Spesbona angusta (Ceres Stream-damsel)

[Melly]

Discovery of two 'extinct' Western Cape insects may signal ecosystem's recovery



By Melanie Gosling

Two little Cape damselflies - thought to have been extinct and one of them last seen 83 years ago - have been rediscovered in the Western Cape.

The insects, related to dragonflies, are believed to have made a comeback because invasive alien vegetation on river banks and around wetlands is being hacked down.

And if damselflies are coming back, scientists say, there is a good chance that the ecosystem in which they were found is also recovering, as they and dragonflies are used as indicators of riverine integrity.

Stuart Taylor, a University of Stellenbosch entymologist, said the damselflies were spotted by a scientist near Franschhoek late last year.

"He alerted us as he thought he may have found those that were thought to be extinct. When we saw them, we knew immediately they were," he said.

The last recorded sighting of the Cape Bluet was in 1962 and the smaller Ceres Stream damselfly in 1920.

Despite intensive searches, they were not seen again until last year.

"We've had students working on dragonflies and damselflies for a number of years and there is a wealth of information they've collected that shows invasive alien vegetation is driving these insects to death," Taylor said.

"Almost all insects are affected by alien vegetation. The aliens acidify streams and this has a knock-on effect and changes many other aspects of the environment."

Dragonflies and damselflies had been collected for study because they were sensitive to change. The main effect of alien vegetation, particularly wattles, on damselflies, was that it cut out the sunlight over the ponds and wetlands where the insects lived.

"Damselflies and dragonflies won't fly unless there is sunlight. It is an energy thing," Taylor said.

It is only in flight that the insects mate, so if they don't fly, their numbers are reduced.

Insect populations have been reduced because much of their wetland habitat has been drained for other uses. Insects are having an increasingly difficult time finding areas in which to live and breed.

Taylor said it was clearly critical to continue removing alien vegetation, particularly around water courses.

"Clearly the Working for Water programme is having a positive effect. When we see the insects coming back, we know the environment is responding positively to this human intervention. It shows it is recovering.

"South Africa has a enormous biodiversity, but a lot of it is being lost."

The saving of any indigenous species "was a good thing".

Published on the web by Cape Times on July 7, 2004.

[Peter]

Taxonomy
Kingdom Phylum Class Order Family
Animalia Arthropoda Insecta Odonata Platycnemididae

Scientific Name: Spesbona angusta
Species Authority: (Selys, 1863)
Common Name(s):
English – Mauve Bluet, Ceres Stream-damsel, Ceres Featherlegs
Synonym(s):
Metacnemis angusta Selys, 1863
Taxonomic Source(s): Schorr, M. and Paulson, D. 2014. World Odonata List. Tacoma, Washington, USA Available at: www.pugetsound.edu/academics/academic-resources/slater-museum/biodiversity-resources/dragonflies/world-odonata-list2/. (Accessed: 17 February 2014).

Assessment Information
Red List Category & Criteria: Vulnerable D2 ver 3.1
Year Published: 2010
Date Assessed: 2007-04-01
Assessor(s): Samways, M.J.
Reviewer(s): Kipping, J., Simaika, J.P., Samways, M.J., Suhling, F. (Odonata Red List Authority) & Pollock, C.M. (IUCN Red List Unit)
Justification:
Metacnemis angusta is currently known from only one population, the species having been rediscovered in 2003 after previously being thought to be possibly extinct. Only one locality is known, which is not within a reserve area. Its known area of occupancy is less than 500 m², and there are conservation efforts underway to remove alien invasive trees in the area. Since the habitat in the area is not currently undergoing continuing decline, and it is also clear that an as yet undiscovered population must exist somewhere nearby to have been able to recolonise this locality, it is currently assessed as Vulnerable based on its restricted range. However, ongoing conservation efforts are required to prevent this species moving into a higher threatened category in the near future.
Previously published Red List assessments:
2007 – Vulnerable (VU)
1996 – Data Deficient (DD)
1994 – Indeterminate (I)
1990 – Indeterminate (I)
1988 – Indeterminate (I)
1986 – Indeterminate (I)

