Population dynamics of two invasive amphipods in the Southwestern Atlantic: Monocorophium acherusicum and Ericthonius punctatus (Crustacea)

Harbours are important sites for the containment and dispersal of invasive species throughout the world, so the study of life history traits of species is important to understand the success of their invasion and their potential effects on the habitat. In recent years several invasive species have been reported in Argentinian harbours; however, studies of the ecology and life history of these species are scarce. We studied the population dynamics and reproductive biology of Monocorophium acherusicum and Ericthonius punctatus, in order to update the published information on the introduced amphipods in Mar del Plata harbour. Both species showed a seasonal pattern characterized by high densities in warmer months, related to the highest reproductive activity and the increase of recruitment in summer and early autumn, and lower densities in the cold season. The sex ratio was always female-biased and the number of eggs carried by females was positively correlated to the size. The present study suggests that both species have colonized Mar del Plata harbour successfully, showing viable populations (cohorts of juveniles, males, females and ovigerous females). This work provides the basis for monitoring the impact generated by introduced amphipods over the existing fauna.     

Population dynamics of Caprella dilatata and Caprella equilibra (Peracarida: Amphipoda) in a Southwestern Atlantic harbour

We studied the population dynamics and reproductive biology of Caprella dilatata and Caprella equilibra in order to provide the basis for understanding the ecological role of both species in Mar del Plata Harbour. Caprellids and organisms from the fouling community were obtained by sampling in the harbour, monthly from April 2014 to March 2015. Mean density of C. dilatata was homogeneous during most of the study period (ca. 50–200 ind/100?g) and reached their maximum in May (ca. 650 ind/100?g), while C. equilibra did not show any differences during the sampling period (ca. 30 ind/100?g). Juveniles of C. dilatata reached their highest densities in May, while ovigerous females were at their maximum values in late spring, summer and early autumn, and no correlation was found between seawater temperature and monthly density. On the other hand, C. equilibra reached its maximum juvenile and ovigerous female densities in summer, and showed a positive correlation with seawater temperature. Sex-ratio was female biased in C. dilatata, but in C. equilibra it was equal between sexes. The number of eggs carried by females was positively correlated to the size in both species. The present study suggests that the population dynamics of C. equilibra are intimately related to seawater temperature, while for C. dilatata no relationship was found. Future studies of ecology and behaviour traits in caprellid species are needed in order to determine the ecological role and the environmental factors that could affect both species.     

Reproductive traits of a nonindigenous amphipod associated with alternative habitat structures in presence of an invasive ecosystem-engineering polychaete

Hydrobiologia - Understanding reproductive traits of invasive species and their modulation by different invaded habitats is crucial for monitoring invasive processes. The invasive ecosystem...     

No Longer The Pristine Confines of the World Ocean: A Survey of Exotic Marine Species in the Southwestern Atlantic

We conducted a comprehensive survey of existing knowledge about exotic marine organisms introduced to the southwestern Atlantic Ocean, including coastal and shelf areas of Uruguay and Argentina. This domain is equivalent to the so-called Patagonian Shelf Large Marine Ecosystem, and corresponds to two biogeographic provinces: warm-temperate (Argentine Province) and cold temperate (Magellanic Province). The search included species that can be confidently categorized as introduced (31) and cryptogenic species (46). We present a comprehensive picture of recorded introductions (the first for this region) and some prominent ecological consequences. Most coastal ecosystems between the La Plata River estuary and central Patagonia have already been modified, or are expected to be so in the short term. Five recent, human-mediated biological invasions have already had a significant ecological impact. A barnacle (Balanus glandula) belt has developed on all rocky shores where none was present 30 years ago, a macro-fouler (Limnoperna fortunei) and a reef-builder (Ficopomatus enigmaticus) have strongly modified estuarine ecosystems, Pacific oyster (Crassostrea gigas) reefs are expanding in shallow bays at a fast rate, and kelp (Undaria pinnatifida) is rapidly modifying nearshore benthic communities along the coasts of central Patagonia. At this point, it is uncertain how many of the cordgrasses (Spartina spp.) found in coastal salt marshes correspond to exotic forms. Only exposed sandy beaches appear to be free from the pervasive ecological impact of invasion by exotic species. Poor knowledge of the regional biota makes it difficult to track invasions.