Zooplankton were collected from the Bridge Tender Marina in Wilmington, North Carolina , using a plankton net . Samples were diluted in whole seawater, aerated, and used within 12 hours of collection. Under a dissecting microscope, individual calanoid copepods were selected using Pasteur pipettes and placed in beakers with bottoms made of Nitex mesh that were submerged in filtered and UV-treated seawater. Before experiments, copepods were dyed red to make the organisms easy to visualize in videos. To dye the plankton, the mesh beaker was submerged in a solution of Neutral Red for 20 minutes .To test the effect of copepod shape and drag without swimming behavior, dead copepods were used as prey. The copepods were selected and dyed as described above, then heat-shocked. To compare copepod swimming behavior with a smaller prey that does not escape, nauplii of Artemia spp. were hatched from frozen cysts by placing cysts in aerated, filtered seawater. Nauplii between 2-3 days old were selected using Pasteur pipettes, were housed in mesh bottomed beakers, and underwent the same dye treatment as the copepods.In some cases prey were captured on the far side of the observed tentacles. If a prey carried in the flow “disappeared” behind an illuminated tentacle and did not re-emerge, we assumed that it was captured. When this occurred, the tentacles were observed carefully in subsequent frames of the video and in every case the captured plankton became visible when the tentacles moved,hydroponic bucket the prey fluttered into view during peak velocities, or the prey washed off the tentacles.
In addition, aerial-view photos of each sea anemone in still water were taken directly after the experiment and captured plankton were noted. No discrepancies occurred between the total number of captured prey counted by the end of the experiment and prey observed on the tentacles once the experiment was complete. Predator-prey interactions were identified by the behavior of the prey . “Pass” described when prey passively swept by the anemone within the capture zone. “Avoid” described when a copepod actively changed trajectory with an escape jump to avoid contact with the predator . A “bump” described when prey passively bumped into a tentacle but continued without a capture or escape. “Escape” described when a copepod bumped into a tentacle then actively swam off . “Capture” described when prey bumped into a tentacle and was held by the anemone. Importantly, captured prey did not always lead to retention , so a final term “loss” was used to describe when prey would dislodge from the tentacle. The interactions “bump” and “escape” do not result in a capture so “loss” only refers to prey removed after a capture. The rates of predator-prey interactions were used to calculate efficiency. In Chapter 2, capture and trapping efficiency were calculated based on the proportion of encountered prey so that these values could be compared between predators with different feeding modes. In this Chapter, “retention efficiency” is defined as the proportion of captured prey that was retained so that we could compare the ability of the predator to hold onto prey that have different swimming behaviors. Since the duration of experiments was short relative to the average ingestion times for sea anemones , most captured and retained prey were not ingested during the videos. Therefore, the retention efficiency for sea anemones feeding on different prey alludes to feeding success but is not a confirmed measure of how much the predators consumed. Most of the zooplankton prey passed through the capture zone of a sea anemone without contacting the predator .
In weak waves, prey passively bumped into the predator, although live copepods came into brief contact with a sea anemone less than nauplii or dead copepods. In strong waves, the proportion of “bump” interactions increased for all prey types. Living copepods were able to avoid or escape the predator more in weak waves than in strong waves, but this difference was not significant. Nauplii and dead copepods do not actively avoid or escape from predators. Yet the proportion of predator-prey interactions that resulted in capture did not vary with exposure to stronger waves.The largest proportion of prey pass near the sea anemone without reacting . When solitary sea anemones preyed upon copepods, the prey avoided or escaped the predator more in weak waves than in strong waves. With a downstream predator, prey avoidance and escape swimming occurred less than in the same flow over solitary sea anemones, and increased in stronger waves, though not significantly . Predator-prey interactions between copepods and solitary sea anemones in still water were included to compare whether the differences in behavior over downstream sea anemones was due to slower flow conditions. In still water, the proportion of prey avoidance and escape responses were also low and increased as flow increased . The proportion of prey captured is not significantly different between solitary or downstream copepods, nor is it affected by increases in flow. Many studies of benthic suspension feeders test the effect of flow on feeding rate by animals in unidirectional flow with passive and uniform prey . Encounter rates increase with water velocity, which leads to higher ingestion rates. In this study, stronger waves led to increased encounter rates only for passive particles, such as dead copepods . For prey that swim and perform escape maneuvers, stronger waves did not significantly enhance encounter rates. In weak waves, sea anemones encountered copepod prey at higher rates than nauplii and dead copepods, which suggests prey swimming behavior affects variability of encounter rates.
