Habitat point records from 1990 UMBSM Harris and Lewis sealochs survey

Six lochs were surveyed by UMBSM/NCC during a visit to Harris and Lewis in 1988 (Howson 1989). Six more were subsequently surveyed in August 1990: Loch Stocknish, East and West Loch Tarbert and Lochs Erisort, Leurbost and Grimshader. Loch Stocknish, on the south-east facing coast of South Harris, is classed as a fjordic `B` type loch by Milne (1972). It is short (4km), has one sill and its inner basin reaches a depth of approximately 40 m. Most of the loch is sheltered from wave action and there are areas of tide_swept sediment in the narrow entrance channels. East Loch tarbert and the Erisort-Leurbost system are classified ad fjords with fjard-like characteristics (Fairbridge 1968). Both have a number of islands protecting the inner loch from wave action and consequently a large range of exposures were encountered in the littoral and sublittoral. East Loch Tarbert has a deep basin (66 m) situated to the north of Scotasay and a tide-swept narrows between Scalpay and South Harris. This loch has extensive areas of shelly sediment which at the time of the survey were being dredged for scallops. Softer muds were found in Loch Ceann Dibig near the head of East Loch Tarbert. Loch Erisort is the longest loch in this series (12 km). It reaches a depth of 56 m near the mouth, but is shallow behind its main sill. It has areas of littoral and sublittoral exposed bedrock but, with Loch Leurbost, was also noted for having a wide range of sediments. At the mouth of Loch Erisort, concealed behind a group of islands, there is a complex of shallow, sheltered channels and small lochs, some of which are brackish. Loch Grimshader is a small (2.5 km) `B` class fjord (Milne 1972) although it has been described as an ob by Earll and Pagett (1984). It has a single basin (maximum depth 13 m), a narrow, shallow, tide-swept entrance and steep bedrock slopes just outside the entrance. West Loch Tarbert is very different in character from the east coast lochs. It is a large open bay, rarely deeper than 30 m and is very exposed to the west. There are no sills, although there is an area of deep water (50 m) in the Soay Sound. The sediments are predominantly muddy sand. There are a considerable number of fish farms throughout these lochs, particularly in Lochs Erisort and Leurbost, and evidence of nutrient overloading was found in localised areas with poor water circulation in Lochs Stocknish, Erisort and Grimshader. There is one SSSI adjoining the north shores of West Loch Tarbert, and the outer region of Loch Erisort is rated as of marine biological importance. Much littoral work has been carried out by Smith (1979, 1982, 1983, 1984) and Powell et al. (1979) but there have been few sublittoral studies in this area. In the present survey seventy