ALBERT

Description: Eleven green algae belonging to the phyla Volvocophyta Chlorophyta, and Charophyta were collected from various freshwater habitats of Sindh (Pakistan) during February 1995 and November 1998 and investigated. Their methanol extracts revealed the presence of D-norandrostane-16-carboxylic acid, β-sitosterol, and trans.-phytol. The unsaturated fatty acids were found in larger proportion (54–94%) than the saturated fatty acids (6–40%). The C15:0 and C16:0 were the most commonly occurring fatty acids, followed by C18:1, C19:1, C15:3, and C17:3 acids. These algae resembled green seaweeds of Pakistan to a great extent in their fatty acid composition. Their methanol extract showed poor antibacterial but a strong antifungal activity. They displayed a significant phytotoxic activity but non-significant cytotoxic, insecticidal, and antitumor activities. Algae belonging to the three phyla exhibited differences in their fatty acid, sterol and terpene compositions as well as in their bioactivities. Species belonging to the same genera revealed specific differences among themselves.

Description: We assessed the effects of light limitation and temperature shift on palatability and induced antiherbivore defense in the brown alga Fucus vesiculosus L. Incubation for 2 wk at light intensities above the compensation point of photosynthesis and in the absence of grazers increased the palatability of F. vesiculosus and its subsequent consumption by the omnivorous isopod Idotea baltica Pallas. This effect correlated with an increased C:N ratio and mannitol content in the algal tissue, presumably due to increased photosynthetic carbon fixation. Mannitol, the primary product of photosynthesis in F. vesiculosus, proved to be a feeding cue for I. baltica, and depletion of the mannitol pool may therefore account for the reduced palatability during light limitation. At light intensities above the compensation point of photosynthesis, F. vesiculosus responded with decreasing palatability when it was exposed to I. baltica grazing. Irrespective of the preceding light regime, such defense induction was prevented during incubation under light limitation. Thus, under low light, defense induction is not only inhibited, but also less necessary due to the relative absence of feeding cues. Upward or downward shifts in water temperature by approximately 10°C also inhibited inducible defense in F. vesiculosus. However, such shifts did not affect algal growth and were therefore the consequence of an impairment of specific defense-related components rather than of resource limitation, unless compensatory growth was given priority over defense.

Description: The impact of moderate environmental stress may be modulated by stress-induced shifts of biotic interactions such as host – epibiont relationships. We studied the stress regime in shallow Western Baltic habitats, the variability of fouling at different temporal and spatial scales, and whether common stressors - low light, high temperature, grazing – affect the abundance and composition of the biofilm on a regionally important macroalga, the bladder wrack Fucus vesiculosus. We further explore the alga’s capacity to chemically modulate the recruitment of microfoulers and whether this ability is impacted by stress. In laboratory, mesocosm and field experiments fouling pressure and epibiotic cover on the algae varied strongly with changing environmental conditions such as temperature, irradiance, depth or grazing. The expectation that abiotic stress affects the fouling-modulating ability of the alga and, thus, indirectly produces the observed variability of epibiosis was not generally confirmed. Indeed, while the strength of chemical antifouling resistance varied seasonally, with a maximum in winter/spring and a minimum in late summer, this could not be related to temporal patterns of environmental stress, fouling pressure, or growth of Fucus. Only the seasonal variation in reproduction seemed to be in phase with antifouling activity. Controlled experiments confirmed that resistance strength was not affected by temperature or grazing, and only moderately by light. We conclude that the fouling modulation ability of Fucus vesiculosus may suffer from light-reduction (e.g. by eutrophication effects) while they are not sensitive to the predicted warming or enhanced grazing.