Sand Habitats Research Articles

Movements, foraging and habitat selection of southern stingrays (Hypanus americanus) in a tropical ecosystem altered by an invasive seagrass

This study provides some of the first evidence of how a common Caribbean fish species that relies on seagrass and sand habitats interacts with an invasive seagrass. The invasive seagrass Halophila stipulacea, first documented in the Caribbean in 2002, has rapidly expanded its range, displacing native seagrasses, and overgrowing bare sand. The southern stingray (Hypanus americanus) uses shallow seagrass and sand habitats for foraging. This paper examined the impacts of the invasive seagrass, H. stipulacea, on southern stingray behavior, foraging and movement patterns using acoustic telemetry and visual observations. From 2015 to 2018, 15 southern stingrays (14 juveniles of unknown sex and 1 female) were tagged with acoustic transmitters and passively monitored within an acoustic array in Brewers and Perseverance Bays, St. Thomas, United States Virgin Islands. The residence time, rates of movement and activity spaces for 50% and 95% utilization distributions (UD) were calculated for day and night periods. Tagged southern stingrays were detected within the array on average for 260 d (range 11–801 d) and residency for all individuals averaged 53% over the monitoring period (1079 d). Mean rates of movement per individual ranged from 40 to 150 m h−1, was lowest during the nighttime and were significantly higher during crepuscular periods. Activity spaces during day and night periods were nearly identical and averaged 0.05 km2 and 0.25 km2 for 50% and 95% UD, respectively. Distances between day and night 50% UD activity spaces was 148 m (range 8–409 m) and mean percent overlap was 38%. In addition to acoustic monitoring, benthic cover of available habitats and visual surveys of stingray behavior and habitat preferences were conducted along fixed transects. Monotypic stands of the invasive H. stipulacea seagrass represented 42% of benthic cover, followed by bare sand (27%), mixed patches of native and invasive seagrasses (23%) and the native Syringodium filiforme (7%). A habitat selection index (HSI) comparing the percent cover of available habitats and habitats occupied by stingrays found a strong preference for the native seagrass S. filiforme (HSI = 2.30) and bare sand (HSI = 1.79) compared to H. stipulacea (HSI = 0.70). Visual surveys also revealed that 50% of foraging stingrays were in S. filiforme, while 28% and 17% were foraging in H. stipulacea and bare sand, respectively. Our results are an important baseline for examining how further expansion of H. stipulacea may affect southern stingray movement patterns and foraging preferences.

Taxonomic studies of Cycas debaoensis (Cycadaceae) from China

Traditionally, species delimitation based on morphological and distributional evidence often leads to over- or underestimation of species diversity. The primary distribution area of Cycas debaoensis includes two habitats, which were initially published as two separate species, i.e., C. debaoensis in the karst habitat, and C. panshuiensis, which was originally published as Cycas gracilis Y.Y. Huang, Y.C. Zhong et Z.F. Lu, in the sand habitat. However, field investigations and population sampling in these two habitats revealed a certain degree of morphological transition and variation among the populations. Subsequent population genetic analysis showed minimal genetic differentiation among the populations in the two habitats, suggesting that they should be merged as a single species. Additionally, the typification of the name C. debaoensis is also discussed.

Role of macroalgal forests within Mediterranean shallow bays in blue carbon storage

