Early Post-settlement Mortality Research Articles

Habitat and morphological characteristics affect juvenile mortality in five coral reef damselfishes

The abundance and distribution of demersal fishes rely on larvae successfully settling from the pelagic environment to a benthic habitat and their subsequent survival. With high mortality rates during this life stage, settling to a habitat that maximizes survival is critical. However, relationships between settlement choices and subsequent survival are poorly understood and may vary among species with different habitat preferences. To test this, we focused on five congeneric (Pomacentrus) damselfish species that are known to differ in their habitat choices and explored whether habitat associations at settlement influenced survival. Newly settled individuals were tagged and monitored daily for two weeks to estimate natural mortality rates. Morphological attributes of fish and characteristics of settlement habitats, including depth, rugosity, benthic substrata, and local fish assemblages, were used to predict mortality. We found that some species displayed stronger associations with specific benthic substrata at settlement, but contrary to expectations, these selected habitat characteristics were relatively weak predictors of survivorship. Our survival analysis revealed that the best predictors of survivorship were rugosity (P. adelus and P. amboinensis) and two morphological traits, body depth and ocellus size (P. chrysurus and P. adelus). Interestingly, we found that P. moluccensis that settled in areas of high coverage of mounding coral experienced increased mortality. Of the remaining substrata, analysis showed that instead of associating with habitat characteristics enhancing survivorship, individuals tended not to associate with habitats characteristics that increased mortality (e.g., Turbinaria and sand). This study highlights the species-specific drivers of early post-settlement mortality in coral reef fishes.

Wettability and Substrate Selection in the Larval Settlement of the Solitary Ascidian Phallusia philippinensis (Phlebobranchia: Ascidiidae).

For marine benthic animals, the selection of substrate by larvae is important for their survival, with early post-settlement mortality often being affected by the microenvironment where they settle. We tested the substrate preference of the larvae of the ascidian Phallusia philippinensis toward nine commercially available substrates. In the present assay, the larvae settled on one of four substrates for seven substrate combinations with different wettabilities; we counted the number of settled larvae on each of the four substrates, and Manly's selection indices were compared to determine the preference rank of each substrate. Larvae significantly preferred more hydrophobic and oleophilic substrates to hydrophilic and oleophobic ones. While it is uncertain how the larvae detect the properties of the substrate surface, they might be able to sense the physical force, such as stickiness and repellent force. Although a hydrophobic surface is not common in a natural marine environment, the use of hydrophobic materials (as flypaper-like tools) for ascidian larvae might help to prevent the settlement of non-indigenous ascidians in aquaculture facilities.

Role of predators in the recruitment of invertebrates in a rocky subtidal community in the southwest Bay of Fundy, NB

ABSTRACTPredation is potentially an influential source of early post-settlement mortality of benthic marine invertebrates, but previous studies demonstrate conflicting results. We investigated the effect of large predators on developing subtidal invertebrate communities in cobble-filled collectors in the southwest Bay of Fundy, Canada. Two predation treatments (exclusion of predators ≥ 7 mm body width or full access for predators < 50 mm) were used to test the effect of large predators, and a partial-cage control tested for caging artefacts. Despite a reduction in the abundance and biomass of large predators, multivariate analyses indicated no effect of predator exclusion on the composition of the prey and micropredator communities. Results indicated that the largest differences were between the predator-access treatment and the other two treatments, which was potentially influenced by the caging material. There were significant but weak positive correlations between the micropredator and the other two communities. Previous studies indicate that at low predation intensity, as seemed to be the case here, other factors may play a stronger role in controlling recruit abundance. Predation control probably varies spatially and temporally, and the influence of large predators was not likely the driving force for early post-settlement mortality in the invertebrate communities measured in this study.

