Recruitment Of Invertebrates Research Articles

Determining the best practice for Sydney rock oyster, Saccostrea glomerata, reef restoration and enhanced ecological benefits

BackgroundShellfish reef restoration is relatively new in Australia, particularly to intertidal estuarine environments. In late 2019/early 2020 the first large-scale shellfish reef restoration project of the Sydney rock oyster, Saccostrea glomerata was undertaken in the Myall and Karuah Rivers, Port Stephens, on the mid north coast of New South Wales (NSW), Australia. The present study aimed to determine whether locally sourced clean conspecific oyster shells, and/or locally quarried rocks were better for natural recruitment of natural S. glomerata for large-scale oyster reef restoration, and subsequent recruitment of fishes and invertebrates. Over two years, recruitment of S. glomerata spat, and associated fishes and invertebrates were assessed on reefs made of: (1) rock, and (2) rock and shell.ResultsThe mean (± SE) density of oyster spat on rock reefs (Myall River: 1790 ± 48, Karuah River: 1928 ± 68) was significantly greater (Myall River: ANOVA Si: MS 2, 18 = 31080167, F = 96.05, P < 0.001, Karuah River: ANOVA Si x Ti: MS 18, 270 = 2965449, F = 5.99, P < 0.001) than on rock and shell reefs (Myall River: 840 ± 40, Karuah River: 1505 ± 75). Rock reefs had significantly greater densities (Myall River: ANOVA Si x Ti: MS 18, 270 = 15657, F = 2.71, P < 0.001, Karuah River: ANOVA Si x Ti: MS 18, 270 = 20322, F = 5.25, P < 0.001) of the most abundant invertebrate, Bembicium auratum (Myall River: 85 ± 9, Karuah River: 100 ± 8) than reefs of rock and shell (Myall River: 59 ± 8, Karuah River: 44 ± 5), but there was no significant difference in the diversity and relative abundance of the most abundant species of fish, Acanthopagrus australis.ConclusionsThis study demonstrates that using locally sourced rock is better for S. glomerata recruitment than shells. Although shell might have benefits that were not investigated in the present study, such as elicit greater social licence for oyster reef restoration projects, but as shown here, it may not be beneficial from an ecological perspective. With the global expansion of the range of different native species of reef oysters for restoration, the appropriate material used for reef bases needs to be chosen for a specific species and purpose.

Crustose coralline algal factors determining the success of limpet (Patellogastropoda: Patellidae) settlement: species, exposure time, area and soluble cues

Crustose coralline algae (CCA) play a key role in invertebrate recruitment, yet their influence on the settlement of patellid limpets is under discussion. This study is aimed at resolving the role of CCA as a settlement inducer for patellid limpets, providing insight into the influence of different CCA-related factors. The larvae of the economically valuable limpet Patella candei were used as a model. Six assays were performed: (1) different CCA assemblages, (2) exposure time, (3) artificial removal of epibionts, (4) substrate area, (5) soluble cues (CCA-conditioned seawater), and (6) substrate selection in a choice experiment. Settlers were identified by velum loss and teleoconch development. Species composition of the CCA assemblages significantly influenced settlement, with a preference for Titanoderma pustulatum and combined Neogoniolithon sp. and Hydrolithon farinosum crusts. The substrates dominated by Agissea inamoena, marginal presence of CCA or which epibionts were artificially removed, were statistically similar to those in the negative control. The ratio of settlers increased until 4 days of exposure, after which it remained stable over time. The results support that CCA releases soluble cues with settlement-inducing effect on P. candei larvae, explaining why the ratio of settlers increased with substrate area. The choice experiment suggests that P. candei larvae have limited selectivity with respect to the substrate surface. In conclusion, the present study points to the relevance of CCA assemblages as settlement substrates for limpet larvae, with an impact on limpet recruitment in the wild as well as on the production of post-larvae for limpet aquaculture.

