Grass Beds Research Articles

Identifying Characteristics of Wildfire Towers and Troughs

Wildfire behavior is dictated by the complex interaction of numerous physical phenomena including dynamic ambient and fire-induced winds, heat transfer, aerodynamic drag on the wind by the fuel and combustion. These phenomena create complex feedback effects between the fire and its surroundings. In this study, we aim to study the mechanisms by which buoyant flame dynamics along with vortical motions and instabilities control wildfire propagation. Specifically, this study employs a suite of simulations conducted with the physics-based coupled fire-atmosphere behavior model (FIRETEC). The simulations are initialized with a fire line and the fires are allowed to propagate on a grass bed, where the fuel heights and wind conditions are varied systematically. Flow variables are extracted to identify the characteristics of the alternating counter-rotational vortices, called towers and troughs, that drive convective heat transfer and fire spread. These vortices have previously been observed in wildfires and laboratory fires, and have also been observed to arise spontaneously in FIRETEC due to the fundamental physics incorporated in the model. However, these past observations have been qualitative in nature and no quantitative studies can be found in the literature which connected these coherent structures fundamental to fire behavior with the constitutive flow variables. To that end, a variety of state variables are examined in the context of these coherent structures under various wind profile and grass height conditions. Identification of various correlated signatures and fire-atmosphere feedbacks in simulations provides a hypothesis that can be tested in future observational or experimental efforts, potentially assisting experimental design, and can aid in the interpretation of data from in situ detectors.

The effect of heat on keratin and implications for the archaeological record

A horncore feature was encountered during excavations at Border Cave, in Member 2 BSL, dated 60–49 ka. The basal half of the horncore lay towards the centre of a combustion feature and was calcined. The tip half lay on a mat of burnt grass bedding towards the edge of the fireplace. It was covered with a black shiny residue, which was also present on nearby stone tools. The feature was jacketed and excavated later under a microscope in the laboratory. Raman spectroscopy identified the residue only as amorphous carbon, indicating the presence of a heated organic substance. Knowing that variation exists in modern and archaeological glue recipes, we wanted to know if the black residue was melted keratin, and if it was, whether it had been used as a substitute for beeswax or latex for hafting. We set out to test the hypothesis by conducting a heating experiment with a modern sheathed horncore. Experimental results showed that keratin does not transform into viable glue when heated. Instead, it reduces immediately to a glassy brittle residue. Our finding strongly supports a scenario of incidental deposition of residue on the archaeological stone tools. Previous combustion experiments have shown that the sediment below a fire can reach 300+ °C through vertical heat transfer. This implies that horn sheaths in archaeological deposits, separated from overlying combustion features by thousands of years, can transform into a black residue that may deposit on nearby stone and bone tools.

Modelling distribution of the common bottlenose dolphin, Tursiops truncatus off the southwest coast of Puerto Rico

Abstract Standardized sightings of the common bottlenose dolphin (Tursiops truncatus) from the south and west coasts of Puerto Rico were quantitatively analyzed to determine the spatio-temporal distribution patterns of sighting location, group size, composition and behavior in relation to key features such as distance from shore, depth and habitat type. Dolphin inhabit primarily the nearshore zone within 5 km of the coast, but they are also associated with edge and slope habitats of the platform and bank/islands off the west coast. Dolphins were rare both over the central portion of the western platform, characterized as a broad area of sand, as well as in deep waters outside the shelf edge zone. Although dolphins were sighted in various habitat types, the most predominant were sea grass beds (44%), sand (25%), and reef (22%). Only 17% of the sightings were in deeper waters, such as the shelf edge and mid platform, which were dominated by hard bottom. Multiple, multivariate correlations based on distance (DISTLM) showed that the only statistically significant predictor for dolphin relative abundances was Habitat Evenness (AIC = 250.89; R2 = 0.12; p = 0.003). On the other hand, for behavior data, DistLM showed that the only significant predictor was average rugosity (AICc = 551.21, R2 = 0.09, p = 0.02), where social behavior was more common in high rugosity areas, while traveling predominated in low rugosity areas. Given the predominately inshore distribution of bottlenose dolphins, their low abundance, and multiyear residency we believe the area off the west coast of Puerto Rico should be designated as a Critical Habitat.

