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首页> 外文期刊>Journal of Experimental Marine Biology and Ecology >Why Are Intertidal Snails Rare In The Subtidal? Predation, Growth And The Vertical Distribution Of Littorina Littorea (l.) In The Gulf Of Maine
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Why Are Intertidal Snails Rare In The Subtidal? Predation, Growth And The Vertical Distribution Of Littorina Littorea (l.) In The Gulf Of Maine

机译：为什么潮间带的蜗牛稀少？缅因州海湾小Littorina Littorea（l。）的捕食，生长和垂直分布

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摘要

The North Atlantic gastropod Littorina littorea exhibits a characteristic "intertidal" distribution: the snail is abundant in the littoral zone but scarce in the shallow subtidal and the relatively few subtidal individuals are larger (in shell size) on average than those in the intertidal zone. For highly mobile species like L. littorea, this vertical distribution is primarily determined by directional movement. Biotic and abiotic factors vary across tidal heights, and natural selection for movement to shore levels where fitness is maximized provides the ultimate (evolutionary) explanation for vertical distribution patterns. In this study, we asked whether variation in growth rate and/or predation pressure among tidal heights provide an ultimate explanation for vertical gradients in L. littorea size and abundance. We used a cage experiment to compare juvenile growth rate among tidal heights and a series of field and laboratory experiments to examine variation in predation pressure among tidal heights and snail size classes. Juvenile growth rates were highest in the low intertidal zone, declining at both higher and lower levels. Predation risk for tethered L. littorea increased with both decreasing tidal height and decreasing body size (shell height). Almost all tethered prey were consumed by shell- breaking predators and a census revealed that the two most abundant such predators were the crabs Carcinus maenas and Cancer borealis. Laboratory feeding experiments were used to compare size-dependent prey vulnerability and prey-size preferences for these two key predators. We found that L. littorea vulnerability decreased with increasing snail size and increased with increasing size of both predator species. However, whereas C. borealis were capable of consuming even the largest L. littorea, most Carcinus were unable to feed on individuals larger than 10 mm in shell height. Additionally, C. borealis preferred larger sizes of L. littorea than did Carcinus. Thus, Carcinus, which co-occurs with L. littorea in the intertidal, is a much less effective predator than C. borealis, which is found primarily in the subtidal. We conclude that predation on L. littorea by C. borealis and other subtidal consumers has resulted in the scarcity of this ecologically important grazer in the subtidal. This effect has been produced both through direct predation and by imposing strong selection for movement of L. littorea to higher tidal zones.
机译：北大西洋腹足纲小鸟Littorina littorea表现出特征性的“潮间带”分布：蜗牛在沿岸带丰富，但在浅潮带下却稀少，并且潮下带的个体平均数（沿壳大小）比潮间带大。对于高度活动的物种，如L. littorea，此垂直分布主要由方向运动决定。生物和非生物因素会随着潮汐高度的变化而变化，自然选择运动到最大适应度的海岸水平将为垂直分布模式提供最终的（进化的）解释。在这项研究中，我们询问潮汐高度之间生长速度和/或捕食压力的变化是否为L. littorea大小和丰度的垂直梯度提供了最终解释。我们使用笼子实验比较潮汐高度之间的幼体生长率，并进行了一系列田间和实验室实验，以检验潮汐高度和蜗牛大小类别之间捕食压力的变化。在低潮间带，青少年的增长率最高，在较高和较低的水平上均下降。随着潮汐高度的减小和体型（壳体高度）的减小，被束缚的L. Littarea的捕食风险也随之增加。几乎所有拴在一起的猎物都被破壳的掠食者吞噬，人口普查显示，这种捕食者中两个最丰富的捕食者是蟹肉蟹和北野蟹。实验室饲养实验用于比较这两个主要食肉动物的大小依赖性猎物脆弱性和猎物大小偏好。我们发现，L。littorea的脆弱性随着蜗牛大小的增加而降低，并且随着两种捕食者物种的大小的增加而增加。但是，尽管北极衣原体甚至能够食用最大的立枯丝杆菌，但大多数Carcinus不能以壳高大于10毫米的个体为食。另外，与Carcinus相比，C.borealis更喜欢L. littorea。因此，在潮间带与枯草杆菌共生的Carcinus是一种比主要在潮下带发现的北极衣原体有效的捕食者。我们得出的结论是，北极衣原体和其他潮下带消费者对L. littorea的捕食导致潮下带这种具有生态重要性的放牧者的匮乏。这种效果既可以通过直接捕食，也可以通过强力选择来将L. littorea移至更高的潮汐带。

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