is a non-burrowing prawn species preferring a sandy or muddy bottom,
and although active at both day and night, it has been shown to display
clear daily rhythms in activity, being less active at night (Natarajan 1989). F. indicus
has a complex ontogenetic developmental cycle involving 12 stages
distributed in three planktonic larval forms (6 nauplii stages, N-1 to
N-6; 3 zoea stages, Z-1 to Z-3; and 3 mysis stages, M-1 to M-3). F. indicus develops from hatching to the post larva (PL) stage over 10 to 18 days in natural conditions (Muthu et al. 1978) and 13 to 14 days under hatchery conditions (Silas et al 1985). As many decapods, F. indicus also has a tri-phasic life cycle (Pitman and McAlpine 2003).
The prawn matures and breeds mostly in offshore coastal waters, and the
larvae are advected in the neuston until recruiting to their estuarine
habitats (Forbes and Cyrus 1991). The PL grows in coastal estuaries, backwaters, or lagoons with a particular preference for mangrove habitats (De Freitas 1986; Mohan and Siddeek 1996; Rönnbäck et al. 2002),
where they spend the juvenile and sub-adult stages, before migrating to
open coastal habitats for breeding. Larvae are often present in the
neuston, except in the period of maximum solar radiation. Seasonal
studies off Kochi (Arabian Sea, India) showed that F. indicus larvae are rare in the plankton from May to September (George 1962; Rao 1964).
late larval stages, PL, and juveniles inhabit shaded environments, such
as mangrove creeks, the larvae are pelagic and can be subjected to high
irradiance in the water column in tropical and subtropical regions.
Moreover, this species is reared in shallow aquaculture ponds and
floating cages (Walford and Lam 1987),
which can also receive high solar radiation in tropical and subtropical
regions. High light intensities have been reported to be detrimental
for the survival of larval stages of penaeid prawn, which are reared
under dim light conditions to increase spawning and early survival
success in aquaculture (Wurts and Stickney 1984).
The shaded habitat of the PL, in mangrove creeks, the low abundance of
planktonic larvae during the months of peak solar radiation, and the
light-sensitivity of early life stages all point at a vulnerability of F. indicus
larvae to high solar radiation and particularly ultraviolet-B (UV-B)
radiation as the most damaging component of solar radiation (Häder et
al. 2007; Hansson and Hylander 2009).
Because of its commercial importance, the physiology, growth, and behavior of F. indicus have been extensively studied (Kutty et al. 1971; Colvin 1976; Emmerson 1984). The resistance of PL to changes in environmental conditions, such as fluctuations in salinity (Kumlu and Jones 1995), pH, and light (Vijayan and Diwan 1995) and the presence of heavy metals (Chinni et al. 2002)
have also been studied intensively. These studies have shown that, in
general, PL can tolerate a wide range of salinity (5–40) and
environmental fluctuations, characteristic of the estuarine environments
A recent meta-analysis (Llabrés et al. 2013) confirmed that marine crustaceans, particularly crustacean larvae, are highly vulnerable to UV-B radiation (Häder et al. 2007; Hansson and Hylander 2009)
and that exposure to ambient levels of UV-B can result in high
mortality, leading to strategies to avoid UV-B exposure, such as
vertical migration by pelagic crustaceans (Williamson et al. 2011).
Indeed, recent assessments have shown zooplankton to be highly
vulnerable to ambient levels of UV-B radiation in the clear waters of
the Red Sea that F. indicus
inhabits, sufficient to cause steep zooplankton mortality at UV-B
radiation levels well below those received at the water surface
(Al-Aidaroos et al. 2014, 2015). Yet, the vulnerability of F. indicus,
or any other penaeid species, to UV-B radiation has not been examined
as yet, despite indirect evidence that they may be vulnerable to high
solar radiation. Therefore, here, we examine the vulnerability of the
different developmental stages of F. indicus to ambient levels of UV-B radiation incident in the Red Sea. We do so using an aquaculture stock of F. indicus
hatched in the laboratory, thereby allowing access to the consecutive
larval stages, from hatched nauplii to PL-5 of this important species.