Low Wave Action Research Articles

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

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

Evaluation of Site Suitability for Artificial Reefs Deployment in Southeast Coast of India Using Geographical Information System as a Management Tool

A planned artificial reef (AR) deployment program as part of a fisheries enhancement might be a useful tool for managers to supplement traditional ways to utilize available space and augment local productivity. Several AR deployment initiatives have been carried out globally, but they are rarely subjected to a rigorous site selection process. We created a site selection procedure in this study that includes systematic stages including exclusion mapping, underwater visual transect, benthic composition, seawater quality, and comparative visual mapping. This research focused on restoring the fishing grounds for artisanal fishermen by deploying AR along the southeast coast of India. The results of each stage in the procedure enabled us to choose suitable locations at a target depth with low wave action, no slope, and a good substrate capable of supporting an AR. Analysis of variance (ANOVA-one way) showed significant (p < 0.05) spatial variation for depth, slope, seawater current, salinity, chlorophyll-a, benthic density, and diversity. The geographical information system (GIS) based model output showed space allocation for AR deployment. The GIS methodology for site selection was developed to be easily adaptable to the demands of diverse artificial reef programs. The integrated strategy has proven to be a successful regulatory intervention for AR deployment practices in order to facilitate coastal restoration and management.

Influence of environmental variables over multiple spatial scales on the population structure of a key marine invertebrate

Quantifying scale-dependent patterns and linking ecological to environmental variation is required to understand mechanisms regulating biodiversity. We conducted a large-scale survey in rocky shores along the SE Brazilian coast to examine spatial variability in body size and density of an intertidal barnacle (Chthamalus bisinuatus) and its relationships with benthic and oceanographic predictors. Both the size and density of barnacles showed most variation at the smallest spatial scales. On average, barnacle body size was larger on shores located in areas characterised by higher chlorophyll levels, colder waters, low wave action and low influence of freshwater. Barnacles were more abundant at wave-exposed shores. We identified critical scales of spatial variation of an important species and linked population patterns to essential environmental predictors. Our results show that populations of this barnacle are coupled to scale-dependent oceanographic variation. This study offers insights into the mechanisms regulating coastal populations along a little studied coastline.

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

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

Variación espacial y temporal de los organismos de un intermareal rocoso: Bahía Panamá, Pacífico Norte, Costa Rica

&lt;p&gt;The intertidal rocky shore of Bahía Panama, within Bahía Culebra in the North Pacific coast of Costa Rica, was sampled to study the biodiversity and the spatial patterns (three sites with differences in wave exposure, and five strata, from low to high tide levels) and temporal variation (a single date in 2007 and 2013) in different microhabitats (over and under rock surface, and crevices). The epibenthic organisms were sampled with quadrats of 25 x 25 cm in each stratum, and cryptic fauna was accounted by both visual census and manual collecting. The general pattern of vertical zonation of organisms at each site showed an increase in variety toward the infralittoral level, as well as in the composition of assemblages or partially in identity of taxa in each stratum. The sheltered section of the rocky coast, with shallow sand bottom (&amp;lt; 1 m), low wave action and greater sedimentation rate, had lower diversity, cover and abundance that increased towards the wave-exposed section, with more abrupt slope in the edge of rocky platform, lower turbidity, and deeper sand bottom (2-3 m). The horizontal change was more evident in epibenthic organisms, followed by the under rock surface inhabitants and finally in crevices. For the epibenthic organisms, a temporal change in assemblages (cover and abundance) was found between the 2007 and 2013, at each site and level (possibly by seasonal upwelling influence), but the spatial structure (vertical and horizontal) of the rocky shore seems the main cause of change in the composition of species. The spatial pattern of change in the biota (sheltered to exposed gradient) could be expected in similar shores of the Central American Pacific. Finally, the 157 species found (16 autotrophic taxa, 22 fishes, and 119 invertebrates) indicate the high biodiversity of this habitat in the tropics, and the importance of their conservation. Rev. Biol. Trop. 62 (Suppl. 4): 85-97. Epub 2014 Diciembre 01.&lt;/p&gt;

Influence of wave action on the partitioning and transport of unattached and floc-associated bacteria in fresh water.

