Mobile Invertebrates Research Articles

Facilitation cascades across space: Monitoring estuarine foundation species from satellites to the microscope

AbstractEstuaries are productive ecosystems that are vulnerable to human impacts and environmental disturbances. Estuaries are often inhabited by foundation species that facilitate other organisms by creating and modifying habitats. However, spatiotemporal variability and underpinning drivers of facilitation from estuarine foundation species are poorly studied, especially in the context of monitoring and conservation. Here, we combined the analyses of satellite, drone, and camera images, close‐up field sampling of quadrats and individuals, and laboratory microscopy, to quantify co‐occurrences between the cockle Austrovenus stutchburyi and green macroalga Ulva spp., and their associated invertebrate communities, across spatial resolutions and environmental gradients in a New Zealand estuary. We found higher abundance of Ulva in winter and higher abundance of Austrovenus at a site near the ocean. Furthermore, Ulva was, across space and time, often attached to Austrovenus, either live or dead shells, suggesting a hierarchy between a primary (cockle) and secondary (macroalgae) foundation species. Finally, Ulva provided a better habitat for mobile invertebrates than Austrovenus, and thereby increased estuarine diversity through a density‐dependent facilitation cascade, which also was consistent in space and time. Overall, our study showed that facilitation cascades can be indirectly inferred and monitored through remote sensing of foundation species using supplementary imaging methods, and that integration of data across scales allows researchers to better understand the drivers and consequences of facilitation from foundation species. These insights may aid in the development of efficient monitoring strategies and ultimately improve the management of estuarine ecosystems.

A marine heatwave changes the stabilizing effects of biodiversity in kelp forests.

Biodiversity can stabilize ecological communities through biological insurance, but climate and other environmental changes may disrupt this process via simultaneous ecosystem destabilization and biodiversity loss. While changes to diversity-stability relationships (DSRs) and the underlying mechanisms have been extensively explored in terrestrial plant communities, this topic remains largely unexplored in benthic marine ecosystems that comprise diverse assemblages of producers and consumers. By analyzing two decades of kelp forest biodiversity survey data, we discovered changes in diversity, stability, and their relationships at multiple scales (biological organizational levels, spatial scales, and functional groups) that were linked with the most severe marine heatwave ever documented in the North Pacific Ocean. Moreover, changes in the strength of DSRs during/after the heatwave were more apparent among functional groups than both biological organizational levels (population vs. ecosystem levels) and spatial scales (local vs. broad scales). Specifically, the strength of DSRs decreased for fishes, increased for mobile invertebrates and understory algae, and were unchanged for sessile invertebrates during/after the heatwave. Our findings suggest that biodiversity plays a key role in stabilizing marine ecosystems, but the resilience of DSRs to adverse climate impacts primarily depends on the functional identities of ecological communities.

Amphipoda from depths exceeding 6,000 meters revisited 60 years on

Abstract In the 1950s, the Danish Galathea Expedition undertook one of the first and most comprehensive explorations of our ocean’s hadal zone, depths extending from 6,000 to nearly 11,000 m, and presented a rich collection of the diversity of Amphipoda. The subsequent papers, however, concluded that these established ‘nothing essentially new’ to the existing knowledge of amphipod biology. Since Dahl’s foundational paper in 1959, amphipods, primarily from the superfamilies Lysianassoidea and Alicelloidea, emerged as one of the best-sampled hadal fauna, as these mobile invertebrates are readily recovered by different sampling techniques. Importantly, amphipods have become the model taxon, helping us to unlock knowledge about life in the hadal zone. In this review, we collate the knowledge gained since the Galathea Expedition and summarise the current understanding of how amphipods that appear during hadal exploration survive the trench environments. We discuss population structures across depth, inter-trench distribution and connectivity, applications in hadal microbiology, and, critically, how the hadal zone is being impacted by anthropogenic activity.