nine sites were surveyed, of which 61 were sublittoral (4 where suction samples were taken) and 18 were littoral. Thirty two habitat/community types are described. Infralittoral bedrock communities ranged from rich Laminaria hyperborea forest in the wave and tide exposed areas to dens L.saccharina in the most sheltered regions. In West Loch Tarbert the kelp forest communities were heavily grazed and the deeper communities effected by scour. Examples of exposed circalittoral bedrock with Leptometra celtica, Swiftia pallida and Diazona violacea were found at the entrance to the east coast lochs. Loch Erisort held a particularly wide range of sediment communities including the species-rich sill, the shallow and seemingly undisturbed sediment with dense Virgularia mirablis and Philine aperta and the shallow, soft muds with very large Suberites domuncula. A dense bed of Ocnus planci, rarely found in such numbers, was found towards the head of the loch. Seventeen habitat/community types and 17 species have been provisionally assessed to be of Local, Regional or National importance. Records currently considered sensitive have been removed from this dataset.1988年，UMBSM/NCC在造访哈里斯岛与刘易斯岛期间完成了6处湖泊的调查（Howson, 1989）。后续又于1990年8月额外调查了6处湖泊：斯托克尼什湖（Loch Stocknish）、东塔伯特湖、西塔伯特湖，以及埃里索特湖（Loch Erisort）、勒尔博斯特湖（Loch Leurbost）与格里姆沙德湖（Loch Grimshader）。位于南哈里斯东南向海岸的斯托克尼什湖，被米尔恩（1972）归类为峡湾型（fjordic）B类湖泊，全长4千米，单道湖槛，内盆地最大水深约40米，湖区大部分区域免受波浪冲击，狭窄入口航道处分布有潮汐冲刷沉积物区域。东塔伯特湖与埃里索特-勒尔博斯特水系被归类为具小峡湾（fjard）特征的峡湾（Fairbridge, 1968），两处湖泊均拥有多座岛屿以保护内湖免受波浪冲击，因此在潮间带与潮下带观测到了广泛的暴露梯度。东塔伯特湖拥有一处位于斯科塔赛岛以北的深盆地（水深66米），以及斯卡尔佩岛与南哈里斯之间的潮汐冲刷狭水道，该湖分布有大面积贝壳沉积物，调查期间此处正开展扇贝拖网捕捞作业。在东塔伯特湖头部附近的钦恩迪比格湖（Loch Ceann Dibig）中发现了软质泥质沉积物。埃里索特湖是本次系列中最长的湖泊（全长12千米），入口附近水深达56米，但主湖槛后方水域较浅，分布有潮间带与潮下带裸露基岩区域，且与勒尔博斯特湖一同以沉积物类型多样而闻名。在埃里索特湖入口处，隐蔽于群岛后方的区域存在一片由浅而封闭的航道与小型湖泊组成的复杂水域，其中部分区域为咸淡水交汇型。格里姆沙德湖是一座小型（全长2.5千米）B类峡湾（Milne, 1972），尽管厄尔与佩吉特（1984）曾将其描述为ob类水域，该湖拥有单一盆地（最大水深13米），入口狭窄且浅，受潮汐冲刷，入口外侧分布有陡峭的基岩斜坡。西塔伯特湖的水文特征与东海岸湖泊截然不同，它是一处大型开放式海湾，水深极少超过30米，且直面西侧海域，暴露性极强，湖区无湖槛，但索伊水道（Soay Sound）内存在一片50米深的水域，沉积物以泥质砂为主。这些湖泊中分布有大量水产养殖场，尤以埃里索特湖与勒尔博斯特湖为甚；在斯托克尼什湖、埃里索特湖与格里姆沙德湖的局部水循环较差区域，发现了营养物过载的证据。西塔伯特湖北岸毗邻一处具有特殊科学价值的地点（Site of Special Scientific Interest，SSSI），埃里索特湖外围区域被评定为具有海洋生物学重要性。此前史密斯（1979、1982、1983、1984）与鲍威尔等人（1979）已开展了大量潮间带研究，但该区域的潮下带研究相对匮乏。本次调查共覆盖79处样点，其中61处为潮下带样点（含4处采用抽吸采样），18处为潮间带样点，共描述了32种生境/群落类型。浅海亚潮带基岩群落涵盖了波浪与潮汐暴露区域内丰富的掌状海带（Laminaria hyperborea）林，以及最隐蔽区域内的高密度糖海带（Laminaria saccharina）林。在西塔伯特湖，海带林群落遭到严重啃食，较深水层的群落则受到沉积物冲刷的影响。在东海岸湖泊的入口处，发现了暴露型近海亚潮带基岩群落的实例，伴生物种包括凯尔特羽星（Leptometra celtica）、苍白柳珊瑚（Swiftia pallida）与紫色被囊动物（Diazona violacea）。埃里索特湖拥有尤为多样的沉积物群落，包括物种丰富的湖槛生境、浅海且看似未受扰动的沉积物区域（其中分布有密集的华丽海笔（Virgularia mirabilis）与开放壳海牛（Philine aperta）），以及浅海软泥区域（其中栖息着大量团集硬海绵（Suberites domuncula））。在湖头部附近发现了密度极高的平足瓜参（Ocnus planci）床，该物种极少以如此规模出现。共有17种生境/群落类型与17个物种被初步评定为具有地方、区域或国家级保护价值。当前被视为敏感的记录已从本数据集中移除。