Community structure and recovery in cryptic intertidal communities reflects dynamics on open‐surface communities

AbstractResearch on intertidal community structure and recovery in the California Current System has largely focused on macrophytes and invertebrates occupying two‐dimensional, readily studied “open” rock surfaces. However, most rocky shores have a “third” dimension that includes channels, cracks, crevices, and overhangs whose organismal assemblages, termed “cryptic communities,” are poorly studied. Cryptic communities not only share many species with those on more accessible surfaces but also include high abundances of colonial invertebrates such as tunicates, sponges, bryozoans, and hydrozoans. We investigated species abundance and diversity of cryptic communities and tested their recovery from disturbance by comparing removal plots to undisturbed controls for ~1.5 years. Additionally, we tested whether community structure and recovery varied with contrasting large‐scale levels of ecological subsidies (invertebrate recruitment, nutrients, and phytoplankton) and local‐scale microhabitat differences (emersion and solar irradiation) on the Oregon Coast. We compared cryptic recovery rates to recovery rates on open‐surface communities. In cryptic communities, site explained most (92%) variance in community structure of undisturbed plots, while microhabitat metrics had little (1.2%) effect. Further, recovery rates were faster at a site with higher subsidy inputs than one with lower subsidies in both cryptic and noncryptic communities. Hence, larger scale environmental drivers appeared more important than local‐scale drivers within cryptic communities. Our research provides novel insight into intertidal cryptic surge channel community structure and dynamics.

A decade of invertebrate recruitment at Santa Catalina Island, California.

Marine fouling communities have long provided model systems for studying the ecology of community development, and settlement plates are the tool of choice for this purpose. Decades of plate deployments provide a baseline against which present-day trends can be interpreted, with one classic trend being the ultimate dominance of plates by colonial and encrusting taxa. Here we report the results of annual deployments of settlement plates from 2010 to 2021 in the shallow sub-tidal of southern California, where the recruitment of invertebrates and algae was recorded photographically, and resolved to functional group (solitary, encrusting, and arborescent) and the lowest taxon possible. The communities on these plates differed among years, with trends in abundances varying by functional group and taxon; solitary taxa consistently were abundant, but encrusting taxa declined in abundance. Seawater temperature and the subsurface concentration of chlorophyll a differed among years, and there was a weak inverse association between temperature and the abundances of encrusting taxa. Long-term increases in seawater temperature therefore could serve as a mechanism causing fouling communities to change. Because of the prominence of encrusting taxa in fouling communities, the shifts in abundance of this functional group reported here may portend ecologically significant changes in fouling communities exposed to warmer seawater because of an alleviation of competition for a classically limiting resource (i.e., space).

Eco-Plastics in the Sea: Succession of Micro- and Macro-Fouling on a Biodegradable Polymer Augmented With Oyster Shell

Impacts of Marine Plastic Debris (MPD) on marine ecosystems are among the most critical environmental concerns of the past three decades. Virgin plastic is often cheaper to manufacture than recycled plastics, increasing rates of plastic released into the environment and thereby impacting ecosystem health and functioning. Along with other environmental effects, MPD can serve as a vector for marine hitchhikers, facilitating unwanted organisms’ transport and subsequent spread. Consequently, there is a growing demand for more eco-friendly replacements of conventional plastic polymers, ideally with fit-for-purpose properties and a well-understood life cycle. We enriched polybutylene succinate (PBS) with three different concentrations of oyster shell to investigate the dynamics of biofouling formation over 18 weeks at the Nelson Marina, Aotearoa/New Zealand. Our study focused on oyster shell concentration as a determinant of fouling assemblages over time. While generally considered as a waste in the aquaculture sector, we used oyster shells as a variable of interest to investigate their potential for both, environmental and economic benefits. Using bacterial 16S and eukaryotic 18S rRNA gene metabarcoding, our results revealed that following immersion in seawater, time played a more critical role than substrate type in driving biofouling community structures over the study period. In total, 33 putative non-indigenous species (NIS) and 41 bacterial families with putative plastic-degrading capability were detected on the different substrates. Our analysis of NIS recruitment revealed a lower contribution of NIS on shell-enriched substrates than unadulterated polymers samples. In contrast, the different concentrations of oyster shells did not affect the specific recruitment of bacterial degraders. Taken together, our results suggest that bio-based polymers and composites with increased potential for biodegradability, recyclability, and aptitude for the selective recruitment of marine invertebrates might offer a sustainable alternative to conventional polymers, assisting to mitigate the numerous impacts associated with MPD.

