Epifaunal invertebrate assemblages associated with branching Pocilloporids in Moorea, French Polynesia

Reef-building corals can harbour high abundances of diverse invertebrate epifauna. Coral characteristics and environmental conditions are important drivers of community structure of coral-associated invertebrates; however, our current understanding of drivers of epifaunal distributions is still unclear. This study tests the relative importance of the physical environment (current flow speed) and host quality (e.g., colony height, surface area, distance between branches, penetration depth among branches, and background partial mortality) in structuring epifaunal communities living within branching Pocillopora colonies on a back reef in Moorea, French Polynesia. A total of 470 individuals belonging to four phyla, 16 families and 39 genera were extracted from 36 Pocillopora spp. colonies. Decapods were the most abundant epifaunal organisms (accounting for 84% of individuals) found living in Pocillopora spp. While coral host characteristics and flow regime are very important, these parameters were not correlated with epifaunal assemblages at the time of the study. Epifaunal assemblages associated with Pocillopora spp. were consistent and minimally affected by differences in host characteristics and flow regime. The consistency in abundance and taxon richness among colonies (regardless of habitat characteristics) highlighted the importance of total habitat availability. With escalating effects of climate change and other localized disturbances, it is critical to preserve branching corals to support epifaunal communities.

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A Numerical Investigation over the Cavitating Flow Regime of a 2D-Hydrofoil

10.5957/fast-2015-041 ◽

2015 ◽

Author(s):

Luca Bonfiglio ◽

Stefano Brizzolora

Keyword(s):

Flow Regime ◽

Leading Edge ◽

Flow Speed ◽

Cavitating Flow ◽

Suction Surface ◽

High Speeds ◽

State Potential ◽

America’S Cup ◽

Sailing Boat ◽

Stable Flow

The advances in sailing boat races have been greatly proven in the recent America’s Cup competition. Sailing boats have reached speeds above 40 knots with a simple concept: the wetted surface of the hull is minimized and the required displacement is obtained through a lifting force produced by submerged hydrofoils working at very high speeds. This is a well-known concept in naval architecture that has been exploited since the beginning of the 20th Century. Hydrofoils used in sailing boat races are yet not designed for cavitating flow, but major changes in the design will be needed in case speed increases above 50 knots. When highspeed crafts (including fast sailing boats) operate significantly above the planing threshold speed, the convenience of completely or partially supporting their weight by lifting hydrofoils is evident (Du Cane (1964)). A very low pressure field induced by high in flow speed triggers water vaporization at ambient temperature: cavitation cannot be avoided and foil shape has to be designed with the goal of maintaining a stable flow regime eventually com-promising the lift. When craft speed arise above 50 knots, the de-sign philosophy for the basic section of the lifting hydrofoil has to radically change and turn to super-cavitating hydrofoils (Auslaender [1962]) being the final goal addressed towards the delay and stabilization of the cavity shape over the hydrofoil surface. In super-cavitating regimes the suction surface of the hydrofoil is fully enveloped in the cavity which (typically) detaches at the leading edge of the foil and closes in the wake well aft the trailing edge. The pressure side of the hydrofoil is the only responsible for lift generation thus the main design target is represented by the shape of the foil surface. Several simplified theories assuming steady state potential flow (mentioned later in this introduction) were developed in the past to deal with this essential design problem.

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Relationships between macrozoobenthos and habitat characteristics in an intensively used area of the Dutch coastal zone

ICES Journal of Marine Science ◽

10.1093/icesjms/fsv060 ◽

2015 ◽

Vol 72 (8) ◽

pp. 2409-2422 ◽

Cited By ~ 8

Author(s):

Maarten F. de Jong ◽

Martin J. Baptist ◽

Han J. Lindeboom ◽

Piet Hoekstra

Keyword(s):

Shear Stress ◽

Species Composition ◽

Coastal Zone ◽

Distribution Patterns ◽

Research Area ◽

Habitat Characteristics ◽

Disposal Site ◽

Bed Shear Stress ◽

Benthic Assemblages ◽

Epifaunal Assemblages

Abstract Distribution patterns and species composition of macrozoobenthos were studied in the Dutch coastal zone in front of the Port of Rotterdam. Relationships between macrozoobenthic assemblages and environmental variables were determined using non-metric dimensional scaling (nMDS) based on 470 boxcore, bottom sledge, and sediment samples collected in spring 2006 and 2008 in a 2500-km2 research area. We investigated two types of benthic assemblages, infaunal assemblages sampled with a boxcorer and epifaunal assemblages sampled with a bottom sledge. Five main in- and epifaunal assemblages were distinguished using clustering techniques and nMDS ordinations. Macrozoobenthic species composition correlated with combinations of measured sediment variables and modelled hydrodynamic variables. Macrozoobenthic species richness and biomass were highest at 20 m deep areas with a grain size of 200 µm, elevated mud and sediment organic matter, and low mean bed shear stress. Considerable interannual differences in macrozoobenthic assemblage distribution were observed which resulted from more Echinoids, Phoronids, and jackknife clams. A distinct, highly productive and species-rich macrozoobenthic white furrow shell Abra alba assemblage coincided in a 8-m deepened shipping lane and near a disposal site for dredged fine sediment. This may be an indication that the benthic system can be changed by these human activities. Modelled bed shear stress is an important variable in addition to sediment variables in explaining distribution patterns in macrozoobenthos.