Although seaweeds rank among the most productive vegetated habitats globally, their inclusion within Blue Carbon frameworks is at its onset, partially because they usually grow in rocky substrates and their organic carbon (Corg) is mostly exported and stored beyond their habitat and thus, demonstrating its long-term storage is challenging. Here, we studied the sedimentary Corg storage in macroalgal forests dominated by Gongolaria barbata and in adjacent seagrass Cymodocea nodosa mixed with Caulerpa prolifera algae meadows, and bare sand habitats in Mediterranean shallow coastal embayments. We characterized the biogeochemistry of top 30 cm sedimentary deposits, including sediment grain-size, organic matter and Corg contents, Corg burial rates and the provenance of sedimentary Corg throughout stable carbon isotopes (δ13Corg) and pyrolysis analyses. Sediment Corg stocks and burial rates (since 1950) in G. barbata forests (mean ± SE, 3.5 ± 0.2 kg Corg m−2 accumulated at 15.5 ± 1.6 g Corg m−2 y−1) fall within the range of those reported for traditional Blue Carbon Ecosystems. Although the main species contributing to sedimentary Corg stocks in all vegetated habitats examined was C. nodosa (36 ± 2 %), macroalgae contributed 49 % (19 ± 2 % by G. barbata and 30 ± 3 % by C. prolifera) based on isotope mixing model results. Analytical pyrolysis confirmed the presence of macroalgae-derived compounds in the sediments, including N-compounds and α-tocopherol linked to G. barbata and C. prolifera, respectively. The sedimentary Corg burial rate linked to macroalgae within the macroalgal forests examined ranged from 5.4 to 9.5 g Corg m−2 y−1 (7.4 ± 2 g Corg m−2 y−1). This study provides empirical evidence for the long-term (∼70 years) sequestration of macroalgae-derived Corg within and beyond seaweed forests in Mediterranean shallow coastal embayments and thereby, supports the inclusion of macroalgae in Blue Carbon frameworks.

Untangling Coastal Diversity: How Habitat Complexity Shapes Demersal and Benthopelagic Assemblages in NW Iberia

Understanding species–habitat relationships is essential for ecosystem-based conservation. This study explores the significance of habitat characteristics and complexity for demersal and benthopelagic communities within a patchwork of coastal habitats, including rocky seabed, macroalgae formations, sandy bottoms, and a combination of rock and sand areas. Species and habitats were surveyed along the north-west (NW) Iberian continental shelf area of Viana do Castelo using baited remote underwater video stations (BRUVS). We found significant differences (p < 0.05) in species assemblages across habitats, with rocky substrates showing the highest diversity and abundance. Sand habitats showed the lowest species richness and abundance, underscoring the importance of habitat complexity to support marine life. Our study also emphasises the role of specific species in shaping the communities, identifying key species such as Trisopterus luscus, Diplodus vulgaris, and Ctenolabrus rupestris as the three most abundant in the region and significant contributors to the observed dissimilarities between habitats. By elucidating the impact of habitat complexity on marine life, our results offer essential baseline data, which serve as a kick-start point to inform sustainable management and conservation strategies for the long-term health and productivity of these vital ecological systems in the North-East Atlantic.

Local habitat composition and complexity outweigh seascape effects on fish distributions across a tropical seascape

ContextThe distribution of animals is influenced by a complex interplay of landscape, environmental, habitat, and anthropogenic factors. While the effects of each of these forces on fish assemblages have been studied in isolation, the implications of their combined influence within a seascape remain equivocal.ObjectivesWe assessed the importance of local habitat composition, seascape configuration, and environmental conditions for determining the abundance, diversity, and functional composition of fish assemblages across a tropical seascape.MethodsWe quantified fish abundance in coral, macroalgal, mangrove, and sand habitats throughout the Dampier Archipelago, Western Australia. A full-subsets modelling approach was used that incorporated data from benthic habitat maps, a hydrodynamic model, in situ measures of habitat composition, and remotely sensed environmental data to evaluate the relative influence of biophysical drivers on fish assemblages.ResultsMeasures of habitat complexity were the strongest predictors of fish abundance, diversity, and assemblage composition in coral and macroalgal habitats, with seascape effects playing a secondary role for some functional groups. Proximity to potential nursery habitats appeared to have minimal influence on coral reef fish assemblages. Consequently, coral, macroalgal, and mangrove habitats contained distinct fish assemblages that contributed to the overall diversity of fish within the seascape.ConclusionsOur findings underscore the importance of structural complexity for supporting diverse and abundant fish populations and suggest that the value of structural connectivity between habitats depends on local environmental context. Our results support management approaches that prioritise the preservation of habitat complexity, and that incorporate the full range of habitats comprising tropical seascapes.