Calcification accretion units (CAUs): A standardized approach for quantifying recruitment and calcium carbonate accretion in marine habitats

Abstract Standardized metrics that quantify a component of ecosystem functioning are essential for evaluating the current status of coastal marine habitats and for monitoring how ecologically important ecosystems are changing in response to global and local environmental change. Calcification accretion units (CAUs) are a standardized tool for quantifying net calcium carbonate accretion, early successional community structure, recruitment of algae and sessile invertebrates and other response metrics that can be determined from image analyses in coastal marine habitats. CAUs are comprised of paired‐settlement tiles that are separated by a spacer. This design mimics the presence of different representative habitats that are common in most marine systems such as exposed benthic surfaces, cryptic spaces inaccessible to grazers and shaded overhangings. The protected space between the tiles facilitates recruitment and inclusion of cryptic taxa in community assemblage estimates. After a period of deployment, CAUs are photographed for image analysis and then decalcified to quantify calcium carbonate accretion rates. The CAU methodology provides a cost‐effective, standardized protocol for evaluating structure and function in marine benthic habitats. We illustrate how CAU data can be used to compare accretion rates and the relative proportion of carbonate polymorphs in ecosystems across the globe. Here we provide a comprehensive standard operating procedure for building, deploying and processing CAUs, to ensure that a consistent protocol is used for accurate data collection and cross‐system comparative studies.

Larval dispersal and recruitment of benthic invertebrates in the Arctic Ocean

Larval dispersal is a fundamental process responsible for colonization and connectivity of benthic invertebrate populations. It is difficult to study larval dispersal in polar environments because weather and climate conditions restrict sample collection to certain seasons. In this study, we leveraged oceanographic moorings as long-term scientific platforms for collecting larvae and recruits of benthic invertebrate species in the Fram Strait and along the continental slope north of Svalbard in 2017–2021. Larval traps and fouling panels were deployed at various depths on 15 moorings at 8 locations, and additional specimens of biofouling were obtained opportunistically from moored instruments. Our results showed a significant difference in species composition between samples collected in Atlantic Water in the West Spitsbergen Current (WSC) and samples collected in Arctic Water near the seafloor and in the East Greenland Current (EGC) in the western part of the Fram Strait. There was also a stark difference between Atlantic Water species in the Fram Strait and on the north Svalbard slope. Most specimens collected in the WSC belonged to species with long-duration planktotrophic larvae, such as the ubiquitous bivalve Hiatella arctica, the bryozoan Alcyonidium mamillatum, and two nudibranchs. Samplers exposed primarily to Arctic water at their given depth and location were dominated by hydrozoans. We observed medusae budding off of the hydroids Stegopoma plicatile and Rhizoragium roseum. Our study demonstrates that the WSC is an important vector for larval dispersal into the central Arctic Ocean. Integration of biological samplers on oceanographic moorings holds great promise for monitoring efforts as climate change progresses, especially in environments where research is challenging and seasonally limited, such as the Arctic.

Habitat Restoration Restores Underwater Soundscapes and Larval Recruitment

Habitat degradation alters many ecosystem processes, and the potential for the reestablishment of ecosystem function through restoration is an area of active research. Among marine systems, coastal habitats are particularly vulnerable to anthropogenic degradation and, in response, are the focus of marine ecological restoration. One of the crucial functions of structurally complex coastal habitats (e.g., saltmarshes, seagrass meadows, kelp forests, coral reefs) are as nurseries to coastal and offshore species, many of whose larvae utilize sound to locate suitable nursery habitat. However, the effect of habitat degradation and subsequent restoration on underwater soundscapes and their function as navigational cues for larvae is unexplored. We investigated these phenomena in sponge-dominated hardbottom habitat in the waters surrounding the middle Florida Keys (Florida, United States) that have been degraded in recent decades by massive sponge die-offs caused by harmful algal blooms. One of the consequences of sponge die-offs are dramatic changes in underwater sounds normally produced by sponge-associated animals. We tested whether soundscapes from healthy hardbottom habitat influenced larval recruitment, and then examined how hardbottom degradation and restoration with transplanted sponges affected underwater soundscapes and the recruitment of larval fishes and invertebrates. Larval assemblages recruiting to healthy areas were significantly different than those assemblages recruiting to either degraded or restored hardbottom areas. Fewer larvae recruited to degraded and restored areas compared to healthy hardbottom, particularly during the full moon. Experimental playback of healthy hardbottom soundscapes on degraded sites did not promote larval community differences although some individual species responded to the playback of healthy habitat soundscapes. These results indicate that habitat-associated soundscapes have idiosyncratic effects on larval settlement, which is diminished by the degradation of nursery habitat but can be reestablished with appropriate habitat restoration.

