Morphological Traits Of Sargassum Horneri And Its Influences On Habitat Structure Of The Seaweed Bed

Starting from the 1980 s, the marine ecology has been destroyed gradually, especially critical in coastal waters due to the intensification of human activities, which changed the component and structure of the benthic biocenosis in coastal rocky waters. Acting as an important benthic biocenosis in coastal rocky areas, macroalgae plays a critical role in the function of ecosystem. Supported by the macroalgae biocenosis, seaweed bed is one of the typical coastal life habitat, which constitute the nearshore marine ecosystem along with mangrove, coral reef and mud flat. Distribution areas of macroalgae and the seaweed bed worldwide have been decreasing in different magnitude due to the influence of nature and human activities. Thus, researches pertaining to the growth and distribution, and to the life history and morphology of macroalgae bring about the attention of environmental protection department and corresponding scientific research scholars. Exploring the inchoate distribution and impact factors, the life history and seasonal variations of morphology of macroalgae will contribute to the ecological protection and the ecological restoration with important substratum, and will contribute to making clear the biological resources maintenance function and functional mechanism of the seaweed bed.This article chooses the seaweed bed of Gouqi Island in Ma‘an Archipelago special marine reserves of Zhoushan city, Zhejiang province as the study area of this article, chooses the supporting and absolutely dominant species macroalgae Sargassum horneri as the study objective. We discuss the hydrodynamism composed by wave and water motion of tide toward the inchoate distribution of Sargassum horneri in the shoaling water of rocky areas in the seaweed bed of Gouqi Island by exploring the discrepancy of spatial distribution of Sargassum horneri between and within sites, and its relationships with wave and water motion of tide. Meanwhile, in order to filtrate the optimum biological parameters for species identification, we analyze the life history and seasonal variations of the morphological traits by annually tracking the biological sample of Sargassum horneri in the seaweed bed of Gouqi Island, hoping to supply us with substratum in morphology research and species identification of Sargassum.The final research results are summarized as follows: 1、Traits in life history and morphology of Sargassum horneri from the Sargassum seaweed bed of Gouqi IslandTo study the life history processes and morphological traits of Sargassum horneri from the Sargassum seaweed bed of Gouqi Island, this article first conducted the investigation of the growth and reproduction during an annual cycle of Sargassum horneri, 16 related morphological trait parameters including individual length, blade, vesicle and receptacle were analyzed. Experimental results showed that growth of Sargassum horneri can be divided into 4 phases within the year according to the occurrence of different biological structures in its life history:(1) seedling period during July to August, during which plants consist of stalk, branch and blade briefly, plants grow with an average rate of 1.52mm·d-1;(2) adult period during August to April of next year, all biological structures were consummated and successively recorded the occurrence of vesicle, secondary branch and receptacle in September, November and April of next year respectively, plants grow with an average rate of 2.01mm·d-1;(3) reproduction period during April to May, the occurrence of receptacles indicate the arrival of reproduction period, while the concentrated dispersion of spores represents the arrival of ―climax‖ of reproduction period, plants grow with an average rate of 3.80mm·d-1;(4) senescence and degeneration period during May to June, the majority of plants begin to ageing with detachment of biological structures, while the average growth rate of plants reachs 0.99mm·d-1 due to the supplement of immature individual. 10 parameters including length, individual biomass and primary branch length showed a significant seasonal variation(p<0.05). This warm-temperate species exhibited a phonological behavior intermediate between tropical and cold-temperate species of Sargassum. Analysis of within- and between-individual stability of 10 traits indicated the lowest stability of primary branch length(Ed=95), which belongs to the best parameters for distinguishing species and may supply us with substratum in morphology research and species identification of Sargassum. 2、Hydrodynamism on inchoate distribution of Sargassum horneri in the seaweed bed of Gouqi IslandSeaweed bed is a kind of neritic habitat based on benthic macroalgae, which can provides many halobios with breeding, foraging, migration and evading ground. Sargassum horneri is the absolutely dominant species and sustaining algae in Gouqi Island, exploring its inchoate distribution and variation law is important to make clear the biological resources maintenance function. This article focus on the inchoate distribution of Sargassum horneri in the shoaling water of seaweed bed in Gouqi Island in 2013 on the basis of earlier work, which indicates that the distribution mechanism between the shoaling water and the abyssal region is different. Among which the amount of sediment in shoaling water is much lower than in abyssal region for 2~3 magnitudes, and wave exposure in shoaling water shows a negative correlationship with the density of plants(r=-0.984,P=0.026),which indicates that in shoaling water, higher wave exposure can not only prevent the deposition of SS, but also prevent the implantation of spores, wave exposure dominates the inchoate distribution of Sargassum horneri in shoaling water. Sediments collected by PVC tube(H/d>15)in different water layer of site S4 increases which the depth of water, the difference of sediment in different layer is extremely significant(P<0.01),while velocity of the water flow in dirrerent layer shows a negative correlationship with sediment(r=-0.998,P=0.030),which indicates in the very shoaling water, the SS failed to deposit and the spores failed to implant are took away from the seaweed bed, thus affect the potential deposition level of SS and the further inchoate distribution of Sargassum horneri. In all, the inchoate distribution of Sargassum horneri in seaweed bed is subject to the hydrodynamism from the synergistic effect of wave exposure and water flow, with the increases of depth, wave exposure and water flow decrease, the inchoate distribution of Sargassum horneri gradually reflected in the functioning of sediment. Such mechanism can provide us with guidances for algae implantation and ecological restoration in off-shore and reef waters. 3、Relationships between Sargassum horneri and habitat traits of the seaweed bed in Gouqi IslandTo study the relationships between the supporting and absolutely dominant species macroalgae Sargassum horneri in the seaweed bed of Gouqi Island and the habitat traits of the seaweed bed, we investigated the cover of macroalgae biocenosis and the distribution density and biomass of Sargassum horneri in Spring, Summer, Autumn and Winter in Xiao Shi Pu(XSP) site in the seaweed bed of Gouqi Island during 2013 to 2014. The research results indicate that during this period, the overall variation trend of the cover of macroalgae biocenosis in the seaweed bed of XSP is: Summer<Autumn<Winter<Spring, while acting as the dominant species in this habitat, there is an obvious downtrend of distribution density along with time, and an highly significant difference of density of Sargassum horneri among 4 seasons(P<0.01), and the seasonal variation trend is: Summer> Autumn> Winter> Spring. However, there is an obvious uptrend of biomass along with time, and an highly significant difference of biomass of Sargassum horneri among 4 seasons(P<0.01), and the seasonal variation trend is: Summer<Autumn<Winter<Spring. Meanwhile, there is a positive correlationship between the biomass of the dominant species Sargassum horneri and the cover of macroalgae biocenosis in this habitat(r=0.956;P<0.01), which indicates that the dominant species Sargassum horneri is the key species in constructing habitat structure in the seaweed bed of Gouqi Island, which will plays an important role in analyzing the habitat structure of the seaweed bed, and in analyzing the optical field, temperature field and the flow field.