Studies On Species Identification, Physiological Characteristics And Community Succession Of Attached Green Algae On Subei Shoal

In this study,6 cruises were conducted to continuously research the attached green macroalgae on the Porphyra aquaculture rafts of the Subei Shoal. The green algae germlings were used as the experiment materials and the PCR-RFLP rapid identification key was established. The germination proportion and quantity of green algae micro-propagules in the seawaters and sediments under different culture temperatures were discussed. The growth rate of U. prolifera thalli under different culture conditions was analyzed. The phytohormones in U. prolifera thalli as well as the change of various hormones’ content when the thalli were cultured under different temperature gradients were measured. The main results are as follows:1. Weight of the attached algae on 1 m-rope of the Porphyra aquaculture rafts was measured regarding as approximate attached biomass. In the three main Porphyra aquaculture areas (Xiaoyangkou, Gaoni and Niluosha) on the Subei Shoal, the attached biomass was different in various period of spring. In Xiaoyangkou and Gaoni, the attached biomass presented an obviously rising trend. While in Niluosha, the attached biomass peaked in middle April and it showed a decreasing trend in May. The species composition of attached green algae was abundant in early and middle March. Five species including U. prolifera, Ulva linza, Blidingia sp., Ulva intestinalis and Ulva clathrate were detected and the U. prolifera’s attached biomass was low. In April and May, the species diversity declined sharply, while the biomass and proportion of the attached U. prolifera increased quickly. The attached green algae’s community succession phenomenon was obvious on the rafts. U. prolifera, U. linza and Bldingia sp. were dominate attached species on the Porphyra aquaculture rafts. Data analysis indicated that seawater temperature was the main influencing factor of this community succession phenomenon.2. When the attached green algae fell off from rafts, at the high tide, they could present three conditions, including floating on sea surface, suspending in seawater column and sinking to seabed. U. prolifera occupied a high percentage in the floating biomass, while in the sinking biomass the dominate species was Blidingia sp. The result of Ship-based enclosure experiments showed that, when the green algae submerged in seawaters, the growth rate of the three main attached green macroalgae species was different. U. prolifera had the highest growth rate.3. The Ulva and Blidingia species along the coastal area of China could form 11 major genetic lineages, including LPP Clade、U. compressa Clade、Ulva pertusa Clade、Blidingia sp. Clade、and 7 unnamed Clades:Clade 1、 Clade 2、 Clade 3、 Clade 4、Clade 5、Clade 6 and Clade 7. By the RFLP analysis of the ITS regions of these green algae species and comparing the shortest 5S spacer fragments, the rapid identification key of Ulva and Blidingia was established. By Using this molecular key, the attached green algae on the Porphyra aquaculture rafts, the floating algae in the nearby sea area, as well as the attached and floating green algae in Qingdao sea area were identified. It showed that our previous morphological identification results was basically right.4. Under different temperature gradients, the germination quantity of green algae micro-propagules in the seawaters and sediments was different. At 5℃, the micro-propagules could not germinate because of the low-temperature stress. At 10℃, they began to germinate and from 10℃ to 20℃ the germination number rise with increasing culture temperature. At 25℃, the germination number began to decline and at 30℃, the quantity decreased obviously. The optimum germination temperatures for various green algae species were also different. Favorable germination temperature for U. prolifera, U. linza, Blidingia sp. and U. flexuosa was 15℃,10℃,20℃ and 25℃ respectively. This result proved that the community succession of the attached green algae on the Porphyra aquaculture rafts was mainly affected by seawater temperature.5. Growth rate of U. prolifera, U. linza and Blidingia sp. was different when cultured under different temperature gradients. Meanwhile, their growth conditions were different when cultured singly or mixedly. The phytohormones in U. prolifera thalli were measured. The results showed that U. prolifera contained IAA, ABA, SA and Z. Under different culture temperature, their content changed obviously. When the content of IAA reached to about 12ng/g, the growth rate of U. prolifera reached to the maximum. For ABA, under low-temperature stress, the concentration was high, while under high-temperature stress, it will highly express only in a certain temperature range. Under different culture temperature, the concentration of SA did not change obviously.