Long-term changes in the production by estuarine macrobenthos affected by multiple stressors

Abstract

The macrobenthic production of an estuarine system was evaluated over a 14-year 12 study period in a seagrass bed and in a sandflat. Over this period, the estuary suffered severe 13 eutrophication and extreme weather events with important impacts on the community, 14impairing system functioning and ultimately the goods and services provided by the estuary 15 (decline in the seagrass bed, decreased community production and/or a boost in the 16 production by opportunist species, such as Hydrobia ulvae). Following the anthropogenic 17 impacts, management measures were introduced which allowed a gradual recovery of the 18 seagrass bed and a new macrobenthic community structure manifested by production 19 increases of slow-growing species, such as Scrobicularia plana and Hediste diversicolor. 20There was a gradual re-orientation of energy into population biomass instead of population 21 density but this was not translated into higher community production, mainly due to the 22 decreased production of opportunist species (H. ulvae and several polychaetes). Several 23 weather extreme events occurred during this post-mitigation phase -floods, heatwaves and 24 droughts, all of which had negative impacts on macrobenthic dynamics and production. The 25 33

Long term variation of an amphipod species’ population secondary production as indicator of incomplete resilience in a temperate estuary

“…In 2006, the complete re-establishment of the communication between both arms of the Mondego estuary occured, ending a series of mitigation measures in the estuary (Marques et al, 2007;Veríssimo et al, 2012). Extreme climate events have also occurred during the last decade, for instance, a major flood came about in the winter of 2000/2001 and heat waves were recorded in 2003 and 2005, the latter accompanied by a severe drought Dolbeth et al, 2011), which had negative impacts especially on the South arm macrobenthic communities, such as Z. noltii biomass decrease after heatwaves and Hydrobia ulvae an S. plana production decline after the floods and severe drought (Cardoso et al, 2008a(Cardoso et al, , 2008bDolbeth et al, 2011), however, no significant events have been recorded ever since in the Mondego estuary.…”

“…This allowed the Z. noltii meadows to recover, at least in spatial extent (4.7 ha in 2006), although biomass (≈100 g AFDW m −2 ) is still much lower than in 1993 (≈250 g AFDW m −2 ) but with positive impacts on the macrobenthic community structure (e.g. considerable increase in production of slow-growing species such as S. plana and H. diversicolor) (Dolbeth et al, 2011). In 2006, the complete re-establishment of the communication between both arms of the Mondego estuary occured, ending a series of mitigation measures in the estuary (Marques et al, 2007;Veríssimo et al, 2012).…”

“…density and biomass increase in key species Hediste diversicolor and Scrobicularia plana (Cardoso et al, 2010). The most important measures were (1) the partial re-establishment of the connection between both arms, improving freshwater circulation and reducing the nutrient load; (2) rerouting most of the Pranto River nutrient enriched freshwater to the North arm, leading to nutrient loading reduction into the South arm and (3) physical protection of the seagrass beds from human disturbance Lillebø et al, 2005;Neto et al, 2010;Dolbeth et al, 2011).…”

“…The system has changed from a low-environmentallyimpacted estuary during the 1980s, becoming strongly eutrophic during the 1990s, to a partially recovered system at the present (Martins et al, 2001;Marques et al, 2003;Dolbeth et al, 2011;Veríssimo et al, 2012).…”

“…These variations reflect the system intrinsic variance, the effects of anthropogenic pressures and/or other types of pressures, and the system's own resistance and resilience to disturbance. Estuaries are also characterized by relatively few species but with abundant populations that can be highly productive in natural conditions, making it difficult to dissociate anthropogenic from natural stress (Elliott and Quintino, 2007;Dolbeth et al, 2011).…”