Juveniles stick to adults: recruitment of the tube-dwelling polychaete Lanice conchilega (Pallas, 1766)

Juveniles of the tube-dwelling polychaete L. conchilega were found attached to adult tubes at an exposed beach in South Wales (U.K.). They attached to the upper part of tubes protruding above the sediment. The aim of this study was to determine the timing of juvenile settlement on to adult tubes, their abundance and size distribution, and the time of detachment and densities in the sediment after re-settlement. Furthermore, to establish whether the sediment composition of juvenile tubes differed from those of adults and the surrounding sediment. In 1998, 1999 and 2000, tubes of adult L. conchilegawere sampled and numbers of attached juveniles were quantified and their sizes measured. Densities of solitary L. conchilega in the sediment were estimated, as well as the size distribution of solitary tubes. On average, 5–13 juveniles were attached to single adult tubes in spring, but numbers varied greatly with up to 72 juveniles on a single tube in April 1998. Availability of a hard substratum and chemical cues are discussed as potential factors triggering the attachment of juveniles to adult tubes. Juveniles started to detach and re-settle in the sediment 1 month after attachment. Once settled in the sediment, juvenile numbers decreased steeply, but the size distribution of solitary L. conchilega suggested that some juveniles survived in the population. However, the extent to which numbers of juvenile recruits contribute to the density of adults remained unclear. Juveniles used a smaller mean particle size for tube building than adults, but both actively selected particles.     

The effects of chemical and visual communication, space availability, and substratum color on growth of the juvenile freshwater prawn Macrobrachium rosenbergii (De Man)

The effects of chemical and visual communication, space availability, and substratum color on the growth of juvenile Macrobrachium rosenbergii (De Man) were studied by recording the changes in average weight and length of prawns kept at controlled densities in the laboratory for periods of 6 wk of in communal and individual compartments with constant unidirectional water currents. Chemically mediated growth inhibition increased in proportion to the number of prawns ahead of a given compartment in the water current. Since ammonia and nitrite concentrations were below reported toxic values, progressive accumulation and transmission through water currents of some other chemically mediated growth inhibitor may explain the observed differences in growth rates between compartments. Growth slowed with increasing prawn density (communal areas) and with decreasing individual compartment size (individual areas). Prawns held in contiguous individual compartments, allowing visual communication, exhibited a significantly (P < 0.01) more rapid growth rate than prawns reared in visually isolated compartments. Growth rates for individuals kept on black substrates were significantly greater (P < 0.05) than those of prawns held in aquaria with white or blue substrates. When substrates composed of all three colors in alternating bands were used, prawns showed a significant preference (P < 0.01) for black backgrounds during the afternoon and for the water column during the morning. Possible implications of these findings to the intensive aquaculture of M. rosenbergii are discussed.     

Studies on the behaviour and substratum preference in juveniles of the marine prawn,Metapenaeus monoceros (Fabricius)

Circadian rhythmicity in the behaviour of the marine prawn, Metapenaeus monoceros (Fab) and its substratum preference has been observed under laboratory conditions. In the morning at 9. a.m. 80% prawns remain buried and in the afternoon at 3 p.m. 60% burrowing was observed. A contrasting situation was observed in the night i.e. 17% burrowing at 9 p.m. and 30% burrowing at 3 a.m. was registered. In the second set of experiments juveniles were subjected to four types of substrata viz. mud, black fine sand, white coarse sand and stones. It was noted that M. monoceros showed more affinity towards the mud and less preference to other substrata. The obtained results are discussed to provide clues for prawn fishing.This work was supported by I.C.A.R., New Delhi through a project on Reprod. Endocr. Edible prawns.     

Distribution,substratum preference and burrowing behaviour of Lovenia elongata (Gray) (Echinoidea: Spatangoida) in the Gulf of Elat ('Aqaba), Red Sea

