High Wave Exposure Research Articles

Wave exposure influences kelp morphological and biomechanical phenotypic plasticity

Despite global and local declines in kelp ecosystems, luxuriant kelp beds persist at the Eastern Shore Islands (ESI) in Nova Scotia, Canada. Kelp beds in other regions of Nova Scotia were defoliated as the invasive bryozoan Membranipora membranacea and warming temperatures weakened kelp tissues and enhanced erosion and dislodgment. We propose that the high wave exposure at the ESI causes morphological and biomechanical phenotypic plasticity of kelp tissues. We compared differences in morphology and mechanical properties of the kelps Laminaria digitata and Saccharina latissima across 3 sites with different wave exposures, and differences in mechanical properties across blade lengths. Both species showed morphological plasticity; higher wave exposure resulted in longer and thicker stipes and thicker blades with increased branching. The mechanical properties of L. digitata showed increased breaking stress (strength) and strain (extensibility) with higher wave exposure, whereas S. latissima did not show mechanical plasticity with increasing exposure. For both species, blades were weaker but more extensible at the meristem and stronger but less extensible near the distal end of the blade. Larger and stronger kelp from high-exposure areas may promote the persistence of kelp beds in the ESI despite local stressors.

Effects of wave exposure and habitat fragmentation on growth and grazing of rocky shore seaweeds: a mesocosm experiment

Seaweeds are foundation species on rocky shores that are exposed to a series of stressors. These include wave exposure, desiccation, grazing, and human activities, with habitat fragmentation as a common result. As part of climate and biodiversity changes, we are expecting increased winds and more frequent storm events, warmer climate, and trophic downgrading of ecosystems, causing overgrazing events. Here, we present the results from a two-factorial mesocosm experiment on the relationship between wave exposure, habitat fragmentation and growth (branching and tip elongation) of Fucus vesiculosus in the intertidal and upper subtidal. We found that intertidal seaweeds branched significantly more at low than high wave exposure. There was no effect of habitat fragmentation on branching, and no effects on tip growth from either wave exposure or habitat fragmentation. The experiment suffered greatly from uncontrolled grazing. Gastropod coverage was higher inside seaweed patches than in the seaweed free areas between and outside of the patches. In basins with highly fragmented seaweed patches, we found more gastropods at low than high wave exposure, whereas in basins with low fragmentation we found more gastropods at higher wave exposure. The percent coverage of gastropods in the basins did not seem to impact seaweed growth.

Invertebrate Responses to Large- and Small-Scale Drivers in Coastal Phragmites australis Beds in the Northern Baltic Sea

Phragmites australis is a common helophyte, covering much of the sheltered and shallow soft bottoms along the coasts of the Baltic Sea. Despite the expansion of P. australis over the past decades, there is little information on aquatic macroinvertebrates within P. australis beds. In this study, we examined the effect of large-scale (wave exposure, nutrients) and small-scale (distance from the seaward edge, live and dead stalk density, epiphyte and rhizome biomass) drivers on the density, taxa richness, diversity, and community structure of epifauna and infauna in monospecific P. australis beds around the Åland Islands and the Archipelago Sea. We found that higher wave exposure and nutrient levels generally supported higher epi- and infauna abundance and taxa richness. The effects on Shannon–Wiener diversity were less evident apart from an increase of the infauna diversity in the Archipelago Sea with increasing nutrient levels. On a local scale, the distance from the seaward edge, live and dead stalk density, and epiphyte biomass had varying effects on both epi- and infauna communities in the different regions. Rhizome biomass had no effect on either the epi- or infauna abundance, taxa richness, or diversity. Furthermore, according to existing studies, other habitats, e.g., Zostera marina meadows, Fucus vesiculosus belts, and vegetated soft-bottomed shallow bays, are generally characterized by more abundant fauna, except for the infauna, which had a higher density in P. australis beds than in vegetated soft-bottomed shallow bays. P. australis are a widespread, expanding, and understudied habitat with an important role in supporting coastal biodiversity.

Wrack line formation and composition on shores of a large Alpine lake: The role of littoral topography and wave exposure.

