Author(s):
Chícharo, Alexandra 
; Leitão, Tânia ; Range, Pedro ; Gutierrez, Cristina ; Morales, Jesus ; Morais, P. ; Chícharo, Luís
Date: 2009
Persistent ID: http://hdl.handle.net/10400.1/5142
Origin: Sapientia - Universidade do Algarve
Subject(s): Alien species; Leptomedusae; Caridea; Gulf of Cadiz; Dams; Ecohydrology
Description
The cnidarian Blackfordia virginica and the adult of the caridean prawn, Palaemon macrodactylus are first recorded from the
Guadiana Estuary. The habitats and environmental conditions under which these species were found are described and the
potential impacts and mitigation measures for their introduction are discussed. The first observations of adults of these species
were made in July 2008, at the transitional zone of the estuary (brackish area). Most samples taken in the middle-estuary were
characterized by large densities of B. virginica (> 100 individuals 100 m-3), while P. macrodactylus was recorded in much
smaller densities (<0.01 individuals m-2). Despite a comprehensive survey of invertebrates done between 1999 and 2003, neither
of these species was previously detected in the Guadiana estuary. These observations may, therefore, coincide with the
introduction of these species to the Guadiana estuary. Small planktonic crustaceans are generally described as the main food
items for B. virginica. Our results show that the presence of the medusa was usually associated with a reduction of densities of
all zooplanktonic organisms, including eggs of Engraulis encrasicolus. The reduction of planktonic biomass could have severe
implications for organisms at upper trophic levels, such as E. encrasicolus, which use the Guadiana estuary as a nursery area and
feed mostly on small planktonic crustaceans. Moreover, the potential consumption of eggs by B. virginica could potentially
increase the impact on the nursery function of the estuary. The other alien species detected, P. macrodactylus, appears to be a
strong invader, able to colonise a wide geographical range. It has a strong osmoregulatory capacity, and is known to inhabit a
wide range of salinities, particularly if compared to similar native species (Crangon crangon and Palaemon longirostris). There
is clear potential for the occurrence of competition for food between P. macrodactylus and the native prawn, due to dietary
overlapping. The Guadiana estuary is under Mediterranean climate influence and is expected to be strongly impacted by climatic
changes in the next decades. Other threat-factors are also present, such as increasing regulation by dams, the construction of new
harbors, and increase shipping activity. It is important, therefore, to study the impact of these new invasions in this estuary and,
based on the ecohydrology approach, propose mitigations measures to be applied in this system and other similar ecosystems
worldwide.