Predation on Bivalves on a Sandy Beach in Soma, Japan

Predation may be an important cause of early postsettlement mortality of bivalves, but little is known of in situ predation processes on bivalves by multiple predators on sandy beaches. To address this issue, bivalve shells in the guts of demersal fishes and benthic invertebrates were counted and measured monthly from April to November 2009 in Soma, Japan. For the Sakhalin surf clams Pseudocardium sachalinense and Raeta pulchella, the frequency of occurrence and number of shells in guts of predators per transect peaked around May–June, when the length of shells in guts tended to be smaller than in later months. These two indices decreased to 0 in July for P. sachalinense and to a low level in August for R. pulchella, which was associated with increasing shell length (ShL) in guts. For the bivalve Mactra crossei, both occurrence and number of shells in guts of predators per transect increased around November in some of the predators. The largest ShL of P. sachalinense in guts tended to be similar among the predators and was 1.1–1.5 mm. The largest ShL of R. pulchella and M. crossei tended to vary among the predators, and were 5.6–17.8 mm and 1.0–7.2 mm, respectively. The spiny sand sea star Luidia quinaria and red tongue sole Cynoglossus joyneri had a high frequency of occurrence and number of shells per gut per transect. These results indicate that predation on P. sachalinense and R. pulchella was most intense in the early postsettlement period of May–June in Soma, Japan. The size of the bivalve shell may have provided protection, but was dependent upon on the predator.

Individual-based simulation of the spatial and temporal dynamics of macroinvertebrate functional groups provides insights into benthic community assembly mechanisms.

The complexity and scales of the processes that shape communities of marine benthic macroinvertebrates has limited our understanding of their assembly mechanisms and the potential to make projections of their spatial and temporal dynamics. Individual-based models can shed light on community assembly mechanisms, by allowing observed spatiotemporal patterns to emerge from first principles about the modeled organisms. Previous work in the Rance estuary (Brittany, France) revealed the principal functional components of its benthic macroinvertebrate communities and derived a set of functional relationships between them. These elements were combined here for the development of a dynamic and spatially explicit model that operates at two spatial scales. At the fine scale, modeling each individual’s life cycle allowed the representation of recruitment, inter- and intra-group competition, biogenic habitat modification and predation mortality. Larval dispersal and environmental filtering due to the tidal characteristics of the Rance estuary were represented at the coarse scale. The two scales were dynamically linked and the model was parameterized on the basis of theoretical expectations and expert knowledge. The model was able to reproduce some patterns of α- and β-diversity that were observed in the Rance estuary in 1995. Model analysis demonstrated the role of local and regional processes, particularly early post-settlement mortality and spatially restricted dispersal, in shaping marine benthos. It also indicated biogenic habitat modification as a promising area for future research. The combination of this mechanism with different substrate types, along with the representation of physical disturbances and more trophic categories, could increase the model’s realism. The precise parameterization and validation of the model is expected to extend its scope from the exploration of community assembly mechanisms to the formulation of predictions about the responses of community structure and functioning to environmental change.

Variability in early post-settlement mortality in intertidal mussels and the role of size at settlement

ABSTRACTEarly post-settlement mortality is difficult to measure in mobile benthic taxa such as mussels. Field studies typically employ settlement collectors that often contain empty shells of dead individuals, which are usually disregarded. Here, empty shells of pediveligers, i.e. recent settlers that died before beginning to grow as juveniles, were used to assess temporal and spatial patterns of early mortality in mussels, whether size at settlement determined mortality, and whether mortality was density-dependent. This study took place at two intertidal sites in a large harbour in central New Zealand where monthly cohorts of mussels were collected over a 2-year period. Monthly mortality varied substantially, ranging from 0% to 42.6%, but not across the two sites that were 27 km apart. Although there was no density-dependent mortality evident within cohorts, the proportion of pediveligers which were dead on collection was highly positively correlated across sites. Live settlers were on average larger than dead settlers, and the size distribution of dead settlers was shifted toward smaller sizes compared to live settlers. At the extremes, of all settlers with shell length of 260 µm or less, 72% were dead on collection. By contrast, for settlers 310 µm or greater in length, 6% were dead. Together, these results (1) suggest that in this system size at settlement may be an important determinant of very early, peri-metamorphic mortality in mussels, with smaller settlers at higher risk, and (2) demonstrate the value in evaluating dead pediveligers for assessing natural early post-settlement mortality in mussels.

