ISSN:
1573-5117
Keywords:
agar
;
cultivation
;
gel strength
;
Gelidium pristoides
;
growth
;
mariculture
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The economically important agarophyte Gelidium pristoides was cultivated at different depths in the ocean in Algoa Bay between March and June 1991. The seaweed was either tied to ropes (whole tufts on limpet shells) or sewn into net bags (plucked fronds only) supported on metal frames. All experiments were run for between 5 and 8 weeks. Growth, agar content and, in one experiment, agar gel strength was measured weekly or fortnightly. Plants in net bags increased their biomass during the first 2 weeks of the experiment but only surface plants had a significantly higher biomass (approx. 20%) by week 2. From the second week fronds rapidly accumulated sediment, became discoloured, and then degenerated from week 3 onward. The agar content of net-grown plants was significantly increased from 32% to 38% in subsurface plants after one week. Thereafter agar content declined steadily as the thalli degenerated. Plants growing on limpet shells survived submersion much better than net-grown plants cultivated at the same time. The practise of wiring shells to ropes was unsatisfactory because this damaged the shells and caused a loss of seaweed biomass. Surface plants did however increase their biomass by up to 19% after 8 weeks in this experiment, but the increases could not be shown to be statistically significant because of high data variance. Surface thalli in this experiment also increased their agar content significantly from 32% to 42% after one week but from weeks 4–8 this dropped off. A second experiment using shells was conducted when sea temperatures had dropped by as much as 5 °C. These plants remained healthy throughout the study and maintained their starting biomass for 2 weeks but then lost biomass as sea temperatures declined further. The agar content of these thalli increased during the first 2 weeks with surface thalli at week 2 having significantly higher agar contents (38–48%) compared with a starting value of 22%. The gel strength of agar extracted from these plants increased significantly during the first three weeks of submersion, in some cases doubling from an initial gel strength of 300 g cm−2 to 600 g cm−2.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00014052
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