DOI: 10.5061/dryad.c45f0
title: Data from: Individual, population, and ecosystem effects of hypoxia on a dominant benthic bivalve in Chesapeake Bay

description: Hypoxia is an environmental stressor that affects abundance, biomass,
 diversity and ecosystem function of benthic assemblages worldwide, yet its
 collective impact at individual, population, and ecosystem levels has
 rarely been investigated. We examined the effects of hypoxia on the
 biomass-dominant clam, Macoma balthica, in the York and Rappahannock
 Rivers (Chesapeake Bay, USA). We (i) surveyed the M. balthica populations
 in both rivers in 2003 and 2004, (ii) determined the effects of low DO on
 M. balthica fecundity in a laboratory experiment, and (iii) employed a
 predator-exclusion field experiment to establish the effects of hypoxia
 and prey density on predation upon M. balthica. The resultant data were
 used to parameterize a matrix model, which was analyzed to define
 potential effects of hypoxia at the population level. In both rivers,
 hypoxia decreased individual clam growth and caused local extinction of
 populations. Hypoxia reduced egg production of M. balthica by 40% and
 increased protein investment per egg. In the predator-exclusion field
 experiment, hypoxia magnified predation rates three-fold and altered the
 functional response of predators to M. balthica from a stabilizing type
 III functional response to a destabilizing type II functional response. In
 a density-independent matrix model, hypoxia resulted in coupled
 source-sink metapopulation dynamics, with hypoxic areas acting as
 black-hole sinks. Increases in the spatial and temporal extent of hypoxia
 caused the populations to decline toward extinction. In a second model
 that incorporated density-dependence, under mild hypoxic conditions
 trophic transfer from M. balthica to predators increased, but at increased
 spatial or temporal extent of hypoxia trophic transfer decreased. The
 major decline in trophic transfer to predators under severe hypoxia
 resulted from diversion of M. balthica biomass into the microbial loop.
 Our model predicted that there are multiple stable states for M. balthica
 populations (high and very low densities), such that the saddle point
 (threshold at which the population switches from one state to the other)
 increased and resilience decreased with the spatial extent of hypoxia. We
 underscore how effects of a stressor at the individual level can combine
 to have substantial population and ecosystem-level effects.
description: Sites and physical
 measurements 2003GPS coordinates and
 measurements of dissolved oxygen, temperature, and salinity taken during
 field surveys in the York and Rappahannock Rivers, VA, in
 2003.Sites and physical
 measurements 2004GPS coordinates and
 measurements of dissolved oxygen, temperature, and salinity taken during
 field surveys in the York and Rappahannock Rivers, VA, in
 2003.Field predation and
 non-predatory mortality ratesCalculated predation
 rates from a caging study on Macoma balthica in the York River in 2006.
 Rates were calculated based on the number of marked clams recovered after
 approximately 4 weeks exposure time. Non-predatory mortality rates were
 based on the recovery of marked dead clams (i.e. undamaged shells). The
 major predator on M. balthica in this system is the blue crab Callinectes
 sapidus.Field predation
 experiment DO DatasondThis file contains the
 measurements of dissolved oxygen (DO) in mg O2/L recorded by a Hydrolab
 DS5X with a luminescent DO probe (Hach Environmental, Loveland, CO) at a
 single deep site during the predation experiment in the York River in
 2006. Date/time represents the data and time (EST) of each
 measurement.Field predation sites
 and physical measurementsThis file contains the
 measurements of dissolved oxygen (DO) in mg O2/L at each site during the
 predation experiment using an YSI 85. Date represents the date of each
 measurement. Latitude and longitude are in decimal degrees. Temperatures
 are in degrees Celsius, salinity in practical salinity units (psu) and
 dissolved oxygen (DO) in mg O2/L.Lab experiment DO and
 tempThis file contains the
 measurements of dissolved oxygen (DO) and temperature in tanks during a
 laboratory experiment examining the effects of low DO on the clam Macoma
 balthica. Treatment represents the nominal dissolved oxygen (mg O2/L)
 treatment group. Replicate represents the replicate tank number. DO is in
 mg O2/L) and temperature is in degrees Celsius. The date is the date of
 each measurement and time is approximate time in EST.Macoma balthica
 densitiesThis file contains the
 average Macoma balthica densities at each site sampled in box cores during
 the field surveys in 2003-2004. The minimum summer DO represents the
 minimum dissolved oxygen concentration (mg O2/L) observed at each site
 during that year. River is represent the river the sample was taken in,
 Date the day the sample was taken, and Site the nominal site at which the
 sample was taken. Note that sites changed location between years, (i.e.
