Destructive hydrogen peroxide production inEucheuma denticulatum(Rhodophyta) during stress caused by elevated pH, high light intensities and competition with other species

Abstract

Growth of Eucheuma denticulatum was studied in the field and in laboratory experiments. Field co-cultivation of E, denticulatum with the green alga Ulva reticulata or the seagrass Thalassia sp. reduced daily growth rate (DGR) of a Tanzanian and a Philippine strain of E. denticulatum by I0-100% and 10-55%, respectively, depending upon the type of water current: a unidirectional water current produced the best growth. Laboratory co-cultivation of a Tanzanian strain of E. denticulatum with U. reticulata also reduced DGR (to 8% of the control) and nitrate-nitrogen uptake rate (to < 30% of the control) of E. denticu]atum and, moreover, it increased epiphytism of a red filamentous alga on E. denticulatum. E. denticulatum monoculture at pH 8"6 4-0"5 or at photosynthetic photon flux densities (PPFDs) higher than its growth optimum (350 4-50 #tool photons m -2 s -I) also increased epiphytism. The lack of a competitive mechanism for inorganic carbon uptake in Eucheuma may have contributed to its reduced growth during co-cultivation. During co-cultivation, elevated pH regimes (pH ~ 8"5) were created around the Eucheuma thalli as a result of photosynthesis, thus decreasing the concentration of CO 2 in the seawater to values around 1 #raM. As Eucheuma depends mainly on the CO 2 in the seawater for its growth, a higher pH can cause CO 2 limitation by decreasing CO2 concentration. Hydrogen peroxide (H202) production from the Tanzanian strain was also determined by luminol-dependent chemiluminescence. H202 production was found to increase with increased pH and PPFD (probably as a result of oxidative stress). Preincubation of plants with catalase for 5 min before addition of luminol prevented chemiluminescence, confirming H20 z as the substrate of the luminol reaction. We suggest that the inefficiency of E. denticulatum in HCO 3 utilisation contributes to its poor growth during field coexistence with seagrasses or Ulva sp. and that carbon deficiency induces H202 production in E. denticulatum.

Effect of Seagrass Cover and Mineral Content on <i>Kappaphycus</i> and <i>Eucheuma</i> Productivity in Zanzibar

“…is reduced by 10-100% (Mtolera et al, 1995a). Eucheuma denticulatum appears to grow best in unidirectional water currents.…”

“…350 µmol photon/m 2 /s with a 12:12 (day: night) photoregime (Mtolera et al, 1995a) using fluorescent tubes (Thorn Polylux 4000) as the light source. Growth medium was natural seawater (NSW).…”

“…Some villagers even allowed us to take measurements of growth rate on their plants. Growth of such plants was determined as detailed in Mtolera et al (1995a).…”

“…Thus, as reported in the Philippines (Doty, 1973), sites for Eucheuma farms are cleared of seagrasses. Mtolera et al (1995a) argued that the inefficiency of E. denticulatum in HCO 3 -utilisation could partly explain its poor growth when in coexistence with seagrasses or Ulva sp. Carbon deficiency in E. denticulatum could induce the production of reactive oxygen species (ROS), e.g.…”

“…At the experimental stage, both local Tanzanian and Philippines strains of K. alvarezii, K. striatum Schmitz and E. denticulatum were used (Mtolera et al, 1995a). The Tanzanian strains had lower growth rate than the Philippine strains and among the Philippines strains, E. denticulatum had a better growth rate than K. alvarezii and K. striatum, and therefore farmers preferred to cultivate the Philippines strain of E. denticulatum.…”