IUCN SSC Mid-Atlantic Island Invertebrates Specialist Group


BackHydroporus guernei Régimbart, 1891

Hydroporus guernei Régimbart, 1891

Predacious diving beetle (English); Aguadeiro (Portuguese)

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Coleoptera
  • Family: Dytiscidae
EN Endangered
IUCN Red List Status:

Countries of Occurrence:
Portugal - Azores


Danielczak, A.


Facilitators / Compilers/s:

Assessment Rationale:

Hydroporus guernei is an endemic species present in Flores, Faial, Pico, S. Jorge, Terceira, S. Miguel and Sta. Maria islands (Azores, Portugal). It has a large extent of occurrence (EOO = ca. 33,600 km²) and small area of occupancy (AOO = 156 km²). The species is common and known from at least 19 locations comprehending seven fragmented subpopulations. In the past, the species has probably strongly declined due to changes in habitat size and quality. The main threat to this species is the impact of introduced species and the agricultural activities (landscape transformation, pollution, habitat destruction). Based on Ferreira et al. (2016) the habitat will further decline as a consequence of climate change (increasing number of droughts). Based upon the small area of occupancy and associated decline in extent of occurrence, area of occupancy and habitat quality it is assessed as Endangered.

Geographic Range:

Hydroporus guernei is an endemic species present in Flores, Faial, Pico, S. Jorge, Terceira, S. Miguel and Sta. Maria islands (Azores, Portugal) (Borges et al. 2010), known from Natural Forest Reserves of Morro Alto and Pico da Sé (Flores); Caldeira do Faial (Faial); Lagoa do Caiado (Pico); Caldeira Sta. Bárbara e Mistérios Negros e Mistérios Negros and Terra Brava (Terceira). The extent of occurrence (EOO) is ca 33,600 km² and the maximum estimated area of occupancy (AOO) is 156 km².

Portugal - Azores
Extent of Occurrence (EOO):
33600 (km2)
Area of Occupancy (AOO):
156 (km2)
Elevation Lower Limit:
200 (m)
Elevation Upper Limit:
1200 (m)
Biogeographic Realms:
Endemic Azores


The species is rare in all known subpopulations in freshwater areas in several islands (Flores, Faial, Pico S. Jorge,Terceira, S. Miguel and Sta. Maria islands). A continuing decline in the number of mature individuals is inferred from the ongoing habitat degradation due to human activities (habitat transformation associated to agricultural activities and cattle pollution) and introduced species (particularly introduced fishes) (Florencio and Lamelas-López 2016). This species is assessed here as severely fragmented as at least 50% of its population can be found in subpopulations that are 1) smaller than would be required to support a viable population, and 2) separated from other habitat patches by a large distance. In fact, the species occurs in fragments that are isolated in a matrix of pastures.

Habitat and Ecology

The species occurs in freshwater habitats (mainly freshwater ponds) located in native forests of Flores, Faial, Pico, S. Jorge, Terceira, S. Miguel and Sta. Maria islands (Azores), with an altitudinal range between 200 and 1200 m. H. guernei also can inhabit artificial environments like artificial water tanks (Svensson 1977, Florencio and Lamelas-López 2016). Adults and larvae are nocturnal predators that lives in the water column of freshwater systems.

Major Threat(s):

The main threat to this species are the impact of introduced species (Gambusia holbrooki) and the agricultural activities (landscape transformation, pollution by herbicides and pesticides and nutrient loads, habitat destruction). However, we may add to these the impact of climatic changes with major impact on habitat shifting & alteration and droughts (Ferreira et al. 2016).

Conservation Actions

The species is not protected by regional law. Its habitat is in regionally protected areas (Natural Parks of Flores, Faial, Pico, S. Jorge and Terceira). Degraded habitats should be restored and a strategy needs to be developed to address the future threat by climate change. Further research is needed into its ecology and life history in order to find extant specimens. It is necessary a monitoring plan for the invertebrate community in the habitat in order to contribute to the conservation of this species. A habitat management plan is needed and anticipated to be developed during the coming years. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2010).