Experimental analysis of artificial lightning breakdown and ignition characteristics in grassland

Lightning fire is an important influencing factor of grassland ecology. It is one of the important ignition sources of grassland fire. The previous researches on lightning fires were mainly focused on forests, but researches on grassland were insufficient. In this paper, the impulse voltage generator was used to evaluate the breakdown characteristics of grass bed. The relationship of breakdown voltage to moisture content and bulk density was obtained. Based on the impulse current generator, an artificial lightning ignition prediction model of impulse current was derived. Results show that the breakdown voltage of grass bed decreases rapidly with the increase of moisture content. With the increase of peak current, the total lightning energy increases, while the heating efficiency decreases.

Anti-Fouling Effects of Saponin-Containing Crude Extracts from Tropical Indo-Pacific Sea Cucumbers.

Sea cucumbers are bottom dwelling invertebrates, which are mostly found on subtropical and tropical sea grass beds, sandy reef flats, or reef slopes. Although constantly exposed to fouling communities in these habitats, many species are surprisingly free of invertebrate epibionts and microfouling algae such as diatoms. In our study, we investigated the anti-fouling (AF) activities of different crude extracts of tropical Indo-Pacific sea cucumber species against the fouling diatom Cylindrotheca closterium. Nine sea cucumber species from three genera (i.e., Holothuria, Bohadschia, Actinopyga) were selected and extracted to assess their AF activities. To verify whether the sea cucumber characteristic triterpene glycosides were responsible for the observed potent AF activities, we tested purified fractions enriched in saponins isolated from Bohadschia argus, representing one of the most active anti-fouling extracts. Saponins were quantified by vanillin-sulfuric acid colorimetric assays and identified by LC-MS and LC-MS/MS analyses. We were able to demonstrate that AF activities in sea cucumber extracts were species-specific, and growth inhibition as well as attachment of the diatom to surfaces is dependent on the saponin concentration (i.e., Actinopyga contained the highest quantities), as well as on the molecular composition and structure of the present saponins (i.e., Bivittoside D derivative was the most bioactive compound). In conclusion, the here performed AF assay represents a promising and fast method for selecting the most promising bioactive organism as well as for identifying novel compounds with potent AF activities for the discovery of potentially novel pharmacologically active natural products.

Spatial and Temporal Trends in Diet for Pinfish (Lagodon rhomboides) from Turtle Grass (Thalassia testudinum) Beds with Contrasting Environmental Regimes in the Lower Laguna Madre, Texas

Seagrass meadows in far South Texas are dominated by turtle grass (Thalassia testudinum), and juvenile pinfish (Lagodon rhomboides) are abundant grazers of seagrass epifauna. As they grow, pinfish exhibit an ontogenetic dietary shift and begin consuming increasing amounts of plant material. In this study, contrasting environmental regimes in two seagrass meadows were examined to identify how they might affect pinfish diets, diet shifts, and growth across the growing season. The eastern site was sheltered from prevailing southeasterly winds by a barrier island, while the western site was shallower and subjected to higher wind energy and turbidity. Gut contents from 290 pinfish were quantified from May through October 2016 and multivariate analyses showed strong but overlapping separation of diets and temporal change in feeding habits. Although there were spatial and temporal differences between the two sites, a site by time interaction indicated different temporal trends. Nonetheless, ooze (amorphous detritus) and aquatic invertebrates (primarily amphipods) were the primary diet items consumed at both localities across time. Pinfish at both sites consumed seagrass, which increased in importance as the growing season progressed, although volume and consumption rate did not differ between sites. Growth rates of pinfish were similar at both sites, but pinfish from the western site were larger and fewer in number across the study. Although pinfish diets differed under different environmental regimes, they were generalist consumers in South Texas seagrass meadows with high diet variability that trended towards herbivory in late summer and fall.

Influence of light on the infection of Aureococcus anophagefferens CCMP 1984 by a "giant virus".

