Merolimnic vs. hololimnic insects: spatio-temporal inconsistency in linking species populations to sampling locations

Introduction:

The present study aimed to reveal the complexity of the spatio-temporal population dynamics of merolimnic and hololimnic insect species in terms of sampling site precision relevant to aquatic macroinvertebrate community metrics used for ecological status assessment/potential assessment of certain waterbodies.

Methods:

Aquatic insect taxa were identified in the laboratory, together with other taxa from composite macroinvertebrate samples collected using the AQEM protocol (AQEM, 2002) covering all microhabitats with at least 5% distribution at the sampling site during Annual Water Quality Monitoring Programmes conducted by the Hydrometeorological Service of Serbia (2009 and 2010) and the Serbian Environmental Protection Agency (2011-2023), resulting in approx. 1700 samples in total.

Results:

Data on aquatic insect taxa collected during a 15-year period (2009-2023) revealed the difficulties in determining the sampling locations of both insect groups. These difficulties can be attributed to the species’ complex annual spatio-temporal variability in population dynamics, comprising cumulative effects of intrinsic (insect behavior, age, and life history traits) and extrinsic factors (primarily microhabitat conditions and heterogeneity).

Conclusions:

Based on the data obtained, it was concluded that the merolimnic insect life cycle is seasonally dependent. The duration of the stage periods varied from year to year, particularly in light of recent climate change. Due to active dispersion, they can reach the most suitable stretches for their emergence.

On the other hand, hololimnic insect species spend their whole life cycle in the water and can only disperse via drift, active swimming, or phoresy (Li et al, 2016), but some aquatic beetle species have flying adults (macropterous forms) and disperse in the ways mentioned above. They can also have mixed populations consisting of both forms (including brachypterous forms).

Both insect group species can be passively carried by heavy rainfall and torrents in downstream stretches, which is also a problem for the determination of their precise sampling location.