Biofouling initial succession on offshore artificial substrate under subtropical conditions

This study presents the initial stages of the macrofouling community on artificial substrate exposed to the offshore subtropical marine environment, and the contribution of depth (3 and 22m), exposure time (1-2-4-7-10-13-weeks), UV-radiation, rainfall, temperature, pH, salinity, water chlorophyll-a, and zooplankton supply to organism establishment. Steel substrates were placed horizontally on the structure of a pipeline monobuoy off the southern shore of Brazil (Tramandaí beach), and the ecological succession was monitored by six random removals per depth during the summer-autumn of 2011. Approximately 88.5% of the quantified settled individuals comprised fouling fauna and 11.5% vagile and sedentary fauna, although the taxa richness was higher for non-sessile invertebrates. Species richness and organism density up to four weeks were significantly higher at 3m-depth. After this period, a higher density of organisms was found at 22m, while during the whole study the species richness and diversity remained higher at 3m-depth. Zooplankton composition did not show a simultaneous temporal relationship with invertebrate recruitment at any depth; however, increasing the exposure time, the similarity between the planktonic and benthic communities also increased. Meroplankton, tychoplankton, and holoplankton were recorded on the substrates. This study showed that the depth of available substrates affects the macrofouling establishment, which is mainly associated with UV-radiation, exposure time, and ecological interspecific interactions.

Corrigendum for Meyer‐Kaiser et al. 2019

Limnology and OceanographyVolume 66, Issue 8 p. 3253-3253 CorrigendumFree Access Corrigendum for Meyer-Kaiser et al. 2019 This article corrects the following: Recruitment of Arctic deep-sea invertebrates: Results from a long-term hard-substrate colonization experiment at the Long-Term Ecological Research observatory HAUSGARTEN Kirstin Meyer-Kaiser, Melanie Bergmann, Thomas Soltwedel, Michael Klages, Volume 64Issue 5Limnology and Oceanography pages: 1924-1938 First Published online: March 21, 2019 First published: 12 July 2021 https://doi.org/10.1002/lno.11861 Editor-in-Chief: Dave Hambright AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Corrigendum for: Meyer-Kaiser, K. S., M. Bergmann, T. Soltwedel, and M. Klages. 2019. Recruitment of Arctic deep-sea invertebrates: Results from a long-term hard-substrate colonization experiment at the Long-Term Ecological Research observatory HAUSGARTEN. Limnol. Oceanogr. 64: 1924–1938. doi: 10.1002/lno.11160 Since the publication of this article, it has been revealed that the crinoid specimens do not belong to Bathycrinus carpenterii but rather the comatulid species Poliometra prolixa (Meyer-Kaiser et al. 2021). In addition, the “small round white sponge” in our 2019 paper is an hexactinellid sponge, possibly Caulophacus arcticus, whereas sponges called “small round white sponge” by other authors working in the HAUSGARTEN belong to the demosponge species Tentorium semisuberites (e.g., Bergmann et al. 2011, Taylor et al. 2017). References Bergmann, M., T. Soltwedel, and M. Klages. 2011. The interannual variability of megafaunal assemblages in the Arctic deep sea: Preliminary results from the HAUSGARTEN observatory (79° N). Deep-Sea Res. I 58: 711– 723. doi:10.1016/j.dsr.2011.03.007 Meyer-Kaiser, K., A. Smith, and T. Soltwedel. 2021. Ontogenetic development of the crinoid Poliometra prolixa in the Arctic deep sea. Invert. Biol. 140: e12331. doi:10.1111/ivb.12331 Taylor, J., T. Krumpen, T. Soltwedel, J. Gutt, and M. Bergmann. 2017. Dynamic benthic megafaunal communities: Assessing temporal variations in structure, composition, and diversity at the Arctic deep-sea observatory HAUSGARTEN between 2004 and 2015. Deep-Sea Res. I 122: 81– 94. doi:10.1016/j.dsr.2017.02.008 Conflict of interest None declared. Volume66, Issue8August 2021Pages 3253-3253 ReferencesRelatedInformation

Two Distinct Bacterial Biofilm Components Trigger Metamorphosis in the Colonial Hydrozoan Hydractinia echinata.

