Influence of benthic macrofauna community shifts on ecosystem functioning in shallow estuaries

Abstract

We aim at identifying how ecosystem functioning in shallow estuaries is affected by rapid shifts in benthic fauna communities. We use the shallow estuary, Odense Fjord, Denmark, as a case study to test our hypotheses that (1) shifts in benthic fauna composition and species functional traits affect biogeochemical cycling with cascading effects on the ecological functioning, which may (2) modulate primary productivity in the overlying water column with feedbacks to the benthic system. Odense Fjord is suitable because it experienced dramatic shifts in benthic fauna community structure from 1998 to 2008. We focused on infaunal species composition and functional traits with emphasis on three dominating burrow-dwelling polychaetes: the native Nereis (Hediste) diversicolor and Arenicola marina, and the invasive Marenzelleria viridis. The impact of functional traits in the form of particle reworking and ventilation on biogeochemical cycles, i.e., sediment metabolism and nutrient dynamics, was determined from literature data. Historical records of summer nutrient levels in the water column of the inner Odense Fjord show elevated concentrations of NH + 4 and NO − 3 (DIN) during the years 2004-2006, exactly when the N. diversicolor population declined and A. marina and M. viridis populations expanded dramatically. In support of our first hypothesis, we show that excess NH + 4 delivery from the benthic system during the A. marina and M. viridis expansion period enriched the overlying water in DIN and stimulated phytoplankton concentration. The altered benthic-pelagic coupling and stimulated pelagic production may, in support of our second hypothesis, have feedback to the benthic system by changing the deposition of organic material. We therefore advice to identify the exact functional traits of the species involved in a community shift before investigating its impact on ecosystem functioning. We also recommend studying benthic community shifts in shallow environments to obtain sufficient knowledge about the drivers and controls before exploring deep-water environments.

Hydrodynamic conditioning of diversity and functional traits in subtidal estuarine macrozoobenthic communities

“…Deep living deposit feeders are often associated with areas with no significant hydrodynamic impact and high organic matter sediments (Rosenberg, 1995), although Wildish and Kristmanson (1997) The spatial heterogeneity in densities, biomass, species richness, community structure and functional traits of macrofauna within the estuary has potential implications for ecosystem functioning. In estuaries, macrofauna community structure regulates ecosystem functioning through, for example, biophysical processes, such as bioturbation and bioirrigation (Biles et al, 2002;Braeckman et al, 2010), and biogeochemical processes, such as nutrient cycling (Kristensen et al, 2014). Such processes can be expected to be more intense in the hotspots with a more diverse and abundant macrofauna community dominated by burrowers.…”

“…However, species do not contribute equally to ecosystem processes and services (Stuart-Smith et al, 2013). Their contribution depends on their biological traits, such as their feeding habit and behaviour (Bremner et al, 2006;Kristensen et al, 2014).…”

Human activities and climate variability drive fast‐paced change across the world's estuarine–coastal ecosystems

“…b). Many other abrupt changes have been observed such as the restructuring of benthic faunal communities and their biogeochemical functions in Denmark's Odense Fjord (Kristensen et al ., ), doubling of copepod abundance in Gulf of Trieste (Conversi et al ., ) and decreases of chlorophyll a in the northern Adriatic Sea (Mozetič et al ., ) and Gulf of Trieste (Mozetič et al ., ), fish populations in the Caspian Sea (Daskalov & Mamedov, ) and nitrogen‐assimilative capacity of the Skagerrak (Conley et al ., ).…”

Seasonality and trophic diversity in molluscan assemblages from the Bay of Tunis (southern Mediterranean Sea)

“…Glemarec & Hily, 1981;Anderlini & Wear, 1992). Shifts in infaunal communities driven by anthropogenic and natural disturbances may lead to functional changes and cause dramatic changes in the performance of the ecosystems (Thrush et al, 2006;Kristensen et al, 2014), but this has been poorly studied in some Mediterranean areas.…”