Biological Response of Planktic Foraminifera to Decline in Seawater pH

Understanding the way in which a decline in ocean pH can affect calcareous organisms could enhance our ability to predict the impacts of the potential decline in seawater pH on marine ecosystems, and could help to reconstruct the paleoceanographic events over a geological time scale. Planktic foraminifera are among the most important biological proxies for these studies; however, the existing research on planktic foraminifera is almost exclusively based on their geochemical indices, without the inclusion of information on their biological development. Through a series of on-board experiments in the western tropical Pacific (134°33′54″ E, 12°32′47″ N), the present study showed that the symbiont-bearing calcifier Trilobatus sacculifer—a planktic foraminifer—responded rapidly to a decline in seawater pH, including losing symbionts, bleaching, etc. Several indices were established to quantify the relationships between these biological parameters and seawater pH, which could be used to reconstruct the paleoceanographic seawater pH. We further postulated that the loss of symbionts in planktic foraminifera acts as an adaptive response to the stress of low pH. Our results indicate that an ongoing decline in seawater pH may hinder the growth and calcification of planktic foraminifera by altering their biological processes. A reduction in carbonate deposition and predation could have profound effects on the carbon cycle and energy flow in the marine food web.

Geologic controls on phytoplankton elemental composition

Planktonic organic matter forms the base of the marine food web, and its nutrient content (C:N:Porg) governs material and energy fluxes in the ocean. Over Earth history, C:N:Porg had a crucial role in marine metazoan evolution and global biogeochemical dynamics, but the geologic history of C:N:Porg is unknown, and it is often regarded constant at the “Redfield” ratio of ∼106:16:1. We calculated C:N:Porg through Phanerozoic time by including nutrient- and temperature-dependent C:N:Porg parameterizations in a model of the long-timescale biogeochemical cycles. We infer a decrease from high Paleozoic C:Porg and N:Porg to present-day ratios, which stems from a decrease in the global average temperature and an increase in seawater phosphate availability. These changes in the phytoplankton’s growth environment were driven by various Phanerozoic events: specifically, the middle to late Paleozoic expansion of land plants and the Triassic breakup of the supercontinent Pangaea, which increased continental weatherability and the fluxes of weathering-derived phosphate to the oceans. The resulting increase in the nutrient content of planktonic organic matter likely impacted the evolution of marine fauna and global biogeochemistry.

Geologic controls on phytoplankton elemental composition

Planktonic organic matter forms the base of the marine food web, and its nutrient content (C:N:Porg) governs material and energy fluxes in the ocean. Over Earth history, C:N:Porg had a crucial role in marine metazoan evolution and global biogeochemical dynamics, but the geologic history of C:N:Porg is unknown, and it is often regarded constant at the “Redfield” ratio of ∼106:16:1. We calculated C:N:Porg through Phanerozoic time by including nutrient- and temperature-dependent C:N:Porg parameterizations in a model of the long-timescale biogeochemical cycles. We infer a decrease from high Paleozoic C:Porg and N:Porg to present-day ratios, which stems from a decrease in the global average temperature and an increase in seawater phosphate availability. These changes in the phytoplankton’s growth environment were driven by various Phanerozoic events: specifically, the middle to late Paleozoic expansion of land plants and the Triassic breakup of the supercontinent Pangaea, which increased continental weatherability and the fluxes of weathering-derived phosphate to the oceans. The resulting increase in the nutrient content of planktonic organic matter likely impacted the evolution of marine fauna and global biogeochemistry.

Three Novel Bacteria Associated with Two Centric Diatom Species from the Mediterranean Sea, Thalassiosira rotula and Skeletonema marinoi

Diatoms are a successful group of microalgae at the base of the marine food web. For hundreds of millions of years, they have shared common habitats with bacteria, which favored the onset of interactions at different levels, potentially driving the synthesis of biologically active molecules. To unveil their presence, we sequenced the genomes of bacteria associated with the centric diatom Thalassiosira rotula from the Gulf of Naples. Annotation of the metagenome and its analysis allowed the reconstruction of three bacterial genomes that belong to currently undescribed species. Their investigation showed the existence of novel gene clusters coding for new polyketide molecules, antibiotics, antibiotic-resistance genes and an ectoine production pathway. Real-time PCR was used to investigate the association of these bacteria with three different diatom clones and revealed their preference for T. rotula FE80 and Skeletonema marinoi FE7, but not S. marinoi FE60 from the North Adriatic Sea. Additionally, we demonstrate that although all three bacteria could be detected in the culture supernatant (free-living), their number is up to 45 times higher in the cell associated fraction, suggesting a close association between these bacteria and their host. We demonstrate that axenic cultures of T. rotula are unable to grow in medium with low salinity (<28 ppt NaCl) whereas xenic cultures can tolerate up to 40 ppt NaCl with concomitant ectoine production, likely by the associated bacteria.

