Julian Cremona talks to us about Seashore Plankton.
Could you tell us a little about your background and what led you to write Seashore Plankton?
My background has always been in education. Biodiversity in all ecosystems has fascinated me since a child with a particular emphasis on invertebrates. Whether collecting insects in my garden or hunted treasures in a seashore strandline at the age of twelve I soon understood that any new found knowledge I enjoyed sharing, giving nature walks and talks to my local natural history society. As a teacher and lecturerer my emphasis was on teaching outdoors and fieldwork. Inevitably I joined the Field Studies Council to concentrate on environmental education. My first book, Field Atlas of the Seashore (Cambridge) was designed to assist students to understand seashore ecology and I was aware then that for anyone to truly comprehend life on our shores plankton was at its heart. My techniques at that time for plankton collection and photography were poor at best and there were no guides on how to do this. This is still the case. In 1996 I started working at FSC Dale Fort Field Centre in Pembrokeshire, educating students in marine biology and plankton was part of the studies at the time, trawling for plankton with students, from a boat. Much of the scientific work on plankton is associated with oceanography with studies made on collections mainly taken off-shore. After nearly sixty years of educating people in seashore ecology I know how important plankton knowledge is to fundamentally understand the complexity of the shore. There are a few good books and papers about identifying planktonic species but they are scientific works and do not look at collecting, studying or look at the interactions between organisms. Most important, there are none dedicated to the seashore.
Plankton collected directly from the seashore is different from that taken off-shore. There is some overlap and so the ID books that exist are useful but there is nothing out there that is specific. The water lapping over the seashore has a more biodiverse variety of organisms compared to off-shore samples. This is because the plankton arrives from three or four different sources: rivers and estuaries, invertebrate larvae released from the seashore, organisms washed by wave action into the plankton and life brought in by wind and tides from the ocean. I felt a whole new approach was needed to make it accessible and try to unravel its complexity. In particular to explain: how to collect samples from the shore rather than a boat; how to look at them; introduce the huge array of organism found there and how they link with the life that we can easily observe.
Although I have written a number of books on the seashore this has been the most difficult. Part of the problem is that you are writing about creatures that few people have seen or can even comprehend and most do not have common names. It is surprising how many people can be expert on seashores but still be unclear on the microscopic plankton that is an essential part of the ecology.
A photograph of a plankton sample, magnified approximately x20, showing an array of diatoms and debris. This image was taken using an inexpensive USB microscope.
Your book focuses on identifying plankton along our coasts. What drew you to focus on the seashore?
Scientifically, marine plankton has been researched and studied under the subject of oceanography with collections taken from boats off-shore. A net is towed behind the boat and is easier than trying to collect from the shore. When I retired from Dale Fort I wanted to continue collecting plankton but with no boat available I had to develop methods of sampling from jetties, sea walls and pontoons that were adjacent to the seashore. After years and many hundreds of samples taken around Wales I was amazed by the biodiversity of shore plankton which is even more astonishing than off-shore collections. Many of the seashore invertebrates produce larval stages that last hours or a few days and these would rarely occur offshore. Samples taken along the shore of an estuary will vary with salinity and nutrients. I can take two samples along the coast, separated by just a few miles, and the species present can be 50 to 70 percent different. Much of this is never discussed in books on plankton because it is all about the oceans. There are many differences between the latter and what will be found in the water that laps the shore. Traditionally, this would be referred to as near-shore plankton but I decided to be more specific and call it seashore plankton, bringing the association closer together. Hopefully, it is a more descriptive title for the book.
A young carid zoea.
With over 400 high-quality photographs, the visual element of this book is stunning. Given your 25 years of experience teaching extreme close-up and macro photography, what were the biggest technical challenges you faced when trying to photograph these live, moving organisms for the book?
Lighting and freezing the action will always be the key challenges. A dead creature will never look natural and live zooplankton can be very active. Over the years I have had help and suggestions from a number of people from the Quekett Microscopical Club sharing their knowledge on lighting and holding specimens. Developing these further probably the most useful technique has been to put a blob of vaseline on the four corners of a coverslip. This prevents the glass crushing the organisms beneath but also allows you to gradually put pressure on it to slowly secure the specimen, reducing movement.
Getting the image sharp with as much in focus as possible is another issue. When magnified a single photograph will have only a small area in focus and to increase this to cover the whole specimen requires a method I started decades ago called focus-stacking, where numerous photos are taken but each has a slightly different focal point. Then the images are merged using software. Individuals isolated from the zooplankton, although active, will usually stop for a few seconds before moving again. The short pause can be sufficent time to take a short videoclip that will secure some frames and possibly allow a change of focus. Using this I have developed a video focus stacking technique specifically for plankton at medium to high magnifications.
A continuing problem is the different aspects of viewing a specimen. Under the microscope it is not easy to change the angle of view and invariably a particular species will always land on the slide the same way up each time. Viewing a larval form from the side will be very different from the top. Many of these techniques are briefly explained in the book.
Sea cucumber: the ossicles on the tentacles of the pentactula larva.
Seashore Plankton is framed as a practical introduction. Do you need expensive, lab-grade equipment to start observing these life-forms?
Not at all but it does depend on how detailed you want to study them. To show children the existence of plankton it just requires a simple USB magnifier (available from Amazon) plugged into a computer to display the material on a screen. You can even take photos. A £100 student microscope will enable a more detailed analysis covering most of the species shown in the book.
An ascidian tadpole larva, possibly of Ciona.
Professor Des Thompson noted that "the very future of life on our planet rests on the viability of the characters in this book." For readers who might just see these as tiny drift-organisms, can you contextualize why seashore plankton are so vital to our global ecosystem?
Plankton accounts for 95% of marine biomass; if we are at all concerned about the conservation of seabirds, whales and dolphins we should look to plankton as all depend on plankton for food. Fish and shellfish for our food is totally dependent on plankton. 50% of all oxygen produced on earth is created by plankton. Some would say that marine plankton is the most biodiverse ecosystem in the world. The weather patterns and cycles of the world are dependent on plankton. Our seashore plankton is part of this global system with many of the larval forms created by the life on our shores drifting off-shore.
Increasingly scientists are realising how important plankton is for controlling climate change. When plankton dies the carbon is taken to the bottom where the majority remains, removed from the atmosphere; a major process of carbon sequestering. The dead and decaying material is referred to as “marine snow” as it slowly sinks. Some species, like the Tunicate Oikopleura, are some of the most important species in the world for sequestering carbon. Explained in the book.
A juvenile Oriental Shrimp Palaemon macrodactylus showing a characteristic spine on the back.
The final section of your book tackles the implications of human activity on plankton ecology. What are the most pressing threats facing coastal plankton communities today, and is there anything we can do on a day-to-day level to support their conservation?
The slow acidification of the oceans is occurring with carbon dioxide dissolving in seawater. This is a global issue for the oceans. In the last few years we have experienced the highest inshore water temperatures recorded. Temperature influences speeds of growth and which species will dominate the plankton, in particular the increase in gelatinous plankton which includes jellyfish and siphonophores.
These are general issues affecting all plankton but probably the most important local problems facing coastal plankton is down to variations in salinity and nutrients. An imbalance of the latter, like nutrients draining from the land and sewage dumping, will greatly change the species of the plankton and in most cases reduce biodiversity. In this regard, what is passing down rivers and estuaries will be especially important.
Order your copy of Seashore Plankton here.