The dynamic interaction of bacteria within bed sediment and suspended sediment (i.e., floc) in a wave-dominated beach environment was assessed using a laboratory wave flume. The influence of shear stress (wave energy) on bacterial concentrations and on the partitioning and transport of unattached and floc-associated bacteria was investigated. The study showed that increasing wave energy (0.60 and 5.35 N/s) resulted in a 0.5 to 1.5 log increase in unattached cells of the test bacterium Pseudomonas sp. strain CTO7::gfp-2 in the water column. There was a positive correlation between the bacterial concentrations in water and the total suspended solids, with the latter increasing from values of near 0 to up to 200 mg/L over the same wave energy increase. The median equivalent spherical diameter of flocs in suspension also increased by an order of magnitude in all experimental trials. Under both low (0.60 N/s) and high (5.35 N/s) energy regime, bacteria were shown to preferentially associate with flocs upon cessation of wave activity. The results suggest that collecting water samples during periods of low wave action for the purpose of monitoring the microbiological quality of water may underestimate bacterial concentrations partly because of an inability to account for the effect of shear stress on the erosion and mobilization of bacteria from bed sediment to the water column. This highlights the need to develop a more comprehensive beach analysis strategy that not only addresses presently uncharacterized shores and sediments but also recognizes the importance of eroded flocs as a vector for the transport of bacteria in aquatic environments.

Characterization of Chironomidae (Diptera) surface-floating pupal exuviae sample sort time from coastal tropical aquatic systems.

Many studies either ignore chironomids or only identify specimens to subfamily or tribe due to the associated difficulty and high cost with processing and identifying larvae. An efficient form of sampling chironomids involves collections of surface-floating pupal exuviae (SFPE). SFPE sample sorting has been shown to be more time efficient than traditional dip-net methods in temperate urban and peri-urban streams. However, no published studies have tested the time efficiency of SFPE sample sorting from coastal tropical aquatic systems. We calculated sort times for SFPE samples collected from a coastal tropical stream and an estuary and used multiple linear regression analysis to quantify the relationship between sample sort time and number of specimens, average body length of specimens, and dry weight of sample residue. The average amount of time required to sort very small samples was 69.3min, while moderate samples averaged 85.6min and large samples averaged 153.5min. However, on average, small samples were nine times more time consuming per specimen than large samples. Additionally, dry weight of small-sized residue and the number of specimens contributed significantly to sort time. Therefore, we recommend collecting larger samples, which can be achieved by sampling for 20min over 200-m reaches for stream sites and 500- to 1,000-m reaches for riverine and estuarine sites. Also, we suggest collecting during periods of low wave action and disturbance by boat wake to reduce the amount of sample residue. This research will enhance project planning and budgeting of future studies using the SFPE method to monitor coastal tropical aquatic systems.

The Effect of Climate on the Chemical Composition of the Coral Reefs around Kubbar Island—Kuwait

Thick recent carbonate sediments cover all the intertidal and subtidal zones consist of mainly different shell and coral reef debris. The chemical investigations of the coral fragments were done on controlled bases, which depend on the coral size and seasons, in order to elucidate the effect of weather parameters on the coral reefs. Geochemical investigation indicated that corals gathered from high-tide mark are mainly contaminated by copper, cobalt, and chromium and the corals gathered from low-tide mark are contaminated by lead and zinc. All the analyzed coral samples are contaminated by copper. The major contamination sights by heavy metals are related to the weather pattern around the islands. Calcium concentration in all the corals indicates a low-Magnesium calcite or aragonite composition, except for some coral samples which were gathered during October from the high-tide mark. Trace element concentration levels show high concentrations at sights of low-wave action around the island during the various seasons. Chemical analysis on the coral derbies indicates compositional variations regarding calcium and magnesium mole% between the seasons and at different locations and it is dependant on wind direction and water salinity. Some localities are iron rich others are aluminum and potassium rich. Generally, aluminum, iron, and potassium occur in lower quantities than the other elements. Therefore, all the chemical data regarding trace elements indicate relationship to weather and environmental parameters.

