Biomineralization markers during early shell formation in the European abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>, Linnaeus

Larval shell formation was investigated in the European abalone Haliotis tuberculata. Stages of mineralization as well as enzymatic and endocrine biomarkers were monitored throughout larval development, from hatching to post-larval stages. Polarized light microscopy and infrared spectroscopy analyses revealed the presence of crystallized calcium carbonate arranged in aragonite polymorphs from the late trochophore stage. A correlation between the main steps of shell formation and enzymatic activities of alkaline phosphatase and carbonic anhydrase was seen. The variations of these biologic activities were related to the onset of mineralization, the rapid shell growth, and the switch from larval to juvenile shell following metamorphosis. Furthermore, a strong increase in the level of calcitonin gene-related molecules was measured in post-larvae, suggesting that endocrine control takes place after metamorphosis. The changes measured for the three biomineralization markers together with mineralogical analysis allowed us to correlate physiologic mechanisms with early steps of abalone shell formation.     

Post-larval development of the common north-west European brittle stars Ophiura ophiura,O. albida and Acrocnida brachiata (Echinodermata: Ophiuroidea)

The post-larval skeletal plate ontogeny of the ophiuroids Ophiura ophiura (Linnaeus) and Acrocnida brachiata (Montagu) from the recently metamorphosed 0.3 mm disc diameter size to a juvenile size of 2.0 mm disc diameter has been examined using scanning electron microscopy. Post-larval development of O. albida Forbes is briefly described for sizes between 1.0 and 2.0 mm disc diameter. Early post-larval development in the 0.2 to 1.0 mm discsize range involves considerable morphogenetic change and necessitates the use of a developmental series in the identification of newly settled ophiuroids. Comparison of these ophiuroids with other closely related species reveals that the post-larvae are readily distinguishable at even the smallest sizes by their transient post-larval morphologies. Abbreviated larval development in A. brachiata is suggested from the egg size and post-larval form. The ophiuroid post-larvae were collected from the shallow sublittoral of Oxwich Bay, Bristol Channel, UK, during the years 1980 to 1982.     

Giant larvae: Prolonged planktonic larval phase in the asteroidLuidia sarsi

The bipinnaria larva of the shelf-dwelling asteroidLuidia sarsi Duben and Koren, 1845, can attain (exceptionally) a length of 35 mm; metamorphosis to the adult benthic phase usually occurs well before this size is reached. A seastar rudiment develops at the oral end of the bipinnaria and, under normal circumstances, it detaches itself from its larval body before reaching a diameter of 5 mm. Midwater trawl samples taken from the surface to 1650 m in the Porcupine Seabight during 1978 and 1979, however, includedL. sarsi larvae with post-larval rudiments of 15 mm diameter and greater. It is shown that the bipinnariae and attached post-larvae both continued to grow until a point was reached when it appeared that the young sea-star could no longer be sustained by the bipinnaria. There is evidence that the largest post-larvae had absorbed the bipinnaria tissue and this, it is concluded, is the final stage before enforced settlement. From the estimated growth rate it is likely that many specimens had been in the plankton for >1 yr, giving this species a capability for long-distance dispersal.     

Temporal patterns of settlement, recruitment and post-settlement losses in a rocky reef fish assemblage in the South-Western Mediterranean Sea

Post-settlement events can significantly alter the density distribution of settlers and subsequently the adult population structure. The temporal and inter-annual variability of settlement and the effects of mortality on recruitment were investigated across 2 years in the vicinities of Cabo de Palos–Islas Hormigas Marine Reserve by visual census and light trap sampling. Settlement was seasonal with greater species richness and abundance in summer. Although temporal synchronization was observed between larval supply and settlement, densities of settlers could not be predicted from post-larval abundances. Timing of settlement was consistent between years but with high inter-annual variation in abundance. High mortality (~80 %) and general decoupling between post-larval and settlement stages suggest that early mortality is driving such patterns. Nevertheless, indications of habitat-mediated mortality were found for benthic species such as Symphodus and Diplodus, highlighting the importance of habitat in shaping population demography.     