Lovenia elongata (Gray), the Indo-West Pacific spatangoid, was studied in the Gulf of Elat ('Aqaba) at the northern end of the Red Sea. The occurrence and local distribution of this macrobenthic burrowing species was determined and related to the particle size distribution of the substrata in which it was found. Its habitat preference is for clean, grassless, sandy bottoms in intertidal areas (beaches and sandbars), and on sublittoral level bottoms of protected bays and lagoons sheltered from heavy wave action. The preferred sediments were found to range from medium to fine sand. The population density, size frequency distribution, growth, reproduction, recruitment, and mortality of a sublittoral population of L. elongata (at Wadi Taba, Sinai) were studied.The mode of life of this burrowing heart urchin was observed in situ and in aquaria. Its burrowing and emergence behaviour are described. Experiments were carried out on the effect of particle size on burrowing behaviour. There are significant differences in the ability of L. elongata to manipulate substrata of varying grain size. The burrowing process was found to be most rapid in natural sand of medium-fine composition, corresponding to the normal sediment of the urchin's habitat. Such sediments were also found to be suitable for successful larval settlement; juveniles did not survive in coarser sand.Differences in population density and spatial distribution between various size groups are attributed to differences in their ability to manipulate the substratum. L. elongata is found to be morphologically suited to sand, particularly medium-fine sand; however, it is restricted by its morphology to shallow burrowing, since it lacks specialized mechanisms for deeper burrowing and funnel building.     

Mineralogical composition of sediment determines the preference for smooth particles by caddisfly larvae during case construction

1. The mineralogical/petrological composition of the substratum influences aquatic organisms in several ways. However, the actual mechanisms are often unclear. Some caddisfly larvae actively concentrate smooth quartz particles in their portable cases thus producing a smooth inner surface of the case wall. 2. The particle surface‐roughness preference of Perissoneura paradoxa (Odontoceridae) McLachlan inhabiting granite areas in relation to the mineral composition and surface roughness of sediment particles was examined. 3. Field surveys revealed that quartz was consistently smoother than other minerals but that it became rougher in larger size fractions, and the relative abundance of quartz decreased in larger size fractions. Consequently, smooth particles were less abundant in larger size fractions of the sediment. When larval cases were compared with sediment, quartz was actively concentrated in smaller cases of early instar larvae but was gradually less abundant in larger cases of well‐grown larvae. Because larvae use larger particles as they grow, late instar larvae develop an unselective choice of mineral types. 4. Subsequently, we experimentally forced the larvae to choose from a mixture of equal amounts of two artificial particles that had different textures (rough and smooth). The proportion of smooth particles chosen by larvae gradually decreased as they grew larger. 5. These results indicate that the larvae varied in their degree of preference according to particle availability in the surrounding sediment, which is governed by mineral composition and weatherability. We suggest that case‐bearing caddisfly can adapt to the local sediment environments by varying their standard and/or criteria for material choice. In this study, the possible mechanism for the variation is discussed.     

Nutritional ecology of the invasive freshwater mysid Limnomysis benedeni: field data and laboratory experiments on food choice and juvenile growth

The introduction of alien species leads to changes in species composition and therefore the trophic structure. The highly invasive freshwater mysid Limnomysis benedeni is established and abundant in Lake Constance since 2006. Our aim was to confirm the assumption that L. benedeni feds on small particles and to identify their food web position. We examined the feeding mode and food preference of adult L. benedeni collected from the field and from laboratory feeding experiments by analysing their stomach contents. Stable isotope analyses (SIA) confirm an omnivorous feeding of L. benedeni. In laboratory growth experiments, we determined the growth of juveniles by feeding juveniles with different natural food sources. Growth was supported by natural biofilm, dreissenid biodeposited material and an algal suspension. Stomach analyses showed clearly that L. benedeni fed on small particles of both benthic and pelagic origin and fed by both filtering and grazing. Absence of high numbers of animal structures in the stomachs and SIA supported the lack of predatory impact in the field, but the mysid probably affects the nutrient cycles in the littoral. L. benedeni seems to play an important role in the trophic relations in Lake Constance and all other water bodies they invaded.     

Habitat selection of juvenile banana prawns, Penaeus merguiensis de Man: Testing the roles of habitat structure, predators, light phase and prawn size

The effects of fish predators, light phase, habitat structure and prawn size on the habitat preferences of juvenile Penaeus (Fenneropenaeus) merguiensis de Man were examined with laboratory experiments. The behaviour of juvenile P. merguiensis within habitats of different structural complexity was also examined. Experiments were carried out in a tank (1.8 m diameter) divided into four habitats representing: bare substratum, leaf litter (little vertical structure), mangrove pneumatophores (regular vertical structure) and mangrove woody debris (heterogeneous vertical structure). The location of 10 prawns was monitored over 270 min (135 min light and 135 min dark), with different prawns five times for each combination of prawn size class, and predator (no predator; Arius graeffei Kner and Steindachner and Lates calcarifer Bloch).In the absence of predators and during the light phase, when observations on prawn behaviour were made, swimming was the most common behaviour (of seven mutually exclusive behavioural categories) with few differences in behaviour between sizes. All size classes of juvenile P. merguiensis selected vertical structure (mangrove debris and pneumatophores) over low vertical structure (leaf litter and bare substratum), in both light and dark conditions and in the presence or absence of predators. When L. calcarifer was present, the selection by prawns of the mangrove-debris habitat increased significantly. This was attributed to an increase in predation risk in the other habitats. L. calcarifer rarely pursued prey amongst the mangrove-debris structure, compared to habitats with less heterogeneous vertical structure (pneumatophores, leaf litter and bare substratum).     