ABSTRACTIn marine environments, the bacterially induced metamorphosis of larvae is a widespread cross-kingdom communication phenomenon that is critical for the persistence of many marine invertebrates. However, the majority of inducing bacterial signals and underlying cellular mechanisms remain enigmatic. The marine hydroid Hydractinia echinata is a well-known model system for investigating bacterially stimulated larval metamorphosis, as larvae transform into the colonial adult stage within 24 h of signal detection. Although H. echinata has served as a cell biological model system for decades, the identity and influence of bacterial signals on the morphogenic transition remained largely unexplored. Using a bioassay-guided analysis, we first determined that specific bacterial (lyso)phospholipids, naturally present in bacterial membranes and vesicles, elicit metamorphosis in Hydractinia larvae in a dose-response manner. Lysophospholipids, as single compounds or in combination (50 μM), induced metamorphosis in up to 50% of all larvae within 48 h. Using fluorescence-labeled bacterial phospholipids, we demonstrated that phospholipids are incorporated into the larval membranes, where interactions with internal signaling cascades are proposed to occur. Second, we identified two structurally distinct exopolysaccharides of bacterial biofilms, the new Rha-Man polysaccharide from Pseudoalteromonas sp. strain P1-9 and curdlan from Alcaligenes faecalis, to induce metamorphosis in up to 75% of tested larvae. We also found that combinations of (lyso)phospholipids and curdlan induced transformation within 24 h, thereby exceeding the morphogenic activity observed for single compounds and bacterial biofilms. Our results demonstrate that two structurally distinct, bacterium-derived metabolites converge to induce high transformation rates of Hydractinia larvae and thus may help ensure optimal habitat selection.

Ecosystem recovery at hypersaline salt marsh remediation projects impacted by the Gulf War Oil Spill

ABSTRACT #1141405 The 1990 Gulf War Oil Spill was the largest marine oil spill in history, spilling an estimated 6–11 million barrels of crude oil into the Arabian Gulf and impacting approximately 800 km of shoreline in Saudi Arabia between the border with Kuwait and Abu Ali Island near Jubail. Many intertidal areas were heavily oiled, severely damaging salt marsh ecosystems and facilitating the growth of thick algal mats, which, in turn, created a physical barrier that restricted tidal exchange and prevented recolonization of marsh flora and fauna at these sites. Remediation projects have been ongoing since early 2010 at 19 project areas throughout the area of impact. Remediation activities are focused on refreshing existing or creating new tidal channels to restore hydrology and tilling the substrate to expose moderately oiled sediment and enhance the degradation of oil and break up laminate algal mats. Additional activities include removal of heavily oiled sediments, re-use of excavated unoiled and lightly oiled sediments to create additional topography in restored marshes, and vegetation planting in selected areas. Monitoring plots for long-term study were established at remediation sites, impacted but untreated sites (set-asides), and nearby reference (comparison) sites. Initial monitoring data were collected before and after remediation activities, which were primarily undertaken between 2010 and 2013. Biannual (spring and fall) monitoring was resumed in fall 2018 and will continue through spring 2022 to characterize ecosystem recovery at these sites. Based on results from fall 2018 and spring 2019, most remediation sites show some level of recovery, indicated by the return of annual vegetation and resident marsh invertebrates in lower elevation plots, and thinner algal mat types and insect burrowing activity at the upper elevations. While the lower portions of untreated sites are beginning to show recruitment of annual vegetation and invertebrates (e.g. crabs), thick, laminated algal mat cover occurs in the middle-upper elevations at untreated sites. Multimetric indices (MMIs) summarizing ecosystem health and stressors were developed to summarize recovery of these projects and evaluate progress at remediation sites relative to set-aside and comparison sites. MMI results indicate that remediation work was effective at reducing stressors in remediation sites compared to set-asides; however, the level of ecosystem recovery is variable across sites, in part depending on the time since restoration.

