Study area: Study was conducted from December 2019 to January 2020 in Nuniachara of Cox’s Bazar sadar. The cultivation of seaweeds in open sea is being carried out using one-step seed production method which requires healthy seaweeds. Taking the above considerations into account, experiment site has been primarily selected at Nuniachara coast of Cox’s Bazar sadar.
Collection of seaweed seed: Wild G. tenuistipitata as seed was collected from Saint Martin’s Island (92º28ʹ40.12ʺE and 20º65ʹ51.43ʺN) of Bay of Bengal of Bangladesh. Seed collection from seabed was permitted from the local government and authenticated the botanical identification of seaweed species as the voucher specimen has been previously deposited at BFRI herbarium.
Production of seeds: The farming/cultivation of seaweeds in open sea was carried out using one-step seed production method. Seeds for seaweed farming was produced by one-step (directly using cut pieces and tied with the ropes) and multi-step (inducing spore release by a particular seaweed in the green house and allowing spores to grow on ropes and nets) methods.
Seaweed culture method: The seeded ropes were arranged in single or double lines in the open sea. Each line was kept attached with two bamboo poles so that it could not be washed away. Plastic floats @ 5 pieces per 25 m long rope were used to keep the ropes moving up and downwards during tides. No fertilizer, insecticides and pesticides were used during seaweed cultivation.
Water parameters: Water temperature, salinity, transparency, pH and dissolved oxygen (DO) were checked every 15 days at the cultivation sites. Transparency was measured using Secci disc. A digital DO meter (HACH, USA) was used to determine the dissolved oxygen content of water. pH was measured using a digital pH meter (HACH, USA). Salinity was determined using refractometer.
Collection and analysis of soil: Soil samples from the sites were collected and after collection, samples were brought back to the laboratory within 6 h for analysis. In the laboratory, the samples were dried and powdered, sieved and kept in a desiccator until further analysis.
Optimization of different factors
Experiment 1: Effect of lunar cycle
This study was conducted to find out the effect of lunar cycle on the yield performance of Gracilaria tenuistipitata. In this experiment, T0 indicates control where the seeds were transplanted three days after full moon and harvested three days before next full moon. On the other hand, T1 indicates that seaweeds were harvested and transplanted in between two consecutive full moons where one highest high tide occurred.
Experiment 2: Effect of harvesting interval
In this experiment, different harvesting intervals (T1 = 10 days, T2 = 20 days, T3 = 30 days, T4 =40 days) were taken to determine the best harvesting time with Gracilaria tenuistipitata by harvesting after 10 days, 20 days, 30 days and 40 days of seeding, respectively for getting maximum production.
Experiment 3: Effect of rope type
Two types of rope (where T1 denotes semi-floating single line method and T2 denotes semi-floating double line method) were followed to evaluate the effect of this method on the yield performance of Gracilaria tenuistipitata.
Experiment 4:Effect of seeding gap
This experiment was carried out for determining the effect of seeding gap where T1,T2,T3 and T4 indicates 10 cm, 20 cm, 30 cm and 40 cm seeding gap, respectively on the yield performance of Gracilaria tenuistipitata.
Statistical analysis: Data were statistically analyzed by statistical package SPSS version 16.0 (SPSS Inc., Chicago, IL, USA). Before all analysis data were analyzed for normality by probability plots and for homogeneity of variances by Levene's test. One way ANOVA was used to determine the significance of each parameter among different treatments. If a main effect was significant, the ANOVA was followed by Tukey's test. Level of significance was made at 95% probability level.