مطالعه پراکنش و تراکم (annelida: lumbriculidae) stylodrilus heringianus در مصب رودخانه‌های چشمه‌کیله و سردآبرود مازندران (حوضه جنوبی دریای خزر)

این مطالعه به منظور شناسایی، تعیین پراکنش و تراکم کرم کم‌تار stylodrilus heringianus طی مدت یک ‌سال به صورت دو ماه یکبار، از آبان ماه 1393 لغایت شهریور ماه 1394 انجام شد. در این بررسی میانگین سالانه دمای آب 0.2±18.2 درجه سانتی‌گراد، شوری آب 0.4±5.7 گرم بر لیتر و درصد مواد آلی رسوبات بستر 0.05±2.29 بود. بافت رسوبات بستر در ایستگاه‌های رودخانه‌ای و مصبی رسوبات درشت‌‌دانه ماسه گراولی و در ایستگاه‌های دریایی رسوبات ریز دانه ماسه سیلتی بود. با توجه به مطالعات تاکسونومیک و مورفولوژیک نمونه‌ها و بهره‌گیری از کلیدهای شناسایی معتبر و ارسال عکس نمونه‌ها به افراد متخصص جهت تایید گونه شناسایی شده، مشخص گردید که نمونه‌ها متعلق به گونه s. heringianus هستند. نتایج حاصل از پراکنش زمانی نشان می‌دهد که بیشترین میانگین تراکم و توده‌زنده این گونه به‌ترتیب در دی ماه (23.7±58.6 تعداد در مترمربع) و اسفند ماه (55±175 میلی‌گرم در مترمربع) و کمترین آن در شهریور ماه (4.3±9.7 تعداد در مترمربع و 7±18 میلی‌گرم در مترمربع) بود. فراوانی و توده‌زنده این گونه در ایستگاه‌های رودخانه‌ای به‌ترتیب (17.3±42.7 تعداد در مترمربع و 40.3±113.3 میلی‌گرم در مترمربع) بود و در ایستگاه‌های مصبی و دریایی مشاهده نشدند. تراکم و توده‌زنده این گونه در رودخانه چشمه‌کیله بیشتر از سردآبرود بود. همبستگی معنی‌داری (0.05>p) بین تراکم و توده‌زنده s. heringianus با عوامل محیطی در آب (دما و شوری) و رسوب (دانه‌بندی و مواد آلی کل) مشاهده گردید. این گونه علاوه بر نقش مهم آن در زنجیره غذایی منابع آبی، به‌ عنوان شاخص زیستی کیفیت آب نیز مطرح است و در صنعت آبزی‌پروری به عنوان غذای زنده مورد استفاده قرار می‌گیرد.

study of the distribution and density of stylodrilus heringianus (annelida: lumbriculidae) along cheshmehkileh and sardabroud estuaries in mazandaran province (south caspian sea)

introduction aquatic oligochaetes are members of a main group of macroinvertebrates and include about 1,700 species (caramelo and martinez-ansemil, 2012) of 13 families with worldwide distribution (martin et al., 2008). these species commonly inhabit within sediments of rivers, streams, lakes, marshes, ponds, springs and ground-waters (collado and schmelz, 2001), showing that these species have been adapted to a wide variety of habitats and environments, such as freshwater, brackish or seawater.the freshwater oligochaete genus stylodrilus is a large and heterogeneous. although the genus has a holarctic distribution, approximately 28, are exclusive to the palaearctic region (martin et al., 2007), except stylodrilus heringianus a peregrine species recorded in the australasian region and assumed to have been introduced by shipping (brinkhurst & jamieson, 1971). from the lumbriculidae family, only two species, l. variegatus and s. heringianus, have cosmopolitan, asexual reproduction (fragmentation) and use as live food in fish farming are the most important factors that have contributed to the distribution of these two species in the world (pinder and brinkhurst, 1994). cheshmehkileh of tonekabon and sardabroud of chalus rivers are the most important, mountainous and permanent rivers running from high elevation to the sea (southern waters of caspian sea). these rivers are important for reproductive migration of two indigenous valuable fisheries species salmo caspius (caspian trout) and rutilus frisii (caspian kutum) as well as other migratory fish (khara, 2016). for these reasons, estuary of these rivers is regarded as a ‘protected area’ and is conserved by the department of environment of iran (doe, 1996). 26 species of aquatic oligochaetes have been reported from inland waters of iran so far, of which only 1 species belongs to the lumbriculidae family and from lumbriculus genus: l. variegatus (ahmadi et al., 2012; basim et al., 2012).  the aim of this study was to introduce stylodrilus heringianus from cheshmehkileh of tonekabon and sardabroud of chalus rivers in the southern caspian sea basin for the first time and investigation of its distribution pattern in the three ecosystems of river, estuary and marine combined with some environmental factors in water (temperature and salinity) and sediment (grain size and total organic matter).methodology sampling of oligochaetes and environmental factors in both sardabroud and cheshmekile rivers, was carried out between november 2014 and september 2015 and random sampling was done at six stations with three replicates for each bimonthly sampling along each river. sampling was done using 0.03 m2 van veen grab for soft sediments at the estuary area and for sampling at inner parts of the river with pebbles a 0.1 m2 and 0.2 mm-mesh size surber sampler was applied. biotic samples were fixed in situ using a 5% formalin solution. in the laboratory, sediments were sieved through mesh sizes of 1, 0.5 and 0.25 mm and specimens were preserved in 70% ethanol and then sorted and counted under a stereomicroscope (nikon smz800, japan) and eventually the wet weight of worms was measured using a digital balance (0.0001 g). for identification at species level, worm specimens were mounted on glass slides in amman’s lactophenol clearing agent (smith, 2001) and covered by a coverslip and left for several hours to a day or two, and then for observation of setae and other details, a microscope was used (nikon e200).