Oil spills: The invisible impact on the base of tropical marine food webs

The Brazilian oil spill, from August 2019 to January 2020, was considered the most extensive accident in tropical oceans. We estimated the concentration of oil droplets that may be available for ingestion by microzooplankton. The collection was carried out in three areas: estuarine plume, bay and reef (Tamandaré, Pernambuco coast). We highlight the contribution of coral larvae in the reef region, surpassing the copepods, evidencing a spawning event. Oil droplets were recorded in all the sampled areas, with a high numerical abundance in the plume. Traces of oil ingestion by Brachyura zoea and Calanoida, Paracalanidae and Oithonidae copepods were observed, suggesting that these groups might have an important role in the degradation and final destination of oil dispersed after spills. The vulnerability of the larval phases of crabs and reef-building corals has been hypothesized, suggesting that the negative effects of oil on zooplankton can affect the recruitment of benthic invertebrates.

Gorgonians Are Foundation Species on Sponge-Dominated Mesophotic Coral Reefs in the Caribbean

Foundation species (FS) regulate ecological processes within communities often facilitating biodiversity and habitat complexity. Typically FS are dominant structure-forming taxa; but less dominant taxa having disproportionate ecological impacts to the community can also be FS. Mesophotic coral ecosystems (MCEs) are deep coral reef (∼30–150 m) communities, often dominated by emergent sponges in the Caribbean Basin. Despite the potential competitive advantage of sponges on MCEs, gorgonians are also common constituents of these reefs. Data from the Bahamas demonstrate increased biodiversity and densities of sponges on mesophotic reefs with gorgonians relative to reefs without these species. Drawing upon fifteen years of field surveys at five sites in the Caribbean Basin we assessed in situ interactions between gorgonians and sponges to quantify outcomes consistent with competition (i.e., tissue necrosis and overgrowth). Gorgonians were effective competitors against a variety of sponges, and two allelochemicals produced by Ellisella elongata were mechanistically important in interactions with Agelas clathrodes. We also examined invertebrate recruitment patterns near gorgonians to assess their role in facilitating MCE biodiversity. Our results indicate that live gorgonians, Antillogorgia bipinnata and E. elongata, facilitate biodiverse recruitment into MCEs, indicating that this process is governed by more than passive hydrodynamics. Collectively, these data indicate that these gorgonians exhibit both positive and negative ecological interactions (i.e., facilitation and competition, respectively) with sponges, and other taxa. Thus, these gorgonians are FS of MCE communities within the Caribbean Basin that display several traits contributing to the ecological structure of these understudied communities.

If You Plant It, They Will Come: Rapid Recruitment of Habitat-Dependent Marine Invertebrates to Transplanted Fragments of an Endangered Soft Coral Species

In recent decades, the transplantation of corals has been a primary focus of restoration strategies in areas where coral populations have declined [...]

Deep-sea bacteria trigger settlement and metamorphosis of the mussel Mytilus coruscus larvae

Bacteria from coast seawaters are widely known to induce larval recruitment of many invertebrates. However, whether and how deep-sea bacteria, that play crucial roles in the ecological and biogeochemical cycles, promote larval recruitment remains little known. Here, the interaction between deep-sea bacterial biofilms (BFs) and Mytilus coruscus larvae was tested. All these nine deep-sea bacterial isolates triggered planktonic-sessile transition, and the highest percentage of post-larvae was observed in Virgibacillus sp. 1 BF. Except for Pseudomonas sp. 3, Pseudoalteromonas sp. 32 and Bacillus sp. 13, other BF cell densities were significantly related to their corresponding inductive efficiency. The deep-sea Virgibacillus sp. 1 BFʼs cue that triggers planktonic-sessile transition was uncovered. Treating Virgibacillus sp. 1 BFs through physic-chemical approaches reduced inducing impact and cell survival. The conditioned water collaborated with formalin-fixed Virgibacillus sp. 1 BF hoisted planktonic-sessile transition efficiency in comparison to each one alone. Thus, two signals derived from deep-sea bacteria trigger planktonic-sessile transition in M. coruscus. This finding firstly demonstrates that deep-sea bacteria has good potential for application in the mussel seed production and provides novel insight to clarify the bacteria-mussel interaction.

