Changes in the Plankton Community According to Oceanographic Variability in a Shallow Subtropical Shelf: SW Atlantic
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Hydrobiologia https://doi.org/10.1007/s10750-019-3936-5 (0123456789().,-volV)(0123456789().,-volV) PRIMARY RESEARCH PAPER Changes in the plankton community according to oceanographic variability in a shallow subtropical shelf: SW Atlantic Ba´rbara Santos Menezes . Luis Carlos Pinto de Macedo-Soares . Andrea Santarosa Freire Received: 6 December 2017 / Revised: 6 March 2019 / Accepted: 8 March 2019 Ó Springer Nature Switzerland AG 2019 Abstract Copepods play a key role in marine revealed distinct seasonal communities. During winter ecosystems, acting as major primary consumers graz- the water was homogeneous, which supported the ing on phytoplankton or feeding on microzooplankton. even distribution of the dominant species and the Plankton communities are mostly structured by nutri- prevalence of the herbivore food chain throughout the ent availability and water temperature. The Subtrop- area. During summer the herbivore food chain ical Southwestern Atlantic Shelf has oligotrophic occurred in the bay area, being displaced by the conditions due to the predominance of the Tropical microbial food chain toward the shelf. The plankton Water in the upper layers. Its condition can change due community is determined by the homogeneity of the to cold water upwelling in summer, the northwards water during winter and by the environmental hetero- spreading of the Plata Plume Water in winter, and geneity during summer. local freshwater discharges. This study aimed to investigate the temporal and spatial variability in Keywords Copepods Á Microplankton Á Geometric plankton community in the shallow shelf off the shapes Á Plata Plume Water Á South Atlantic Central Brazilian coast (* 27°Sto48°W). Results of the Water PERMANOVA analysis and co-occurrence networks Handling editor: Juan Carlos Molinero Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-019-3936-5) con- Zooplankton plays a key role in marine food webs, tains supplementary material, which is available to authorized mainly in the energy transfer from primary producers users. to higher trophic levels. About 70% of the marine B. S. Menezes (&) Á A. S. Freire mesozooplankton in coastal ecosystems are copepods, Laborato´rio de Crusta´ceos e Plaˆncton, Programa de Po´s- which act as major primary consumers grazing on Graduac¸a˜o em Ecologia, Departamento de Ecologia e phytoplankton in the grazing food web or feed on Zoologia, Universidade Federal de Santa Catarina, Floriano´polis, SC 88040-900, Brazil microzooplankton (20–200 lm), thereby linking the e-mail: [email protected] microbial to the grazing food chain (Longhurst, 1985; Calbet & Saiz, 2005; Sommer et al. in press). L. C. P. de Macedo-Soares Although almost all copepods are generalists, many Laborato´rio de Ecologia do Ictioplaˆncton, INCT-Mar COI, Instituto de Oceanografia, Universidade Federal do species are recognized to exhibit preferential trophic Rio Grande, Rio Grande, RS, Brazil regime (Bjo¨rnberg, 1981). The microzooplankton, 123 Hydrobiologia mainly ciliate protists, is considered a trophic link rich South Atlantic Central Water (SACW) (Mo¨ller between the microbial loop and the grazing food et al., 2008). In the SBB northern boundary, phyto- chain, feeding on nano- and picoplankton not captured plankton biomass increased by 80% after SACW by larger predators, such as copepods (Fernandes, upwelling and opportunistic copepods became dom- 2004; Stoecker et al., 2014). inant, establishing the herbivore food chain. In the In oligotrophic marine systems, large diatoms are absence of the SACW, the microbial trophic chain less effective in nutrient acquisition at low concentra- prevailed with pico- and nanophytoplankton domi- tions; thus, picoplankton, tiny diatoms, and dinoflag- nance and high contribution of microzooplankton ellates become dominant (Pomeroy, 1974). In this (Guenther et al., 2008). In winter the northward environment, the copepods diet is based on ingestion spreading of the Plata Plume Water (PPW) carries of ciliates, and a long and complex food chain is nutrients to the region (Acha et al., 2004;Mo¨ller et al., constituted (Calbet & Saiz, 2005). In eutrophic 2008). The expansion of the PPW triggered high environments, large diatoms are dominant and the phytoplankton abundance in the coastal zone (Mo¨ller grazing on phytoplankton by copepods is increased, et al., 2008) and occurrence of fish larvae and forming the classic food chain based on herbivores Argentine anchovy (Engraulis anchoita Hubbs & (Azam et al., 1983). In oligotrophic coastal environ- Marini, 1935) in the southern SBB (Macedo-Soares ments, plankton communities are strongly affected by et al., 2014), but its effect on