High Wave Action Research Articles

The behavior of sympatric sea urchin species across an ecosystem state gradient.

In temperate macroalgal forests, sea urchins are considered as a keystone species due to their grazing ability. Given their potential to shape benthic communities, we monitored the habitat use by three sympatric sea urchin species and compared their behaviors in a vegetated habitat (VH) and an adjacent isoyake habitat (IH). We monitored the environmental conditions and sea urchin density along deep and shallow transects of the VH and IH for over a year. The benthic rugosity at both sites were also surveyed. A mark-recapture experiment was conducted on the two most abundant sea urchins, Diadema setosum and Heliocidaris crassispina, to elucidate sea urchin movement patterns and group dynamics. We found that exposure to waves was highest at the VH while the IH was sheltered. The deep IH experienced the least amount of light due to high turbidity. Water temperature patterns were similar across sites. The VH benthic topography was more rugose compared to the smoother and silt-covered IH substate. Peak macroalgal bloom occurred three months earlier in IH, but macroalgae persisted longer at the shallow VH. Among the sympatric sea urchins, H. crassispina was most abundant at the shallow VH and was observed in pits and crevices. The most abundant across IH and in the deep VH was D. setosum, preferring either crevices or free-living, depending on hydrodynamic conditions. The least abundant species was D. savignyi, and most often observed in crevices. Small and medium sea urchins were most often observed at the IH site, whereas larger sea urchins were more likely observed at the VH. The mark-recapture study showed that D. setosum was found to displace further at the IH, and H. crassispina was more sedentary. Additionally, D. setosum was always observed in groups, whereas H. crassispina was always solitary. The behaviors of sympatric urchins, Diadema savignyi, D. setosum and H. crassispina, differed in response to changes in the benthic environment and physical conditions. Sea urchin displacement increased when rugosity and wave action were low. Habitat preference shifted to crevices in seasons with high wave action. In general, the mark-recapture experiment showed that sea urchins displaced further at night.

Blue mussels in western Norway have vanished where in reach of crawling predators

Blue mussels (Mytilus spp.) are declining around the world. In western Norway, they have widely disappeared from rocky shores but still thrive on floating structures. Other refugia are cracks in rocks, exposed sites, and low-salinity habitats. Climate change, pollution, disease, parasites, hybridization, and failed recruitment might not alone be able to create such distribution patterns. We hypothesized that crawling predators that are unable to reach floating structures may drive the present decline in western Norway. A known crawling predator without a pelagic stage and sensitive to low salinity and high wave action is the dogwhelk Nucella lapillus. Tributyltin (TBT) contained in anti-fouling paint rendered this snail sterile, but TBT is now banned, and populations are recovering rapidly. We first surveyed floating structures together with nearby rocky shores for blue mussels and dogwhelks. Blue mussels were present on all surveyed floating docks (65% area covered), but only on 18% of rocky shores (≤5% area covered). Similarly, blue mussels were found on 83% of tree branches suspended in water without bottom contact, but only on 1% when branches touched the seafloor. We then conducted a predator exclusion experiment with caged blue mussels (40-80 mm). In cages, mortality due to factors other than dogwhelks was extremely low (<1%) and confirmed that blue mussels continue to thrive when out of reach of predators. If dogwhelks or other crawling predators such as crabs or sea stars created the observed distribution pattern, then environmentally friendly mariculture with blue mussels growing on rafts and longlines might still have high potential in Norway.

The Impact of Seasonal Weather Changes on the Accumulated Sediments within Back-Reef Environment around Umm Al-Maradim island- Kuwait

This study is based on petrographic, geochemical and mechanical analysis of all collected samples from the intertidal zone around the southern Umm Al-Maradim Island in Kuwait. The objective is to interpret the impact of seasons conditions on coral buildups around the island. Petrographic study revealed that the intertidal area is a part of a back-reef environment which is composed of the accumulation of broken up coral debris, coralline algae, foraminifera, echinoderms particles, bivalves, and gastropods. Generally, most abundant grain sizes along the shores are coarse and very coarse sand size, indicating short distance of transport and high wave action. Short transportation distance and fast sedimentation resulted in the accumulation of poorly sorted and strongly coarse to coarse skewed sediments. Detailed study of the samples shows variations in grain size parameters as well as type of accumulated sediments between the different seasons and locations along the island, which is mainly related to the differences in wind intensity, changes in prevailing wind direction, and biological activities affecting the coral reefs. Geochemical study suggests an aragonitic and low-Mg calcite composition for the coral fragments, as well as a pathetic relationship between all tested major elements within the collected sediments.

