Effect of short-term meteorological disturbance on submergem aquatic vegetation and associated fauna

Study Extent

The Patos Lagoon (PLE) is the largest coastal lagoon in South America with ~ 11,000 km², comprising shallow flats (~170 km²) with less1.5 m depth and a deeper main channel. The hydrodynamics and physicochemical characteristics of PLE are highly dependent of local and remote winds action, fluvial discharge and regional precipitation. The salinity of estuarine region is fresh in raining, but in dry seasons the outflow and inflow are dominated by NE and SW wind, respectively, generating saline scenarios. This study was conducted in Justino Bay (-32.07; -52.22), a preserved region where seasonal seagrass beds are dense and more perennial. The hydrodynamics in edge shallow areas is caused by the wind meanly south, generating the predominance of fine sandy sediments. Due to the fresh water input and the poor water circulation salinity ranges from 0 to 20, according to the seasons.

Sampling

The field works were carried out hours or one day before and after four occluded fronts passage, using before as control, according to BACI model (Before/After, Control/Impact; UNDERWOOD, 1996). Sampling fieldwork were in Summer (B: 2019/03/08 and A: 2019/03/13), Autumn (B: 2019/05/08 and A: 2019/05/13), Winter (B: 2019/08/23 and A: 2019/08/28) and Spring (B: 2019/11/08 and A: 2019/11/18). Sampling followed a hierarchical model where SAV Meadow, Sandflat and SAV Edge habitats were sorted. The habitats were divided in three transects (T1, T2, T3). In each transect two sediment samples (A, B) and three macrozoobenthic and seagrass samples (A, B, C), one measure of environmental parameters and water column depth were taken. Vegetal visual coverage (quadrat, 1 m²; N total = 216 samples), canopy height (216 observations) and biomass (core, 00.08 m²; 216 samples) were collected. Plants biomass were sorted out according to leaf morphology for taxonomic identification and below and aboveground biomass were separated for dry weight determination (48 h at 60 °C). Benthic macrofauna (core: 0.008 m²), stratified in 0 - 0.1 m (N total = 216) and 0.1 - 0.2 m (N total = 216), were sampled and sieved through a 300 µm mesh. Macrofauna was fixed with 4 % formalin, identified and preserved in alcohol 70 %. Sediment samples were sampled (total N=144), with cylindrical core (0.002 m², 0.1 m depth) and analyzed using sieving and pipetting indirect method. Sedimentary organic matter content (total N=144) were determined by ignition method.

Quality Control

The sampled material was processed by specialists, based on accepted and applied manuals for sampling (LANA et al., 2006; TURRA; DENADAI, 2015), taxonomy (AMARAL; RIZZO; ARRUDA, 2006; BUCKUP; BOND-BUCKUP; ARENZON, 1999; LARKUM; ORTH; DUARTE, 2006; RIOS, 1994) and methodology (DAVIES, 1974; LAVERY; KENDRICK, 2001; SUGUIO, 1973). Taxonomic validity was verified using the World Register of Marine Species (WoRMS; www.marinespecies.org) and in National Center for Biotechnology Information (https://www.ncbi.nlm.nih.gov).

Method steps

1. Submarged Aquatic Vegetation: During each sampling event, SAV visual coverage and canopy height (quadrat, 1 m²), and biomass (core: 0.1 X 0.1 m) were collected in each transect and habitat (N total = 216 samples). In the laboratory, plants fresh biomass was separated from macrobenthic organisms and sorted out in R. maritima/ Z. palustris and in P.striatus according to leaf morphology. Below (roots and rhizomes) and aboveground (shoots and leaves) biomass were separated for determination of dry weight (48 h, 60 °C; McKenzie et al., 2003).
2. Benthic Macrofauna: Benthic macrofauna were sampled with cylindrical core (0.008 m²), stratified between 0 - 0.1 m and 0.1 - 0.2 m, for each transect and habitat (N total = 216 samples for each stratum). The samples were sieved through a 300 µm mesh and kept fresh just to pre-sort fauna and flora. Macrofauna was fixed with 4 % formalin, identified and preserved in alcohol 70 %.
3. Environmental Parameters: Surface water temperature (mercury thermometer) and salinity (portable RH0-90 refractometer) were taken at the beginning of each field sampling. Sediment samples were performed in duplicate for each transects and habitat with cylindrical core (0.002 m², 0.1 m depth, total N=144) for granulometric analyses and determination of organic matter content. Granulometry was analyzed using method described by Suguio (1973). Organic matter content was determined by the loss on ignition method (DAVIES, 1974)

This dataset has occurrences records of plants and animals organisms belonging to eight phyla, 15 classes, 21 families and 16 species. Our equipment and sampling methodology aimed to capture benthic macrofauna and marine macrophyte, but we registered other seagrass associated fauna occurrence in dataset. In this way we rank the main organisms taxa.

1. Laeonereis acuta
   rank: species
2. Heteromastus similis
   rank: species
3. Nephtys fluviatilis
   rank: species
4. Alitta succinea
   rank: species
5. Heleobia australis
   common name: Snail rank: species
6. Erodona mactroides
   common name: Erodon Corbula rank: species
7. Monokalliapseudes schubarti
   rank: species
8. Sinelobus stanfordi
   common name: A tanaid rank: species
9. Uromunna peterseni
   rank: species
10. Diastylis sympterygiae
    rank: species
11. Heleobia charruana
    common name: snail rank: species
12. Capitella nonatoi
    rank: species
13. Oligochaeta
    rank: class
14. Paraprionospio pinnata
    rank: species
15. Amphipoda
    rank: order
16. Balanidae
    common name: craca rank: family
17. Hydrozoa
    rank: class
18. Cassidinidea fluminensis
    rank: species
19. Gastropoda
    common name: snail rank: class
20. Heleobia
    common name: snail rank: genus
21. Tagelus plebeius
    common name: Stout tagelus rank: species
22. Nemertea
    common name: Proboscis worm rank: phylum
23. Chironomidae 
    common name: Mosquitoes rank: family
24. Odonata
    common name: Dragonflie rank: order
25. Ostracoda
    rank: class
26. Hydrachnidia
    common name: water mite rank: suborder
27. Miliolina
    rank: genus
28. Foraminifera
    rank: phylum
29. Nematoda
    common name: Worm rank: phylum
30. Cladocera
    common name: Water fleas rank: superorder
31. Copepoda
    rank: subclass
32. Mysidacea
    common name: Opossum shrimp rank: order
33. Callinectes 
    common name: crab rank: genus
34. Cicadellidae
    common name: Leafhopper rank: family
35. Penaeidae
    common name: Shrimp rank: family
36. Coleoptera
    common name: Beetle rank: order
37. Cyrtograpsus angulatus
    common name: Crab rank: genus
38. Collembola
    rank: order
39. Homoptera
    common name: Grasshopper rank: suborder
40. Hymenoptera
    common name: Winged ant rank: order
41. Salpidae
    common name: Salpa rank: family
42. Zannichellia palustris
    rank: species
43. Potamogeton striatus
    rank: species
44. Ruppia maritima
    common name: Widgeon grass rank: species

Seagrass Meadow, Seagrass Edge, Sandflat, Justino Bay, Patos Lagoon Subtropical Estuary, Rio Grande, Rio Grande do Sul, Southern Brazil.