Download Supervisor: Kersey Sturdivant McCurdy Post

Supervisor: Kersey Sturdivant
McCurdy Post-Doctoral Scholar
Duke University Marine Lab
252-504-7678
[email protected]
http://fds.duke.edu/db/Nicholas/msc/faculty/sks33
Internship Opportunity:
I am seeking one qualified student for a 10-week summer internship to oversee and
implement a project assessing the metabolic and cardiorespiratory responses of marine
worms to hypoxia at varying temperatures using stop-flow respirometry. Experience with
the stated methodology (outlined below) or discipline is not necessary, training will be
provided. The process of stop-flow respirometry is mostly automated; the intern will be
responsible for overseeing the automation process and changing worms once a set of
experiments is run. There is a very small learning curve; it takes only a week to learn how
to operate the system. When the system is running there will be plenty of free time for
the student to work on something else (write a novel perhaps?).
The study will take place at the Virginia Institute of Marine Science’s (VIMS) Eastern
Shore Laboratory (ESL) in Wachapreague, VA. There are dorms on site and the student
will be part of an academic community of national and international students based at the
ESL during the summer. I would describe the ESL in Wachapreague as quaint and
peaceful. The new seawater lab and teaching/lecture/dry lab are both very impressive
and well equipped. The Island House is the restaurant most go to and has recently
changed owners and improved a lot (within the past 2 years). It is not important that the
student have a car, to get to the grocery store and other restaurants in the area, as the
community at ESL is very inclusive and helpful. The atmosphere during the summer is
fantastic with the lab bustling with enthusiastic scientists researching a plethora of
topics. There is certainly an opportunity to meet and network with other students, lab
techs, field crew, and senior researchers. There are plenty of good Mexican restaurants
and a lot of cute farm stands selling local produce. More information about VIMS ESL
can be found here: www.vims.edu/esl/
This internship does not offer a salary stipend but will cover all expenses including travel
to and from the location, lodging, and meals.
A detailed project description is included below. Interested students should submit a
short (paragraph) statement of interest via email by April 5, 2013.
Project Description
Title:
Metabolic and cardiorespiratory responses of the spionid polychaete Paraprionospio
pinnata and nereid polychaetes Nereis succinea to hypoxia at varying temperatures.
In collaboration with Dr. Richard Brill of the Virginia Institute of Marine Science
(VIMS), polychaetes collected in the Neuse River will be transported to the Virginia
Institute of Marine Science's Eastern Shore Laboratory (ESL) in Wachapreague, VA.
Once there Dr. Brill's Loligo respirometry system will be used to assess the
cardiorespiratory responses of spionid and nereid polychaetes in a declining oxygen
environment at various temperatures.
Objectives
Collect spionid and nereid polychaetes from the Neuse River with a Young grab, using
NOAA vessel R/V Carson II. In collaboration with Dr. Richard Brill, polychaetes
collected in the Neuse will be transported to the Virginia Institute of Marine Science's
eastern shore laboratory in Wachapreague, VA. Once there Dr. Brill's Loligo
respirometry system (sans appropriate sized chambers) will be used to assess the
cardiorespiratory responses of spionid and nereid polychaetes in a declining oxygen
environment at various temperatures.
Significance
Little is known about the respiratory function of spionid and nereid polychaetes during
low dissolved oxygen (DO), though both have been observed actively burrowing during
severe hypoxia (Sturdivant et al. 2012). Given the eurytopic nature of both species in
sublittoral systems, and their ability to remain active during hypoxia, these polychaetes
could play a vital bioturbative role, aiding the diffusion of anaerobic compounds out of
the sediments and into the water column during summertime hypoxia in the Neuse River.
Further, their abilities to deal with the perturbation of fluctuating DO denotes the
importance of these species as macrobenthic production for epibenthic predators and
demersal fish in disturbed systems like the Neuse.
Background
Eutrophication, an increase in the supply and accumulation of organic matter to a system
(Nixon, 1995; Rabalais, 2004), of estuarine and marine ecosystems is pervasive and has
led to a series of counter acting benthic community impacts (Rosenberg, 1985; Nixon,
1995). Reductions in benthic species richness and increases in abundance and biomass
are the most obvious and have been documented in many systems (Pearson and
Rosenberg, 1978; Rosenberg, 1985). In addition, DO, which is essential in microbial and
metazoan metabolism, has declined in many systems experiencing eutrophication and
given rise to hypoxia and anoxia (Diaz and Rosenberg, 2008). In this study hypoxia is
defined by DO concentrations ≤2.8 mg O2 l-1. Paraprionospio pinnata and Nereis
succinea are both cosmopolitan species that inhabit sublittoral sediments in the Pacific
and Atlantic Oceans (Zenkevich 1951, Quiroga et al. 2007). The numerical and
production dominance of each species in benthic community often makes them a key
species of a system. The genus and species of both polychaetes has been suggested to
display metabolic plasticity during hypoxia (Schӧttler 1979, Gonzalez and Quiñones
2000), and each was observed burrowing during near anoxic conditions (Sturdivant et al.