Larval period and its influence on post-larval life history: comparison of lecithotrophy and facultative planktotrophy in the aeolid nudibranch Phestilla sibogae

The variable duration of the pelagic phase of metamorphically competent larvae of benthic marine invertebrates is set by an interaction between environmental factors and larval traits that together influence the chance that a larva will encounter and respond to a suitable settlement site. In the Hawaiian aeolid nudibranch Phestilla sibogae Bergh, an extended competent larval phase resulted in a cascade of negative effects on larval and post-larval life-history traits. When raised as fed (i.e., facultatively planktotrophic) larvae, an extended larval period resulted in lower larval survival, slightly lower metamorphic success, and delayed reproduction. When raised as unfed (i.e., lecithotrophic) larvae, an extended larval period resulted in lower larval and post-larval weights, survival, metamorphic success, and reproductive output, and also resulted in a longer juvenile period and delayed reproduction. The chance nature of locating a settlement site generally spreads these negative effects over all larvae of a cohort, and so balances the relative fitness of the genetic lineages within a population.     

Population structure of the Spanish sardine Sardinella aurita: natural morphological variation in a genetically homogeneous population

The importance of larval dispersal in determining the distribution and abundance of benthic marine organisms is well recognized; however, the contribution of post-larval dispersal has not been measured. I compared the dispersal of swimming larvae with that of rafting colonies in a population of compound ascidians, Botrylloides sp., living attached to leaves of the eelgrass Zostera marina in Tomales Bay, California, USA in 1990–1992. Colonies rafting on broken eelgrass traveled over 200 times farther and had comparable recruitment success relative to swimming larvae. The recruitment of rafting colonies into new habitats was facilitated by the ability of thesecolonial animals to grow asexually onto surrounding substrata. Rafting colonies brooded larvae that were subsequently relased after the colony settled into a new habitat. These results suggest that colonization of new habitats can occur by post-larvae as well as larvae, and that long-range dispersal by species with short-lived larvae may occur by post-larval rafting.     

Influence of substratum heterogeneity and settled barnacle density on the settlement of cypris larvae

On the Atlantic coast of Canada, Semibalanus balanoides (L.) is widely distributed in the mid-intertidal zone, whereas in the Gulf of St. Lawrence, this species is mostly limited to crevices. We tested the hypothesis of regional differences in microhabitat selection by barnacle larvae at settlement in 1984 and 1985 at St. Andrews, New Brunswick, Canada. Since larvae settle in microhabitats already colonized by adults, the relative influence of settled barnacle density and of different scales of substratum heterogeneity on settlement were evaluated experimentally at Capucins, Québec, (Gulf of St. Lawrence) and at St. Andrews, New Brunswick (Atlantic coast). On a large scale (>10 cm deep crevices) of heterogeneity, results show that, in the Gulf, cypris larvae settled nearly exclusively (93%) in natural crevices rather than on adjacent horizontal surfaces. On the Atlantic coast, settlement was more important outside than inside of crevices, when the substrata were either natural or artificial. This result is unique and contrasts sharply with all known reports on barnacle settlement in relation to surface contour. The influence of barnacle density on settlement was greater than that of large scale heterogeneity. On a small scale (<1.5 cm deep cracks), the presence of conspecifics had a stronger effect on settlement than heterogeneity in both regions. Field observations showed a relationship between larval settlement density and percentage of adult cover. Settlement increased up to 22 or 30% (Gulf and Atlantic coast) of adult cover and decreased afterwards. The results confirm the hypothesis of larval selection for cryptic habitats in the Gulf and the opposite behaviour (preferences for horizontal surfaces) on the Atlantic coast. This microhabitat selection is apparent at large scales of heterogeneity, whereas at small scales, the presence of conspecifics is the predominant factor.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis

The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s^-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.     

