The Seasearch Guides have helped to revolutionise marine recording. Focused firmly on identification in the field, the books use top-quality photography, diagrams and clear text to highlight the things to look for in a typical encounter underwater or on the shore – i.e. the features that are most useful to recreational divers and rockpoolers. Having previously tackled seaweeds, fishes and sea anemones, among other groups, the latest in the series shines a light on the crustaceans, a diverse and fascinating group whose members are ubiquitous in marine environments.
Ahead of publication of Marine Crustaceans of Britain and Ireland, we had the pleasure of talking to the authors, Lin Baldock, Charlotte Bolton and Iain Dixon, about the inspiration for the book and their hopes for how it will contribute to recording efforts.

This is the latest instalment in the popular series of Seasearch photographic guides to marine life. Could you tell us a bit more about the series and its aims?
Charlotte says: As with so much about the community-based Seasearch project, the series emerged organically from the perceived need to support volunteer recorders and to ensure that the data produced was as accurate as possible. The series of guides follow on from the original UCS mini-prints (remember having to stick in the photos yourself?). Chris Wood (the first National Seasearch Coordinator from 2003 to 2016) was responsible for either authoring guides or persuading people to write one on their specialist subject – all done on a voluntary basis. They had pride of place on my bookshelf when I first started carrying out Seasearch surveying and recording and I particularly wanted to expand and update the range during my tenure as National Coordinator. Retirement has given me more ‘spare time’ to dedicate to this. Concentrating on in situ pictures to emphasise visual recognition and remove the need for sampling, with the images sourced from the recording community as well as the authors, the guides are both accessible and inclusive. Early editions were published by the Marine Conservation Society, then Wild Nature Press (bringing Julie Dando’s exquisite design eye and Marc Dando’s wonderful linework) took over, and now Princeton University Press (PUP) since their acquisition of Wild Nature Press. Without the support of these publishers the guides simply would not exist – it’s a very niche market!

And how did crustaceans come to feature in the series? Can you share the origins of this guide?
Charlotte says: Crustaceans were an obvious candidate for the Seasearch guide treatment, but we needed to find authors willing to write the book! Robert Kirk (head of Princeton Nature at PUP) was always keen to see a crustaceans guide and is a big fan of the series. Lin Baldock stepped up to the challenge (in the process revealing her familial connection to the group), Iain Dixon earned his PhD studying amphipods so was an obvious choice for that group and I came on board (as author, upgraded from series editor) to provide the interface between the experts and the book audience – it was a steep learning curve and an unexpectedly immense amount of work.

Crustaceans are amazingly varied, ranging from planktonic copepods through the Britain’s biggest arthropod, the European Lobster. How did you decide which species to cover when dealing with such a diverse group?
Lin says: It was a real challenge selecting the species we might include and the list was growing right up until the press proofs were delivered. The criteria we used to narrow the list were as follows:
- Is it likely to be encountered by divers, snorkelers and beach walkers in the intertidal and shallow waters (<30m) around Britain and Ireland? (This excludes extremely rare species)
- Can the species be accurately identified in the field without the need to resort to collection and microscopic examination?
- Is the animal large enough for the critical features for accurate identification to be captured in field photographs?
The minute planktonic species so vital to pelagic marine ecosystems and the plethora of highly specialised parasitic crustaceans are mentioned and users pointed to freely available ID resources on the internet. We felt it was important that wherever possible we should provide pointers to articles that are freely available through open access.
Charlotte says: We wanted to cover ‘everything’ and in fact sneaked in pycnogonids as a bonus group bearing a resemblance to spindly spider crabs despite not being crustaceans… Obviously this was wildly ambitious and constrained by the page count available as well as the availability of images and the likelihood of being observed and recorded. The initial plan evolved and the book actually ended up being about 40% larger than originally anticipated.