Wrack lines are a key formation along shorelines that provide organic matter and bring ecological diversity to the local environment. Although wrack line formation has been extensively studied along marine beaches and estuaries, in contrast, knowledge about the environmental variables that promote wrack line formation within inland lakes is widely lacking. In one of the first studies to focus on wrack line formation on lakesides, we analysed the dimensions, volume, elevation and particulate composition of 36 wrack lines across 20 shore sections of a large, oligotrophic Alpine lake with natural water level fluctuations (Lake Constance-Obersee). Using multivariate partial least squares (PLS) regression, we identified the key environmental variables that drive wrack accumulation in lakeside areas. Our results demonstrate that wrack line volume increased with (1) the width of the eulittoral zone as an indicator of the swash conditions (up-rush vs. down-wash), (2) high exposure to wind waves as indicated by the total effective fetch, (3) high exposure to ship waves (catamaran ferry), and (4) the width of the sublittoral zone as an indicator of the availability of source material (Chara spp.) and of the wave energy dissipation rate of the incoming deep water waves. Sediment texture played only a minor role. Wide eulittoral zones and high ship wave exposure favoured high proportions of lake-borne components (Chara remains, mollusc shells), while the reverse was true for land-based components. Anthropogenic wastes were only present in small proportions. We discuss four main factor groups influencing the amount of wrack in marine beaches and on lakeshores considering similarities (waves, breakers, swash, dissipation, relief) and differences (tides vs. annual water level fluctuations) of the two systems, and point out research gaps. We demonstrate that wrack line formation is also important in large inland lakes and can be analysed using basic ideas from relevant marine studies.

Conservation and management of olive ridley sea turtles and their nesting habitat: A study at Rushikulya rookery, Odisha, east coast of India

Odisha coast, along the east coast of India, has the world's largest mass nesting sites (rookeries) for olive ridley (Lepidochelys olivacea) sea turtles. It has three rookeries namely Gahirmatha, Devi and Rushikulya. Olive ridley sea turtles and their habitat along the Odisha coast often face natural and anthropogenic threats leading to failure of mass nesting (arribada) and a population decline. The focus of the present study is to understand the coastal processes near the Rushikulya rookery, assess the impacts of natural and anthropogenic threats to the nesting population and their habitat, and suggest a management plan for the conservation of sea turtles and their habitat. Coastal processes and the associated geomorphological changes, shoreline change, and cyclonic disturbances at the Rushikulya rookery from 2008 to 2019 were studied. It is revealed that the natural threats for arribada are cyclonic storms, high wave exposure, and sand spit growth leading to erosion of the nesting habitat and debris accumulation. Coastal processes, such as east-southeast to south-southeast waves with moderate wave height, lunar semidiurnal tide, moderate southwest current, and predominantly southerly and easterly winds with moderate speed, are identified as favourable conditions for the sea turtles prior to and during an arribada. The study reveals that nesting on the sand spit is vulnerable because of frequent wave exposure and washout, while the beach to the north of the estuary is the most preferred and safe habitat for arribada. Coastal development, incidental capture, entanglement in gill nets, fisheries bycatch and illegal take are revealed as the major anthropogenic threats. Based on natural and anthropogenic threats, the local knowledge of the fishermen and the status of legislation, the study suggests an integrated regional management plan for the conservation of olive ridley sea turtles and their nesting habitat.

How does invasive Spartina densiflora respond to contrasting environmental conditions in its native region?

Coastal salt marshes are recognized worldwide as diverse and productive environments, providers of many ecosystem services, and as places where a wide variety of taxa live, nest, nurse, and/or feed. Along the Atlantic coast of South America, the austral cordgrass Spartina densiflora displays great phenotypic variations that may favor it to thrive on a wide range of substrates, inhabiting not only the typical soft bottom marshes, but also on cobble beaches and rocky shores. These Patagonian rocky salt marshes, unlike other salt marshes, develop predominantly on top of wave-cut platforms made of sedimentary rock, highly exposed to wave action, and with a dwarf Patagonian phenotype of S. densiflora commonly dominating the vegetation. In this work we evaluate experimentally the hypothesis that this phenotype is a plastic response that maximizes the survival of S. densiflora on rocky bottom environments exposed to wave action. Our results strongly suggest that the austral cordgrass S. densiflora is able to adjust its morphological characteristics in relation to contrasting environmental changes, allowing it to survive in a broad spectrum of coastal environments, including rocky shores with little accumulation of mud and high wave exposure. The typical plants transplanted from the muddy marsh to the rocky marsh exhibited lower height (80%) than the typical control in muddy marsh and than the Patagonian plants in rocky marsh (38%), additionally the typical transplants in the rocky marsh showed no visible damage to their leaves or stems. Our research provides new evidence to understand the success of this species across non-native regions worldwide where it is considered an aggressive invasive bioengineer.