The pelagophyte Aureococcus anophagefferens has caused recurrent brown tide blooms along the northeast coast of the United States since the mid-1980’s, and more recently spread to other regions of the globe. These blooms, due to the high cell densities, are associated with severe light attenuation that destroys the sea grass beds which provide the basis for many fisheries. Data collected by transmission electron microscopy, PCR, and metatranscriptomic studies of the blooms, support the hypothesis that large dsDNA viruses play a role in bloom dynamics. While a large (~140 nm) icosahedral virus, with a 371 kbp genome, was first isolated more than a decade ago, the constraints imposed by environmental parameters on bloom infection dynamics by Aureococcus anophagefferens Virus, (AaV) remain unknown. To investigate the role light plays in infection by this virus, we acclimated A. anophagefferens to light intensities of 30 (low), 60 (medium) or 90 μmol photons m-2 s-1 (high) and infected cultures at these irradiance levels. Moreover, we completed light shift experiments where acclimated cultures were exposed to even lower light intensities (0, 5, and 15 μmol photons m-2 s-1) consistent with irradiance found during the peak of the bloom when cell concentrations are highest. The abundance of viruses produced per lytic event (burst size) was lower in the low irradiance acclimated cultures compared to the medium and high acclimated cultures. Transferring infected cultures to more-limiting light availabilities further decreased burst size and increased the length of time it took for cultures to lyse, regardless of acclimation irradiance level. A hypothetical mechanism for the reduced efficiency of the infection cycle in low light due to ribosome biogenesis was predicted from pre-existing transcriptomes. Overall, these studies provide a framework for understanding light effects on infection dynamics over the course of the summer months when A. anophagefferens blooms occur.

Regional Collaboration Among Countries in the Indian Ocean for Better Coastal and Ocean Governance

The Mangroves for the Future initiative (MFF) has operated since 2006 as a strategic regional and partnership-led programmeworking in response to the continued degradation of coastal ecosystems, which threatens the livelihoods and security of coastal communities and makes them more vulnerable to impacts from climate change. MFF follows the principle that healthy coastal ecosystems (principally mangroves, coral reefs and sea grass beds) can contribute significantly to human well-being and the resilience of man and nature to climate change. In its initial phase to 2010, MFF supported India, Indonesia, Maldives, Seychelles, Sri Lanka and Thailand to deliver a targeted response to the Indian Ocean tsunami in 2004. Since then, country membership has expanded to include Bangladesh, Cambodia, Myanmar, Pakistan and Viet Nam and the initiative has grown towards a wider response to the current and emerging challenges for coastal management in the Indian Ocean and South China Sea regions. MFF is also engaged with Malaysia on an outreach basis; and with the Philippines as a dialogue country. Co-chaired by International Union for Conservation of nature (IUCN) and United Nations Development Programme (UNDP) and with ASEAN Centre for Biodiversity (ACB), Food and Agricultural Organization of the United Nations (FAO), United Nations Environmental Programme (UNEP), and Wetland International (WI) as institutional partners, MFF provides a unique platform for representatives from governments, civil society and private sectors to meet, discuss and take actions together at both regional and national scales. At the regional level, MFF is governed by a Regional Steering Committee that provides strategic leadership for policy change and advocacy and also serves as a forum for country to country information exchange and discussions on emerging issues of regional importance. Within each MFF member country, a National Coordination body has oversight on the programme implementation as guided by its National Strategy and Action Plan and delivery of the small, medium and regional grant facilities1. Through its inclusive partnership approach, MFF has significantly strengthened the collaboration between the key stakeholders from governments, civil society, and private sectors addressing national and regional coastal zone management issues. In particular, the MFF initiative has supported national and local governments in developing and implementing participatory and sustainable resource management strategies, and, through awareness and capacity building activities, empowered coastal communities to participate in the decision making processes relating to the management of the natural resources on which they depend for their livelihoods. The present paper elaborates successful examples of regional collaboration initiated through MFF that have contributed to better coastal governance in India Ocean region. The examples include the transboundary cooperation between Pakistan and Iran in Gawatar Bay, between India and Sri Lanka for in the Gulf of Mannar, and between Guangxi and Quang Ninh Provinces in China and Viet Nam. The paper also highlights the importance of the Sustainable Development Goals, especially the Goal 14 and concepts like Blue Economy for sustainable ocean and coastal management in the light of the rapid development in maritime trade, race for exploration of the ocean bed for mineral resources, unsustainable exploitation of fish resources, and increasing pollution load to ocean waters from rapidly developing coastal urban growth in the Indian Ocean region.

