Opossum Shrimp

Opossum Shrimp

Author: Jamie Lenihan

Common Names:  Mysid Shrimp, Opossum Shrimp

Scientific name:  (Order) Mysida

Size range: 5-25mm long (mature length)


Identifying Features

Mysida is an order of over 1000 species of similar shrimp-like crustaceans. The creatures get their name from the presence of a ‘brood pouch’ – an egg chamber attached to the female. This pouch gives the female Mysida a distinctive ‘bulge’, allowing them to be easily identified. While there are many types of Mysida that are pale, and even transparent, there are also varieties that have bold orange and brown colourations. Additional features include compound eyes protruding from stalks, and a rigid carapace that covers the creature’s head and the thorax. While very similar in appearance to shrimp, Mysida don’t have free-swimming larvae, and are hence classified differently.

Habitat

Mysids can be found living in both freshwater and salt-water environments. The majority of these creatures are free-living, and survive as independent organisms; however, there are some mysids that have been noted to develop commensal relationships with other animals such as sea anemones and hermit crabs. Mysids are usually observed occupying low-light areas at the bottom of lakes during the day. They then migrate upwards at night to food on zooplankton and phytoplankton. In the ocean, mysids can be found as both near the surface, near the ocean floor, and everywhere in between. Some species may burrow themselves into the sand during a low tide.

Food (Prey)

Most Opossum shrimps are generally regarded as omnivorous and feed mainly on algae, detritus, and zooplankton. Pelagic Mysida filter particles as they swim, while benthic species consume small particles they gather from combing their body and legs. Other species even favour a nearly entirely carnivorous diet. These Mysida will scavenge and feed on the remains of copepods, amphipods, zooplankton, and even other Mysids. In fact, it’s not unusual for parent mysids to eat some of their own young if they have to!

Predators

Mysids are very abundant in population and reproduce quickly. This has resulted in them being the ideal prey for a whole host of creatures and perfect for culturing by humans. Baleen whales, cephalopods, small fish, shrimp, rays, rockhopper penguins, rockfish and seahorses all have mysids as a significant part of their diets. Mysids are one of the most commonly human-cultured foods for use in commercial farms and aquariums. Mysids are fed to farmed shrimp, cephalopods, fish larvae, and many juvenile sea creatures that are otherwise difficult to nurture.

Life Cycle and Reproduction

Juvenile mysids are very similar in appearance to their adult counterparts, but are smaller in size (typically less than 10mm). The length of the adult female’s body is a good indicator of brood size. The larger the creature the more eggs, and hence, the more offspring it is capable of having. In most species, the male develops an elongated limb-like organ that is used to transfer sperm to the female. There are, however, some species that release sperm directly into the water around them. The female then uses her thoracic legs to create a current that directs the sperm towards her. A mysid will usually take between 13 and 20 days to reach full size, but anywhere between 6 weeks and two years to reach sexual maturity. The factors that affect the rate of development are primarily water temperature and food availability. Although mysids generally have smaller number of offspring, they have a short reproduction cycle of only 4-7 days. This allows them to quickly generate a massive population.

Video by Conor Graff

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Dungeness Crab

Author:

Duncan Bailey and Paul Guevarra

Dungeness Crab

Common name:  The Dungeness Crab

Scientific name:  Metacarcinus magister

Size Range: The carapace width of the Dungeness Crab is typically under 20 cm (7.9 in), but can be up to 25 cm (9.8 in). Females can be up to 18 cm (7 in) wide.


Identifying Features

Dungeness Crabs have five pairs of legs, the first pair of which end in claws that are used for defense and for tearing apart large food items. The crab uses its other appendages to pass food up to its mouth. Dungeness Crabs are grey-brown in colour with a purple carapace, a yellow underside, and yellow claws with white tips.

Habitat 

Dungeness Crabs are found along the west coast from Santa Barbara, California to Alaska. The crabs live in sand-mud or Eelgrass beds. They prefer sandy offshore waters, but younger crabs can be found in the intertidal zone. Dungeness Crab can be found in the shallow waters of bays in the intertidal zone and as deep as 225 m (750 ft).

