Intertidal Habitats Research Articles

Vertical arrays of artificial rockpools on a seawall provide refugia across tidal levels for intertidal species in the UK

Eco-engineering of coastal infrastructure aims to address the insufficient intertidal habitat provided by coastal development and flood defence. There are numerous ways to enhance coastal infrastructure with habitat features, but a common method involves retrofitting artificial rockpools. Often these are ‘bolt-on’ units that are fixed to existing coastal infrastructure but there is a paucity of literature on how to optimise their arrangement for biodiversity.In this study, 24 artificial rockpools were installed at three levels between High Water Neaps and Mean Tide Level on a vertical concrete seawall on the south coast of the UK. The species abundance of the rockpools and adjacent seawall were surveyed at low tide for 2 years following rockpool installation and compared. Over the course of the study, sediment had begun to accumulate in some of the rockpools. At the 2-year mark, the sediment was removed and assessed for macrofauna. Algal biomass of the seawall and rockpools was estimated using previously obtained dry weight values for the dominant algae taxa.After 2 years, it was determined that artificial rockpools successfully increase species richness of seawalls, particularly at higher tidal levels where water-retaining refugia are crucial for many species. The rockpools hosted 37 sessile taxa and 9 sessile taxa were recorded on the seawall. Rockpools increased the vertical elevation for brown canopy-forming seaweeds by providing better attachment surfaces. Although the retained sediment only hosted 3 infaunal species, it was observed to provide shelter for shore crabs during surveys. As sea levels and ocean and air temperatures continue to rise, vertical eco-engineering arrangements will play a crucial role in allowing species to migrate up the tidal zone, negating habitat loss and localised extinction.

Habitat characteristics shaping zoantharians’ distribution at intertidal habitats of the Canary Islands

Ocean warming is facilitating the proliferation of zoantharians worldwide due to their thermophilic affinities. However, other anthropogenic factors, such as declining water quality, have been appointed to favour the occurrence of zoantharians dominated areas and barrens. Subtropical and tropical intertidal habitats are especially vulnerable to zoantharians outbreaks due to the progressive increase in ocean temperature and because it is where most human pressure is concentrated. The aim of this study was to evaluate the abundance of intertidal zoantharians populations, related to habitat characteristics (rugosity and submerged substrate) and the presence of other benthic organisms, such as sessile invertebrates and macroalgae. Number and coverage of zoantharian colonies were recorded in transects (20 × 4 m) along 25 intertidal rocky platforms of the Canarian Archipelago, and photographic techniques in quadrats were used to examine the relationships between the percentage of substrate cover of zoantharians, macroalgae and sessile invertebrates by means of correlations analyses. Results indicated that high levels of rugosity favour the abundance and coverage of Palythoa aff. clavata and Zoanthus pulchellus, and the proportion of submerged substrate was also important in determining Zoanthus coverages. The presence of extensive macroalgae communities was seen to reduce zoantharian coverages, being the only sessile organisms that were able to outcompete them for space in the Canary Islands. Thus, this study provided valuable information about patterns of abundances and coverages of intertidal zoantharians useful for future monitoring of intertidal populations of zoantharians in Canary Islands and their interaction with surrounding marine organisms.

How restoration engineering measures can enhance the ecological value of intertidal flats

Restoration engineering measures, such as managed realignments or building groins, modify the environmental characteristics of coastal intertidal ecosystems. Creating physical modifications that are beneficial to an intertidal system's ecology necessitates an in‐depth understanding of the relationships between the abiotic and biotic components of a given intertidal habitat. In this study, we evaluate how hydrodynamics and sediment characteristics drive the development of the benthic macrofauna community during the first 5 years following engineering measures to enhance benthic macrofauna diversity at three locations. The creation of low‐energy habitats through groins (Knuitershoek and Baalhoek) and a managed realignment dike breach (Perkpolder) led to the accumulation of fine sediments in all three impact sites. Biomass of benthic macrofauna quickly increased between 2016 and 2020, with successional processes being more important in Perkpolder, where the habitat was started completely from scratch due to a managed realignment, than at Knuitershoek or Baalhoek, where habitat conditions were improved by adding groins. In addition, the density of benthos‐eating birds, especially oystercatchers, increased at some of the modified sites. While a low‐energy habitat may harbor more diverse assemblages of benthic macrofauna than a highly dynamic one, the extremely high silt content, which is typical for low‐energy habitats, may slow benthic community development. The observed increase of biomass at our impact sites highlights the value of the interventions, while the delays in the response of the benthic macrofauna community emphasizes the need for extensive monitoring both in time and space and the identification of underlying abiotic–biotic mechanisms.

