About

James Hench is an Associate Professor of Oceanography at Duke University, affiliated with the Department of Civil and Environmental Engineering. He holds a B.S. from North Carolina State University (1991), an M.S. from Stanford University (1992), and a Ph.D. from the University of North Carolina, Chapel Hill (2002). His research focuses on marine science and conservation, with particular emphasis on coral reef dynamics, hydrodynamics, and the interactions between physical and biological processes in marine environments. Hench has contributed to understanding wave and current interactions with coral reef structures, boundary layer dynamics, and the effects of hydrodynamic disturbances on coral reef recovery and resilience. His work involves both field observations and modeling approaches to elucidate the complex processes shaping coral reef ecosystems and their responses to environmental stressors.

Research topics

• Environmental science
• Ecology
• Oceanography
• Geology
• Physics
• Geography
• Biology
• Computer Science
• Mathematics
• Mechanics
• Materials science
• Geometry
• Classical mechanics
• Remote sensing
• Environmental resource management
• Thermodynamics

Selected publications

• Coral restoration for coastal resilience: Integrating ecology, hydrodynamics, and engineering at multiple scales

  Ecosphere · 2023 · 39 citations

  Senior authorCorresponding
  • Environmental resource management
  • Environmental science
  • Ecology

  Abstract The loss of functional and accreting coral reefs reduces coastal protection and resilience for tropical coastlines. Coral restoration has potential for recovering healthy reefs that can mitigate risks from coastal hazards and increase sustainability. However, scaling up restoration to the large extent needed for coastal protection requires integrated application of principles from coastal engineering, hydrodynamics, and ecology across multiple spatial scales, as well as filling missing knowledge gaps across disciplines. This synthesis aims to identify how scientific understanding of multidisciplinary processes at interconnected scales can advance coral reef restoration. The work is placed within the context of a decision support framework to evaluate the design and effectiveness of coral restoration for coastal resilience. Successfully linking multidisciplinary science with restoration practice will ensure that future large‐scale coral reef restorations maximize protection for at‐risk coastal communities.

  PublisherOA PDFDOI

• Boundary layer dynamics and bottom friction in combined wave–current flows over large roughness elements

  Journal of Fluid Mechanics · 2021 · 17 citations

  Senior authorCorresponding
  • Mechanics
  • Physics
  • Classical mechanics

  In the coastal ocean, interactions of waves and currents with large roughness elements, similar in size to wave orbital excursions, generate drag and dissipate energy. These boundary layer dynamics differ significantly from well-studied small-scale roughness. To address this problem, we derived spatially and phase-averaged momentum equations for combined wave–current flows over rough bottoms, including the canopy layer containing obstacles. These equations were decomposed into steady and oscillatory parts to investigate the effects of waves on currents, and currents on waves. We applied this framework to analyse large-eddy simulations of combined oscillatory and steady flows over hemisphere arrays (diameter $D$ ), in which current ( $U_c$ ), wave velocity ( $U_w$ ) and period ( $T$ ) were varied. In the steady momentum budget, waves increase drag on the current, and this is balanced by the total stress at the canopy top. Dispersive stresses from oscillatory flow around obstacles are increasingly important as $U_w/U_c$ increases. In the oscillatory momentum budget, acceleration in the canopy is balanced by pressure gradient, added-mass and form drag forces; stress gradients are small compared to other terms. Form drag is increasingly important as the Keulegan–Carpenter number $KC=U_wT/D$ and $U_c/U_w$ increase. Decomposing the drag term illustrates that a quadratic relationship predicts the observed dependences of steady and oscillatory drag on $U_c/U_w$ and $KC$ . For large roughness elements, bottom friction is well represented by a friction factor ( $f_w$ ) defined using combined wave and current velocities in the canopy layer, which is proportional to drag coefficient and frontal area per unit plan area, and increases with $KC$ and $U_c/U_w$ .

  PublisherOA PDFDOI

• An Island Mass Effect Resolved Near Mo’orea, French Polynesia

  Frontiers in Marine Science · 2020 · 26 citations

  • Oceanography
  • Environmental science
  • Geology

  We sought to resolve the extent, variability, and magnitude of productivity enrichment around a high tropical island consistent with the phenomenon of an Island Mass Effect (IME). Key biogeochemical constituents and physical oceanographic parameters were measured offshore over the upper 500 m from July 27 to August 7, 2014 around the Society Island of Mo’orea in French Polynesia in association with the nearshore measurements of the Mo’orea Coral Reef Long Term Ecological Research program. High-resolution synoptic sampling in a rectangular grid around the island revealed vertical and horizontal patterns in hydrographic conditions, inorganic nutrients, rates of productivity, and concentrations of organic matter that are characteristic of oligotrophic gyre ecosystems. Within the upper euphotic zone (0 – 75 m), levels of net primary productivity (NPP), chlorophyll a (Chl), heterotrophic bacterioplankton productivity (BP), and particulate organic carbon (POC) exhibited concurrent enhancement at stations located within 5 to 15 km of shore, relative to stations farther offshore. These observations of enhanced productivity near an island are consistent with an IME. Particulate organic matter nitrogen isotopes (POM- δ15N) were significantly lower near the island than at stations farther offshore, further emphasizing spatial differences in water column biogeochemistry consistent with an IME. Vertical profiles suggest thermocline shoaling and mixing associated with the pycnocline impinging on the island’s submerged flanks and coral reef slope may have contributed to the decreasing depth and increasing intensity of chlorophyll-a concentration in the DCM at nearshore stations relative to farther offshore. Shipboard measurements of an anticyclonic flow within the upper 75 m of the water column in the vicinity of Mo’orea suggest that retention of inorganic nutrients and organic matter near Mo’orea may also have contributed to the patterns in NPP, Chl, BP, POC and POM- δ15N, providing a potential mechanistic understanding of the processes driving an IME.

