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Monocorophium acherusicum

Meagan Mackenzie 2017


Monocorophium acherusicum is a biofouling amphipod which was first documented by Costa in 1853. The 5mm, tube-building crustacean can be found across the globe in variety of marine habitats due to its adaptive nature (Beermann & Franke, 2011; Hayes et al., 2005). This filter feeding, omnivore, can occur in high densities, typically in regions where resources such as algae and sediments are present (Marchini, Gauzer & Occhipinti-Ambrogi, 2004; Acton, 2013; Hayes et al., 2005). M. acherusicum are iteroparity and tend to have high fecundity, particularly in warmer periods (Rumbold et al., 2016). The marine invertebrate is commonly found in benthic communities however males are also known to enter the pelagic zone in search for mates (Conlan, 1991).

The classification of M. acherusicum is as follows (WoRMS Editorial Board2017):

Kingdom: Animalia
   Phylum: Arthropoda
     Subphylum: Crustacea
        Class: Malacostraca
           Subclass: Eumatacostraca
              Superorder: Peracarida
                 Order: Amphipoda
                    Family: Corophiidae
                      Genus: Monocorophium
                         Species: Monocorophium acherusicum

Physical Description

Amphipods can be identified by the presence and absence of three morphological features, the absence of a carapace, fusion of the first thoracic segment to the head and a two-part abdomen, each part consisting of three segments (Phillips, n.d.). This order is one of the most abundant groups, making identification a difficult task (Rumbold et al., 2016).

M. acherusicum are yellowish-brown in colour, where the brown tends to form a band like pattern along the pereon and peducle’s. The organism is dorso-ventrally flattened with enlarged dorsal antennae (Hayes et al., 2005). This species has been historically misidentified as the females closely resemble M. insidiosum and the species share a vast number of characteristics with fellow Corophiidae such as M. sextonae (Phillips, n.d.). Male M. acherusicum have a few different characteristics such as an absent/highly reduced rostrum (Phillips, n.d.).



M. acherusicum have been found to foul on human infrastructure such as buoys, jetties and ships (LeCroy, Richardson & Cobb, 2011; Hayes et al., 2005).  Due to its adaptable lifestyle, the species can be found in both freshwater and saltwater environments, in shallow waters and at depths of 80m in the zoocoenosis zone (Sezgin & Katağan, 2007; LeCroy, Richardson & Cobb, 2011; Rumbold et al., 2016). The species tends to favour benthic communities due the species reliance on algae and detritus matter. Such materials are used for the construction of u-shaped tubes which enables the organism to seek shelter and reduce exposure to predation.  Other organisms such as sponges, seagrasses, hydroids and tunicates are surfaces in which M. acherusicum utilize for tube settlement (LeCroy, Richardson & Cobb, 2011). 

Salinity, food availability, competition and pollutants are a few factors which can impact the abundance of M. acherusicum (Rumbold et al., 2016). Warmer seasons influence reproduction as higher temperatures increase growth rates and sexual maturation (Rumbold et al., 2016). The sex ratio has been suggested to be female dominated as males tend to be exposed, more than their counter parts (Rumbold et al., 2016). A correlation between the size of females and brood has also been found, larger females tend to have larger broods (Rumbold et al., 2016). This species can also be found at densities of 60-70 specimens per 100cm2 (Beermann & Franke, 2011). Its ability to acquire phenotypic plasticity, has enabled the invertebrate to invade a vast number of ecosystems. The success of fouling ships and invasions, reflects a wide tolerance to conditions, as this lifestyle would require an emersion response and a thermal response (Lewis, Bergstrom & Whinam, 2006).  


Females are oviparous and use their abdomen to brood embryos (Lee, Lee & Park, 2008). Female amphipods have a small window for fertilisation which ranges from minutes to a couple of hours (Conlan, 1991). Post molting and during ovulation, is the prime time for males to deposit sperm as the eggs have been released through the genital pores into the brood pouch (Conlan, 1991). The eggs can reach this region as the cuticle is flexible enough due to the molting event (Conlan, 1991). The brood pouch is located between the bases of the pereopods, on the pereon (Foster et al., 2009). Research has conflicted seasonality of breeding, however recruitment in summer is likely (Rumbold et al., 2016).