Spatio-temporal patterns of coral recruitment at Vamizi Island, Quirimbas Archipelago, Mozambique

Spatial and temporal patterns of recruitment of reef corals were assessed for the first time in Mozambique by deploying settlement plates at various spatio-temporal scales between October 2012 and October 2013. The abundance of juvenile corals (5−50 mm in diameter) was assessed along transects. Settlement of acroporids was highly seasonal, with 97% of spat settling between July and October 2013. Pocilloporids settled throughout the year, peaking slightly between October 2012 and January 2013. The annual mean larval settlement of up to 1 135 spat m−2 was comparable to that on other East African reefs, but was dominated by acroporids, which constituted over 80% of all spat, whereas pocilloporids settle in higher densities in Kenya and South Africa. The peak settlement season also differed from other African locations. A greater proportion of variance in settlement rates occurred at the spatial scale of kilometres (between sites) and centimetres (between settlement plates) than at the scale of metres (between subsites), implying that most patchiness occurs at those scales. The peak in acroporid settlement coincided with the period of multispecific spawning, with settlement occurring as early as nine days after a spawning event. As no similar spawning events have been reported for other reefs in the area, our results suggest that these spawning events strongly influence overall annual settlement rates and promote high levels of self-seeding at Vamizi. There was no relationship between settlement of larvae to settlement plates and juvenile density on adjacent reefs, suggesting either variable levels of early post-settlement mortality or high interannual variability in settlement.

The distribution of the invasive non-native gastropod Crepidula fornicata in the Milford Haven Waterway, its northernmost population along the west coast of Britain

The invasive non-native gastropod Crepidula fornicata is well established in the Milford Haven Waterway (MHW) in south-west Wales, UK, since its first introduction to this ria in 1953. Whilst it reaches high densities within the MHW and has extended its range to the south of this ria, there has been very little northward expansion. Here, we report findings of a series of intertidal and subtidal surveys in 2009 and 2010 where we monitored the population density and the vertical distribution of C. fornicata at its northern range limit in Wales (the MHW). We also characterised the composition of the surface substrata of the seabed in the MHW to provide some insight into how the availability of certain settlement substrata may limit its distribution along the west coast of Britain. We found locally very dense aggregations (maximum 2748 ± 3859 individuals m−2, mean ± SD) in the shallow subtidal and low intertidal of the MHW. Subtidally, highest densities were found in areas of high gravel content (grain sizes ~16–256 mm), suggesting that the availability of this substrata type is beneficial for its establishment at a site. In the intertidal, on the other hand, high gravel content was indicative of low C. fornicata abundance, possibly because gravelly shores are an indicator of very exposed conditions that, at least in the intertidal, may result in high levels of early post-settlement mortality and low recruitment. C. fornicata was absent from the entrance of the MHW, possibly due to the lack of suitable settlement substrata. The presence of substantial populations in the MHW suggests that C. fornicata’s population growth and potential expansion in Welsh coastal waters is not fully limited by prevailing environmental conditions in the region, but that other processes may affect its local distribution.

Spatial patterns of larval settlement and early post-settlement survivorship of Mytilus galloprovincialis in a Galician Ría (NW Spain). Effect on recruitment success

