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Sargassum thunbergii is an economically significant algal species in China. During its cultivation, the decomposition of dead thalli releases nutrients into the surrounding water, a process influenced by environmental factors such as dissolved oxygen and sediment. To understand the decomposition process of S. thunbergii under the influence of dissolved oxygen and sediments, a laboratory simulation was conducted to study its decomposition under various environmental conditions. The changes in biomass, as well as the carbon, nitrogen, phosphorus, lignin, cellulose, and hemicellulose content of S. thunbergii, were analyzed. Additionally, the microbial composition of the sediment was examined. The results indicated that both high oxygen levels and the presence of sediments accelerated the decomposition of S. thunbergii, leading to reductions in the content of carbon, nitrogen, phosphorus, lignin, cellulose, and hemicellulose. Compared to the low oxygen group, the high oxygen group experienced the fastest mass loss of S. thunbergii. However, the differences in nitrogen and phosphorus content changes between high and low oxygen conditions were not significant (p > 0.05). Furthermore, the sediment microorganisms were primarily composed of the phyla Proteobacteria, Firmicutes, and Desulfobacterota, which were closely associated with the life cycle of seaweed. These findings demonstrate that the decomposition of S. thunbergii is a complex process influenced by multiple factors. High oxygen, low oxygen, and sediments all promoted the decomposition of S. thunbergii, releasing substantial nutrients. Therefore, it is recommended that in the decay period of S. thunbergii, the decayed thalli should be promptly removed from aquaculture areas to prevent secondary pollution. [ABSTRACT FROM AUTHOR]

Recent Sargassum horneri blooms, altering marine ecosystems, highlight an urgent need to understand their impact on phytoplankton and the regulation of organic matter export from the euphotic zone. To this end, we examined the effects of floating Sargassum on the phytoplankton size composition and their rates of sinking and lysis in the area of floating Sargassum horneri near the Zhoushan archipelago. We found that the presence of floating Sargassum horneri significantly influences the marine ecosystem by increasing the proportion of pico-sized phytoplankton, indicating community miniaturization. This shift suggests a novel mechanism by which floating macroalgae may alter the structure and function of phytoplankton communities. Our findings also indicate that these macroalgae enhance the sinking and lysis rates of phytoplankton, which could have profound effects on the vertical transport of organic matter and biogeochemical cycling in the ocean. The potential aggregation of pico-sized phytoplankton may facilitate their sinking in the surface layer, possibly leading to a reduction of lysis rates because of competition with floating seaweed. Conversely, in deeper layers, the decomposition of phytoplankton could result in the formation of aggregates of pico-sized phytoplankton, accelerating their sedimentation. These results highlight the complex interactions between phytoplankton size, lysis and sinking rates, and underscore the importance of considering these dynamics in understanding carbon export and sequestration in marine environments. [ABSTRACT FROM AUTHOR]

Holopelagic Sargassum spp. (sargassum) are the founding species of diverse communities in the Sargasso Sea. Since 2011, a new area of concentration of these algae was formed in the equatorial North Atlantic and Caribbean Sea. We analyzed elemental composition, and the small mobile fauna associated with sargassum collected at 41 stations, during two expeditions in the Caribbean Sea in 2018 and 2019, that covered open-sea stations in two marine ecoregions, and coastal stations (< 20 km from the shore) in one of them. Metal(loid) concentrations generally followed the order As > Zn > Cu > Cd > Se > Pb > Hg, and contents of As (195.5 ± 13.7 µg g−1), Cd (0.59 ± 0.02 µg g−1), and Hg (0.22 ± 0.09 µg g−1) were highest in S. fluitans III in the South-Western-Caribbean ecoregion. Mean [Ctot] per ecoregion varied between 26.1 and 30.1 mg g−1, and variation was mainly accounted for by higher [Cinorg] (likely produced by calcifying epibionts) in the South-Western Caribbean (10.12) compared to the Western Caribbean (8.92 and 7.19); this tendency that was also found for [Ntot] (between 1.06 and 1.27), and these contents were positively correlated with seawater chlorophyll concentrations. Sixty-six taxa of mobile fauna were identified, with the phylum Arthropoda being most abundant and diverse. The faunal community composition was similar in both open-sea regions, but differed in the coastal stations, which was mostly explained by differential relative abundance of Latreutes fucorum, Carpias minutus, Litiopa melanostoma, and some fish species. The Caribbean open-sea rafts harbor a diverse fauna comparable to that found in the Sargasso Sea, and likely provide similar ecosystem services, and thus merit similar protective efforts as those directed towards sargassum in the Sargasso Sea. [ABSTRACT FROM AUTHOR]

Pelagic Sargassum macroalgal rafts in the North Atlantic support sessile and motile epifauna that attract ecologically and economically important migratory organisms. Three prevalent pelagic Sargassum morphotypes vary in their degree of branching and foliation, and thus have different structural complexities that can influence their respective value as motile epifauna habitat. Sargassum fluitans III and S. natans I have denser foliation, creating a complex habitat; in contrast, S. natans VIII is more open and architecturally simple. In 2015/2016, 373 dip net samples of algae were collected from the Tropical Atlantic, Greater Caribbean, Gulf of Mexico, Gulf Stream, and Sargasso Sea. 20,975 individual motile epifauna from 32 taxa were recorded. Sargassum fluitans III supported higher densities of individuals and greater numbers of taxa than S. natans VIII or S. natans I, a pattern attributed to its more complex architecture and consistent with communities on benthic and floating macroalgae. Most assemblages comprised a few dominant and many rare motile epifauna; when compared to historical studies, dominant motile epifauna had shifted. These findings suggest important differences in ecological value between pelagic Sargassum morphotypes with implications for coastal and pelagic conservation strategies, which warrant consideration given recent shifts in morphotype distribution and recurring pelagic Sargassum inundation events. [ABSTRACT FROM AUTHOR]