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Reef environments shape microbial partners in a highly connected coral population

10.1101/2020.10.27.357095 ◽

2020 ◽

Author(s):

NG Kriefall ◽

MR Kanke ◽

GV Aglyamova ◽

SW Davies

Keyword(s):

Microbial Communities ◽

Environmental Variability ◽

French Polynesia ◽

Coral Host ◽

Coral Population ◽

Fitness Consequences ◽

Variable Environments ◽

Show Evidence ◽

Acropora Hyacinthus ◽

Reef Zones

ABSTRACTCorals from more thermally variable environments often fare better under thermal stress compared to those from less thermally variable environments, an important finding given that ocean warming threatens corals worldwide. Evidence is mounting that thermal tolerance can be attributed to the coral itself, as well as microbial communities present within the holobiont (coral host and its associated microorganisms). However, few studies have characterized how thermally variable environments structure multiple holobiont members in situ. Here, using 2b-RAD sequencing of the coral and metabarcoding of algal (ITS2) and bacterial (16S) communities, we show evidence that reef zones (locales differing in proximity to shore, physical characteristics, and environmental variability) structure algal and bacterial communities at different scales within a highly connected coral population (Acropora hyacinthus) in French Polynesia. Fore reef (more stable) algal communities were on average more diverse than the back reef (more variable), suggesting that variability constrains algal diversity. In contrast, microbial communities were structured on smaller scales with site-specific indicator species and enriched functions across reef zones. Our results illuminate how associations with unique microbial communities can depend on spatial scale across highly dispersive coral populations, which may have fitness consequences in thermally divergent regions and rapidly changing oceans.

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Transition of flow regime along a marine-terminating outlet glacier in East Antarctica

The Cryosphere Discussions ◽

10.5194/tcd-7-4913-2013 ◽

2013 ◽

Vol 7 (5) ◽

pp. 4913-4936 ◽

Cited By ~ 1

Author(s):

D. Callens ◽

K. Matsuoka ◽

D. Steinhage ◽

B. Smith ◽

F. Pattyn

Keyword(s):

Flow Regime ◽

Methodological Approach ◽

Flow Speed ◽

Upstream Region ◽

Outlet Glacier ◽

Bed Topography ◽

Sediment Bed ◽

Dronning Maud Land ◽

Downstream Section ◽

Downstream Area

Abstract. We present results of a~multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (> 2000 m) than previously thought. According to the new data, West Ragnhild Glacier discharges 13–14 Gt yr−1. Therefore, it is one of the three major outlet glaciers in Dronning Maud Land. Glacier-bed topography is distinct between the upstream and downstream section. In the downstream section (< 65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level while the upstream region is more mountainous. Spectrum analysis of the bed topography reveals a clear contrast between these two regions, suggesting that the downstream area is sediment covered. The bed returned power varies by 30 dB within 20 km near the bed flatness transition, which suggests that water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~ 250 m yr−1) can only be explained if basal motion accounts for ~ 60% of the surface motion. All above lines of evidence (sediment bed, wetness and basal motion) and the relative flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region which are more stable due to their bed geometry (e.g. Shirase Glacier).

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Different nitrogen sources speed recovery from corallivory and uniquely alter the microbiome of a reef-building coral

PeerJ ◽

10.7717/peerj.8056 ◽

2019 ◽

Vol 7 ◽

pp. e8056 ◽

Cited By ~ 3

Author(s):

Mallory M. Rice ◽

Rebecca L. Maher ◽

Rebecca Vega Thurber ◽

Deron E. Burkepile

Keyword(s):

