Amphipods

Amphipods are a type of crustacean belonging groups such as crabs, lobsters, and shrimp [1]. Amphipods can be found in both marine and terrestrial environments, with currently 10,753 known species [1]. In aquatic environments, amphipods are often referred to as as scuds, shrimp, or side swimmers [1]. Terrestrial species may be called land hoppers or beach/sand flies [1]. Amphipods are often considered keystone species due to their high population densities and their significant role in food webs [3].

Figure 1: Aquatic amphipod

Taxonomy

  Class: Malacostraca  
     Subclass: Eumalacostraca 
         Phylum: Anthropoda
            Order: Amphipoda
               Family: Gammaridae     

Figure 2: Amphipod Anatomical Diagram

Description

Amphipods can range from 1 to 340 millimeters long [2], with a laterally compressed, segmented body and prominent antennae [4]. Amphipods lack a carapace, which is the hard upper shell seen on crayfish or lobsters [5]. Amphipoda means "different feet", referring to their three pairs of pleopods and three pairs of uropods. Conversely, Isopods, a related group of crustaceans, means "same feet" [1]. Most amphipods are detritivores, feeding on decaying plant and animal matter. This feeding style plays a vital role in ecosystems, as it breaks down organic material [5]. Similar to crayfish, amphipods must periodically molt their exoskeleton in order to grow [6].

Habitat

Aquatic: Aquatic amphipods can be found in both marine and freshwater environments and are often found at the bottom of the given substrate [5]. Some aquatic amphipods may be seen burrowing in the substrate, creating small tunnels or depressions where they can hide from predators and forage for food [5]. In doing so, this behavior also plays a role in sediment turnover [5].

Terrestrial: Terrestrial amphipods live on the top half inch of soil, relying heavily on its moisture to survive [6]. Amphipods do not contain a waxy layer on their exoskeleton, and are therefore prone to desiccation in dry environments. Significant changes in soil moisture or habitat disturbance can quickly impact their populations [6].

Figure 3: Marine amphipod feeding on algae in substrate

Life Cycle

Most amphipod species complete their life cycle in one year or less [6]. Female amphipods can produce hundreds of eggs within a single brood [6]. These eggs are kept in a pouch called a marsupium, located on the underside of the female, offering protection as the eggs develop [7]. Depending on the species and water temperature, it may take 1 to 20 weeks for the eggs to fully develop [7]. Once the eggs hatch, the juvenile amphipods look like small versions of the adults and become sexually mature after growing and molting several times [6].

Ecosystem Importance

Amphipods are considered secondary producers within aquatic and terrestrial food webs [8]. They primarily feed on organic materials, such as algae and detritus, which helps recycle nutrients [8]. Additionally, amphipods serve as a major food source for certain juvenile fish species [8].

References

[1] Horton, T., Lowry, J., De Broyer, C., Bellan-Santini, D., Coleman, C. O., Daneliya, M., ... & Zeidler, W. (n.d.). World Amphipoda Database. World Register of Marine Species. https://www.marinespecies.org/amphipoda/#:~:text=The%20order%20Amphipoda%20is%20part,and%20three%20pairs%20of%20uropods.

[2] iNaturalist. (n.d.). Amphipoda. https://www.inaturalist.org/taxa/47628-Amphipoda

[3] Eawag. (2023, October 3). Amphipods: A miraculous increase in biodiversity. https://www.eawag.ch/en/info/portal/news/news-detail/amphipods-a-miraculous-increase-in-biodiversity/

[4] ScienceDirect. (n.d.). Amphipod. Elsevier. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/amphipod

[5] Missouri Department of Conservation. (n.d.). Scuds, sideswimmers (amphipods). https://mdc.mo.gov/discover-nature/field-guide/scuds-sideswimmers-amphipods#:~:text=Habitat%20and%20Conservation,at%20the%20bottom%20of%20ponds.

[6] Buss, L. W., & Bextine, B. (2009). Amphipods (Publication No. IN377). University of Florida IFAS Extension. https://edis.ifas.ufl.edu/publication/IN377

[7] ScienceDirect. (n.d.). Amphipoda. Elsevier. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/amphipoda

[8] ScienceDirect. (n.d.). Amphipod. Elsevier. https://www.sciencedirect.com/science/article/pii/S002209812300117X

[9] Hudson River Park Trust. (n.d.). Amphipod. https://hudsonriverpark.org/the-park/parks-river-project/science/wetlab/invertebrates/amphipod/