WENTLOOGE LEVEL INVERTEBRATE SURVEY, 2019 David Boyce
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WENTLOOGE LEVEL INVERTEBRATE SURVEY, 2019 David Boyce DC Boyce Ecologist October 2019 1. INTRODUCTION This report details the findings of an invertebrate survey carried out under contract to Green Ecology. The survey aims to assess the importance for invertebrates of the area of Wentlooge Level shown on Figure 2.1 below. The site is in Wales, on the Gwent Levels; an extensive area of grazing marsh on the north-western side of the Bristol Channel. Wentlooge Level lies in the western part of this area, between the cities of Cardiff to the west and Newport to the east. A central grid reference for the site approximates to ST276817. The grazing marsh ditches of the Gwent Levels support a nationally important assemblage of aquatic plants and invertebrates. It also has one of the last remaining UK populations of the threatened shrill carder bumblebee Bombus sylvarum. For these reasons, much of the area is notified as a series of Sites of Special Scientific Interest (SSSI). The whole of the Wentlooge Level site lies within the Gwent Levels – St. Brides SSSI. Both the shrill carder bumblebee and the brown-banded carder bumblebee Bombus humilis, which also has a strong population on the Gwent Levels, are additionally listed in Section 7 of the Environment (Wales) Act 2016 as Species of Principal Importance for the conservation of biodiversity in Wales. 2. METHODS The first phase of survey work was undertaken in two blocks of two days, the first session being carried out on the 1st and 2nd of May 2019 and the second on the 22nd and 23rd May. The first session primarily involved sampling the aquatic invertebrate fauna of the ditches (known on the Gwent Level as reens) and the second on survey of the terrestrial fauna. Two further visits were made to the site; on the 8th and 20th of August; the main objective of which was to survey populations of shrill carder bumblebee and brown-banded carder bumblebee. A second aim of the August session was to undertake general invertebrate survey work on an additional area of land at the north-eastern edge of the site (compartment F). This was not included in the initial project specification but was added to the proposed development area subsequent to completion of the May surveys. Both B. humilis and B. sylvarum are rapidly declining species that have nationally important populations on the Gwent Levels. The latter is now only known from a few places in southern Britain, with grazing marsh levels being one of its most important habitats. For the bumblebee surveys, all Bombus species recorded in each survey unit/sub-unit were noted, with the number of shrill and brown-banded carder bees being counted, along with the flower species at which they were seen foraging. Where possible, bumblebees were identified in the field to species level, with any ‘difficult’ specimens netted for examination in a tube with a hand lens. Fortunately, the shrill carder bumblebee is easily distinguished in the field. Workers of the white-tailed and buff-tailed bumblebees (Bombus lucorum and B. terrestris respectively) are indistinguishable without microscopic examination. As these are both very common and widely distributed, they were recorded as B. lucorum/terrestris workers. Males and queens of these two can be easily identified and were recorded to species level. Note also that B. lucorum is a complex of three very similar sibling species, which are only reliably distinguished by DNA analysis. For the purposes of this study, all records of this taxon refer to the B. lucorum aggregate. Because it was a relatively large site, it was not feasible in the time available to survey the whole area in detail for invertebrates. The main emphasis for more detailed invertebrate surveys was on those habitats likely to have the greatest invertebrate interest (eg. ditches with shallow margins and a diverse flora; stands of relatively unimproved species-rich grassland; short ruderal vegetation). Other less promising habitat types (eg. shaded and/or dried-out ditches; improved/semi-improved species-poor grassland; species-poor tall ruderal vegetation) were also surveyed, but in less detail, with the aim being to ensure coverage of the range of main invertebrate habitats represented at Wentlooge Level. In addition to general spot-searching techniques, some more specialised sampling methods were employed to ensure all potentially important habitat features were sampled effectively. The aquatic invertebrate survey was carried out using a simplified version of the standard methods developed for a national survey of the ecology of ditch systems by Buglife (Palmer et al., 2010). Seven ditch lengths were sampled in May 2019. At each of these, three sample points were established that contained habitat thought likely to support rich aquatic invertebrate assemblages. These three samples were considered collectively to constitute a single