Spatial distribution of PAHs and microbial communities in intertidal sediments of the Pearl River Estuary, South China

The exploration of sediment pollution caused by PAHs and its impact on microbial communities can provide valuable insights for the remediation of sediments. The spatial distribution of PAHs and their impact on the microbial community within the Pearl River Estuary were investigated in this study. The findings revealed that the total concentration ranges of 16 PAHs were between 24.26 and 3075.93 ng/g, with naphthalene, fluorene, and phenanthrene potentially exerting adverse biological effects. More PAHs were found to accumulate in subsurface sediments, and their average accumulation rates gradually decreased as the number of rings in PAHs increased, ranging from 180 % for 2-ring to 36 % for 6-ring. The phyla Proteobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi were found to dominate both surface and subsurface sediments The correlation between microbial genera and PAHs contents was weak in sediments with low levels of PAHs contamination, while a more significant positive relationship was observed in sediments with high levels of PAHs contamination. The physicochemical properties of sediments, such as pH, soil structure and Cu significantly influence bacterial community composition in highly contaminated sediments. Additionally, the network analysis revealed that certain bacterial genera, including Novosphingobium, Robiginitalea and Synechococcus_CC9902, played a pivotal role in the degradation of PAHs. These findings are significant in comprehending the correlation between bacterial communities and environmental factors in intertidal ecosystems, and establish a scientific foundation for bioremediation of intertidal zones.

The impact of settleable atmospheric particulate on the energy metabolism, biochemical processes, and behavior of a sentinel mangrove crab

We use the sentinel mangrove crab, Minuca rapax, as a model to investigate the effects of metallic settleable particulate matter (SePM) on wetland. Multiple levels of energetic responses, including (i) metabolic rate and energy budget, (ii) oxidative stress, and (iii) behavioral response by righting time, were assessed as well as the metal and metalloid content in crabs exposed to 0, 0.1 and 1 g.L−1 of SePM, under emerged and submerged conditions over five days, simulating the rigors of the intertidal habitat. Al, Fe, Mn, Cr, and Y exhibited a concentration-dependent increase. Metal concentrations were higher in submerged crabs due to the continuous ingestion of SePM and direct exposure through gills. Exposure concentration up to 1 g.L−1 decreased metabolic rate and enzymatic activities, reduced assimilation efficiency and energy for maintenance, and induces a slower response to righting time, probably by metal effects on nervous system and energy deficits. In conclusion, SePM exposure affects the redox status and physiology of M. rapax depending on he submersion regime and SePM concentration. The disruption to the energy budget and the lethargic behavior in M. rapax exposed to SePM implies potential ecological alterations in the mangrove ecosystem with unknown consequences for the local population.

Extraction of 10 m Resolution Global Mangrove in 2022

With the intensification of global climate change, there is an increasing emphasis on protecting natural resources. Mangrove forests, critical to tropical and subtropical intertidal ecosystems, have garnered considerable attention in recent years for their strong carbon sink capacity, rich species diversity, and abundant natural resources. This study utilizes the 2020 global mangrove vector data as a baseline to construct a reasonable buffer zone by calculating the increase in mangrove crown width. The Google Earth Engine (GEE) platform and its Sentinel-2 data from 2022 are employed to acquire synthetic images across all regions using the mosaic algorithm. Then, mangrove forests are extracted using the Otsu algorithm, and a map depicting the global spatial distribution of mangrove forests in 2022 is obtained. The average overall accuracy of the extracted mangrove forests in this study reaches 92.4%, and it is determined that the global mangrove forest area expanded by 4920.6 km2 between 2020 and 2022, This study provides crucial data support for the global monitoring of mangrove changes and holds significant importance for protecting and restoring mangrove ecosystems.

