海带森林由厚厚的海带目（Laminariales）大型褐藻所构成，这些藻类悬挂在海底的岩石上随海水波动起伏，朝着光线来源向上生长，它们密集成群，就像陆地上的树木一样，因此得名“森林”。但和陆地森林一样，这些海底森林最近也受到了气候变化的威胁。近年来，美国加利福尼亚海岸附近的海带森林已基本消失，这一切都始于2013年一个神秘的“斑块”，也就是海洋表面温度异常增暖事件“暖水块”（warm blob，又称“暖泡”），由太平洋上空的大气变化造成。“暖水块”给加州的海带森林带来了巨大的影响。海洋温度的升高导致了海星死亡，海星通常控制着海胆的数量，而海胆以海带为食。因此，“暖水块”的到来引起了海胆数量的爆炸性增长，这些生物疯狂地进食，据大自然保护协会（The Nature Conservancy）估计，海胆吃掉了加州海岸96%的海带。加拿大太平洋的海带森林也承受着巨大的压力，数量正在萎缩。在美国太平洋西北区的普吉特海湾，某些区域的海带森林仍完好无损，但另一些区域则不然，这意味着我们还有机会研究海带的重要性，并尝试拯救它。健康的海带森林通常是一处静谧的避风港，为数百个物种提供了结构复杂的栖息地，包括底栖无脊椎动物、小型鱼类，一直到食物链顶端的灰鲸。海獭会将身体扭入海带中，这样它们就可以安然入睡而不用担心随海流漂走，醒来时前爪一挥就能吃到早餐。海带森林还能缓冲海浪的冲击，为海洋生物创造一个物理避难所。它们储存了大量的碳，被科学家称为“海洋红杉”。与陆地森林一样，海带森林也通过光合作用产出氧气并吸收二氧化碳，这可以减少海洋酸化，保护更脆弱的海洋动物。海带森林有很多好处，最近又得到了新的验证：太平洋西北部的标志性物种鲑鱼（即三文鱼）也在利用海带。渔民们以前就说过这种情况，美国沿海流域研究所（Coastal Watershed Institute）的海洋生物学家安妮·谢弗（Anne Shaffer）也是这么说的。她研究海带森林已有三十多年。她还记得，几年前一个生物学家突然说：“鲑鱼不会去海带森林的。”她立刻反驳说：“我觉得它们会。”于是她开始证明这一点。谢弗在美国华盛顿的艾尔瓦河（Elwha）河口研究海带森林。十多年前，艾尔瓦河上有两座水坝，阻碍了鲑鱼洄游。但现在，河流畅通无阻，并创造了好几公顷的新海滩栖息地，同时也丰富了水下生态系统。艾尔瓦河的水流到淡水湾后，在河口形成了一个大回旋，也就是说艾尔瓦河的水会绕流入海带森林，谢弗团队已经花了七年多的时间，对使用这片海带森林的海洋生物进行浮潜调查。她发现，海带森林的作用随季节而变化。她今年发表的研究表明，几种濒危鲑鱼，包括帝王鲑（Oncorhynchus tshawytscha）、银鲑（Oncorhynchus kisutch）、大马哈鱼（Oncorhynchus keta）和粉红鲑（Oncorhynchus gorbuscha），肯定利用了海带森林，还是以多种方式利用的。幼年鲑鱼和幼年“饵料鱼”（forage fish）在沿海岸线迁徙时，海带森林就是它们的避难所。海带们还提供了托儿场所，让这些动物可以休息和觅食，因为这里有着更丰富的浮游动物群落，幼年鱼类可以在这里成长，然后为向近海和不同栖息地的更大过渡做好准备。具体来说，鲑鱼在海带森林中发现的浮游动物类型是不同的。有几种被称为密切相关无脊椎动物的关键物种，这些物种与海带有关，而且也是幼年鲑鱼和饵料鱼高度选择的物种。在成长的过程中，鲑鱼也可以利用海带捕食小鱼。谢弗表示，幼年鲑鱼会把它们的猎物赶到一起，借助海带把它们团成一团，然后……[查看全文]
Turns Out Undersea Kelp Forests Are Crucial to Salmon
Starre Vartan: Kelp forests are made up of thick, undulating ribbons of brown algae that hang on to rocks at the seafloor and grow toward the light above.