Effect of Seagrass on Current Speed: Importance of Flexibility vs. Shoot Density

Water flow through seagrass beds transports nutrients, affects sediment stability and chemistry, and imposes hydrodynamic forces on shoots that alter canopy configuration. Past studies done under diverse conditions yielded conflicting results about the effects of shoot density on flow through seagrass bed canopies. We used eelgrass, Zostera marina, to study how the density of flexible shoots affect the hydrodynamics of seagrass beds (canopies) in unidirectional water flow. By exposing randomly-arranged shoots of uniform length to current velocities controlled in a flume, the effects of shoot density and downstream distance (position) could be determined without confounding factors. Comparison of velocity profiles within beds to those upstream of the beds showed that flow was slower in the beds. However, shoot density, position, and current velocity did not affect the percent reduction in flow velocity in a (sea)grass bed. Turbulence enhances mixing of substances carried in the water. Here, turbulence intensity (index of the importance of turbulent velocity fluctuations relative to average current velocity) was lower when ambient flow was faster, but was not affected by shoot density or position, Drag, the hydrodynamic force on a shoot that bends it over in the flow direction, provides another measure of how the canopy affects flow experienced by a shoot. Drag was not affected by current velocity, shoot density, or position in the bed. Gaps between shoots can enhance light and flow penetration into the canopy, but when shoots are bent over by flow, they can cover gaps. Faster ambient currents caused greater gap closure, which at each current speed was greater for high shoot densities. Thus, canopy gap closure did not correlate with percent flow reduction in grass beds or with drag on individual shoots, both of which were independent of shoot density and ambient current velocity. Since changing shoot density does not affect the flow in a grass bed exposed to a given ambient current, our results are inconsistent with the hypothesis that the high shoot densities observed in grass beds in habitats exposed to rapid flow are due to a direct, adaptive response of the grass to the flow environment.

The Fossil Cypraeidae of the Pinecrest Member (Unit 7) and Kissimmee River Valley Equivalent, Tamiami Formation of Southern Florida: (Mollusca: Gastropoda: Cypraeidae)

Following the disappearance of the seven Buckingham Member (Unit 10) Cypraeidae from the Myakka Lagoon System (Myakka), there was a hiatus represented by two strata at Sarasota (Pinecrest Members 9 & 8) in the early Piacenzian Pliocene, 3.6 million years ago (“mya”), from which no Cypraeidae have been recorded. This was followed by the warmest and most tropical conditions of the entire Pliocene. The sea grass beds and mud flats, which were the preferred habitats of the Pinecrest Cypraeidae, returned in force. The depositional strata which resulted, Pinecrest (Unit 7) and its Kissimmee River Valley Equivalent, were very thick and probably represent a long period of uninterrupted deposition. Eight new species in six genera emerged in Myakka. In the Kissimmee River Valley (Kissimmee), six new species in three genera (one new) emerged as the first and earliest known Cypraeidae species from that area. This represented geographically separate, but parallel, evolutionary tracks. Pinecrest Members 6 & 5 represented a repeat of the conditions experienced during Pinecrest Members 9 & 8, resulting in the disappearance of all Pinecrest (Unit 7) Cypraeidae from Myakka and Kissimmee.

