Biology Reference
In-Depth Information
1992; Jennings and Steinberg
1997
; Harder et al.
2004
; Hellio et al.
2004
). On the
other hand, it has been demonstrated that the capacity to resist an attack depends on
the host susceptibility to epiphytes. As mentioned earlier, the presence of different
types of carrageenan in the different reproductive phases of
Chondrus crispus
confers a differential adaptation in recognizing an attack by endophytic organisms
(Bouarab et al.
1999
,
2001b
).
Farming of red algal eucheumoids in South-East Asia has been threatened recently
by the occurrence of various diseases, mainly “ice-ice”, during which parts of the
plant turn white from primary or secondary attacks by bacteria and fungi, as well as
heavy colonization by endo/epiphytic filamentous red algae (EFAs) of the
Polysiphonia
type, which results in swelling of the host tissue followed by fragmen-
tation and rotting (Critchley et al.
2004
). In successive outbreaks of epiphyte infesta-
tion, in the Calaguas Islands, the impact of the disease was economically, socially,
and environmentally very serious as the farmers became disillusioned and they either
moved to other cultivation sites (thus further propagating the epidemy) or returned to
the environmentally damaging practices of dynamite or cyanide reef fishing. Produc-
tion thus declined markedly in this region, from 6,000T per year during 1997-1999 to
nil in 2001. At the levels of the Philippines production
Kappaphycus alvarezii
(“Cottonii”) farms also are sensitive to smothering by other pest weeds, such as the
green algae
Ulva
and
Chaetomorpha
and the brown alga
Hydroclathrus
,aswellasto
grazing by siganidae herbivory fishes (e.g., rabbit fish) and to marked fluctuations in
water temperature due to warm water events. Farmers now tend to grow Cottonii for
45 days (or less) instead of 60 days, resulting in a lower quality of the harvest in terms
of biomass and colloid content. The productivity of some
Kappaphycus
farms is
decreasing and one estimate indicates that the losses due to diseases now represent
about 15% of the potential crop of the Philippines and Indonesia, with a conservative
estimated value of US$ 5-10 million to the farmers. That this does not show up yet in
the production figures is due to the extension of production areas (i.e., increased
hectarage of farming activities, but there is a marked decline in productivity per unit
area in certain farms). If the situation is not addressed there is a very real risk that the
raw material source in many areas of production could be compromised if a particu-
larly virulent epiphyte/pathogen strain were to arise. In Malaysia also, cultured
seaweed became susceptible to epiphytes in the dry seasons between March-June
and September-November. Findings revealed
Neosiphonia savatieri
as the dominant
infecting epiphyte, representing up to 80-85% of the epiphytes present during peak
seasons. Besides
N. savatieri
,
Neosiphonia apiculata
,
Ceramium
sp
.
,
Acanthophora
sp., and
Centroceras
sp. were observed in smaller quantities (Vairappan
2006
;
Vairappan et al.
2008
).
Similarly, there is general agreement that epiphytism is one of the major
biological problems in
Gracilaria
farms (Pringle et al.
1989
, reviewed by Fletcher
1995
) due to the high density of individuals essentially maintained under monocul-
ture conditions. These conditions are known to make the host more susceptible to
pests in general and to epiphytes in particular (Friedlander
1992
). Competition
between hosts and their epiphytes has been demonstrated under natural and artifi-
cial conditions of growth (Arrontes
1990
; Friedlander and Ben-Amotz
1991
;
