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Crabs and Shrimps of the Pacific Coast

A Guide to Shallow-Water Decapods

from Southeastern Alaska to the Mexican Border

By Dr. Gregory C. Jensen





Dr. Jensen’s Announcement of his Book on *Crust-L


In the announcement of his new book that appeared on *Crust-L, a mailing list for crustacean scientists, Dr. Jensen, a professor at the University of Washington (Seattle, Washington, USA) who oversees the undergraduate research program at the School of Aquatic and Fishery Sciences, said:


“This combination book/e-book includes every shallow-water species of crab and shrimp found from the Aleutian Islands to the Mexican border—300 species in all—in color.  The print book includes numerous sidebars ranging from behavior and biology to historical vignettes, while the accompanying CD-book contains all of the species profiles in a convenient PDF file, so it can be put on a phone or tablet and taken anywhere.  Each piece of information in the PDF is hyperlinked to the reference list (2,600 links), while hundreds of other links connect to additional photos that show particular features, comparisons to similar species and even short video clips showing various behaviors.  Interactive keys to many of the groups are also provided, including both a color key for identifying live hermit crabs and a separate one for preserved specimens that have lost their color.”



What the Table of Contents Looks Like




Forward by Dr. Richard C. Brusca


Dr. Richard C. Brusca is an invertebrate zoologist, marine biologist, conservation ecologist, Southwestern naturalist and desert rat.  He is Executive Director (Emeritus) of the Arizona-Sonora Desert Museum.  He is also a Research Scientist at the University of Arizona and the Centro de Investigación en Alimentación y Desarrollo (CIAD) in Mexico.  He is the author of over 160 research publications and 13 books, including the largest-selling text on invertebrate zoology (Invertebrates, Sinauer Associates, available in four languages).


In the forward to Dr. Jensen’s book Dr. Brusca says: “Greg Jensen set out to produce the most up-to-date, informative, colorful, engaging field guide to decapods of temperate Pacific shores possible, and he has succeeded admirably.  This book is a treasure, and it is natural history at its best.  It follows in the tradition of T.H. Butler’s Shrimps of the Pacific Coast of Canada (1980) and Josephine Hart’s Crabs and Their Relatives of British Columbia (1984), but it far exceeds them in every way.  Nowhere else can one find color photographs and intricate anatomical and ecological notes for so many living Pacific decapod crustaceans.”


“Greg’s writing is engaging, laced with dry humor and packed with a naturalist’s insight.  This book is information-rich, in every way.  The narratives ring true and are in the voice of a seasoned naturalist who has spent a great deal of his life in the field—and much of what you read in this book has never been published elsewhere.  The biographical vignettes of famous carcinologists are both entertaining and enlightening.”


“The e-book bonus of interactive links is a huge benefit, providing users with images and videos of these beasts in nature.  And the species keys are a wonderful addition to the literature that will be valued by both amateurs and specialists for many years to come.  This is a book for every Pacific coast naturalist, scientist and beachcomber.  Every time you use it, it will offer up new and exciting information about the decapod you are examining, and bring a smile to your face.”



Shrimp News’ Comments


I have at least a dozen books on crustaceans and crustacean taxonomy, and this one, Crabs and Shrimps of the Pacific Coast by Gregory Jensen, has taken the genre to a whole new level with high-quality pictures, writing, layout and organization.  Lucid and meticulously researched, it provides an invaluable contribution to our understanding of crustacean behavior.  It’s even printed on higher-quality paper than any of the other books in my collection, and it comes with a CD version that’s extensively cross-linked, making it very easy to jump to related articles and references elsewhere in the book.  The CD contains clear, up-close videos of crustacean behavior that you are not likely to ever have seen before.  If you get the book and CD, I recommend you watch the one-minute video of a squat lobster (Munida quadrispina) matingYou can actually see the male using his modified fifth leg to put sperm onto the pleopods of the female.  The book has 240 pages, over 1,000 high-definition color pictures, detailed contents and index pages, and a long list of references.


What value does this book hold for the shrimp farmer?  The forward, preface, acknowledgments and introduction contain more crustacean lore than any book I’ve ever read.  They describe the general characteristics of all crustaceans, their feeding behaviors, growth patterns, reproduction, development, predators, parasites and diseases.  Those 21 pages are worth the price of the book (a very modest $34), especially when considering its high quality, pictures and the CD.  I have provided some excerpts from those pages below.