Evaluation of growth adaptation of Cinnamomum camphora seedlings in ionic rare earth tailings environment

The root system is an important organ for nutrient uptake and biomass accumulation in plants, while biomass allocation directly affects essential oils content, which plays an essential role in plant growth and development and resistance to adverse environmental conditions. This study was undertaken to investigate the differences and correlation of biomass allocation, root traits and essential oil content (EOC), as well as the adaptations of camphor tree with different chemical types to the ionic rare earth tailing sand habitats. Data from 1-year old cutting seedlings of C. camphora showed that the biomass of C. camphora cuttings was mainly distributed in root system, with the ratio of root biomass 49.9–72.13% and the ratio of root to canopy 1.00–2.64. The total biomass was significantly positively correlated with root length (RL), root surface area (RSA) and dry weight of fine roots (diameter ≤ 2 mm) (P < 0.05). Root biomass and leaf biomass were negatively and positively with specific root length (SRL) and specific root surface area (SRSA), respectively. Leaf biomass presented a positive effect on EOC (P < 0.05), with the correlation coefficient of 0.808. The suitability sort of these camphor trees was as follows: C. camphora β-linalool, C. camphora α-linaloolII, C. camphora α-linaloolI being better adapted to the ionic rare earth tailings substrate, C. camphora citral being the next, and C. porrectum β-linalool and C. camphora borneol being the least adaptive. EOC played a positive role in the adaptation of C. camphora (R2 = 0.6099, P < 0.05). Therefore camphor tree with linalool type is the appropriate choice in the ecological restoration of ionic rare earth tailings. The study could provide scientific recommendations for the ecological restoration of ionic rare earth tailings area combined with industrial development.

Seasonal variability of lotic macroinvertebrate communities at the habitat scale demonstrates the value of discriminating fine sediment fractions in ecological assessments.

Despite lotic systems demonstrating high levels of seasonal and spatial variability, most research and biomonitoring practices do not consider seasonality when interpreting results and are typically focused at the meso-scale (combined pool/riffle samples) rather than considering habitat patch dynamics. We therefore sought to determine if the sampling season (spring, summer and autumn) influenced observed macroinvertebrate biodiversity, structure and function at the habitat unit scale (determined by substrate composition), and if this in turn influenced the assessment of fine sediment (sand and silt) pressures. We found that biodiversity supported at the habitat level was not seasonally consistent with the contribution of nestedness and turnover in structuring communities varying seasonally. Habitat differences in community composition were evident for taxonomic communities regardless of the season but were not seasonally consistent for functional communities, and, notably, season explained a greater amount of variance in functional community composition than the habitat unit. Macroinvertebrate biodiversity supported by silt habitats demonstrated strong seasonal differences and communities were functionally comparable to sand habitats in spring and to gravel habitats in autumn. Sand communities were impoverished compared to other habitats regardless of the season. Silt habitats demonstrated a strong increase in Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa and functional richness from spring into autumn, while vegetation habitats displayed a peak in EPT abundance in summer. Only silt and sand habitats demonstrated temporal variability in functional evenness suggesting that these habitats are different in terms of their resource partitioning and productivity over time compared to other habitats. Gravel and vegetation habitats appeared to be more stable over time with functional richness and evenness remaining consistent. To accurately evaluate the influence of fine sediment on lotic ecosystems, it is imperative that routine biomonitoring and scientific research discriminate between sand and silt fractions, given they support different biodiversity, particularly during summer and autumn months.