A legacy of invasive sun corals: Distinct mobile invertebrate assemblages at near-reef coral-dominated rubble

Fast-growing and reproducing sun corals have successfully invaded rocky reefs around the Atlantic Ocean, markedly reducing the diversity of fouling invertebrates and macroalgae, and profoundly changing the composition of reef-associated mobile invertebrates. Here, we address sun-coral rubble depositions and report, for the first time, the effects of sun corals on near-reef soft-bottom invertebrate assemblages. Abundance, richness and diversity were higher at rubble habitats compared to bare sandy grounds, which could be a positive effect of substrate complexity. All those parameters were also higher at rubble patches dominated by sun-coral fragments compared to rubble patches dominated by pebbles or shell fragments, also suggesting possible additive effects of coral-borne chemical attraction (sun-coral specific, as inputs of other coral species were virtually absent). Different epifaunal groups were exclusive of rubble habitats and a subset of those exclusive of sun-coral rubble, explaining the incremental richness across habitats. The relative abundance of the two dominant groups – polychaetes (p) and amphipods (a) – contributed the most to the observed contrasts on community structure, as their proportion (p:a) changed from 10:1 in bare sand to nearly co-dominance in coral rubble. While previous research suggested that spreading sun corals reduce prey supply for fish foraging on reef walls, our results suggest they may increase prey abundance and diversity at the adjacent non-consolidated habitat, possibly reshaping trophic pathways connecting the benthic and the pelagic environment.

Cryptic biodiversity inhabiting coral reef sponges

AbstractSponges host a wide range of cryptic biodiversity both internally and externally. This study quantified the biodiversity inhabiting, or associated with, three morphologically distinct coral reef sponges. Coelocarteria singaporensis, Coscinoderma mathewsi and Ircinia microconulosa were collected from fringing reefs at Orpheus Island, central Great Barrier Reef, across monsoonal seasons (wet and dry) and diurnal periods (morning, afternoon and night for C. singaporensis) to quantify Sponge Associated Biota (SAB). A total of 8489 SAB was sorted from 77 sponges. Twenty‐six taxa, across 3 kingdoms and 12 phyla were recorded. Sponge‐associated biota was dominated by Mollusca in all three sponge hosts (range ~ 46%–50%) but taxa were found from a number of other phyla including, Arthropoda, Annelida, Echinodermata, Cnidaria, Foraminifera and Nemertea. There was no effect of season on abundances of SAB within the three species of sponge, but there was a significant effect associated with sponge host species, driven by a higher number of SAB in C. singaporensis and I. microconulosa. The diurnal patterns of SAB within C. singaporensis showed consistent abundances of mobile invertebrate groups with molluscs, echinoderms and arthropods dominating these samples. This study also highlights the ecological role and contribution of SAB in the reef ecosystems.

Fire severity is an important driver of land snail declines after the black summer bushfires in Australia

Many ecosystems globally evolved with fire. However, there is a gap in our knowledge regarding the effect of fires on less mobile invertebrates. Land snails in Australia are a diverse group with a high level of endemism, but we understand very little of their ecology, especially how they are affected by large fires.We studied the short-term (one year after a fire event) response of 1) land snail species composition, 2) snail abundances, and 3) impacts on 18 priority species to an unprecedented large fire event throughout south-eastern Australia in 2019/2020 (Black Summer). Our study ranged over >100,000 km2, surveying162 sites. Our study revealed that land snail species composition changed significantly depending on fire severity class, regardless of habitat type (rainforest or eucalypt forest) or climate. Medium and high severity fire caused snail abundance to decline significantly, with micro-snails being more sensitive to medium and high severity fires. Abundance dropped by 75 % and 64 % for micro-, and macro-snails respectively, but low severity fire did not have a significant impact on abundance. For most priority species, fires affected more than half of their known extent of occurrence although most species were found in all fire severities. However, severity category was an important driver in determining the probability of occurrence of priority species. To conserve Australia's land snail species, we must know how they are affected by disturbances. Our results suggest that the total area and severity of fires will determine the impact of fires on land snails.

Sea anemone microhabitats enhance the diversity and biomass of mobile invertebrates on temperate rocky shores

Sea anemones of the genus Anthopleura are abundant in rocky intertidal communities of the eastern Pacific, but their role as habitat and facilitators of biodiversity in this system has been overlooked. We provide evidence for a previously undescribed mechanism of facilitation associated with these cnidarians on temperate rocky shores. Sea anemones in the genus Anthopleura slowly release stored water at low tide, which helps them maintain ideal temperature conditions via evaporative cooling. This behavior results in leakage of water to surrounding intertidal habitats, producing unique microhabitats in the upper intertidal zone. We hypothesized that mobile invertebrate communities would use this habitat during low tides to ameliorate abiotic stress. In an in situ experiment spanning 3 sites along the coast of California, USA, it was found that maximum temperatures and relative desiccation rates were lower in sea anemone-associated microhabitats as compared to adjacent rock habitats. Observational surveys revealed higher richness and biomass of mobile invertebrates in sea anemone microhabitats, and these differences were supported by manipulative experiments that included both adding and removing sea anemones. Our results support a novel community-wide facilitation driven by an adaptation of intertidal sea anemones. The effects of sea anemone microhabitat on upper shore biodiversity were associated with site and sea anemone species and may suggest a facilitative role of a temperate cnidarian-algal mutualism in mitigating stress and enhancing biodiversity.