Differential reproductive investment, attachment strength and mortality of invasive and indigenous mussels across heterogeneous environments

Environmental heterogeneity challenges both indigenous species and invaders and can play a defining role in the dynamics of their interactions. We compare bay and open coast habitats to show how environmental heterogeneity and seasonality affect survival and physiological performances of invasive (Mytilus galloprovincialis) and indigenous (Perna perna) intertidal mussels. P. perna had significantly higher attachment strength than M. galloprovincialis. Attachment was strongly correlated with hydrodynamic stress and was lower for both species in bays. Both species had a major spawning event when wave action was weakest. In bays, there was no correlation between gonad index (GI) and attachment strength for either species, but on the open coast GI was negatively correlated with attachment. In bays, maximum GI of M. galloprovincialis was 64% higher than for P. perna, while on the open coast values did not differ between the two. Thus, on the open coast, both species invest more energy in attachment but P. perna can accommodate energetic demands of increased byssal production without altering gonad production, while M. galloprovincialis cannot. Mortality was significantly correlated to sand stress, while the correlation with wave action was very weak in bays and non-significant on the open coast probably because sand stress peaked during periods of low wave action. The success of the invader and thus the outcomes of its interaction with the indigenous species are governed by habitat-to-habitat variability. In this case the invasive species is likely to prove a weaker competitor on the more stressful and energetically demanding open coast.

Organismal defenses versus environmentally mediated protection from herbivores: Unraveling the puzzling case of Desmarestia viridis (Phaeophyta)

The role of anti-herbivore organismal defenses in algae–herbivore interaction is frequently investigated without taking into account the potential role of environmental factors in mediating the interaction. Here we reexamine the interaction between the highly acidic, brown alga Desmarestia viridis and the green sea urchin, Strongylocentrotus droebachiensis, by incorporating a previously overlooked facet, the effect of changes in the wave environment on the ability of the urchin to establish contact with the alga. Factorial experiments in a wave tank (presence versus absence of waves; real versus mimic algae) showed that the aggregation of urchins on D. viridis was more than 2-fold greater in the absence than in the presence of waves. Similar numbers of urchins made contact with natural and mimic D. viridis plants, both with and without waves, indicating that any external release of chemicals (acid) from the alga had no perceptible repulsive effect on the urchin. The ability of the urchins to climb onto D. viridis increased markedly when urchin density attained a critical level. These results were consistent with field observations that urchins readily attack D. viridis under conditions of low wave action but do not under conditions of moderate wave action. We conclude (1) that the chemical makeup of D. viridis alone is neither necessary nor sufficient to limit contacts by the urchins and that (2) wave action is a major factor explaining the survival of D. viridis on urchin barrens, because waves limit the movements of the urchins towards the alga. We recommend that studies addressing marine algal defenses against herbivores be more comprehensive and examine interactions between algal traits, the physical environment, and the abundance and behavioral repertoire of herbivores.

Changes in octocoral communities and benthic cover along a water quality gradient in the reefs of Hong Kong

Cover of the main reef benthic groups, and abundances and taxonomic richness of octocorals were surveyed in the reefs of Hong Kong, and related to spatial and water quality gradients. Nutrient and particle concentrations are high throughout the area, with concentrations declining from the south towards the north-eastern region. Regression tree analyses showed that hard coral cover was most strongly related to water clarity, that macroalgal cover was highest in areas with high wave action and high water clarity, and that crustose coralline algae were negatively related to sedimentation. Octocoral communities (42 species in 23 genera) were dominated by zooxanthellae-free taxa; those few species with zooxanthellae were restricted to reefs with low wave action and high water clarity in the north-eastern region. The water quality gradient spans from conditions that are marginal for zooxanthellate octocorals while still supporting diverse scleractinian communities, towards an estuarine endpoint where zooxanthellate octocorals cease to exist and hard coral communities are reduced to a few resilient colonies. The data suggest that the types, abundances and richness of zooxanthellate octocorals, and the shift from zooxanthellate to azooxanthellate octocoral communities, may act as useful indicators of water clarity in regions where long-term water quality data are unavailable.