Seasonal variation in the land hermit crab, Coenobita rugosus H. Milne Edwards, 1837 (Decapoda, Anomura) and a preliminary study of land hermit crabs as a bioindicator of turtle nesting at Penghu County Wang-An Island green turtle nesting refuge, Taiwan

Abstract The present study surveyed the land hermit crab species, body size, shell type, and shell suitability, at five sites over four seasons in the Penghu County Wang-an Island Green Turtle Nesting Refuge. Coenobita rugosus H. Milne Edwards, 1837 was the only species recorded and found at three sites (Tiantai Hill, Xi’an Reservoir, and Tudigong). The density index of hermit crabs exhibited notable variations across the sites, showing no significant variation with the changing seasons. The bush habitat displayed a higher density index compared to the sand habitat. Additionally, the sites differed significantly in terms of the shell type and body size of the hermit crabs. Further, no significant relationship was established between abundance and weather factors or between crab abundance and sea turtle nesting. This investigation is a preliminary examination of the possibility of land hermit crabs being used as bioindicators for breeding of sea turtles.

Mapping coral reef habitats of Apo Reef Natural Park, Sablayan, Occidental Mindoro, Philippines

Limited spatial information on Philippine oceanic coral reef resources poses a challenge to conservation and management. In the face of an increased occurrence of natural disturbances, repetitive, broad-scale spatial information is critical in determining large-scale patterns that help managers resolve the potential trajectory of the coral reef ecosystems, elucidating whether it will recover or continue to decline. In this study, we provide a decent habitat map of Apo Reef Natural Park using freely available Sentinel-2 data using the Google Earth Engine (GEE) cloud computing platform. Through the use of training and validation data, we implemented supervised classification via the classification and regression trees (CART) algorithm. The results successfully delineated four major habitat classes across ARNP with an acceptable level of accuracy (58.8%). These habitat classes are: Mixed Live Coral and DCA habitat, DCA habitat, Mixed Rubble and DCA habitat, and Sand habitat. In total, we mapped over 6,000 hectares of shallow subtidal habitats across a 27,000-hectare protected area. Among the classes, sand-dominated habitats had the largest coverage in the shallow subtidal section of the reef complex. The total hard coralline substrate was estimated to cover over 3,800 hectares. The impact of consecutive, high-intensity disturbances that hit ARNP resulted in the predominance of algae-covered habitat types, which in turn resulted in relatively high classification errors of DCA habitats, and Mixed Live Coral and DCA habitats. It is expected that as the reef recovers, accuracy in discerning these habitat types will eventually increase. The study shows the utility of the GEE platform in conducting low-cost, broad-scale monitoring of oceanic reef complexes at a resolution that is acceptable for management purposes.

Relating benthic sensitivity and status to spatial distribution and intensity of trawling in the Eastern Mediterranean

The ecosystem approach to fisheries management needs information of not just where bottom trawlers operate but also on their impact on the seabed, which is also highly relevant to the EU Marine Strategy Framework Directive (MSFD) Descriptor D6, seafloor integrity. In this study, we assess the benthic impact of bottom trawling in the Eastern Mediterranean in areas primarily fished by the Greek fleet. Seabed habitat sensitivity was modelled using macrofaunal longevity and biomass relationship based on data from more than 800 locations, representing 9 MSFD benthic habitats, and benthic status was assessed using the relative benthic status indicator. The pressure of seabed trawling was higher in circalittoral mud and circalittoral sand habitats showing a heterogeneous distribution pattern with intensive trawling in localized areas mainly coastal. Benthic status was high for all habitats reflecting the low trawling intensity and impact in most of the study area compared to other regions of Mediterranean or European waters. The results constitute the benchmark for benthic status in relation to trawling intensity in Eastern Mediterranean allowing to identify regions that are most at risk, and to prioritize management actions.

