Earthquake impacts on microcrustacean communities inhabiting groundwater-fed springs alter species-abundance distribution patterns

Abstract

Earthquakes are important natural events, yet their impacts on animal communities are poorly known. Understanding earthquake impacts on groundwater communities is essential to assess their resilience and hence to perform conservation actions. We investigated how a 6.3 M_w earthquake that occurred in 2009 altered the community structure (diversity, evenness, dominance, species abundance distributions and beta-diversity) of microcrustaceans (Crustacea Copepoda) inhabiting springs fed by the Gran Sasso Aquifer (Central Italy). Sampling was done in low-discharge (1997), high-discharge (2005), and post-seismic (2012) hydrological years. Stygobites (obligate groundwater species) and non-stygobites (non-obligate groundwater species) showed different patterns. A high-water discharge in 2005 altered abundance patterns of non-stygobites. The earthquake re-established former abundance patterns. Stygobites were less affected by high-water discharge in 2005, and showed strong increases in diversity and evenness after the earthquake. This effect was due to the fact that the earthquake induced a strong population decline of previously dominant stygobites (especially of Nitocrella pescei) in the aquifer, and subsequently at the main spring outlets, thus allowing a more equitable species-abundance distribution. These results highlight the importance of considering species ecology to understand the effects of a significant earthquake event on animal communities.

Figure 1

Rank-abundance distribution of the copepods of Tirino Springs (Central Italy) in pre-seismic (1997, grey diamonds; 2005, black squares) and post-seismic (2012, red dots) years. Panel a: comparison for all species. Regression statistics for the 1997 pre-seismic community: log(abundance) = (−0.122 ± 0.004) × rank + (2.479 ± 0.044), R² = 0.984, F_1,19 = 1190.221, P < 0.0001. Regression statistics for the 2005 pre-seismic community: log(abundance) = (−0.144 ± 0.004) × rank + (3.026 ± 0.045), R² = 0.988, F_1,19 = 1593.945, P < 0.0001. Regression statistics for the post-seismic community: log(abundance) = (−0.119 ± 0.007) × rank + (2.478 ± 0.081), R² = 0.941, F_1,17 = 255.883, P < 0.0001. The 1997 community followed the lognormal series series but was modelled here for comparative purposes. Panel b: comparison for non-stygobites. Regression statistics for the 1997 pre-seismic community: log(abundance) = (−0.201 ± 0.013) × rank + (2.433 ± 0.094), R² = 0.961, F_1,10 = 245.442, P < 0.0001. Regression statistics for the 2005 pre-seismic community: log(abundance) = (−0.205 ± 0.010) × rank + (2.998 ± 0.076), R² = 0.977, F_1,11 = 461.579, P < 0.0001. Regression statistics for the post-seismic community: log(abundance) = (−0.175 ± 0.015) × rank + (2.573 ± 0.100), R² = 0.940, F_1,9 = 141.585, P < 0.0001. Panel c: comparison for stygobites. Regression statistics for the 1997 pre-seismic community: log(abundance) = (−0.299 ± 0.023) × rank + (2.654 ± 0.127), R² = 0.961, F_1,8 = 174.495, P < 0.0001. Regression statistics for the 2005 pre-seismic community: log(abundance) = (−0.422 ± 0.033) × rank + (3.161 ± 0.165), R² = 0.965, F_1,6 = 166.370, P < 0.0001. Regression statistics for the post-seismic community: log(abundance) = (−0.307 ± 0.039) × rank + (2.292 ± 0.173), R² = 0.926, F_1,5 = 62.997, P = 0.0005. In all cases, errors refer to standard errors.