Spatial and temporal variability of the zooplankton community in Valdés Biosphere Reserve, Patagonia, Argentina: Nuevo Gulf case study
Introduction
Zooplankton is a key component in marine ecosystems, transferring energy from primary producers to higher trophic levels and contributing to the overall biogeochemical cycles (Calbet and Saiz, 2016). Zooplankton diversity and biomass were both identified as biological Essential Ocean Variables (EOVs) due to their ecological relevance and their potential to inform about environmental changes that may have societal importance (Miloslavich et al., 2018). Therefore, monitoring plankton in general is important because these organisms constitute the base of the marine food web, play important roles in biogeochemical cycles, thus in the global climate, being at the same time sensitive to ecosystem perturbations (Muller-Karger et al., 2013, 2018).
The Argentine Patagonian shelf presents high biological productivity and biodiversity (Bisbal, 1995; Gregg et al., 2005; Sherman and Duda, 1999), supporting a large fishing activity and being an important breeding area for marine mammals and seabirds (Acha et al., 2019; Gregg et al., 2005; Sánchez and Bezzi, 2004). The Valdés Biosphere Reserve (VBR) encompasses the Patagonian steppe and Argentine Sea eco-regions, where fragile ecosystems are present. There is therefore a need to protect their key species, especially considering that the coastal marine environment is affected by increasing anthropogenic stress. In the last decades, important changes have been registered in the Southwest Atlantic Ocean, including surface and subsurface ocean warming (Franco et al., 2020). Warming can affect pelagic ecosystems in complex ways, including shifting patterns of species, changing biogeographical ranges and decreasing energy transfer efficiency (Gamfeldt et al., 2015).
Recent works have compiled and described mesozooplankton distribution known to date in some regions of the Argentinian Shelf (e.g. Acha et al., 2019; Cepeda et al., 2018; Dutto et al., 2019), highlighting that data is still scarce and poor “insufficiently studied” for some of the taxonomic groups (Boltovskoy and Valentin, 2018). In particular, these works did not include the study of the north Patagonian gulfs forming the VBR, i.e., the San José Gulf (SJG) and the Nuevo Gulf (NG), which are areas of great importance for marine conservation. These gulfs are located in the Valdés Peninsula Protected Area, a natural reserve designated as a World Heritage Site and Biosphere Reserve by the United Nations Educational, Scientific and Cultural Organization (UNESCO 1999). The VBR is recognized worldwide as an essential habitat for marine mammals and other top predators, which have been studied for several decades now (Crespo et al., 2019; Degrati et al., 2020; Jarma et al., 2019). In contrast, despite the ecological importance of zooplankton for this ecosystem, its composition and variability are not yet well characterized. In addition, recently D'Agostino et al. (2019) showed that mesozooplankton, mainly calanoid copepods, are the primary potential vector of phycotoxins in the pelagic food web, accumulating and transferring toxins within the system, which highlights the importance of systematic monitoring of the zooplankton composition and abundance. There is in addition a need for baseline information to allow the detection of changes in the pelagic food web and elucidate possible effects on the marine ecosystem as a whole. The aim of this study is to contribute to this baseline and provide further knowledge on the mesozooplankton community composition and distribution within the NG in relation to environmental variables during austral spring and summer. We further include a short review of all zooplankton studies conducted in NG to date.
Section snippets
Study site
The NG (42° 42′ S, 64° 30’ W) is a semi-enclosed basin with a surface area of 2400 km2, an average depth of 80 m and maximum depth of 180 m (Rivas and Beier, 1990). It has a narrow (16 km) opening and a shallow sill which restrict the exchange of water with the open sea, so the waters in the NG are consequently more influenced by atmospheric forcing than by shelf waters (Rivas, 1990; Rivas and Ripa, 1989, Fig. 1). The extended residence time in the Gulf results in a greater annual thermal
Hydrography
Mean temperature was higher in summer (p < 0.05), both in the surface layer (16.55 °C ± 0.58) and intermediate layer (12.75 °C ± 0.33), compared to the spring season (11.20 °C ± 0.4 and 10.67 °C ± 0.25 for surface and intermediate layers, respectively; Table 1). Salinity was homogeneous, with no variations with station, seasons or depth (p = 0.89), with an average value of 33.98 psμ ± 0.04 (values for all stations are shown in Table 1).
The average Chl a concentration was higher (p < 0.05) in
Discussion
The importance of the Valdés Biosphere Reserve. Marine protected areas have been recognized for their value enhancing the conservation, including the preservation of genetic resources, key species, critical ecosystem and landscapes, while providing the scientific knowledge and human values to support sustainable development and management (Claudino-Sales, 2019; Ishwaran et al., 2008; Reed, 2016). Only a few studies conducted in the Valdés Biosphere Reserve (VBR; Deguignet et al., 2014) analyzed
Conclusions
Baseline environmental and biological data are essential to understand how species and habitats would respond to natural and man-made variations. Although plankton studies in the NG date back to the 90s, and variations of large mesozooplankton groups may be noted, the lack of sustained monitoring makes temporal interpretations difficult. Mesozooplankton distribution in the NG varies during the year and this variation is essentially determined by seasonal characteristics, especially high
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We would like to thank G. Bravo, G. Trobbiani, L. Epherra, N. Ortíz, R. (Bebo) Vera, J. Crespi and JP. Pisoni for the fieldwork planning and collection of the samples, as well as C. Derisio and A. Berasategui for their time and help with zooplankton identification. We thank A. Baldoni and INIDEP for salinity samples analysis. We are grateful to the LAMAMA and LOQyCA groups (CESIMAR) for providing laboratory facilities. We also thank P. Bermejo and G. Williams for helping us to measure Chl a.
References (66)
- et al.
Estimating copepods' abundance with paired nets: implications of mesh size for population studies
J. Sea Res.
(2010) The southeast south-american shelf large marine ecosystem - evolution and components
Mar. Pol.
(1995)- et al.
The seasonal dynamics of plankton communities relative to the foraging of the southern right whale (Eubalaena australis) in northern Patagonian gulfs, Península Valdés, Argentina
Continent. Shelf Res.
(2018) - et al.
Morphology of the mandibular gnathobases of the copepods Calanus australis and Calanoides carinatus: evidence of omnivory
Zool. Anz.
(2020) - et al.
Influence of a tidal front on zooplankton abundance, assemblages and life histories in Península Valdés, Argentina
J. Mar. Syst.
(2014) - et al.
Occurrence patterns of Alexandrium tamarense (Lebour) Balech populations in the Golfo Nuevo (Patagonia, Argentina), with observations on ventral pore occurrence in natural and cultured cells
Harmful Algae
(2006) - et al.
Synoptic oceanography of San Jorge Gulf (Argentina): a template for Patagonian red shrimp (Pleoticus muelleri) spatial dynamics
J. Sea Res.
(2015) - et al.
Contrasting structural patterns of the mesozooplankton community result from the development of a frontal system in San José Gulf, Patagonia
Estuar. Coast Shelf Sci.
(2017) - et al.
Small-scale variation in the diet of the South American Sea lion (Otaria flavescens) in northern Patagonia (Argentina)
Reg. Stud. Mar. Sci.
(2019) - et al.
Spatio-temporal dynamics of mesozooplankton in the subantarctic Beagle Channel: the case of Ushuaia Bay (Argentina)
Reg. Stud. Mar. Sci.
(2019)