Macroalgal cover on coral reefs: Spatial and environmental predictors, and decadal trends in the Great Barrier Reef.

Macroalgae are an important component of coral reef ecosystems. We identified spatial patterns, environmental drivers and long-term trends of total cover of upright fleshy and calcareous coral reef inhabiting macroalgae in the Great Barrier Reef. The spatial study comprised of one-off surveys of 1257 sites (latitude 11-24°S, coastal to offshore, 0-18 m depth), while the temporal trends analysis was based on 26 years of long-term monitoring data from 93 reefs. Environmental predictors were obtained from in situ data and from the coupled hydrodynamic-biochemical model eReefs. Macroalgae dominated the benthos (≥50% cover) on at least one site of 40.4% of surveyed inshore reefs. Spatially, macroalgal cover increased steeply towards the coast, with latitude away from the equator, and towards shallow (≤3 m) depth. Environmental conditions associated with macroalgal dominance were: high tidal range, wave exposure and irradiance, and low aragonite saturation state, Secchi depth, total alkalinity and temperature. Evidence of space competition between macroalgal cover and hard coral cover was restricted to shallow inshore sites. Temporally, macroalgal cover on inshore and mid-shelf reefs showed some fluctuations, but unlike hard corals they showed no systematic trends. Our extensive empirical data may serve to parameterize ecosystem models, and to refine reef condition indices based on macroalgal data for Pacific coral reefs.

Wave exposure affects the persistence of kelp beds amidst outbreaks of the invasive bryozoan Membranipora membranacea

In certain regions of the northwest Atlantic, rocky subtidal habitats have transitioned from luxuriant kelp beds to turf dominated ecosystems. Encrustation by the invasive epiphytic bryozoan Membranipora membranacea has accelerated the defoliation of macroalgal stands, particularly on the southwestern shore (SWS) of Nova Scotia. In contrast, at the Eastern Shore Islands (ESI) in Nova Scotia, a temperate island archipelago with relatively high wave exposure, kelp beds persist. We investigated how spatial and temporal dynamics of the dominant kelps (Saccharina latissima and Laminaria digitata) and M. membranacea relate to wave exposure. We examined canopy cover and density of kelps using video transects and quadrat sampling at 6 sites of different wave exposures at ESI and a highly wave exposed site on the SWS (Shag Rock), where kelp also persists, in summer and autumn 2018-2020. We measured percent cover of adult colonies of M. membranacea on kelps from autumn 2018 to autumn 2020, and density of settlers in 2019. Colony cover of M. membranacea was comparable across the range of wave exposures at ESI, whereas settler density peaked at intermediate wave exposure. Despite annual outbreaks of the bryozoan, kelp beds at ESI persisted over multiple years, in contrast to a declining trend at Shag Rock. Overwinter recovery of kelps at ESI following bryozoan-induced seasonal declines the preceding autumn indicate that, in contrast to sites on the SWS, these colder more wave exposed kelp beds may be resilient to defoliation.

Patch dynamics driven by wave exposure in subtidal temperate seaweeds are exacerbated by warming oceans

