北海城市红树林中的红树蚬属贝类

Occurrence and Distribution of Mud Clam,Polymesoda spp.in Mangroves of Beihai City

关键词:  红树蚬属  分布  红树林  北海市

Key words:  Polymesoda spp.  distribution  mangroves  Beihai city

摘要:

[目的] 掌握北海城市红树林中的红树蚬属贝类的种类组成、分布密度和分布特征。[方法] 在3个样地的高中低潮滩分别设置站位开展样方调查，测定沉积物粒度和盐度；挖掘采集红树蚬属贝类并鉴定物种，计算分布密度；测量所采集贝类个体的壳尺数据，进行统计分析。[结果] 共采集到红树蚬属贝类559个，平均分布密度4.14 ind/m²；壳长为34.1~76.4 mm，平均为52.1 mm。不同壳长的个体数占总个体数的比例呈钟形分布，壳长46~50 mm的个体数最多。3个样地间沉积物粉砂含量差异显著，粉砂含量高的样地红树蚬属贝类分布密度低。所采集到的样品分属红树蚬和歪红树蚬2种，平均分布密度分别为2.37 ind/m²和1.77 ind/m²，平均壳长分别为52.4 mm和51.6 mm。壳长51~55 mm的红树蚬和壳长46~50 mm的歪红树蚬个体数分别占各自对应物种个体总数的比例最高。随着壳长的增大，壳长/壳高比值无显著变化，壳长/壳宽比值持续降低，红树蚬和歪红树蚬壳长分别达到50 mm和55 mm后，壳长/壳宽比值显著降低。[结论] 北海城市红树林中有红树蚬和歪红树蚬2种红树蚬属贝类分布，资源量相对丰富，个体相对较小。红树蚬的生长速度较歪红树蚬快，二者性成熟后壳宽均加速生长。潮流和滩涂高程可能是红树蚬属贝类成贝分布密度的决定性因素，成贝分布密度与沉积物粒度的相关性可能是潮流的影响结果。高程低的潮滩，成贝分布密度低。

Abstract:

[Objective] To explore the species composition, distribution densities, and distribution characteristics of mud clams Polymesoda spp. in mangroves at Beihai city.[Methods] Sample survey was carried out in three sampling sites at high, middle, and low tidal flats in mangrove to collect and identify the samples of mud clams. Granularities and salinities of sediments at sampling sites and sizes of the sampled clams were measured and the densities of the clams were calculated for statistical analysis.[Results] A total of 559 mud clam individuals were collected. The average distribution density of the clams was 4.14 ind/m².Shell lengths of the clams ranged from 34.1 mm to 76.4 mm and were 52.1 mm at average. The ratio of the individual number of clams with different shell length featured a bell-shaped curve distribution.The number of the clam individuals with a shell length of 46 mm to 50 mm was the largest. The contents of silt-clay from three sampling sites differed significantly from each other, and lower density of mud clams were found in sampling site with higher content of silt-clay. The collected samples belonged to two species,Polymesoda erosa and Polymesoda expansa,with the average distribution density of 2.37 ind/m² and 1.77 ind/m²,the average shell length of 52.4 mm and 51.6 mm respectively. The number of Polymesoda erosa with a shell length of 51-55 mm and the number of Polymesoda expansa individuals with a shell length of 46-50 mm accounted for the highest proportion of the total number of individual species. With the increase of shell length, the ratio of shell length/shell high had no significant changes, but the ratio of shell length/shell width continued to decrease. When shell length of P.erosa and P.expansa reached 50 mm and 55 mm respectively, the shell length/shell width ratio decreased significantly.[Conclusion] Two species of mud clams Polymesoda spp. were found in mangroves at Beihai city, relatively abundant in number and comparatively small at size. The growth rate of P.erosa was faster than P.expansa. The growth of shell width of both clams accelerated after sexual maturity.The tidal current and tidal flat elevation might be the decisive factors for the distribution density of mud clam.The correlation between the distribution density of adult mud clam and sediment granularities might be the result of tidal current.The distribution density of adult mud clam was low in the tidal flat with low elevation.