Steep Islands Research Articles

Experimental study on regular wave breakage and nonlinear characteristics on the terrain of steep coral islands and reefs

Experimental study on regular wave breakage and nonlinear characteristics on the terrain of steep coral islands and reefs

Mechanisms controlling giant sea salt aerosol size distributions along a tropical orographic coastline

Abstract. Sea salt aerosol (SSA) is a naturally occurring phenomenon that arises from the breaking of waves and consequent bubble bursting on the ocean's surface. The resulting particles exhibit a bimodal distribution spanning orders of magnitude in size that introduces significant uncertainties when estimating the total annual mass of SSA on a global scale. Although estimates of mass and volume are significantly influenced by the presence of giant particles (dry radius >1 µm), effectively observing and quantifying these particles proves to be challenging. Additionally, uncertainties persist regarding the contribution of SSA production along coastlines, but preliminary studies suggest that coastal interactions may increase SSA particle concentrations by orders of magnitude. Moreover, our knowledge regarding the vertical distribution of SSA particles in the marine boundary layer remains limited, resulting in significant gaps in understanding the vertical mixing of giant aerosol particles and specific environmental conditions facilitating their dispersion. By addressing these uncertainties, particularly in regions where SSA particles constitute a substantial percentage of total aerosol loading, we can enhance our comprehension of the complex relationships between the air, sea, aerosols, and clouds. A case study conducted on the Hawaiian island of O`ahu offers insight into the influence of coastlines and orography on the production and vertical distribution of giant SSA size distributions. Along the coastline, the frequency of breaking waves is accelerated, serving as an additional source of SSA production. Furthermore, the steep island orography generates strong and consistent uplift under onshore trade wind conditions, facilitating vertical mixing of SSA particles along windward coastlines. To investigate this phenomenon, in situ measurements of SSA size distributions for particles with dry radii (rd) ≥ 2.8 µm were conducted for various altitudes, ranging from approximately 80 to 650 m altitude along the windward coastline and from 80 to 250 m altitude aboard a ship offshore. Comparing size distributions onshore and offshore confirmed significantly higher concentrations along the coastline, with 2.7–5.4 times greater concentrations than background open-ocean concentrations for supermicron particles. These size distributions were then analyzed in relation to environmental variables influencing SSA production and atmospheric dynamics. It was found that significant wave height exhibited the strongest correlation with changes in SSA size distributions. Additionally, simulated sea salt particle trajectories provided valuable insight into how production distance from the coastline impacts the horizontal and vertical advection of SSA particles of different sizes under varying trade wind speeds. Notably, smaller particles demonstrated reduced dependence on local wind speeds and production distance from the coastline, experiencing minimal dry deposition and high average maximum altitudes relative to larger particles. This research not only highlights the role of coastlines in enhancing the presence and vertical mixing potential of giant SSA particles, but also emphasizes how important it is to consider the influence of local factors on aerosol observations at different altitudes.

Low-level jets drive the summer intra-seasonal variability of the Canary upwelling system

The role of low-level jets in the intra-seasonal variability of the Canary upwelling system during summer is assessed with a fully coupled, high resolution (3km) ocean-atmosphere numerical simulation. Here, low-level jets include the main continental coastal jet, the tip jets of Madeira and the tip-jets of the steep Canary Islands. The coastline shape, orography of northwest Africa and the proximity of Canary islands lead to complex interactions between the jets, that result in strong surface wind intra-seasonal variability on the multiweek time scale. That variability is forced by oscillations in the shape and position of the Azores subtropical anticyclone, through a strong oscillation in the atmospheric boundary layer height. At the coast, coastal-trapped oscillations with a propagation speed, planetary boundary height, offshore extension, and surface pressure compatible with a Kelvin wave occasionally propagate northward, against the synoptic scale surface pressure. While similar processes have already been observed in California, the mechanisms here described appear to result from interactions of continental coastal processes with a set of steep islands close to the coast. The sensitivity of these dynamics to climate change is a challenging question.

