It ain’t easy being green…unless you’re a kelp humpback shrimp

Eyes Under Puget Sound – Critter of the Month

Top o’ the morning to you! Did you remember to wear something green to celebrate St. Patrick’s Day? Take a lesson from the kelp humpback shrimp, who woke up dressed and ready in its Irish best.

Over the hump
Irish flag with Phylogentic classification over top.  Genus Hippolyte, Species Hippolyte clarki

Like other members of the family Hippolytidae, the kelp humpback shrimp has an abdomen that protrudes in the back, giving it a “humpback” appearance. For very obvious reasons, it is also sometimes called the green shrimp, the little green shrimp, or the grass shrimp. Its slender body is usually bright green with dark spots, but it can also be brownish or reddish in color. The female reaches 3 cm in length, while the male is smaller.

 Top view of a speckled shrimp sitting vertically on a clump of brown and green eelgrass

A brown kelp humpback shrimp blends in with a dead eelgrass blade. Image courtesy of Aaron Baldwin, Alaska Dept of Fish and Game.


The kelp humpback shrimp, Hippolyte clarki, may be easily mistaken for the California green shrimp, Hippolyte californiensis, a species which co-occurs in the southern part of its range from Alaska to Baja California (and is now suspected to occur in the Pacific Northwest as well). If you have a microscope or strong magnifier, you can tell these almost-twins apart by looking at the rostrum, a beak-like projection or snout on the head of many shrimps. The rostrum of H. clarki is long and slightly upturned with three points on the tip, while that of H. californiensis ends in only two points.

 Elongate, green shrimp snout with blue speckles on a light blue background

The rostrum of Hippolyte clarki has three points at the tip. Photo courtesy of Dave Cowles,

Green around the gills

You won’t find this little shrimp at a pub enjoying a pint of Guinness. In fact, you might not find it at all — its color is perfect for blending in with the eelgrass (Zostera marina) it clings to in the northern part of its range. It may also be found living on kelp (Nereocystis or Macrocystis sp). It feeds by scraping algae off the eelgrass and kelp blades, and it also likes the occasional bit of protein in the form of tiny invertebrates – the shrimp equivalent of corned beef and cabbage?


Close up side view of bright green shrimp head with blue speckles and round golden compound eye that looks like a disco ball.

Close-up of the head of a kelp humpback shrimp. Photo courtesy of Dave Cowles,

The kelp humpback shrimp may not grant wishes or lead you to a pot of gold, but it does provide many important ecological benefits. As it eats, it incorporates nutrients from the algae into its body. When the shrimp is eaten by juvenile fishes like rockfish (Sebastes spp), this energy is transferred to higher levels in the food web. The eelgrass and kelp beds where this shrimp lives also serve as nursery grounds for many other commercially important fish and invertebrates, which may depend on the kelp humpback shrimp as a food source.

Luck o’ the Irish

Translucent, yellow-green colored shrimp with a white back stripe, noticeably contrasts with the filamentous red algae it is sitting on.

Um…your camouflage isn’t working! A kelp humpback shrimp hangs out on some red algae. Photo courtesy of Kevin Lee,

The kelp humpback shrimp’s life history has not been well-studied, so there is much to learn about them, including how they will be affected by a changing climate. Species that are dependent on specialized habitats are often unlucky when faced with environmental disturbance, and there has been recent evidence of kelp and eelgrass coverage declining in Puget Sound.

In June 2020, the sediment team will be conducting monitoring in Padilla Bay, WA for our new Bays of Ecological Importance program. This will be our very first time sampling in intertidal and eelgrass ecosystems and with a little luck, we will spot some of these well-camouflaged critters and contribute to the body of knowledge about their habitat.

A smiling female scientist in hard hat and lifejacket conducts field work on a boat

Dany is a benthic taxonomist, a scientist who identifies and counts the sediment-dwelling organisms in our samples as part of our Marine Sediment Monitoring Program. We track the numbers and types of species we see to detect changes over time and understand the health of Puget Sound.

Dany shares her discoveries by bringing us a benthic Critter of the Month. These posts will give you a peek into the life of Puget Sound’s least-known inhabitants. We’ll share details on identification, habitat, life history, and the role each critter plays in the sediment community. Can't get enough benthos? See photos from our Eyes Under Puget Sound collection on Flickr.