consumption’ is designated “A” status. Anything from water with “B” grading needs to be depurated for no less than 42 hours, “C” grade shellfish must be relaid in cleaner waters in the hope of removing impurities and “D” grade water is pretty hopeless (and indeed may actually be on fire…).

So the mussels you will find in restaurants or shops in the U.K. will have either been grown in A or B-grade waters, and probably have been through a process of depuration in either case.


Depuration, the process of removing impurities, for mussels is usually done by placing them in a tank of clean seawater that is then itself circulated through a filtration and purification system. As the mussels sit in the continually-cleaned water they gradually lose any impurities that they may have acquired.

IS it safe to eat mussels I have foraged from the shore then?

Well… maybe. It depends on what you mean by ‘safe’. If you want a firm guarantee that the mussels that you have just plucked from the rock are free from toxins, viruses, bacteria, parasites, unwanted chemicals and everything else then you won’t get one. But if you want to be able to reduce the risks of eating foraged mussels (and indeed, lots of other coastally-harvested wild foods) then there are fairly simple precautions you can take (see below).

Just remember – a LOT of effort has gone into making sure that the ‘wild’ mussels served to you on a plate on the Menai Straits or from the Fowey estuary are ‘clean’ and safe for human consumption. Just because they are the same species and growing on roughly the same section of British coastline doesn’t mean that the ones you can (legally and ethically) harvest from the beach are “just the same”.

Reducing the risks in foraged mussels (and other things too)

There are a couple of oft-repeated ‘rules’ attached to mussels with regards to cooking and eating them:

  1. Avoid gathering them in months without an ‘R’ in them (May-August)
  2. Throw away any that do not open after cooking

The first rule is sometimes dismissed as being a piece of general guidance dating from a time when refrigeration was non-existent, and transporting mussels from shore to city was unwise in the hot summer months. This is, like many overly-simple explanations, complete cobblers. A much more sensible reason for avoiding shellfish during the height of the summer months (in the northern hemisphere anyway) is that this is the peak season for algal blooms, and also the time that many species are most active in their feeding – so if you avoid the summer there is a lower chance of eating something that is contaminated with a toxin.

The second rule I will come to later, but scientific research suggests that the generally-accepted belief that a mussel that does not open after being cooked is not necessarily a sign of it being unhealthy/contaminated/dead, nor that a mussel that opens up fully after being cooked is indeed healthy.

There are several simple steps that you can take to reduce (but not completely remove) the risks of eating foraged mussels:

  • Avoid the summer months (see above)
  • Pay attention to local news, particularly with regards to algal blooms, water contamination, and stories of unexpected illness from eating seafoods of all types
  • Check the noticeboards that are displayed at harbours and access points for notifications of contamination – particularly algal blooms or chemical spills
  • Avoid harbours and marinas, areas with heavy marine traffic and places where sewage (even treated) flows into the water
  • Avoid picking mussels after periods of heavy rain where contaminants from the land may have been washed onto the shore
  • Avoid the outflows of old mines and industrial sites (particularly Cornish tin mines etc)
  • Scrub mussels under running clean water to remove barnacles etc
  • Cook mussels as soon after picking as possible (and cook them well – but this still does not remove the toxins from algal blooms)
  • Do not eat any mussels that do not open fully after cooking (but read this article too)

All of the above are fairly simple and aren’t that restrictive for the forager. There are also ethical and legal issues to consider – a minimum landing size (MLS) for mussels is something you will need to abide to in most cases (usually 51mm but check for your area).The Welsh Government has several useful links on this page – most apply to commercial fishing but it does show that there is a world of legislature that is attached to what may be seen as a very simple and innocent act. There is, at the time of writing, a ban on collecting mussels from the Conwy Estuary and other temporary restrictions may be in place for your area.

beach foraging north wales

Final words of advice

This post does sounds a little bit pessimistic, but the facts cannot be argued with – shellfish can harbour some fairly nasty organisms, toxins and chemicals. Some of these are probably present in every wild mussel (E.Coli for example) but can be easily removed by cooking. Others are much less common (such as algal blooms) but their impact can be much more severe and are almost impossible to get rid of in the cooking process.

If you are sensible about where you collect mussels from, when and how you cook them then you will probably be safe – in fact the most hazardous part of your foraging trip will be the drive there and back. Like every foraging activity though you need to be aware that it is potentially hazardous, and that recognising and reducing those risks is as important as identifying the edible species in the first place.

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1 Comment
  1. Really helpful! Thank you.

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