Petroleum hydrocarbons in Brazilian Northeast continental shelf waters: baseline values

Water quality on the continental shelf off the eastern Brazilian Northeast region was investigated in two oceanographic campaigns during winter and summer, when vertical profiles of salinity, temperature, turbidity, chlorophyll and dissolved oxygen were recorded. Dissolved / dispersed petroleum hydrocarbons (DDPH) were also analyzed in sub-superficial water samples using fixed wavelength fluorescence spectroscopy methods. Shelf waters are dominated by Tropical Waters, with high salinity (> 36.5 g kg-1) and temperature (> 26 °C) and little continental influence. Turbidity was higher during winter, which may be due to the higher continental contribution and/or higher wave action. Chlorophyll was mostly < 1 µg L-1 and dissolved oxygen saturation was predominantly high (> 90%), but innermost costal stations were influenced by the Capibaribe estuary. Median DDPH concentrations were as low as 0.07 and 0.04 µg L-1 Carmópolis oil equivalents during winter and summer respectively, and 0.02 µg L-1 chrysene equivalent for both periods. An exception was observed off Suape Harbor (0.35 µg L-1 Carmópolis oil equiv. and 0.13 µg L-1 chysene equiv.), suggesting navigation activities as the main local source. The overall DDPH median of 0.06 μg L-1 Carmópolis oil equivalents and 0.02 μg L-1 chrysene equivalents are proposed as the baseline concentration for non-polluted coastal water for the tropical western Atlantic Ocean margin.

Isolation and characterization of halophilic isolates from Indian salterns and their screening for production of hydrolytic enzymes

Bacterial halophiles are unicellular organisms that can withstand a variety of stresses, and since the hydrolytic enzymes generate are typically stable, specific, and usable under high salinity, extreme temperature, wave action, and tide fluctuation, they are of particular interest. Due to their superior functionality in a wide range of extreme conditions found in different industries, the search for novel extremozymes and extremoproteins has been carried out over the last few decades. Moderately halophilic bacteria were isolated from three salterns in Tamil Nadu (Thoothukudi, Marakkanam, and Kanyakumari), Ernakulum in Kerala, and Ribandar salterns in Goa, India. Most of the halophilic isolates were found to be Gram-positive and also their pigmentation ranged from creamy white to yellow and yellow to bright orange. Out of 1127, characterization of twenty-eight halophilic isolates was carried out by morphological, biochemical, and molecular techniques. They ranged over different genera: Staphylococcus, Stenotrophomonas, Bacillus, Pseudomonas, Enterobacter, Ochrabactrum, and Oceanobacillus. Hydrolases such as amylase, lipase, protease, and cellulase were screened in halophilic bacterial isolates. For the first time, Bacillus paramycoides have been found to produce lipase. At least one enzyme activity was detected in each isolate. Extracellular enzymes were produced by Bacillus sp., Staphylococcus sp., and Pseudomonas sp. Highest protease activity was produced by six isolates with the enzyme activity ranging from 144.27 to 201.25 U/mg. Only a few isolates showed cellulolytic activity. These extracellular enzymes are very important and have a promising role from the viewpoint of industries because they are intrinsically salt tolerant.