Organic matter processing in a [simulated] offshore wind farm ecosystem in current and future climate and aquaculture scenarios.

The rapid development of blue economy and human use of offshore space triggered the concept of co-location of marine activities and is causing diverse local pressures on the environment. These pressures add to, and interact with, global challenges such as ocean acidification and warming. This study investigates the combined pressures of climate change and the planned co-location of offshore wind farm (OWF) and aquaculture zones on the carbon flow through epifaunal communities inhabiting wind turbines in the North Sea. A 13C-labelled phytoplankton pulse-chase experiment was performed in mesocosms (4 m3) holding undisturbed hard-substrate (HS) communities, natural sediment with infauna, and mobile invertebrate predators. Carbon assimilation was quantified under current and predicted future-climate conditions (+3 °C and -0.3 pH units), as well as a future-climate co-use scenario with blue mussel (Mytilus edulis) aquaculture. Climate change induced an increase in macrofaunal carbon assimilation as well as an organic enrichment of underlying sediments. Dynamic (non-)trophic links between M. edulis and other HS epifauna resulted in shifts among the species contributing most to the phytoplankton-derived carbon flow across climate scenarios. Increased inter- and intraspecific resource competition in the presence of M. edulis aquaculture prevented a large increase in the total assimilation of phytoplankton by HS fauna. Lower individual carbon assimilation rates by both mussels and other epifauna suggest that if filter capacity by HS epifauna would approach renewal by advection/mixing, M. edulis individuals would likely grow to a smaller-than-desired commercial size. In the same scenario, benthic organic carbon mineralisation was significantly boosted due to increased organic matter deposition by the aquaculture set-up. Combining these results with in situ OWF abundance data confirmed M. edulis as the most impactful OWF AHS species in terms of (total) carbon assimilation as well as the described stress responses due to climate change and the addition of bivalve aquaculture.

Temporal consistency of a facilitation cascade on shallow rocky reefs

Facilitation cascades are increasingly recognized as key drivers of biodiversity in a variety of habitats, yet their temporal variability remains poorly investigated. On shallow subtidal rocky reefs, positive interactions between the canopy-forming species, Halopithys incurva, and its epiphyte, Jania rubens, enhance the abundance and diversity of the associated mobile invertebrate assemblage. By means of a field experiment manipulating the presence of J. rubens on H. incurva plants, we investigated whether the effects of this facilitation cascade varied over time scales of months. Despite seasonal fluctuations in its biomass, J. rubens enhanced total invertebrate abundance and species richness by 64% and 45%, respectively, throughout the experiment. Our results suggest that the presence of J. rubens, likely by providing novel microhabitats and increasing resource availability, sustains invertebrate biodiversity of shallow macroalgal forests consistently between warm and cold periods. Understanding the temporal dynamics of facilitation cascades and their mechanisms can help inform management strategies targeting biodiversity conservation and restoration under current and future climates.

Skull and partial skeleton of a new pachycetine genus (Cetacea, Basilosauridae) from the Aridal Formation, Bartonian middle Eocene, of southwestern Morocco.

Pachycetus paulsonii, Pachycetus wardii, and Antaecetus aithai are middle Eocene archaeocete whales found in Europe, North America, and Africa, respectively. The three are placed in the new basilosaurid subfamily Pachycetinae. Antaecetus is a new genus known from Egypt and Morocco, and the only pachycetine known from a substantial postcranial skeleton. The skull of A. aithai described here resembles that of Saghacetus osiris in size, but lacks the narrowly constricted rostrum of Saghacetus. Antaecetus is smaller than Pachycetus and its teeth are more gracile. Upper premolars differ in having two rather than three accessory cusps flanking the principal cusp. Pachycetines differ from dorudontines in having elongated posterior thoracic and lumbar vertebrae like those of Basilosaurus, but differ from basilosaurines and from dorudontines in having conspicuously pachyosteosclerotic vertebrae with dense and thickly laminated cortical bone surrounding a cancellous core. Pachycetinae are also distinctive in having transverse processes on lumbar vertebrae nearly as long anteroposteriorly as the corresponding centrum. We infer from their pachyosteosclerotic vertebrae that pachycetines were probably sirenian-like slow swimmers living in shallow coastal seas and feeding on passing fish and mobile invertebrates.

