Grace Saba

Winter and spring controls on the summer food web of the coastal West Antarctic Peninsula

Understanding the mechanisms by which climate variability affects multiple trophic levels in food webs is essential for determining ecosystem responses to climate change. Here we use over two decades of data collected by the Palmer Long Term Ecological Research program (PAL-LTER) to determine how large-scale climate and local physical forcing affect phytoplankton, zooplankton and an apex predator along the West Antarctic Peninsula (WAP). We show that positive anomalies in chlorophyll-a (chl-a) at Palmer Station, occurring every 4-6 years, are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode (SAM). Favorable conditions for phytoplankton included increased winter ice extent and duration, reduced spring/summer winds, and increased water column stability via enhanced salinity-driven density gradients. Years of positive chl-a anomalies are associated with the initiation of a robust krill cohort the following summer, which is evident in Adélie penguin diets, thus demonstrating tight trophic coupling. Projected climate change in this region may have a significant, negative impact on phytoplankton biomass, krill recruitment and upper trophic level predators in this coastal Antarctic ecosystem.

Increased Feeding and Nutrient Excretion of Adult Antarctic Krill, Euphausia superba, Exposed to Enhanced Carbon Dioxide (CO2)

Ocean acidification has a wide-ranging potential for impacting the physiology and metabolism of zooplankton. Sufficiently elevated CO2 concentrations can alter internal acid-base balance, compromising homeostatic regulation and disrupting internal systems ranging from oxygen transport to ion balance. We assessed feeding and nutrient excretion rates in natural populations of the keystone species Euphausia superba (Antarctic krill) by conducting a CO2 perturbation experiment at ambient and elevated atmospheric CO2 levels in January 2011 along the West Antarctic Peninsula (WAP). Under elevated CO2 conditions (∼672 ppm), ingestion rates of krill averaged 78 µg C individual−1 d−1 and were 3.5 times higher than krill ingestion rates at ambient, present day CO2 concentrations. Additionally, rates of ammonium, phosphate, and dissolved organic carbon (DOC) excretion by krill were 1.5, 1.5, and 3.0 times higher, respectively, in the high CO2 treatment than at ambient CO2 concentrations. Excretion of urea, however, was ∼17% lower in the high CO2 treatment, suggesting differences in catabolic processes of krill between treatments. Activities of key metabolic enzymes, malate dehydrogenase (MDH) and lactate dehydrogenase (LDH), were consistently higher in the high CO2 treatment. The observed shifts in metabolism are consistent with increased physiological costs associated with regulating internal acid-base equilibria. This represents an additional stress that may hamper growth and reproduction, which would negatively impact an already declining krill population along the WAP.

Nitrogen Consumption and Metabolism in Marine Zooplankton

Publisher Summary This chapter focuses on the important role that zooplankton play in nitrogen cycling by following the path of the food from ingestion to all aspects and stages of metabolism. It begins with a discussion of N consumption, including the nitrogenous composition of available food types, rates of N consumption, and effects of food quality. The various aspects of N metabolism, emphasizing the importance to biogeochemical cycling and coupling with other major elements (carbon, phosphorus) are also discussed. Considerable progress in our understanding of the role of marine zooplankton in nitrogen cycling has been made in the last two decades. Studies are now at the stage where large data sets are being compiled, and it is possible, for example, to reasonably predict ammonia excretion as a function of body mass for a given organism and temperature using regression equations—and avoid doing experimental incubations. These individual, size-specific excretion rates can be scaled up to a community rate if total biomass and size structure of the community is known. A common theme throughout this review is that more information is needed on the role of marine protozoa, gelatinous zooplankton, and of taxa living below the euphotic zone in N consumption and metabolism. Consumption of phytoplankton and bacteria by microzooplankton are key processes in N transformations in the ocean.

Abundance, Composition, and Sinking Rates of Fish Fecal Pellets in the Santa Barbara Channel

Rapidly sinking fecal pellets are an important component of the vertical flux of particulate organic matter (POM) from the surface to the oceans interior; however, few studies have examined the role fish play in this export. We determined abundance, size, prey composition, particulate organic carbon/nitrogen (POC/PON), and sinking rates of fecal pellets produced by a forage fish, likely the northern anchovy, in the Santa Barbara Channel. Pellet abundance ranged from 0.1–5.9 pellets m−3. POC and PON contents averaged 21.7 µg C pellet−1 and 2.7 µg N pellet−1. The sinking rate averaged 787 m d−1; thus pellets produced at the surface would reach the benthos (~500 m) in <1 day. Estimated downward flux of fish fecal POC reached a maximum of 251 mg C m−2 d−1. This is equal to or exceeds previous measurements of sediment trap POM flux, and thus may transport significant amounts of repackaged surface material to depth.