Prey

The Dungeness Crab feeds on a wide variety of organisms including; marine worms, mollusks (bivalves, oysters, clams, snails, etc.), small crustaceans (shrimp) small fish, and smaller crabs. They use their claws to tear their food into smaller pieces. They then use two small mandibles to crush food. The food then passes through the “gastric mill”, a collection of tooth like structures, which further crushes and breaks down food for digestion.

Predators

The predators of the Dungeness Crab include fishes such as Dogfish (Squalus sp.), hake, halibut, Lingcod (Ophiodon elongates), sculpins, and Wolf Eels (Anarrhichthys occelatus).  Octopuses as well as humans also eat them.

Life Cycle

Mating occurs in near-shore coastal locations outside of estuaries. Mating occurs most commonly in May and June between hard-shelled male crabs and newly molted, soft-shelled female crabs. The female stores the sperm in a seminal receptacle until the fall, when the eggs are fertilized. When the eggs are extruded, the resulting mass, often called the sponge, is attached to the female. A large female can carry over 2.5 million eggs. Females carrying eggs usually bury themselves in sandy beaches during the fall.  Eggs hatch 2 to 3 months after being laid. Dungeness Crab larvae are planktonic and propel themselves using tidal currents. They pass through the zoea stage and then the megalops stage.  During the megalops stage they are very fast swimmers and large swarms of them can be found in sandy bays zipping around the surface of the water looking somewhat like sea lice with their large heads and legs tucked in.  They also have reflective green eyes at this stage.  Some larvae will hitch hike on jellyfish in order to travel to estuaries.  After the megalops stage they will molt into a juvenile crab that is only around 1cm across.  They settle to the sandy bottom in shallow coastal waters and begin to dig into the sand to hide. When they sense food they quickly emerge from the sand to find it.  Each crab will molt up to 15 times in its life, which is estimated to be 8 to 13 years.

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Coonstripe Shrimp

Coonstripe Shrimp

Author:  Noah Spriggs and Zach Lansdell

Common Names: Coon Stripe Shrimp, Dock Shrimp

Scientific Name: Pandalus danae Stimpson, 1857

Size Range: Up to 14cm (about 6 inches) in length, 7.5 to 10cm average.


Identifying Features:  The Coonstripe Shrimp is a medium sized crustacean that can be identified by the thin diagonal stripes along its abdomen. It varies in colour, but often has a mix of brown, red, and white surrounding its semi-translucent body. The translucency is used for camouflage and may make them difficult to spot from the surface. This shrimp has large antennae about the length of its body used for feeling around, with large eyes located directly behind them. Along with its large tail, the Coonstripe shrimp has 5 pairs of swimmerets used for forwards momentum.

Habitat: The Coonstripe shrimp generally prefers to stay hidden during the day. Its usual choices are pilings, piers, breakwaters, and sunken logs, but can also be found in bottom sands by rapid currents. During the night they wander and feed, their antennae help them hunt in the dark. They are found in depths ranging from 18 meters up to 200 meters; the young ones are found in shallower water than the adults. The Coonstripe Shrimp occur from California, all the way up the coast to Alaska.

Food: The Coonstripe Shrimp is very aggressive towards its prey, and is also a big feeder. It eats large zooplankton and small crustaceans using its 3 pairs of marillea (feeding hands) to scoop food into their mouth. They also have a small set of pinchers located on their second set of legs used for handling food. It primarily feeds on polychaetes, small sea worms with bristles, which it captures by charging or cornering.

Predators: The Coonstripe Shrimps primary predators are the Lingcod (Ophidian elongate) and the Pelagic Cormorant.  The Cormorant can dive up to 100 feet (30m) to catch the shrimp, and the lingcod scrapes against the sea floor scooping up the shrimp. When the shrimp see these predators coming, they flick their tail forward giving them massive backwards momentum to escape into crevices or to give them enough time to swim away. The Coonstripe shrimp is used for commercial purposes, but is not endangered.