Circadian shelter occupancy patterns and predator–prey interactions of juvenile Caribbean spiny lobsters in a reef lagoon

The spiny lobster, Panulirus argus, is predominantly nocturnal, remaining inside shelters during the day and foraging outside at night, presumably to minimize predation risk. Predation risk generally decreases with increasing lobster size. Therefore, this study examined the hypothesis that size would influence this basic circadian pattern. Video cameras continuously recorded the shelter occupancy of juvenile lobsters (n = 72) having a carapace length (CL) of 30–62 mm that were tethered to shelters in a shallow reef lagoon. The lobsters’ shelter occupancy was 100% during the day, but declined linearly from shortly before sunset to a minimum of 50% shortly after midnight and then increased linearly, reaching 100% by 1 h after sunrise. The percent time the lobsters spent in the shelters followed a similar trend, but there was wide variability at night (0–100%) for individual lobsters. Lobsters left their shelters 2–30 times night⁻¹, with a majority of excursions lasting <10 min. These results suggest that juvenile P. argus minimize predation risk by remaining in their shelters as long as possible but offset the energetic cost of this behavior by foraging close to their shelters for several short periods at night. This emergence pattern contrasts with those of early benthic phase lobsters (<15 mm CL), which seldom leave their shelters, and adults (>80 mm CL), which have a dusk/early evening peak in activity and leave the shelter for extended periods of time during the night. Furthermore, a minimum shelter occupancy in the middle of the night appears especially well adapted to avoid exposure to daytime predators. Videotaped observations also included interactions between lobsters and two dominant lobster predators, the triggerfish, Balistes capriscus, and the octopus Octopus cf. vulgaris. Lobsters responded differently to these predators: remaining in the shelter when attacked by a triggerfish and fleeing the shelter when attacked by an octopus. Triggerfish were nearly twice as likely to attack a lobster that was outside of the shelter than inside. Once under attack, however, a lobster had nearly the same chance of surviving if it was inside or outside. Results suggest that the patterns of shelter use and emergence change as lobsters grow, probably reflecting the interplay between perception of predation risk and the need to forage. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Life history strategy of a southern European population of brown shrimp (Crangon crangon L.): evidence for latitudinal changes in growth phenology and population dynamics

This study provides a comprehensive examination of the life cycle dynamics of the brown shrimp (Crangon crangon L.) in the Mondego estuary, Portugal, a habitat located near the southern edge of the range of this species in European waters. The phenology of all life stages was documented (from the occurrence of ovigerous females, developing embryos, planktonic larvae and benthic post-larvae), and migration patterns of larvae into and out of the estuary were examined. Temperature-dependent functions of egg and larval development were combined with data on field abundance to predict the timing and magnitude of occurrence of larvae and recruits. Compared to brown shrimp at higher latitudes, southern conspecifics grow slower, mature earlier and have smaller brood sizes, and larvae have a more protracted settlement period. The Mondego estuary, besides acting as nursery area, is a dynamic platform for C. crangon to use in different stages, sizes and seasons.     

Reproductive biology and early life history of the hermaphroditic feather star Dorometra sesokonis (Echinodermata: Crinoidea)

Reproduction and larval/post-larval development of the one of the smallest known comatulid Dorometra sesokonis were studied on the coral reefs of Sesoko-jima Island, Okinawa, Japan. Breeding individuals were found every month from May 2003 to April 2004 indicating continuous reproduction. Individuals possessed both mature ovaries and testes, and were therefore characterized as simultaneous hermaphrodites. This species was observed to be an external brooder in which the embryos developed on the surface of parental genital pinnules until the doliolaria larval stage, and subsequently released doliolariae settled on substrata within 4 days after hatching. Larvae then metamorphosed into the post-larval cystidean stage, which lasted for more than a month. The reproductive features of this species are unique among crinoids, and, together with juvenile morphological features observed in adults, can be interpreted as adaptations to their cryptic habitat, which is subject to frequent natural disturbances.     

