Plankton Dataset During Austral Spring and Summer in the Valdés Biosphere Reserve, Patagonia, Argentina

Abstract

The present dataset served to evaluate the plankton community composition and abundance in Nuevo Gulf (42°42′ S, 64°30′ W), a World Heritage Site in Argentinian Patagonia and part of the Valdés Biosphere Reserve. It reports zooplankton abundance (>300 µm) and phytoplankton concentration (10–200 μm) during the spring and summer seasons from 2019 to 2021. Special attention was given to the taxonomic classification of zooplankton, leading to the first identification of jellyfish species within the Gulf and the detection of an unreported copepod for the area (Drepanopus forcipatus). Samples were collected at two depths—a surface and a deeper layer—to assess vertical distribution patterns of plankton communities and explore potential environmental drivers influencing their variability. This dataset provides a valuable baseline for future studies analyzing temporal variations in the Gulf’s plankton communities. Moreover, it encourages the local scientific community to contribute data and promote open access to marine biodiversity records in the region.

Dataset: 10.17632/bydzxvx9h2.1

Dataset License: CC-BY-4.0

1. Introduction

Nuevo Gulf (NG; 42°42′ S, 64°30′ W) is a semi-enclosed coastal basin located in Argentinian Patagonia, within the Valdés Biosphere Reserve, a UNESCO World Heritage Site (2014) [1]. It has a narrow opening (16 km) to the continental Shelf in the South Atlantic Ocean, which allows water exchange and influences its oceanographic conditions. The Gulf has a relatively shallow depth (between 40 and 50 m) as well as deeper areas (up to 180 m), with heterogeneous environmental conditions [2]. It is characterized by strong tidal currents, seasonal stratification, and high biological productivity, making it an important habitat for planktonic communities and higher trophic levels. In this context, NG is recognized as an important area for mating and calving for the southern right whales (Eubalaena australis) [3] as well as a feeding hotspot for this species [4]. Additionally, the region supports other marine mammals, including sea lions (Otaria flavescens) and dolphins (Lagenorhynchus obscurus, Delphinus delphis), as well as seabirds such as cormorants (Leucocarbo atriceps) [5,6].

The region has a temperate climate, with sea surface temperature varying seasonally from approximately 9 °C in winter to 20 °C in summer. Phytoplankton blooms are prominent in spring and autumn [7]; driven by nutrient availability and hydrodynamic processes, they support a diverse zooplankton assemblage. Nuevo Gulf is an ecologically significant area, hosting a variety of marine species, including fish and invertebrates, as well as marine megafauna such as marine mammals and seabirds. However, plankton data for this region remain scarce and fragmented, highlighting the need for more comprehensive and systematic studies.

2. Data Description

The dataset consists of 32 samples of zooplankton abundance (expressed as ind m⁻³) and 27 samples of phytoplankton concentration (expressed as cells L⁻¹) collected during the spring and summer seasons from 2019 to 2021 at three or more sites depending on weather conditions (Figure 1). The data represent organisms in the >300 μm size fraction for zooplankton and the 10–200 μm size fraction for phytoplankton. The dataset reports seasonal abundance or concentration, along with plankton taxa composition to the lowest identifiable level. A metadata sheet is included and provides sampling information (geographic site coordinates, dates, depth, etc.).

Taxonomic Coverage

Taxonomic coverage includes a broad range of taxa, from protozoa, crustaceans, and marine invertebrates to various phytoplankton groups.

• Phylum: Arthropoda, Echinodermata, Chordata, Mollusca, Cnidaria, Annelida, Protista, Ciliophora, Cryptophyta, Heterokontophyta, Euglenophyta, Prasinophyta, and Chrysophyta.
• Class: Copepoda, Malacostraca, Asteroidea, Ophiuroidea, Actinopterygii, Bivalvia, Hydrozoa, Scyphozoa, Polychaeta, Dinoflagellata, Protozoa, Ciliata, Cryptophyceae, Bacillariophyceae, Euglenophyceae, Prasinophyceae, and Chrysophyceae.
• Order: Calanoida, Harpacticoida, Euphausiacea, Decapoda, Amphipoda, Asteroidea, Ophiurida, Semaeostomeae, Leptomedusae, Hydroida, Siphonophorae, Polychaeta, Noctilucales, Cryptomonadales, Centrales, Pennales, Euglenales, and Silicoflagellales.
• Family: Calanidae, Oithonidae, Acartiidae, Euphausiidae, Penaeidae, Portunidae, Gammaridae, Asteriidae, Ophiuridae, Campanulidae, Clytiidae, Hydridae, Rhizophysidae, Prayaidae, Pelagiidae, Nereididae, Syllidae, Noctilucidae, Parameciidae, Cryptomonadaceae, Coscinodiscaceae, Naviculaceae, Fragilariaceae, Gonyaulacaceae, Symbiodiniaceae, Euglenaceae, Pyramimonadaceae, and Silicoflagellaceae.
• Genus: Evadne, Podon, Paracalanus, Ctenocalanus, Drepanopus, Oithona, Acartia, Calanoides, Calanus, Noctiluca, Aequorea, Amphinema, Bougainvillia, Clytia, Cosmetirella, Eucheilota, Euphysa, Hybocodon, Laodicea, Leuckartiara, Mitrocomella, Obelia, and Chrysaora.
• Species: Evadne nordmanni, Podon spp., Paracalanus parvus, Ctenocalanus vanus, Drepanopus forcipatus, Oithona spp., Acartia spp., Calanoides carinatus, Calanus australis, Noctiluca spp., Aequorea coerulescens, Amphinema rugosum, Bougainvillia muscus, Clytia hemisphaerica, Clytia gracilis, Clytia lomae, Clytia simplex, Cosmetirella davisi, Eucheilota ventricularis, Euphysa aurata, Hybocodon chilensis, Laodicea undulata, Leuckartiara octona, Mitrocomella brownei, Mitrocomella frigida, Mitrocomella polydiademata, Obelia spp., and Chrysaora plocamia.

