Biology Reference
In-Depth Information
sufficiently abundant in regions where aquaculture operations are expanding (Paul
and de Nys
2008
). The downside of the easy cultivation is that several potentially
invasive
Caulerpa
species have been commercialized and can be easily purchased
from aquarium shops or ordered online. The aquarium industry has enormously
facilitated the transportation of these species to distant geographic locations and
hence the potential for introductions into natural habitats with serious ecological
consequence (Zaleski and Murray
2006
; Stam et al.
2006
).
The main invasive traits in
Caulerpa
species are high growth rates, propagation
via fragmentation (i.e., 1 cm small fragments of
C. taxifolia
are able to give rise
to viable single siphonous-cell three-dimensional structures up to 5 m long),
broad environmental tolerances, survival out of the water in humid conditions for
several days, and in some cases, such as in
Caulerpa racemosa
and
C. taxifolia,
production of secondary metabolites and allelopathic compounds that act as herbi-
vore deterrents and/or inhibit other floral components during space competition
(e.g., Meinesz
1999
; Vroom and Smith
2001
; Gollan and Wright
2006
; Wright and
Davis
2006
; Klein and Verlaque
2008
; Raniello et al.
2007
).
12.4.6
Ulva
Species
The cosmopolitan genus
Ulva
Linnaeus, commonly known as the “sea lettuce,” is
represented by species distributed in all oceans and estuaries of the world, 17 of
which have been recorded in the Mediterranean Sea (Guiry and Guiry
2008
).
Several species in this genus are commercially cultivated for human consumption
in Asian countries or as a component in integrated multi-trophic aquaculture
systems, e.g., for bioremediation of effluent and as a feed crop for abalone aqua-
culture in South Africa (Bolton et al.
2009
). Furthermore, due to their higher
biomass yield and the higher photosynthetic activity compared to the terrestrial
crops,
Ulva
spp
.
are considered as a promising aquatic crop for biofuel production
(Bruhn et al.
2011
).
Some Ulva species are problematic to identify morphologically due to the
extreme phenotypic plasticity in different environments (Hayden and Waaland
2004
). Among them,
Ulva ohnoi
Hiraoka et Shimada, a green-tide-forming alga
described from Japan, has been recently found in ballast water tanks of container
ships in the Mediterranean Sea and may represent a newly introduced species in the
basin (Flagella et al.
2010
).
Ulva ohnoi
together with
Ulva prolifera
(M
uller)
J. Agardh were two of the species responsible for the world largest drifting
macroalgal bloom in 2008 estimated as approx. one million tons of harvestable
biomass (Qingdao, China, before the Olympic sailing competition; Leliaert et al.
2009
; Pang et al.
2010
).
Ulva
species are well known for their broad environmental tolerance, high
growth rate, and photosynthetic activity. They represent early successional, oppor-
tunistic species, often occurring in degraded or polluted (high nitrogen)
environments, mainly due to their simple morphological features and the high
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