The State of the Mediterranean Marine and Coastal Environment

directly attributed to invasive non-indigenous species, sudden changes in abundance of native species, as well as some local extirpations associated with non-indigenous species, have been reported (UNEP/MAP/BP/RAC 2009). Socio-economic impact The economic impact of non-indigenous species touches a variety of sectors, including fishing (fouled nets), aquaculture (reduced light), shipping (clogged propellers, impaired navigation), public health (toxic algae), and tourism (nuisance) (EEA and UNEP 1999). Economic losses have been documented in France and Italy as a result of fishing nets being clogged by non-indigenous macroal- gae ( Womersleyella setacea and Acrothamnion preissii ) (UNEP/MAP 2012). The jellyfish Rhopilema nomadica has a negative impact on tourism, fisheries, and coastal installations in the eastern Mediter- ranean. The tiny, single-cell dinoflagellate Gambierdiscus , found in waters off thewest coast of Crete, causes ciguatera, a food-borne ill- ness that results from eating certain species of reef fish (SOE 2009). On the other hand, some non-indigenous species are or have the potential to be important fishery resources. Examples in the Mediterranean include conch ( Strombus persicus ), prawn ( Marsupenaeus japonicus , Metapenaeus monocerus , and Metap­ enaeus stebbingi ), crab ( Portunus pelagicus ), and fish such as mullids ( Upenaeus moluccensis and U. pori ), lizard fish ( Saurida undosquamis ), Red Sea obtuse barracuda ( Sphyraena chryso­ taenia ), clupeid ( Dussummieria acuta , Herklotsichthy punctatus ),

Non-indigenous species over the 20th Century

Number of new species detected per decade

120

Zoobenthos Phytobenthos Fish Zooplankton Phytoplankton

100

80

60

40

20

0

Before 1900

1910

1930

1950

1970

1990

1920

1940

1960

1980

2000

Source: UNEP/MAP, Marine pollution indicators Fact sheets , 2004.

bluefish ( Pomatomus saltator ), and rabbitfish ( Siganus rivula­ tus ) (EEA and UNEP 2006). A non-indigenous species of prawn ( Metapenaeus monoceros ) has partially replaced the native prawn Penaeus kerathurus in Tunisia with no effect on the over- all catch of prawns (UNEP/MAP 2012).

57

HUMAN PRESSURE, STATE AND IMPACTS ON MEDITERRANEAN ECOSYSTEMS