The role of wind fetch in structuring Antarctic seabird breeding occupancy

Avian breeding sites located along shorelines may allow easy access to aquatic food sources, but risk exposing birds and nests to high wind and wave action. One measure of exposure is wind fetch, the distance of open water over which wind can blow uninterrupted. By calculating fetch weighted by prevailing wind direction for breeding colonies of pursuit‐diving seabirds in the Antarctic Peninsula, we show that different members of this guild have opposing relationships to coastline exposure. Gentoo Penguins Pygoscelis papua preferentially occupied more enclosed sites with lower fetch. Surprisingly, however, Chinstrap Penguins Pygoscelis antarcticus and Antarctic Shags Leucocarbo bransfieldensis appear to prefer more exposed sites. Although considerable research has been devoted to understanding Antarctic seabird habitat suitability, the role of wind and wave exposure has not been considered in depth, in part because comprehensive data on colony presence and absence have only recently been made available. We propose several mechanisms for why fetch may act to differentiate niches among this guild. These findings may increase our ability to identify suitable breeding areas for these and other near‐shore breeding species as they respond to climate change.

Dietary and habitat niche partitioning in congeneric cryptobenthic reef fish species

Ecological niches hold critical information concerning the eco-evolutionary dynamics that govern biodiversity and abundance patterns. Cryptobenthic reef fishes account for approximately half of all reef fish species and are an abundant and important group on coral reefs worldwide. Yet, due to their small size and inconspicuous lifestyles, relatively little is known about the ecological niches of most cryptobenthic species. Here, we use gut content DNA metabarcoding to determine dietary niche overlap and prey richness in four sympatric species of cryptobenthic reef fishes in two genera (Acanthemblemaria aspera, A. spinosa, Enneanectes altivelis, and E. matador). Furthermore, we test whether dietary differentiation corresponds with differences in species distribution patterns across twelve sites on the Mesoamerican Barrier Reef in Belize. Our approach reveals dietary partitioning among the four species, which is further supported by low edge density and high modularity in the resulting trophic network. A. spinosa and E. matador consume a significantly higher richness of prey items than their congeners. This result corresponds with non-random distributions and co-occurrence patterns in both species pairs: the two high prey richness species (A. spinosa and E. matador) co-occur more frequently than predicted by chance, but they are exclusive to exposed forereef sites with high wave action. In contrast, their congeners occur across exposed forereef and sheltered backreef sites, but they do not increase in numbers at sheltered sites. Our findings suggest that A. spinosa and E. matador monopolize a wide variety of prey in exposed habitats, but they are unable to meet the energetic demands of their adaptation to high-flow habitats in sheltered areas, possibly due to lower prey availability. This, in turn, indicates strong ecological differentiation among closely related species of cryptobenthic fishes, driven by links between diet, physiology, prey availability, and wave exposure.

Macrocystis (Laminariales, Phaeophyceae) in South Africa: distribution, morphology, and potential susceptibility to warming events

Macrocystis pyrifera (Laminariales), widely known as “giant kelp,” is dominant on temperate coastlines of the eastern Pacific and the Southern Hemisphere. It is recorded in South Africa, but with very little information available on its distribution and ecology. Here, we document the known distribution and provide an account of the basic population structure and morphology of three populations of South African M. pyrifera. It is confined to sheltered sites inside forests of the dominant kelp (typically Ecklonia maxima), along only ca. 200 km of coastline on the cool temperate southern west coast. It is absent from most of the Benguela upwelling system further north on the west coast and also from the adjacent warm temperate conditions to the east. This “angustifolia” ecomorph in South Africa generally only grows to 2–3 (maximum 10) m in upright length and has much higher upright density than in global regions where the large “pyrifera” ecomorph is dominant. A series of controlled thermal stress experiments was also carried out to investigate the upper limit of thermal tolerance of photosynthesis of South African M. pyrifera, in comparison with the locally dominant kelp E. maxima. Thermal stress experiments found mean oxygen production by M. pyrifera to be greatest at 15 °C, but declining above 17.5 °C. In comparison, mean oxygen production by E. maxima was greatest at 17.5 °C, but was significantly reduced at 22.5 °C. It is likely that temperature tolerance determines the eastward limit of the species in South Africa, but other factors, probably including high wave action, limit its north-westerly spread. These findings highlight the potential vulnerability of the species in South Africa to documented anomalous warming events such as marine heat waves.

