Gilbert T. Rowe

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.

Do meio- and macrobenthic nematodes differ in community composition and body weight trends with depth?

Nematodes occur regularly in macrobenthic samples but are rarely identified from them and are thus considered exclusively a part of the meiobenthos. Our study compares the generic composition of nematode communities and their individual body weight trends with water depth in macrobenthic (>250/300 µm) samples from the deep Arctic (Canada Basin), Gulf of Mexico (GOM) and the Bermuda slope with meiobenthic samples (<45 µm) from GOM. The dry weight per individual (µg) of all macrobenthic nematodes combined showed an increasing trend with increasing water depth, while the dry weight per individual of the meiobenthic GOM nematodes showed a trend to decrease with increasing depth. Multivariate analyses showed that the macrobenthic nematode community in the GOM was more similar to the macrobenthic nematodes of the Canada Basin than to the GOM meiobenthic nematodes. In particular, the genera Enoploides, Crenopharynx, Micoletzkyia, Phanodermella were dominant in the macrobenthos and accounted for most of the difference. Relative abundance of non-selective deposit feeders (1B) significantly decreased with depth in macrobenthos but remained dominant in the meiobenthic community. The occurrence of a distinct assemblage of bigger nematodes of high dry weight per individual in the macrobenthos suggests the need to include nematodes in macrobenthic studies.

An alternative view of the role of heterotrophic microbes in the cycling of organic matter in deep-sea sediments

Abstract The role of microbial heterotrophs in deep-ocean sediment communities is explored using a simplified model of the cycling of carbon within a generic, size-based food web. Measurements of potential rates of respiration and growth of bacteria appear to be low, given the high concentrations of both microbial biomass and dissolved organic matter (DOM) in pore waters. This enigma can be explained theoretically by assuming that much of the microbial biomass is restricted in function at high pressure and low temperature, that a large fraction of the dissolved organic carbon (DOC) is refractory, and that the small fraction of the DOM that is labile and thus available must be liberated from the particulate pool by extracellular enzyme activity, viral infection or through the feeding processes of the metazoans. Free-living heterotrophic microbes in the sediments thus play a minor role in metazoan food webs, providing only a small fraction of the nourishment of metazoans. On the other hand, microbial heterotrophs appear to be responsible in part for the high levels of refractory DOM observed to accumulate in the deep ocean.

Deep-ocean Environmental Long-term Observatory System (DELOS):- Long-term (25 year) monitoring of the deep-ocean animal community in the vicinity of offshore hydrocarbon operations

The deep-sea environment into which oil company operations are gradually extending is generally poorly understood with surveys regularly discovering new habitats and communities of animals previously unknown to science. By establishing long-term monitoring of the deep-sea physical environment and biological activity in that environment it should be possible to compensate to a large degree for the previous lack of knowledge. Here we describe the DELOS system for monitoring the deep ocean at 1400 m depth in Block 18 off Angola in the Atlantic Ocean. DELOS comprises two platforms, one in the near field within 50 m of a sea floor well, and another in the far field 5 miles from any sea floor infrastructure. Both platforms comprise a suite of instrumentation for characterizing the deep-ocean environment. The DELOS platforms are autonomous from sea floor hydrocarbon infrastructure and require Remotely Operated Vehicle (ROV) intervention every 6 months to recover instrumentation for service. The DELOS platforms are due for installation early in 2008.

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.n

Mercury accumulation in Lethrinus nebulosus from the marine waters of the Qatar EEZ

Total mercury (THg) and methylmercury (MeHg) were recorded in the commercial demersal fish Lethrinus nebulosus, caught from six locations in Qatar EEZ (Exclusive Economic Zone). Concentrations of THg decreased in the order: liver˃muscle˃gonad. THg concentrations in fish tissue ranged from 0.016ppm in gonad to 0.855ppm (mgkg-1w/w) in liver tissues, while concentrations in muscle tissue ranged from 0.24 to 0.49ppm (mgkg-1w/w) among sampling sites. MeHg concentrations were used to validate food web transfer rate calculations. Intake rates were calculated to assess the potential health impact of the fish consumption. There is no major threat to human health from the presence of Hg in L. nebulosus, based upon reasonable consumption patterns, limited to no more than three meals of L. nebulosus per week.