Shallow Benthic Habitats Research Articles

Effects of macroalgae and sea urchin grazing pressure on zoantharians growth under laboratory conditions

In the context of ocean warming, thermophilic organisms such as zoantharians are expanding and altering shallow benthic habitats. Here, a four-month laboratory experiment was performed to examine the influence of three types of macroalgae morphotypes common in the Canary Islands (turf algae, Lobophora spp., and crustose coralline algae) on the growth of two zoantharian species, Palythoa caribaeorum and Zoanthus pulchellus. Additionally, the grazing effects of echinoids Diadema africanum and Paracentrotus lividus were assessed as facilitators of substrate colonization by means of controlling macroalgae cover. Colony and algal coverages were measured at the beginning, middle and end of the experiment, and increments were calculated. Results indicated a general decrease in zoantharian colony sizes in contact with different algal types in the absence of sea urchins. However, P. caribaeorum colonies showed significant growth in the presence of D. africanum, highlighting the ecological importance of sea urchins in zoantharian population proliferation and subsequent community modification. This study represents the first investigation into zoantharian-macroalgae interactions under controlled conditions.

Hull fouling marine invasive species pose a very low, but plausible, risk of introduction to East Antarctica in climate change scenarios

AbstractAimsTo identify potential hull fouling marine invasive species that could survive in East Antarctica presently and in the future.LocationAustralia's Antarctic continental stations: Davis, Mawson and Casey, East Antarctica; and subantarctic islands: Macquarie Island and Heard and McDonald Islands.MethodsOur study uses a novel machine‐learning algorithm to predict which currently known hull fouling MIS could survive in shallow benthic ecosystems adjacent to Australian Antarctic research stations and subantarctic islands, where ship traffic is present. We used gradient boosted machine learning (XGBoost) with four important environmental variables (sea surface temperature, salinity, nitrate and pH) to develop models of suitable environments for each potentially invasive species. We then used these models to determine if any of Australia's three Antarctic research stations and two subantarctic islands could be environmentally suitable for MIS now and under two future climate scenarios.ResultsMost of the species were predicted to be unable to survive at any location between now and the end of this century; however, four species were identified as potential current threats and five as threats under future climate change. Asterias amurensis was identified as a potential threat to all locations.Main conclusionsThis study suggests that the risks are very low, but plausible, that known hull fouling species could survive in the shallow benthic habitats near Australia's East Antarctica locations and suggest a precautionary approach is needed by way of surveillance and monitoring in this region, particularly if propagule pressure increases. While some species could survive as adults in the region, their ability to reach these locations and undergo successful reproduction is considered unlikely based on current knowledge.

Human proximity suppresses fish recruitment by altering mangrove-associated odour cues

Human-driven threats to coastal marine communities could potentially affect chemically mediated behaviours that have evolved to facilitate crucial ecological processes. Chemical cues and their importance remain inadequately understood in marine systems, but cues from coastal vegetation can provide sensory information guiding aquatic animals to key resources or habitats. In the tropics, mangroves are a ubiquitous component of healthy coastal ecosystems, associated with a range of habitats from river mouths to coral reefs. Because mangrove leaf litter is a predictable cue to coastal habitats, chemical information from mangrove leaves could provide a source of settlement cues for coastal fishes, drawing larvae towards shallow benthic habitats or inducing settlement. In choice assays, juvenile fishes from the Caribbean (Belize) and Indo-Pacific (Fiji) were attracted to cues from mangroves leaves and were more attracted to cues from mangroves distant from human settlement. In the field, experimental reefs supplemented with mangrove leaves grown away from humans attracted more fish recruits from a greater diversity of species than reefs supplemented with leaves grown near humans. Together, this suggests that human use of coastal areas alters natural chemical cues, negatively affecting the behavioural responses of larval fishes and potentially suppressing recruitment. Overall, our findings highlight the critical links that exist between marine and terrestrial habitats, and the importance of considering these in the broader conservation and management of coastal ecosystems.