Gone with the wind: environmental variation influences detection efficiency in a coastal acoustic telemetry array

Range tests play a critical role in designing acoustic telemetry studies, guiding equipment configuration, deployment techniques, and the analysis of animal movement data. These studies often strive to capture the effects of environmental variation on detection efficiency over time but are frequently limited in spatial and temporal scale. This could lead to disparities between test results and the circumstances encountered during animal tracking studies. In this study, we evaluated detection range and efficiency at two distinct spatial and temporal scales in a dynamic intertidal ecosystem. Two range tests were conducted, the first being a small-scale study using 6 receivers deployed over 1 month. Using modern acoustic receivers with built-in transmitters and environmental sensors, we then conducted a large-scale range test with 22 receiver stations over a full year to approximate the area and duration of a typical animal movement study. Differences in detection range between the two studies occurred as a result of environmental variation and tag power output, with midpoint ranges estimated as 123 m (small scale, low power), 149 m (small scale, high power) and 311 m (large scale, very high power). At both scales, wind speed emerged as the most influential factor explaining temporal variation in predicted detection efficiency. However, this effect was modulated by wind direction which varied as a result of land sheltering and fetch between the two study scales. At the small scale, detection efficiency decreased with winds from the south and east, while at the large scale, northern and westerly winds were most detrimental. Water temperature had a positive effect on predicted detection efficiency at both scales, while relative water level was positive at the small scale and negative at the large scale. Additional factors, including precipitation and Topographic Position Index, were found to influence detection efficiency at a large scale. Moreover, sensors associated with receivers in the larger array revealed the significant influences of receiver tilt and ambient noise. These discrepancies in the outcomes of the two studies underscore the critical role of scale in range test design and emphasize the need for long-term, in situ range testing at relevant spatial scales.

Trehalose along with ABA promotes the salt tolerance of Avicennia marina by regulating Na+ transport.

Mangroves grow in tropical/subtropical intertidal habitats with extremely high salt tolerance. Trehalose and trehalose-6-phosphate (T6P) have an alleviating function against abiotic stress. However, the roles of trehalose in the salt tolerance of salt-secreting mangrove Avicennia marina is not documented. Here, we found that trehalose was significantly accumulated in A. marina under salt treatment. Furthermore, exogenous trehalose can enhance salt tolerance by promoting the Na+ efflux from leaf salt gland and root to reduce the Na+ content in root and leaf. Subsequently, eighteen trehalose-6-phosphate synthase (AmTPS) and 11 trehalose-6-phosphate phosphatase (AmTPP) genes were identified from A. marina genome. Abscisic acid (ABA) responsive elements were predicted in AmTPS and AmTPP promoters by cis-acting elements analysis. We further identified AmTPS9A, as an important positive regulator, that increased the salt tolerance of AmTPS9A-overexpressing Arabidopsis thaliana by altering the expressions of ion transport genes and mediating Na+ efflux from the roots of transgenic A. thaliana under NaCl treatments. In addition, we also found that ABA could promote the accumulation of trehalose, and the application of exogenous trehalose significantly promoted the biosynthesis of ABA in both roots and leaves of A. marina. Ultimately, we confirmed that AmABF2 directly binds to the AmTPS9A promoter in vitro and in vivo. Taken together, we speculated that there was a positive feedback loop between trehalose and ABA in regulating the salt tolerance of A. marina. These findings provide new understanding to the salt tolerance of A. marina in adapting to high saline environment at trehalose and ABA aspects.