Over the past decades, ocean temperatures have been steadily increasing and are projected to continue to do so, stressing many temperate marine organisms. Changing temperatures do not affect ecosystems in isolation, but interact with many other factors in shaping ecological communities. We investigated the changes over 2 decades in subtidal temperate seaweed communities over a wave exposure gradient in Western Australia, a global warming hotspot. We found higher diversity in the seaweed community and a higher proportion of biomass of species with a warm affinity (expressed as the tropicalization index: TI) over time. There was no decline in biomass of the dominant habitat-forming kelp Ecklonia radiata on low wave exposure reefs, while it was patchier and comprised a lower proportion of the total seaweed biomass on the medium and high wave exposure reefs. Furthermore, the presence of E. radiata was disproportionally associated with low abundances of seaweeds with warm affinity. The increasing patchiness of E. radiata likely provided a competitive release for other seaweeds, and the increase in abundance of Scytothalia dorycarpa likely provided a compensatory effect which resulted in a lower than expected TI. We found no indication of an ameliorating effect by wave exposure, and conclude that the patch dynamics driven by wave exposure are more likely exacerbated by increasing ocean temperatures on subtidal temperate reefs. If this continues, the reduction in E. radiata and increase in warm affiliated seaweeds will result in a more diverse seaweed community, but one with a lower standing biomass.

Exposure of Loggerhead Sea Turtle Nests to Waves in the Florida Panhandle

Wave wash-over poses a significant threat to sea turtle nests, with sustained exposure to waves potentially resulting in embryonic mortality and altered hatchling locomotor function, size, and sex ratios. Identifying where and under what conditions wave exposure becomes a problem, and deciding what action(s) to take (if any), is a common issue for sea turtle managers. To determine the exposure of sea turtle nests to waves and identify potential impacts to hatchling productivity, we integrated a geographic information system with remote sensing and wave runup modeling across 40 nesting beaches used by the Northern Gulf of Mexico Loggerhead Recovery Unit. Our models indicate that, on average, approximately 50% of the available beach area and 34% of nesting locations per nesting beach face a significant risk of wave exposure, particularly during tropical storms. Field data from beaches in the Florida Panhandle show that 42.3% of all nest locations reported wave exposure, which resulted in a 45% and 46% decline in hatching and emergence success, respectively, relative to their undisturbed counterparts. Historical nesting frequency at each beach and modeled exposure to waves were considered to identify priority locations with high nesting density which either experience low risk of wave exposure, as these are good candidates for protection as refugia for sustained hatchling production, or which have high wave exposure where efforts to reduce impacts are most warranted. Nine beaches in the eastern Florida Panhandle were identified as priority sites for future efforts such as habitat protection or research and development of management strategies. This modeling exercise offers a flexible approach for a threat assessment integration into research and management questions relevant to sea turtle conservation, as well as for other beach species and human uses of the coastal environment.

Coastal processes and nearshore hydrodynamics under high contrast wave exposure, Bateau-cassé and Stamboul coasts, Algiers Bay

The coastal dynamics along the sandy beaches in the Algiers bay is strongly influenced by the hydrodynamic agents, morphological factors, human activities, societal infrastructure and presence of hard structures, which disrupts their hydro-sedimentary balance. The present work contributes to the knowledge of hydrodynamic and morpho-sedimentary forcing mechanisms at sandy beaches by focusing on the impact of extreme sea-weather events of the two most contrasting periods of the year (winter and summer) on coastal processes. Two beaches in the eastern part of Algiers bay were studied by combining field measurements of currents and sediment flux with numerical models (MIKE 21/3 Coupled Model FM). The model validation was done based on the measured nearshore current and sediment transport during low to moderate energy swell conditions with current meter ‘Global water Fp101’ and ‘Krauss sediment traps’. Time series of wind and wave established by Infoplaza Marine weather database were used as input at the open boundaries of the model domain. The results showed a reversal of the dominant direction of the longshore currents, and a very high prevalence of cross-shore sediment transport over longshore sediment transport (LST) due to the coarse grain size of the sediment (very coarse sand). The results indicated that, waves coming from the west prevail in winter have an average wave height varies from 1.5 to 2.1 m, driven a longshore current of 0.17–0.27 m/s, with an estimated seasonal cross-shore sediment transport between 1530 and 5540 m3/year/m. During the summer season, waves approaching from the northeast dominate with an average of Hs that does not exceed 1 m, these waves generate a rip current equal to 0.24 m/s and this current can generate a cross-shore sediment flux in the order of 4000 m3/year/m. The results also reveal the development of morphological landforms represented in the submerged longshore bars at the shallow water depending largely on the hydrodynamic conditions and the cross-shore flux between the land/sea interfaces.