Geographic Range
Range Description: The species is endemic to the Western Cape, South Africa. Until recently, this species was thought to be possibly extinct, having not been recorded since 1920. However, it was rediscovered in December 2003 in Dutoitsrivier, near Villiersdorp (Samways and Tarboton 2006) at one site which had been restored through the removal of alien invasive trees.
Countries occurrence:
Native:
South Africa (Western Cape)
Estimated area of occupancy (AOO) - km2: 500
Number of Locations: 1
Range Map: Click here to open the map viewer and explore range.

Population
Population: Its current population size is not known, however it is possibly stable at present.
Current Population Trend: Stable
Additional data:
♦Population severely fragmented: No

Habitat and Ecology
Habitat and Ecology: Bush-fringed pools in river braids (Samways 2006 in press) with the water weed Aponogeton.
Systems: Terrestrial; Freshwater

Threats
Major Threat(s): The streams in the Ceres area (where it was recorded in 1920) have been radically transformed and indeed some no longer flow due to over-extraction of water for the fruit industry. Other threats come from shading of the habitat by alien invasive trees (Acacia mearnsii) and damming of streams. Alien fishes, especially the rainbow trout (Onycorhynchus mykiss), may also be a threat.
Conservation Actions [top]

Conservation Actions: Removal of riparian invasive alien plants is beneficial for this species. Currently it is known only from a site where alien invasive trees have been removed. Research into population numbers and range, and trends/monitoring of the species would be valuable.
 
Bibliography
IUCN. 2010. IUCN Red List of Threatened Species (ver. 2010.3). Available at: www.iucnredlist.org. (Accessed: 2 September 2010).
Pinhey, E. 1984. A survey to the dragonflies (Odonata) of South Africa. Part 1. Journal of the Entomological Society of southern Africa 47: 147-188.
Samways, M.J. 1999. Diversity and conservation status of South African dragonflies (Odonata). Odonatologica 28: 13-62.
Samways, M.J. 2002. A strategy for national red listing invertebrates based on experiences with Odonata in South Africa. African Entomology 10: 43-52.
Samways, M.J. 2004. Critical species of Odonata in southern Africa. International Journal of Odonatology 7: 255-262.
Samways, M.J. 2006. Honing Red List assessments of lesser known taxa in biodiversity hotspots. Biodiversity and Conservation 16(9): 2575-2586.
Samways, M.J. 2006. National Red List of South African Odonata. Odonatologica 35: 341-368.
Samways, M.J. and Tarboton, W. 2006. Rediscovery of Metacnemis angusta (Selys, 1863) in the Western Cape, South Africa (Zygoptera: Matycnemididae). Odonatologica: In press.
Samways, M.J. and Taylor, S. 2004. Impacts of invasive alien plants on red-listed South African dragonflies (Odonata). South African Journal of Science 100: 78-80.
Samways, M.J., Taylor, S. and Tarboton, W. 2005. Extinction reprieve following alien removal. Conservation Biology 19: 1329-1330.
Tarboton, W. and Tarboton, M. 2005. A fieldguide to the damselflies of South Africa. Privately published by the authors, Nylstroom.

Citation: Samways, M.J. 2010. Spesbona angusta. The IUCN Red List of Threatened Species 2010: e.T13257A3431878. dx.doi.org/10.2305/IUCN.UK.2010-3.RLTS.T13257A3431878.en. Downloaded on 23 November 2015.

[surroundx]

Samways, M. J. and Tarboton, W. (2006). Rediscovery of Metacnemis angusta (Selys) in the Western Cape, South Africa, with description of male and redescription of female (Zygoptera: Platycnemididae). Odonatologica 35(4): 401-404.