An investigation of the relationship between sediment particles size and the development of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea

The relationship between median grain size of sediments and the abundance in the wild of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea, were investigated. The impact of substratum particle size on the growth and survival of germlings was examined in the laboratory. In the wild, the average annual density of algal mats was 7,950 ind m⁻². The algal mats mainly occurred in sands and exhibited patchy distribution. Statistical analysis indicates significant spatial analysis differences and a significant relationship between density and the ratio of sands to silts, suggesting that the distribution and density of this species were related to particle size. In laboratory experiments, the survival rate of U. prolifera germlings was the lowest value (22%) on sediments with a median grain size of 63–125 μm. Laboratory experiments have generally shown a positive relationship between attachment or survival of the alga and substratum particles size. Our laboratory results indicate a clear link between germling settlement/survival and substratum particle size. These results explain the spatial differences in abundance observed in the field in relation to the distribution and ratio of sands to silt on the Muan flats.     

Use of a generalised linear model to test habitat preferences: the example of Zingel asper, an endemic endangered percid of the River Rhône

SUMMARY 1. A study of microhabitat preferences was conducted on Zingel asper , an endangered endemic species from the Rhône catchment. A generalised linear model allowed us to test statistically the non-random habitat selection and the effect of season and site on this habitat selection.
2. The analysis detected significant preferences for the three physical variables considered: water depth, water velocity and substratum size.
3. A seasonal shift in the substratum size preference was found: preference for stones increasing during the spawning season. Depth preference varied between sites, suggesting a possible plasticity in habitat selection.
4. These results suggest that the availability of suitable physical habitat plays a significant role in determining fish distribution in the River Beaume.     

Substratum preferences and planulae settling of two red sea alcyonaceans: Xenia macrospiculata Gohar and Parerythropodium fulvum fulvum (Forskl)

The settling behaviour and substratum preferences of the planulae of the Red Sea soft corals Xenia macrospiculata Gohar and Parerythropodium fulvum fulvum (Forskl) were examined in the laboratory. The planulae of the two species have a short pelagic phase and they tend to settle immediately upon leaving the parent colonies. Mucous secretion is used by the larvae for crawling and adhering to the substratum. They exhibit an aggregated pattern of settlement. The developing polyps are found in depressions or pits of the substratum. The planulae preferentially settle on rough substrata and avoid smooth surfaces. They search for substrata covered with an organic coating, composed of turf or crustose coralline algae. Such substrata create better conditions for larval settlement and metamorphosis. The planulae of P. f. fulvum exhibit a striking preference for upside-down attachment on undersides of the substrata, while Xenia macrospiculata utilizes both substratum faces for settlement. Light intensity seems insignificant in determining attachment sites. The findings of the experiments correspond well with the distributional patterns of juveniles of the two species as found in the natural environment. The specific requirements for settling of both species increase their chances of successful development and thus enhance their survival.     

Recruitment of the infaunal bivalve Soletellina alba (Lamarck, 1818) (Bivalvia: Psammobiidae) in response to different sediment types and water depths within the intermittently open Hopkins River estuary

Studies examining recruitment processes for soft-sediment macroinvertebrate fauna in intermittent estuaries are rare and most studies of active habitat selection have been tested in the laboratory rather than the field. The present field study examined whether recruitment of the infaunal bivalve Soletellina alba was influenced by water depth and sediment particle size in the intermittent Hopkins River estuary, southern Australia. The number of recruits in sediment trays differed between water depths, but active habitat selection was not evident across treatments of varying sediment particle size. The use of sediments with varying particle sizes also provided an opportunity to identify potential discontinuities in body-size distributions of recruits associated with varying habitat architecture. The length (mm) of recruits was converted to the same scale used to express sediment particle size (i.e. phi units: ? = − log₂ of sediment particle size). The size of recruits differed across water depths, but did not differ across treatments with fine (? = 3) versus coarse (? = 1) sediment, and no relationships were apparent between bivalve size and sediments consisting of varying particle size. These patterns of recruitment do not correspond with the distribution of adult S. alba within the Hopkins River estuary. Previous sampling has shown that abundances of juvenile and adult S. alba are variable across time, site and water depth, but are often greater at the deeper water depth (1.05 m below the Australian Height Datum). However, recruitment during the present study was greatest at the shallower water depth (0.05 m below AHD), and the apparent absence of active habitat selection suggests that the distribution of adults is unlikely to be attributable to differences in recruitment associated with sediments of varying particle size.     

