MACROBENTHOS COMPOSITION FROM THE RIO LAGARTOS HYPERHALINE COASTAL LAGOON SYSTEM, YUCATAN, MEXICO

Study Extent

The information in this dataset was obtained from the Río Lagartos coastal lagoon system, NE Yucatan Peninsula, Mexico at the coordinates 21°26´, 21°38´ N and -87°30´, -88° 15’ W. This east-west-oriented system runs parallel to the coast, is ca. 80 km and is divided into three basins hydrologically connected through very narrow channels. It is hyperhaline through much of its length, with a strong salinity gradient from the head, to the east, where salinity reaches values >100, to the mouth, located at its westernmost side, where salinity reaches seawater values (ca. 34). Macrobenthos samples were obtained from 16 stations distributed throughout the lagoon, in stations of 0.5-1 m depth. The samplings were performed at the end of each climatic season in the region: the rainy season (2017-09-26/2017-10-05), the northerly winds season (2018-02-22/2018-02-28), and the dry season (2018-05-15/2018-05-22), during one year.

Sampling

Macrobenthos samples were obtained from the Río Lagartos coastal lagoon system, located in the north-eastern Yucatán Peninsula (21°26´, 21°38´ N and -87°30´, -88° 15’ W), as part of the Salinity Gradient Energy project of the Centro Mexicano de Innovación en Energía (CEMIE) Océano. Macrobenthos samples were collected from a total of 16 stations distributed along the lagoon considering the three main basins in the system: Río Lagartos to the west (Stations: 3, 6, 9, 12, 15), Las Coloradas in the middle (Stations: 20, 21, 22, 23, 25) and El Cuyo to the east (Stations: 27, 29, 30, 32, 35, 38). The distribution of the sampling stations according to the three different basins was based on previous studies of the distribution of physical-chemical parameters (Valdes & Real, 2004), fish (Vega-Cendejas & Hernández de Santillana, 2004), and algae (Ortegón-Aznar et al., 2001) in the lagoon, which indicated that the three basins can be considered as environmentally and biologically distinct areas. Samples were collected at depths ranging from 0.5 to 1.5 m using a Ponar standard dredge (9”x 9” or 22.9 x 22.9 cm; 0.052 m2 grab operating area), or a cylindrical PVC core (6” diameter; 0.018 m2 operating area) when the substrate was too hard, and the dredge did not penetrate the ground. In some stations where mangrove was close, epibenthic fauna on the roots of red mangrove Rhizophora mangle (Linnaeus, 1753) were also obtained, by gently scraping them from the root surface, over a 20 x 20-cm2 area, at mid-depth in the water column. Two replicates per station were obtained, and the sediments were sieved through a 500 μm mesh size to separate the macrofauna. Samplings were carried out at the end of each climatic season in the region: the rainy season (2017-09-26/2017-10-05), the northerly winds season (2018-02-22/2018-02-28), and the dry season (2018-05-15/2018-05-22), during one year. The biological material was initially anesthetized with magnesium chloride, and preserved in 4% formaldehyde. In the laboratory, samples were preserved in 70% ethanol, and the macrobenthos were sorted and identified, under a stereomicroscope (at x10-x40 Leica EZ4) or a microscope (at 20x-100x Nikon Eclipse Ci), using the adequate literature. The specimens were deposited in different biological collections, and a catalogue number was assigned. At each station, salinity was measured in the water column at depths between 0.15 and 0.35 m using a multiparameter Aquaprobe AP-5000. A refractometer was used to measure salinity when values exceeded 60, and a Baume hydrometer was used when salinity was > 80.

