Attraction to stomata was seen in iceberg lettuce and basil, not in arugula, parsley, and tomato. Brandl and Amundson reported that the age of romaine lettuce leaves is correlated with population size of E. coli O157:H7 and S. enterica Thompson on leaves.These authors also observed that exudates on the surface of younger leaves have higher nitrogen content than that of older leaves, which may contribute to determining the bacterial population size on the leaf. Thus, it is tempting to speculate that the genetic variability existent among plant genotypes regarding the chemical composition of their organ exudates may be a determinant for human pathogen behavior and ability to colonize plants. Finally, Mitra et al. studied the effect of different methods of inoculation on internalization and survival of E. coli O157:H7 in three cultivars of spinach. Among the organs studied, the spinach phylloplane and the stem provided the most and least suitable niche for this bacterium colonization, respectively. Although the leaf surface was the best “territory” for E. coli, the leaf morphologies of each cultivar affected the ability of this bacterium to survive. Collectively, all these studies point out that the plant genotype, age, leaf morphology, chemical composition of exudates, and the primarily infected organ affect the outcome of bacterial colonization of plants and the process may not be a generalized phenomenon, consequently shaping specific human pathogen and plant interactions.Flow habitat is critical for rocky intertidal organisms that rely on water motion to deliver prey. Benthic suspension feeders are bottom-dwelling organisms that feed on small particles or zooplankton prey.

Passive suspension feeders depend on ambient flow to bring food to an extended capture surface as they do not actively generate feeding currents. Suspension-feeding organisms live in a wide range of flow habitats from shallow coasts to abyssal depths,nft hydroponic system and from polar to tropical latitudes. Animals that use this feeding strategy are important components of benthic communities and play a key role in transporting material from the water column to the ocean floor . How does the fluid environment in which suspension feeders live affect predator-prey interactions? It is first necessary to understand how flow conditions fluctuate in habitats where benthic suspension feeders live. On rocky intertidal coasts, variation in flow occurs at a wide range of spatial and temporal scales. Spatial variation can depend on the local topography or bathymetry, fractal geometry of the coast, and the recruitment and distribution of organisms to the community . Temporal variation can occur due to small-scale fluctuations in the flow , waves , large eddies , the flood and ebb of a tide , the spring and neap phase of a tide , season , and climate patterns . As a result, rocky intertidal organisms are exposed to rapidly-fluctuating velocity, reversals of flow as waves pass through shallow habitats, hydrodynamic forces imposed by breaking waves, turbulent eddies of different sizes that mix the water, and tides that constantly alter the water level . Measuring small-scale variations of flow over intertidal habitats at high-frequencies and high-resolution is possible with several instruments and techniques . The acoustic Doppler velocimeter is suitable for collecting flow data in the intertidal because it can be positioned directly above an organism and takes high-frequency data at a remote sample volume below the probe. The ADV emits sound pulses which reflect off particles in the sample volume. The signal reflected back to receivers is used to calculate velocity in three directions. To capture the range of fluctuations that sea anemones experience in the rocky intertidal, an ADV can collect repeated measures of fine-scale variation in flow between two contrasting sites, over long time periods.

Other common instruments used to quantify flow in the intertidal are not suitable for this study of small-scale predator-prey interactions. For example, dynamometers measure maximum velocity experienced by intertidal organisms . Although a fine-scale grid of these instruments can address spatial heterogeneity of peak velocities, temporal variation is reduced to a single peak velocity event averaged over the time the instrument is deployed. Oceanographic instruments that collect high-frequency data over long time scales, such as acoustic Doppler current profilers , are unable to take measurements close to the substratum . The height of the instrument would also exceed the depth of water during much of the tidal cycle. While exposed, it would be unable to record the incoming or outgoing tide. The purpose of this study was to quantify the flow experienced by a suspension feeding sea anemone in two habitats , across a range of small-scale to large-scale temporal variation. We examined: the variations in flow around sea anemones; how the local flow habitats compared to measures of freestream flow, how daily tides and monthly tidal phases affect local flow over sea anemones; and to what extent offshore weather and wave conditions influenced the flow environment around benthic suspension-feeders. Flow was measured over colonies of the sea anemone Anthopleura elegantissima at two sites with contrasting exposure to waves . The ‘wave-exposed’ site was in Horseshoe Cove, in the Bodega Marine Reserve along the Sonoma Coast in California, USA ; the ‘wave-protected’ site was in Campbell Cove, on the leeward side of Bodega Head . At each site, the sea anemones used in this study occupied a relatively flat portion of the rocky shelf, with no obvious upstream obstacles. This species of aggregating sea anemone reproduces asexually by undergoing fission, forming a dense, homogenous bed of genetically identical sea anemones. An acoustic Doppler velocimeter measured water velocity at 25 Hz sampling rate in shoreward , alongshore , and vertical directions. The ADV was suspended from a horizontal bar of an aluminum sawhorse frame that had supporting legs on either side positioned to avoid interfering with flow .