3. Methods

Plankton samples were collected during daytime on 11 October 2019; 17 January 2020; 9 October 2020; and 20–21 January 2021 at multiple stations spaced approximately 14 km apart. These stations were widely distributed across Nuevo Gulf (NG) to account for potential variations in oceanographic conditions (Figure 1).

At each sampling site, a 5-liter Niskin bottle was deployed to collect discrete water samples from two depths (1 and 70 m, representing surface and intermediate samples, respectively), according to a previously described homogeneous upper layer and changes in the vertical water column properties at ca. 50 m for temperature, density, and nutrients [8]. These samples were preserved in amber-colored bottles with neutral Lugol’s solution (final concentration 4%), stored in a dark, cool environment, and sent to CADIC for plankton analysis once the samples collected in spring and summer for each year were ready. Samples for quantitative zooplankton analysis were collected using horizontal net tows (40 cm diameter, 300 µm mesh pore size) at approximately 30 ± 7 m (subsurface layer) and 70 ± 16 m (intermediate layer) and ballasted with different weights to attain the desired depths [9]. The volume of filtered water was calculated using a mechanical flowmeter (General Oceanics Inc., Miami, FL, USA) while traveling for 7 min at 2 knots. Samples from both layers were then stored in 250 or 500 mL plastic flasks and preserved in 4% formaldehyde.

3.1. Zooplankton Analysis

Zooplankton organisms were identified and counted under a binocular stereomicroscope (Leica SAPO, Wetzlar, Germany) to determine abundance (ind m⁻³) based on either total counts or aliquot-based estimates. When samples were very abundant, quantification was carried out by examining aliquots (5 mL) randomly extracted from homogenized samples (200 mL) and returned to the sample until 10% of the total volume of each sample had been counted [10]. Jellyfish were identified at the lowest possible taxonomic level and counted under a binocular stereoscopic microscope (Nikon SMZ645, Tokyo, Japan) to obtain abundance (ind m⁻³) based on total counts [10,11,12,13].

3.2. Other Plankton Identification and Quantification

Enumeration and taxonomic identification of the plankton community within the sampled size fraction (10–200 μm) were performed using the Utermöhl method [14]. For this, 50 mL of the sample was left to settle for 24 h in sedimentation chambers (27.44 mm in diameter). After this period, samples were examined using an Iroscope SI-PH inverted microscope (Cuernavaca, Mexico). Phytoplankton were classified into major groups based on morphotype and size into dinoflagellates, diatoms (centric and pennate separately), prasinophytes, cryptophytes, silicoflagellates, and unidentified flagellates, following established classification criteria [15]. Moreover, ciliates belonging to protozoa were identified as an abundant group. Total cell concentration was determined by performing a complete chamber count under a 25× objective lens. Phytoplankton abundances are reported as cells L⁻¹.

4. Scientific Relevance and Considerations

This dataset serves as a key reference for understanding plankton biodiversity in the NG, part of the VBR. It provides baseline data to track shifts in community composition and abundance due to environmental changes, as observed in this and neighboring areas [7,16]. By documenting seasonal plankton variations, this open-access dataset will support long-term ecological monitoring. The taxonomic resolution also led to the identification of a new copepod species and several jellyfish with improved vertical resolution (two depths).

While this dataset provides valuable information, some limitations should be considered for ecological interpretation. Sampling was limited to specific sites within the NG during two seasons (spring and summer, 2019–2021) and may not fully represent plankton diversity across the entire Gulf. Additional sampling at other locations and during fall or winter could reveal important seasonal patterns and better capture spatial variability. A more thorough examination of intermediate depths could also enhance our understanding of vertical distribution patterns.