A spider survey in a protected area of La Palma (Canary Islands, Spain) reveals five new records for the island

Abstract. During a survey of spiders in the protected area of Montaña de La Breña (La Palma, Canary Islands), a total of 54 species from 24 families were recorded. Porrhoclubiona minor, Leptodrassus albidus, Macarophaeus varius, Silhouettella loricatula and Ballus chalybeius are reported for the first time for La Palma.

The Canary Islands are an archipelago of volcanic origin located off northwest Africa, comprising seven major islands. The second-highest island, La Palma, is 1.77 million years old and comprises two large volcanoes; the extinct northern shield volcano and the southern volcanic ridge, the most active volcanic region in the Canaries (Troll & Carracedo 2016). Due to its height, in this island five main vegetation belts are present; spurge scrub (0-200 m of altitude), thermo-sclerophyllous woodland (200-500 m), laurel forest (500-1200 m), pine forest (1200-1900) and summit broom scrub (above 1900 m) (Garzón-Machado et al. 2013). Among them, laurel forest may be one of the most interesting ecosystems because, as for most taxa, in this ecosystem spider richness reaches its maximum (Suárez 2018). In La Palma, there are well preserved laurel forest areas in the northeast as well as some relicts at mid-altitudes in the southeast.
Among the more than 500 spider species that have been reported for the Canary Islands, 127 can be found at La Palma (Suárez 2018, Bellvert 2018. However, distribution patterns within the island remain unknown as there are many localities with just few species recorded and even gaps without any single record (empty quadrats in Fig 1a). This poorly understood distribution, usually called 'Wallacean shortfall', is important as the lack of knowledge is a problem in conservation biology when making practical decisions (Bini et al. 2006), especially in protected areas. For this reason, in this article a spider survey in the protected area of Montaña de la Breña (Fig 1b) has been conducted in order to increase the known distribution of the spider species of the island. In this protected area, four species have been previously reported; Nigma tuberosa Wunderlich, 1987 (Dictynidae), Oecobius palmensis Wunderlich, 1987 (Oecobiidae), Pholcus ornatus Bösenberg, 1895 (Pholcidae) and Lasaeola striata (Wunderlich, 1987) (Theridiidae) (Gobierno de Canarias 2018).

Material and methods
The study site, Montaña de la Breña (Protected Area Code: ES7020072), is a Special Area of Conservation of the Natura 2000 Network with a surface of 26.15 ha located in the southeast of the island at an altitude of 565 m. This old tephritic volcanic cone is covered mainly by a dry laurel forest while on the southern slope there is a canary pine (Pinus canariensis) plantation as well as a nitrophilous shrubby community of Artemisia thuscula and Rumex lunaria (García et al. 2018). The study area was divided into four sectors, matching with the 500 m × 500 m quadrats used in the Canary Biodiversity Da-taBase (Gobierno de Canarias 2018). The coordinates of the centres of the four sectors are 28.6342ºN/17.7826ºW (Sector 1), 28.6340ºN/17.7806ºW (Sector 2), 28.6326ºN/17.7813ºW (Sector 3) and 28.6325ºN/17.7825ºW (Sector 4).
Sampling was conducted between November 2014 and January 2015 (three days; 14 hours of sampling effort) and between November 2018 and January 2019 (two days; 4 hours of sampling effort), applying several collecting methods, following the COBRA protocol (Cardoso et al. 2009), such as active aerial searching (AAS), litter sifting (LIT), beating (BET), sweeping (SWE), ground and wood searching (GWS) and pitfall trapping (PIT). Active collecting methods (AAS, BET, SWE and GWS) were conducted during an hour per plot and per date. A grid of 48 non-baited pitfall traps were laid, filled with propylene glycol and retired after two weeks. Regarding sifting, a total number of 6 samples of 2 m 2 of leaves litter were obtained with a Winkler sieve. Then, spiders were extracted from those samples with the Berlese funnel method. The habitats were not documented. All specimens are preserved in 70 % ethanol and deposited in the collection of the first author. Global distribution data were taken from the World Spider Catalog (2018).

Results
A total number of 430 individuals (undeterminable juveniles excluded) were collected, belonging to 54 species of 24 different families. Regarding richness per quadrat, both Sectors 1 and 4 harboured up to 23 species, while in Sectors 2 and 3, 36 and 34 species were found, respectively (Tab. 1).

Dictynidae
Lathys dentichelis (Simon, 1883) Determination. Wunderlich (1992 (Wunderlich, 1987), epigyne in ventral view; b. Porrhoclubiona minor (Wunderlich, 1987), male palp in prolateral and retrolateral view; c. of species for La Palma to 132. Regarding the study site, 51 species have been newly reported for this protected area. Moreover, Sectors 2 and 3 are, with this new information, among the richest 500 m × 500 m quadrats of La Palma. Sector 1 and 4 were the ones where the least richness was found, mainly because the sampling area was lower than in Sector 2 and 3. The sampling methods which recovered the higher species abundance was foliage beating (131 individuals), followed by vegetation sweeping (120 individuals). However, the higher richness was recovered by sifting, with 27 species. Twenty species were collected just with one type of sampling method, which points the importance of applying several methods to potentially survey every single niche. A total of 160 females (37.2 %) and 70 males (16.0 %) was collected, thus indicating that more than half of the specimens were adults. Neoscona crucifera, an introduced species, was the most abundant one with 38 individuals. It was followed by Kochiura aulica (36 specimens), Porrhoclubiona minor (30) and Oxyopes kraepelinorum (28). All of these species were collected all four plots. The most abundant species that was collected in just one plot was Minicia gomerae, with 11 individuals just in the Sector 3. In contrast, 11 species were represented by just one individual. It is noticeably that almost 50 % of the species collected (29 species) were Macaronesian endemics, which indicates the high level of endemicity of the spider assemblages in laurel forest areas. Also, they were more abundant (207 individuals) than introduced species (61). In general, introduced species were more linked to the nitrophilous community than to the laurel forest, but some individuals were collected in the more preserved areas. As Montaña de la Breña is a narrow laurel forest relict, even a higher richness should be expected in the wider and more humid laurel forests of the north of La Palma.
A similar research was carried out by the first author in the same area following the same protocol (García et al. 2018) and obtained 839 specimens of 102 beetle species, almost double the number of spiders in this study, but the proportion of endemic species was the same for both groups. This pattern is rather common in the Canary Islands; beetles seem to be much more diverse and abundant than spiders as was shown by Hernández-Teixidor et al. (2009, 2011 in malpaís de La Rasca (Tenerife) and by Oromí et al. (2003) and Macías et al. (2004) on the islet of Montaña Clara, both conducted in sweet spurge shrubs. In this study, the family Theridiidae was the one with the highest richness (10 species) while in Hernández-Teixidor et al. (2011) and Macías et al. (2004), that family only recovered four and three species, respectively. Also, in those studies the number of Salticidae and Gnaphosidae species was higher than in this study, thus indicating that species belonging to those families maybe more adapted to xeric conditions while Theridiidae species seem to prefer more humid areas.
Spider inventories in the Canary Islands are still necessary because the spider fauna is not well studied (Wunderlich 2011: 353) and chorological data is crucial to assess the conservation status of the endemic spider species. Moreover, if these surveys are repeated through time, reliable trends in distributional range and population size can be measured. Cardoso et al. (2017) suggested that most endemic spiders from Madeira are in a favourable situation as laurel forests are well preserved. As the spider assemblage in the Canary laurel forest highlights for its richness and endemicity, conservation efforts should be focused on the protection of this habitat in order to preserve its biota.