Primary production and plankton assemblages in the fisheries ground around San Jorge Gulf (Patagonia) during spring and summer

Abstract

The San Jorge Gulf, and the littoral to its north, is one of the most important fishing grounds for Argentina. Nevertheless, phytoplankton production has been scarcely studied. Here we analyzed during spring (2008) and summer (2009) the phytoplankton biomass, production, and the composition of phytoplankton and protozooplankton; their possible trophic relationships, and physical conditioners. At the south coast of the gulf during spring micro-nano-plankton (diatoms and dinoflagellates) were predominant and responsible for the maximum integrated production, comparable to that reported for the rich Argentinian shelf-break. Part of the organic carbon produced there was consumed by heterotrophic dinoflagellates, adding a trophic level to the food web. While at the center of the gulf, a conspicuous deep chlorophyll maximum would probably add organic matter to the bottom. During the following summer ( 2009), the ultrafraction represented the largest contribution to total phytoplankton biomass, and was dominated by Synechococcus sp. This, plus the abundance of ciliates, indicate the prevalence of a microbial food web during summer. It has been found that the frontal zones in the north and south of the gulf, favoring high phytoplankton biomass and its maintenance due to high primary production, provide a favorable food environment for impregnated female shrimp in spring, and for larvae during summer.

Patterns and Trends in Chlorophyll‐a Concentration and Phytoplankton Phenology in the Biogeographical Regions of Southwestern Atlantic

“…In R5 both blooms start 1 month later than in R4, probably because of the later onset of stratification of the water column at this higher latitude. The strong Chl‐a peak observed in R5 is consistent with previous observations in the San Jorge Gulf, where bloom intensity reached ∼9 mg m −3 in 2008 and high Chl‐a values (>1.5 mg m −3 ) persisted during summer (Figure 2 and Segura et al., 2021). The northern Patagonian mid‐shelf front (R4) appears as a ∼80 km band of high chlorophyll concentration offshore of the 50 m isobath.…”

“…These differences are in agreement with the separation of two different regions by SOM. The Patagonian temperate fronts (R5) represent important spawning and nursery areas for several commercial species (e.g., Argentine red shrimp, Argentine hake, southern king crab; Segura et al, 2021). R4, in turn, is one of the main spring spawning and nursery areas for the northern population of E. anochoita (Marrari et al, 2013).…”

Patterns and trends in Chlorophyll-a concentration and phytoplankton phenology in the biogeographical regions of Southwestern Atlantic

“…The strong peak of R5 is consistent with previous observations in the San Jorge Gulf, where bloom intensity reached ~9 mg m -3 (2008) and high values (> 1.5 mg m -3 ) persisted during summer (Fig. 2, Segura et al, 2021). The northern Patagonian mid-shelf front (R4) is a ~80 km band of high chlorophyll concentration offshore of the 50 m. During spring-summer the front is developed, by the vertical stratification of waters located ~80 m offshore with a thermocline overlying colder nutrient-rich waters (MC), separating the vertically mixed nutrient-poor coastal waters (R2) (Lucas et al, 2005;Martos and Piccolo, 1988).…”

“…These areas allow for the development of economically important fisheries: The Patagonian temperate fronts (R5) are an important spawning and nursery area of several commercial species (e.g. Argentine red shrimp, Argentine hake, southern king crab, Segura et al 2021), and R4 is one of the main spring spawning and nursery area for the northern population of E. anochoita (Marrari et al, 2013). The seasonal pattern of these regions agrees with the canonical cycle of temperate seas, where the chlorophyll maxima is associated with the onset of stratification in spring, and a second smaller peak during fall, when the thermocline weakens and deeper nutrient rich waters entrain the surface layer (Carreto et al, 1995;Akselman, 1996;Rivas and Beier, 1990).…”

“…coastal upwelling, thermo-haline circulation, tidal forcing; Acha et al, 2004) which can lead to strong phytoplankton blooms, mainly dominated by diatoms, coccolithophores and dinoflagellates (e.g. Alvain et al, 2008;Guinder et al, 2018;Segura et al, 2021;Delgado et al, 2019). As a result of climate change, the region is showing clear evidence of environmental changes, largely associated with an increase in sea surface temperature (SST; Hobday and Pecl, 2014), changes in wind patterns (Leyba et al, 2019), the poleward migration of western boundary currents (Artana et al, 2019) and intensification and/or increase in the frequency and intensity of climate variability events (ENSO, Southern Annular Mode, droughts, heatwaves; e.g.…”