Taming Fogo Island: Late-Holocene volcanism, natural fires and land use as recorded in a scoria-cone sediment sequence in Cabo Verde

Cabo Verde remained uninhabited until 1460 CE, when European sailors founded a settlement in Santiago, and soon after in Fogo island. The degree to which different island ecosystems in Cabo Verde have been transformed by humans remains uncertain because of a scarcity of historical information and archaeological evidence. Disentangling these processes from natural ones is complicated in islands with a history of volcanic impacts and other natural hazards. In this paper, we apply microfossil (pollen, non-pollen palynomorphs and phytoliths) and sedimentological analyses (granulometry, X-ray diffraction, loss on ignition and tephrostratigraphy) to a 2-m sediment sequence deposited in a scoria cone from 4100 cal year BP (calibrated years before 1950 CE) to the present. The organic-rich basal sediments indicate that between 4100 and 2600 cal year BP the pre-settlement landscape of Fogo was an open grassland, where fire was infrequent and/or small-scale. An increase in volcanic glass deposition after 2600 cal year BP, peaking ca. 1200 cal year BP, suggests that there was a progressive activation of Fogo’s volcanic activity, contemporaneous with increased fire frequency and erosion pulses, but with little impact on local grassland vegetation. While dating uncertainty is high, the first evidence of intensive local land use by early settlers was in the form of cultivation of Zea mays, abundant spores of coprophilous fungi (i.e. Sporormiella), and peaks in charcoal concentrations between 800 and 400 cal year BP. This was followed by large increases in pollen from pigeon pea ( Cajanus), a diverse array of exotic trees ( Cupressus, Grevillea), and invasive shrubs ( Lantana). The introduction of these taxa is part of recent human effort to ‘tame’ this steep, dry and hazardous island by reducing erosion and providing firewood. An important outcome of these efforts, however, is a loss of fragile native biodiversity.

Identifying and Dating Mont Saint-Michel’s Early Monastic Buildings, c. 1070–1228

ABSTRACTOne of the best-known monastic settlements of western Europe, the abbey of Mont Saint-Michel occupies the summit of a prodigiously steep island site off the coast of Normandy in northern France. The church was built between 1023 and c. 1080–85. The monastic buildings, to the north of the church, were arranged vertically as much as horizontally, reflecting the constraints of the site. They appear to have comprised three adjacent and interconnecting buildings, two of three storeys, the other of two. However, two of these three ranges were overbuilt in the early thirteenth century by an ambitious development which became known as the Merveille (c. 1212–28). This article seeks to identify the buildings that the Merveille replaced and thus the entire complex as it existed in the twelfth century. This inevitably involves a certain amount of speculation and perhaps for this reason the complex has hitherto been largely ignored, important though it is for an understanding of the abbey’s early history. The article also discusses other building projects relevant to the monks, such as the cemetery, the twelfth-century Hôtellerie and the thirteenth-century infirmary and mortuary chapel, and analyses the genesis of the Merveille. Among the findings or propositions are that the monks’ cemetery was housed in what may once have been a ducal palace; that the abbey’s cloister occupied the same position as it does today but was at a lower, mezzanine level and was smaller than the present cloister; that the chapter house and infirmary were probably adjacent to the west walk of the cloister; that the original provision for kitchen and cellar and for sleeping space was inadequate; and that the Merveille, which was the work of Abbot Raoul des Îles, was not entirely new-build as sometimes thought, but a transformation and redevelopment of buildings that already existed.

Heavy Rare Earth Elements and the Sources of Continental Flood Basalts

AbstractHeavy rare earth elements (HREEs) in mafic and ultramafic volcanic rocks are useful recorders of mantle source processes because their ratios are not easily modified by differentiation. Here we utilize REEBOX PRO, a simulator of adiabatic decompression melting of the mantle, to study the behavior of HREEs in the formation of continental flood basalt (CFB) parental magmas in the mantle. We simulate partial melting of depleted peridotite, pyrolitic peridotite, pyroxenite, and peridotite-pyroxenite mixtures at mantle potential temperatures of 1350–1650°C and lithospheric thicknesses of 50–150 km, and compare the results to natural data. Many large igneous provinces are typified by low-Ti and high-Ti CFBs with contrasting HREE patterns. Our results show that low-Ti CFBs originate mainly from peridotitic sources. Flat mid-ocean ridge basalt-like HREE patterns typical of low-Ti CFBs can be generated beneath thick lithosphere (~100 km), given that mantle potential temperatures are high (>1500°C) and garnet is completely consumed from the source. We thus challenge the common interpretation that flat HREE patterns always indicate shallow sources for CFB parental magmas. High-Ti CFBs require pyroxenite-bearing sources (≥10%). Contrary to a common view, their steep oceanic island basalt-like HREE patterns can be generated beneath quite a thin lithosphere (~50 km), which is due to increased garnet stability in pyroxenite sources. When applied to CFBs of the Karoo large igneous province, the results are compatible with a model where a mantle plume penetrates a progressively thinning Gondwana lithosphere.