Interactive effects of light and substrate colour on the recruitment of marine invertebrates on artificial materials

Marine invertebrate larvae are highly phototactic during early stages of larval period and greatly influenced by light, colour and other physio-chemical properties of the substrates. In the present study, the effects of light and substrate colour on recruitment of marine invertebrates were investigated. Four different colour panels (red, green, blue and yellow acrylic sheets) and colourless panel (clear transparent acrylic sheet) were suspended at 2 m depth in the central Red Sea for 4 weeks during two seasons (spring and summer). The effects of substrate colour on invertebrate recruitment were tested under light and shade conditions. The results revealed significant variations in the recruitment of invertebrates between different colour panels and the panels exposed to light and shade. Higher densities of invertebrates were observed on the panels exposed to shade but the bryozoans abundance was high on the panels exposed to light. Tube worms and bryozoans preferred blue colour panels and the abundance of barnacles and bivalves were high on red colour panels. Significant interaction between substrate colour and light was observed in the abundance of barnacles, tube worms, bivalves and bryozoans. In conclusion, this study indicated the ability of some marine invertebrate larvae to discriminate coloured substrates depending on the light intensity.

An unusual microbiome characterises a spatially-aggressive crustose alga rapidly overgrowing shallow Caribbean reefs

Several species of crustose coralline algae (CCA) and their associated microbial biofilms play important roles in determining the settlement location of scleractinian corals on tropical reefs. In recent decades, peyssonnelid algal crusts (PAC) have become spatial dominants across large areas of shallow Caribbean reefs, where they appear to deter the recruitment of scleractinians. Our genetic investigations of PAC in St. John, US Virgin Islands, amplifying the large-subunit ribosomal RNA and psbA protein D1 marker genes, revealed them to be identical to Ramicrusta textilis previously reported overgrowing corals in Jamaica. Specimens of PAC sampled from the Honduras were likewise identical, confirming that this crustose alga inhabits the easternmost and westernmost regions of the Caribbean. We also analysed 16S rDNA tag amplicon libraries of the biofilms associated with PAC and sympatric CCA, which is favoured for coral settlement. Our results show that the microbial communities on PAC (vs. CCA) are characterized by significantly lower numbers of the epibiotic bacterial genus Pseudoalteromonas, which facilitates the recruitment and settlement of marine invertebrates. From these data, we infer that PAC are therefore unlikely to be attractive as settlement sites for coral larvae. Given the significant ecological change anticipated on these reefs due to increasing cover of PAC, there is an urgent need to further investigate competitive interactions between PAC and scleractinian corals, and elucidate the role of PAC and their associated microbiomes in accentuating phase shifts from coral to algae on tropical reefs.

Abalone Recruitment in Low-Density and Aggregated Populations Facing Climatic Stress

Understanding spatial and temporal patterns in the recruitment of marine invertebrates with complex life histories remains a critical knowledge gap in marine ecology and fisheries. As marine invertebrates are facing multiple stressors from overfishing and climatic stress, it is important to evaluate the conditions that facilitate recruitment in low-density populations. The red abalone Haliotis rufescens historically supported an economically important fishery in California, but the fishery was sequentially closed as stocks declined, and the last fished area was closed in 2018 following the collapse of the kelp forests in Northern California. Here, red abalone recruitment was evaluated annually from 2012 to 2016 and monthly from 2016 to 2017 in Central California where red abalone naturally occur in highly aggregated but low-density populations because of sea otter predation. Trends in wind-driven upwelling, temperature, wave forces, and food resources (kelp) were evaluated over the same time period as factors that could affect recruitment patterns. Recruitment was annually consistent except in 2015, when recruitment declined by 76%, likely because of reproductive failure during the second year of the North Pacific marine heat wave. The monthly recruitment assessment was the first field assessment of red abalone recruitment over a full year, and it showed that red abalone can recruit year-round. There were no clear recruitment patterns associated with seasonal wind-driven upwelling or relaxation patterns, and kelp density was constant over the study period; however, conditions at the study sites included three key features that may provide optimal conditions for consistent recruitment: (1) spatial abalone aggregation, (2) a sheltered embayment that may retain larvae, and (3) persistent algal food resources. These results can inform statewide and global abalone recovery and management programs.

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.