Subtle Differences in the Representation of Consumer Dynamics Have Large Effects in Marine Food Web Models

Projecting ocean biogeochemistry and fisheries resources under climate change requires confidence in simulation models. Core to such models is the description of consumer dynamics relating prey abundance to capture, digestion efficiency and growth rate. Capture is most commonly described as a linear function of prey encounter or by rectangular hyperbola. Most models also describe consumers as eating machines which “live-to-eat,” where growth (μ) is limited by a maximum grazing rate (Gmax). Real consumers can feed much faster than needed to support their maximum growth rate (μmax); with feeding modulated by satiation, they “eat-to-live.” A set of strategic analyses were conducted of these alternative philosophies of prey consumption dynamics and testing of their effects in the StrathE2E end-to-end marine food web and fisheries model. In an experiment where assimilation efficiencies were decreased by 10%, such as might result from a change in temperature or ocean acidity, the different formulation resulted in up to 100% variation in the change in abundances of food web components, especially in the mid-trophic levels. Our analysis points to a need for re-evaluation of some long-accepted principles in consumer-resource modeling.

Nutrient Distribution in Eastern Indonesian Waters

Nutrients are needed for the growth of phytoplankton as a basic component in the marine food web. The concentration of nutrients in waters relates to primary productivity and it will influence fisheries stocks. So far, research on nutrients in the deep sea is rarely carried out in Indonesia. This study aims to determine water quality, horizontal and vertical distribution of nutrients in eastern Indonesian waters, which can be used as baseline data for deep-sea nutrients in Indonesia. The study was conducted from October 29 to November 15, 2017. Sampling was carried out in 20 stations with seven layers. Nutrient measurements were conducted based on Strickland and Parsons (1972). Our results showed that the concentrations of phosphate, nitrate, nitrite, ammonium, and silicate ranged from 0.000-0.060 mg/l, 0.001-0.321 mg/l, 0.000-0.009 mg/l, 0.004-0.024 mg/l and 0.085-1.090 mg/l, respectively. In general, the highest concentration of nutrients was found in Maluku Sea. The vertical distribution of nitrate, phosphate, and silicate shows that the increasing concentrations as increasing depth, except for nitrite and ammonium. The maximum nitrite concentration appears in the northern area, while the ammonium distribution has homogenous pattern.

Trait-mediated shifts and climate velocity decouple an endothermic marine predator and its ectothermic prey

Climate change is redistributing biodiversity globally and distributional shifts have been found to follow local climate velocities. It is largely assumed that marine endotherms such as cetaceans might shift more slowly than ectotherms in response to warming and would primarily follow changes in prey, but distributional shifts in cetaceans are difficult to quantify. Here we use data from fisheries bycatch and strandings to examine changes in the distribution of long-finned pilot whales (Globicephala melas), and assess shifts in pilot whales and their prey relative to climate velocity in a rapidly warming region of the Northwest Atlantic. We found a poleward shift in pilot whale distribution that exceeded climate velocity and occurred at more than three times the rate of fish and invertebrate prey species. Fish and invertebrates shifted at rates equal to or slower than expected based on climate velocity, with more slowly shifting species moving to deeper waters. We suggest that traits such as mobility, diet specialization, and thermoregulatory strategy are central to understanding and anticipating range shifts. Our findings highlight the potential for trait-mediated climate shifts to decouple relationships between endothermic cetaceans and their ectothermic prey, which has important implications for marine food web dynamics and ecosystem stability.

Development of Optimal Digesting Conditions for Microplastic Analysis in Dried Seaweed Gracilaria fisheri

Currently, research on the accumulation of microplastics (MPs) in the marine food web is being highlighted. An accurate and reliable digestion method to extract and isolate MPs from complex food matrices has seldom been validated. This study aimed to compare the efficacy of MP isolation among enzymatic-, oxidative-, and the combination of two digestion methods on red seaweed, Gracilaria fisheri. The dried seaweed sample was digested using three different methods under various conditions using enzymes (cellulase and protease), 30% H2O2, and a combination of enzymes and 30% H2O2. The method possessing the best digestion efficiency and polymer recovery rate of MPs was selected, and its effect on spiked plastic polymer integrity was analyzed by Raman spectroscopy. As a result, the enzymatic method rendered moderate digestion efficiency (59.3–63.7%) and high polymer recovery rate (94.7–98.9%). The oxidative method using 30% H2O2 showed high digestion efficiency (93.0–96.3%) and high polymer recovery rate (>98%). The combination method was the most effective method in terms of digestion efficiency, polymer recovery rate, and expenditure of digestion time. The method also showed no chemical changes in the spiked plastic polymers (PE, PP, PS, PVC, and PET) after the digestion process. All the spiked plastic polymers were identifiable using Raman spectroscopy.

Respiration Rates, Metabolic Demands and Feeding of Ephyrae and Young Medusae of the Rhizostome Rhopilema nomadica

Jellyfish (cnidarians and ctenophores) affect the marine food web through high feeding rates and feeding efficiency, but in contrast to their great importance in the ecosystem, our knowledge of their dietary requirements is limited. Here we present the results of respiratory and feeding trials of the rhizostome Rhopilema nomadica, the dominant scyphozoan in the waters of the Eastern Mediterranean, which often establishes massive swarms, mainly in the summer months. Through multiple measurements of oxygen demand in R. nomadica at bell diameters of 3–49 mm, we were able to assess its minimum energetic requirements. These, and the results of the feeding trials on individuals of the same bell diameter range, show that R. nomadica is a very efficient predator. When presented with prey concentrations of 100 prey items per liter, a single hourly feeding session provided between 1.15 and 3 times the estimated daily basal carbon requirement. Our findings suggest that R. nomadica is well adapted to its environment, the hyperoligotrophic waters of the eastern Mediterranean, able to efficiently exploit patches of plankton, possibly at rates even higher than what we observed under laboratory conditions.