Sampling estuarine copepods at different scales and resolutions: a study in Rio de la Plata

Abstract

In the Rio de la Plata salinity, temperature, chlorophyll a (chl a), and densities (ind. m−3) of the copepods Acartia tonsa and Paracalanus parvus were measured from January to November in 2003 by following a nested weekly and monthly design. Such sampling yielded two separate datasets: (i) Yearly Dataset (YD) which consists of data of one sampling effort per month for 11 consecutive months, and (ii) Seasonal Weekly Datasets (SWD) which consists of data of one sampling effort per week of any four consecutive weeks within each season. YD was assumed as a medium-term low-resolution (MTLR) dataset, and SWD as a short-term high-resolution (STHR) dataset. The hypothesis was, the SWD would always capture (shorter scales generally captures more noise in data) more detail variability of copepod populations (quantified through the regression relationships between temporal changes of salinity, temperature, chl a and copepod densities) than the YD. Analysis of both YD and SWD found that A. tonsa density was neither affected by seasonal cycles, nor temporal variability of salinity, temperature and chl a. Thus, compared to STHR sampling, MTLR sampling did not yield any further information of the variability of population densities of the perennial copepod A. tonsa. Analysis of SWD found that during summer and autumn the population densities of P. parvus had a significant positive relationship to salinity but their density was limited by higher chl a concentration; analysis of YD could not yield such detailed ecological information. That hints the effectiveness of STHR sampling over MTLR sampling in capturing details of the variability of population densities of a seasonal copepod species. Considering the institutional resource limitations (e.g. lack of long-term funding, manpower and infrastructure) and the present hypothesis under consideration, the authors suggest that a STHR sampling may provide useful complementary information to interpret results of longer-term natural changes occurring in estuaries.

Does the copepod community of the Ganges River estuary of India indicate ecological stress?

“…al., 1991;Bhattacharya et al, 2014a). Paracalanus parvus, which is generally found in coastal, neritic and brackish waters, is a warm-water herbivorous copepod that generally feeds on diatoms (Checkley, 1980;Paul and Calliari, 2019). A study of hourly changes of the copepod community of the Muriganga revealed that P. parvus has an overlapping niche with B. similis when the Muriganga remains ecologically stable; however, after any cyclonic disruption P. parvus is replaced by A. tortaniformis Paul et al, 2020b).…”

“…Estuarine ecological studies have traditionally focused on the patchy distribution of copepods, presence/absence of certain species, values of various diversity indices, and their relationships with environmental gradients, to draw inferences on the ecological stress of estuaries (Lawrence et al, 2004;Rice et al, 2015;Paul et al, 2016;Paul and Calliari, 2019). Changes of diversity, abundance and distribution of copepods are, therefore, considered as indicators of ecological stresses of estuaries that arise from abiotic, seasonal, climate changes and human-interventions (Sinha et al,1996;Hoof and Peterson, 2006;Sullivan et al, 2007;Lin et al, 2011;Paul et al, 2016;Araujo et al, 2017).…”