Declining bivalve species and functional diversity along a coastal eutrophication-deoxygenation gradient in the northern Gulf of Mexico
Data files
Oct 25, 2024 version files 550.86 KB
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Harnik_atal_CSR_data_live_abund_trait_env.csv
543.40 KB
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Harnik_etal_CSR_data_live_nind_per_sample.csv
1.41 KB
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README.md
6.05 KB
Abstract
Coastal eutrophication and hypoxia are growing challenges globally, yet their impacts can be difficult to evaluate because of limited biomonitoring that typically postdates the onset of these stressors. We address this limitation by investigating how the taxonomic and functional diversity of marine bivalve communities vary with primary productivity, dissolved oxygen, temperature, and seafloor sediment properties across the northern Gulf of Mexico, a region that includes one of the world’s largest dead zones. We hypothesized that taxonomic and functional richness would decline in eutrophic and hypoxic coastal environments. Live bivalve mollusks were sampled at 15 stations, spanning more than 600 km of continental shelf habitat. Individuals were identified to species and characterized based on feeding, mobility, fixation, life position relative to the sediment-water interface, and body size. Alpha and beta species and functional diversity were computed using Hill numbers and linear models used to assess their covariation with regional environmental conditions. Species and functional diversity were highest in less eutrophic environments characterized by normoxic conditions, and lowest in more eutrophic environments where oxygen was more limited. Community-level differences were underlain by functional shifts, with abundant shallow-infaunal, deposit and mixed feeders in more eutrophic settings, in contrast with less eutrophic settings where suspension feeders were more abundant. Median body size increased with eutrophication, possibly as a result of hypoxia-induced declines in predator and competitor populations. These results suggest that intensifying nutrient loading and deoxygenation in the coastal zone will cause declines in multiple dimensions of benthic biodiversity with implications for ecosystem function.
https://doi.org/10.5061/dryad.4tmpg4fhk
The dataset contains taxonomic and functional data for approximately 1500 live-collected individual marine bivalves that were sampled at a total of 15 stations on the continental shelf in the northern Gulf of Mexico in May and June 2018. Environmental data for each sampling station are also included.
Description of the data and file structure
Data in “Harnik_atal_CSR_data_live_abund_trait_env.csv” are organized as follows.
ID_Date: the date that the individual was identified to species in the lab; format is Month/Day/Year
State: the U.S. state that the individual was sampled offshore of; LA, Louisiana; AL, Alabama; FL, Florida
Sample_Year: the year in which that individual was sampled; all were collected in 2018
Station: the station where the individual was sampled; stations are indexed by 2-letter State (e.g., LA) and a station ID (e.g., 21) from west (21) to east (25) in each region
Sample: unique ID for the sediment grab or boxcore sample that individual was collected in; format is 2-letter State, 2 number station ID, sample ID, and L for live-collected
Live_or_Dead: field indicating whether individual was live-collected (Live) or sampled as empty shell (Dead); all individuals in this dataset were live-collected.
Family: the family that individual belongs to
Genus: the genus that individual belongs to
Species: the species that individual belongs to
Shell_Length_mm: the anterior-posterior dimension of the shell parallel to the hinge; measured in millimeters
Shell_Height_mm: the dorsal-ventral dimension of the shell perpendicular to the length measurement; measured in millimeters
Geometric_Mean_mm: the geometric mean of shell length and shell height; measured in millimeters
Shell_Area: the body size of the individual, calculated using shell area, as approximated by an ellipse; measured in millimeters squared
Taxon: species ID for the individual, consisting of its concatenated genus and species names; format Genus_species
func_grp_long: categorical functional group ID based on individual’s concatenated categorical traits (mobility, fixation, feeding, and substrate)
Latitude: latitudinal coordinate for the station where the individual was sampled
Longitude: longitudinal coordinate for the station where the individual was sampled
Depth_meters: water depth for the station where the individual was sampled
SiltClay_Percentage: weight percent of silt and clay sediment for the station where the individual was sampled
SST_meanJAS_depth15m_WOA: mean July-August-September sea surface temperature (in °C) from 1955 through 2017 for the station where the individual was sampled
SST_sdJAS_depth15m_WOA: standard deviation in July-August-September sea surface temperature (in °C) from 1955 through 2017 for the station where the individual was sampled
DO_meanJAS_depth15m_WOA: mean July-August-September dissolved oxygen concentration (in µmol/kg) from 1955 through 2017 for the station where the individual was sampled
DO_sdJAS_depth15m_WOA: standard deviation in July-August-September dissolved oxygen concentration (in µmol/kg) from 1955 through 2017 for the station where the individual was sampled
NPP_mean: mean net primary productivity (in mgC/m2/day) from 2003 through 2018, calculated by averaging data for each month and then calculating the mean across months for the station where the individual was sampled
NPP_sd: standard deviation in net primary productivity (in mgC/m2/day) from 2003 through 2018 for the station where the individual was sampled
mobility: categorical trait describing the mobility of the individual
fixation: categorical trait describing the fixation of the individual
feeding: categorical trait describing the feeding type of the individual
substrate: categorical trait describing the life position of the individual relative to the substrate
reference: primary literature reference used to determine mobility, fixation, feeding, and substrate
notes: secondary literature reference used to determine mobility, fixation, feeding, and substrate; NA indicates that a secondary reference was not used
Data in “Harnik_etal_CSR_data_live_nind_per_sample.csv” are organized as follows.
LA_sediment_grabs: the number of live bivalves in each boxcore sample collected at the five stations on the continental shelf offshore of Louisiana
AL_sediment_grabs: the number of live bivalves in each boxcore sample collected at the five stations on the continental shelf offshore of Alabama
FL_sediment_grabs: the number of live bivalves in each sediment grab collected at the five stations on the continental shelf offshore of Florida
Cells containing numerical values indicate the number of live bivalves collected in a sediment sample
Cells containing ‘NA’ values are not applicable; i.e., the nth sediment sample was not collected in that region
Sharing/Access information
All data used in this study are archived here.
Code/Software
“Harnik_atal_CSR_code_analyses.R” includes all R code used to analyze data in “Harnik_atal_CSR_data_live_abund_trait_env.csv” and “Harnik_etal_CSR_data_live_nind_per_sample.csv” and generate associated figures and tables.
Codes include the calculation of generation of coverage-based sampling curves for regions and stations; alpha and beta taxonomic and functional diversity estimates at different diversity orders; analysis of the relationship between environmental conditions and alpha diversity; analysis of the relationship between geographic distance and beta diversity; bootstrap procedure to assess the linear relationship between taxonomic and functional diversity at different diversity orders; ordination of taxonomic, functional, and environmental dissimilarities; calculation of species relative abundance for each region; comparison of regional shell size distributions; comparison of regional sample sizes.