Microbial Community ◽

Nitrogen Source ◽

Nutrient Loading ◽

Seawater Temperature ◽

French Polynesia ◽

Ocean Warming ◽

Coral Growth ◽

Coral Host ◽

Coral Microbiome ◽

Algal Symbiont

Corals are in decline worldwide due to local anthropogenic stressors, such as nutrient loading, and global stressors, such as ocean warming. Anthropogenic nutrient loading, which is often rich in nitrate, inhibits coral growth and worsens corals’ response to warming while natural sources of nitrogen, such as ammonium from fish excretion, promotes coral growth. Although the effects of nutrient loading and ocean warming have been well-studied, it remains unclear how these factors may interact with biotic processes, such as corallivory, to alter coral health and the coral microbiome. This study examined how nitrate vs. ammonium enrichment altered the effects of increased seawater temperature and simulated parrotfish corallivory on the health of Pocillopora meandrina and its microbial community. We tested the effects of nitrogen source on the response to corallivory under contrasting temperatures (control: 26 °C, warming: 29 °C) in a factorial mesocosm experiment in Moorea, French Polynesia. Corals were able to maintain growth rates despite simultaneous stressors. Seawater warming suppressed wound healing rates by nearly 66%. However, both ammonium and nitrate enrichment counteracted the effect of higher temperatures on would healing rates. Elevated seawater temperature and ammonium enrichment independently increased Symbiodiniaceae densities relative to controls, yet there was no effect of nitrate enrichment on algal symbiont densities. Microbiome variability increased with the addition of nitrate or ammonium. Moreover, microbial indicator analysis showed that Desulfovibrionaceae Operational taxonomic units (OTUs) are indicators of exclusively temperature stress while Rhodobacteraceae and Saprospiraceae OTUs were indicators of high temperature, wounding, and nitrogen enrichment. Overall, our results suggest that nitrogen source may not alter the response of the coral host to simultaneous stressors, but that the associated microbial community may be distinct depending on the source of enrichment.

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Transition of flow regime along a marine-terminating outlet glacier in East Antarctica

The Cryosphere ◽

10.5194/tc-8-867-2014 ◽

2014 ◽

Vol 8 (3) ◽

pp. 867-875 ◽

Cited By ~ 18

Author(s):

D. Callens ◽

K. Matsuoka ◽

D. Steinhage ◽

B. Smith ◽

E. Witrant ◽

...

Keyword(s):

Flow Regime ◽

Methodological Approach ◽

Flow Speed ◽

Upstream Region ◽

Outlet Glacier ◽

Bed Topography ◽

Sediment Bed ◽

Basal Sliding ◽

Dronning Maud Land ◽

Downstream Section

Abstract. We present results of a multi-methodological approach to characterize the flow regime of West Ragnhild Glacier, the widest glacier in Dronning Maud Land, Antarctica. A new airborne radar survey points to substantially thicker ice (>2000 m) than previously thought. With a discharge estimate of 13–14 Gt yr−1, West Ragnhild Glacier thus becomes of the three major outlet glaciers in Dronning Maud Land. Its bed topography is distinct between the upstream and downstream section: in the downstream section (<65 km upstream of the grounding line), the glacier overlies a wide and flat basin well below the sea level, while the upstream region is more mountainous. Spectral analysis of the bed topography also reveals this clear contrast and suggests that the downstream area is sediment covered. Furthermore, bed-returned power varies by 30 dB within 20 km near the bed flatness transition, suggesting that the water content at bed/ice interface increases over a short distance downstream, hence pointing to water-rich sediment. Ice flow speed observed in the downstream part of the glacier (~250 m yr−1) can only be explained through very low basal friction, leading to a substantial amount of basal sliding in the downstream 65 km of the glacier. All the above lines of evidence (sediment bed, wetness and basal motion) and the relatively flat grounding zone give the potential for West Ragnhild Glacier to be more sensitive to external forcing compared to other major outlet glaciers in this region, which are more stable due to their bed geometry (e.g. Shirase Glacier).

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An Application of the HFACS Method to Aviation Accidents in Africa

Aviation Psychology and Applied Human Factors ◽

10.1027/2192-0923/a000093 ◽

2016 ◽

Vol 6 (1) ◽

pp. 33-38 ◽

Cited By ~ 4

Author(s):

Isaac Munene

Keyword(s):

Human Factors ◽

Physical Environment ◽

Human Factor ◽

Flight Training ◽

African Countries ◽

Causal Factors ◽

Aviation Accidents ◽

Factors Analysis ◽

Adverse Weather ◽

Decision Errors

Abstract. The Human Factors Analysis and Classification System (HFACS) methodology was applied to accident reports from three African countries: Kenya, Nigeria, and South Africa. In all, 55 of 72 finalized reports for accidents occurring between 2000 and 2014 were analyzed. In most of the accidents, one or more human factors contributed to the accident. Skill-based errors (56.4%), the physical environment (36.4%), and violations (20%) were the most common causal factors in the accidents. Decision errors comprised 18.2%, while perceptual errors and crew resource management accounted for 10.9%. The results were consistent with previous industry observations: Over 70% of aviation accidents have human factor causes. Adverse weather was seen to be a common secondary casual factor. Changes in flight training and risk management methods may alleviate the high number of accidents in Africa.

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