Seasonal and synoptic spatio-temporal variability on larval delivery mechanisms inferred from mussel settlement patterns in the Portuguese coast

Demographic connectivity is the process by which population persistence and growth are affected by the dispersal of individuals. In sessile marine species that disperse by planktonic larvae and form metapopulations, the interaction between oceanographic forcing and larval biology drives the spatial extent and magnitude of larval delivery to suitable habitat patches. The present study investigates the supply of Mytilus galloprovincialis larvae to rocky intertidal habitats located within and around two marine protected areas (MPA) in central Portugal, one located on the exposed coast and the other one in a sheltered bay, using time series of settlement intensity and oceanographic variables. The results indicate that larval delivery at short time scales (days) is strongly dependent on the interaction of upwelling circulation with coastline topography. In the exposed MPA, located on a coastal island, the magnitude of mussel larval delivery is limited by the dynamics of an upwelling front and filament that intercepts the island as upwelling increases and decreases. In the sheltered bay, under an upwelling shadow, the upwelling front promotes recirculation of the water mass, intensifying larval retention and settlement. The results are also consistent with larval transport distances of tens of kilometres and ongoing connectivity between the two MPA. This study highlights the relevance of coastal topography and its interaction with mesoscale hydrodynamics in the modulation of larval delivery, crucial for the persistence of populations and communities and in systematic conservation planning.

Changes in the composition of invertebrate assemblages from wave-exposed intertidal mussel stands along the Nova Scotia coast, Canada.

Rocky intertidal habitats occur worldwide and are mainly characterized by primary space holders such as seaweeds and sessile invertebrates. Some of these organisms are foundation species, as they can form structurally complex stands that host many small invertebrates. The abundance of primary space holders is known to vary along coastlines driven directly or indirectly by environmental variation. However, it is less clear if the invertebrate assemblages associated to a foundation species may remain relatively unchanged along coastlines, as similar stands of a foundation species can generate similar microclimates. We examined this question using abundance data for invertebrate species found in mussel stands of a similar structure in wave-exposed rocky habitats at mid-intertidal elevations along the Atlantic coast of Nova Scotia (Canada). While the most abundant invertebrate species were found at three locations spanning 315 km of coastline, species composition (a combined measure of species identity and their relative abundance) differed significantly among the locations. One of the species explaining the highest amount of variation among locations (a barnacle) exhibited potential signs of bottom-up regulation involving pelagic food supply, suggesting benthic-pelagic coupling. The abundance of the species that explained the highest amount of variation (an oligochaete) was positively related to the abundance of their predators (mites), further suggesting bottom-up forcing in these communities. Overall, we conclude that species assemblages associated to structurally similar stands of a foundation species can show clear changes in species composition at a regional scale.

Intertidal and shallow subtidal marine tardigrades from the British Virgin Islands with a description of a new Batillipes (Heterotardigrada: Batillipedidae)

This is the first survey of marine tardigrades from the British Virgin Islands, though two species were previously reported from St. Croix, U.S. Virgin Islands. In June 2016, we collected subtidal and intertidal sand samples from various locations throughout the British Virgin Islands. We found 602 tardigrades in 18 of 21 samples, and these included 12 taxa, one of which, Batillipes wyedeleinorum sp. nov., is new to science and described here. We compared abundance and species diversity in intertidal and subtidal samples and found significantly greater abundance in intertidal habitats but no significant difference in the number of observed species between the two habitats. We calculated Chao 1 species richness, which indicated higher estimated richness in intertidal habitats and 15 ± 3.7 species (x̅ ± SD) in both habitats combined. Non-metric Multidimensional Scaling revealed differences in species composition between the two habitats with some species showing clear preferences for one or the other.

Contrast in larval sensitivity to low pH in sea urchins from neighbouring seagrass meadows at Inhaca Island, Mozambique

Ocean acidification presents a major threat to marine life, and a large body of evidence has documented its negative effects on various marine species and ecosystems. Recent meta-analyses highlight the key role of local adaptation and have linked species’ sensitivity to extremes of the present range of pH variability. More specifically, ‘physiological tipping points’ can be correlated with the lowest experienced pH where the organisms live. We verified this hypothesis by comparing the responses of larvae of the collector urchin Tripneustes gratilla originating from two neighbouring seagrass meadows at Inhaca Island in southern Mozambique. The two seagrass meadows experience different conditions: the site at the Inhaca Marine Biology Research Station (Estação de Biologia Marítima de Inhaca, EBMI) is subtidal, and the site at Banguá is intertidal. Larvae of adults collected from the two sites were cultured in the laboratory under four different target pH treatments (8.04, 7.67, 7.46 and 7.29) for 7 days. The results showed an overall negative effect of lower pH on survival and growth as well as on an index of symmetry. Larvae originating from the intertidal seagrass habitat at Banguá which experiences large pH fluctuations were more sensitive to a lower pH than those from the subtidal seagrass habitat at EBMI. This finding suggests that different mechanisms for pH tolerance and local adaptation may apply in subtidal versus intertidal environments. Consequently, the unifying principle that physiological tipping points are correlated with the extreme low pH in the present range of variability, may reach its limit in increasingly extreme environments under natural conditions.