 site M2 in 2003 in the York was at a different location than site M2 in
 2004). Site location and raw DO measurements are available in the Sites
 and physical measurements files.Macoma balthic
 densities.csvMacoma balthica lengths
 and massesThis file contains the
 average Macoma balthica shell lengths in mm and ash free dry masses (AFDM)
 in mg at each site sampled during the field surveys 2004. River represents
 the river the sample was taken in, Site represents the site name, Date
 represents the date the sample was taken. The average summer DO represents
 the average dissolved oxygen concentration (mg O2/L) observed at each site
 during that summer. Site locations and raw DO measurements are available
 in the Sites and physical measurements 2004 file.Macoma balthic lengths and
 masses.csvMacoma balthica
 recruitsThis file contains the
 Macoma balthica recruit (shell length &lt; 3 mm) densities at each site
 sampled during the field survey in the Rappahannock River in Feb. 2004.
 River represents the river the sample was taken in; Site represents the
 site name; Date represents the date the sample was taken. The minimum
 summer DO represents the minimum dissolved oxygen concentration (mg O2/L)
 observed at each site during that year. Site location and raw DO
 measurements are available in the Sites and physical measurements
 files.Macoma balthic
 recruits.csvMacoma balthica shell
 lengthsThis file contains the
 Macoma balthica shell lengths (in mm) at each site sampled during the
 field surveys 2004. River represents the river the sample was taken in,
 Site represents the site name, Date represents the date the sample was
 taken. The average summer DO represents the average dissolved oxygen
 concentration (mg O2/L) observed at each site during that summer. Site
 location and raw DO measurements are available in the Sites and physical
 measurements files.Macoma balthic shell
 lengths.csvMacoma balthica
 survivalThis file contains the
 average Macoma balthica survival at each site sampled during the field
 survey in 2004. Survival is calculated as the average density in the fall
 sampling divided by the average sampling in the spring at each site. River
 represents the river the sample was taken in, Site represents the site
 name, Date represents the date the sample was taken. The average DO
 represents the average dissolved oxygen concentration (mg O2/L) during the
 summer months observed at each site during that year. Site locations and
 raw DO measurements are available in the Sites and physical measurements
 files, and the raw densities are available in the Macoma balthica
 densities file.mb-HSP70 and
 fecundityThis file contains the
 measurements units mb-HSP70/clam and the number of eggs/clam in the
 laboratory experiment. Examining the effects of dissolved oxygen on Macoma
 balthica. Mb-HSP70 is a protein expressed in Macoma balthica. Eggs/clam
 could only be calculated for the &gt; 4.0 mg/L treatment, and the &lt; 2.0
 mg/L treatment; blank indicate no data is available. Treatment represents
 the nominal dissolved oxygen (mg O2/L) treatment group. Replicate
 represents the replicate tank number within each
 treatment.mb-HSP70 and protein in
 eggsThis file contains the
 measurement of units mb-HSP70/egg and the µg protein/egg in a laboratory
 experiment on the effects of dissolved oxygen on Macoma balthica. Mb-HSP70
 is a protein expressed in Macoma balthica eggs. Treatment represents the
 nominal dissolved oxygen (mg O2/L) treatment group. Clam represents the
 replicate clam number.