The legs were secured from slipping by placing them on pegs that were glued into the rocky shelf using epoxy. This also ensured the ADV was positioned in the same place during repeated measurements over the course of a year. The body of the ADV was hose-clamped to a length of speed rail that was able to slide vertically along a fixed piece of matching rail on the aluminum frame. The height of the probe of the ADV was lowered or raised to measure a sample volume at five heights above a bed of sea anemones. The ADV was slid into position , then firmly secured by wing screws. This configuration meant that measurements could be repeated over the same anemone bed,hydroponic nft system in the same position, and at multiple heights. The ADV was cabled to a computer that was housed in a watertight box on dry ground. Once the ADV was slid to a particular measurement height, data was recorded for three minutes. Flow was measured at each height for 4 minutes to ensure the complete profile was collected in <30 minutes. The influence of local wind conditions on flow habitat over sea anemones was tested. Wind speed data was collected by the Bodega Marine Laboratory anemometer, located on top of the lab . Data was downloaded from the Bodega Ocean Observing Node website . The wind speed was averaged per hour, for each day that flow measurements were collected. The time of day that flow measurements were taken determined the hourly average wind speed selected. Correlations between ambient wind speeds and mean shoreward peak velocity were tested using Pearson correlation coefficients. The effect of incoming wave height on the flow microhabitat above sea anemones was tested using wave data from two nearby instruments. Remotely-sensed, high frequency radar measurements of wave height were collected from a sensor located at the Bodega Marine Lab . Wave height measurements were also collected by a National Oceanic and Atmospheric Administration buoy located in 116m of water, 22 km offshore . Wave height data were averaged per hour for each day flow measurements were collected. Pearson correlation coefficients tested the relationship between the height of incoming waves and flow microhabitat. A linear regression was performed for significant results to determine the percentage of variation explained by the relationship. In this study, flow microhabitats above sea anemones were not significantly different than free stream flow.

Free stream velocity was estimated using measurements taken at 9 cm above the sea anemones. Velocity measurements collected higher above the substratum , and therefore more likely to represent free stream velocity, were limited. The water depth required to submerge the ADV probe at this height reduced the amount of time available for taking measurements so there were fewer samples with which to compare sea anemone microhabitat. Also, as waves passed by the trough of the wave exposed the ADV probe to air which created intermittent gaps in the data. Peak velocities at 17cm were not significantly different from measurements at 9 cm , so flow measured at 9cm was used as a metric of free stream velocity. In this study, flow microhabitats above sea anemones were not significantly different than free stream flow . Free stream velocity was estimated using measurements taken at 9 cm above the sea anemones. Velocity measurements collected higher above the substratum , and therefore more likely to represent free stream velocity, were limited. The water depth required to submerge the ADV probe at this height reduced the amount of time available for taking measurements so there were fewer samples with which to compare sea anemone microhabitat. Also, as waves passed by the trough of the wave exposed the ADV probe to air which created intermittent gaps in the data. Peak velocities at 17cm were not significantly different from measurements at 9 cm , so flow measured at 9cm was used as a metric of free stream velocity. The temporal variation due to the flood and ebb of a tidal cycle, or the spring and neap of a tidal phase, did not affect the flow habitat over sea anemones. Instead, spatial variation between the exposed and protected sites dominated. Although relative terms that describe sites like ‘exposed’ and ‘protected’ are ambiguous , the contrast between the two flow habitats provided an important comparison. The differences between the two sites in this study demonstrated a range of flow environment in which sea anemones live.The use of offshore measurements of waves is not a reliable predictor of the flow over benthic organisms . Similarly, in this study the offshore wave height measured by a high-frequency radar explained 50% of the variation in water velocity over sea anemones. Again, spatial variation and local topography plays a large role in the flow experienced by benthic organisms in the rocky intertidal so that buoy measurements ought to be used as predictors only once tested. At the exposed site, measurements over sea anemones were only collected during August. However, measuring throughout the year might not have been necessary to estimate the peak velocities experienced by sea anemones at this site. The wave height was <2.5 m during days when peak velocities were measured at the exposed site. The peak velocities over benthic organisms did not demonstrate a positive trend with wave height, which would have suggested that larger wave might have led to higher flows over sea anemones. Helmuth and Denny observed no increase in force measured onshore with significant wave height above 2-2.5m, suggesting a microsite-specific maximum force, presumably set by wave breaking. Knowing the mechanisms that drive flow over a study organism or at a particular site is necessary to determine the spatial and temporal scales relevant to study. Measuring flow can be achieved with a wide range of instruments and variables to describe the fluid environment. The metrics used in a particular study ought to be tailored to answer the research question and be measured at the appropriate frequency and duration. Measures of free stream flow or using offshore wave height data may or may not predict local flow over benthic organisms, depending upon the topography of the shore. Using these measurements as indicators of the flow experienced by benthic organisms must be tested first. For suspension feeders that are intrinsically linked to the fluid environment, it is necessary to understand how flow conditions fluctuate in habitats where these organisms live.