Discovery of deep-sea acoels from a chemosynthesis-based ecosystem.

Chemosynthesis-based ecosystems such as hydrothermal vents and hydrocarbon seeps harbour various endemic species, each uniquely adapted to the extreme conditions. While some species rely on obligatory relationships with bacterial symbionts for nutrient uptake, scavengers and predators also play important roles in food web dynamics in these ecosystems. Acoels, members of the phylum Xenacoelomorpha, are simple, worm-like invertebrates found in marine environments worldwide but are scarcely understood taxa. This study presents a novel genus and species of acoel from a deep-sea hydrocarbon seep off Hatsushima, Japan, Hoftherma hatsushimaensis gen. et sp. nov. Our multi-locus phylogenetic analysis revealed that the acoels are nested within Hofsteniidae, a family previously known exclusively from shallow waters. This finding suggests that at least two independent colonization events occurred in the chemosynthesis-based environments from the phylum Xenoacoelomorpha, represented by hofsteniid acoels and Xenoturbella. Previous reports of hofsteniid species from low-oxygen and sulfide-rich environments, including intertidal habitats with decomposing leaves, in addition to H. hatsushimaensis gen. et sp. nov. from a deep-sea hydrocarbon seep, imply a common ancestral adaptation to sulfide-rich ecosystems within Hofsteniidae. Moreover, the sister relationship between solenofilomorphid acoels predominating in sulfide-rich habitats indicates common ancestral adaptation to sulfide-rich ecosystems between these two families.

Spatiotemporal variation in size and abundance of juvenile Chinese mitten crab (Eriocheir sinensis) in Yangtze Estuary

IntroductionIntertidal habitat preferences and spatiotemporal variation in the abundance of juvenile Chinese mitten crab Eriocheir sinensis in Yangtze Estuary are reported.MethodsThe size and abundance of this crab are reported for mud flat, gravel, root belt, and marsh habitats in this estuary’s lower, middle, and upper reaches from June 2021 (spring) to February 2022 (winter) using quadrat method.ResultsJuvenile E. sinensis of carapace length (CL) 5.5 ± 2.1 mm (mean ± standard deviation) were collected; no juveniles were found in February 2022. Crab abundance in root belt and gravel habitats usually exceeded that of marsh habitat; no juveniles were found in mud flat habitat. The greatest abundances and smallest individuals were found when megalopa recruited in early spring (June); juvenile abundance decreased sharply afterwards, and crabs were absent from the intertidal during winter. Size and relative growth rate of juvenile crabs were greater in root belt and gravel habitat than in marsh habitat from June to August. Recruitment primarily drove changes in crab abundance and size during June and July, and temperature best correlated with changes in the winter. Many stage I juveniles (CL < 3.1 mm) occurred in the lower estuarine reaches, while stage III and IV juveniles (CL 3.9–6.5 mm) primarily occurred in the middle and upper estuarine reaches.DiscussionAlthough intertidal wetland habitat in Yangtze Estuary is severely degraded and reduced in area, it remains important for recruitment and maintenance of mitten crab populations. An understanding of the habitat requirements of this species will benefit management of this crab resource and the prioritized restoration of intertidal habitat.