Long-term monitoring of temperate macroalgal assemblages inside and outside a No take marine reserve

Macroalgal communities have an essential role in the shallow benthic habitats of temperate seas, where changes in their composition can resonate through entire coastal ecosystems. As all major ecosystems on Earth, algal beds have already been affected by multiple disturbances. Passive conservation tools, such as marine protected areas or No-take zones, have the potential to reduce some of the anthropogenic impacts by limiting human activity. However, without a good knowledge of the natural community dynamics, it is not easy to discern between changes fruit of the intrinsic variability of biological communities and the ones caused by human-related stressors. In this study, we evaluated the natural variability of macroalgal communities' composition inside and outside a Mediterranean No-Take marine reserve during 15 years. We described their temporal dynamics considering their main drivers and we tested the effect of protection in seaweed beds. We did not find differences either in the composition of the macroalgal assemblages or the total algal cover between protected and non-protected locations over the fifteen years of study. Nevertheless, we observed a positive effect of the protection increasing the cover of some specific species, such as the canopy-forming Treptacantha elegans. Our results highlight the importance of obtaining long-term data in ecological studies to better understand the natural variability of marine communities. Accordingly, a robust understanding of the community dynamics would help us to avoid misinterpretations between ‘impacted’ or ‘in-recovery’ communities when recovery times are longer than the study periods.

Object-Based Mapping of Coral Reef Habitats Using Planet Dove Satellites

High spatial resolution benthic habitat information is essential for coral reef protection and coastal environmental management. Satellite-based shallow benthic composition mapping offers a more efficient approach than traditional field measurements, especially given the advancements in high spatial and temporal resolution satellite imagery. The Planet Dove satellite constellation now has more than 150 instruments in orbit that offer daily coverage at high spatial resolution (3.7 m). The Dove constellation provides regularly updated imagery that can minimize cloud in tropical oceans where dense cloud cover persists. Daily image acquisition also provides an opportunity to detect time-sensitive changes in shallow benthic habitats following coral bleaching events, storms, and other disturbances. We developed an object-based coral reef habitat mapping approach for Dove and similar multispectral satellites that provides bathymetry estimation, bottom reflectance retrieval, and object-based classification to identify different benthic compositions in shallow coastal environments. We tested our approach in three study sites in the Dominican Republic using 18 Dove images. Benthic composition classification results were validated by field measurements (overall accuracy = 82%). Bathymetry and bottom reflectance significantly contributed to identifying benthic habitat classes with similar surface reflectance. This new object-based approach can be effectively applied to map and manage coral reef habitats.

Seasonal ecosystem metabolism across shallow benthic habitats measured by aquatic eddy covariance

AbstractShallow benthic habitats are hotspots for carbon cycling and energy flow, but metabolism (primary production and respiration) dynamics and habitat‐specific differences remain poorly understood. We investigated daily, seasonal, and annual metabolism in six key benthic habitats in the Baltic Sea using ~ 2900 h of in situ aquatic eddy covariance oxygen flux measurements. Rocky substrates had the highest metabolism rates. Habitat‐specific annual primary production per m2 was in the order Fucus vesiculosus canopy > Mytilus trossulus reef > Zostera marina canopy > mixed macrophytes canopy > sands, whereas respiration was in the order M. trossulus > F. vesiculosus > Z. marina > mixed macrophytes > sands > aphotic sediments. Winter metabolism contributed 22–31% of annual rates. Spatial upscaling revealed that benthic habitats drive > 90% of ecosystem metabolism in waters ≤5 m depth, highlighting their central role in carbon and nutrient cycling in shallow waters.

Multi-Frequency, Multi-Sonar Mapping of Shallow Habitats—Efficacy and Management Implications in the National Marine Park of Zakynthos, Greece

In this work, multibeam echosounder (MBES) and dual frequency sidescan sonar (SSS) data are combined to map the shallow (5–100 m) benthic habitats of the National Marine Park of Zakynthos (NMPZ), Greece, a Marine Protected Area (MPA). NMPZ hosts extensive prairies of the protected Mediterranean phanerogams Posidonia oceanica and Cymodocea nodosa, as well as reefs and sandbanks. Seafloor characterization is achieved using the multi-frequency acoustic backscatter of: (a) the two simultaneous frequencies of the SSS (100 and 400 kHz) and (b) the MBES (180 kHz), as well as the MBES bathymetry. Overall, these high-resolution datasets cover an area of 84 km2 with ground coverage varying from 50% to 100%. Image texture, terrain and backscatter angular response analyses are applied to the above, to extract a range of statistical features. Those have different spatial densities and so they are combined through an object-based approach based on the full-coverage 100-kHz SSS mosaic. Supervised classification is applied to data models composed of operationally meaningful combinations between the above features, reflecting single-sonar or multi-sonar mapping scenarios. Classification results are validated against a detailed expert interpretation habitat map making use of extensive ground-truth data. The relative gain of one system or one feature extraction method or another are thoroughly examined. The frequency-dependent separation of benthic habitats showcases the potentials of multi-frequency backscatter and bathymetry from different sonars, improving evidence-based interpretations of shallow benthic habitats.