Nursery habitat use for larval and juvenile Pacific herring Clupea pallasii in Miyako Bay on the Pacific coast of northern Japan

To clarify nursery habitat use for larval and juvenile Pacific herring Clupea pallasii, we collected eggs, larvae, and juveniles at several sampling sites in inner Miyako Bay from 2012 to 2016. Adult C. pallasii used sea grass beds on the west side of inner Miyako Bay as a spawning area. In contrast, their offspring grew up to approximately 100 mm in total length (TL) on the east side of the inner bay, where they stayed until July. C. pallasii seemed to leave the nursery area on the east side of the bay with the rise in temperature in August. Therefore, C. pallasii shifted habitats with ontogenetic development, from the west side of the inner bay in the egg stage, to the east side of the inner bay in the larval and early juvenile stages, and then to the central bay area in the later juvenile stage. Environmental surveys showed lower salinity near the bottom of the east side than the west side of inner Miyako bay, suggesting that larval and juvenile C. pallasii appeared to use the area with low salinity on the east side of Miyako Bay as a nursery.

The Fossil Cypraeidae of the Buckingham Member (Unit 10), Tamiami Formation of Southern Florida: (Mollusca: Gastropoda: Cypraeidae)

The oldest recorded fossil Cypraeidae from southern Florida date from the late Zanclean-early Piacenzian Pliocene (circa 3.8-3.6 million years ago - hereinafter “mya”) in the Myakka Lagoon System, a shallow water estuary that lies beneath the present day Sarasota area. Shallow water sea grass beds and nascent shoreline mangrove forests hosted seven Cypraeidae species in five genera. Determining the origins of these species is challenging as only steinkern casts have been found in adjacent lower layers. However, enough features are present in two of the casts to infer the ancestral presence of two of the genera. For the other genera and species, a comparison of features with the northern Florida Panhandle Cypraeidae populations dating from the Burgdigalian Miocene (16-20 mya) does suggest certain affinities. However, no direct lineage can be asserted with any confidence. The sea bed deposit layer of this period has been designated the Buckingham Member of the Tamiami Formation of southern Florida.

First report of a rare snake eel, Allips concolor McCosker, 1972 (Anguilliformes: Ophichthidae) from Indian waters

The monospecific genus Allips is reported here for the first time from Indian waters, from a specimen collected from the sea grass bed outside the Nalban bird Sanctuary, Chilika lagoon, India, with its morphometric characters, vertebrae and teeth pattern. The rare small eye snake eel A. concolor was earlier described by McCosker, 1972 on the basis of a single specimen. After that, there are very rare reports on this particular species especially on its morphometry after McCosker (1972). This paper extends the range of A. concolor McCosker, 1972 from eastern Andaman Sea and Northern Territory, Australia to Indian waters. A detailed discussion on the distribution and habitat is also provided in this paper.

CARACTERIZACIÓN MORFOLÓGICA Y MOLECULAR DE Isostichopus sp. EN EL MAR CARIBE COLOMBIANO

Isostichopus sp. (Aspidochirotida: Stichopodidae) are sea cucumbers widely distributed in the Caribbean Sea. Amongst them, Isostichopus badionotus is one of the most harvested species. It shows a wide range of morphotypes widespread in the Caribbean region including different habitats (muddy, sandy and rocky bottoms, and sea grass beds). In Colombia, three morphotypes can be distinguished; two of them live in sea grass beds while the third one is found on rocky substrates. The present study describes the morphological characteristics of these morphotypes and analyzes their genetic structures through 16S rDNA and COI data. Our phylogenetic analyses show that the morphotype living on rocky substrates is morphologically and genetically distinct from the two other morphotypes and might not correspond to I. badionotus, the only species of the Isostichopus genus previously reported for this region. Key words: cucumbers, COI, 16S rDNA, Isostichopus badionotus

New Excavations at Border Cave, KwaZulu-Natal, South Africa

ABSTRACTNew excavations at Border Cave use high-resolution techniques, including FT-IR, for sediment samples and thin sections of micromorphology blocks from stratigraphy. These show that sediments have different moisture regimes, both spatially and chronologically. The site preserves desiccated grass bedding in multiple layers and they, along with seeds, rhizomes, and charcoal, provide a profile of palaeo-vegetation through time. A bushveld vegetation community is implied before 100,000 years ago. The density of lithics varies considerably through time, with high frequencies occurring before 100,000 years ago where a putative MSA 1/Pietersburg Industry was recovered. The highest percentage frequencies of blades and blade fragments were found here. In Members 1 BS and 1 WA, called Early Later Stone Age by Beaumont, we recovered large flakes from multifacial cores. Local rhyolite was the most common rock used for making stone tools, but siliceous minerals were popular in the upper members.