Social-ecological Factors, Stock Status, and Governance Relating to a Shellcraft Fishery in the Indo-Pacific Region

Shellcraft is a livelihood activity that utilizes shells and skeletal remains of marine taxa for producing ornamental and decorative items. Despite an increasing importance of shellcraft in coastal areas of the Indo-Pacific region, information necessary for stakeholders to identify and respond to change through policy and management decisions is often lacking for fisheries that support this activity. To address this knowledge gap, a quantitative approach was taken to evaluate social-ecological factors (the what, where, how much, who, when, how, how often, and how long) in a “shellcraft fishery” centered at the Nusa Islands of Papua New Guinea. More than 151,100 individuals across 69 marine taxa were fished annually for shellcraft at the Nusa Islands; fishing was infrequent and quantities fished were low for most taxa when compared with other small-scale fisheries. Fishing most taxa had no association with the main demographic divisions within households although, in terms of participation and catch richness, women were the main actors. Gleaning, combing, and free-diving were the only fishing techniques used, with taxa primarily fished by gleaning intertidal habitats during the day. To contextualize sustainability of this fishery, local ecological knowledge-based perceptions of stock status for the marine taxa fished were examined. Considerations for governance, which included synthesis of existing regulatory measures and aspirations, are also discussed. Since shellcraft occurs throughout the Indo-Pacific region and there are commonalities in taxa utilized, this study provides a basis for comparative analysis of shellcraft fisheries within the region.

Disentangling the effect of space, time, and environmental and anthropogenic drivers on coastal macrobenthic β diversity in contrasting habitats over 15 years

Coastal zones are biodiversity hotspots and deliver essential ecosystem functions and services, yet they are exposed to multiple and interacting anthropogenic and environmental constraints. The individual and cumulative effects of these constraints on benthic communities, a key component of coastal ecosystems, and their variability across space and time, remains to be thoroughly quantified to guide conservation actions. Here, we explored how the presence of biogenic habitats influences the response of benthic communities to natural and anthropogenic constraints. We investigated this effect in both intertidal and subtidal habitats exposed to different pressures. We used data collected in the North-East Atlantic over 15 years (2005–2019) as part of the REBENT monitoring program, covering 38 sites of bare sediments, intertidal seagrass beds and maerl beds. We collected a range of environmental variables and proxies of anthropogenic pressures and used variation and hierarchical partitioning with redundancy analyses to estimate their relative effect on macrobenthic communities. We used descriptors modeling spatial and temporal structures (dbMEMs) to explore the scale of their effects and potential missing predictors. The selected variables explained between 53 % and 64 % of macrobenthic β diversity depending on habitat and depth. Fishing pressures, sedimentary and hydrodynamics variables stood out as the most important predictors across all habitats while proxies of anthropogenic pressures were overall more important in intertidal habitats. In the intertidal, presence of biogenic habitat strongly modulated the amount of explained variance and the identity of the selected variable. Across both tidal levels, analysis of models' residuals further indicated that biogenic habitats might mitigate the effect of extreme environmental events. Our study provides a hierarchy of the most important drivers of benthic communities across different habitats and tidal levels, emphasizing the prominence of anthropogenic pressures on intertidal communities and the role of biogenic habitats in mitigating environmental changes.

Regime shifts in rocky intertidal communities associated with a marine heatwave and disease outbreak.

Long-term, large-scale experimental studies provide critical information about how global change influences communities. When environmental changes are severe, they can trigger abrupt transitions from one community type to another leading to a regime shift. From 2014 to 2016, rocky intertidal habitats in the northeast Pacific Ocean experienced extreme temperatures during a multi-year marine heatwave (MHW) and sharp population declines of the keystone predator Pisaster ochraceus due to sea star wasting disease (SSWD). Here we measured the community structure before, during and after the MHW onset and SSWD outbreak in a 15-year succession experiment conducted in a rocky intertidal meta-ecosystem spanning 13 sites on four capes in Oregon and northern California, United States. Kelp abundance declined during the MHW due to extreme temperatures, while gooseneck barnacle and mussel abundances increased due to reduced predation pressure after the loss of Pisaster from SSWD. Using several methods, we detected regime shifts from substrate- or algae-dominated to invertebrate-dominated alternative states at two capes. After water temperatures cooled and Pisaster population densities recovered, community structure differed from pre-disturbance conditions, suggesting low resilience. Consequently, thermal stress and predator loss can result in regime shifts that fundamentally alter community structure even after restoration of baseline conditions.

