Stream invertebrate populations: do they vary more across time or across space?

Posted on December 28, 2013

Understanding how aquatic invertebrate communities vary across time and space can be critical to the success of stream biomonitoring and restoration programs.  However, at present most available information relates to  invertebrate assemblages of rivers and lowland streams, very few studies having been done on headwaters.  To address this imbalance, benthic invertebrate surveys were carried out in Haduvka Brook, a headwater woodland stream in the Czech-Moravian highlands.  Six different stream mesohabitats were sampled monthly for a year using a Hess stream bottom sampler with a 100 μm mesh.  Multivariate (principal component) data analysis revealed two main environmental gradients, which were related to (a) the amount of coarse organic matter (including woody debris and leaf litter) and (b) hydraulic conditions, as indicated by substrate grain size.  The two gradients respectively explained 42 and 36% of the variance in the environmental data.  The two gradients and the time of year (month of sampling) were then used to predict invertebrate abundance.  In this analysis, the amount of coarse organic matter, but not the hydraulic gradient, was  significant.  When different functional groups (shredders, gatherers/collectors and grazers) were examined separately, the abundances of all of them varied with the amount of coarse organic matter, which therefore seemed to be important as a general source of habitat space for invertebrates, as well as a food source for shredders.  Invertebrate abundances also varied significantly with the time of year, but the amount of variation explained by time was only half that explained by spatial gradients.  Time patterns were also inconsistent, perhaps because a number of different factors, such as temperature, light, disturbance and species interactions, can affect seasonal abundance.  Therefore, in this study local habitat variation was more important than seasonal dynamics in its influence on biological diversity.

Reference:   Straka, M., Syrovatka, V., Helesic, J.  2012.   Temporal and spatial macroinvertebrate variance compared: crucial role of CPOM in a headwater stream.  Hydrobiologia 686, 119–134.