Effects of elevated temperature and ultraviolet (uv) irradiation on the chemical ecology of the colonial marine tunicates clavelina spp. (ascidiacea)
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Date
2003-03
Authors
Syed Ibrahim, Sharifah Nora Asfiah Binti
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Abstract
Very little is known about ascidians, especially within Malaysian waters. The potential
effects of elevated temperature and/or ultraviolet (UV) light on these urochordates are
unknown. Thus, Clave/ina fecunda at the Pulau Payar Marine Park (Latitude 6° 03 'N,
-~-c~mgitude 100° 02'E in the Strait of Malacca) was investigated vis-a-vis its taxonomy,
associations, chemical ecology (anti-foulant, anti-feedant, ichtyotoxic properties, etc.)
and the effects of thermal stress on its secondary metabolites. Another species,
Clave/ina lepadiformis from Helgoland island (54° 11 'Nand 7° 53' E in the North Sea)
was investigated vis-a-vis the effects ofUV on its respiration and viability.
The blue tunicates abundantly found in the Pulau Payar Marine Park have been
identified as Clave/ina fecunda. It hosts numerous organisms from 10 taxa groupings.
In terms of association (host) specificity, the results showed that there was statistically.
- significant host-specificity. The flatworms always chose the ascidians Clave/ina
fecunda, always preferring unstressed hosts. The temperature threshold level at which
dissociation occurred was 34.3°C.
Clave/ina fecunda zooids are found to retract, their tunics thicken and siphons closed
when subjected to elevated temperature. Differences between the respiration rates of C.
fecunda in the control and thermal-treated groups were significant (p<0.05).
Although the anti-fouling effect is not statistically significant, Clave/ina focunda is
-found to have a delaying effect on the fouling succession. Elevated temperature does not
significantly affect the anti-fouling properties when compared to the Control groups.
However, there was a masking effect by·-acclimationlhandling: elevated temperature
actually increased the antifouling efficacy of C. fecunda. Acclimation/handling
promotes tile fouling. The normal succession dominancy of Bryozoan 'a' (at Week-7),
Tubeworms (Week-14) and Bivalves (Week-23) were delayed when ascidian extracts ,
were applied.
Clave/ina fecunda is also found to have physical anti-predation property (i.e. its tunic).
It possesses chemical anti-feedant properties but probably masked by handling to result
in a statistically insignificant outcome. Thermal-treatment promotes predation for some
food matrices and test organisms.
In terms of ichtyotoxic properties, crude extracts of Clave/ina fecunda have ichtyotoxic
properties in the lipophilic component. Elevated temperature increased the ichtyotoxic
effects. Order of ichtyotoxicity (from most to least):
Lipophilic-T > Crude-T > Lipophilic-N > Crude-N > Non-Lipo-T > Non-Lipo-N >Controls
The tunics of Clave/ina lepadiformis are capable of blocking considerable ultraviolet
(UV) light. UV affects viability of Clave/ina lepadiformis after a 7-hour exposure or
more. The respiration rate of UV -exposed C. lepadiformis was lower than that of the
Controls.
In conclusion, elevated temperature and UV affect Clave/ina fecunda's behaviour,
physiology and biochemistry, with serious implications for marine biodiversity. Several
recommendations are made. Limiting factors· are acknowledged .
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Keywords
Elevated temperature , Ultraviolet (uv) irradiation , Tunicates clavelina spp. (ascidiacea)