Evaluation of seabed mapping methods for fine-scale classification of extremely shallow benthic habitats – Application to the Venice Lagoon, Italy

Recent technological developments of multibeam echosounder systems (MBES) allow mapping of benthic habitats with unprecedented detail. MBES can now be employed in extremely shallow waters, challenging data acquisition (as these instruments were often designed for deeper waters) and data interpretation (honed on datasets with resolution sometimes orders of magnitude lower). With extremely high-resolution bathymetry and co-located backscatter data, it is now possible to map the spatial distribution of fine scale benthic habitats, even identifying the acoustic signatures of single sponges. In this context, it is necessary to understand which of the commonly used segmentation methods is best suited to account for such level of detail. At the same time, new sampling protocols for precisely geo-referenced ground truth data need to be developed to validate the benthic environmental classification. This study focuses on a dataset collected in a shallow (2–10 m deep) tidal channel of the Lagoon of Venice, Italy. Using 0.05-m and 0.2-m raster grids, we compared a range of classifications, both pixel-based and object-based approaches, including manual, Maximum Likelihood Classifier, Jenks Optimization clustering, textural analysis and Object Based Image Analysis. Through a comprehensive and accurately geo-referenced ground truth dataset, we were able to identify five different classes of the substrate composition, including sponges, mixed submerged aquatic vegetation, mixed detritic bottom (fine and coarse) and unconsolidated bare sediment. We computed estimates of accuracy (namely Overall, User, Producer Accuracies and the Kappa statistic) by cross tabulating predicted and reference instances. Overall, pixel based segmentations produced the highest accuracies and the accuracy assessment is strongly dependent on the number of classes chosen for the thematic output. Tidal channels in the Venice Lagoon are extremely important in terms of habitats and sediment distribution, particularly within the context of the new tidal barrier being built. However, they had remained largely unexplored until now, because of the surveying challenges. The application of this remote sensing approach, combined with targeted sampling, opens a new perspective in the monitoring of benthic habitats in view of a knowledge-based management of natural resources in shallow coastal areas.

Using GIS Methods to Evaluate Rhodolith andSargassumBeds as Critical Habitats for Commercially Important Marine Species in Bahía Concepción, B.C.S., México

Bahía Concepción was once recognized as a very productive coastal lagoon not only for the Peninsula of Baja California but also for all Mexico. However, lack of proper management has resulted in the closure of various fisheries, such as the Calico scallop, Argopecten ventricosus, in 1994. One of the main challenges for the management of coastal resources is the selection of critical habitats for conservation considering the economic activities of the communities associated with them. This study used Geographic Information Systems (GIS) and remote sensing to assess the roll of rhodoliths and Sargassum spp. as critical habitats in Bahía Concepción for endangered and commercial species. Underwater surveys, on 72 randomly selected sites within the bay, were conducted to characterize the shallow benthic habitats, fish and invertebrate species abundance and richness during the spring of 2011. Analyses show that rhodoliths are important for the invertebrate assemblages and for at least 4 species protected under the Mexican law, NOM-059, for threatened species. Sargassum spp. and seagrass beds are also relevant for diversity but their annual life cycle limits the time when these are available as habitat for other species. GIS tools proved an innovative and effective method to provide essential information to protect critical habitats such as rhodoliths, Sargassum spp. and seagrasses, for the recovery and conservation of diversity.

