Ontogenetic Changes in Defensive and Nutritional Characteristics of Juvenile Kelps and their Effects on Community Structure

9513988凡阿尔斯泰纳海带森林是许多具有重要商业价值的鱼类和贝类物种的重要育苗场。构成这些森林的海藻是各种海洋动物的食物和躲避捕食者的场所。海带森林中的海带每年大量死亡，形成了可以被幼年海带殖民的开阔地带。为了了解海带森林是如何维持的，有必要了解幼年海带是如何在开阔地区建立起来的，以及环境因素是如何影响它们的建立的。像许多海洋生物一样，海带产生大量的后代，但只有少数存活下来成为成年海藻。许多海带后代在沉入海底后几周内死亡，因为它们被蜗牛和海胆吃掉。当它们第一次定居时，幼年海带相对于它们的捕食者来说非常小，它们的组织很薄，很容易被吃掉。然而，一些种类的海带比其他种类的海带更不容易被吃掉，这些物种经常成为海带床上的优势物种。目前人们对这些物种为什么不太可能被食草动物吃掉知之甚少，但初步数据表明，它们的存活可能是由于它们组织中高浓度的化学防御。先前的研究表明，海藻的化学防御系统令蜗牛和海胆反感，许多食草动物会避免化学防御的海藻个体。这项研究将使用野外和实验室实验来研究幼年海带的生化和结构特征，这些特征会影响食草动物的觅食。以下问题将被解决：(1)幼年海带是否比成年海带投入更多的资源来防御草食动物的攻击，或者它们是否优先将资源分配给生长而不是防御？(2)不同地点的海带是否使用不同的策略来分配资源用于防御而不是生长？如果是，在特定地点使用的策略是否由场地的环境特征决定？海带产生的多酚防御化合物对所有类型的食草动物都有效吗？；(4)没有大量投资于防御的幼年海带是不是更好的竞争对手，因为它们有更多的资源投资于生长？这项研究的结果将为这些重要栖息地的维持机制提供洞察力。它们还将作为确定环境变化对捕食者和猎物之间相互作用的影响的基础。

9513988 Van Alstyne Kelp forests are habitats that are important nursery grounds for many commercially important species of fish and shellfish. The kelps that make up these forests serve as food and shelter from predators for a variety of marine animals. Large numbers of kelps within kelp forests die each year creating open patches that can be colonized by juvenile kelps. In order to understand how kelp forests are sustained, it is necessary to know how juvenile kelps become established in open areas and how environmental factors affect their establishment. Like many marine organisms, kelps produce large numbers of offspring but only a few survive to become adults. Many kelp offspring die within a few weeks after they settle to the bottom because they are consumed by snails and sea urchins. When they first settle, juvenile kelps are very small relative to their predators and their tissues are thin and easily consumed. However, some species of kelps are less likely to be consumed than others and these species often become the dominant species in kelp beds. Little is currently known about why these species are less likely to be consumed by grazers, but preliminary data suggest their survival may be due to high concentrations of chemical defenses in their tissues. Previous research has shown that seaweed chemical defenses are distasteful to snails and sea urchins, and that many grazers will avoid chemically defended seaweed individulas. This study will use field and laboratory experiments to examine the biochemical and structural features of juvenile kelps that affect grazing by herbivores. The following questions will be addressed (1) Do juvenile kelps invest greater amounts of resources in defending themselves against attacks by herbivores than adult kelps, or do they preferentially allocate resources for growth rather than defense?; (2) Do kelps at different locations use different strategies in allocating resources towards defense versus growth? If so, is the strategy use d at a particular location determined by environmental features of the site?; (3). Are the polyphenolic defensive compounds that are produced by kelps effective against all types of herbivores?; and (4) Are juvenile kelps that do not invest heavily in defenses better competitors because they have more resources to invest in growth?. The results of this study will provide insights into the mechanisms by which these important habitats are sustained. They will also serve as a basis for determining the effects of changes in the environment on interactions between predators and their prey.