Life Cycle: The Coonstripe shrimp is a protandrous hermaphrodite. They start out as males, and as they age they usually transform into females when the need arises. Before reproducing, females molt into a new, specialized egg-carrying shell, the males deposit a packet of sperm on the underside of the females. The usual spawning period is November, when the eggs are fertilized, to April, when the eggs are released. The eggs are carried until they hatch, and a typical female can carry anywhere from 100-4000 eggs, depending on their size. The Coonstripe shrimp’s lifespan is around 3 years.

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Graceful Decorator Crab

The Graceful Decorator Crab

By Maddi Larson

Scientific name:  Oregonia gracilis

Common names:  Graceful Decorator Crab, Slender Decorator Crab, Decorator Crab, and Spider Crab

Size range: The Graceful Decorator Crab, measured across the carapace and including the legs, can grow up to 5 cm (2 inches).


Identifying features:  The Graceful Decorator Crab is the most spidery of all the intertidal spider crabs, and has long and slender legs. This crab has quite an amazing adaptation for camouflage: it has sharp spines all over its body that allow it to actively decorate itself with things such as bits of seaweed, little pieces of sponge and any thing else in their environment that makes them blend in. Also, the first legs have pinchers specifically designed for handling the decorations. If the Graceful Decorator Crab is taken from one environment and moved to another it will shed its previous decorations and use the new material. The crab is triangle-shaped as the carapace is wider at the posterior end. Underneath the camouflage, it is mostly reddish-brown.

Habitat:  The Graceful Decorator Crab lives intertidal to 436 m (1,430 ft). It ranges from North Alaska to Central California, and in Japan. The Split Nose Decorator Crab (Oregonia bifurca) lives near it at 500 m (1,650 ft). Other types of decorator crabs live near it as well, including Hyas lyratus and Scyra actuifrons. In addition the Graceful Decorator Crab has a mutalistic relationship with hydrozoans and other corals.

Prey:  The Graceful Decorator Crab eats algae and kelp, plankton and the flesh of dead animals.

Predators:  One predator is the Pacific halibut and other possible predators include octopus, fish and sea otters off the Pacific coast. The effective camouflage of the Decorator Crab keeps it well hidden from predators.

Life Cycle: The spawning season is usually between May and August because that is when there are planktonic blooms. Males reach maturity after their last molt, which is about 9-11 cm and females reach maturity when they become about 8-10 cm.  Eggs that are ready to hatch are reddish-brown while eggs that have recently hatched are orange-red.

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Bering Hermit Crab


Common Name: Bering Hermit Crab

Author: Avria Chrystall & Joy Trinh-Day

Scientific Name: Pagurus beringanus

Size Range: Bering Hermit Crabs grow to about an average of 2.5 inches. (6.4 cm)

Identifying Features:

Bering hermit crabs have 10 legs, however some of them aren’t fully developed and remain inside of their shell.   Three pairs of legs remain outside of the shell and the front two in claws. Its legs are often grey, brown and/or green. You can identify them by the red and occasionally white bands around their legs and joints.

Habitat:

The Bering Hermit Crabs like to live in partially protected waters particularly around rock formations and other rocky areas. They live around 17 meters from sea level and tend to live in areas that remain underwater even at low tide.

Food:  

Bering Hermit Crabs are omnivorous scavengers. Their diet relies on what is available and where they live. They will eat algae and any other particles of food that they can find.

Predators:

The Rosy Lip Sculpin is one of the Bering Hermit Crabs Predators. Seagulls also eat the crabs at low tide.

Life Cycle:

After meeting and deciding to mate, both the male and female crabs arise slightly from their shells.  The male gives reproductive material to the female in a capsule. The female will then put up to several thousand eggs on her left side where she will carry them until the yolk sack is gone and the eggs have changed from red to a dark gray colour. These eggs will burst at first contact with salt water releasing the hermit crab larvae to fend for themselves.  They will float in currents before until they are old enough to find their own discarded shell.

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