Spatial Abundance and Colour Morphotype Densities of the Rock-Boring Sea Urchin (Echinometra lucunter) at Two Different Habitats

The rock-boring sea urchin Echinometra lucunter is a common echinoderm found throughout the intertidal zone along the northeastern coast of, Toco, Trinidad. Sea urchin abundance, size distribution, and colour morphotypes at two sites: Pequelle Bay (SB) and Grande L’Anse (GA) were quantified using 1 m2 quadrats, accessible during extreme low tides, and in two environments, notably low and high wave action. Percent coverage of cnidarian and macroalgae were estimated in each quadrat. Sea urchin densities were 9.9–17.8 urchins/m2 in high wave action, and 25.2–60.7 urchins/m2 in low wave action environments. Size (measured as maximum sea urchin diameter) are highest between 21 and 50 mm for both black and red colour morphotypes. Black colour morphs were significantly larger than red morphs (ANOVA, F2, 175 = 5.55, p < 0.05). Sea urchins at low energy environments were significantly larger than those found in high energy environments for all years (p < 0.05). Mean hard coral, soft coral, and macroalgae cover did not show any relationship with habitat type or urchin densities. Although sea urchin abundance and distribution were variable, larger urchins were more likely to be found in low wave action environments, and smaller urchins were mostly found in the open, and exposed to high wave action.

Assessment Assessment of benthic and coral community structure in an inshore reef in Balok, Pahang, Malaysia

Abstract. Hanapiah MFM, Saad S, Ahmad Z, Yusof MH, Khodzori MFA. Assessment of benthic and coral community structure in an inshore reef in Balok, Pahang, Malaysia. Biodiversitas 20: 872-877. Inshore water reef closer to human activities are often neglected since they are not protected by marine park management. Little is known on how this reef responses to challenging environment in terms of abundance, diversity and benthic community composition. This study provides a quantitative assessment on the benthic community composition at 5 reef sites in Balok, Pahang, Malaysia and observed the ecological adaptation in the reef community towards turbid water environment. Balok reef has 39% overall coral cover with very low macroalgae abundance (4%). A total of 28 coral genera from 12 families have been recorded with Porites the most dominant genus in the coral assemblages. Most reef sites in Balok are categorized under conservation class 1 (CC1), which indicated that resilient and survival of the reef rely on stress-tolerators taxa. The data presented here showed that Balok reef is highly resilient towards constant exposure to high sedimentation and wave action.

Variations in the density of two ectoparasitic gastropods (Coralliophila spp.) on scleractinian corals on a coast-reef scale

Ectoparasitic gastropods living and feeding on coral hosts are now being reported as ubiquitous elements of coral reef environments. While there have been several reports of the damage being caused by these gastropods in the Asia-Pacific region, detailed information on ectoparasitic gastropods from the Western Indian Ocean region is scarce. Small islands such as Mauritius are largely dependent on coral reefs for tourism and protection of the coastal zone against natural disasters and high wave action, thereby highlighting the need to conserve and manage coral reefs sustainably. This requires an assessment of potential threats, including ectoparasitic gastropods, to coral reefs. In an effort to enhance our knowledge on ectoparasitic gastropods from the Western Indian Ocean region, the present study investigates variations in the density of ectoparasitic gastropod species feeding on coral hosts at three zones, namely the coast, lagoon and reef flat during summer and winter in 2016 and 2017 at Flic en Flac, west coast of Mauritius. Fifteen random quadrats were surveyed at each zone and ectoparasitic gastropod density was expressed as the number of individuals m−2. Three line intercept transects of 30 m each were surveyed at each zone to determine the percentage coral cover in October 2016. Two ectoparasitic gastropod species, Coralliophila erosa and C. radula, identified both morphologically and genetically, were found to be associated only with Acropora muricata and Porites lutea, respectively. Distribution of the coral host along the coast-reef scale seemed to affect the densities of the gastropods. No C. erosa was recorded on the reef flat where the percentage cover of branching coral was lowest (54.67 ± 2.40%). Similarly, no C. radula was observed at the coast where the percentage cover of massive coral was as low as 5.00 ± 2.08%. The density of both ectoparasitic gastropods differed significantly among the zones and between the years (Kruskal-Wallis, p 0.05). This study constitutes the first report on the variations in the density of ectoparasitic gastropods on a coast-reef scale at a tropical site in Mauritius and may have implications for coral reefs conservation and management.