Changes in the upper ocean mixed layer and phytoplankton productivity along the West Antarctic Peninsula

The West Antarctic Peninsula (WAP) has experienced significant change over the last 50 years. Using a 24 year spatial time series collected by the Palmer Long Term Ecological Research programme, we assessed long-term patterns in the sea ice, upper mixed layer depth (MLD) and phytoplankton productivity. The number of sea ice days steadily declined from the 1980s until a recent reversal that began in 2008. Results show regional differences between the northern and southern regions sampled during regional ship surveys conducted each austral summer. In the southern WAP, upper ocean MLD has shallowed by a factor of 2. Associated with the shallower mixed layer is enhanced phytoplankton carbon fixation. In the north, significant interannual variability resulted in the mixed layer showing no trended change over time and there was no significant increase in the phytoplankton productivity. Associated with the recent increases in sea ice there has been an increase in the photosynthetic efficiency (chlorophyll a-normalized carbon fixation) in the northern and southern regions of the WAP. We hypothesize the increase in sea ice results in increased micronutrient delivery to the continental shelf which in turn leads to enhanced photosynthetic performance. This article is part of the theme issue ‘The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change’.

Gliders as maturing technology: Using gliderpalooza as means to develop an integrated glider community

Underwater autonomous gliders have transitioned from exotic experimental systems to becoming a standard platform capable of collecting data over a critical range of spatial and temporal scales in the ocean. The data are proving to be extremely valuable for addressing a wide range of basic and applied research questions. These communities are growing from distributed research and/or education groups. It is crucial as systems continue to evolve that there is an effort to “harmonize” data products while preserving the diversity of approaches/science/experimentation. As the gliders have matured and new battery solutions provide additional energy, there is an increased focus on the integration of a wider range of sensors to be incorporated into gliders. Many of these new classes of sensors will be particularly effective for characterizing biological processes in the coastal ocean. As biological sensors generally provide proxy estimates of a parameter, developing robust quality control and assurance procedures is critical. These new sensors will be more power intensive thus requiring the development of planning tools for increasing energy efficiency during missions. Given the significant growth in the highly distributed glider community, efforts are now focusing on the development mission planning tools to allow for efficient operation of glider fleets. To further collaboration and standardization of the growing number of glider operators we have initiated a series of community efforts called glider paloozas. We had an exceptional turnout last year, encompassing 18 U.S. and Canadian partners, 28 gliders, 36 glider deployments, and spatial coverage from coastal regions of Newfoundland to the Gulf of Mexico and offshore to Bermuda. The coordinated effort focused on several research themes including continental shelf circulation, fish migrations, and storm activity. The main goals of last years effort were to produce a seamless flow of real-time glider data into the Global Telecommunications System (GTS) via DMAC and into the regional ocean models and demonstrate the potential of a U.S. national glider network. This is in line with the goal to increase glider data accessibility from Federal and Academic oceanographic modeling communities, the U.S. Integrated Ocean Observing System (IOOS), and other federal funding agencies (i.e., NSF). In order to demonstrate the value and necessity of the planned U.S. national glider network and build on last years successes, we hope to continue these efforts and require that all glider data produced by Gliderpalooza 2015 participants be uploaded by the individual operators to the DAC 2.0 and into GTS.

The ocean is our classroom: A 4-year research track for undergraduate exploration, research and discovery in oceanography

Mitigating and adapting to climate change while the global human population continues its projected growth will be the dominant choice challenge confronting the present generation of undergraduates over their professional lifetimes. Todays students should be prepared to develop solutions that will involve the sea, but life-changing at-sea research experiences for undergraduates are limited. The rapid expansion of ocean observatories provides a solution. We have demonstrated in our own observatory how undergraduate student research can be enabled as a yearround activity during a students full undergraduate career starting on day 1. What began as the Challenger Glider Mission has spread to other observatory technology and science activities both locally and in remote polar regions.

Phytoplankton dynamics and bottom water oxygen during a large bloom in the summer of 2011

During the summer of 2011 a large phytoplankton bloom occurred off the New Jersey coast, which was monitored using an existing ocean observatory. There was public concern about the root causes of the phytoplankton bloom and whether it reflected anthropogenic loading of nutrients from the Hudson River or whether it reflected coastal upwelling. We used the MARACOOS network to determine what were the likely drivers of the phytoplankton bloom. The bloom was studied using satellites, HF radar, a Hydroid REMUS and Webb Slocum gliders. Chlorophyll concentrations were over an order of magnitude larger than the decadal mean of ocean color data and the bloom was initiated by upwelling winds throughout the month of July that continued to dominate the wind patterns until the passage of Hurricane Irene. The high concentrations of phytoplankton resulted in the supersaturated oxygen values in the surface waters; however the flux of organic matter resulted in oxygen saturation values of <;60% in the coastal bottom waters, which is sufficient to stress benthic communities in the MAB. Discrete samples identified the bloom was dominated by mixed assemblages of motile dinoflagellates. The passage of Hurricane Irene increased the oxygen saturation at depth by close to 20%, but was not sufficient to terminate the bloom. A re-analysis of the CODAR clearly indicated that the shelf wide bloom most likely originated from nearshore the New Jersey coast. Upwelling provided the source water that fueled the bloom. Alternating winds transported the bloom offshore and across the Mid-Atlantic Bight. This is consistent with past studies that observed regions of recurrent hypoxia on the New Jersey inner shelf are more related to coastal upwelling than riverine inputs.