Larval settlement and recruitment play an important role on the population dynamics of marine benthic invertebrates, and are key factors in the management of aquaculture industries. In order to check the current strategies of mussel seed gathering from collector ropes in the Ria of Ares-Betanzos (NW Spain), this work analyses the seasonal and spatial variability of larval settlement and recruitment of the mussel Mytilus galloprovincialis, as well as the relationship between settlement and recruitment. Our results highlight the importance of the hydrographic characteristics of the Ría de Ares-Betanzos on the spatial distribution of larval settlement and on the early post-settlement mortality, which determines recruitment success. The spatial distribution of larval settlement, with higher abundances in the northern-shore but significant larval retention in the southern culture areas, is in agreement with the positive subtidal circulation of this embayment and the larger residence times in the southern shore. The positive subtidal circulation of the Ría favours larval transport from the culture areas located in the south to the northern shore, while the larger residence times allow larval retention in the southern shore. The strong linear relationship between settlement and recruitment suggest density-independent mortality and allowed estimating recruitment abundances and short-term survival rates. The highest and lowest post-settlement mortalities were registered at the most external and sheltered locations respectively, suggesting that the vulnerability to the hydrodynamic stress may be the main cause of early post-settlement mortality of mussel juveniles on suspended substrates. Our results confirm that the sheltered culture polygons located in the inner area of the Ría of Ares-Betanzos are favourable environments for the recruitment of Mytilus galloprovincialis spat, supporting the current strategies of seed gathering from collector ropes in the Ría of Ares-Betanzos.

Early post-settlement mortality of the scallop Pecten fumatus and the role of algal mats as a refuge from predation

Abstract Early post-settlement mortality is one of the main processes determining distribution and abundance patterns of marine benthic invertebrates. Most scallops have an attached phase as spat before they release the byssus and move onto the soft sediments. Thus, spat differ from other stages of life in their use of microhabitat, lack of mobility, and therefore in their vulnerability to mortality processes such as predation. However, the contribution of predation to explain levels of mortality experienced by spat and early juvenile scallops is unknown. Complex habitats such as seagrasses and algae provide a substrate upon which spat can attach and might confer an advantage as a refuge from predation. This study investigates the contribution of early post-settlement predation on abundance of Pecten fumatus and determines the role of the algae Hincksia sordida as a refuge from predation. Data were collected using field observations, a predator exclusion experiment, and tethering techniques. Mortality of up to 85% during the first weeks after settlement appeared to have prevented the establishment of an adult population at our study site. Mats of the macroalgae H. sordida provided a settlement substrate for P. fumatus spat. However, increased algal biomass did not provide greater protection from predation to juvenile scallops than lower algal biomass. Our study suggests that prey survival in submersed vegetation is likely to be dynamic among years, and affected by prey behaviour and density as well as the characteristics of the submerged vegetation.

Direct seeding of mass-cultured coral larvae is not an effective option for reef rehabilitation

