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

Abstract

a b s t r a c tDuring the last decades many estuaries underwent ranges of environmental pressure due to increasing anthropogenic pressures and the undertaken of mitigation measures to prevent the impoverishment of these areas. The Mondego estuary (NW Atlantic coast of Portugal), a mesotidal shallow estuary, is one typical case of this. In the 1980s, the system was characterized by rich and stable animal and vegetal communities, with no eutrophication symptoms (pre-eutrophication period), whereas during the 1990s, massive seasonal macroalgal blooms were observed and the concomitant adverse consequences on the system's biodiversity were registered (eutrophication period). More recently (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010), eutrophication symptoms have gradually decreased due to several mitigation actions, whilst recent studies indicate that the system is recovering in terms of biodiversity and structure (post-mitigation period). The population dynamics and productivity of Echinogammarus marinus (Leach) (Amphipoda, Gammaridae), a key species associated to fucoids in many Northern Atlantic estuaries, was analyzed and compared throughout these three distinct periods in the Mondego estuary, using data collected between April 2009 and March 2010 and data from the 1980s (pre-eutrophication) and 1990s (eutrophication period). The goal of this study was to test if the long-term variation of E. marinus would somehow reflect the range of environmental conditions observed in the system from the 1980s until 2010. Results showed that, in the three different periods, the species exhibited higher densities during spring, with continuous sexual activity throughout the year, multivoltine life cycle and seasonal sex-ratio fluctuations. Moreover, salinity was a major factor affecting the amphipod population in all three periods. On the other hand, differences related to the production of E. marinus were detected, being clearly higher in the 1980s (pre-eutrophic period), followed by the last decade (post-mitigation period) and, finally, the 1990s (eutrophication period), where population production and density values were the lowest of all three periods. These results suggest that E. marinus production parameters reflected the decline in environmental conditions during the 1990s, as well as the partial recovery resulting from the application of mitigation measures, exhibiting a good sensitivity to environmental pressures, namely eutrophication. Therefore, we propose that in the last years, the Mondego estuary has been under an incomplete resilience period, characterized by some environmental improvement compared to the 1990s but still distant from the 1980s condition. Overall, E. marinus production parameters seem to be good indicators of the system's environmental condition and might be useful regarding monitoring programmes in most Northern Atlantic estuaries.

Increasing temperature decreases the predatory effect of the intertidal shannyLipophrys pholison an amphipod prey

“…Both organisms used in this study are resilient inter‐tidal species (Milton, ), the temperature ranges for E. marinus are from 5·4–31·7° C (Leite et al., ), which is far higher than the 17·5° C recorded optimal temperature for the northerly distributed L. pholis (Horn & Gibson, ; Francisco et al., ). Davenport & Vahl () experimentally identified 16° C as the peak temperature for consumption of seaweed in L. pholis .…”

“…Furthermore, E. marinus is an effective indicator species due to its prevalence, susceptibility to abiotic perturbation 152 J . S O U T H E T A L. and its importance as a prey species to higher trophic levels (Múrias et al, 1996;Leite et al, 2014). Echinogammarus marinus is an important prey species of L. pholis and other marine intertidal species; thus, it is a sympatric species and therefore will experience the same perturbations to environment as L. pholis.…”

“…Littoral amphipods such as Echinogammarus marinus are typically mesograzers (Dick et al., ) and can have wide‐ranging influence on community structuring across a range of trophic levels (Duffy & Hay, ; Maranhão et al., ; Haggitt & Babcock, ; Dick et al., ; Kelly & Dick, ). Furthermore, E. marinus is an effective indicator species due to its prevalence, susceptibility to abiotic perturbation and its importance as a prey species to higher trophic levels (Múrias et al., ; Leite et al., ). Echinogammarus marinus is an important prey species of L. pholis and other marine intertidal species; thus, it is a sympatric species and therefore will experience the same perturbations to environment as L. pholis .…”

Effects of acute and chronic temperature changes on the functional responses of the dogfish Scyliorhinus canicula (Linnaeus, 1758) towards amphipod prey Echinogammarus marinus (Leach, 1815)

“…We investigated predation by juvenile Scyliorhinus canicula (lesser-spotted dogfish) on amphipod prey Echinogammarus marinus. Both species are ubiquitous in temperate waters (Ellis and Shackley 1997;Duffy and Harvilicz 2001), resilient (Múrias et al 1996;Revill et al 2005;Leite et al 2014) and pliable laboratory species (Sims 2003). These are ecologically relevant species as E. marinus has large impacts upon community structuring (Duffy and Hay 2000;Dick et al 2005), and is an important prey species (Leite et al 2014) that can additionally be considered a proxy for other small crustacean species and small fish due to strong swimming behaviours.…”

“…Both species are ubiquitous in temperate waters (Ellis and Shackley 1997;Duffy and Harvilicz 2001), resilient (Múrias et al 1996;Revill et al 2005;Leite et al 2014) and pliable laboratory species (Sims 2003). These are ecologically relevant species as E. marinus has large impacts upon community structuring (Duffy and Hay 2000;Dick et al 2005), and is an important prey species (Leite et al 2014) that can additionally be considered a proxy for other small crustacean species and small fish due to strong swimming behaviours. S. canicula is a generalist benthic predator (Kaiser and Spencer 1994;Domi et al 2005) with high abundances (Genner et al 2010;Sguotti et al 2016) that have been found to increase with increasing temperature (Sguotti et al 2016).…”