Sediment distribution pattern in the Rias Baixas (NW Spain): main facies and hydrodynamic dependence

The analysis of over seven hundred samples of sediments have made it possible to define a detailed distribution of seabed surface sediment properties like grain size, carbonate and organic matter content of the rías of Vigo, Pontevedra and Arousa (NW Spain). Furthermore, the comparison of these three rías allows establishing a general facies distribution pattern for a ría and interpreting the hydrodynamic processes, characterized the marine and fluvial prevalence. In a simplified way, three main facies domains are characterized that delimit the area of influence of the different hydrodynamical phenomena: (a) siliciclastic sand with gravel, mainly associated with the river mouths, areas of important fluvial influence; (b) siliciclastic mud with high organic matter content, located in the inner and in the deeper areas of the rías, reflecting low wave action; and (c) biogenic sands with low organic matter content located at the margins of the external ría, where the presence of gravel may occasionally occur associated to the more wave exposed areas. The wide range of wave energy conditions along the rías determines a distinct pattern distribution of facies. Moreover, the comparison of the granulometric characteristics between sediment samples of a ría and a estuary shows that the former is a more energetic sedimentary environment.

Effects of the benthic cyanobacterium Lyngbya majuscula on larval recruitment of the reef corals Acropora surculosa and Pocillopora damicornis

Coral reef degradation resulting from a multitude of stressors is occurring on a global scale (Hoegh-Guldberg 1999; Hughes et al. 2003). The outcome of reef degradation is often a decrease in live coral, followed by the proliferation of algae (termed a phase shift) (Hughes 1994; McCook 1999). Successful coral recruitment is critical to the regeneration of reefs, and recruitment failuremay be a major reason that reefs are not recovering from phase shifts (Hughes and Connell 1999; Hughes and Tanner 2000). When reefs become dominated by macroalgae, larval access to suitable settling habitat is decreased (McCook et al. 2001), and sediments trapped within algal turfs may reduce survival of coral spat (Sato 1985). Rates of coral recruitment are inversely correlated to algal biomass (Birkeland 1977; Rogers et al. 1984). Interactions between benthic cyanobacteria and corals have not been examined experimentally to date, but recent studies have documented cyanobacterial blooms on coral reefs in Guam (Nagle and Paul 1998; Thacker and Paul 2001), atoll islands across Micronesia and the Northwest Hawaiian Islands (especially near iron shipwrecks, J. Maragos, personal communication), and off Broward county, Florida (authors’ personal observations). Also, cyanobacteria are often dominant in the turfs that first colonize dead coral skeleton after mortality caused by coral bleaching (Diaz-Pulido and McCook 2002). The environmental factors that contribute to cyanobacterial bloom formation in the benthic marine environment have not been definitively identified, but low wave action (Thacker and Paul 2001), phosphate levels (Kuffner and Paul 2001), and iron bioavailability (J. Maragos, personal communication) may be worth examining in the field. There could be other mechanisms for reductions in coral recruitment rates besides the preemption of space by weedy primary producers. Many benthic species of algae (Hay et al. 1987; Schmitt et al. 1995) and cyanobacteria (Nagle and Paul 1998; 1999; Pennings et al. 1997) produce toxic secondary metabolites that act as anti-herbivory and anti-fouling agents (see Paul et al. 2001 for review). Lyngbya majuscula, in particular, has been shown to produce three bioactive compounds (malyngolide, malyngamide A and malyngamide B) that deter feeding in juvenile parrotfishes (Thacker et al. 1997). Given the generalized toxicity and multi-function nature of many secondary metabolites produced by marine algae and cyanobacteria (Paul et al. 2001), it would not be surprising if these or other chemicals perform allelopathic roles as well. In this study we examine the effects of Lyngbya majuscula on the larvae of two species of corals, Acropora surculosa (broadcast spawner) and Pocillopora damicornis (brooder), to test whether the presence of Lyngbya majuscula has a negative effect on coral larval survival or recruitment beyond levels that would be expected due to space preemption.

北海道忍路湾におけるキタムラサキウニの摂食活動の季節変化

Bimonthly observations of feeding activity of the sea urchin Strongylocentrotus nudus transplanted from coralline flats were carried out between September 1989 through July 1990 by providing the kelp Laminaria religiosa in Oshoro Bay, the Sea of Japan coast of Kokkaido, Japan.Feeding activity of the sea urchins varied chiefly with their annual reproductive cycle. Feeding activity was high in May when their gonads were in the growing stage, while feeding activity was low in September when gonads were in the pre-mature. The sea urchins could not feed in winter due to low temperature (ca. 5°C) and high wave action. It was suggested that the sea urchins on coralline flats should be transplanted to calm inlets before June and provided with the kelps as a diet in order to promote the growth of their gonads in short-period.

