DOI: 10.5061/dryad.4tmpg4fhk
title: Declining bivalve species and functional diversity along a coastal eutrophication-deoxygenation gradient in the northern Gulf of Mexico

description: 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.
description: # Declining species and functional diversity along a coastal
 eutrophication-deoxygenation gradient
 [https://doi.org/10.5061/dryad.4tmpg4fhk](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.