Method steps

1. The sampling stations were planned before the sampling survey and recorded in a Garmin GPS, model GPSMAP 64s. Once on the field, a local fishing boat was used to get to each of the stations, and velocity was lowered to avoid the disturbance of the bottom when the station was reached. After getting to the desired sampling point, the boat was stopped and the position was again recorded on the GPS. Following, the salinity was measured from the boat using a multiparameter Aquaprobe AP-5000, getting measurements between depths of 15 and 35 cm. A refractometer was used to measure salinity when values exceeded 60, and a Baume hydrometer was used when salinity was > 80, and two measurements were obtained with each device. After that, the Ponar standard dredge was released from the boat at a height of ca. 1-1.5 m from the bottom. If the sample was appropriately obtained, it was put in a deep plastic tray and the procedure was repeated at a distance between 1 and 5 m from the first collection. If the grab did not penetrate de substrate, two people participating in the sampling survey got down from the boat and collected the sample with a 6”-diameter, 70 cm-height, cylindrical PVC core, with a serrated lower edge, and equipped with a top plug and lateral handles. The core was introduced into the sediment without the plug between 15 and 20 cm and the top plug was inserted in order to avoid the loss of sample during core extraction. The core was gently pulled, with light lateral movements, and the sample was deposited in a deep plastic tray. The procedure was repeated at a distance between 1 and 5 m, ensuring the presence of non-disturbed bottom due to the displacement of the people performing the samplings. Once the two replicates were collected, each tray was left on one side of the boat and all the team descended from the boat except for one, who took care of the trays. For each replicate (tray), one person held a TYLEX 12 cm high, 500 m mesh size sieve and another one put some sediment in the sieve using a small plastic shovel. Sediment sieving was performed adding water from the bottom of the sieve, by putting it in contact with the lagoon water. Sieving was continued until the sample was reasonably clean and the clean sample was put in a plastic bag kept in the boat. The procedure was continued until the whole sample was sieved and clean. When the sample was in the bag, magnesium chloride was added in order to anesthetize the organisms. After ca. 10 minutes, 4% formaldehyde was added. The replicates were identified by putting a tracing-paper label inside the bag, in which the identifiers of the sampling survey, date, sampling station, type of sample and number of replicate were written using a pencil. Additionally, the bag was identified in the outside with duct tape, where the same information was written using an indelible marker. The bags were put in a 20 L plastic bucket and stored in the boat. This procedure was repeated in the 16 stations sampled. At the end of the sampling survey, the samples were transported to the laboratory “Laboratorio de Biología de la Conservación”, from the Science Faculty of the UNAM Campus in Yucatan, located at the Parque Científico y Tecnológico de Yucatán, where they were stored at room temperature inside the same buckets. Before processing, the samples were gently rinsed with water through a 500 m sieve and then they were preserved in 70% ethanol. The macrobenthos specimens were sorted from the sediment and identified to large taxonomic groups under a stereomicroscope (at x10-x40 Leica EZ4) or a microscope (at 20x-100x Nikon Eclipse Ci), and counted. Each large taxonomic group from each replicate was stored in small cryovials or Eppendorf tubes adequately identified with tracing paper inside the tubes and using an indelible marker outside the tubes. The specimens from each taxonomic group were sent to the adequate taxonomists, who identified the groups to genus or species level using the literature specified in this dataset. When possible, the samples were included in biological collections for their future preservation. Mean values of the salinity recorded at each station were obtained. All the information of abundance of each genus or species from each replicate was inserted in an Excel worksheet together with the salinity values at each station. The macrobenthos data were transformed to presence-absence data before inserting the information in the dataset.

1. ACARI
   rank: subclass
2. AMPHIPODA
   rank: order
3. BIVALVIA
   rank: class
4. CUMACEA
   rank: order
5. GASTROPODA
   rank: class
6. HOLOTHUROIDEA
   rank: class
7. ISOPODA
   rank: order
8. MYSIDA
   rank: order
9. OPHIUROIDEA
   rank: class
10. POLYCHAETA
    rank: class
11. PYCNOGONIDA
    rank: class
12. SIPUNCULA
    rank: phylum
13. TANAIDACEA
    rank: order

The information in this dataset was obtained from the Río Lagartos coastal lagoon system, located in the northeastern Yucatan Peninsula, Mexico, inside the Ría Lagartos Biosphere at the coordinates 21°26´, 21°38´ N and -87°30´, -88° 15’ W. This east-west-oriented system runs parallel to the coast, and is ca. 80 km long, with a total surface area of about 98 km2. The lagoon is divided into three basins hydrologically connected through very narrow channels and has a mean depth of 0.5 m, with some deeper locations, up to 3.5 m. It is hyperhaline through much of its length, with a strong salinity gradient from the head, to the east, where salinity reaches values >100, to the mouth, located at its westernmost side, where salinity reaches seawater values (ca. 34). Hyperhaline conditions are a consequence of low rainfall (<500 mm/year), high evaporation (~2000 mm/year), absence of overland freshwater inputs, long residence times, and the physical/geomorphological characteristics. The samplings were performed in 16 stations distributed throughout the lagoon, in stations of 0.5-1 m depth.