Population Characteristics of the Mid-Littoral Chthamalid Barnacle C. stellatus (Poli, 1791) in Eastern Mediterranean (Central Greece)

Barnacles are key space-occupiers in rocky shore communities on European coasts. Barnacles of the species Chthamalus stellatus (Poli, 1791) were collected between June 2014 and May 2015 from two sites, two stations per each site with varying degree of exposure to wave action and anthropogenic pressure (trampling), in the Eastern Mediterranean (Pagasitikos Gulf, Central Greece). This study addresses a knowledge gap in population characteristics of C. stellatus populations in the Eastern Mediterranean, assessing population structure and allometric relationships. Patterns of distribution and abundance (density and percentage cover) were studied both temporally (seasonally) and spatially (water level and site). Morphometric characteristics exhibited spatiotemporal variation. Population density was significantly higher at the site with higher wave exposure. The population cover exhibited high levels of similarity among shore levels, both spatially and temporally. Spatial distribution exhibited a clumped pattern of dispersion in autumn, winter, and spring, mainly in the sheltered site. Six dominant age groups were identified, with the dominant cohort in the third-year class. Significant negative allometric relationships were exhibited between all morphometric characteristics. Differences in growth patterns among populations were indicated, with a higher rate of growth at the site of lower wave exposure.

Relative roles of biological and physical processes influencing coral recruitment during the lag phase of reef community recovery

Following disturbances, corals recolonize space through the process of recruitment consisting of the three phases of propagule supply, settlement, and post-settlement survival. Yet, each phase is influenced by biophysical factors, leading to recruitment success variability through space. To resolve the relative contributions of biophysical factors on coral recruitment, the recovery of a 150 km long coral reefs in Palau was investigated after severe typhoon disturbances. Overall, we found that benthic organisms had a relatively weak interactive influence on larval settlement rates at the scale of individual tiles, with negative effects mainly exerted from high wave exposure for Acropora corals. In contrast, juvenile coral densities were well predicted by biophysical drivers, through both direct and indirect pathways. High densities of Acropora and Poritidae juveniles were directly explained by the availability of substrata free from space competitors. Juvenile Montipora were found in higher densities where coralline algae coverage was high, which occurred at reefs with high wave exposure, while high densities of juvenile Pocilloporidae occurred on structurally complex reefs with high biomass of bioeroder fish. Our findings demonstrate that strengths of biophysical interactions were taxon-specific and had cascading effects on coral recruitment, which need consideration for predicting reef recovery and conservation strategies.

The Relative Role of Mangroves on Wave Erosion Mitigation and Sediment Properties

Fringe mangroves face waves daily and are thought to protect against erosion in low wave energy sites and undergo erosion if exposed to high wave energy. We aimed to understand the effects of fringe mangroves on erosion and sediment dynamics and of wave exposure on seedling density at three sites of increasing wave energy. Sediment properties (mean grain size, sorting, and bulk density) were assessed within each site in unvegetated and mangrove-vegetated shores in wet and dry seasons. In addition, we estimated seasonal erosion/accretion rates for 2.4 years and seedling density in two zones from the forest edge with contrasting wave exposure. Regression analysis was carried out to explain sediment properties and erosion rate variance in response to the vegetation volume that opposes wave energy and to explain erosion rates in response to wave energy. Mangrove-vegetated shores reduced erosion rates from 3 to 15 times in the two sites with higher wave energy, while the vegetated site with the lowest wave energy experienced accretion compared to minor erosion along the unvegetated shore. Shores with greater Rhizophora mangle basal areas and vegetation volumes favored deposition of particles with low settling rates, different sediment classes, reduced erosion rates, and increased shoreline stability. Mangrove seedling density decreased between 2 and 43 times from the low wave exposure zone to the high wave exposure zone at the forest edge in studied sites. In order to increase vegetation volume, coastal adaptation based on mangroves must limit human disturbances and facilitate epiphytic relationships with oysters.

Exposure to Heat Wave During Pregnancy and Adverse Birth Outcomes: An Exploration of Susceptible Windows.