Site mediates performance in a coral‐seeding trial

Coral seeding is a promising intervention being tested and applied in global reef‐restoration efforts. However, high mortality of newly settled corals, particularly in degraded environments, is one of several hurdles to overcome to up‐scale this technique. Incorporating design features that mitigate drivers of mortality could increase coral‐seeding effectiveness. Here we tested five ceramic seeding‐device designs that incorporated various features intended to act as coral microrefugia. Devices seeded with Acropora tenuis spat were deployed to three sites on a shallow mid‐shelf reef on the central Great Barrier Reef (GBR), and survival was assessed after 219 days. Average yield (device‐level survival) was moderate across the device designs (22%) and all devices performed comparably. However, there was a nearly threefold increase in survival at one site compared with the other, similar sites less than 100 m away. Assessment of the benthic community around each device suggested that the sites hosted similar communities, although multivariate analyses identified a weak but significant positive relationship between survival and the first principal component (only 17% of variance), characterized by higher cover of sponges and epilithic algal communities. These results suggest that within‐reef scale variations (10s of meters) in environmental conditions, or variations in community constituents not investigated here (e.g. grazing fishes, mobile invertebrates), may impact the success of coral seeding. Further investigations into the drivers of coral survival at fine spatial scales, particularly abiotic conditions, are required to guide the placement of coral‐seeding devices and to predict their effectiveness.

Independent Effects of Species Removal and Asynchrony on Invariability of an Intertidal Rocky Shore Community

Ecological stability depends on interactions between different levels of biological organization. The insurance effects occur when increasing species diversity leads to more temporally invariable (i.e., more stable) community-level properties, due in part to asynchronous population-level fluctuations. While the study of insurance effects has received considerable attention, the role of dominant species that contribute with particular functional traits across different level of organizations is less understood. Using a field-based manipulative experiment, we investigated how species richness and different types of parameters at the population level, such as the invariability of dominants, population invariability, and population asynchrony, influence the community invariability. The experiment involved the repetitive removal of the canopy forming algaMazzaella laminarioides(hereafter “Mazzaella”) during 32 months in two rocky intertidal sites of northern-central Chile. We predicted that the invariability of dominants enhances community invariability, that the effect of multispecies population-level parameters on community invariability are dependent on species richness, and that subdominant algae are unable to fully compensate the loss of canopies of the dominant species. Biomass of algae and mobile invertebrates was quantified over time. We observed independent effects ofMazzaellaremoval and community-wide asynchrony on community invariability. While canopy removal reduced community invariability, population asynchrony boosted community invariability regardless of the presence of canopies. In addition, filamentous and foliose algae were unable to compensate the loss of biomass triggered by the experimental removal ofMazzaella. Canopy removal led to a severe decrement in the biomass of macrograzers, while, at the same time, increased the biomass of mesograzers. Asynchrony stemmed from compensatory trophic responses of mesograzers to increased abundances of opportunistic algae. Thus, further work on consumer-resource interactions will improve our understanding of the links between population- and community-level aspects of stability.

Climate‐driven substitution of foundation species causes breakdown of a facilitation cascade with potential implications for higher trophic levels

Abstract Climate change can alter ecological communities both directly, by driving shifts in species distributions and abundances, and indirectly by influencing the strength and direction of species interactions. Within benthic marine ecosystems, foundation species such as canopy‐forming macro‐algae often underpin important cascades of facilitative interactions. We examined the wider impacts of climate‐driven shifts in the relative abundances of foundation species within a temperate reef system, with particular focus on a habitat cascade whereby kelp facilitate epiphytic algae that, in turn, facilitate mobile invertebrates. Specifically, we tested whether the warm‐water kelp Laminaria ochroleuca, which has proliferated in response to recent warming trends, facilitated a secondary habitat‐former (epiphytic algae on stipes) and associated mobile invertebrates, to the same degree as the cold‐water kelp Laminaria hyperborea. The facilitative interaction between kelp and stipe‐associated epiphytic algae was dramatically weaker for the warm‐water foundation species, leading to breakdown of a habitat cascade and impoverished associated faunal assemblages. On average, the warm‐water kelp supported >250 times less epiphytic algae (by biomass) and >50 times fewer mobile invertebrates (by abundance) than the cold‐water kelp. Moreover, by comparing regions of pre‐ and post‐range expansion by L. ochroleuca, we found that warming‐impacted kelp forests supported around half the biomass of epiphytic algae and one‐fifth of the abundance of mobile invertebrates, per unit area, compared with unimpacted forests. We suggest that disruption to this facilitation cascade has the potential to impact upon higher trophic levels, specifically kelp forest fishes, through lower prey availability. Synthesis. Climate‐driven shifts in species' distributions and the relative abundances of foundation organisms will restructure communities and alter ecological interactions, with consequences for ecosystem functioning. We show that climate‐driven substitutions of seemingly similar foundation species can alter local biodiversity and trophic processes in temperate marine ecosystems.