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 525:105-116 (2015) - DOI: https://doi.org/10.3354/meps11171 Direct seeding of mass-cultured coral larvae is not an effective option for reef rehabilitation Alasdair J. Edwards1,*, James R. Guest1,5, Andrew J. Heyward2, Ronald D. Villanueva3, Ma. Vanessa Baria3, Iris S. F. Bollozos3, Yimnang Golbuu4 1School of Biology, Ridley Building, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom 2Australian Institute of Marine Science, University of Western Australia Oceans Institute (M096), Crawley 6009, Western Australia, Australia 3The Marine Science Institute, College of Science, University of the Philippines Diliman, 1101 Quezon City, Philippines 4Palau International Coral Reef Center, PO Box 7086, Koror, Palau 96940 5Present address: Advanced Environmental Biotechnology Centre, Nanyang Technological University, 1 Cleantech Loop, CleanTech One, #06-08, Singapore 637141 *Corresponding author: alasdair.edwards@newcastle.ac.uk ABSTRACT: Large-scale rearing of coral larvae during mass spawning events and subsequent direct introduction of competent larvae onto denuded reefs (‘larval seeding’) has been proposed as a low-tech and affordable way of enhancing coral settlement and hence recovery of degraded reefs. While some studies have shown positive short-term effects on settlement, to date, none have examined the long-term effects of larval seeding for a broadcast-spawning coral. Here, we test whether larval seeding significantly increases coral recruitment rates both in the short (5 wk) and longer (~6 mo to 1 yr) term. Larvae of Acropora digitifera were reared ex situ, and ~1 million larvae were introduced to 7 artificial reefs (ARs) while 7 others were left unseeded. Settlement tiles deployed on both seeded and control ARs were retrieved for examination 5 and 30 wk after seeding. In addition, the presence of visible coral recruits on the AR surfaces was monitored before and for ~13 mo post-seeding. Density of acroporid spat was significantly higher on seeded tiles than on controls 5 wk after seeding, but this effect had vanished by 30 wk. Comparison of the densities of new visible Acropora recruits between seeded and control ARs showed no significant difference ~13 mo after seeding. Larval seeding therefore had no long-term effect due to high post-settlement mortality (which appeared to be density-related). Results suggest that reef-rehabilitation methods that aim to harness coral sexual reproduction might better focus on rearing juveniles through early post-settlement mortality bottlenecks. KEY WORDS: Larval seeding · Coral reef rehabilitation · Larval rearing · Acropora digitifera · Mass spawning · Density-dependent mortality · Palau Full text in pdf format PreviousNextCite this article as: Edwards AJ, Guest JR, Heyward AJ, Villanueva RD, Baria MV, Bollozos ISF, Golbuu Y (2015) Direct seeding of mass-cultured coral larvae is not an effective option for reef rehabilitation. Mar Ecol Prog Ser 525:105-116. https://doi.org/10.3354/meps11171 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 525. Online publication date: April 09, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Assessing techniques to enhance early post-settlement survival of corals in situ for reef restoration

For degraded coral reef systems with limited larval supply, active restoration techniques may provide a means of replenishing adult coral populations. Settling or seeding large numbers of sexually-produced larvae directly onto denuded substrate is a potential restoration tool that can eliminate the costs associated with rearing coral spat in culturing facilities. However, the long-term potential to enhance recruitment using seeding techniques has generally been limited due to high post-settlement mortality. Using the brooding coral Porites astreoides (Lamarck, 1816), we explored two potential strategies-choosing favorable substrate communities and caging recently settled spat-to enhance early post-settlement survival during seeding efforts. Larvae were collected from adult colonies in the laboratory and, once competent to settle, were seeded directly onto the reef substrate. Settled spat were individually mapped and monitored using fluorescence techniques, and found to have a low survivorship with <3%-15% surviving after 1 mo, and <1% after 5 mo. Techniques to enhance survival, including choice of substrate and post-settlement caging, did not significantly influence the high rates of natural mortality. These results underscore the general lack of knowledge regarding the major factors that drive the magnitude of early post-settlement mortality, and future identification of these mortality factors may lead to suitable techniques to enhance survival in seeding efforts.

Post-settlement growth and mortality rates of juvenile scleractinian corals in Moorea, French Polynesia versus Trunk Reef, Australia

Patterns and processes affecting juvenile scleractinian corals have received very little attention due to difficulties associated with detecting small corals on natural substrata. However, processes occurring during juvenile life stages are likely to play a strong role in population ecology. In particular, spatial differences in juvenile demographic rates may result in prominent differences in population and community structure for corals. In the present study, we compared the density, taxonomic composition, size structure, growth and mortality rates of juvenile corals (≤50 mm) and the cover and composition of adult coral assemblages among sites on Trunk Reef (central Great Barrier Reef) and Moorea (French Polynesia). There was significant regional variation in the taxonomic composition of coral assemblages within both adult and juvenile assemblages, with Pocillopora being the predominant coral genus in Moorea and Acropora at Trunk Reef. However, there were no differences in the density, growth or mortality rates of juvenile corals between Moorea and Trunk Reef. Most of the variation in these variables was evident at the small (within-reef) scale, with exposed sites having lower densities and higher rates of mortality of juvenile corals than sheltered sites at both locations. The lack of geographic variation in the density, growth and mortality rates of juvenile corals is interesting given that the cover of adult coral was 3-fold higher on Moorea (31.1%) than Trunk Reef (10.8%), suggesting that adult coral assemblages are structured more by differential adult mortality, larval settlement or very early post-settlement mortality (before colonies can be observed in situ), rather than demographic rates of juvenile growth or mortality.