How did you set about the task of gathering photos? Did you have to make dedicated field trips for some images?
Iain says: Photos were gathered from the authors’ collections, but most came from a wide circle of friends and contacts in the wider Seasearch community. Obtaining images from as wide a variety of people as possible is important as a means of ensuring buy-in, spreading the word and gaining feedback for improvements. On the whole this gave us most of what was needed and, because of the serendipitous nature of wildlife spotting and photography, dedicated field trips were generally unlikely to yield the specific results that might have been required.
Lin says: I had always been fascinated by crustaceans so I had built up an extensive image library of the larger crustaceans found around British and Irish coasts over the years. Our main source of images, however were contributions from members of the Seasearch community who themselves have been collecting images from all around our coasts for decades. We are hugely grateful to those many individuals who freely provided their images for us to use, without this invaluable library of pictures to hand we would have struggled to get hold of all the images we needed.
There was one group for which we did make a focused effort to collect images specially for the guide: the hermit crabs. The classic guides to this group of charismatic crabs require the animal to be sampled and reduced to a series of body parts resembling an Airfix kit while focusing on microscopic detail of the mouthparts or other inconspicuous appendages in order to name the species. Contributions of detailed macro photographs from a number of enthusiastic Seasearchers proved that the eight species of hermit crab likely to be found in shallow British and Irish waters can be reliably identified using the colour of live animals specially their legs, antennae and antennules. In fact a review of images submitted by Seasearchers showed that some species of hermit crab are much more common in habitats such as Scottish sea lochs than the records available on national databases would suggest.

We hear a lot about shifting marine communities, with the spread of warm-water species and arrival of invasives. Are we seeing changes in our crustaceans too?
Lin says: Yes, indeed the crustaceans as a group are not immune to changes in distribution. Changes in distribution are always hard to pin down but my impression (being based in Dorset) is that there are a number of native species which we have included in the guide which are now rare or no longer occur along the south coast of England despite the fact that the type locality for the species was located there. I call these ‘climate change losers’ which are retreating north or into deeper, cooler waters.
Non-native species are of course an ever present threat: examples are the Chinese Mitten Crab with its highly destructive behaviour of burrowing into muddy river banks seriously threatening the integrity of our flood defences in some parts of the country, or the replacement of our native Green Shore Crab by the invasive Brush-clawed Shore Crab in the estuaries of eastern England. Records of changing distributions raise the semantic puzzle of whether the species is an introduced non-native crustacean or simply a native species extending its geographical range northwards as climatic conditions change to suit its requirements. Just before the guide went to press we were alerted to a first record of a non-native crab species from the Solent highlighting the fact that we should constantly be on the lookout for the new and exotic.
Iain says: Yes, range changes over time are apparent in crustaceans as in all groups; certain species once thought to be mainly southern in distribution are now being observed further north and new species from warmer parts of Europe are appearing on the south coast. At the same time, species familiar in more northern waters are disappearing as our waters become warmer.

Finally, what do you hope this guide will do for interest in, and recording of, crustaceans?
Charlotte says: Hopefully it will persuade people to look more closely at what they are seeing on the shore or underwater – it has certainly opened my eyes. It should also highlight how much information can be gleaned from images taken with modern compact cameras – it’s not necessary to spend thousands of pounds nor to sacrifice animals in search of a label. One mark of success will be if the range descriptions and distribution maps rapidly become outdated because people have been encouraged to go out and see what they can find (and record it!).
Iain says: We very much hope that this guide shows that it is possible to identify species by direct observation and from photographs, and that species collection, dissection and microscopic examination is not always absolutely necessary. We hope that this guide sheds light for many and encourages closer examination, particularly of those groups which might formerly have been thought of as being ‘too difficult’. The more examination and recording that goes on, the more guides like this will improve and develop.
Lin says: We hope the guide will stimulate people’s interest in the group and provide an introduction to the huge diversity encompassed by the crustaceans. With my Seasearch recording hat on I anticipate a flood of species sightings helping us to build up a better picture of our crustacean fauna and future changes in distribution driven by shifts in climate or the introduction of non-natives. I am also hopeful that we may find better, more reliable ways to identify species in the field, thus teasing out some of the uncertainties which still exist in distinguishing species in some groups, particularly the spider crabs for example.
The 
















































