Naturalist Fact: Grass Shrimp

Grass Shrimp (Palaemonetes sp.)

grass shrimp

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Grass shrimp have multiple common names, including grass shrimp, popcorn shrimp, glass shrimp, glass pawns, jumpers, and hardbacks.  Compared to commercial species of shrimp, grass shrimp are quite small, rarely exceeding two inches in length.  These tiny decapods are often nearly transparent (hence the one common name of glass shrimp), and have a well developed rostrum or horn on the dorsal and forward portion of the head, much like many commercial shrimp species.  This ‘horn’ can be quite sharp and may aid in defense against predators.  Little teeth-like projections found on and around this rostrum are used to help determine the particular species of grass shrimp under a dissecting scope (different placements), although many errors in species identification are made due to the morphological similarities.

These shrimp exist in many estuarine environments, and are often associated with some sort of underwater structure such as submerged plants and very commonly, oyster reef habitats.  Structure such as submerged grasses or oyster beds provide ample protection from predators like fish, and also provide the shrimp with a food source.  These shrimp typically stay along the edges of creeks in very shallow water, but have been found up to fifty feet deep.  Grass shrimp are typically considered detritivores, feeding mainly upon dead or decaying plant matter; however their diets can consist of a wide variety of organisms.  In captivity grass shrimp have been known be cannibalistic, and will also predate on tiny polychaetes, oligochaetes and nematodes (marine worms) in the wild.  Because these tiny crustaceans often fall prey to fishes and other carnivores, they are extremely important as a link between trophic levels.  Energy and nutrients are transported between primary producers and higher trophic levels with grass shrimp being an important vector.  More research is needed to assess the populations of grass shrimp and how humans may be affecting these ecologically important organisms.

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