But don’t get the idea that this is a book of about the popular shrimp species that are farmed because none of them occur on the Pacific Coast of North America.  The only farmed shrimp mentioned in the book is the Pacific brown shrimp (Farfantepenaeus californiensis), a cool water species that occurs from San Francisco Bay, California, USA, to Peru in South America.  To the best of my knowledge, californiensis is only farmed at one farm, Aonori Aquafarms in Baja California, Mexico.  In the 1980s, the spot shrimp (Pandalus platyceros), which ranges from the southern Aleutian Islands to the Mexican border, was studied as a possible candidate for cage culture, and it is pictured and described in the book, but it was never farmed successfully.



  What a Typical Page Looks Like  



Excerpts from Book


Introduction: The species covered in this book all belong to the largest and best-known group within the Crustacea, known as the Malacostraca.  In addition to shrimp  and crabs, this group includes amphipods (e.g., “sand fleas”), isopods (including the terrestrial sowbugs and pillbugs), mysids (opossum shrimp) and other less familiar forms.  Among the characteristics uniting this group are a total of 19 body segments divided among three major body divisions (five in the head, eight thoracic and six abdominal) with the female and male genital openings on the sixth and eighth thoracic segments, respectively.  All of the species dealt with here belong to the Order Decapoda.  As the name suggests, they are characterized by having five pairs of legs (deca = ten, poda = feet), with three of the original eight thoracic appendages having been recruited to function as mouthparts.  The taxonomic divisions within the Decapoda are not as clear and there is still much to be learned about the relationships of the different groups.


Only a few penaeid shrimp  (Penaeoidea) occur within diving depths along our Pacific coast, but in tropical and subtropical waters they are an abundant and diverse group of tremendous economic importance.  In addition to trawl fisheries, many are intensively cultured, often to the great detriment of coastal ecosystems and mangroves.  Penaeids have a gill structure unique among decapods and also differ in reproduction, being the only ones to freely spawn their eggs instead of brooding them on the abdomen.


Nearly all of the shrimp along the Pacific coast of the United States and Canada belong to the Caridea, but despite their strong resemblance to the penaeids, they are probably more closely related to crabs.  At first glance there would seem to be little in common between a crab and a shrimp, but their body plans are actually quite similar.  A crab is essentially a shrimp with its abdomen reduced in size and folded tightly beneath its body, and if you straighten out the abdomen of a crab this becomes more apparent.  The large, muscular abdomen of a shrimp is used for quickly swimming backwards to escape predators, while paired appendages called pleopods or swimmerets are used both to swim forward and also for brooding the eggs.


Feeding: Decapods that actively seek out prey usually have a highly developed sense of smell.  Chemosensory hair-like setae (aesthetascs) on the first antennae are responsible for detecting odors, and the flicking motions of the antennae are their way of refreshing the signal.  Contact chemoreception—essentially the sense of taste—is found in setae on the dactyls of the walking legs.


Once the food is located, the claws are used to tear off pieces and convey them to the mouth.  There it is manipulated by the maxillipeds and maxillae and shredded further by the mandibles before being swallowed.  It first passes through a short esophagus into the cardiac stomach, where digestive juices begin breaking it down, and then to the gastric mill at the rear of the stomach.  As the name implies, this impressive set of cardiac stomach teeth grinds the food into small particles that pass into a second chamber, the pyloric stomach.


The main function of the pyloric stomach is to filter out any indigestible material.  By now the good stuff has been reduced to liquid and minute particles, and the remaining bits of shell, sand and other unwanted material need to be removed.  Unlike our digestive tract, which is basically a long tube, that of a decapod splits into two pathways at this point.  The liquefied material that passes through the filter goes into the hepatopancreas or digestive gland, a large organ responsible for absorbing the nutrients from the food.  The hepatopancreas is composed of thousands of tiny tubules that give it a tremendous amount of surface area for nutrient absorption (in contrast, we get our large surface area by having 20 or so feet of small intestine).  Since there is no exit, indigestible material would just get lodged in there without the pyloric filter.


The indigestible material passes into the hindgut where it is formed into feces and expelled.  The hindgut is the so-called “vein” that is pulled from a penaeid shrimp tail before cooking.  The only reason this is removed in these shrimp and not in carideans like Pandalus is because they ingest much more sand, so it tends to be gritty.  So yes, you’ve undoubtedly been eating shrimp poop, but it’s not at all equivalent to the bacteria-laden stuff humans put out.  It can’t be that bad: the squat lobster Munida quadrispina, with its tail curled under and toward its head, can often be seen recycling this material right back into its mouth.



