Clifton C. Nunnally

Global Patterns and Predictions of Seafloor Biomass Using Random Forests

A comprehensive seafloor biomass and abundance database has been constructed from 24 oceanographic institutions worldwide within the Census of Marine Life (CoML) field projects. The machine-learning algorithm, Random Forests, was employed to model and predict seafloor standing stocks from surface primary production, water-column integrated and export particulate organic matter (POM), seafloor relief, and bottom water properties. The predictive models explain 63% to 88% of stock variance among the major size groups. Individual and composite maps of predicted global seafloor biomass and abundance are generated for bacteria, meiofauna, macrofauna, and megafauna (invertebrates and fishes). Patterns of benthic standing stocks were positive functions of surface primary production and delivery of the particulate organic carbon (POC) flux to the seafloor. At a regional scale, the census maps illustrate that integrated biomass is highest at the poles, on continental margins associated with coastal upwelling and with broad zones associated with equatorial divergence. Lowest values are consistently encountered on the central abyssal plains of major ocean basins The shift of biomass dominance groups with depth is shown to be affected by the decrease in average body size rather than abundance, presumably due to decrease in quantity and quality of food supply. This biomass census and associated maps are vital components of mechanistic deep-sea food web models and global carbon cycling, and as such provide fundamental information that can be incorporated into evidence-based management.

Anthropogenic “Litter” and macrophyte detritus in the deep Northern Gulf of Mexico

A deep-sea trawl survey of the Northern Gulf of Mexico has documented the abundance and diversity of human-generated litter and natural detrital plant material, from the outer margin of the continental shelf out to the Sigsbee abyssal plain. Plastics were the most frequently encountered type of material. Litter and debris were encountered more frequently in the eastern than in the western GoM. Land-derived plant material was located primarily within the head of the Mississippi Canyon, whereas ocean-derived plant material was spread evenly throughout the NE GoM. Human discards were principally from ships offshore. Some of the material was contained in metal cans that sank to the sea floor, probably in order to conform to international agreements that prohibit disposal of toxic material and plastics. The Mississippi Canyon was a focal point for litter, perhaps due to topography, currents or proximity to shipping lanes.

Sedimentary Oxygen Consumption and Nutrient Regeneration in the Northern Gulf of Mexico Hypoxic Zone

ABSTRACT Nunnally, C.C.; Rowe, G.T.; Thornton, D.C.O., and Quigg, A., 2013. Sedimentary oxygen consumption and nutrient regeneration in the Gulf of Mexico hypoxic zone. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 84–96, Coconut Creek (Florida), ISSN 0749-0208. Seasonal summer stratification and enhanced nutrient loading of the Louisiana continental shelf (U.S.A.) west of the Mississippi River create hypoxic regions that affect large areas of the benthos. Total sediment oxygen uptake and nutrient recycling were measured during different, (e.g. pre, early, late and post) hypoxic regimes using shipboard Batch Micro-Incubation Chambers (BMICs) in 2004 to 2005 and again in 2007 to 2009. Sediment community oxygen consumption during oxic regimes (dissolved oxygen > 63 µmol L-1) was -9.5 ± 0.7 mmol O2 m-2 d-1 (mean ± SE), almost twice that measured (-5.8 ± 0.6 mmol O2 m-2 d-1) during suboxic conditions. During the summer when hypoxia occurred, the benthos consumed nitrate and nitrite (-0.14 ± 0.04 and -0.10 ± 0.02 mmol N m-2 d-1 respectively) and produced ammonium (1.6 ± 0.39 mmol N m-2 d-1). Elevated sediment community oxygen consumption and nutrient remineralization occurred near terrestrial river inputs associated with the Mississippi and Atchafalaya Rivers. Net release of dissolved inorganic nitrogen, in the form of ammonium, peaked during late summer. Released ammonium may be a source of nutrients for primary production in bottom waters, and can also provide reduced nitrogen for nitrification and microbial respiration, both of which may reinforce the intensity and duration of hypoxia. Based on chamber results, sediments actively scavenged phosphate from the bottom waters (-98.4 ± 21.3 µmol P m-2 d-1) and released silicate (2.62 = 0.31 mmol Si m-2 d-1). The addition of reactive nitrogen and removal of phosphorous due to benthic community metabolism could potentially be accentuating phosphorous limitation on the continental shelf.

Polychaete Annelid Biomass Size Spectra: The Effects of Hypoxia Stress

Quantitative benthic samples were taken during spring and summer at three locations on the Louisiana continental shelf from 2004 to 2012 to assess the influence of hypoxia on the mean sizes (wet weight) of polychaete annelid worms. While the mean body size over the entire study of 64 samples was 3.99 ± 4.66 mg wet weight per individual, the mean ranged from 2.97 ± 2.87 mg during consistently hypoxic conditions ( 2 mg/L). The variations in size within assemblages were estimated from conventional biomass size spectra (BSS) and normalized biomass size spectra (NBSS) across a broad range of oxygen concentrations. The decline in size was due to the elimination of large species under hypoxic conditions (<2 mg/L), not a reduction in size within species. At “severe” levels of hypoxia (<1 mg/L), the smallest species also declined in abundance, whereas the ubiquitous “medium-sized” Paraprionospio pinnata flourished. These results suggest that there will be enhanced selection for small sizes and species with enlarged branchial palps such as those in P. pinnata if, as predicted, hypoxia becomes more commonplace in time and space worldwide.

Macrobenthos in the central Arabian Gulf: a reflection of climate extremes and variability

AbstractThe arid subtropical ecosystem of the central Arabian Gulf was used to explore the combined effects of low primary productivity, high salinities, and variable temperatures on the composition and structure of benthic macrofauna at 13 sites encircling the Qatar Peninsula in winter and summer (or late spring) of 2010 and 2011. The low abundance, biomass, and remarkably high species turnover may be a reflection of the oligotrophic, thermally variable, hypersaline coastal environment. The number of species and within-habitat diversity was lowest in the highest salinities but increased with finer-grained sediments and lower salinity. A remarkable temporal variation in species composition observed may reflect insufficient primary production to sustain new populations recruited from the seasonal exchange of water from the adjacent Sea of Oman. Low abundances accompanied by continued replacement of species may be a “new model” for extremely arid conditions associated with global warming.

Undetected Blooms in Prince William Sound: Using Multiple Techniques to Elucidate the Base of the Summer Food Web

Prince William Sound supports many commercially and culturally important species. The phytoplankton community dynamics which support and sustain the high biomass and diversity of this ecosystem are largely unknown. The aim of this study was to describe the phytoplankton community composition during the summer, the time at which this system supports many additional migrants and commercially important fisheries. Phytoplankton community composition (pigments), dissolved nutrients, Secchi depth, total and particulate organic carbon and nitrogen, and export to deep water were measured during the summers of 2008–2010. In addition, natural abundance stable isotopes (δ13C and δ15N) of particulate organic matter (POM) and faunal samples were measured in 2010. The analysis of the phytoplankton community composition using multivariate statistics showed that changes over the summer were driven by changes in the proportion of the dominant groups: diatoms, dinoflagellates, cyanobacteria, cryptophytes, chlorophytes, and prasinophytes. These changes were driven by changes in nutrients including an organic nitrogen source, phosphate, and silica and correspond to shifts in particulate concentrations. A consistent pattern was observed each year: a large Noctiluca sp. bloom in June concurrent with low nutrients, low diversity, and high particulate organic carbon (POC) concentrations was followed by a shift in the phytoplankton community to a more diverse smaller size class community in July and equilibrating in August. This annual summer bloom could be an important contributor to the energy and nutrient inputs at the base of the regional marine food web.