Exploring Benthic Scavenger Assemblages, a Multi-Habitat Approach in NW Iberian Peninsula

Scavenging fauna plays an integral role in ecosystem functioning, nutrient cycling and circulating organic matter. Thus, baseline data of scavenger assemblages on the NW coast of the Iberian Peninsula that provides information on the abundance of species in different habitats is crucial to understanding the distribution of this understudied group. Two different types of baited traps, to capture scavenging megafaunal and scavenging benthopelagic macrofaunal assemblages, were deployed to compare them among rocky, pebbled and sandy bottoms at shallow subtidal on the northern coast of Portugal. Results showed significant differences in the structure of scavenger assemblages. Scavenging megafaunal assemblages differed between sandy and the other two studied habitats, whereas benthopelagic macrofaunal assemblages differed between pebbles and rocky habitats. This suggests that different drivers seem to shape the structure of benthopelagic macrofauna and megafauna. Regarding megafauna, the dominance of Tritia gastropods in sand habitats in comparison with its absence in rock and its very low abundance in pebbles was mainly responsible for the differences. However, in benthopelagic macrofauna, differences in assemblages between pebbles and rock were more related to changes in the relative abundance of crustacean species (Cirolana cranchii and Socarnes erythrophthalmus) that were less abundant in pebbles.

Species characterization of soft bottom habitats by depth and sediment particle size on the Catalan coast (NW Mediterranean): unexpected species composition of the assemblages

The aim of the study is to describe the macrofaunal composition of marine soft bottom habitats on the Catalan coast between a depth of 3 and 35 meters, considering all groups of macroinvertebrates. The study also aims to compare our data with previous studies focused on the NW Mediterranean and to define the variables that drive assemblage composition. Depending on the species composition and the structure of the assemblages, six different habitats, mainly defined by depth and sediment granulometry, are described. Shallow (&lt;20 m) and deep (&gt;20 m) habitats are easily distinguished and are subdivided in three habitats each: (1) very coarse and coarse sediments (coarse sediments); (2) medium, fine and very fine sands (fine sediments); and (3) muddy sediments. Fine sediments in both shallow and deep waters have emerged as the most common and extensive habitats along the coast up to a depth of 35 meters. Neither coarse nor muddy habitats are frequent. The characterization of shallow habitats produced some unexpected results with respect to previous studies: Spisula subtruncata and Lucinella divaricata were dominant, while neither Ditrupa arietina nor Owenia fusiformis, previously mentioned as dominant polychaetes in shallow fine sand habitats, were common. Polychaetes were, in general, the dominant group (both in species richness and abundance) in the six habitats, except in shallow fine sediments, which were dominated by mollusks. The study is a benchmark for future monitoring of soft bottom habitats on the Catalan coast to a depth of 35 meters.

Blinded by the bright: How species‐poor habitats contribute to regional biodiversity across a tropical seascape

AbstractAimConservation efforts have traditionally addressed the threat of biodiversity loss by prioritizing regions and habitats with high endemic species richness. However, species‐poor habitats often harbour distinct, valuable and/or functionally unique species that contribute to regional diversity. In the tropical marine realm, the ‘mangrove‐seagrass‐coral reef continuum’ has dominated both the scientific literature and marine spatial planning. Bare sediment habitats are also part of this continuum and often comprise the majority of bottom area, as they do in most regions worldwide, but are understudied and rarely considered in conservation. To address this information gap, we partition the relative contributions of five habitats in the coastal mosaic (forereefs, patch reefs, seagrass, mangroves and bare sand) to fish diversity across a tropical seascape.LocationCarrie Bow Cay, Belize Barrier Reef.MethodsUsing diver visual censuses, we assessed fish community composition at three replicate sites from each of the five habitats annually for 5 years. We then partitioned diversity into within (α) and between (β) habitat contributions, and further partitioned β‐diversity into components attributed to species replacement and richness difference. Finally, we determined the local contributions to β‐diversity (LCBD) by each habitat and identified the key individual species behind these contributions.Main ResultsTropical sand flats contributed uniquely and disproportionately to regional fish species diversity, despite having the fewest species overall. Sand flats also had higher‐than‐expected local contributions to β‐diversity (LCBD) and had the highest percentage of species not found in other habitats.Main ConclusionsOur results demonstrate that previously understudied sand habitats harbour a relatively unique assemblage of species compared with other nearby habitats. Marine spatial planning aimed at maximizing the preservation of total biodiversity (including unique species) in the tropics should consider sand habitats.