sample station. Each aquatic sample has been allocated a survey number (ie. AQ1-7) and the location of the sample stations is shown on Figure 2.1. Before beginning to collect aquatic invertebrates, an eight-figure GPS reading of the location of the sample was recorded. In each sub-sample, a pond net was used to collect material from patches of vegetation that exhibited the greatest small-scale mosaic structure until the net began to fill to the point that it became more difficult to push. This generally took between one to three minutes and the net was usually about a quarter to a third full of plant material (about two to three litres by volume). The sample was then spread out onto a white polythene sheet and invertebrates were recorded/collected for eight to ten minutes as the material was teased apart. Further details of the sampling method can be found in Palmer et al. (2010). Some additional casual aquatic invertebrate sampling was carried out in shallow water margins using a sieve. The main taxonomic groups to be covered by the aquatic survey were water beetles (Coleoptera), water bugs (Hemiptera), dragonflies/damselflies (Odonata) soldierflies (Diptera: Stratiomyidae) and water snails (Mollusca). Some other invertebrate taxa were also collected where these were easily identified or were in groups familiar to the surveyor (eg. Stenus rove beetles). For the terrestrial surveys, grassland, wetland and ruderal vegetation was mostly sampled by sweeping with a heavy-duty entomological sweep net or tapping specific invertebrate foodplants over a tray. Ground-active invertebrates in grass tussocks and litter were sampled by shaking them out over a white plastic tray. Catches were collected into tubes with either ethyl acetate or iso-propyl alcohol. The terrestrial invertebrate taxa collected were those that would provide the most useful information on the habitats being surveyed. For example, the ground beetles (Coleoptera: Carabidae) include a number of habitat specialists restricted to eutrophic wetlands such as grazing marsh ditch edges. For the purposes of this survey, a series of six survey units have been identified (survey units A to F on Figure 2.1). These follow the ownership boundaries into which the site is sub- divided. Where there were potentially important invertebrate habitats that warranted more accurate delineation, these ownership units have been further divided into sub-units (eg. A1). These survey units/sub-units are shown on Figure 2.1 below. Figure 2.1. Location of invertebrate survey units at Wentlooge Level, 2019 3. RESULTS A full list of all invertebrate species found at Wentlooge Level in 2019 is given in Table 3.1 below, along with their conservation status where applicable, and the survey units in which they were recorded. Sub-section 3.1 lists all of those species with a formal conservation status that are regarded as key species when assessing the importance of the site for invertebrates. In sub-section 3.2, this provisional list of key species is used to produce a list of key habitat features for invertebrates at Wentlooge Level. Key habitats are defined here as being those that support at least one of the key species identified in sub-section 3.1. The emboldened status categories given in the table and after the species name in sub- section 3.2 refer to those invertebrates that have a formal rarity/threat status ascribed to them by the UK government conservation agencies. These are defined as follows: S7 – Species of Principal Importance for the conservation of biodiversity in Wales. These are listed in Section 7 of the Environment (Wales) Act 2016. RDB2 – UK Red Data Book Category 2 – Vulnerable. Taxa which are known from 15 or fewer 10 km squares of the National Grid (hectads) and which are decreasing and will become endangered in the near future if the causal factors continue operating. NT – IUCN Near Threatened. A taxon is Near Threatened when it has been evaluated against the IUCN criteria and does not currently qualify for Critically Endangered, Endangered or Vulnerable status, but is close to qualifying, or is likely to do so soon. Nb. – Nationally Scarce Category B. Taxa thought to occur in between 30 and 100 hectads. This and the Na category have been subsumed into a single NS category in second status reviews. NS. – Nationally Scarce. In second status reviews, the Na and Nb sub-divisions have been subsumed into a single category covering species occurring in 16 to 100 hectads. Unlike the previous ‘N’ category, which covered the same range, this amalgamation does not necessarily result from inadequate information on the British distribution. Table 3.1. Checklist of invertebrates recorded at Wentlooge Level, 2019 Species scientific name Species English name Status Survey units Bithynia tentaculata Common Bithynia AQ1,3,4,5,7 Valvata piscinalis Common valve snail AQ4 Valvata cristata Flat valve snail AQ4 Deroceras laeve Marsh slug AQ4 Arion ater Large black slug C2 Arion subfuscus agg.