Influence of fish grazing and sedimentation on the early post-settlement survival of the tabular coral Acropora cytherea

Processes operating in the early life stages of corals are critical in ultimately establishing patterns of adult abundance. Mortality, in particular, is assumed to be very high during the first few months to years post-settlement, but the sources of this mortality are largely unknown. This study quantified early post-settlement survival for Acropora cytherea, spawned and reared in captivity and settled onto terracotta tiles. Replicate tiles were then deployed in the field at Lizard Island, in northern section of the Great Barrier Reef to examine the effects of grazing and sedimentation on survival of corals in two different habitats, the exposed reef crest and sheltered back reef. Overall, survivorship was broadly comparable between habitats, ranging from 37.7 to 64.5 % per month on the exposed reef crest and 53.1–64.3 % on the sheltered back reef. On the reef crest, the exclusion of herbivores increased survivorship by 22.4 %, from 42.1 to 64.5 % per month. Moreover, survivorship within the reef crest was negatively correlated with the density of parrotfish feeding scars on tiles after 4 weeks. In contrast, the exclusion of herbivores had no detectable effect on survivorship within the back reef, and no feeding scars were observed on tiles in this habitat. Difference in grazing-induced mortality between habitats is most likely related to differences in herbivore size and abundance, with parrotfish biomass being 5.5-fold greater on the reef crest than the back reef. Surprisingly, tile orientation had no effect on survivorship of A. cytherea in either habitat, despite a marked difference in the sediment cover on vertical (0 %) versus horizontal tiles (30 %) in the back reef. This is in marked contrast to previous studies that have reported sedimentation is a major cause of early post-settlement mortality in corals. Clearly, processes that cause mortality of newly settled corals, such as grazing and sedimentation, vary spatially.

Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 481:147-159 (2013) - DOI: https://doi.org/10.3354/meps10221 Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality Brittany T. Jenewein1, Louis A. Gosselin1,2,* 1Department of Biological Sciences, Thompson Rivers University, 900 McGill Road, Kamloops British Columbia V2C 0C8, Canada 2Department of Biology, University of Victoria, Victoria British Columbia V8W 3N5, Canada *Corresponding author. Email: lgosselin@tru.ca ABSTRACT: We examined the sensitivity of newly settled Mytilus trossulus to heat and desiccation, as well as the ontogeny of sensitivity through the early benthic phase. Laboratory experiments were conducted to determine the sensitivity of mussels to the full range of temperatures and desiccation levels experienced in the field. Mussels of 1 to 2 mm shell length (SL) experienced a threshold of heat tolerance at 34°C and a threshold of desiccation tolerance at vapour pressure deficit levels of 1.01 kPa. Extended periods of temperatures reaching or exceeding lethal levels for newly settled M. trossulus occurred relatively rarely in Barkley Sound, British Columbia, Canada, whereas lethal levels of desiccation occurred often during the recruitment season and were usually sustained for several hours. Desiccation, therefore, appears to be a substantially greater threat to recently settled M. trossulus than heat. A final laboratory experiment characterized the changes in sensitivity to desiccation that occur as mussels increase in size. Mussels became highly tolerant to desiccation when they reached a size of 2 to 3 mm SL. This size closely corresponds to the size at which juvenile M. trossulus relocate from protective filamentous algal habitat to adult habitat, suggesting ontogenetic shifts in habitat use by juvenile M. trossulus are a response to changing sensitivity to desiccation. If so, the future survival of newly settled mussels, and thus possibly the local persistence of mussel populations, may depend upon the persistence of protective algal microhabitats under changing climate conditions. KEY WORDS: Early post-settlement mortality · Mortality factors · Physiological stress · Weather · Settlement · Recruitment · Population regulation · Climate change Full text in pdf format PreviousNextCite this article as: Jenewein BT, Gosselin LA (2013) Ontogenetic shift in stress tolerance thresholds of Mytilus trossulus: effects of desiccation and heat on juvenile mortality. Mar Ecol Prog Ser 481:147-159. https://doi.org/10.3354/meps10221 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 481. Online publication date: May 07, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Effects of Tidal Elevation and Substrate Type on Settlement and Postsettlement Mortality of the Sydney Rock Oyster,Saccostrea glomerata, in a Mangrove Forest and on a Rocky Shore