A Multidisciplinary Approach for A Better Knowledge of the Benthic Habitat and Community Distribution in the Central and Western English Channel

About 80% of the seabed of the English Channel (EC) is covered by coarse sediment, from coarse sand to pebbles. Quantitative data on the benthic macrofauna in these types of sediment remains are rare due to the difficulty of using grab corers in such hard substrates. The deepest central part of the EC (45–101 m depth) was prospected during two VIDEOCHARM surveys in June 2010 and June 2011 to increase knowledge of such sublittoral coarse sediment benthic habitats. Sampling focussed on a longitudinal transect in the deepest part of the EC (13 boxes), extending from the western approach to the Greenwich meridian. Both indirect (side scan sonar, Remote Operated Vehicule) and direct (grab sampling with benthos determination, and grain-size analyses) approaches were used and combined, permitting description of the benthic habitats and communities using seven methods. Five benthic EUNIS habitats (European Nature Information System) were reported: MC3215, MD3211, MC4, MC3212 and MC4215, of which two extended main habitats (MC3211 and M23212) corresponded to an eastern/western gradient from sandy gravel to sandy gravel and pebbles sediment. Three other spatially discrete habitats were associated with poor coarse sand and gravel habitats as well as sandy gravel and pebbles with the presence of the brittle star Ophiothrix fragilis. Taxonomic richness of both extended habitats was on the same order of magnitude as the coarse sand habitat reported elsewhere in the EC, whilst the abundances were among the lowest in deeper areas with low nutrient input and low primary production. The epifauna appeared relatively homogenous in this type of sediment at the scale of the sampling area and was not determined to assign a EUNIS habitat/class. ROV footage illustrated the presence of large epifauna and provided valuable information to ground truth in other sampling methods such as side scan sonar mosaic. Grab photos showing surface sediment was relevant to determine the sediment type, whilst granulometric analyses gave additional information on fine particles content (typically very low).

Diet composition and trophic niche differentiation of Neogobius melanostomus along an invasion gradient in a large lowland river

The Ponto-Caspian goby Neogobius melanostomus (Pallas 1814) is a widespread non-native fish species in European rivers. It occurs in high abundance and can potentially alter the food webs of invaded water bodies profoundly. However, the invasion process usually goes unnoticed, and changes in food webs during the early stages of invasions are rarely described. Here, we studied populations of N. melanostomus along an invasion gradient in the Elbe River (Germany) and tested the effects of time since invasion on the diets and the associated trophic dynamics in two dominant habitats, i.e., rip rap and sand. Results showed that the abundance and biomass of N. melanostomus was lowest at the most recently invaded sites. The trophic niche space quantified by stable isotopes (δ ¹³ C and δ ¹⁵ N) showed that populations at earlier invaded sites exhibited a wider trophic niche than those at the most recently invaded sites. Diptera and Crustacea were the most abundant taxa in N. melanostomus guts at both habitat structures. At rip rap habitats, N. melanostomus showed a significant increasing preference for Crustacea and a decreasing one for Gastropoda along the invasion gradient. At sand habitats no significant relationships between the invasion gradient and electivity index for N. melanostomus were detected. We demonstrated that the invasion stage and habitat in which N. melanostomus occurs affect the feeding preference of this invasive fish and that these factors are therefore important for tracing changes in the macroinvertebrate communities of affected river systems.