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.

Epibiont community composition of red mangroves Rhizophora mangle are contingent on root characteristics

Foundation species traits that structure communities are rarely experimentally examined; thus, a predictive understanding of their functions lags behind patterns of observed species associations. Red mangrove Rhizophora mangle roots form complex living habitats that support diverse epibiont communities, making them a model system for testing links between variation in foundation species traits and associated biodiversity. Here, we compared epibiont community composition between living and non-living mangrove roots, as well as root mimics, to test how foundation species traits affect community structure. We also quantified the community structure of associated mobile invertebrates to examine their relationship with secondary foundation species (e.g. sponges, bivalves) that grow on the roots. After 14 mo of colonization and succession, substrate composition (i.e. mangrove, wood, PVC) had significant effects on community composition, richness, and abundance of sessile epibionts and mobile invertebrates. Non-living mangrove roots were 5 times more likely to deteriorate, and consequently had the lowest epibiont richness and abundance. We found strong positive relationships between mobile invertebrate richness and the abundance, measured as biomass, and richness of sponges and bivalves, suggesting that variation among roots in secondary foundation species play an important role in mediating mobile invertebrate community composition. This study highlights the functional role of habitat structure and how rapidly that function can be lost without biogenic maintenance. Our results indicate the importance of facilitation cascades in fostering diverse mobile invertebrate communities and highlight both advantages and limitations in using artificial structures in restoration programs.

Evidence for genetic isolation and local adaptation in the field cricket Gryllus campestris.

Understanding how species can thrive in a range of environments is a central challenge for evolutionary ecology. There is strong evidence for local adaptation along large-scale ecological clines in insects. However, potential adaptation among neighbouring populations differing in their environment has been studied much less. We used RAD sequencing to quantify genetic divergence and clustering of ten populations of the field cricket Gryllus campestris in the Cantabrian Mountains of northern Spain, and an outgroup on the inland plain. Our populations were chosen to represent replicate high and low altitude habitats. We identified genetic clusters that include both high and low altitude populations indicating that the two habitat types do not hold ancestrally distinct lineages. Using common-garden rearing experiments to remove environmental effects, we found evidence for differences between high and low altitude populations in physiological and life-history traits. As predicted by the local adaptation hypothesis, crickets with parents from cooler (high altitude) populations recovered from periods of extreme cooling more rapidly than those with parents from warmer (low altitude) populations. Growth rates also differed between offspring from high and low altitude populations. However, contrary to our prediction that crickets from high altitudes would grow faster, the most striking difference was that at high temperatures, growth was fastest in individuals from low altitudes. Our findings reveal that populations a few tens of kilometres apart have independently evolved adaptations to their environment. This suggests that local adaptation in a range of traits may be commonplace even in mobile invertebrates at scales of a small fraction of species' distributions.

Greater functional similarity in mobile compared to sessile assemblages colonizing artificial coastal habitats

Among anthropogenic habitats built in the marine environment, floating and non-floating structures can be colonized by distinct assemblages. However, there is little knowledge whether these differences are also reflected in the functional structure. This study compared the functional diversity of sessile and mobile invertebrate assemblages that settle over three months on floating vs. non-floating artificial habitats, in two Chilean ports. Using morphological, trophic, behavioral, and life history traits, we found differences between mobile and sessile assemblages regarding the effect of the type of habitat on the functional diversity. Compared to sessile assemblages, a greater functional similarity was observed for mobile assemblages, which suggests that their dispersal capacity enables them to balance the reduced connectivity between settlement structures. No traits, prevailing or selected in one or the other habitat type, was however clearly identified; a result warranting for further studies focusing on more advanced stages of community development.