Kelp is found in dense groups, like trees on land, hence the name "forests."But just like forests on land, lately these underwater forests have come under threat from climate change.The kelp forests off California's coasts have largely disappeared in recent years. It all started in 2013 with a mysterious "blob."That's what scientists called this blobbish patch of warmer-than-normal ocean water, which was created by changes in the atmosphere above the Pacific.The blob brought drastic changes to the California kelp forests. Elevated ocean temperatures led to a die-off of sea stars.Sea stars typically control the population of sea urchins. Sea urchins eat kelp.And so the coming of the blob created an explosion of urchins. The creatures went on an eating spreethat, by some estimates, cleared 96 percent of the kelp from beneath the California coast.For now, the forests in Puget Sound, where I live, are intact in some regions but not in others. That means there's both time to research kelp's importance and to try to save it.[CLIP: Kelp forests underwater]Vartan: A healthy kelp forest, which you just heard, is typically a quiet safe haven. They provide complex habitat to hundreds of species, including benthic invertebrates, small fish and animals all the way up the food chain to gray whales. Sea otters twist their bodies into the kelp. That way they can sleep without drifting and wake to breakfast a forepaw's swipe away.Forests of kelp dampen wave energy and create a physical refuge for marine life. They also store so much carbon that scientists call them the "sequoias of the sea."Like terrestrial forests, they also bolster oxygen via photosynthesis and absorb carbon dioxide. In the sea, that reduces acidification that kills more vulnerable marine animals.There are so many benefits—and recently a newly verified one: salmon, those Pacific Northwest icons, also use kelp. Fishers had previously said this was the case, and so did Anne Shaffer, a marine biologist with the Coastal Watershed Institute in Washington State. She's studied kelp forests for more than three decades.She remembers from a few years ago ...Shaffer: A biologist with the state who blurted out, "Well, salmon don't use kelp forests." And, you know, my immediate retort was "Except when they do."Vartan: So she set out to prove it.I met with her about 10 miles up the coast from her HQ in Port Angeles, Washington, on the coast of the Strait of Juan de Fuca. We hiked out to the mouth of the Elwha River, where Anne does some of her research into kelp forests.A little more than 10 years ago the Elwha had two dams that prevented salmon migration. But now the river flows free, and it has created acres of new beach habitats and enriched the underwater ecosystems, too.[CLIP: Elwha River flowing into the Strait of Juan de Fuca]Shaffer: This is the mouth of the Elwha. And what happens is the water comes out of the Elwha river, comes into Freshwater Bay, and then there's a big gyre that forms right here. And so basically what happens is this plume of Elwha water will circle around right into that kelp bed where surveys are.[CLIP: Walking along the sandy and rocky shore]Vartan: Anne and her team, including undergraduate students, have spent more than seven years taking snorkelling surveys of who uses the kelp forest here.[CLIP: Young kelp researchers audio]She's found that it varies seasonally. Her research, published this year, showed that several types of endangered salmon, including Chinook, coho, chum and pink salmon, definitely use kelp—in multiple ways.Shaffer: So juvenile salmon, juvenile forage fish, as they're migrating along the shoreline, they're their areas of refuge. And they also provide a nursery ground so these animals can rest and feed because they have the richer zooplankton communities and grow and then get ready for these bigger transitions to offshore and different habitats.Vartan: Specifically the type of zooplankton the salmon found in kelp was different.Shaffer: There were these few key species of what are called vitally associated invertebrates, and those are the ones that are associated with kelp, and those are also the ones that are very highly selected for by juvenile salmon and forage fish.Vartan: But as they grow, the salmon can also use the kelp to prey on smaller fish, too.Shaffer: Salmon will actually herd their prey. These little guys, little juvenile salmon, will herd their prey up into a ball and then just...[full transcript]
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