Rapid observations of ocean dynamics and stratification along a steep island coast during Hurricane María.

Hurricanes are extreme storms that affect coastal communities, but the linkages between hurricane forcing and ocean dynamics remain poorly understood. Here, we present full water column observations at unprecedented resolution from the southwest Puerto Rico insular shelf and slope during Hurricane María, representing a rare set of high-frequency, subsurface, oceanographic observations collected along an island margin during a hurricane. The shelf geometry and orientation relative to the storm acted to stabilize and strengthen stratification. This maintained elevated sea-surface temperatures (SSTs) throughout the storm and led to an estimated 65% greater potential hurricane intensity contribution at this site before eye passage. Coastal cooling did not occur until 11 hours after the eye passage. Our findings present a new framework for how hurricane interaction with insular island margins may generate baroclinic processes that maintain elevated SSTs, thus potentially providing increased energy for the storm.

SPATIAL DISTRIBUTIONS IN GROUNDWATER DISCHARGE ON VARIOUS TIDAL FLATS IN A SMALL AND STEEP ISLAND, WESTERN JAPAN

To manage and conserve the seagrass bed and ecosystem in tidal flats, this study examined to confirm spatial distribution in groundwater (SGD) on tidal flats with the area of around 100 m square in a small and steep island. Various groundwater and nutrient discharges were observed at the W and E sites. 1) Based on the water budget, the groundwater flux was estimated to be 8.68 m/yr or 23.9 mm/day in E, and 17.75 m/yr or 48.6 mm/day in W, respectively. 2) Spatial distributions of groundwater contribution ratio (%) in pore water at W was around 60% in average, which was 8 times of that in E site. 3) The NO3-N concentration in pore water at W site was about 30 times of that at E because of the low attenuation rate with high groundwater velocity. 4) The temporal variation in groundwater flux with tidal fluctuation indicated 2.5 m/day in maximum and -4.0 m/day in minimum. This huge difference between the average flux and maximum indicated also large seawater recirculation and heterogeneous distribution of SGD. This heterogeneous distribution at this tidal flat would contribute to the activity of seagrass and diversity of ecosystem.

Stream flow composition and sediment yield comparison between partially urbanized and undisturbed coastal watersheds-case study: St. John, US Virgin Islands.

In steep dry-tropical islands, rural and urban development can lead to accelerated soil erosion and the delivery of land-based materials into marine ecosystems. The objective of this paper was to compare stream water composition, clay minerology, and sediment yield between a partially urbanized (Coral Bay) and an undisturbed (Lameshur) coastal watersheds in St. John, US Virgin Islands (USVI). The saturation index of streamflow water samples was calculated using "The Geochemist's Workbench" software and most likely precipitated minerals from observed storm events was then compared with X-ray diffraction on soil clay mineralogy. The spatial distribution on both annual mean (2010) erosion rates and storm event-wise (Hurricane Otto) sediment yield among the two study watersheds were modeled using the revised and modified universal soil loss equations (RUSLE; MUSLE), respectively. Cations concentration in stream flow water samples and sediment yield were higher for the partially urbanized (Coral Bay) compared to the undisturbed (Lameshur) watershed. Our findings suggest that rural/urban development may increase stream water cations concentration and inputs of sediment to downstream ecosystems. Future studies evaluating the effect of management practices such as pavement or other stabilization of dirt roads and their impact on stream water quality and quantity and sediment yield are crucial for the proper sediment management in the study watersheds and potentially in other rural-urbanizing tropical watersheds.

Eddy Wake Generation From Broadband Currents Near Palau

AbstractWake eddies are frequently created by flow separation where ocean currents encounter abrupt topography in the form of islands or headlands. Most previous work has concentrated on wake eddy generation by either purely oscillatory (usually tidal) currents, or quasi‐steady mean flows. Here we report measurements near the point of flow separation at the northern end of the Palau island chain, where energetic tides and vertically sheared low‐frequency flows are both present. Energetic turbulence measured near the very steeply sloping ocean floor varied cubically with the total flow speed (primarily tidal). The estimated turbulent viscosity suggests a regime of flow separation and eddying wake generation for flows that directly feel this drag. Small‐scale (∼1 km), vertically sheared wake eddies of different vorticity signs were observed with a shipboard survey on both sides of the separation point, and significantly evolved over several tidal periods. The net production and export of vorticity into the wake, expected to sensitively depend on the interplay of tidal and low‐frequency currents, is explored here with a simple conceptual model. Application of the model to a 10‐month mooring record suggests that inclusion of high frequency oscillatory currents may boost the net flux of vorticity into the ocean interior by a depth dependent factor of 2 to 25. Models that do not represent the effect of these high frequency currents may not accurately infer the net momentum or energy losses felt where strong flows encounter steep island or headland topography.