Assessment of the hyperspectral sensor CASI-2 for macroalgal discrimination on the Ría de Vigo coast (NW Spain) using field spectroscopy and modelled spectral libraries

Hyperspectral remote sensing from aircraft and satellite sensors is an important tool for mapping shallow benthic habitats in areas where high spectral and spatial resolutions are needed e.g. spatially heterogeneous coastal environments. However, the acquisition of hyperspectral images sometimes involves a high economic investment and there is no prior guarantee of their utility. Physics-based methods like bio-optical models are an alternative to assess sensors without purchasing the images. In this study we used a simple bio-optical model that simulates reflectance spectra for waters with variable depth and benthic macroalgal cover. The modelled spectral library was used to assess the capability of CASI-2 sensor to recognise different benthic macroalgal species. Reflectance spectra of 17 macroalgal species were used in the model simulations. Uni- and multi-variate statistical analyses were used to evaluate the spectral differences between several species. The results show that only a few species seem to be clearly differentiable: Codium tomentosum, Laminaria saccharina and Corallina officinalis. Therefore, further bio-optical modelling was applied at the level of taxonomic groups rather than species level. Emerged green, brown and red macroalgae as well as sand can be differentiated from each other when using the CASI-2 sensor. The bio-optical simulations showed that the three macroalgal groups can be separated from each other in waters shallower than 4m when CASI-2 is used. Green and brown macroalgae can be differentiated from deep water if the water depth does not exceed 6m whereas red macroalgae can be optically separated from deep water when the water depth is less than 5m. Sea-beds covered with the three macroalgal groups are separable from sandy sea-beds in waters shallower than 10 m.

Settlement behavior in shore crabs Carcinus maenas: why do postlarvae emigrate from nursery habitats?

In contrast to general settlement models of invertebrate larvae, recent Swedish studies of settlement of the shore crab Carcinus maenas indicate that many postlarvae close to metamorphosis emigrate from their preferred settlement habitats. In the present study, we assessed physical and biological factors affecting shore crab settlement and emigration from nursery habitats, and explored possible ultimate factors in this behavior. Postlarval abundance in the field was not affected by the tidal phase, but varied significantly according to the light conditions. Settlement densities on artificial substrates were significantly higher during the day compared to at night. In contrast, densities of planktonic postlarvae were highest at night. This result suggests that the postlarvae cling to shallow benthic habitats during the day and swim in the plankton at night. Mesocosm experiments demonstrated that most postlarvae remained in the benthos during the day, even in suboptimal habitats, but that a large proportion (on average 58%) actively emigrated at dusk, irrespective of settlement conditions. Emigration rates were significantly higher and metamorphosis rates lower in open sand compared to mussel habitats, whereas food levels and settlement densities had only small effects on the settlement process. Emigrated postlarvae were at a significantly earlier developmental stage and metamorphosed on average 1 d later than the megalopae that remained in the benthic habitat. Post-larvae >2 d from metamorphosis emigrated even from optimal settlement conditions. These results suggest that settlement in shore crabs is not an irreversible process once a late-stage postlarva has found a settlement habitat, but involves 2 separate behavioral components: (1) the selection of a benthic habitat during the day, which is mainly affected by the availability of refuges from predation; and (2) the choice to stay or emigrate the following night, where emigration is induced by a decrease in light and determined mainly by the development stage of the postlarvae. We propose a conceptual model of settlement in the shore crab where the dynamic behavior of the postlarvae is an adaptation to diel differences in predation risk between the settlement habitat and the plankton.

THE ECOLOGY OF NOSTOC

ABSTRACTNostoc is a genus of filamentous cyanobacteria that can form macroscopic or microscopic colonies and is common in both terrestrial and aquatic habitats. Much of the success of Nostoc in terrestrial habitats is related to its ability to remain desiccated for months or years and fully recover metabolic activity within hours to days after re‐hydration with liquid water. Nostoc can also withstand repeated cycles of freezing and thawing and, thus, is an important component of extreme terrestrial habitats in the Arctic and Antarctic. The ability to fix atmospheric N2can provide an advantage in nitrogen‐poor environments. Nostoc also has the ability to screen damaging ultraviolet light in terrestrial and shallow benthic habitats. The genus potentially could be important in paddy rice culture because it fixes nitrogen that may later be released and used by plants; it also may play a role in soil formation and may increase nitrogen input to natural aquatic and terrestrial ecosystems. The abilities to survive in terrestrial habitats and fix N2are important in symbiotic interactions with fungi (lichens), liverworts, hornworts, mosses, ferns, cycads, and the angiosperm Gunnera. Nostoc is somewhat resistant to predation; this probably is related to production of large amounts of sheath material, synthesis of microcystin‐like toxins by some strains, and formation of colonies that are too large for many algivores to consume. Some organisms can subsist on Nostoc, although it may not be a preferred food source. Lytic cyanophages also infect Nostoc, but little is known about population control of Nostoc in its natural environment, Late Precambrian fossils resembling Nostoc have been described, and Nostoc possibly has been an important component of many terrestrial and aquatic communities since that time.