Photosynthetic and water-related physiological characteristics of Periploca sepium in response to changing soil water conditions in a shell sand habitat

This study was performed to observe the effects of water on photosynthesis and water-related physiology in dominant shrubs in shell sand habitats. Four-year-old Periploca sepium seedlings were used as model species. A gradient of 12 water levels was established by artificially supplying the shell sand with water up to saturation and then allowing natural evapotranspiration to occur. The photosynthetic, chlorophyll fluorescence and stem sap flow parameters of P. sepium were measured under a range of water conditions. The different soil water conditions were classified according to the responses of these parameters. (1) With the increase in the relative water content (RWC) of the shell sand, the parameters of leaf photosynthesis, chlorophyll fluorescence and water-related physiology in P. sepium showed significant critical responses. The net photosynthetic rate (Pn), transpiration rate (Tr), instantaneous water use efficiency (WUE), potential water use efficiency (WUEi), maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII) and daily accumulation of stem sap flow all increased first and then decreased with increasing RWC, but the corresponding water conditions associated with their maximum values were not the same. An RWC of 69.40% was determined to be the optimal water condition for photosynthesis and water-related physiological activity in P. sepium. At an RWC of 36.61%, the mechanism of photosynthetic inhibition in P. sepium changed from stomatal limitation to nonstomatal limitation; this was also the minimum water requirement for maintaining normal photosynthetic processes. An RWC of 50.27% resulted in the highest WUE in P. sepium, indicating that moderate drought stress increased WUE. (2) Based on the quantitative relationship between the photosynthetic parameters of P. sepium and the shell sand water gradient, the soil water availability was classified into 6 water grades. The RWC range for maintaining strong photosynthesis and high WUE in P. sepium was 63.22–69.98%. (3) Gas exchange in P. sepium was inhibited under drought and waterlogging stresses. Under these conditions, the photosynthetic electron transport chain was blocked, and the dissipation of light energy as heat increased, which ultimately led to a decline in photosynthetic productivity; moreover, transpiration and dissipation were aggravated, and water transmission and utilization processes in P. sepium were hindered. A significant negative feedback regulation mechanism in the photosynthetic and water-related physiological processes of P. sepium was observed; this mechanism allowed P. sepium growing in shell sand to be highly adaptable to water stress.

Edge effects influence the composition and density of reef residents on subtidal restored oyster reefs

Within estuarine and coastal ecosystems globally, extensive habitat degradation and loss threaten critical ecosystem functions and necessitate widescale restoration efforts. There is abundant evidence that ecological processes and species interactions can vary with habitat characteristics, which has important implications for the design and implementation of restoration efforts aimed at enhancing specific ecosystem functions and services. We conducted an experiment examining how habitat characteristics (presence; edge vs. interior) influence the communities of resident fish and mobile invertebrates on restored oyster (Crassostrea virginica) reefs. Similar to previous studies, we found that restored reefs altered community composition and augmented total abundance and biomass relative to unstructured sand habitat. Community composition and biomass also differed between the edge and interior of individual reefs as a result of species‐specific patterns over small spatial scales. These patterns were only weakly linked to oyster density, suggesting that other factors that vary between edge and interior (e.g. predator access or species interactions) are likely more important for community structure on oyster reefs. Fine‐scale information on resident species' use of oyster reefs will help facilitate restoration by allowing decision makers to optimize the amount of edge versus interior habitat. To improve the prediction of faunal use and benefits from habitat restoration, we recommend investigations into the mechanisms shaping edge and interior preferences on oyster reefs.

Leveraging eDNA metabarcoding to characterize nearshore fish communities in Southeast Alaska: Do habitat and tide matter?

AbstractNearshore marine habitats are critical for a variety of commercially important fish species, but assessing fish communities in these habitats is costly and time‐intensive. Here, we leverage eDNA metabarcoding to characterize nearshore fish communities near Juneau, Alaska, USA, a high‐latitude environment with large tidal swings, strong currents, and significant freshwater input. We investigated whether species richness and community composition differed across three habitat types (sand beaches, eelgrass beds, and rocky shorelines) and between high and low tides. Additionally, we tested whether replication of field samples and PCR reactions influenced either species richness or composition. We amplified a 12S mitochondrial locus in our samples and identified 167 fish amplicon sequence variants, which were grouped into 24 unique taxa based on sequence similarity, with approximately half of these taxa resolved to single species. Species richness and composition inferred from eDNA differed substantially among habitats, with rock habitats containing fewer taxa and fewer overall detections than sand and eelgrass habitats. The effect of tide was not significant on its own, but a significant habitat‐tide interaction was documented, with the most pronounced differences in taxa between tides found in sand habitats. Power analyses indicated that additional field sampling is useful to detect small changes in species richness such as those due to tide. PCR replicates typically identified few additional taxa. Our results provide important information that can be used to guide future studies, most notably, that the influence of tide on eDNA results appears to be minimal and potentially isolated to certain habitats. This suggests that replication across tides may not be vital for future eDNA studies and that additional replication across space—particularly across heterogeneous environments—likely is a better allocation of sampling effort.