Recent Advances in Research and Forecasting of Tropical Cyclone Track, Intensity, and Structure at Landfall

This review prepared for the fourth International Workshop on Tropical Cyclone Landfall Processes (IWTCLP-4) summarizes the most recent (2015-2017) theoretical and practical knowledge in the field of tropical cyclone (TC) track, intensity, and structure rapid changes at or near landfall. Although the focus of IWTCLP-IV was on landfall, this summary necessarily embraces the characteristics of storms during their course over the ocean prior to and leading up to landfall. In the past few years, extremely valuable observational datasets have been collected using both aircraft reconnaissance and new geostationary and low-earth orbiting satellites at high temporal and spatial resolution for TC forecasting guidance and research studies. Track deflections for systems near complex topography such as that of Taiwan and La Reunion have been further investigated, and advanced numerical models with high spatial resolution necessary to predict the interaction of the TC circulation with steep island topography have been developed. An analog technique has been designed to meet the need for longer range landfall intensity forecast guidance that will provide more time for emergency preparedness. Probabilistic track and intensity forecasts were also developed to better communicate on forecast uncertainty. Operational practices of several TC forecast centers are described herein and some challenges regarding forecasts and warnings for TCs making landfall are identified. This review concludes with insights from both researchers and forecasters regarding future directions to improve predictions of TC track, intensity, and structure at landfall.

The South Georgia Wave Experiment: A Means for Improved Analysis of Gravity Waves and Low-Level Wind Impacts Generated from Mountainous Islands

AbstractGravity waves (GWs) play an important role in many atmospheric processes. However, the observation-based understanding of GWs is limited, and representing them in numerical models is difficult. Recent studies show that small islands can be intense sources of GWs, with climatologically significant effects on the atmospheric circulation. South Georgia, in the South Atlantic, is a notable source of such “small island” waves. GWs are usually too small scale to be resolved by current models, so their effects are represented approximately using resolved model fields (parameterization). However, the small-island waves are not well represented by such parameterizations, and the explicit representation of GWs in very-high-resolution models is still in its infancy. Steep islands such as South Georgia are also known to generate low-level wakes, affecting the flow hundreds of kilometers downwind. These wakes are also poorly represented in models.We present results from the South Georgia Wave Experiment (SG-WEX) for 5 July 2015. Analysis of GWs from satellite observations is augmented by radiosonde observations made from South Georgia. Simulations were also made using high-resolution configurations of the Met Office Unified Model (UM). Comparison with observations indicates that the UM performs well for this case, with realistic representation of GW patterns and low-level wakes. Examination of a longer simulation period suggests that the wakes generally are well represented by the model. The realism of these simulations suggests they can be used to develop parameterizations for use at coarser model resolutions.

Characterizing seawater oxygen isotopic variability in a regional ocean modeling framework: Implications for coral proxy records

AbstractReconstructions of the El Niño–Southern Oscillation (ENSO) are often created using the oxygen isotopic ratio in tropical coral skeletons (δ18O). However, coral δ18O can be difficult to interpret quantitatively, as it reflects changes in both temperature and the δ18O value of seawater. Small‐scale (10–100 km) processes affecting local temperature and seawater δ18O are also poorly quantified and contribute an unknown amount to intercoral δ18O offsets. A new version of the Regional Ocean Modeling System capable of directly simulating seawater δ18O (isoROMS) is therefore presented to address these issues. The model is used to simulate δ18O variations over the 1979–2009 period throughout the Pacific at coarse (O(50 km)) resolution, in addition to 10 km downscaling experiments covering the central equatorial Pacific Line Islands, a preferred site for paleo‐ENSO reconstruction from corals. A major impact of downscaling at the Line Islands is the ability to resolve fronts associated with tropical instability waves (TIWs), which generate large excursions in both temperature and seawater δ18O at Palmyra Atoll (5.9°N, 162.1°W). TIW‐related sea surface temperature gradients are smaller at neighboring Christmas Island (1.9°N, 157.5°W), but the interaction of mesoscale features with the steep island topography nonetheless generates cross‐island temperature differences of up to 1°C. These nonlinear processes alter the slope of the salinity:seawater δ18O relationship at Palmyra and Christmas, as well as affect the relation between coral δ18O and indices of ENSO variability. Consideration of the full physical oceanographic context of reef environments is therefore crucial for improving δ18O‐based ENSO reconstructions.

