Data from: Invertebrate biodiversity in cold groundwater fissures in Iceland

Iceland has an abundance of fissures that are parallel to the Mid-Atlantic
ridge where bedrock cracks as a result of continental rifting. Some
fissures penetrate the aquifer and expose the groundwater within the
bedrock, becoming springs. As such, groundwater fissures have uniform and
constant physical and chemical environment but they can differ greatly in
morphology. In addition, there is often great variation in depth within
fissures and substrate types contrast between vertical rock wall and more
heterogenous horizontal bottom. The variation in morphological environment
may create dissimilar habitats with unique characteristics and/or
influence distribution of resources. Our objective was to study
macrozoobenthos communities in cold groundwater fissures in Iceland in
relation to physical habitat by comparing invertebrate diversity and
density both between fissures with different morphological characteristics
as well as between substrate types and depths within fissures. Samples
were collected in two fissures in SW Iceland, Silfra and Flosagjá.
Assemblages were similar between fissures except for higher densities of
cladocerans in Flosagjá fissure. Within fissures, there was significant
difference in Shannon diversity between substrate types in Flosgjá and
ostracods were found in significantly higher densities on bottom. The
distribution of all other taxa groups was homogenous in both fissures
regardless of depth gradient and substrate. Invertebrates were found to be
living within and around a biofilm that covered the entire substrate.
These biofilm mats are made from Cyanobacteria and benthic diatoms, which
are successful under low light conditions and may minimize any effect of
the heterogeneous habitat creating a uniform and suitable microhabitat for
invertebrates regardless of depth and substrate type.