The swash zone selects functionally specialized assemblages of beach
interstitial meiofauna (Platyhelminthes, Proseriata)
Abstract
Life is not a beach for those animals that survive in the rough
ecological conditions found in marine sandy beaches—and yet,
microscopic animals thrive on them. We explore the drivers for
meiofaunal diversity in beaches by analysing taxonomic and functional
patterns of 348 flatworm communities across 116 reflective beaches in
the Western Mediterranean, totalling 152 species (61.2% new to
Science). First, we confirm that species richness does not differ
between beach hydrodynamic levels (swash, shoaling and surf) but rather
depends on the characteristics of each beach. Second, we demonstrate
that species composition across those levels depends on the species
traits, in addition to geographical and abiotic factors. Third, we
highlight that the species functional space has a lower richness than
expected and a lower redundancy in the wave-exposed swash level compared
to the shoaling and subtidal levels, suggesting a trait-based ecological
filtering. Finally, we show that those differences depend on the higher
frequency of hydrodynamics-related traits in the species of the swash
level. Our results suggest that the rough hydrodynamic conditions in the
swash level favour a unique combination of species traits, which might
be linked to ecological speciation in flatworms but also in other
interstitial animals.