Dissolved and particulate DNA dynamics during a spring bloom in the Antarctic Peninsula region, 1986–1987

Dissolved and particulate DNA (D-DNA and P-DNA, respectively) concentrations were measured at 69 stations in a 25,000 km 2 section of Bransfield Strait, during the austral summer period (December 1986 to March 1987). During the development of the seasonal spring bloom of phytoplankton (December and January), surface water P-DNA (0.2–202μm) exhibited an order-of-magnitude concentration gradient, from values of ≥25 μg DNA I −1 in the productive coastal water near the northern end of Gerlache Strait to ≥4 μg DNA l −1 in the more oligotrophic waters of Drake Passage. P-DNA concentrations were highly correlated with other biochemical indices of microbial biomass (e.g. chlorophyll α and ATP). A majority (≥50%) of the P-DNA was contained in the 0.2–20 μm size category. Estimates derived from DNA:ATP ratios and from direct measurements of bacterial cell abundance suggest that most of the P-DNA during the spring bloom period was associated with living phytoplankton cells, with little, if any, non-living, P-DNA. In contrast to these characteristics of the spring bloom period. P-DNA during post-bloom conditions (March) was low (4–6 μg DNA l −1) and nearly constant throughout our study area, was nearly exclusively (≥80%) contained in the 0.2–20 μm size category, and was nearly exclusively (≥90%) comprised of non-living DNA. D-DNA was ubiquitously distributed in the near-surface waters throughout the RACER study area in December, with concentrations ranging from 6 to 16 μg DNA l −1. However, there was no spatial correlation with either microbial biomass or microbial productivity. By January, surface water D-DNA concentrations had decreased to values ≤10% of the December values (≤1 μg DNA l −1 and by the February to March sampling periods, D-DNA was undectetable throughout our study areas (≤0.1 μg DNA l −1). The dynamics of the D-DNA pools were not well correlated with microbial biomass and production. Rather, the seasonal D-DNA distributions appeared to be controlled by the advection of D-DNA enriched water masses across our study area in December, followed by replacement with D-DNA depleted waters. We hypothesize that the early season D-DNA may be derived from microbial communities in melting ice or from diagenesis in shallow benthic habitats. The results of a box model calculation of P-DNA and D-DNA inventories and fluxes in Bransfield Strait suggest that the northern Gerlache Strait is a major exporter of P-DNA, either as a result of horizontal advection or active transport of macrozooplankton populations.

Habitat utilization by sympatric arctic charr Salvelinus alpinus L. and brown trout Salmo trutta L. in Lake Atnsjø, south‐east Norway

SUMMARY. 1. Habitat utilization, as well as inter‐ and intraspecific relations of different size groups of arctic charr (Salvelinus alpinus (L.)) and brown trout (Salmo trutta L.) in Lake Atnsjø, south‐east Norway, were investigated by analysing food and spatial niches from monthly benthic and pelagic gillnet catches during June‐October 1985.2. Small individuals (150–230 mm) of both arctic charr and brown trout occurred in shallow benthic habitats. However, they were spatially segregated as arctic charr dominated at depths of 5–15 m and brown trout at depths of 0–5 m.3. Larger (>230 mm) arctic charr and brown trout coexisted in the pelagic zone. Both species occurred mainly in the uppermost 2‐3 m of the pelagic, except in August, when arctic charr occurred at high densities throughout the 0–12 m depth interval. On this occasion, arctic charr were segregated in depth according to size, with significantly larger fish in the top 6 m. This was probably due to increased intraspecific competition for food.4. The two species differed in food choice in both habitats, Arctic charr fed almost exclusively on zooplankton, whereas brown trout had a more variable diet, consisting of surface insects, zooplankton. aquatic insects and fish.5. The data suggest that the uppermost pelagic was the more favourable habitat for both species. Large individuals having high social position occupied this habitat, whereas small individuals lived in benthic habitat where they were less vulnerable to agonistic behaviour from larger individuals and less exposed to predators. The more aggressive and dominant brown trout occupied the more rewarding part of the benthic habitat.