The Unexpected Crustaceans of the San Pedro River.

The San Pedro River seems like a peaceful desert river, offering little more than an escape for nature lovers. However, beneath the surface lives a surprising cast of tiny and sometimes troublesome crustaceans. From fairy shrimp to crayfish, the river's story goes deeper than the birds and butterflies you see flying overhead.

READ: Exploring The San Pedro Riparian National Conservation Area

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San Pedro River. / Photo by Val Davidson/TSM. / Elements by Canva

Aquatic Life In Arizona?

It may seem strange to talk about aquatic life in the desert, yet the San Pedro River supports a diverse array of underwater species. According to the Bureau of Land Management, there are 13 species of native fish, such as longfin dace and desert sucker.

The San Pedro also houses numerous invertebrates, including aquatic insects and fairy shrimp, which help form the foundation of the river's food web. There are also numerous invasive species such as crayfish, bullfrogs, and the yellow bullhead fish.

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San Pedro House. / Photo by Harley Noble/TSM. / Elements by Canva

Shrimp

The San Pedro River is home to fairy shrimp, which aren't technically true marine shrimp. Fairy shrimp are tiny crustaceans closely related to lobsters and crabs. They never get larger than 2 inches and hatch in temporary pools after it rains. They survive dry periods through dormant eggs that can wait months or years for water to return.

Common Arizona species include Dumont's fairy shrimp (Streptocephalus henridumontis) and the beavertail fairy shrimp (Thamnocephalus platyurus), one of the largest fairy shrimp found in the state.

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Fairy Shrimp. / Photos and Elements by Canva

Crayfish

While fairy shrimp are native crustaceans, crayfish tell a different story. Arizona has no native crayfish, yet several introduced species have established populations in the state. Researchers documented red swamp crayfish (Procambarus clarkii) in the San Pedro River in 2010, raising concerns about their potential impact on an already stressed ecosystem.

These crayfish are known for burrowing into banks, altering habitats, and competing with native aquatic species. This can worsen erosion and harm the river's natural structure. Because invasive crayfish can be difficult to remove once established, continued monitoring remains important.

Crayfish/Crawfish. / Photos and Elements by Canva

The San Pedro River is home to dozens of unique animals, such as crustaceans, migratory monarch butterflies, hummingbirds, fish, and beavers. If you ever visit the river, stop and take a closer look at the little creatures that surround you. You'll quickly realize this simple desert river is actually a world of hidden life, with new discoveries waiting to be found.

CONTINUE READING: How Beavers Support Ecosystems Along The San Pedro River