Infraorder Caridea

(Page 95)


Shrimp are familiar to most of us as the main course of a seafood dinner or as tiny curled tails sprinkled on salad.  While very attractive in a culinary sense, this form provides no hint of the delicate beauty, grace and color of the living animals.  Only a handful of Pacific coast shrimp  grow large enough to attract attention as human food, yet this area is home to an incredible variety of smaller species that are important prey of many fish, birds and other animals.  Their attractiveness as food for other animals has forced them to adopt a number of strategies to evade capture.  One of the best known of these is the so-called “caridean escape response,” a very effective behavior that has also been adopted by many non-shrimp like lobsters and crayfish.  By forcefully snapping the abdomen down and underneath, the animal propels itself backwards using the large surface area of the flattened tail fan to push against the water.  Such a mechanism requires a lot of muscle to be effective, and it is precisely that heavily muscled abdomen that makes them so desirable as food.


If the initial escape attempt fails, the shrimp may resort to other tactics.  When captured, some of the spinier shrimp  bend their abdomens dorsally toward their heads in what has been called the “cataleptic” position, exposing spines along the lower edges of their abdomens and presumably making them much more difficult for a predator to swallow.  Similarly, the long, sharp, toothed rostrums of many shrimp aid in defense by reducing the number of possible ways a small fish can swallow them, and shrimp sometimes escape when the fish tries to reposition them for swallowing.  Some species flare out their antennal scales to expose the spines at their tips and make them harder to ingest.  Anyone who has handled large, live prawns barehanded can attest to the sharpness of their rostrums and telsons.


Not all shrimp are armed with long rostrums and this feature is very much correlated with habitat.  Those that spend much of their time concealed beneath rocks and in crevices tend to have short rostrums and stockier bodies; long rostrums are presumably impractical in such close confines.  Species with short rostrums only emerge after dark when there is less risk of fish predation.  Conversely, those living in more exposed locations such as on open mud or in eelgrass and algae do not have as effective a refuge from daytime predators and typically have very long, sharp rostrums.


Whether concealed beneath rocks or living among algae, most of the smaller shrimp  are cryptically colored.  Those living among algae often exactly match the color of their surroundings, so that within a single species there may be bright red, green or brown individuals depending on the kind of seaweeds with which they are associated.  As a general rule these tend to have a fairly uniform coloration while those living among rock and shell show more variation in color and pattern.  One common pattern, for example, is an ivory-white carapace and a bright green abdomen; such “disruptive coloration” serves to break up the outline of the shrimp and make it difficult to distinguish from its surroundings.  If all specimens looked like this, a fish might soon learn to key in on it, but odds are the next shrimp it encounters will have an entirely different pattern.  Female shrimp are often more strongly colored than males, and this is probably due to the different responsibilities of the sexes in reproduction.  While the males of some species can get away with being largely transparent, females must conceal both the developing ovary beneath their carapace and the eggs on their pleopods during brooding.  By keeping both the carapace and side plates of the abdomen an opaque, cryptic color, they can keep both the ovary and eggs hidden from view, an important consideration since both typically go through considerable color changes over the course of their development.  Although shrimp are not usually thought of as having claws, all species found on the Pacific coast have at least one pair of small pincers used for grooming and to handle food.  All the different families of shrimp  can be easily recognized (at least in the lab) by the size, shape and position of these limbs.




(Sidebar, Bottom of Page 219)


The gills of decapod crustaceans are enclosed and protected by the sides of the carapace.  Water is forced through the gill chamber by flapping motions of the gill bailer or scaphognathite, a flattened, plate-like extension of the second maxilla.  Water is drawn in near the base of the walking legs, moves across the gills, and is expelled out the front.


Crustaceans are literally “blue bloods” because they use the respiratory pigment hemocyanin to transport oxygen.  Unlike the bright red hemoglobin of our blood, the blue color is extremely faint.



Denaturing Proteins or How the Lobster Got His Red

(Side Bar, Bottom of Page 231)


The varied and beautiful colors of crabs and shrimp  all turn to red or orange when they are cooked.  This is because heat breaks down the bonds between proteins and a carotenoid pigment, astaxanthin, that is present in the exoskeleton and tissues of crustaceans.  Different protein/astaxanthin combinations impart different colors, but once they are separated the astaxanthin is free to show its true color.