The tube building amphipod has numerous marine predators such as small fish, shrimp, crabs and Tetrastemma elegans (McDermott, 1976; Nelson, 1980). Scyphopolyps have also been captured actively eating M. acherusicum (Figure 1) (Di Camillo et al., 2010). Predation can be limited with the construction of tubes which as previously mentioned, provides shelter for the organism. M. acherusicum and other amphipods, play a pivotal role in the development of juvenile fish as they prey on such organisms to support growth (Jeong, Suh & Kang, 2012). 

Figure 1

Life History and Behaviour


Amphipods are amongst the most important secondary producers as they can act as trophic mediators between various consumers (Jeong, Suh & Kang, 2012). In eelgrass habitats M. acherusicum, has been found to have a mixed diet consisting of zooplankton, epiphyets and biologically processed eelgrass (Jeong, Suh & Kang, 2012). Other amphipod species within the same region have been found to have an herbivorous diet (Jeong, Suh & Kang, 2012). Such findings suggest, species may have a niched role in the community. Due to M. acherusicum mixed diet, it suggests that the species may be opportunistic and seasonal changes may impact the diet. Minimal research on species specific feeding ecology has been done and would perhaps be useful to give insight into species specific roles. 

Gnathopods are important appendages for feeding as they collect particles for consumption and the beating of pleopods are valued for creating currents. Within their tubes, water is continuously flowing, as a flux is generated (Gonzalez) form the beating of the pleopods (Thiel & Watling, 2015). Circulating the water increases the likelihood of particles entering the tube which allows the suspension and deposit feeders to trap and consume nutrients. An omnivorous diet can be supported in M. acherusicum from Figure 2. It is suggested that plant matter may be present in the gut however contents analysis would be beneficial to identify specifics. M. acherusicum, have a complete gut, with anterior mouth and posterior anus which is within the urosome region (von Vaupel Klein, Charmantier-Daures & Schram, 2015).

Figure 2


There are two categories that have been identified as male precopulatiry mating behavior in amphipod males, mate guarding and searching (Conlan, 1991). Mate guarding is the “capture” of a mate prior to molting, followed by persistent guarding to restrict interactions with other males, particularly to prevent fertilization (Conlan, 1991). Guarding can be further split into two subcategories, attenders and carriers.  Carriers grasp onto the dorsum or lateral plates of the female until molting has occurred (Conlan, 1991). Attenders simply remain in close proximity to their hostage, this can be achieved by the male placing his body on top of hers, lingering nearby or sharing tubes. In contract, searchers only have contact during copulation and can either enter the pelagic zone or remain in the benthic zone in search of mates. M. acherusicum, specifically is yet to be allocated into a specific mating category however other Corophioidea species were identified as mate-guarders and favoured attender behaviours (Conlan, 1991).


An observation of potential cleaning behaviour was detected, as the anterior peducles of the second antennae was tucked towards the ventral surface, interacting with gnathopods (Video 1).  Such movement requires muscular contraction. The antennae and appendages are highly muscularised, as identified in Figure 3. Antagonistic muscles are responsible for appendage movement and muscle networks also surround the gut, more so the stomach and rectum (von Vaupel Klein, Charmantier-Daures & Schram, 2015). Amphipods are capable of body movement via extension or flexion, which can enable them to swim 4-14cm/s (Hallberg, 2010; von Vaupel Klein, Charmantier-Daures & Schram, 2015)M. acherusicum can be seen in action in the second video.

Video 1: M. acherusicum cleaning the second antennae 

Video 2: M. acherusicum interacting with detritus
Figure 3

Anatomy and Physiology

Key Features

Key morphological features of M. acherusicum (Figure 4) (Bousfield & Hoover, 1997)

  1. Urosome with distinct lateral notch, uropod 1 inserted laterally
  2. Rostrum recessed
  3. Antenna 1 – peduncular bulging proximally and narrowing distally
  4. Antenna 2 – strongly pediform, peduncular segment 5 is shorter than 4, posterior margin with small proximal toothe and few setae; flagellum short 
  5. Pleon plates weakly setose, or absent

As represented in figure 4, other characteristics includes, gnapthopods, pereopods and pereon. Pereopods consist of the coxae, basis, ischium, merus, carpus, propodus and dactylus (1-7) (LeCroy, Richardson & Cobb, 2011). Female and male M. acherusicum are distinguished from anatomical structures such as the number of spines on appendages. Females have 3-4 pairs of spines on their second antennae and numerous spines on their first antennae (Beermann & Franke, 2011). Males have weak setose on the second antennae, whereas females have whorls of setae (Bousfield & Hoover, 1997).

