Salinity regulation of copepod egg production in a large microtidal estuary

Abstract

Calliari et al.: Salinity regulation of copepod production 1 Salinity regulation of copepod egg production in a large microtidal estuary Salinity is a key variable for ecological processes in estuaries. Acartia tonsa is a typical estuarine copepod whose responses to salinity have been thoroughly studied in the laboratory. However, results cannot be extrapolated to the field, and formal comparisons between lab and field responses to salinity were not attempted. Here we compare lab-based with field copepod egg production rates (EPR) from the Río de la Plata estuary (RPE), with focus on A. tonsa. Field work was conducted between 2009 and 2011 in the mixing zone of the RPE. Water temperature, salinity and chlorophyll-a varied over ample ranges (temperature: 10.54-24.56ºC, salinity: 2.83-32.99, chlorophyll-a: 0.62-7.27 mg m-3). A. tonsa was the strongly dominant species. EPR ranged between 6.7 and 95.7 eggs female-1 day-1 , and correlated to salinity, temperature (weakly), but not to chlorophyll. The relationship between A. tonsa's EPR (EPR AT) and salinity was consistent with that obtained under laboratory conditions: a humped pattern with a maximum at intermediate salinities. However, differences were also evident, e.g., higher EPR AT was measured in the field. We speculate that discrepancies derive from nutritional differences between field and reference (laboratory) data sets. Besides salinity, food quality and quantity may be first order drivers of A. tonsa's productivity in the RPE.

Feeding ecology of Brevoortia aurea larvae (Clupeidae, Alosinae) from Río de la Plata estuary off Uruguay

“…Pepin and Penney, 2000;Robert et al, 2011;Llopiz, 2013;Temperoni and Viñas, 2013). In particular A. tonsa matches well all such qualities as prey features, i.e., size range, quality as food, abundance in estuaries (Calliari et al, 2004;Calliari et al, 2019;Derisio et al, 2014;Machado et al, 2017;Rodríguez-Graña et al, 2018). In fact, the high abundance of copepods and in particular of A. tonsa in the RPE (up to 10,000 ind.…”

“…The actual occurrence of competition and concomitant ecologically relevant densitydependent effects requires a significant impact of predation pressure on prey populations. No evidence exists so far on that matters, and given the typically high prey densities and planktonic production rates in the RPE (Ferrari and Pérez, 2002;Calliari et al, 2018Calliari et al, , 2019, the emergence of competition seems unlikely. In any case, the likeliness of any potential competition decreases as development advances and dietary overlap diminishes.…”

Response of planktonic copepods of the White Sea to the water salinity changes in acute and chronic experiments

“…The scarcity of data on the salinity tolerance in different developmental (copepodite) stages of the same species, as it is observed for M. longa in our study, also requires attention. Up to date, the studies are focused either on copepod embryos (Charmantier and Charmantier-Daures, 2001) or adult stages (Calliari et al, 2019;Dutz and Christensen, 2018) with the only exception for Eurytemora affinis from the Baltic Sea (Karlsson et al, 2018). Different response to the osmotic stress in ontogeny is reported for isopods (Charmantier and Charmantier-Daures, 1994), shrimps (Torres et al, 2011;Vázquez et al, 2016), and crabs (Charmantier et al, 1998;de Jesus de Brito Simith et al, 2012).…”