Key Findings

• Arthropod species diversity generally decreases with increasing latitude, although the extent varies between regions. Moreover, the fauna is extremely habitat-specific and changes in habitat characteristics impact the occurrence of species. The extent of cryptic and genetic diversity is poorly known.
• Arthropod communities are highly variable in both time and space.
• The key role of arthropods is identified in connecting trophic levels, for example decomposers release nutrients enabling plant growth and herbivorous arthropods on these plants acting as prey items for parasitoids and vertebrates.
• The considerable gaps in our knowledge of Arctic arthropods make drawing conclusions concerning long-term changes particularly challenging. Long-term monitoring is largely lacking. Large interannual population variations amongst arthropods can mask general trends. Responses of arthropods are often very site specific which precludes generalisations of the response of arthropods to environmental change and again highlights the requirement for longer-term data and greater geographical representation.
• Complicated links exist between the FECs. Few arthropod species can be categorised in only one FEC, for example flies which may also act as pollinators, herbivores, food for vertebrates and hosts for parasitoids.
• Variable and contradictory responses are seen for many groups when time series data does exist. Significant declines in several species of fly were documented with 80% decreases in abundance in some habitats, including among important pollinator species. By contrast, a major group of decomposer arthropods, the springtails (Collembola), showed overall increases in abundance yet declines in diversity in some habitats in Kobbefjord. The Nordic Moth Monitoring Scheme time series data indicate that changes in species richness and abundance vary significantly depending on location and demonstrate the spatial and annual variation that is typical for many groups of arthropods.
• The declines, or changes, in arthropod abundance, activity and diversity observed are resulting in an increased phenological mismatch with other trophic levels and with potential consequences for other species groups, for example, their role in pollination services or as prey items for breeding birds with hard to predict consequences.

Monitoring Advice

Arthropods are highly diverse and under-studied. They serve as important connections between trophic levels and several are important indicators of changing environments. The START reports on six FECs: pollinators, decomposers, herbivores, prey for vertebrates, blood-feeding insects, and predators and parasitoids. Only a few localized trends are provided due to high variability and lack of monitoring.

• Implement long-term sampling programs at strategic sites with rigorous standardized trapping protocols.
• Collect baseline data, including structured inventories, using standardized protocols for FECs and key attributes.
• Work with Indigenous Knowledge holders, Local Knowledge holders, and/or citizen science to identify regionally important species to monitor, and key locations for long-term monitoring activities.
• Focus monitoring efforts on taxa that: (a) are well-studied with existing data; (b) respond to, or are vulnerable to, change; and/or (c) have possible range shifts.
• Monitor dominant habitats at a variety of sites at both small and large geographic scales.
• Monitor relevant microhabitat environmental parameters, in addition to climatological variables, and connect to biological trends at relevant scale.
• Focus on critical FEC attributes, including ecosystem processes such as pollination, decomposition, and herbivory.
• Continue specimen sorting, identification and reporting and construct a complete trait database.
• Complete molecular sequence libraries, increase international collaboration to collate, analyze, archive, and make data accessible. 

Conceptual model of the FECs and processes mediated by more than 2,500 species of Arctic arthropods known from Greenland, Iceland, Svalbard, and Jan Mayen.

The number of species in each FEC for the North Atlantic region of the Arctic (circular outline) and the overlap between the CBMP–Terrestrial Plan FECs. The link width indicates the number of species linking two FECs. The larger the link the more species that are found in linking FECs.