Figure 4

Chemical Communication

The antennae of amphipods withhold chemosensory structures, making these features highly important for receiving information related to food abundance, predator detection and intraspecific interactions (Breithaupt and Thiel, 2010). Since the invertebrates are within water, chemicals can be transferred throughout the substance and/or remain on the specimens and be detected from direct contact. The reproductive status of females for example, could be identified by chemical compounds and would be highly advantageous for males if detection occured. Sensory hairs, the aesthetascs are species specific and possibly sex dependent (Breithaupt and Thiel, 2010). Bundles of these sensory hairs are called callynophore, which tend to be favoured by males, possibly due to their copulation behaviour (Breithaupt and Thiel, 2010).  Studies on other tube dwelling amphipods such as M. gryllotalpa and Corophium volutator have found that the males are receptive to waterborne chemicals, as receptive females were favoured over non-receptive females (Breithaupt and Thiel, 2010). There has however been limited studies on such behaviour and further research is required for the order.

Biogeographic Distribution

M. acherusicum has been identified globally in regions such as the Black Sea, Australia, California, North Atlantic, Mediterranean Sea, North Coast of Europe, South East of Africa, India, Korea, Japan, China, New Zealand and South America (Sezgin Katağan, 2007; Hayes et al., 2005; Rumbold et al., 2016; Lewis, Bergstrom & Whinam, 2006; Lee, Lee & Park 2008; Zakhama-Sraieb, Sghaier & Charfi-Cheikhrouha, 2009) (Figure 5). Due to its minute size, phenotypic plasticity and transportation mechanisms, other regions are thought to have been exploited.

Figure 5

Evolution and Systematics

Sexual Dimorphism

The enlargement of anterior appendages such as the second antennae and second gnathopods, has developed in some species (Conlan, 1991). Mate guarding species seem to have developed such morphological features perhaps due to selective pressure. Pelagic searchers also tend to have an enlarged, pronounced second antennae in comparison to benthic searchers (Conlan, 1991). Enlargement, may reflect sensory capabilities and an increase in aggressive interactions particularly amongst mature males. This selection would be favoured to defend mates, determine reproductive state, enhance weaponry and disrupt or enhance carrying activities.


Corophiinae encompasses the polymorphic genus Corophium (Bousfield & Hoover, 1997). This genus consists of thirteen genera, six of which have primitive unfused urosomal segments and commonly burrow in soft sediment (Bousfield & Hoover, 1997). The other seven genera have fused urosomal segments and typically construct open-ended tubes on hard substrates (Bousfield & Hoover, 1997). The genus Monocorophium translates as, mono meaning one and the generic root Corophium referencing, the fused urosome (Bousfield & Hoover, 1997). This group may be polyphyletic, and the ancestor has been suggested to have unfused urosome segments. A few key features of the genus are the urosome, with fused segments and the uropods arising from lateral notches. Key characteristics of M. acherusicum can be found in the Key Features Section, above. The phylogeny of Amphipoda is under debate due to the vast quantity of species, wide distribution and shared physical attributes.

Conservation and Threats

The invasion of M. acherusicum into new region was commonly due to the movements of ships (Hayes et al., 2005). The species would become part of a fouling community on the submerged surface of ships and from then, would either remain or be dispersed along the sea channels. M. acherusicum can alter sediment structure and impact primary producers due to their interactions with algae and detritus matter. This disruption can be due to the consumption of material for nutritional value or for the construction of tubes. The species is regarded as a relative low threat however further research is required into regional specific impacts (Hayes et al., 2005).

Quarantine and standardised cleaning protocols are important to limit the transportation of biological matter (Lewis, Bergstrom & Whinam, 2006). Typically, terrestrial material is highly regulated, however marine organisms are less so, perhaps due to the logistics of operations and an “open” system. Though this species is not considered hazardous, rather a relative low risk, controlling the distribution and population of the organisms is not urgent.


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