Selection on life-history traits across a wave exposure gradient in the tidepool copepod Tigriopus californicus (Baker)

Marine intertidal organisms inhabiting different wave exposure regimes can face different abiotic conditions and selection regimes. In this paper, salinity and temperature conditions for the tidepool habitat of the marine copepod Tigriopus californicus (Baker) are described across a wave exposure gradient, and the selective impact of salinity on life-history traits is inferred from laboratory and field studies. I found that desiccation and osmotic stress in the tidepool habitat of T. californicus were higher at an outer coast compared to a protected site in California. In the outer coast area with high wave action, tidepool salinity varied spatially, fluctuated temporally, and was at least two times greater than seawater salinity on average; tidepools frequently dried completely. Conversely, tidepool salinity in the protected area with low wave action was moderate and did not vary spatially or temporally. Culturing females at different salinities and temperatures suggested that there is a trade-off between osmoregulatory maintenance and growth or reproduction. At high salinity age of first reproduction and interclutch interval increased, and reproductive rate decreased. Extreme salinity produced age-specific mortality in the laboratory, where juveniles suffered significantly greater mortality than adults in salinity stress experiments. Hypersaline conditions in seven natural tidepool populations were associated with a decrease in the proportion of the population composed of juveniles, and an increase in the proportion of adult females, suggesting that juveniles experienced higher mortality. Unlike previous studies of benthic organisms outside tidepools, I found that higher osmotic and desiccation stress occurred in T. californicus tidepool habitats in areas exposed to high wave energy, not in protected areas. The effects of abiotic conditions on life history traits and age-specific mortality suggest the selection exists for local adaptation to different wave exposure regimes.

Effects of wave energy, topographic relief and sediment transport on the distribution of shallow-water gorgonians of Puerto Rico

Environmental factors controlling the distribution of shallow-water gorgonians of Puerto Rico were inferred from a Reciprocal Averaging ordination analysis. The data set included several samples taken before and after the passage of Hurricane David and the mass mortality of the sea urchin Diadema antillarum. We could infer only a single environmental gradient associated with the distribution of gorgonians. Stations at opposite extremes of this gradient were characterized by combinations of high wave action with low topographic relief, or low wave action with high topographic relief. This gradient was also associated with sediment transport across the bottom (bedload). A detailed examination of ordination results in relation to Hurricane David and the Diadema mortality indicated that sediment transport, rather than water movement and topographic relief, is more directly related to the distribution of shallow-water gorgonians.

Coastal hydrodynamics, geomorphology and sedimentary environments of two major Javanese river deltas. Program and preliminary results from the Snellius-II expedition (Indonesia)

River outflow, sediment transport, depositional processes and facies, as well as delta morphology of the rivers Solo and Porong (East Java, Indonesia) have been studied in detail during the Indonesian-Dutch Snellius II expedition (1984–1985). The humid tropical climate of Java in combination with the mountainous relief and the presence of easily erodible volcanic soils in relation to an intensive agriculture, results in a tremendous soil erosion and denudation rates are extremely high. Since river flow in the dry season is strongly reduced, sediment transport is mainly restricted to the wet season. Every wet season large volumes of sediment are carried towards the sea and the surplus of sediment in the coastal zone has resulted in the formation of two major river deltas. The Solo delta, a single-delta, is made up of one straight major channel with only few and small natural crevasses. Prominent natural levees are present; a consequence of the fact that in the wet season maximum outflow of the river coincides with high water. The development of this delta is considered to be a direct response to the high outflow velocities of the river, the huge mudload in the wet season and the low current and wave action. The Porong delta is a half-circular, lobate delta with a multidistributary network of channels which resulted in a regular distribution of sediment. A small part of the delivered sediments in both deltas escapes to sea and is seized by offshore, monsoon-induced coastal currents. The monsoon-type climate has a significant influence on depositional processes by determining river regime and sediment transport, by modifying river outflow and generating a coastal drift of water and suspended sediments.