Size and weight estimations of the spangled emperor (Teleostei: Lethrinidae: Lethrinus nebulosus) from bone measurements elucidate the fishing grounds exploited and ancient seasonality at Akab (United Arab Emirates)

AbstractThe presence of emperor fishes has been reported in several archaeo‐ichthyological studies in Eastern Arabia. The spangled emperor (Lethrinus nebulosus) is one of the main species currently composing annual landings in the central and southern Persian Gulf. Its presence outlines the importance of the coastal environments exploited during different life cycle stages, such as open‐water reefs and sheltered embayments, including grass beds. Osteometrical methods for estimating the life‐size from bones were developed during the last few decades. Measurements taken from the bones of 32 fresh spangled emperors, collected from a fish market in Umm al‐Quwain (United Arab Emirates) in February 2017, were exploited to calculate regression equations (power fits), allowing size estimations from archaeological remains. Because of the difficulties in identifying emperor species using bones, we also tested and discussed the validity of a generic model.The Neolithic site of Akab has provided more than 37,000 fish remains, mostly belonging to kawakawa tunas, trevallies, and seabreams, which suggest that fishing was essentially carried out during the winter. Relatively few bones (totalling 100 measurements) were identified as belonging to spangled emperors. However, because of the ecological features of this species, estimated sizes permitted investigations into which fishing grounds were exploited, and even provided new evidence regarding ancient seasonality of coastal occupation in Eastern Arabia.

Impacts of wintering redhead ducks (Aythya americana) on seagrasses in the northern Gulf of Mexico

While it has been well established that waterfowl can sometimes control the distribution and abundance of seagrasses, relatively little is known about their effects in the northern Gulf of Mexico (nGOM). Seagrass meadows provide critical habitat for commercially important finfish and shellfish and as winter waters continue to warm, the nGOM will likely become increasingly appealing for wintering waterfowl. We measured the impact of redhead duck (Aythya americana) foraging on mixed shoalgrass (Halodule wrightii) and widgeon grass (Ruppia maritima) beds using caging experiments (1.5 × 1.5 m) at three locations in the nGOM. Time-lapse photography provided estimates of the abundance and feeding activities of the birds. Redhead ducks actively and regularly fed in all experimental areas; however, flock sizes were significantly smaller than previously recorded in Texas and south Louisiana. In general, there was little evidence of grazing effects on R maritima biomass. H. wrightii biomass followed expected seasonal patterns in both grazed and ungrazed treatments, and while both grazed and ungrazed biomass increased over the two years of the study, greater biomass increases occurred in ungrazed treatments. Similar to conclusions from previously conducted studies, we found no evidence that waterfowl were overexploiting their seagrass food resources.

A Study of Co-occurrences of Foraminifera and Mussels in a Polluted Nova Scotian Wetland, Atlantic Canada