Habitat value of bivalve shellfish and seaweed aquaculture for fish and invertebrates: Pathways, synthesis and next steps

AbstractAquaculture can have negative environmental impacts, adding to the suite of anthropogenic stressors that challenge coastal ecosystems. However, a growing body of scientific evidence indicates that the commercial cultivation of bivalve shellfish and seaweed can deliver valuable ecosystem goods and services, including provision of new habitats for fish and mobile invertebrate species. We completed a systematic literature review of studies focused on understanding habitat‐related interactions associated with bivalve and seaweed aquaculture, and a brief meta‐analysis of 65 studies to evaluate fish and mobile macroinvertebrate populations at farms and reference sites. Bivalve and seaweed aquaculture were associated with higher abundance (n = 59, range: 0.05× to 473×, median lnRR = 0.67) and species richness (n = 29, range: 0.68× to 4.3×, median lnRR = 0.13) of wild, mobile macrofauna. Suspended or elevated mussel and oyster culture yielded the largest increases in wild macrofaunal abundance and species richness. We describe the major mechanisms and pathways by which bivalve and seaweed aquaculture may positively influence the structure and function of faunal communities—including provision of structured habitat, provision of food resources and enhanced reproduction and recruitment—and identify the role of the species cultivated and cultivation gear in affecting habitat value. Given the continued deterioration of coastal habitats and increasing investments into their restoration, understanding how industry activities such as aquaculture can be designed to deliver food within ecological limits and have positive influences on ecosystem goods and services is essential in ensuring ecological, social and economic objectives can be achieved.

Fine-scale responses of mobile invertebrates and mesopredatory fish to habitat configuration

As habitat-forming species continue to decline globally, it is important to understand how associated communities respond to habitat loss and fragmentation. Changes in the density and spatial configuration of habitat have important consequences for associated communities. However, tests of these factors are often confounded by morphological variation of habitat-formers, which can be resolved by using standardised habitat-mimics. Furthermore, few studies have incorporated the role of predators in mediating the observed effects. To test whether predators mediate the abundance of invertebrates among algal habitats of varying configuration (isolated vs patches, and positions within patches), we placed macroalgal mimics into subtidal estuarine habitats for one month to sample epifaunal communities. At the same time, we conducted underwater video surveys of fish communities to quantify fish communities and their feeding behaviour among the artificial habitats. Isolated habitats did not differ from patch habitats, however, patch edges had the highest epifaunal abundance, where fish were least commonly observed. Observed fish feeding was highest in the middle of patches and increased fish observations and feeding in habitats with reduced epifaunal communities suggest that mesopredatory fish are mediating epifauna in patches, with predation pressure altered by the spatial configuration of the habitat. This contrasts to previous studies that focus on predators that congregate outside patches and suggest that fragmentation leads to reduced invertebrate abundance at habitat edges in contrast to centres. However, this study highlights that in habitat patches housing small mesopredators that also benefit from the increased structure, the centre of the patch experiences higher predation and therefore fewer epifauna in contrast to patch edges and individual algal mimics.

Temporal and spatial variation in adult and juvenile mobile fauna associated with natural and artificial coastal habitats

Coastal habitats are important for commercially exploited and protected species of fish and larger mobile invertebrates. The addition of artificial structures within the marine environment has the potential to alter the connectivity between habitats and to affect metapopulations of a region. Baited remote underwater videos (BRUV) were used to investigate the spatial and seasonal variation in abundance of adult and juvenile mobile species associated with subtidal natural and artificial habitats within Poole Bay on the south coast of England in 2019. Metrics included the relative maximum abundance (MaxN), number of species seen (S), assemblage structure and size range of fish. Higher values of MaxN and S were recorded on artificial structures in the spring and early summer; however, this pattern was reversed by mid-summer and early autumn when more fish were recorded on the natural reefs. Yet overall differences in MaxN and S between habitats were not significant. Differences in assemblage composition between habitats varied monthly, but this was mostly driven by particular sites. Although most fish observed were juveniles, there were some seasonal differences in the size of fish using natural and artificial sites, especially bib (Trisopterus luscus), black bream (Spondyliosoma cantharus), bass (Dicentrarchus labrax) and pollack (Pollachius pollachius). The artificial habitats in this region appeared to be important in certain months, so temporal studies of this type need to be incorporated within surveys, particularly those in proximity to protected areas.