Description:
Gammarus setosus is a small shrimp-like animal (Phylum Arthropoda, Order Amphipoda). Like all amphipods their body is protected by an exoskeleton that is laterally compressed (flattened from side to side) and curved into a c-shape. Mature adults can reach a length of 35 mm, with females growing larger than males.
G. setosus are classified in the Order Amphipoda because they have limbs with specialized functions (amphi = different, poda = foot). Ten pairs of jointed appendages arise from the three body sections. The last 5 pairs of appendages in the thoracic section are mainly used for walking while the 3 pairs of abdominal appendages are used for swimming and gas exchange.
On the head, G. setosus have two kidney-shaped, sessile compound eyes, which can detect the presence of light and movement. It is not known if they can detect colour or form clear images. They also have two pairs of antennae, which contain chemoreceptors to detect odours in their environment.
G. setosus are typically a translucent grey, green or brown which helps them blend in with their environment. However, if they are dying, they will often turn orange or pink.
G. setosus are classified in the Order Amphipoda because they have limbs with specialized functions (amphi = different, poda = foot). Ten pairs of jointed appendages arise from the three body sections. The last 5 pairs of appendages in the thoracic section are mainly used for walking while the 3 pairs of abdominal appendages are used for swimming and gas exchange.
On the head, G. setosus have two kidney-shaped, sessile compound eyes, which can detect the presence of light and movement. It is not known if they can detect colour or form clear images. They also have two pairs of antennae, which contain chemoreceptors to detect odours in their environment.
G. setosus are typically a translucent grey, green or brown which helps them blend in with their environment. However, if they are dying, they will often turn orange or pink.
Ecology:
Gammarus setosus live in low intertidal and subtidal areas along the northern coasts of the Pacific and Atlantic Oceans. They tend to crawl the ocean floor consuming small bits of organic detritus, such as decaying algae and animal matter; therefore, they are primarily detritivores. But, depending upon food availability, they may also be predators, herbivores or omnivores.
G. setosus avoid predators such as fishes (e.g. sculpin) and nemertean worms by seeking refuge under loose rocks and algae or swimming short distances. Other predators include birds such as gulls and even baleen whales such as Gray whales.
G. setosus avoid predators such as fishes (e.g. sculpin) and nemertean worms by seeking refuge under loose rocks and algae or swimming short distances. Other predators include birds such as gulls and even baleen whales such as Gray whales.
Life History:
Gammarus setosus have an estimated life span of 2-4 years. At maturity the male will attach to the female for several days until internal fertilization is complete. The female carries the fertilized eggs in a brood pouch on her ventral surface to protect the eggs from predators. In the spring the embryos hatch as a small version of the adults. The young are dispersed by the constant movement of the waves and currents.
To learn more:
Steele, V.J. and Steele, D.H. 1970. Biology of Grammarus (Crustacea, Amphipoda) in Northwestern Atlantic. Canadian Journal of Zoology 48(4): 659-671. Doi: 10.1139/z70-124.