Life at the extreme: meiofauna from three unexplored lakes in the caldera of the Cerro Azul volcano, Galápagos Islands, Ecuador

Abstract

On Isla Isabela, Galápagos Archipelago, three so far unexplored lakes were investigated in the caldera of Cerro Azul, one of the most active volcanoes in the world. The lakes face recurrent desiccation and eruption events and showed distinct differences in their water chemistry. Thirty cores from the upper 15 cm of sediment indicate distinct differences in the composition of meiobenthic communities between the lakes. In total, 27 different aquatic metazoan species could be distinguished. Numerically, rotifers dominated in two of the lakes, with mean densities up to 4.56 9 10 6 individuals m -2 while the third lake was dominated by a gastrotrich of the genus Chaetonotus (0.67 9 10 6 individuals m -2 ). The largest lake harboured up to 14.4 9 10 6 nematodes m -2 , which is the highest nematode density thus far reported for a freshwater habitat. The lakes yielded few nematode species (S = 7, N = 887) and calculation of the ShannonWiener index (H 0 ) indicated an exceptionally low nematode diversity. The nematode community of one lake was clearly dominated by an undescribed suction-feeding Mesodorylaimus (59.6%), the community of the other lake by the epistrate feeder Achromadora pseudomicoletzkyi (89.3%), whereas the third lake surprisingly contained no nematodes.The benthic nematode biomasses for the two nematode-containing lakes differed by a factor 50. The food webs of the three lakes are presumed to have an exceptionable simply structure.

Meio- and Macrofaunal Communities in Artificial Water-Filled Tree Holes: Effects of Seasonality, Physical and Chemical Parameters, and Availability of Food Resources

“…In our study, the high densities of rotifers, up to 56 million individuals m −2 (mean 20 millions m −2 ), shows that the artificial tree holes can be quickly colonized by rotifers, but based on densities up to 5.8 million m −2 , nematodes can also be considered as good colonizers. In fact, only in the periphyton of three Swedish lakes, in the sediment of the volcanic lake in Galapagos, and in the sediment of Lake Constance were a greater number of nematodes recorded [ 10 , 45 , 46 ].…”

Nematode distributions as spatial null models for macroinvertebrate species richness across environmental gradients: A case from mountain lakes

“…Furthermore, nematodes can also be transported by birds in their gut contents (Frisch, Green, & Figuerola, 2007), which indicates the importance of digestive-resistant forms of nematodes, as suggested by Jacobs (1984). In fact, the most likely hypothesis for the presence of cosmopolitan freshwater nematode species in the Galápagos Islands is through very occasional bird-mediated transport (Abebe & Coomans, 1995;Muschiol & Traunspurger, 2009 Jacobs, 1984;Michiels & Traunspurger, 2005). Therefore, we suggest that the potential of nematode species richness distribution as a null model for the species richness of other invertebrates could be tested across other gradients, biogeographic regions, and ecosystem types, in future research comparisons between different organismal groups.…”

“…Furthermore, nematodes can also be transported by birds in their gut contents (Frisch, Green, & Figuerola, ), which indicates the importance of digestive‐resistant forms of nematodes, as suggested by Jacobs (). In fact, the most likely hypothesis for the presence of cosmopolitan freshwater nematode species in the Galápagos Islands is through very occasional bird‐mediated transport (Abebe & Coomans, ; Muschiol & Traunspurger, ). Overall, even if carried by active flyers, dispersal dynamics is, from the nematode perspective, passive, and fundamentally stochastic, which is important to understand the relevance of spatial factors in shaping biodiversity patterns.…”

Cosmopolitism and endemism in free-living nematodes

“…A very peculiar isolated situation is the freshwater environment inside an oceanic island. Such a case was studied by Eyualem-Abebe and Coomans (1995) and Muschiol and Traunspurger (2009): they found in the islands Floreana, San Cristobal and Isabela (Galápagos) a total of 25 freshwater nematode species, but only three of them (12%) were presumably endemic. The other species were cosmopolitan or already known to the Southern hemisphere.…”

“…This is in contrast with the other animals of this archipelago where 30-80% are endemic (depending on the species group). The authors summarized the problematic of defining endemism in nematodes highlighting that "the South American nematode fauna is insufficiently known" and that "the existence of cryptic species […] can be difficult to detect solely on morphological characters" (Muschiol and Traunspurger 2009). Other instances of lacustrine environments where one would expect to find endemic species are still existing ancient (Tertiary) lakes with Lake Baikal being the most ancient (30 million years old for the cuvette, and 6 million years old for the hypolimnion) and deepest (1642 m).…”