Biology Reference
In-Depth Information
declining yields. (
) The annual production of crabs has reached more than
400,000 t valued more than 20 billion RMB in 2005 in China
” (Li et al.
2007
).
The food on our tables today comes mostly from a small number of widely
cultivated plant and domesticated animal species. Most of them are historical
intentional introductions. For example, the earliest archeological records of agri-
culture in India 2400-1750
BC
show crop species of west Asian origin (Hutchinson
1976
), while the transport of crop species between Europe, Africa, and Asia peaked
with the establishment of direct intercontinental sea trade in the 1400s (National
Research Council
1996
). There is no evidence that the main crops, such as cereals,
oil seeds, fruits, and vegetables, were invasive in their native range. However, over
the last 10,000 years modern cultivars (from “
culti
vated
var
iety”) have been
continuously selected for maximum performance in a range of environments. In
addition, modern farming practices such as fertilization, irrigation, crop rotation,
the use of pesticides, and genetically assisted breeding have provided extraordinary
growth rates and production of high biomass. Interestingly, many invasive seaweed
species or ESUs fit the profile of successful agricultural cultivars because
they exhibit evolutionary traits for e.g., fast growth, high reproductive capacity,
grazing resistance, and wide ecophysiological tolerances to persist in different
environments.
...
12.4.1 Commercially Used Invasive Seaweeds
Seaweeds have been highly valued food resources for thousands of years, especially
in Asia. Today, seaweed harvesting and mariculture is an actively growing global
industry with a currently estimated total annual value of approximately six billion
USD (McHugh
2003
). Seaweeds are used mainly as food products for direct human
consumption, sources of bulk chemicals such as hydrocolloids and other higher
value biochemical compounds, fertilizers, and animal feed additives (see Chap.
22
by Buchholz et al.). The farming of seaweeds has expanded rapidly as demand has
outstripped the supply available from natural resources (McHugh
2003
).
Many cultivated seaweed species, harvested in their native range, have been
intentionally or unintentionally introduced (reviewed in Schaffelke and Hewitt
2007
) and are often highly valued for their invasive traits, especially for fast growth
rates and biomass accumulation, and often low levels of epiphytism and resistance
to herbivores. The commercialization of invasive seaweeds and the exploitation of
species-specific invasive traits are often considered to be positive for the economic
development of the regional community (Pickering et al.
2007
). However, this has
to be balanced with the potential negative side effects on the ecological integrity of
the “recipient” environments due to accidental release or escape of invasive spe-
cies, which are difficult to manage. The following sections present brief summaries
of the most important commercially used seaweed species, which are also high-
profile invaders.
