Habitat point records from 1984-85 Harris lower Torridge estuary littoral survey

In common with all estuaries, that of the Torridge has a wide range of habitat types, ranging from fine, clean sand to pure mud with high organic content. Such diversity of habitats might be expected to support a similarly high diversity of organisms, especially since the estuary is so thoroughly scoured by tidal activity - thus preventing the kind of accumulation of organic material which leads to eutrophication but whilst still permitting the organisms to take advantage of the rich, detrital food supply borne by river and sea. This expected diversity is absent. It is only those shores which are either rocky or sufficiently stony to act as rocky shores which support a variety of plant and animal species - a situation which is, of course, common on 'ordinary' sea-shores - i.e. outside estuaries. Whilst it is true that estuarine faunas are always restricted, it is surprising to find, for example, that the sandy shores support such very reduced faunas of errant species and that, despite considerable searching, no evidence could be found for the presence of either the gastropod Hydrobia ulvae nor the amphipod Corophium volulator on any of the muddy shores. Both of these species are usually very common in estuaries. It is not inconceivable that the lack of these species was due to the season during which this survey was carried out - but that would not entirely explain the apparent total absence of the accumulated shells of the gastropod along strand lines where they frequently occur in enormous quantities in other situations. There is no doubt that some of the muddier shores in the Appledore region accumulate very large quantities of organic debris, apparently washed down in the river-flow and deposited on these shores due to the flow pattern of the river near its mouth. Such organic material is one of the prime sources of food for invertebrates - but an excess of this material, especially when it is not effectively cleared away by water movements, can lead to ecological trouble due to the accumulation in the colloidal muds of hydrogen sulphide, with accompanying anoxia. Whilst the larger, naturally occuring debris of this sort (leaf-litter and remains of salt-marsh plants) were readily detectable, more metabolised debris, such as sewage waste, was not detectable by methods employed fro this study - but would, if accumulated in these sites, exacerbate the problem due to its more rapid bacterial breakdown. Despite the lack of species diversity, the plants and animals do exist within the Torridge estuary appear to be successful. The abundance of Scrobicularia plana and Mytilus edulis at their representative sites has already been recorded, along with comment concerning the large size to which both species grow. Algal cover on the hard shores is good and, for an estuary, interestingly diverse. There is apparently no accumulation of Ulva lacuta thus indicating that no stagnation of dissolved plant nutrients occurs within the estuary - a situation which could scarcely be expected to arise in an estuary with such sweeping tidal activity.

与所有河口相似，托尔里奇河口的栖息地类型极为丰富，从细腻、洁净的沙粒到有机含量极高的纯泥，种类繁多。这样的栖息地多样性本应支撑起生物种群的极高多样性，尤其是鉴于河口地区受潮汐作用之彻底冲刷——从而避免了导致富营养化的有机物质积累，同时仍允许生物利用河流和海洋带来的丰富碎屑食物。然而，预期的多样性并未出现。仅有那些岩石质或足以充当岩石海岸的足够多岩石的岸线，才能支持多种植物和动物物种的繁衍——这种状况在‘普通’海岸线上是极为常见的，即河口之外。尽管河口生物群落总是受限，但发现沙质海岸支持的迁徙物种生物群落如此之少，以及尽管进行了相当广泛的搜索，但在任何泥质海岸上均未发现腹足类动物 Hydrobia ulvae 和甲壳类动物 Corophium volulator 的存在，这一点令人惊讶。这两种物种在河口地区通常非常普遍。这些物种的缺失可能归因于本调查进行的季节——但这并不能完全解释为什么在通常情况下大量出现的腹足类动物贝壳在岸边线路上完全不见。毫无疑问，苹果多地区的一些泥质海岸确实积累了大量的有机废物，这显然是由于河流的流动模式在河口附近将这些废物冲刷下来并沉积在这些岸线上。这类有机物质是无脊椎动物食物的主要来源之一——但过量积累，尤其是在水流无法有效清除的情况下，会导致由于氢硫酸在胶体泥中的积累以及伴随的缺氧而引发生态问题。尽管此类较大的自然碎片（如叶落和盐沼植物残骸）易于检测，但通过本研究采用的方法无法检测到更多已代谢的碎片，如污水废物——但如果这些废物在这些地点积累，由于其细菌分解速度更快，将会加剧问题。尽管物种多样性不足，但托尔里奇河口内的植物和动物似乎依然能够成功繁衍。Scrobicularia plana 和 Mytilus edulis 在其代表性地点的丰富度已经被记录，并对其生长的巨大体型进行了评论。硬质海岸的藻类覆盖良好，对于一个河口来说，其多样性令人感兴趣。显然，乌尔瓦藻 Ulva lacuta 并未在此积累，这表明在河口内并未发生溶解植物营养物质的停滞——在一个潮汐活动如此剧烈的河口，这种情况的出现几乎是不可能的。