Depositional environment and facies relationships of the Cretaceous ironstone of the Agbaja Plateau, Nigeria

The Maastrichtian oolitic ironstone examined caps the mesas of the Agbaja Plateau, which covers an area approximately 150 km 2 and is situated NW of Lokoja, near the confluence of the Benue and Niger rivers, in the Cretaceous Middle Niger Basin of Nigeria. This basin is one of six depositional (Mesozoic to Recent) basins in Nigeria and is a shallow trough filled with Campanian to Maastrichtian, marine to fluviatile strata on the Pre-Cambrian basement. Four major lithofacies of ironstone may be discerned on the basis of semi-quantitative X-ray diffraction analyses of borehole samples. These are from oxidized to more dehydrated and reduced conditions: (1) goethite + kaolinite; (2) hematite + geothite + kaolinite; (3) maghemite/magnetite + goethite + kaolinite; (4) siderite + magnetite + kaolinite. The maghemite/magnetite + geothite + kaolinite facies is dominant. The ironstone was deposited during a major transgression. It overlies either a carbonaceous mudstone/shale or clay/sandstone, which is underlain by a fluviatile sandstone. Primary oxidized ironstone minerals were formed in nearshore fluviatile environment, and transported into deeper water. Through re-working and diagenesis, ironstone deposition continued under estuarine and reducing conditions with evidence of low energy wave action at the top of the ironstone.

Tactics of Acclimation: Morphological Changes of Sponges in an Unpredictable Environment

Reciprocal transplants of genetically identical fragments of intertidal sponges between environments of high and low wave action exhibit great variability in the timing of their responses to environmental change. Sponges quickly begin production of stiffer and stronger tissues in high wave energy environments but delay formation of new, weak tissues in calm habitats. This may be due to the risks of forming wave-intolerant tissue in a temporally variable, unpredictable environment. These results suggest that the evolution of acclimatory control is linked to environmental predictability and concomitantly to risks of acclimatory errors.

Beach changes on a monsoon coast, Peninsular Malaysia

The northeast monsoon (November-February) has a greater impact than the southwest monsoon (May-August) on the east coast of Peninsular Malaysia. Beach changes from the southwest monsoon to the northeast monsoon are abrupt, compared to the gradual recovery of the beach from the northeast monsoon to the southwest monsoon. Although its impact varies yearly, the northeast monsoon leaves behind a beach in which the backshore and the upper foreshore are relatively undisturbed by low wave action in the succeeding monsoon until the onset of the next northeast monsoon. The impact of the northeast monsoon on the beaches is essentially erosional; the foreshore and backshore are cut back, ridges are flattened and the beach profile is smoothed out. In contrast, the beaches are accretional during the southwest monsoon; accretion takes place on the foreshore and decreases in intensity landward. Ridges, bars, berms and cuspate features are more common during the southwest monsoon than during the northeast monsoon. Foreshores with sand less than 0.5 mm diameter tend to build a relatively steeper gradient in the southwest monsoon than in the northeast monsoon; foreshores with sand more than 0.5 mm diameter are unable to build a relatively steeper gradient in the southwest monsoon and in fact have a slightly lower gradient in the southwest monsoon. Beach cusps of the northeast monsoon are found at a higher level on the beach and are spaced 24.38-30.48 metres (80-100 feet); they remain in a degraded form and are succeeded in the southwest monsoon by another series at a lower level on the beach with spacings at 15.24-18.29 metres (50-60 feet). The ridge and runnel topography is more common in the southwest monsoon than in the northeast monsoon. For beaches with such topography in both monsoons, the ridges and runnels are more pronounced and of a higher amplitude in the southwest monsoon than in the northeast monsoon. Under constructive wave action, the ridges migrate upbeach and eventually merge with the upper foreshore or the berms. Where there is an abundant supply of fine sand, the ridge topography is further enhanced by aeolian action. Beach vegetation also helps to maintain the height and configuration of the ridges. The alternation of 'cut' during the northeast monsoon and 'fill' during the southwest monsoon in an area of active ridge formation will eventually produce a successive series of parallel ridges. The monsoons also affect the direction and magnitude of the littoral transport. The nearshore topography acts as a reservoir for material removed from the beaches during the northeast monsoon and a source of migratory forms moving landward and upbeach during the southwest monsoon.