Wave–beach sediment interaction with shoreline changes along a headland bounded pocket beach, West coast of India

Grain size analysis was carried out to understand the behavior of sediment distribution in a pocket beach and to examine the relationship between the sediment distribution on surficial beach sediments with the wave energy and shoreline changes. Three seasons surficial beach sediment were sampled, and statistical characteristics were analyzed for September 2014, February 2015, and July 2015. The Mike-21 spectral wave model was utilized to estimate the wave energy distribution and shoreline changes were also mapped using Resourcesat-2 (LISS IV) satellite images and net shoreline movement method was adopted for shoreline change analysis. Because, shoreline changes directly indicate the erosion and accretion pattern of coastal zones. The analyzed sediment statistical parameters were correlated with the wave energy and shoreline changes. Based on the correlation, it was found that wave determines the sediment distribution pattern on Vengurla sandy beach. The result suggests that the beach sediment was mostly medium sand with moderately well sorted, fine skewed to coarse skewed with platykurtic, mesokurtic, and leptokurtic characteristics. The study area was under influenced medium wave to high wave action. The backshore samples have an average skewness of 0.030 Φ, which suggests depositional settings, whereas the bermline and foreshore have an average skewness of − 0.392 and −0.075 Φ, respectively, illustrating the erosional conditions. The sediment categorization results indicated that the backshore is stable, while the bermline is partly eroded as well as accreting in nature. The results show that the wave energy is playing a vital role in sediment distribution and transportation.

Laboratory Study on Cross Shore Sediment Budget over Submerged Breakwaters

The objective of this study is to understand the characteristics of the cross-shore sediment transport over the submerged breakwater through quantitative observations of wave breaking, undertow, and the characteristics of near bottom velocity profiles such as skewness, asymmetry around the permeable or impermeable submerged breakwaters. A series of laboratory experiments were conducted in a 2D wave flume with uniformly sloping 1/20 movable bed of uniform sand grains (D50 =0.15 mm). Either permeable or impermeable breakwaters was installed and four regular incident wave conditions were selected so that generated waves cover both daily or stormy wave conditions. Boundary detection technique was used to obtain the temporal and spatial variation of bed profile and then to calculate cross shore sediment transport rate, CTR, from the images captured by multiple high speed and normal video cameras. Tracer particles were used in the experiment and PIV was applied to capture the velocity field around the submerged breakwater. The experimental results indicate that the impermeable breakwater is generally more effective than the permeable breakwater in terms of the reduction of the seaward CTR over the submerged breakwater but the amount of CTR was very sensitive to the breaking point especially in the case of impermeable breakwater. Increase in acceleration skewness caused low CTR in impermeable breakwater case even with a relatively high wave action on the lee of the breakwater.

Are Sri Lankan Reefs Losing the Resilience? An Example from Coral Reefs in Sallitive Island

