Assessment Rationale:

Pisaura acoreensis is an Azorean-endemic nursery web spider species that occurs on eight islands of the Azorean archipelago (Azores, Portugal) (only absent in Corvo) (Borges et al. 2010). It has a relatively large Extent of Occurrence (EOO = ca. 40,514 km²) and a small Area of Occupancy (AOO = 228-336 km²). The species is only abundant in very pristine sites (e.g. sites with a high habitat quality index sensu Gaspar et al. 2011) and is rare in most sites. Currently an invasive plant, Hedychium gardnerianum, is impacting some of the areas where the species occurs, decreasing the quality of the habitat. Based on Ferreira et al. (2016) the habitat will further decline as a consequence of climate change. Based upon the relatively small AOO of the species and continuing decline of its habitat area and quality, it is assessed as Near Threatened (NT). We suggest as future measures of conservation: (1) regular monitoring of the species; and (2) control of invasive species namely Hedychium gardnerianum.

Geographic Range:

Pisaura acoreensis is a nursery web spider species that occurs on eight islands of the Azorean archipelago (Azores, Portugal) (only absent on Corvo) (Borges et al. 2010). Within these eight islands it is known from seventeen Natural Forest Reserves: Caldeiras Funda e Rasa and Morro Alto e Pico da Sé (Natural Park of Flores); Caldeira do Faial and Cabeço do Fogo (Natural Park of Faial); Mistério da Prainha, Caveiro and Caiado (Natural Park of Pico); Pico Pinheiro and Topo (Natural Park of S. Jorge); Biscoito da Ferraria, Pico Galhardo, Caldeira Guilherme Moniz, Caldeira Sta. Bárbara e Mistérios Negros and Terra Brava (Natural Park of Terceira); Graminhais and Pico da Vara (Natural Park of S. Miguel) and Pico Alto (Natural Park of S. Maria). The Extent of Occurrence (EOO) is ca. 40,514 km2 and the Area of Occupancy (AOO) is 228-336 km2 .

Population:

The species is only abundant in very pristine sites (e.g. sites with a high habitat quality index sensu Gaspar et al. 2011) and is rare in most sites. Despite the fact that Pisaura acoreensis has been recorded between 340 and 1,092 m elevation, the species is particularly abundant only between 700 and 1,092 m. Many of the known sites are currently being invaded by invasive plants (e.g. Hedychium gardnerianum) or degraded by uncontrolled cattle trampling in some native shrub grasslands. A continuing decline in the number of mature individuals is inferred from monitoring schemes (Borges et al. 2016) and from the ongoing habitat degradation. Current Population Trend: Decreasing.

Habitat and Ecology

Despite the fact that this species has been recorded between 340 and 1,092 m elevation, Pisaura acoreensis is particularly abundant only between 700 and 1,092 m in very pristine sites (see Gaspar et al. 2011). This species builds a typical nursery web in association with herbaceous vegetation and is particularly abundant in Calluna vulgaris. It is frequent in open spaces in forest, high elevation small patches of natural grasslands and bogs; and it is also possible to find it in the canopy of endemic trees. Systems: Terrestrial.

Major Threat(s):

Currently, the rapid advance and expansion of invasive plants species is the major threat (particularly Hedychium gardnerianum), which is leading to a change in the structure of the forest and natural grasslands and the cover of bryophytes and ferns in the soil, which impact the species' habitat quality. Ongoing soil erosion due to trampling by dairy cattle (cattle are entering the native areas in Flores, Pico and S. Jorge island without control by the Conservation Managers) is another threat. Based on Ferreira et al. (2016) the habitat will further decline as a consequence of climate change (increasing number of droughts and habitat shifting and alteration). 

Conservation Actions

The species is not protected by regional law, but its habitat is in regionally protected areas (Natural Parks of Faial, Flores, Pico, S. Jorge, Terceira, S. Miguel and S. Maria). Degraded habitats on some islands, degraded due to invasive plant species, should be restored (e.g. S. Maria) and a strategy needs to be developed to address the current threat posed by invasive species on all islands as well as the future threat from climate change. The management of cows entering native areas in some islands is also critical. A habitat management plan is needed and one is anticipated to be developed during the coming years. Formal education and awareness is needed to allow future investments in restored habitats invaded by invasive plants; while further research is needed into its ecology and life history in order to obtain adequate information on population size, distribution and trends. An area-based management plan is also necessary for the most disturbed sites including invertebrate monitoring to contribute to a potential species recovery plan. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2011).