Deepwater marine litter densities and composition from submersible video-transects around the ABC-islands, Dutch Caribbean

Baseline data on anthropogenic seafloor debris contamination in the year 2000 is provided for 24 submersible video transects at depths of 80–900m, off the Dutch ABC-islands (Aruba, Bonaire, Curaçao), in the southeastern Caribbean Sea. In total, 202 objects were documented from a combined 21,184m of transect, ranging from sandy lower island-slope to rocky upper island-slope habitat. Debris densities differed significantly with depth. Highest debris accumulation (0.459 items 100m−2 or 4590 items per km2) occurred at depths of 300–600m on more shallow-sloping (20–30°) sand and silt bottoms. The overall average debris density was 0.27 objects per 100m2 (or 2700 items per km2), which is an order of magnitude higher than most other deepwater debris studies. What we describe may be representative for other small, populated, steep volcanic Caribbean islands. Food and beverage-related items were the single largest usage category identified (44% of objects; mostly glass beverage bottles).

Other Atlantics:

Other Atlantics:

Tropical cyclone inundation potential on the Hawaiian Islands of Oahu and Kauai

The lack of a continental shelf in steep volcanic islands leads to significant changes in tropical cyclone inundation potential, with wave setup and runup increasing in importance and wind driven surge decreasing when compared to more gently-sloped mainland regions. This is illustrated through high resolution modeling of waves, surge, and runup on the Hawaiian Islands of Oahu and Kauai. A series of hurricane waves and water levels were computed using the SWAN+ADCIRC models for a suite of 643 synthetic storm scenarios, while local wave runup was evaluated along a series of 1D transects using the phase-resolving model Bouss1D. Waves are found to be an extremely important component of the inundation, both from breaking wave forced increases in storm surge and also from wave runup over the relatively steep topography. This is clear in comparisons with debris lines left by Hurricane Iniki on the Island of Kauai, where runup penetration is much greater than still water inundation in most instances. The difference between steeply-sloping and gently-sloping topographies was demonstrated by recomputing Iniki with the same landfall location as Hurricane Katrina in Louisiana. Surge was greatly increased for the mild-slope Iniki-in-Louisiana case, while pure wind surge for Iniki-in-Kauai was very small.For the entire suite of storms, maxima on Kauai show predicted inundation largely confined to a narrow coastal strip, with few locations showing more than a few hundred meters of flooding from the shoreline. As expected, maximum flooded areas for the 643 storms were somewhat greater than the Iniki inundation.Oahu has significantly more low-lying land compared to Kauai, and consequently hypothetical tropical cyclone landfalls show much more widespread inundation. Under direct impact scenarios, there is the potential for much of Honolulu and most of Waikiki to be inundated, with both still water surge and wave runup contributing. Other regions of Oahu show inundation confined to a more narrow coastal strip, although there is still much infrastructure at risk.Even for very strong storms in Oahu and Kauai, maximum still water surge is relatively small, and does not exceed 3m in any storm modeled. In contrast, hurricane waves several kilometers from shore regularly exceed 10m due to the lack of a continental shelf.

Pretend (review)