Coral reefs are known to undergo phase shift in to macro-algae and reefs have lost the capacity to remain in or return to a coral-dominated state. This shift will not only affect corals, but the others heavily depend on heterogeneous habitat afforded by corals. Sallitivu in Panichchankerni, Eastern province, is a small island (41328 m2). The Island is surrounded by a ring of coral reef with an elevated breaking reef crest, seaward slope and centred shallow lagoon (&lt;1.2m at high tide). The shore is entirely a thick layer of washed coral rubbles. The archived aerial photographs confirmed these coral rubbles present only after 2004 tsunami.Underwater visual census were carried out within the reef lagoon and three sites in reef slope using 30 m long belt transect. In addition to diversity of corals and algae, percentages of live, dead and bleached coral cover were recorded. The reef lagoon is shallow (10-60 cm) and much of the reef crest is exposed at low tide. Within the reef lagoon, the live coral cover was &lt;5%. Around 15% was observed recently bleached, 12% were overgrown by algae; Padina sp, Halimeda sp, Sargassum sp, Caulerpa recemosa and Dictyota sp, and the rest was dead corals smothered by sediments. The seaward slope with high wave action was mostly smothered dead corals with live corals &lt;3%. Coral colonies were represented by Acroporidae (branching and table corals)-Acropora cytherea, A. divaricata, A. formosa, A. gemmifera, A. grandis, A. hemprichii, A. hyacinthus, A. latistella, Acropora sp., A. nobilis, and A. robusta; (Foliaceous)-Montipora aequituberculata and M. hispida; Faviidae (sub massive and encrusting)-Favites halicora, Favites spinosa, Leptastrea purpurea and Platygyra daedalea; Pocilloporidae (Lace/cauliflower) -Pocillopora damicornis; Poritidae (Massive/submassive)-Porites evermanni, P. paliformis, and P. rus. Live corals observed were immature. Southern end of the reef slope had emerging corals among unstable coral rubbles. It is assumed that the degradation was started post-tsunami and continued due to natural stresses. The recovery of corals may hindered by macro-algal growth and resulting accumulation of sediments, smothering due to less wave action within reef lagoon and resulting recruitment and settlement failure. Recent bleaching would be due to exposure to direct sunlight during the change of tides and low sea level. Increasing oxygen level due to algal blooms would also prone for bleaching. Avoiding such undesirable phase shifts from coral dominance to algae and reverse them when occur, requires an urgent reform of scientific approaches to understand the processes causing the degradation. A better understanding on why some reefs rapidly degrade and others do not is critical. Most reef conservation efforts are directed toward reserve implementation, but new approaches are needed to sustain ecosystem function since demarcation of a marine reserve alone would not benefit in improving reef resilience.Keywords: Phase-shift, Coral reefs, Macro-algae, Bleaching, Sallitive Island

Relocation of soft mud deposits: An example from the Archipelago Sea, northern Baltic Sea

Active sedimentation is one of the distinguishing characteristics of the Baltic Sea. This has led to the formation of fractally-distributed soft sediment deposits (muds) that can be up to several meters thick. In this study we examined, for the first time, stability of soft sediment deposits within a 3km2-sized sedimentary basin in the northern Baltic Sea (Eastern Archipelago Sea, Finland) using acoustic profiling (28kHz and 3.5kHz) and 200kHz multibeam surveys, on three occasions from 2011 to 2013. Sub-bottom profile data and rasterized deposit thickness data revealed maximal annual thickness changes between −1.1m erosion or +1.1m deposition along primary survey lines, and skimming of up to 9% of the soft deposit area. The most notable finding was the significant instability of mud. When examined at local scale there was substantial and very localized erosion and deposition (apparent horizontal movement of unconsolidated mud 250–400m per year) between 2012 and 2013. Maximum relocation of unconsolidated deposits was approximately 0.3km3a−1 with 94% export to the exterior area (2011–2012), and was likely affected by abnormally high wave action in the northern Baltic Sea during the period of observation. The combination of acoustic and mathematical techniques is shown to be highly suited to examination of temporal variations in sub-bottom level environments.

Atmospheric depression-mediated water temperature changes affect the vertical movement of chum salmon Oncorhynchus keta

The Sanriku coastal area, Japan, is one of the southern-most natural spawning regions of chum salmon Oncorhynchus keta. Here, we report their behavioral response to changes in ambient temperature after the passage of an atmospheric depression during the early spawning season. Before the passage, all electrically tagged fish moved vertically for several hours to depths below the shallow thermocline at >100 m. However, during the atmospheric depression, the salmon shortened the duration of their vertical movements and spent most time at the surface. The water column was homogenous at <150 m deep except for the surface. The descending behavior may have been discontinued because the cooler water below the thermocline was no longer in a thermally defined layer, due to strong vertical mixing by high wave action. Instead, they likely spent time within the cooler water temperatures at the surface of bays to minimize metabolic energy cost during migration.