Pull the trigger: interplay between benthic and pelagic cues driving the early recruitment of a natural bivalve assemblage

AbstractLarval settlement and recruitment are crucial phases in the benthic‐pelagic life cycle of marine benthic invertebrates that controls population dynamic and habitat connectivity. Our study investigated potential triggers driving the settlement of bivalve larvae in a highly dynamic intertidal coarse sand habitat. The early recruitment rate of five dominant bivalve families and abiotic conditions, particulate (&lt;20 µm) organic matter and sediment organic matter, were monitored from May to October 2014. Pelagic particulate organic matter (&lt;20 µm) was dominated by picoplankton throughout the sampling period, with a substantial diatom bloom in spring. Sediment was characterized by fresh organic matter in spring, as suggested by the dominant contribution of polyunsaturated fatty acids, and by a higher proportion of bacterial fatty acid markers during late summer. Different dynamics were also observed in early bivalve recruitment rates, with four different patterns observed over the sampling period. Multiple regression analysis on selected bivalve families showed species‐specific responses to trophic settlement triggers. Indeed, the larva recruitment rate of Mytilidae paralleled pelagic concentration of picoeucaryotes, with the peak early recruitment rate occurring in spring. Surprisingly, the early recruitment rate of Mactridae larvae showed a significant relation to bacterial concentration in the surficial sediment at the end of summer. While the Mytilidae results in such a eutrophic system confirmed those of a previous study in oligotrophic lagoons, therefore supporting the trophic settlement trigger hypothesis, more work is needed to understand the potential role of bacteria in the early recruitment of Mactridae. These results highlight for the first‐time inter‐specific differences in trophic cues that potentially trigger primary settlement in natural bivalve assemblages.

Artificial coral reefs as a localised approach to increase fish biodiversity and abundance along the North Bali coastline

&lt;abstract&gt; &lt;p&gt;Coral reefs face worldwide decline from threats such as climate change, destructive fishing practices, overfishing and pollution. Artificial reefs have shown potential as a method to mitigate localised habitat loss and biodiversity decline on degraded coral reefs. The health of coral reefs in Indonesia and their associated faunal populations have displayed a downward trend in recent decades, and community-managed non-government organisations have started using artificial reefs to restore local degraded reef habitats. In this study, we demonstrate how locally-managed NGOs and communities in north Bali, Indonesia have implemented artificial reef projects, and assess the associated benefits to biodiversity. Using Remote Underwater Video (RUV) over a 3 month period in north Bali, fish assemblages on two artificial reefs of different ages (new and mature) were compared to two nearby natural habitats: degraded sand flats and relatively healthy coral reefs. When compared with a nearby degraded sand habitat, both artificial reefs displayed a significantly higher number of species, which for the mature artificial reef was not statistically different to a nearby coral reef. Community structure was also compared, again showing similarity between artificial reefs and natural coral reefs, but differing in a few species, including specific damselfish and wrasse. This study is one of few which highlight the potential of artificial reef habitat enhancement in Indonesia, and suggests that these structures can provide ecologically equivalent mobile faunal communities to a natural reef on a localised scale. As such, well designed projects may be able to provide some local ecosystem services lost from degraded coral reefs, and become an important focus for coastal communities.&lt;/p&gt; &lt;/abstract&gt;