Selectivity of Perinereis aibuhitensis (Polychaeta,Nereididae) feeding on sediment

Deposit feeding polychaetes play an important role in the acceleration of the biogeochemical processes of the sediment through bioturbation. Feeding is one of the important factors of bioturbation. However, knowledge of the feeding biology of polychaetes, especially the subsurface deposit feeder, is limited. The objective of this study is to characterize the feeding selection of Perinereis aibuhitensis with different body weights. The animals were fed with natural sediment from their original habitat in the lab. The feed intake and particle size of sediment were measured to find any evidence of feeding selection. A two-way ANOVA showed that the particle size class significantly affected the particle size frequency of the ingested and the remaining sediment (P?P?>?0.05). Bivariate correlation analysis showed that the particle size frequency of sediment, ingested and remaining sediment in different size classes were linearly related (P?P?P?P. aibuhitensis preferred smaller particles in the sediment, which was limited by the particle size distribution of the sediment in which they live. The nitrogen and organic carbon contents in the faeces might be the thresholds when P. aibuhitensis selects sediment particles as food. These results demonstrated the particle selectivity of P. aibuhitensis, and may be applicable to other subsurface deposit feeding polychaetes.     

Patterns of food and microhabitat resource use by two benthic gobiid fishes

The mechanisms responsible for different patterns of habitat use by two benthic gobiid fishes, Acentrogobius sp. 1 and A. sp. 2, which displayed identical food use but resided in shallow and deep zones of coarse and fine sediments, respectively, in Lake Hamana, Shizuoka Prefecture, Japan, were investigated by field removal and laboratory sediment-grain size selection experimentation. Following field manipulation, involving removal of both species, the distribution patterns of each were found to be similar in both control and manipulated quadrats, suggesting their differential habitat use patterns may be the outcome not of competition but of differing preferences for habitat characteristics. Results of a sediment-grain size selection experiment in the laboratory suggested a weak preference of A. sp. 2 for fine sediment, while A. sp. 1 showed no grain size preference. The observed difference in the distribution patterns between these two species, therefore, may possibly have resulted from, at least in part, a combination of differences in their preference for sediment grain size and other habitat characteristics such as water depth.     

Utilisation of a recovering wetland by a commercially important species of penaeid shrimp

Penaeid shrimp represent an important group of valuable exploited species known to either directly utilise saltmarsh habitat, or utilise saltmarsh-derived productivity. Consequently, both areal coverage and primary productivity of saltmarsh habitat has direct consequences for the productivity of these important fisheries, and they are likely to be key beneficiaries of habitat repair. This study aimed to establish quantitative estimates of abundance of School Prawn, Metapenaeus macleayi, across a recovering wetland system; Hexham wetland in the Hunter River. Six surveys were conducted across the wetland using a specialised benthic sled, and absolute abundance of School Prawn was estimated. School Prawn were consistently more abundant in certain areas of the wetland (the highest abundance site supported 1017 prawns per 100 m²), and the average density across the wetland was 244 prawns per 100 m². All areas of the wetland (except the area closest to the wetland mouth) supported the full range of size classes, and multiple cohorts of prawns moved through the system during the sampling program. The asymmetry observed in the distribution of prawns across the wetland is likely to be due to a combination of water quality and inter-specific interactions. These results show that the recovering wetland is supporting a high abundance of School Prawn. Our estimates of recruitment for School Prawn will also be useful in gauging the potential increases in fisheries productivity arising from habitat repair in this, and other systems.     