How to Use the CD Version of the Book


In the CD version of this book, each tidbit of information is linked to a full reference of the original source.  If you move your cursor over the second half of the link, you’ll get a screen tip showing the brief citation (e.g., Smith 1980); if you click on the first half you’ll be sent to the page where the whole reference is listed.  Make sure you have your “back” button activated so you can return to where you were before clicking.  In almost all cases, Jensen dug up the original source (and found a lot of misquoted things that have been passed down through the years); if he was unable to see the source, he noted that in the pop-up screen tip.  The mouse-over screen tip doesn’t work with a touchpad-type device like an iPad or iPod since there is no cursor, so when it goes to the reference page the linked reference will be the one at the top of the screen.


  The Cover of the CD Version of the Book  



The interactive keys can be used to determine the families of west coast decapods and from there the photographs can be used to determine the species.  For some, you can continue on to the key for the particular family, though in most cases this will only be practical if you have the specimen in hand and a dissecting microscope for close examination.  Each species description includes the following categories of information:


Scientific Name: Click on this to see a list of other scientific names that have been applied to the species at some time in the past.  The name and date following the scientific name indicate the person who described the species as new to science. If the name is in parentheses, this indicates that the species has been reassigned to a different genus since its original description; clicking on it will give you the reference for the original description.


Common Name: The common names used are (for the most part) those recommended by the American Fisheries Society, except in those cases where a pre-existing name was already well entrenched in popular publications or the diving community.  Clicking on the name will send you to a list of all the common names that have been applied to that species.


Photograph: Clicking on the main photo accompanying each description sends you to a list of all the published color photos in other books that show the same species.


Identification: This section emphasizes characteristics that will help you identify live specimens encountered in the field, either directly or from your photographs.  Live specimens often have distinctive colors and/or patterns that can quickly disappear when the animal dies or is preserved.  When referring to “teeth” along the edge of the carapace, this is in reference to points or crenulations along the margin of the carapace, and the counts here include the one immediately following the eye.


Similar Species: This section provides distinguishing characteristics of the species that may be confused with another species.  It may also include features for identifying preserved specimens when color is no longer useful, some of which may require the use of a dissecting microscope or magnifying glass.  Hyperlinks are provided for comparative pictures or diagrams pointing out special distinguishing characteristics.


Size: Maximum recorded size is given as carapace width for crabs, carapace length for hermit crabs, and total body length (tip of rostrum to end of telson) for shrimp.  Each is hyperlinked to the original source.  Some of the shrimp lengths are derived from the “carapace length” (rear of the eye to the rear of the carapace).  Carapace lengths are often used because trawl-caught shrimp frequently have broken rostrums.


Range: This is the maximum-recorded extent of distribution, along with the area of greatest abundance, again linked to the original source.


Habitat: The type of area where the species is normally found, along with the depths at which it is known to occur.


Remarks: This section contains additional information on feeding habits, behavior, symbiotic associations, utilization and other notes of interest.  The often-meager pickings of this section highlight just how little is known about the ecology of many of the species along the Pacific coasts of the United States and Canada.  The last sentence typically notes the number of larval stages, if they have been described.


Information: The book is available through Amazon.com and from MolaMarine (3808 Sundown Drive, Bremerton, Washington 98312, USA) for the amazingly low price of $34.95, which includes tax, shipping and the author’s autograph.  At the Mola Marine website you can view a video of Dr. Jensen explaining the workings of the CD-book.


Sources: 1. Crabs and Shrimps of the Pacific Coast.  Dr. Gregory C. Jensen.  MolaMarine.  2014.  2. *Crust-L, an email-based mailing list for crustacean scientists.  Subject: New Crab and Shrimp Book.  Gregory Jensen (gjensen@u.washington.edu).  January 30, 2014.  3. An E-Guide to West Coast Decapods, Alaska to Mexico (the CD that comes with Crabs and Shrimps of the Pacific Coast).  MolaMarine.  2014.  4. Email to Shrimp News International from Gregory Jensen.  Subject: Questions Crabs and Shrimps of the Pacific Ocean.  February 24, 2014. 5. Bob Rosenberry, Shrimp News International, February 28, 2014.


*Crust-L is an email-based mailing list for crustacean scientists.  Subscribing to Crust-L is easy.  Send an email to sympa@vims.edu from the email address where you want to receive messages.  In the subject line of your message, type in “subscribe Crust-L, Your First Name and Your Last Name”.  Don’t enter anything in the message body.  If you have any questions or problems subscribing to Crust-L, Click Here.

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