Several studies have investigated the acute effects of high ambient temperature or extreme weather on preterm birth and stillbirth. However, little was known about whether there are any particular stages during which high ambient temperature or heat wave exposure is most harmful to fetal growth. The aim of this study was to examine the effects of heat wave exposure in different gestational months on the risk of preterm birth and stillbirth. Based on all singleton birth records between 2000 and 2010 and the corresponding environmental data in Brisbane, Australia, we explored relationships between heat wave exposure in different months of pregnancy and preterm birth or stillbirth. Six heat wave definitions were used in this study. After controlling for confounding factors, hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using extended Cox proportional hazards regression models with time-dependent covariates. For most heat wave definitions, the adjusted HRs of preterm birth varied by different gestational months and ranged from 1.08 (HR = 1.08; 95% CI = 1.00, 1.18) to 1.53 (HR = 1.53; 95% CI = 1.41, 1.68). Heat wave exposure in early pregnancy was more likely to increase the risk of stillbirth compared with heat wave exposure in late pregnancy. Overall, we found relationships between preterm birth and heat wave exposure in all months of pregnancy based on most heat wave definitions. We did not find a specifically high period of susceptibility during pregnancy for preterm birth associated with heat wave exposure. However, earlier gestational months might be key exposure windows for heat-wave-affected stillbirth.

Sedimentation in a shallow brackish water lagoon influenced by wind-induced waves - A methodical study

In shallow aquatic ecosystems, wave-induced water motions affect the whole water column down to the sediment. To estimate the influence of these motions on short-term sedimentation rates (SR) in a shallow wind-exposed lagoon, we used plate traps (PTs) which, in contrast to cylindrical traps (CTs), allow trapped matter to become resuspended. In a series of experiments, we varied distance to the sediments, water depth, incubation time, and studied the SRs of total suspended matter and of suspended organic matter at varying conditions of wave exposure. The coefficient of variation of SRs did not change with incubation time. While SRs were similar on both trap types at very low wave exposure, they decreased with increasing wave exposure on the PTs probably due to instantaneous resuspension. In the CTs, SRs increased with increasing wave exposure. This resulted in about 55 times higher SRs in the CTs than on the PTs at high wave exposure. We conclude that CTs are not suitable to estimate natural SRs in wave-affected waters as they overestimate SRs. Our results indicate that SR obtained by PTs, which were here used for the first time in a wind-exposed, non-tidal ecosystem, are a far better estimate for natural short-term SRs.

The shape of success in a turbulent world: wave exposure filtering of coral reef herbivory

Summary While environmental filters are well‐known factors influencing community assembly, the extent to which these modify species functions, and entire ecosystem processes, is poorly understood. Focusing on a high‐diversity system, we ask whether environmental filtering has ecosystem‐wide effects beyond community assembly. We characterise a coral reef herbivorous fish community for swimming performance based on ten functional traits derived from fish morphology. We then investigate whether wave exposure modifies the functional make‐up of herbivory, and the absolute and relative feeding frequency of distinct feeding functional groups. Herbivorous fish species conformed to either laterally compressed or fusiform body plans, which differ in their morphological design to minimise drag. High wave exposure selectively limited the feeding function of the deepest body shapes with highest caudal thrust efficiency, and favoured fusiform bodies irrespective of pectoral fin shape. Traditionally recognised herbivore feeding functional groups (i.e. grazers–detritivores and scrapers–small excavators) differed in swimming performance, and in their capacity to feed consistently across levels of wave exposure. We therefore emphasise the distinctness of their ecological niche and functional complementarity. Species within the same feeding functional group also had contrasting responses to wave exposure. We thereby reveal a further ecological dimension of niche partitioning, and reiterate the risk of assuming functional redundancy among species with a common feeding mode. Contrasting responses of species within feeding functional roles (i.e. response diversity) allowed the preservation of critical trophic functions throughout the gradient (e.g. macroalgal browsing), and likely explained why overall levels of herbivory were robust to filtering. Whether ecosystem functioning will remain robust under the additive effects of environmental stress and human‐induced disturbances remains to be tested. A lay summary is available for this article.

Sensitivity of coral recruitment to subtle shifts in early community succession.

