Spatial distribution of macrofauna in a littoral zone with drifting macroalgae in the Neva estuary

Abstract

This study focuses on the influence of drifting algae (Cladophora glomerata) and oxygen depletion on the distribution and biomass of macrofauna in the shallow stony-sandy littoral of the Neva estuary, easternmost part of the Baltic Sea. Great masses of decaying drifting algae (315-445 g dry weight m -2), oxygen depletion (5.4-24.5% or 0.6-2.8 mg L-1), and subsequent low biomass of macrofauna (0.5-2.9 g wet weight m-2) were recorded in the near-shore area (5-20 m). At greater distances (30-60 m from the shore) the biomass of drifting algae decreased, hypoxia was not recorded, and no internal significant differences in the total biomass of benthic macrofauna (24.3-30.8 g wet weight m-2) were found. The biomass of the macroinvertebrate community of the drifting algae reached 4.1-5.5 g wet weight m-2 at distances of 10-20 m from the shore, and was at least 20 times lower in the area closest to the shore (5 m). Amphipods and chironomids contributed to the total biomass 42% and 26%, respectively. Species with opportunistic life strategies and high resistance to oxygen depletion are able to survive and dominate in coastal areas of the Neva estuary with temporary hypoxia induced by macroalgal decomposition.