Reviewed by: Pretend Hope Morrison Plecas, Jennifer. Pretend; written and illus. by Jennifer Plecas. Philomel, 2011. [32p]. ISBN 978-0-399-23430-9 $15.99 Reviewed from galleys R 4–7 yrs. “‘Pretend,’ Jimmy said to Dad, ‘that this couch is a big boat, and that we’re floating in the ocean.’” It takes Dad a while to warm up to the ins and outs of pretend play (“Say, ‘Oh no, what are we going to do?,’” Jimmy instructs his dad), but he is soon imagining with the best of them, occasionally offering details that Jimmy then gloms onto (when Dad proclaims that he stepped on a crab, Jimmy immediately steps on one, too). Their adventure takes them on a fishing trip, up a steep island mountain, and finally to camp, where they build a fort and rest. While the story of the pair imagining an adventure together is sweet and the details of that adventure are well pitched to the audience, it is the line-and-watercolor illustrations that really carry the concept. Plecas effectively moves the compositions through the stages of transformation, so that in the opening spread, Dad is in fact on a couch, in the next the couch is floating in rocky waters, and in the next the couch is gone altogether and the father and son are side by side in a rickety rowboat. The bulk of the tale is portrayed in the imagined setting, but Plecas occasionally brings the story back to the house, offering the audience glimpses of what Jimmy and Dad’s afternoon might really look like (the mountain climbing begins at the bottom of the stairs, the fort is shown as a few chairs and a blanket in one picture and branches and leaves in the next). The slender line and childlike informality of the figure drawing enhance the homey appeal. Saturday afternoon fort-builders will readily warm to this father-son story. Copyright © 2011 The Board of Trustees of the University of Illinois

Research of Equilibrium Composition Map in Conic Quantum Dots

We present equilibrium composition maps in InGaAs/GaAs conic strained quantum dots, using the finite element method and quadratic programming optimization method. The axis-symmetric model is adopted. We compare the steep islands with the shallow islands and determine the influence of entropic energy. The difference of equilibrium composition maps between the single dot and the quantum dot stacks is also discussed.

Shell‐bearing Mollusca (Bivalvia and Gastropoda) from submarine caves in Hong Kong

In October 2002, the Hong Kong Marine Caves Expedition was convened jointly by the Swire Institute of Marine Science, The University of Hong Kong and the Natural History Museum, London. The expedition explored the marine cave habitats of Hong Kong and their fauna. This paper describes the diversity of marine cave molluscs collected using SCUBA from two marine caves at Conic Island and Steep Island in the eastern waters of Hong Kong. Twenty, and eight species of shell‐bearing epifaunal bivalves and gastropods, respectively, were collected from the ceilings and walls of the two caves. Another 11 infaunal bivalve species were collected from the sediment‐filled floors of the caves. Of the species identified, eight are new records for Hong Kong. These are the bivalves Spondylus anacanthus, Hiatella cf. orientalis, Panomya turgida, Nuculana sp., Abra cf. fujitai, Pinguitellina cf. nux, and Lyonsiella cf. parva, and the epitonid gastropod Epitonium bullatum. The epibenthic molluscs recorded during this survey were mostly adults whereas the endobenthic bivalves were all juveniles. Although the above species are recorded from Hong Kong for the first time, they have been identified from non‐cave habitats elsewhere. In particular, the often singular presence of juvenile infaunal bivalves in the cave sediments suggests their opportunistic colonization by such species and thus further evidence for a lack of endemicity. That the epibenthic molluscs are non‐endemic is probably also because Hong Kong's submarine caves are very modern, that is, Middle Holocene.

The joint Swire Institute of Marine Science, Hong Kong, and Natural History Museum, London, Hong Kong Submarine Caves Expedition, 2002: discussion, conclusions and recommendations for conservation

Some two hundred taxa have been recorded from Hong Kong's submarine caves. Of these, at least eleven are new to science. The majority of species occurring on the walls and roofs in particular, however, are not cave endemics and have been recorded from other habitats in Hong Kong and elsewhere. Unlike the Tethyan karsted limestone caves of Japan and the Philippines in the Asian region, and elsewhere, Hong Kong's cave fauna is similar to other local sea bed habitats at similar depths, probably because of their modernity. Although the sediments that make up the cave's floors appear more stable (in terms of their faunistic composition), there is evidence that they are periodically infilled and flushed out. This may be either on a seasonal basis or following severe tropical storm and typhoon events. It is therefore likely that the infaunal taxa of the cave's floors are partly sustained by episodic colonization. Notwithstanding the lack of an identifiable endemicity, the caves act as refugia for a number of otherwise rare taxa, for example, the ahermatypic corals Balanophyllia eguchii and Tubastrea falkneri, and fishes gain protection within them from locally intense fishing activities. The caves also appear to contain epifaunal communities that are representative of earlier, undisturbed times and environmental conditions in Hong Kong. It is recommended that (i) the two caves on Conic Island and Steep Island be designated as Sites of Special Scientific Interest; (ii) that other caves be searched for and studied and (iii) more long‐term studies be made of their physical environments and the communities they support.