Experimental studies on the foraging behavior of the sand fiddler crab Uca pugilator (Bosc, 1802)

The purpose of this study was to test the hypothesis that foraging sand fiddler crabs. Uca pugilator (Bosc), move through the habitat in response to low substratum food levels even though these movements may take the crabs considerable distances from the safety of the burrow area. Chl a and ATP concentrations were used as measures of food density in foraged and unforaged substratum. Field and laboratory feeding experiments showed that crab foraging intensity in a habitat patch was directly correlated with food density in the patch either in the presence or absence of alternative food patches. Other experiments showed that sand fiddlers can respond to differences in food level on a scale of millimeters and do this by probing the substratum with minor chelae. Food levels in aggregations of non-ingested particles harvested by sand fiddlers, feeding pellets, correspond to low foraging intensities predicted from foraging experiments and crabs exhibit low foraging intensities on substratum patches derived from feeding pellets. Substratum food levels in two distinct areas corresponded to high predicted foraging intensities and there was no consistent trend in the level of food in the burrow vs. the nonburrow microhabitats. These results suggest that the movements of foraging sand fiddlers are to some extent controlled by the reduction in substratum food levels due to feeding during a single foraging episode. Sand fiddlers can extract over 70% of the food from harvested substratum over a broad range of substratum food densities but harvest only 42% of the available substratum.     

象山港日本对虾增殖放流的效果评价

日本对虾是中国近海重要的增殖品种,2010年象山港分两批次放流日本对虾苗种约1.67亿尾。通过对放流苗种存活状况、洄游分布、生长特性及回捕情况的跟踪调查,对象山港日本对虾的增殖效果做出初步评价。结果表明:(1)日本对虾放流苗种在8月中旬成为补充群体,集中于港区底部进行索饵育肥;9月中旬,第1、2批放流苗种的平均体长分别达到95.4 mm和71.4 mm,成活率分别约为0.79%和1.06%;10月上旬,随着港区水温降低,增殖苗种资源量锐减。(2)协方差分析表明:日本对虾增殖群体和自然群体的体长-体重关系存在显著性差异,增殖群体的体征状况明显优于自然群体。(3)日本对虾放流苗种在港区主要为桁杆拖虾和地笼网渔业所利用,在港区滞留期间,回捕率约为0.25%。总结发现:栖息地破坏及放流苗种的过早利用是制约象山港日本对虾增殖效果的重要因素,优化增殖策略、保护港区生态环境应是今后港区增殖工作的重点。     

Quantification of sediment reworking by the Asiatic clam Corbicula fluminea Müller, 1774

Active organisms modify the substratum in which they dwell. This process, called “bioturbation”, affects the way that biogeochemical fluxes are mediated at the substratum–water interface. In the frame of this work, the bioturbation potential of the Asiatic clam Corbicula fluminea was characterized and quantified. We measured the displacement of fluorescent particles by C. fluminea burying in a size-based experimental design in order to explore the effects of body-size on sediment reworking. Our results stress that C. fluminea belongs to the functional group of biodiffusors, and that C. fluminea can be considered as an intermediate sediment reworker. We suggest that bioturbation was mainly induced by the pedal-feeding activity of the clams. Results also showed that, though large clams induced displacement of particles deeper into the sediment, small clams showed the highest net sediment reworking activity. This result was in contrast to the initial hypothesis of biovolume as the main driver for particle displacement by bioturbating organisms. Life-history traits and specific features of pedal-feeding could explain the observed pattern.     

Sediment accumulation predicts the distribution of a unionid mussel (Elliptio complanata) in nearshore areas of a Canadian Shield lake

1. The importance of native freshwater mussels for ecosystem processes depends on their density, size distribution and activity. In lakes, many of the factors that affect mussels (fish hosts, habitat, food) could be directly or indirectly related to wind‐driven physical processes. 2. We tested whether the abundance and size of Elliptio complanata in the shallow, nearshore areas of a medium‐sized lake were related to site exposure, substratum type and fish distribution. To disentangle some of the correlated variables known to affect mussel distribution, we used paired exposed and sheltered sampling sites along the 7‐km fetch of the lake basin. 3. The distribution of sediment characteristics in nearshore areas was highly predictable. The mean depth of accumulated soft sediments decreased with increasing fetch at wind‐exposed sites, but increased with increasing fetch at sheltered sites. Sediments were deeper along the main shoreline than around islands. Deeper sediments tended to be finer and higher in silt content and organic fraction. 4. The density and proportion of juvenile mussels along the main shoreline varied in a unimodal way with sediment depth. These results suggest that wind‐driven physical forces affect the transport of young juveniles to sediment depositional areas and create sediment conditions that influence their growth and survival. In contrast, the proportion of juvenile mussels around islands was not related to sediment characteristics, but decreased with remoteness of the island, suggesting that the distribution of juvenile mussels may be limited by fish movements. These results are tentative since they do not include buried juvenile mussels. 5. We also found a unimodal relationship between total mussel density (juveniles and adults) and sediment depth but, in contrast to the relationship for juveniles only, it applied to all sites with soft sediments, including islands. We conclude that factors related to sediment depth affect the growth and survival of adult mussels around islands and that these factors are strong enough to modify the pattern of distribution established via dispersal during earlier life stages. 6. The mean shell length of adults at different sites within the lake basin ranged from 60 to 85 mm. Mussel shell length decreased with increasing fetch at sites exposed to the prevalent winds, but was relatively constant on the sheltered side of peninsulas and islands. The size of unionid mussels in different parts of the lake seems to be determined both by their exposure to physical forces and by sediments. 7. The local distribution of E. complanata is determined, directly and indirectly, by wind‐driven forces. These processes are likely to be important for other benthic organisms affected by similar habitat conditions (e.g. sediment characteristics, physical disturbance).     