  PublisherOA PDFDOI

• Estimating Geometric Properties of Coral Reef Topography Using Obstacle‐ and Surface‐Based Approaches

  Journal of Geophysical Research Oceans · 2020 · 6 citations

  Senior authorCorresponding
  • Geology
  • Geometry
  • Remote sensing

  Abstract In shallow water systems like coral reefs, bottom friction is an important term in the momentum balance. Parameterizations of bottom friction require a representation of canopy geometry, which can be conceptualized as an array of discrete obstacles or a continuous surface. Here, we assess the implications of using obstacle‐ and surface‐based representations to estimate geometric properties needed to parameterize drag. We collected high‐resolution reef topography data using a scanning multibeam sonar that resolved individual coral colonies within a set of 100‐m 2 reef patches primarily composed of mounding Porites corals. The topography measurements yielded 1‐cm resolution continuous surfaces consisting of a single elevation value for each position in a regular horizontal grid. These surfaces were analyzed by (1) defining discrete obstacles and quantifying their properties (dimensions, shapes), and (2) computing properties of the elevation field (root mean square (rms) elevations, rms slopes, spectra). We then computed the roughness density (i.e., frontal area per unit plan area) using both analysis approaches. The obstacle and surface‐based estimates of roughness density did not agree, largely because small‐scale topographic variations contributed significantly to total frontal area. These results challenge the common conceptualization of shallow‐water canopies as obstacle arrays, which may not capture significant contributions of high‐wavenumber roughness to total frontal area. In contrast, the full range of roughness length scales present in natural reefs is captured by the continuous surface representation. Parameterizations of bottom friction over reef topography could potentially be improved by representing the contributions of all length scales to total frontal area and drag.

  PublisherOA PDFDOI

• Increasing comparability among coral bleaching experiments

  Ecological Applications · 2020 · 158 citations

  • Computer Science
  • Ecology
  • Environmental science

  Coral bleaching is the single largest global threat to coral reefs worldwide. Integrating the diverse body of work on coral bleaching is critical to understanding and combating this global problem. Yet investigating the drivers, patterns, and processes of coral bleaching poses a major challenge. A recent review of published experiments revealed a wide range of experimental variables used across studies. Such a wide range of approaches enhances discovery, but without full transparency in the experimental and analytical methods used, can also make comparisons among studies challenging. To increase comparability but not stifle innovation, we propose a common framework for coral bleaching experiments that includes consideration of coral provenance, experimental conditions, and husbandry. For example, reporting the number of genets used, collection site conditions, the experimental temperature offset(s) from the maximum monthly mean (MMM) of the collection site, experimental light conditions, flow, and the feeding regime will greatly facilitate comparability across studies. Similarly, quantifying common response variables of endosymbiont (Symbiodiniaceae) and holobiont phenotypes (i.e., color, chlorophyll, endosymbiont cell density, mortality, and skeletal growth) could further facilitate cross-study comparisons. While no single bleaching experiment can provide the data necessary to determine global coral responses of all corals to current and future ocean warming, linking studies through a common framework as outlined here, would help increase comparability among experiments, facilitate synthetic insights into the causes and underlying mechanisms of coral bleaching, and reveal unique bleaching responses among genets, species, and regions. Such a collaborative framework that fosters transparency in methods used would strengthen comparisons among studies that can help inform coral reef management and facilitate conservation strategies to mitigate coral bleaching worldwide.

  DOI

Recent grants

• Collaborative Research: Combined Waves and Currents over Multi-Scale Topography: From Boundary Layer Dynamics to Parameterization

  NSF · $100k · 2021–2026

• Collaborative Research: Relating Topographic Complexity and Circulation Patterns on Coral Reefs from Colony-Scale to Reef-Scale

  NSF · $290k · 2014–2019

Frequent coauthors

• Stephen G. Monismith

  Stanford University

  30 shared

• Antoine Collin

  École Pratique des Hautes Études

  25 shared

• Johanna H. Rosman

  University of North Carolina at Chapel Hill

  22 shared

• Russell J. Schmitt

  University of California, Santa Barbara

  19 shared

• James J. Leichter

  Scripps Institution of Oceanography

  17 shared

• Nicholas J. Nidzieko

  University of California, Santa Barbara

  16 shared

• Sally J. Holbrook

  University of California, Santa Barbara

  15 shared

• Matthias Troyer

  14 shared

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