First report of the microgastropod Ammonicera japonica (Omalogyridae Habe, 1972) in Korea

The intertidal zone of Jeju Island, Korea, is characterized by well-developed volcanic rocks with high wave action. During low tide, numerous small tidal pools are formed on the rocky intertidal zone, which provide shelter and habitats for benthic organisms. Previous investigation indicated that many species of micromolluscans inhabit the tidal pools; however, only a few studies have reported the ecology and identification of these microshells. In this study, we have identified a microgastropod, Ammonicera japonica Habe, 1972 (Omalogyridae), from a tidal pool on the southern coast of Jeju Island. Morphological identification of the species was based on scanning electron microscopy (SEM) of the protoconch and teleoconch. A. japonica was found to be associated with encrusting coralline algae distributed on the bottom of the tidal pools. This is the first report of A. japonica from Korea, and the specimen was registered at the National Marine Biodiversity Institute of Korea (MABIK MO00157413).

Species specific effects of three morphologically different belowground seagrasses on sediment properties

Roots and rhizomes of seagrass play an important role in coastline zone by anchoring the substrate firmly which prevent resuspension and also controlling sediment biogeochemistry. The aim of this study was to compare the physical and chemical differences of sediments for 3 seagrass species, which have different root morphology between summer (February 2013) and the monsoon month (September 2013). Seven seagrass communities were studied and are: the mono stand of Halophila ovalis, Thalassia hemprichii, and Cymodocea rotundata, the mixed patches of H. ovalis with T. hemprichii, H. ovalis with C. rotundata, and T. hemprichii with C. rotundata and the mixed patches of 3 seagrass species. The roots of seagrasses were the main driver of differences in sediment properties; the branched, long root species, C. rotundata, showed an increasing redox potential by means of oxygen releasing from their roots. The unbranched, long root with dense root hair species, T. hemprichii, tended to cause more poorly sorted sediments. The carbon storage was also estimated and results showed a trend of higher organic carbon density was in the multispecific patches, the mono specific patches and bare sand, respectively. Season also influenced the sediment properties; high wave action in the monsoon stirred up the sediments, this led to lower organic carbon density and high redox potential. Our results suggest that the roots of seagrass species both increase and decrease sediment properties.

Fabrication of flexible blade models from a silicone-based polymer to test the effect of surface corrugations on drag and blade motion

Macrocystis blades develop longitudinal corrugations in regions with strong current and wave action. This study examined the effect of corrugations on blade motion and blade drag by constructing flexible blades with different corrugation amplitude and a control blade with no corrugation. The models were designed to be dynamically and geometrically similar to natural blades. Acrylic molds were etched using a laser cutter and filled with a silicone-based polymer to create flexible model blades with sinusoidal corrugations. The corrugated and flat model blades were tested in a water channel using drag force measurements and video analysis. The corrugated blades experienced a drag per surface area reduction of up to 60% compared to the flat blade. Additionally, the corrugated models exhibited smaller motion, as quantified by the maximum vertical displacement. The reduction in drag may explain why corrugations are observed in exposed regions of high current and wave action, where a reduction in drag provides important protection against breakage.

Estimating relative risk of within-lake aquatic plant invasion using combined measures of recreational boater movement and habitat suitability.

Effective monitoring, prevention and impact mitigation of nonindigenous aquatic species relies upon the ability to predict dispersal pathways and receiving habitats with the greatest risk of establishment. To examine mechanisms affecting species establishment within a large lake, we combined observations of recreational boater movements with empirical measurements of habitat suitability represented by nearshore wave energy to assess the relative risk of Eurasian watermilfoil (Myriophyllum spicatum) establishment. The model was evaluated using information from a 17 year (1995–2012) sequence of M. spicatum presence and absence monitoring. M. spicatum presence was not specifically correlated with recreational boater movements; however its establishment appears to be limited by wave action in Lake Tahoe. Of the sites in the “High” establishment risk category (n = 37), 54% had current or historical infestations, which included 8 of the 10 sites with the highest relative risk. Of the 11 sites in the “Medium” establishment risk category, 5 had current or historical M. spicatum populations. Most (76%) of the sites in the “Low” establishment risk category were observed in locations with higher wave action. Four sites that received zero boater visits from infested locations were occupied by M. spicatum. This suggests that the boater survey either represents incomplete coverage of boater movement, or other processes, such as the movement of propagules by surface currents or introductions from external sources are important to the establishment of this species. This study showed the combination of habitat specific and dispersal data in a relative risk framework can potentially reduce uncertainty in estimates of invasion risk.