Distribution and microhabitat associations of the juveniles of a high-value sea cucumber, <Emphasis Type="Italic">Stichopus</Emphasis> cf. <Emphasis Type="Italic">horrens,</Emphasis> in northern Philippines

There is considerable global interest in rebuilding depleted populations of sea cucumbers (Echinodermata, Holothuroidea) to address conservation and economic goals. For the vast majority of holothurian species, the habitat and food requirements of the juvenile stage are poorly understood. We investigated the distribution and microhabitat associations of juveniles of a commercially important sea cucumber, Stichopus cf. horrens, in the shallow, shoreward side of a coral reef (or backreef) in northern Philippines (16°21′38.7″N, 119°59′47.9″E). Relationships between juvenile density and the physical, chemical and biological characteristics of their habitat were examined. Potential food sources of the juveniles were also investigated using elemental and stable isotope analysis. Results showed that juveniles are more abundant in seagrass areas and the transition zone between seagrass and the rubble-dominated reef flat. A non-metric multidimensional scaling (MDS) plot indicated that juvenile density was most positively associated with coarser sand and rubble (>0.5 mm) and seagrass (Thalassia hemprichii) abundance (2D stress = 0.11). Juvenile density was also positively associated with sediment organic matter from plant detritus to a lesser extent. Elemental and isotope analysis of one site indicated that epiphytes were the primary food source of juveniles, while sediment detritus from microalgae and seagrass was a secondary food source. This study corroborates anecdotal evidence regarding the importance of seagrass to S. cf. horrens as potential refugia and source of high-quality food for its juveniles. These findings underscore the need to protect the nursery habitats of wild juveniles and provide critical information for the selection of suitable natural habitats for releasing cultured juveniles of this important species.     

Caractérisation de la production particulaire par l’oursin Echinometra mathaei sur les récifs Indo-Pacifiques : influence des peuplements coralliens et implications sur la dynamique sédimentaire

The characteristics of the sedimentary grains produced by the sea urchin Echinometra mathaei were described from two reef sites: a fringing Acropora-dominated reef at La Reunion island (Indian Ocean) and a barrier Porites-dominated reef at Moorea island (French Polynesia). The composition of the sediment produced by Echinometra was determined from SEM observations. The size and shape of the particles were measured by using image analysis method. The grain diameters range between a few micrometres and 2 mm, with a large predominance (more than 80 %) of particles smaller than 400 μm. The grain size distribution is dependent on the nature of the grazed substratum. Echinometra individuals collected at La Reunion on branching Acropora colonies produce a higher proportion of particles smaller than 200 μm compared to those collected at Moorea on massive Porites colonies. At Moorea, more grains having a diameter comprised between 200 and 500 μm are produced. The microstructure of coral substrata affects the mean particle diameter, which is 192,17 μm for a Acropora substratum and 244,69 μm for a Porites substratum. Since the sediment derived from Acropora erosion is finer, the proportion of suspended material that is exported from the reef is greater at La Reunion than at Moorea. We estimate that, for similar erosion rates and hydrodynamic conditions, the production of sands by Echinometra mathaei is higher and the retention of this erosional sediment more effective on reefs dominated by massive Porites than on Acropora-dominated reefs. This result is in accordance with the proportions of suspension-moving grains that have been previously measured on Moorea and La Reunion reefs. This study highlighted the effect of coral communities on the production of particles related to the bioerosion and on the sedimentary budget.