An introduction to invertebrate surveying
Invertebrates are hugely significant within the ecosystem globally, as they form the basis level of many food chains. Without invertebrates, the trophic levels above would ultimately suffer and then collapse, leading to trophic cascades and ecosystem collapse. Immense pressure is building upon invertebrates, primarily driven by global agricultural intensification, habitat loss and the likely prospect that global average temperatures will rise above 1.5 degrees in the coming decades and get to 2 degrees by the end of the century. Invertebrate populations across many biomes are drastically declining, thus highlighting the need for active surveying of invertebrate populations within a range of habitats. The implementation of habitat management strategies to aid ecosystem resilience to global warming is of high importance.
The study: an overview
A new project that is being led by the Sanger Institute aims to study the genetic diversity of 1,000,000 flying insects found within the UK. We at Natural England are aiding in the collection of data for this study, through the sampling of invertebrates present in one of our woodland sites, Yarner Wood. To successfully catch these invertebrates, a malaise trap is placed in the woodland and left overnight, giving sufficient time for flying invertebrates to be caught. This trap is then emptied after 24 hours, and invertebrates are bought back to the lab for identification. Following identification, these invertebrates are then placed into plates and sent to the Sanger Institute, so that their genome can be analysed through DNA barcoding.
In the Lab at Natural England
Invertebrates from the malaise trap are fairly distributed between the surveyors. The invertebrates are studied individually to identify each one to order level, and where possible, a lower taxonomic rank. This is achieved by placing the invertebrate into a plastic dish with a few drops of phosphate buffered saline (PBS) so the specimen can float. The plastic tray is then placed under a microscope so that analysis can begin (Figure 1).
Figure 1. The lab at Natural England picturing one of our work stations (left) and some organisms from the malaise trap, which have been taxonomically grouped in a plastic tray after microscopic analysis (Images by Isabel Almond).
To be able to narrow down the invertebrate’s taxonomic rank, specific detail must be identified. For example, to identify an invertebrate as a ‘True Fly’ (Order: Diptera), we know that ‘halteres’ should be present, which are small, club-like features on the body of Diptera. These halteres evolved from a pair of ancestral hindwings. Many of the invertebrates that have been processed at Yarner Wood have fallen into the orders Diptera, Hymenoptera or Collembola (Figure 2).
Figure 2. Images taken through the microscope, picturing a springtail within the order Collembola (left), and flies within the order Diptera (Images by Isabel Almond).
However, we also found the occasional beetle, which fall into the taxonomic group Coleoptera
|Figure 3. A soldier beetle, Malthinus seriepunctatus under the microscope at the Natural England lab (Image by Isabel Almond).|
The Bioscan project aims to conduct DNA analysis of the specimens collected from the 100 sample sites from around the UK. The technique employed involves placing either the whole specimen, or a body part of the specimen, into a specifically manufactured tray (Figure 4). Upon placing the individual specimen into a tube, the invertebrate’s order is recorded in an excel spreadsheet, along with the unique code of the tube that it has been placed in. These trays are then sent off for further analysis in the laboratory at the Sanger Institute to determine the invertebrate down to species level, which is achieved by using this PCR barcode technique.
In addition to this, BIOSCAN is also developing a ‘mini-barcoding panel’ that will be dedicated to using techniques that aim to reveal external information about the invertebrates collected. This includes information such as the plants they pollinate, the type of parasites that they have come into contact with and the invertebrate’s diets.
Figure 4. Plastic tray containing individual specimens to be sent off for DNA barcoding. Each tube is identified by having a unique letter and number combination (Image by Oliver Pitts).
Afternoon activities with Natural England
During a busy morning identifying our invertebrates caught in the most recent malaise trap, two of our team members, Albert Knott (Natural England’s Reserves Manager Dartmoor NNRs) and Pete Boardman (Natural England Evidence Team), were busy sweep netting within a variety of habitat types: All pictures taken by Albert Knott.
- H1: Mire with pools and bog myrtle
- H2: Hedgerow and field
- H3: Mire of wet heath with sphagnum, cottongrass, bog asphodel and heather
- H4: Wet woodland
- H5: Splayed river edge
We then had the pleasure of seeing how the abundance and diversity of invertebrates changed with these vastly different habitat types. Each team member took on a different habitat, with some finding hugely different results! Here is a brief summary of how our invertebrates differed.
- Despite H1 being characterised by pools, there were also slightly higher drier areas, as well as low and open, and low and bushy areas consisted of bog myrtle. This made the habitat ideal for a range of Diptera, with smaller flies using the pool edges, and larger hoverflies and crane flies passing through. A variety of Hemiptera were also present, alongside some common Arachnaea, such as orb and raft spiders.
- Invertebrates found in the dry hedgerow and field habitat (H2) were predominantly made up of Orthoptera, whilst also containing a big variety of Diptera. Hemiptera, Lepidoptera and Coleoptera were also present.
- H3 was similarly comprised of Orthoptera, majoritively bush crickets. Raft spiders and leaf hoppers were also present, and one member of the team found a larval tortoise bug.
- The wet woodland of H4 was characterised by three structural layers. Firstly, a range of older trees, underneath these the ground flora was comprised of a range of grasses and rushes, then finally a wet ground layer. This structural diversity meant that this habitat was home to a range of Diptera, especially craneflies, which thrive in these ideal conditions of still water sitting underneath the grasses. Also present were harvestmen within the order Opiliones, and finally a range of Araneae.
- Analysis of H5 was interesting, as this habitat of splayed river edge was very similar to that of the malaise trap site used in the Sanger Institute study. The results showed majoritively Diptera, some moths in Lepidoptera and again, a range of Aranaea. These groups were all found in the initial malaise trap too, showing a similar group composition to those invertebrates sent away to the Sanger Institute.
Authors: Isabel Almond and Oliver Pitts
Conservation & Access Trainees
Dartmoor National Park Authority