The influence of environmental conditions onParasagitta friderici(Chaetognatha) abundance in a subtropical estuary (south Brazil)

Abstract

Estuarine chaetognath population dynamics are poorly known worldwide. We have conducted eight seasonal campaigns (October 2007–August 2008) sampling three sectors in the subtropical Babitonga Bay estuary (26°S 48°W) in order to depict chaetognath abundance and population structure dynamics and test the influence of hydrography and food availability and type. Of three species sampled, Parasagitta friderici represented >93% of abundance in all samples and was examined in detail. There were no differences in P. friderici abundance between the sectors of the estuary, related to its high tolerance to low salinity, a feature not common for most chaetognath species. Salinity tolerance is an important adaptive characteristic to thrive within estuarine systems, and probably is responsible for the dominance of P. friderici in coastal and brackish water environments throughout most of its distribution. Juveniles dominated the population most of the year, except in February–April when abundances were lower and adults predominated. These results suggest that recruitment occurs continuously throughout the year, being more intense between October and January (spring to early summer) and in May (autumn) when densities and proportion of juveniles were higher. General Additive Models suggest that temperature and zooplankton biomass are significant (P < 0.05) factors influencing juvenile abundance while only the latter influenced the adults. We conclude that food availability is the most important driver in the studied population of P. friderici and recruitment peaks, which lead to high densities, seem to occur following peaks of their copepod prey along with particular temperature conditions (22–23°C).

Diversity, seasonal abundance, and environmental drivers of chaetognath populations in North Inlet Estuary, South Carolina, USA

“…Similarly, we observed the percentage of individuals with eggs present was moderately correlated with temperature (surface r = .455; bottom r = .460). This finding aligns with previous studies, which identified temperature as a significant driver in juvenile abundance(Nogueira Júnior et al, 2019), as well as egg development and laying times (reviewed inAlvariño, 1990), with laying occurring earlier in the day on warm days and most species breeding primarily in spring, although noting breeding does occur year-round in tropical waters.…”

“…There were not enough individuals found in this study to make conclusions regarding S. bipunctata's reproductive seasonality. et al, 2019;Owre, 1960;Pierce, 1951;Pierce & Wass, 1962;Ulloa et al, 2000). While this study found weak correlations between salinity and chaetognath abundance, primarily oceanic species (such as F. enflata, S. bipunctata, and Sagitta megalopthalma) have demonstrated significant positive relationships between chaetognath assemblages and salinity levels (Gilmartin et al, 2020).…”

“…Salinity had a slight positive correlation with both chaetognath abundance (surface r = .205; bottom r = .117) and egg presence (surface r = .274; bottom r = .286). As chaetognaths have weak osmoregulatory functioning, salinity is an important factor in their geographic distribution and their tolerance to low salinity levels directly influences their presence in estuaries (Bieri, 1959 ; Coston‐Clements et al, 2009 ; Nogueira Júnior et al, 2019 ; Owre, 1960 ; Pierce, 1951 ; Pierce & Wass, 1962 ; Ulloa et al, 2000 ). While this study found weak correlations between salinity and chaetognath abundance, primarily oceanic species (such as F. enflata , S. bipunctata , and Sagitta megalopthalma ) have demonstrated significant positive relationships between chaetognath assemblages and salinity levels (Gilmartin et al, 2020 ).…”

“…While research into the ecology of chaetognaths, specifically related to their seasonality (Gilmartin et al, 2020; Lozano‐Cobo et al, 2017; Nogueira Júnior et al, 2019; Tse et al, 2008), has increased over the last few decades, there is still a gap in our scientific understanding of estuarine species' geographic distribution and the environmental factors which drive their abundance and reproduction. O'Brien (1977) and Tiselius and Peterson (1986) suggested chaetognath distribution and species composition depend on temperature and salinity levels.…”