Abstract Studies of foraminiferal assemblages in intertidal marshes and subtidal creeks usually rely upon sediment samples collected along transects, such that associations with other organisms often go unnoticed. We show that ecologically useful data can be obtained by sampling that is stratified by substrate and microenvironment. The tidal wetland at Lower LaHave, Nova Scotia, Atlantic Canada (44º16′37.39″N, 64º19′46.45″W, area ∼1 km2) comprises mostly sandy sediment occupied largely by the low marsh grass Spartina alterniflora. The wetland is situated next to LaHave Estuary, which is polluted with domestic waste. Microenvironments within the marsh were sampled for total (living + dead) foraminiferal assemblages. The mass of dried sediment examined at each site was used to calculate the foraminiferal number (FN, number of foraminiferal tests per gram of sediment). Sediment samples from the intertidal grass beds reflect a typical low- to high-marsh zonal distribution of benthic foraminifera [FN = 24.7 ± 16.6 g−1 (mean ± standard deviation); n = 716 tests]. Samples from a tidal channel yielded few tests (FN = ∼0.3 ± 0.7 g−1; n = 22). Clutches of the mussel Mytilus edulis occurred in areas of strong current action within the channel and on lower energy slip-off slopes. Mussel clutches from the channel base yielded few tests (FN = ∼0.7 ± 0.7 g−1; n = 25), mostly Miliammina fusca. Clutches from slip-off slopes yielded a significantly richer assemblage (FN = 8.7 ± 4.6 g−1; n = 229) dominated by Elphidium umbilicatulum. We concluded that mussel clutches in low energy areas can be suitable habitat for E. umbilicatulum, either associated with structural complexity of the clutches or with waste products excreted by mussels that may stimulate growth of bacteria or microalgae upon which the foraminifera feed. The results from this study provide a baseline for examining the biotic impact of remediation of the LaHave River on the Lower LaHave wetland.

Sea surface temperatures and seagrass mortality in Florida Bay: Spatial and temporal patterns discerned from MODIS and AVHRR data

Two major episodes of seagrass mortality have occurred in Florida Bay in the past 30 years: The first occurred between 1987 and 1991 and the second began in 2015. In both episodes, dense beds of turtle grass (Thalassia testudinum) were decimated. Elevated water temperature and hypersalinity have been implicated as contributing factors in both mortality events. During both die-off events seagrass beds on shallow (Z≈0.3 m) mudbanks in western Florida Bay were disproportionately affected when compared to neighboring seagrass in deeper basins (Z≈1.5 m). A network of in situ monitoring stations has measured sea surface temperature and salinity at hourly intervals in 16 basins in Florida Bay from August 2009 to the present day and these data aided in diagnosing the 2015–2016 die-off event. However, very few in situ observations of sea surface temperature have been collected on Florida Bay's shallow mudbanks as most are inaccessible by boat. As a result, our understanding of the role of elevated SST in shaping the spatial patterns of seagrass mortality is hindered by the spatial distribution of the in situ monitoring data and its record length. Therefore, we turn to remotely sensed SST data to expand our spatial coverage to include the entire Florida Bay ecosystem and to extend the record length to include the 1987–1991 die-off event. 1 km MODIS SST shows that shallow mudbanks were consistently warmer (by up to 6°C) than nearby deeper basins. While water depth is likely the primary driver of spatial variability in SST, Landsat-8 surface reflectance data suggest that shallow seagrass beds could have suffered from the added influence of low surface reflectance, which might have further contributed to their thermal stress. Daily 0.25° AVHRR SST shows that the August maximum SST has increased by 1°C from 1981 to 2016, which is a cause for concern for the future of seagrass in Florida Bay. Correlation of monthly AVHRR SST anomalies with the multivariate ENSO index shows that ENSO can only partially explain the anomalous temperatures. When viewed together, the in situ and remotely sensed SST suggests that both extended exposure to anomalously warm temperatures and large, rapid changes in temperature could have contributed to seagrass mortality during both events.

Secondary Flow Structures in Open Channel with Patchy Gravel and Vegetated Beds

Secondary flows are present in open channel due to the complex three-dimensional flow structures as a result of the existing natural features (e.g. different boundaries) affecting the flow. This paper experimentally examined the structure of secondary flow in open channel with a patchy gravel and vegetated beds using two different experimental conditions. A high resolution three-dimensional instantaneous velocity measurement over the gravel and vegetated bed were made using the acoustic Doppler velocimeter (ADV) and the secondary flow quantities determined. The results reveal that the magnitude of secondary flow over the gravel bed in experiment one is relatively large with occurrence of down-flow, and up-flow over the flexible vegetated bed. The lateral interaction and momentum transfer between the two-bed roughness (gravel and vegetated beds) is achieved by the secondary flow, at the lower region of the flow, the transverse motion is directed from the gravel bed towards the grass bed, and at the upper region, and the flow is transported laterally in the opposite direction.