Patterns of settlement and postsettlement mortality determine the distribution and abundance of sessile marine organisms. In mangrove forests and on rocky shores of eastern Australia, the Sydney rock oyster, Saccostrea glomerata, displays a pattern of declining abundance with increasing tidal elevation that might be related to or independent of the tidal elevation gradient in the substrate (bare, dead conspecifics, live conspecifics) available for attachment. We conducted parallel manipulative experiments on a rocky shore and in a mangrove forest to assess (1) the relative importance of tidal elevation and substrate type (bare, live oysters, or dead oysters) in determining the spatial distribution of new (<1 mm) S. glomerata recruits and (2) the contribution of settlement and postsettlement processes in setting patterns of spatial variation in established oyster populations. Patches of habitat with either live oysters, dead oysters, or no conspecifics were established at 3 tidal elevations at each site, and natural settlement and postsettlement mortality were monitored through time. At each site, and regardless of the substrate provided, we detected a similar pattern of fewer new S. glomerata recruits and greater postsettlement mortality on the high intertidal shore rather than the mid or low intertidal shore. Substrate type, by contrast, influenced the abundance of new recruits, but not subsequent postsettlement mortality. Consequently, over a period of months, direct effects of tidal elevation rather than effects of substrate type determined spatial patterns of oyster recruitment on the rocky shore and in the mangrove. Consequently, we documented that on a rocky shore and in a mangrove forest, settlement and early postsettlement mortality vary similarly across tidal elevation gradients and substrate types to determine the distribution of S. glomerata.

Predation on coral settlers by the corallivorous fireworm Hermodice carunculata

Coral predation by the fireworm Hermodice carunculata was investigated by presenting settlers ( 90 %) in the presence of small-, mid- and large-sized fireworms, respectively. In contrast, fireworms hardly preyed on adult corals, irrespective of their sizes. Our results suggest an ontogenic shift in the diet of H. carunculata and in the susceptibility of corals to predation by fireworms. H. carunculata, in particular small-sized individuals, could be an important cause for early post-settlement mortality in corals. The corallivore could reinforce recruitment bottlenecks and reduce coral recovery after disturbances.

New estimates of early post-settlement mortality for intertidal mussels show no relationship with meso-scale coastline topographic features