The induction of larval settlement and metamorphosis of two sea urchins,Pseudocentrotus depressus and Anthocidaris crassispina,by free fatty acids extracted from the coralline red alga Corallina pilulifera

Lipophilic inducers of larval settlement and metamorphosis of Pseudocentrotus depressus and Anthocidaris crassispina, two commercially important sea urchin species in Japan, were isolated from the foliose coralline red alga Corallina pilulifera (collected in 1990 near Saga, Japan) and identified. Larval assays of the fractions obtained by silica gel column chromatography of the total lipids showed that non-polar groups of lipids were effective at inducing larval settlement and metamorphosis. The effective fractions were further subjected to gel filtration (Sephadex LH-20) and also to silica gel column chromatography, and the effective components isolated as single spots by thin-layer chromatography. The components at a concentration of ca. 0.4 mg paper^-1 (sample was adsorbed on a paper with 20 cm²) induced high rates of larval settlement of both P. depressus and A. crassispina. Chemical analyses of the components revealed a mixture of free fatty acids (FFAs), dominated by eicosapentaenoic acid (20:5, 41 to 50%), palmitic acid (16:0, 11 to 17%), arachidonic acid (20:4, 9 to 15%), and palmitoleic acid (16:1, 4 to 5%). In assays with the four standard FFAs, only 20:4 and 20:5 induced larval settlement and metamorphosis of the two species, while 16:0 and 16:1 were ineffective. The larvae underwent significant rates of settlement and metamorphosis in response to the two former FFAs at levels as low as 0.18 mg paper^-1. Amongst the free fatty acid components of the alga, 20:5 was isolated as the chemical inducer of larval settlement and metamorphosis of the sea urchins in the laboratory.     

Preliminary rearing experiments on the larvae of Sergestes lucens (Penaedia,Natantia, Decapoda)

Sergestes lucens Hansen, a mesopelagic shrimp fished commercially in Suruga Bay, Japan, was successfully reared from egg to post-larval stage V under laboratory conditions. Chaetoceros ceratosporum and Artemia nauplii were found to be satisfactory food in the laboratory during rearing. Growth, mortality, food preference, and feeding and swimming activities during the various developmental stages were investigated. Temperature changes greatly affected the speed of development and the mortality of the larvae. The optimum temperature range for larval development was 18° to 25°C. The growth rate (length) of larval stages was as rapid as 0.16mm/ day at 20 °C and 0.21 mm/day at 23 °C. The larvae first started feeding on phytoplankton at elaphocaris stage I, and then gradually became predators in the post-larval stages. It is suggested that the critical period for the species occurs in the elaphocaris stages. Environmental data, vertical distribution of the species, and data obtained from laboratory experiments suggest that the fluctuation in the abundance of S. lucens is greatly influenced by the water temperature at around 50 m from June to August. Feeding mechanisms observed in the post-larval stages are described.     

Light responses of the larva of the serpulid polychaeteGaleolaria caespitosa

AdultGaleolaria caespitosa were collected at Cape Banks and Balmoral Bay, both in the vicinity of Sydney, Australia, from October 1985 to February 1986. Planktotrophic larvae of this serpulid polychaete are negatively phototactic at irradiance levels between 10 and 2 000x10¹⁴ q cm^-2 s^-1. The effective spectral range lies below 530 nm. Early metatrochophore larvae are less strongly photonegative; later they become photopositive. The photopositive phase persists into the actively swimming 3-setiger stage. Older setigerous larvae are photoneutral, demersal and positively thigmotactic. The strength of the photonegative response is not affected by the level of irradiance. The photopositive response is weaker at low levels of irradiance. The photonegative behaviour of young larvae may keep them at an optimal level for feeding. The subsequent photopositive phase may increase chances of being washed ashore and the terminal, photoneutral, thigmotactic phase may be important in the selection of a suitable site for settlement. Comparisons are made with light responses of two other serpulid species. Larval responses to light may be important infitness, especially in relation to successful niche occupation by adults.     

