| In the present study, the population ecology of Zostera marina L. was studied in Shuangdao Bay, Weihai, Shandong. Annual shoot density, biomass and, morphological characteristics of Z. marina in intertidal zone and subtidal zone were investigated and their differences were analyzed, and its sexual reproduction characteristics and reproductive strategy were also surveyed. Our results can indicate the plastic daption of Z. marina to environment factors such as atmosphereic exposure, water temperature and light and support the view that clone growth adominate the population regeneration of eelgrass. The main results are summarized as follows:1. From March in 2014 to March in 2015, we surveyed shoot density, biomass and morphological characteristics of Z. marina in intertidal zone and subtidal zone monthly. The results are:1) The shoot density in two habitats showed obvious seasonal variations, it reached maximum in April, with 507.81/m2 in intertidal zone and 487.04/m2 in subtidal zone, the minimum in August (130.37/m2and 64.61/m2), the average of intertidal zone poplutions was 1.38 times of the subtidal poplutions.2) The biomass in two habitats showed obvious seasonal variations, with maximum in July (370.40 g/m2 and126.37g/m2), the ratio of the two habitats on the ground and underground biomass was also significant different, the former was three times of the latter, and in subtidal zone it reached more than seven times.3) The leaf length, leaf width and rhizome diameter in two habitats were obvious differece, and our results indicated that the largest leaf length in subtidal zone reached maximum in June(184.1cm)and was 3.8 times of intertidal zone, the leaf width and rhizome diameter were 1.35 times and 1.22 times respectively.4) These seasonal variations were strongly correlated with seasonally varied water temperature and light intensity. Biomass was positive index with water temperature (R=0.863), negative index with light (R=0.855) and leaf length, width and rhizome diameter was positive linearly with water temperature, negative linearly with light.2. From February to July in 2014, we studied sexual reproductive characteristics of Z marina population in Shuangdao Bay. The results are:1) In population scale, sexual reproduction of eelgrass in 2014 was from mid-March to mid-July, which lasted about 120 days. Reproductive shoots appeared in March 18, initial appearance of anthesis and the first visible fruit date occurred in April 17 and May 16; seed release climax occurred in June 30 respectively; reproductive shoots begun to die in July 14 and its sexual season ended in late July.2) The average number of reproductive branch was 5.1 per shoot; the maximum number of spathes per shoot was 20.0; the spathes of bottom branch and top branch are more than others, but there was no significant difference between them with an average of 3.8 per spathes.3) The fruit number and ripe seed production of eelgrass were 177.5 and 82.1 per shoot respectively, abortion rate was low with the mean value of 23%; Potential seed yield and actual seed yield of the population was 2663/m2.3. Reproductive strategies of eelgrass in Shuangdao Bay was surveyed and analyzed. The results showed that:The reproductive shoot ratio and reproductive allocation was only 12.9% and 21.5% respectively. The rate of seedling emergence was 1.8% and the seedlings survivaledonly sixty days (from mid-March to mid-May). From October to November and March, eelgrass populations showed strong ability of clone growth, and their generation rate of new ramets were 23.97% and 21.17% respectively. From August in 2013 to spring in 2014 when reproductive shoot formed,6.9 new ramets were generated per clonal fragment. Lots of clonal ramets died in summer due to reduced light intensity. Therefore, only 7.1% of ramets could eventually become reproductive raments and to completed the life cycle. Clonal growth played more roles in eelgrass population regeneration in Shuangdao Bay. |
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