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 463:193-204 (2012) - DOI: https://doi.org/10.3354/meps09859 New estimates of early post-settlement mortality for intertidal mussels show no relationship with meso-scale coastline topographic features Charles E. O. von der Meden1, 2,*, Francesca Porri1, Christopher D. McQuaid1 1Coastal Research Group, Department of Zoology and Entomology, Rhodes University, Grahamstown 6140, South Africa 2Present address: South African Environmental Observation Network, Egagasini Node, 5th flr Foretrust Building, Martin Hammerschlag Way, Cape Town, Private Bag X2, Roggebaai 8012, South Africa *Email: vdmeden@hotmail.com ABSTRACT: For organisms with planktonic larvae, the early post-settlement stage is a particularly vulnerable one, likely to influence distribution patterns in subsequent life stages. Although substantial post-settlement mortality is well known in several marine invertebrate taxa (e.g. barnacles), few estimates exist for benthic invertebrates, such as mussels, that have mobile settlers. Furthermore, estimates of early post-settlement mortality (within 2 d of settlement) are sparse for most groups. In addressing the difficulties involved with quantifying early mortality of mobile settlers, the present study builds on a sequential-deployment method to estimate the post-settlement mortality of the intertidal mussel Perna perna. Trials were run at 16 sites, split evenly between bay and open coast locations, and were repeated over 2 sampling cycles. By comparing post-settlement mortality estimates from bays and open coast sites, we investigated whether such topographic features produce differential mortality. Post-settlement mortality estimates showed substantial levels of mortality but did not differ significantly between bay and open coast sites. Early post-settlement mortality (i.e. mortality of primary settlers up to 2 d old) ranged from 31 to 94% but averaged 54 and 64% in the 2 sampling cycles. Estimates of total post-settlement mortality (i.e. inclusive of primary and secondary settlers) had a similar range and averaged 66% in Cycle 1 and 67% in Cycle 2. Apart from confirming significant mortality rates of early mussel settlers, these findings suggest that intertidal abundance patterns of recruits and adults, often associated with topographic features of coastlines, are more likely a result of initial settlement patterns than of differences in post-settlement mortality. KEY WORDS: Post-settlement mortality · Coastline topography · Bays · Perna perna · Intertidal mussels · Pelagic-benthic coupling Full text in pdf format PreviousNextCite this article as: von der Meden CEO, Porri F, McQuaid CD (2012) New estimates of early post-settlement mortality for intertidal mussels show no relationship with meso-scale coastline topographic features. Mar Ecol Prog Ser 463:193-204. https://doi.org/10.3354/meps09859 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 463. Online publication date: August 30, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Effects of predators and grazers exclusion on early post-settlement coral mortality

Mortality of newly settled individuals is a key factor in shaping adult population size and distribution of many marine invertebrates. Despite this recognized importance, few studies have addressed early post-settlement mortality rates and causes in reef-building corals. To investigate the effects of exclusion of macro-predators and grazers on mortality of Acropora striata (Verrill) recruits, a caging experiment was completed at Moorea, French Polynesia. More than half of the recruits died within 7 days in the field, and although the exclusion of macro-predators and grazers did not significantly reduce nor enhance mortality, it certainly altered their cause. In the presence of macro-predators and grazers, coral recruits faced significant predation-induced mortality (50.0% of dead recruits presented a heavily damaged or missing skeleton). Conversely, in the absence of macro-predators and grazers, dead recruits were mainly intact (91.7%), and most likely suffered from competition with turf algae and associated sediment trapping. These results underline complex interacting effects of predation, competition with turf algae, and sedimentation on coral early post-settlement mortality.

Pre- and post-settlement factors controlling spatial variation in recruitment across a cold-seep mussel bed

The size structure of a population of the mussel 'Bathymodiolus' childressi shifts dra- matically across the mussel bed encircling the Brine Pool NR 1 cold seep in the Gulf of Mexico. While the fringes of the bed are inhabited by large mussels, small juveniles are abundant only at the edge of the pool, leading to the inference that larvae settle preferentially near the source of methane. We used in situ experiments to test whether this shift in size distribution is structured by differences in larval supply, settlement, substratum selection by settling larvae, juvenile mortality, growth, or predation across the mussel bed. We investigated the variation of these factors adjacent to the pool, at the fringes of the mussel bed, and also 2 m away from the bed. Neither the supply of larvae nor the density of settlers (<0.5 mm long) collected on settlement plates differed among the 3 zones. Juve- niles (mean length: 9 mm) survived and grew equally well in all 3 zones. Survival was higher in caged than in uncaged juveniles (5 to 15 mm long), but mortality of uncaged juveniles was similar at all distances from the pool, suggesting that predation alone does not cause the observed differences in size structure. We reject the prevailing hypothesis that the distribution pattern can be attributed to settlement preferences of larvae alone. We hypothesize that very early post-settlement mortality, secondary settlement, and/or later migration of juveniles play a role in establishing and maintaining the persistent pattern of size structure across this mussel bed.