Settlement patterns of newly settled plaice (Pleuronectes platessa) in a non-tidal Swedish fjord in relation to larval supply and benthic predators

In demersal fish species with a pelagic larval stage, settlement patterns may be a consequence of variations in larval supply, habitat selection at settlement, and processes acting between the time of settlement and the time of benthic sampling. This study describes temporal (1994-1998) and spatial variation in plaice (Pleuronectes platessa L.) settlement densities in four semi-isolated nursery areas with similar habitat characteristics, in the non-tidal Gullmarsfjord on the west coast of Sweden. Juvenile abundance varied by a factor of ten, both among years and among nursery grounds. For the 3 years when larval sampling was undertaken (1994-1996) and all nursery areas, there was a significant positive relationship between larval supply and juvenile abundance (linear regression: r²=0.45, n=24, P<0.001). On the southern side of the fjord, a significant positive relationship between larval and juvenile abundance was found in one area (r²=0.62, n=6, P<0.05). The absolute mortality rate of plaice after settlement was related to the initial settlement density (r²=0.95, n=20, P<0.001), and to the abundance of predatory shrimps Crangon crangon (r²=0.44, n=20, P<0.01). Plaice otoliths were found in 6% of the shrimp stomachs analysed from an area with high density (13.3 m^-2) of newly settled plaice. The present study suggests that the density of juvenile plaice was limited by larval supply to the nursery grounds. Consistency in the relative abundance of juveniles among nursery grounds between years also suggested that some nursery areas may be in the settlement shadow of others. The irregular nature of the coastline in combination with larval depletion could thereby cause small-scale (10³-10⁴ m) variation in settlement densities of the same order of magnitude as the inter-annual variability in recruitment to individual nursery grounds.     

Seasonal variation in the diversity and abundance of pelagic larvae of Antarctic marine invertebrates

Most marine benthic macroinvertebrate species reproduce via a larval phase but attempts to explain the occurrence of different larval strategies (feeding or non-feeding, pelagic or benthic) in different habitats have been largely inconclusive. There have been very few year-round surveys of meroplankton at any latitude and in consequence fundamental data on the diversity, abundance, and timings of larval life history phases are lacking. There has been considerable debate regarding the viability of pelagic larvae in cold waters with highly seasonal primary production but there has been only one year-round study of meroplankton in the Southern Ocean, and that was outside of the Antarctic Circle. We present data from the first year-round survey of meroplankton assemblages at a location within the Antarctic Circle. We surveyed abundances of meroplanktonic larvae over 1.5 year at Rothera Point, West Antarctic Peninsula (67°34′S, 68°07′W). Larvae were collected in monthly diver-towed net samples close to the seabed at 20 and 6 m total water depths at each of three locations and were identified and counted live immediately after sampling. A total of 99 operationally defined taxonomic types representing 11 phyla were recorded but this is likely to be an underestimate of true diversity because of inherent difficulties of identification. Larvae were present in all months of the year and although planktotrophic larvae were more abundant in summer, both feeding and non-feeding types were present in all months. Comparisons of seasonal larval abundances with data from a settlement study at the same sites and from the literature show that larvae of mobile adults settle in summer regardless of developmental type, whereas sessile taxa settle in all seasons. We suggest that this is a consequence of differences in the food requirements of mobile and sessile fauna and that the availability of food for post-larval juveniles is more critical for survival than factors affecting the larval stage itself.     

Critical swimming speeds of late-stage coral reef fish larvae: variation within species,among species and between locations

The swimming abilities of larval fishes are important for their survival, potentially affecting their ability to avoid predators, obtain food and control dispersal patterns. Near settlement swimming abilities may also influence spatial and temporal patterns of recruitment. We examined Critical speed (U-crit) swimming ability in late stage larvae of 89 species of coral reef fishes from the Great Barrier Reef and the Caribbean. Coefficients of variation in U-crit calculated at the individual level were high (28.4%), and this was not explained by differences in size or condition factor of these same larvae. Among species U-crit ranged from 5.5 cm s⁻¹ to 100.8 cm s⁻¹ (mean=37.3 cm s⁻¹), with 95% of species able to swim faster than the average current speed around Lizard Island, suggesting that most species should be capable of influencing their spatial and temporal patterns of settlement. Inter-specific differences in swimming ability (at both the family and species levels) were significantly correlated with size and larval morphology. Correlations were found between swimming performance and propulsive area, fineness ratio and aspect ratio, and these morphological parameters may prove useful for predicting swimming ability in other taxa. Overall, the swimming speeds of larvae from the same families at the two locations were relatively similar, although the Lutjanidae and Acanthuridae from the Caribbean were significantly slower than those from the great barrier reef. Differences in swimming speed and body form among late stage larvae suggests that they will respond differently to factors influencing survival and transport during their pelagic phase, as well as habitat use following settlement.     