Seeing across variable ecological and social environments: comparative eye morphology of marine and terrestrial hermit crabs (Decapoda: Anomura: Coenobitidae, Paguridae)

Abstract Vision is a ubiquitous sensory modality adapted to vastly different environments, which place variable selection pressures on both macro- and microscopic dimensions of external eye morphology. The hermit crab clade (Crustacea: Decapoda: Anomura) spans environments from sea to land, yet, no systematic comparisons in eye morphology have been made between any species. We compared three species of hermit crabs inhabiting different ecological and social environments: two terrestrial species, one of which (Coenobita compressusH. Milne Edwards, 1837) is highly social and inhabits a flat, open diurnal habitat, and another (C. clypeatus Herbst, 1791) is its sister species that inhabits a rugged forested nocturnal habitat; and a third (Pagurus longicarpusSay, 1817) inhabits a marine intertidal habitat and is less social. We compared macroscopic eye morphology between species as well as microscopic differences in ommatidium-facet density and diameter within eyes. We found that eye dimensions (length, width, and thickness), but not overall volume, differed significantly between marine and terrestrial species. Furthermore, the highly social C. compressus had a significantly larger eye volume compared to its sister species, C. clypeatus, which is not as social. Larger eyes in C. compressus might be linked to its social lifestyle, where vision has been shown to be critical to finding conspecifics. All three species had a higher density of facets in the ventral compared to dorsal region of the eye. Our comparisons of external eye morphology revealed microscopic similarities but notable macroscopic variation between species, thus laying a foundation for future phylogenetically controlled tests within this species-rich clade, including comparisons of internal eye morphology.

Immediate Impact of the 2021 Harmful Algal Bloom in Southeast Hokkaido on the Rocky Intertidal Benthic Community and Its Spatial Variation

There has been a limited number of studies on the effects of harmful algal blooms (HABs) on natural rocky intertidal ecosystems. From mid-September to early November 2021, an unprecedented HAB caused by Karenia selliformis hit the Pacific coast of southeast Hokkaido, Japan, for the first time, causing massive mortalities among marine organisms. To clarify the immediate impacts of the HAB on the abundance of 10 rocky intertidal species in four functional groups (macroalgae, sessile invertebrates, molluscan grazers, and molluscan carnivores), we focused on two questions: (1) How did the HAB affect the abundance of each species differently at the regional scale? and (2) How did the impacts of the HAB on the abundance of each functional groups vary spatially, and was the spatial variation of the HAB impacts related to the spatial distribution of the cell density of HAB species? To study these issues, we compared census data for 17 years before the HAB and within one month after it for five shores on the southeast coast of Hokkaido. The results showed that two macroalgae species and all three molluscan grazer species declined significantly after the HAB. Moreover, the decrease in molluscan grazers was significantly correlated with cell density. These results suggest that the impacts of the HAB in southeast Hokkaido on the abundance of rocky intertidal organisms are highly variable depending on species and locality, presumably because of differences in species-specific tolerances to HAB toxins and the spatial variation in the density of the HAB organisms.

Abundances and characteristics of microplastics in core sediments of the Persian Gulf coast, Iran

The presence of microplastics in tidal sediments is a growing ecotoxicological concern for sea and benthic health. This investigation was designed to record and characterize the vertical prevalence of microplastics (MPs) in intertidal sediments of the Persian Gulf (around Bushehr city, Iran). Sediments of three depths (0-10 cm, 10-20 cm, and 20-30 cm) were sampled during low tide in six sites along the coastal zone of Bushehr, Iran. MP particles were found in all evaluated areas and sediment depths. The average abundance of MPs in all of the sediment samples was 117.96 ± 97.75 particles kg−1 dry sediment. No differences were found in the MPs number among the sites. The most dominant microplastics in surface sediments were 2-5 mm in size. In all areas, fibers and fragments were more abundant. Particles in higher depths (0-10 cm) were often colorless (white, and transparent). Raman spectroscopy indicated the presence of polystyrene, polyethylene, polyvinyl chloride, polyethylene terephthalate, and polypropylene in the samples. Further research is required to evaluate the possible interaction between MPs and layers of sediments. Waste management and proper wastewater disposal are critical to control MPs pollution in intertidal ecosystems around coastal cities.