The differences in how flow affected encounter rates for three prey types were not mirrored in capture or retention rates. For passive prey, more encounter rates with a benthic predator did not result in greater rates of capture. Copepods in weak waves encountered a predator at a higher rate than nauplii, but capture rates were similar, which indicates that the capture and subsequent retention of prey does not scale equally from encounter rates for prey with different behavior. Importantly, retention rates were low for both nauplii and copepods in both weak and strong flow regimes. Dead copepods represented the extreme range of retention rates since these prey were retained at high rates in weak waves, but were not retained at all in strong waves. The comparisons between rates of encounter and capture for prey with different swimming behavior suggests the importance of evasive responses in avoiding contact with a predator,stackable planters reducing passive bumps into predators, and jumping free after getting captured. The proportion of predator-prey interactions between nauplii and dead copepods were similar . Copepod avoidance might have reduced passive bumping into predators in weak waves, but the proportion of capture remained the same in weak and strong waves. Downstream sea anemones encountered fewer prey than solitary sea anemones. Upstream neighbors can deplete water of prey as flow passes over the clone. The encounter, capture, or retention of prey by downstream sea anemones was independent of flow. Although these predators encountered fewer prey than solitary sea anemones, they retained approximately the same rate of prey. For benthic suspension feeders, turbulent and wavy flow enhanced encounter rates for passive prey but not for prey with active swimming behavior. Higher encounter rates of passive prey did not result in higher capture or retention rates. Similarly, feeding in the presence of neighbors lowers encounter rates but retention efficiency remains the same in weak and strong wakes. This study highlights the use of realistic flow conditions, prey with swimming behavior, and in the presence of neighbors to examine passive suspension feeding in benthic organisms. Soil is vital to humankind and our livelihood.Soil processes affect the quality of the food we eat, the water we drink, the air we breathe, and is the foundation of our living and transportation infrastructures.As the world’s population continues to grow and society expects a wider range of food selections, to provide this more selective world with nutritious food and feed will largely depend on our ability to maintain and sustain productive agricultural soils.Recognizing that soils have a central place in achieving food security, we note that the available arable land resource is decreasing at an alarming pace.In fact, we are at a point in time of what could be designated as a decade of peak agricultural land globally, indicating that the world’s area of productive arable land is nearing its maximum.This is so because the annual expansion rate of new farmland is becoming less than the land area removed from agriculture.Causes for reduction in productive farmland are its conversion to urban and industrial development,taken out of production because of it being degraded such as by soil erosion, compaction or salinization, and threatening public health because of soil contamination.It is estimated that about 15% of the world’s total land area has been degraded.In addition to the acreage of productive agricultural land decreasing, freshwater resources are also becoming scarce as populations increase, demanding additional water for domestic and industrial use.
Moreover, while diverting increasing volumes of water for maintaining healthy freshwater environments and ecosystems, water for irrigated agriculture is becoming restricted in many arid and semi-arid regions.We note that whereas only about 15% of the world’s agricultural land is irrigated, it produces about 45% of global food production and even more for fruit and vegetables.As high-quality freshwater availability is becoming a major constraint globally, increasing water use efficiency of irrigated agriculture is becoming essential.This form of agricultural intensification means to do more with less while simultaneously minimizing its environmental footprint and mitigating its contributions to climatic changes and/or adapting to it.Additional constraints on agricultural production include public debates and policy changes regarding its environmental impacts on soil, air, and water quality, the use of genetically modified foods, as well as the threat of a changing climate.Among various mitigation and adaptation options, one calls for sustainable intensification of agriculture, water- and climate-smart agricultural practices, as well as for conservation agriculture to improve soil health and to minimize environmental impacts on soil, water, and air quality.In addition, other non-soil related practices are suggested, such as closing crop yield and nutrient gaps and reducing food waste.Collectively, any of these land and water management practices serve to enhance soil quality, reduce the environmental footprint, conserve freshwater resources, reduce soil degradation while sustaining food production.Hence, the preservation of our soils is crucial.It is no wonder then that we must address causal factors of soil degradation, such as by water and wind erosion, soil contamination and soil salinity.We note that the room to expand cropland beyond the estimated 12% of the terrestrial land surface is limited, because most productive lands are already in agricultural use, whereas converting additional land would lead to either increasing environmental impacts of marginal lands or destruction of the world’s richest natural ecosystems.The importance of sustainable land management was recently acknowledged in the IPCC.Special Report on Climate and Land , highlighting interactions and feed backs between our changing climate, land degradation, sustainable land management and food security, stating: “Land provides the principal basis for human livelihoods and well-being including the supply of food, freshwater and multiple other ecosystem services, as well as biodiversity.Human use directly affects more than 70%of the global, ice free land surface.Land also plays an important role in the climate system.” Among the most prevalent forms of soil degradation, in addition to air and water erosion and soil contamination, is human-induced soil salinization.Soil salinization occurs by the accumulation of water-soluble salts in the plant rooting zone, thereby impacting water and soil quality, and inhibiting plant growth.Osmotic changes in soil water caused by total salinity reduce the ability of plants to take up water from the soil.In addition, specific ions such as Na and Cl negatively impact plant physiology and become toxic when absorbed by the plant at higher than beneficial amounts.Besides, Na accumulation in surface clay-mineral soils cause soil swelling and dispersion thereby reducing water infiltration and soil drainage and causing water logging and flooding in sodic soils.The geological salinization is by far the largest fraction of the approximately 1 billion haof salinized land, making up about 7% of the earth’s land surface.In addition, approximately one-third of the world’s irrigated land is salt-affected in some way , equal to about 70Mha.