Community succession following disturbance depends on positive and negative interactions, the strength of which change along environmental gradients. To investigate how early succession affects coral reef recovery, we conducted an 18-month experiment in Palau, using recruitment tiles and herbivore exclusion cages. One set of reefs has higher wave exposure and had previously undergone a phase shift to macroalgae following a major typhoon, whereas the other set of reefs have lower wave exposure and did not undergo a macroalgal phase shift. Similar successional trajectories were observed at all sites when herbivores were excluded: turf algae dominated early succession, followed by shifts to foliose macroalgae and heterotrophic invertebrates. However, trajectories differed in the presence of herbivores. At low wave exposure reefs, herbivores promoted coralline algae and limited turf and encrusting fleshy algae in crevice microhabitats, facilitating optimal coral recruitment. Under medium wave exposure, relatively higher but still low coverage of turf and encrusting fleshy algae (15-25%) found in crevice microhabitats inhibited coral recruitment, persisting throughout multiple recruitment events. Our results indicate that altered interaction strength in different wave environments following disturbance can drive subtle changes in early succession that cascade to alter secondary succession to coral recruitment and system recovery.

Impacts of water depth and substrate type on Vallisneria natans at wave-exposed and sheltered sites in a eutrophic large lake

Water depth, substrate type and wave exposure are major environmental factors influencing the growth and distribution of submerged macrophytes. However, we lack knowledge on the ecological reactions of submerged macrophytes to those factors during an entire growth period in a eutrophic lake with a Secchi depth of less than 50cm. We investigated the interactive effects of water depth (60, 120 and 200cm), waves (exposed vs. sheltered) and substrate nutrient level (fertile sludge vs. brown clay) on the survival, growth and morphology of Vallisneria natans using a new type of rhizotron in a 252-day field experiment. Plant length, leaf number, ramet number, root length, root number and biomass generally decreased with increased water depth at both wave conditions and in both substrates. When exposed to wave, the biomass of V. natans in water at 200cm depth rapidly declined in both substrates. When sheltered to wave, aboveground biomass at 60cm water depth first declined to zero with many buried rhizomes remained. The tuber germination rate decreased with increasing water depth during the second year of germination. No plants sprouted at 200cm water depth except at the case of exposed wave and sludge substrate. Ramet number was influenced most by water depth, followed by aboveground biomass, leaf number, plant length, and survival rate. Wave shelter and brown clay enhanced the impacting strength of the water depth. Wave exposure exhibited no negative influence on survival percentage, whereas sludge had a positive influence on plant survival in deep water after overwintering. Waves negatively affected the rate of increase of plant growth in sludge but positively in clay. The positive joint effects of wave exposure and low-nutrient substrate were mainly on plant length and biomass. Water depth had a negative influence that predominated over substrate and waves regarding plant survival and growth. Moreover, this negative influence may be aggravated by an increasing risk of submersed macrophyte loss caused by decreased belowground growth under high water levels, high wave exposure and high-nutrient conditions. Decreasing the water depth could be an useful measure for submerged macrophyte restoration in freshwater habitats, even in turbid eutrophic water.

Relationship Between Estuarine Shellfish Fauna and Physical Environmental Characteristics for Estuary Conservation in Kyushu, Japan

The establishment of a conservation strategy or restoration goal for river estuaries requires knowledge of potential biota or possible habitat characteristics. In this study, we investigated the relationship between estuarine fauna and macro scale physical indicators on Kyushu Island, Japan to provide basic information for estuarine conservation. As a result of the classification of shellfish fauna by similarity, the Kyushu region was divided into three groups, namely, 1) southern Kyushu with high wave exposure, long fetch, and low tidal variation; 2) the Ariake and Yatsushiro seas with low wave exposure, short fetch, and high tidal variation; and 3) northern Kyushu with an intermediate fetch and tidal variation. In addition, a number of sites, such as Nakatsu Port, Sone tideland, and the Honmyou River, were classified into geographically different groups. This is because the physical characteristics of these sites were similar to classified groups or shellfish fauna were significantly altered by artificial impacts. As a result of discriminant analysis, the discrimination hit rate of species inhabiting the inner bay or tidal flat was high, whereas that for species using a wide variety of bottom sediment environment was low. To improve the accuracy of the discriminant model, it is necessary to collect more detailed physical information, such as habitat type, salinity concentration, or grain diameter of bottom sediment. To establish a conservation or restoration strategy, there is a need for classifying taxonomic groups or physical characteristics.