mesozooplankton is still seasonal nutrient inputs whether by upwelling events, poorly understood. tidal fronts, or plume fronts produced by freshwater Located in the SBB southern boundary, the Santa discharges of continental runoff (Acha et al., 2004; Catarina shelf (* 26 to 29°S and 48°W) is the limit Branda˜o et al., 2015). These seasonal events can between tropical and temperate bioregions (Long- temporarily change the environment from olig- hurst, 2006). This region is recognized as the major otrophic to meso- or eutrophic condition and therefore Brazilian fishing ground (Castello et al., 2009). affect the food chain. Besides, copepods are good Studies on the plankton community associated the hydrological indicators due to their high abundance temporal variation of meroplankton and holoplankton and relatively short life cycle often associated with with the water masses and the SACW upwelling water masses (Bjo¨rnberg, 1981; Bradford-Grieve (Resgalla, 2011; Rutkowski et al., 2011). Copepods et al., 1999). and cladocerans were also associated with water Cell size has been widely studied in phytoplankton masses in the Santa Catarina shallow shelf (Domin- ecology either to estimate carbon fixation, energy gos-Nunes & Resgalla, 2012). In spite of the role of flow, or primary production (Rodrı´guez et al., 2001; copepods in plankton communities, other studies in Cermen˜o et al., 2006). In addition to size, the the area were restricted to the occurrence of copepod geometric shape is an important functional trait to species (Lopes et al., 2006; Boos et al., 2012). The understand the dynamics of phytoplankton communi- phytoplankton was also associated with water masses ties (Naselli-Flores & Barone, 2011). However, there and seasonal changes with the dominance of large is still little knowledge about the relation between centric diatoms near the coast, small pennates along geometric shapes and the environment. Recent studies the mid-shelf, and flagellates over the 40- and 120-m in this field were carried out in the Adriatic Sea isobaths prior to SACW intrusion (Brandini et al., (Stanca et al., 2013) and in the Mediterranean Sea 2014). Based on the water mass dynamics in the Santa (Bernardi Aubry et al., 2017) showing phytoplankton Catarina shelf and the plankton trophic structure geometric shapes can be impacted by environmental driven by nutrient enrichment, our hypotheses are variability. that copepods and microplankton should also respond The Southern Brazilian Bight (SBB) located at * to the seasonality of the water masses establishing two 22° to 28°S is an oligotrophic system due to the types of the food chain. First, the herbivore food chain predominance of Tropical Water (TW) in the upper should occur under the nutrients input of SACW layers. However, during summer the interaction intrusion and the dispersion of coastal plumes, based between the northeastern wind and the bottom topog- on diatoms and herbivore copepods. Second, under raphy improves the availability of nutrients in the oligotrophic conditions, the food chain based on euphotic zone, through upwelling of cold and nutrient- heterotrophic plankton such as ciliates and 123 Hydrobiologia dinoflagellates as well as detritivores and carnivore Seawater and plankton were sampled in 6 of the 11 copepods should be established. sampling stations (Fig. 1). Water was collected with This study investigated the spatial variability in Van Dorn bottles at three selected depths (0.5 m, copepods and microplankton composition in distinct intermediary depth, and close to the bottom) for situations: (i) in the coastal area under the influence of analysis of dissolved nutrients and chlorophyll-a con- local river plume during winter and summer, (ii) in the centration. The intermediary depth was determined as 50-m isobath, influenced by shelf waters in winter and the depth of fluorescence peak, the thermocline depth, South Atlantic Central Water intrusion in summer. or half of the water column when both were absent. The nutrient and chlorophyll-a data were provided by the MAArE project team. Samples of 250 ml for Method quantitative analysis of microplankton were collected using Van Dorn bottles on subsurface of the water Study area column. Zooplankton was sampled using the cylindri- cal-conical net with 0.5-m diameter mouth and Oceanographic cruises were carried out in the central 200-lm mesh size, coupled with General Oceanics area of the Santa Catarina coast, which is part of the flowmeter. At each station, horizontal tows were Southern Brazilian Bight. The Santa Catarina shelf is a performed on the water column subsurface over 3 min subtropical system and represents the boundary for coastal stations and 5 min for Iso50 stations. The between tropical and temperate marine fauna (Long- mean (± SE) volume of water filtered by the net