Bertness Mark D, Grosholz Edwin
Section of Population Biology and Genetics, Brown University, Box G, 02912, Providence, RI, USA.
Oecologia. 1985 Sep;67(2):192-204. doi: 10.1007/BF00384283.
Although mussel beds are common in many intertidal habitats, the ecological significance of the aggregated distribution of mussels has not been examined. The ribbed mussel, Geukensia demissa, is found in dense aggregations on the seaward margin of many salt marshes in New England. Here, we examine the population structure of G. demissa in a New England salt marsh and investigate experimentally the costs and benefits of aggregation.Size, growth rate, and settlement rates of mussels decrease with increasing tidal height, whereas survivorship and longevity increase with increasing tidal height. Winter ice dislodges mussels from the substratum, resulting in mortality over all size classes, whereas crab predation results in the mortality of smaller mussels. The intensity of each of these mortality agents decreases with increasing tidal height. Effects of intraspecific competition on individual growth and mortality also decrease with increasing tidal height.At high densities, individual growth rates were reduced, with depression of growth rates most pronounced on smaller individuals. Mortality from sources other than intraspecific crowding, however, was reduced at high mussel densities, including mortality due to winter ice and crab predators. As a result, our data suggest that the mussel population at our study site would be reduced by 90% in only five years and no juveniles would survive through their second year without an aggregated distribution.Juveniles settle gregariously with or without adults present. The aggregated distribution of settlers and the postsettlement movement of smaller mussels to favorable microhabitats result in size and age class segregation within the population. This probably reduces intraspecific competition for food, while maintaining the survivorship advantages of an aggregated distribution.
虽然贻贝床在许多潮间带栖息地很常见，但贻贝聚集分布的生态意义尚未得到研究。有肋贻贝（Geukensia demissa）在新英格兰许多盐沼的向海边缘密集聚集。在此，我们研究了新英格兰一个盐沼中有肋贻贝的种群结构，并通过实验探究了聚集的成本和收益。贻贝的大小、生长速率和附着率随潮高增加而降低，而存活率和寿命则随潮高增加而增加。冬季的冰会将贻贝从基质上冲走，导致所有大小类别的贻贝死亡，而螃蟹捕食则导致较小贻贝死亡。这些死亡因素的强度都随潮高增加而降低。种内竞争对个体生长和死亡的影响也随潮高增加而降低。在高密度下，个体生长速率降低，较小个体的生长速率受抑制最为明显。然而，在贻贝高密度时，种内拥挤以外的其他来源导致的死亡率降低，包括冬季冰和螃蟹捕食者造成的死亡率。因此，我们的数据表明，我们研究地点的贻贝种群在短短五年内将减少90%，如果没有聚集分布，没有幼体能够存活到第二年之后。幼体无论有无成体在场都会聚集附着。定居者的聚集分布以及较小贻贝在定居后向有利微生境的移动导致种群内大小和年龄组的分离。这可能会减少种内对食物的竞争，同时保持聚集分布的生存优势。