Early recognition of sediment during settlement of<Emphasis Type="Italic"> Eupolymnia nebulosa</Emphasis> (Polychaeta: Terebellidae) larvae

Analysis of the displacements and activity of larval stages of the terebellid polychaete Eupolymnia nebulosa were carried out on different sediment types collected in the Bay of Banyuls-sur-Mer (western Mediterranean). Results indicated sediment recognition by the larvae. Time devoted to exploration and settlement trials were significantly longer when sediments of similar granulometry had been previously reworked by adults. There were increased responses of settling larvae if the tentacles of adults of the same species had previously been in contact with the tested sediment. The early settlement activity was stronger at the sediment boundaries and increased in the coarse sediment. Our results suggest that larvae are able to recognize biologically bioturbed sediments and modify their behaviour accordingly. There is a larval settlement before the competent stage. Possible consequences of early settlement and the limitation of dispersal in Eupolymnia nebulosa larvae are discussed together with the results of automated measurements of early larval swimming.Communicated by S.A. Poulet, Roscoff     

Measuring settlement intensity of echinoderms on coral reefs

A pilot study was conducted at Davies Reef on the central Great Barrier Reef between 20 November 1991 and 20 January 1992 to assess the suitability of settlement collectors for measuring larval settlement rates of echinoderms on coral reefs. The collectors were deployed for two months during summer when many echinoderm species are known to spawn. A total of 657 newly settled echinoderms were recovered from just 47 collectors, each having a volume of just 0.005 m³ but with a utilisable surface area of about 1.44 m², indicating that competent-to-settle larvae were very abundant during the sampling period. Echinoids (7.8 sampler^-1) and ophiuroids (5.6 sampler^-1) were the most abundant groups on the collectors. Asteroids (0.2 sampler^-1) and crinoids (0.3 sampler^-1 were less common. The asteroids were all identified to species and included the crown-of-thorns starfish Acanthaster planci, Choriaster granulatus and Culcita novaeguineae. The newly settled echinoids could not be distinguished from each other but included Echinometra mathaei and Mespilia globulus. The abundance of each of the five different classes of echinoderms on the samplers was correlated with their abundance on the natural substratum. Significant spatial variability was found in settlement rates of echinoids over 1000s of metres and ophiuroids over 100s of metres, but not over smaller spatial scales. It is concluded that the collectors can provide a useful tool for monitoring spatial and temporal variability in settlement rates of echinoderms on coral reefs and for testing hypotheses about patterns of larval dispersal.     

Experimental investigation into the effects of suspended sediment on fertilisation, larval survival and settlement in a scleractinian coral

Laboratory and field experiments were used to determine whether high (≃100 mg l⁻¹), low (≃50 mg l⁻¹) and control (≃0 mg l⁻¹) levels of suspended sediment affected fertilisation, larval survival, and larval settlement in the scleractinian coral Acropora digitifera (Dana, 1846). Both high- and low-sediment treatments significantly decreased fertilisation, but post-fertilisation embryonic development was not inhibited by suspended sediments. Larval survival and larval settlement were significantly reduced in high- and low-sediment treatments. No difference was found between high- and low-sediment treatments in any of the three post-spawning processes investigated, suggesting that they are susceptible to sediment concentrations which are not exceptionally high even under natural conditions (>50 mg l⁻¹). The introduction of an additional stress in the form of high levels of suspended sediments coupled with naturally high variability in recruitment may have a considerable effect on the successful supply and settlement of coral larvae to a reef. Given that many coral communities are open reproductive systems, the consequences of disturbance events are not likely to be restricted to the impact area. Recruitment to a population may be reduced significantly in the presence of high levels of suspended sediments because of effects on larval survival and settlement. Recruitment of larvae to adjacent populations may also be affected due to a decreased fertilisation success and potential increases in mortality of larvae passing through the affected site. Received: 13 August 1998 / Accepted: 22 July 1999