Oil carbon entered the coastal planktonic food web during the Deepwater Horizon oil spill AbstractThe Deepwater Horizon oil spill was unprecedented in total loading of petroleum hydrocarbons accidentally released to a marine ecosystem. Controversial application of chemical dispersants presumably accelerated microbial consumption of oil components, especially in warm Gulf of Mexico surface waters. We employed δ 13 C as a tracer of oil-derived carbon to resolve two periods of isotopic carbon depletion in two plankton size classes. Carbon depletion was coincident with the arrival of surface oil slicks in the far northern Gulf, and demonstrated that subsurface oil carbon was incorporated into the plankton food web.

Field and laboratory experiments are designed to measure Sargassum biomass per area (density), surface reflectance, nutrient contents, and pigment concentrations. An alternative floating algae index‐biomass density model is established to link the spectral reflectance to Sargassum biomass density, with a relative uncertainty of ~12%. Monthly mean integrated Sargassum biomass in the Caribbean Sea and central West Atlantic reached at least 4.4 million tons in July 2015. The average %C, %N, and %P per dry weight are 27.16, 1.06, and 0.10, respectively. The mean chlorophyll‐a (Chl‐a) concentration is ~0.05% of the dry weight. With these parameters, the amounts of nutrients and pigments can be estimated directly from remotely sensed Sargassum biomass. During bloom seasons, Sargassum carbon can account for ~18% of the total particulate organic carbon in the upper water column. This study provides the first quantitative assessment of the overall Sargassum biomass, nutrients, and pigment abundance from remote sensing observations, thus helping to quantify their ecological roles and facilitate management decisions.

The pelagic brown macroalgae Sargassum spp. have grown for centuries in oligotrophic waters of the North Atlantic Ocean supported by natural nutrient sources, such as excretions from associated fishes and invertebrates, upwelling, and N2 fixation. Using a unique historical baseline, we show that since the 1980s the tissue %N of Sargassum spp. has increased by 35%, while %P has decreased by 44%, resulting in a 111% increase in the N:P ratio (13:1 to 28:1) and increased P limitation. The highest %N and δ15N values occurred in coastal waters influenced by N-rich terrestrial runoff, while lower C:N and C:P ratios occurred in winter and spring during peak river discharges. These findings suggest that increased N availability is supporting blooms of Sargassum and turning a critical nursery habitat into harmful algal blooms with catastrophic impacts on coastal ecosystems, economies, and human health.

A majority of the world's largest net-based fisheries target planktivorous forage fish that serve as a critical trophic link between the plankton and upper-level consumers such as large predatory fishes, seabirds, and marine mammals. Because the plankton production that drives forage fish also drives jellyfish production, these taxa often overlap in space, time, and diet in coastal ecosystems. This overlap likely leads to predatory and competitive interactions, as jellyfish are effective predators of fish early life stages and zooplankton. The trophic interplay between these groups is made more complex by the harvest of forage fish, which presumably releases jellyfish from competition and is hypothesized to lead to an increase in their production. To understand the role forage fish and jellyfish play as alternate energy transfer pathways in coastal ecosystems, we explore how functional group productivity is altered in three oceanographically distinct ecosystems when jellyfish are abundant and when fish harvest rates are reduced using ecosystem modeling. We propose that ecosystem-based fishery management approaches to forage fish stocks include the use of jellyfish as an independent, empirical "ecosystem health" indicator. DEDICATION. This paper is dedicated to our beloved friend and colleague, Hermes Mianzan, for his innumerable contributions to fisheries, zooplankton, and gelatinous zooplankton ecology.