Monocorophium insidiosum

Monocorophium insidiosum is a species of small amphipod crustacean commonly found in brackish, intertidal, and subtidial environments across Europe, Asia, and parts of North America. Monocorophium insidiosum is important in estuarine environments and benthic food webs because of its ecological versatility and tube-building habit.

Monocorophium insidiosum has gnathopods (claw-like appendages) with 2-4 inner spines on the tips. Adults can grow to be up to 5 mm in length.^[2][3]

Monocorophium insidiosum is found in estuarine and coastal environments. It is frequently seen in the English Channel, Mediterranean Sea, North Sea, Baltic Sea, and Japanese coastal regions.^[4] Reports have also confirmed its presence along parts of the American coastline.^[5] Monocorophium insidiosum favors high-turbidity conditions and lives on muddy or sandy substrates.^[4] Although population decreases occur below 1 PSU, it may survive in brackish water with salinities as low as 1.2–5.7 PSU, indicating its resilience to changing salinity conditions.^[6]

Monocorophium insidiosum is known for its tube-building behavior. It constructs protective tubes using a mixture of organic material (such as algae and detritus) and inorganic particles (like sand). These tubes aid in feeding and predator avoidance by stabilizing the amphipod in water currents.^[7]

Males use their antennae to detect female pheromones and engage in precopulatory mate guarding by carrying females until molting occurs. Fertilization takes place within the female's brood pouch, where embryos develop into juveniles before being released. Monocorophium insidiosum can molt up to 20 times during its lifetime.^[8]

Parasitism can influence behavior. For instance, the nematode Skrjabinoclava sp. has been shown to manipulate the behavior of Monocorophium insidiosum, increasing the likelihood of predation by birds such as the sandpiper (Calidris pusilla), thereby aiding the parasite's life cycle.^[9]

Monocorophium insidiosum exhibits multivoltine reproduction, producing multiple generations per year. Lifespan is typically 5–6 months. Females reach sexual maturity at around 2.2 mm in length and are more abundant in populations than males. Reproduction occurs year-round with seasonal peaks in spring and fall.^[10] Larger females tend to produce more eggs.

Seasonal fluctuations affect population density, with numbers peaking in spring and summer and declining in fall and winter. Generations often overlap due to continuous reproductive activity.^[11]

Monocorophium insidiosum is an omnivorous suspension feeder but can also engage in deposit feeding. It consumes phytoplankton, algae, and organic detritus.^[12] Additionally, Monocorophium insidiosum serves as an important food source for a variety of fish and shorebirds, making it a key link in coastal food webs.

Studies have shown that temperature significantly influences development. Warmer temperatures accelerate growth and reproductive cycles but also reduce lifespan. This flexibility allows Monocorophium insidiosum to adjust to different environmental conditions.^[12]