2012).
The Neuse River estuary has a watershed of ~16000 km2 and empties into Pamlico
Sound (Boyer et al. 1993). Nitrogen loading to the estuary comes from agriculture
(including animal production), municipal wastewater, industrial discharges to surface
waters and atmosphere, stormwater runoff, and atmospheric releases from multiple
sources within the water- and air-shed, resulting in seasonal hypoxia (Paerl et al. 1998).
Approach
Sediment samples will be collected in mid-July in the mesohaline portion of the Neuse
River, using a Young grab (440 cm2 to a depth of 10 cm). Samples will be sieved in the
field through a 0.5-mm screen to target the macrofaunal species Paraprionospio pinnata
and Nereis succinea. When identified, the worms will be placed in a mini mesocosm at
25 oC and a salinity of 16-20 psu for storage and transport; these physical conditions
match the bottom summertime conditions of the mesohaline Neuse River. Once 30
individuals of each species are collected and stored, they will be transported to
Wachapreague, VA for experimental trials. The day before trials, worms will be moved
into a respirometer with a layer of clean sediment on the bottom of the chamber to allow
the worms to burrow. Hypoxia trials will be conducted on 10 worms of each species at
the acclimation temperature of 25 oC and on 10 different worms of each species (20
worms total) after an acute increase in temperature to 30 oC. Hypoxia trials will
commence once metabolic rate stabilizes after the acute temperature change, ~3h. At
each temperature data will be collected during normoxia (oxygen levels >85% oxygen
saturation) and after stepwise reduction in oxygen to 75, 50, 30, 20, and 10% saturation.
Each stepwise decline in oxygen saturation will occur over a 30 min period. Worms still
active during 10% saturation will be observed and documented until mortality.
Stopflow respirometry (Steffensen 1989) will be used to determine the resting metabolic
rate, which is defined as the oxygen consumption of quiescent, post-absorptive worms
exhibiting low levels of spontaneous activity (Jobling 1993). Metabolic rate
measurements will be conducted in the respirometer. The respirometer will be submerged
in an outer water bath and intermittently flushed with water from the outer bath, where
oxygen levels will be controlled via a gas equilibration column bubbled with air (during
normoxia) or nitrogen (during hypoxia), controlled by custom hardware outlined in
Horodysky et al. (2011).
Resting metabolic rate, VO2 (mg O2 h-1) will be determined every 20 min by calculating
the slope of the decline in respirometer oxygen content when the flush pump is turned
off. VO2 = ΔCwO2 x Δt-1 x Vresp x α-1, where ΔCwO2 is the slope of the linear regression of
change in water oxygen content over time, Δt is the length of the time interval over which
VO2 was measured (h), Vresp is the volume of the respirometer adjusted for worm volume
and α is the solubility coefficient of water. Measurements of microbial respiration will be
performed immediately prior to introducing worms to and after removing worms from the
respirometer to determine the rate of change over the course of the experiment. Oxygen
extraction (EO2 in %) will be calculated during closed respirometer intervals as EO2 =
100(CI - CE)*( CI)-1, where CI is the oxygen content of the water in the respirometer (i.e.
inhalant water) and CE is the oxygen content in the exhalant water. Oxygen extraction
will be measure every 2-3 s and used to calculate a single mean EO2 at each oxygen level.
The effect of oxygen saturation at 25 or 30 oC on mean VO2 will be tested using repeated
measures ANCOVA with mass of worms (mg) included as a covariate. The effect of
oxygen saturation level at 25 or 30 oC on mean EO2 will be tested using a repeated
measures ANOVA.
Literature Cited
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Diaz RJ, Rosenberg R (2008) Spreading dead zones and consequences for marine
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anaerobic metabolism of polychaetes from the continental shelf off central-south
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Horodysky AZ, Brill RW, Bushnell PG, Musick JA, Latour RJ (2011) Comparative
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