Macroalgal removal is a critical ecosystem function yet few studies have considered its temporal variability, especially on impacted reefs with limited herbivorous fish biodiversity. To address this, we quantified macroalgal removal and mass-standardised bite rates of herbivorous fishes monthly from July 2016 to June 2017 using a series of transplanted Sargassum ilicifolium assays and underwater video cameras on three degraded coral reefs in Singapore: Pulau Satumu, Kusu Island, and Terumbu Pempang Tengah. Our results revealed a distinct temporal pattern in macroalgal herbivory (proportion of biomass removed and mass-standardised bite rates) rates across all sites, increasing from July and decreasing from January, with the highest rates recorded in December (28.10 ± 3.05 g 3.5 h−1; 208.24 ± 29.99 mass-standardised bites 3.5 h−1) and the lowest in May (0.86 ± 0.17 g 3.5 h−1; 9.55 ± 3.19 mass-standardised bites 3.5 h−1). These coincided with the S. ilicifolium growth cycle, confirming previous evidence that herbivory rates are closely linked to macroalgal condition. Video analyses revealed nine species feeding over a year (31,839 bites; 8702.89 mass-standardised bites), with Siganus virgatus responsible for ∼ 80% of the total mass-standardised bites. Siganus virgatus took the largest proportion of bites monthly, except between April and June, when Scarus rivulatus was dominant, suggesting temporal constraints in functional roles. [ABSTRACT FROM AUTHOR]

Ocean warming and increasing incidence of marine heatwaves (MHW) challenge the survival of marine organisms. While the impacts of climate scenario-based ocean warming are well investigated, the response of organisms to extreme events such as MHW is less understood. In this study, the thermal tolerance of the amphipod Hyale niger, an ecologically important amphipod in southeast Australia, and its algal host Sargassum linearifolium, were determined. For H. niger, a broad temperature range (2–33 °C) was tested in 6-day exposures in three seasons (summer, autumn and winter) and extended to 11 days in summer. Despite the 7 °C difference in mean habitat temperature across seasons, H. niger had a similar broad thermal optimum (Topt) range with ≥ 90% survival across a 17–20 degree temperature range. The upper lethal temperature with 50% mortality in the 6-day tests was also similar across seasons (LT50 29–30 °C). In 11-day tests in summer, the LT50 was reduced to 26 °C. Cold tolerance of H. niger indicated potential for poleward migration. Sargassum linearifolium had a similar broad thermal tolerance with a 50% reduction in the photosynthetic capacity at 33 °C. Temperature significantly affected survival of H. niger depending on the size and sex. The decrease in the Topt range over time pointed to the deleterious influence of prolonged heatwaves. The broad thermal tolerance of H. niger and S. linearifolium suggests that this important amphipod–host system may be resilient to habitat warming. [ABSTRACT FROM AUTHOR]

Several ecological models explain the success of introduced seaweeds by herbivore-prey interactions. The 'enemy release hypothesis' states that invaders benefit from a lack of natural enemies compared to the recipient community. The 'novel weapons hypothesis,' however, highlights the importance of chemical defense compounds of introduced species that are more effective in invaded regions than native counterparts. In order to explain the tremendous invasion success of the brown alga Sargassum muticum, we compared the palatability and nutritional value of S. muticum individuals from their native and invaded habitat (Japan and North Sea, respectively) with noninvasive congeneric species from Japan ( S. fusiforme, S. horneri), and a native competitor from the North Sea ( Fucus vesiculosus). Different feeding assays using artificial food with either freeze-dried algae or algal extracts and three dominant North Sea mesograzers were performed to detect feeding preferences. All herbivores preferred the local brown alga F. vesiculosus, followed by North Sea S. muticum, while Sargassum spp. from Japan were the least preferred. Since nutritional value did not correlate with feeding preference and algal extracts had the same effect as algal powder, we could demonstrate a deterrent activity of algal secondary metabolites. The preference of herbivores for the sympatric S. muticum population compared to the allopatric Japanese population could indicate a resource allocation from chemical defense to reproduction and growth. Due to the low palatability of Sargassum spp. from Japan, it might be reasonable to include additional Sargassum species in North Sea monitoring to prevent their establishment in European waters. [ABSTRACT FROM AUTHOR]

Pelagic forms of the brown algae (Phaeophyceae) Sargassum spp. and their conspicuous rafts are defining characteristics of the Sargasso Sea in the western North Atlantic. Given rising temperatures and acidity in the surface ocean, we hypothesized that macrofauna associated with Sargassum in the Sargasso Sea have changed with respect to species composition, diversity, evenness, and sessile epibiota coverage since studies were conducted 40 years ago. Sargassum communities were sampled along a transect through the Sargasso Sea in 2011 and 2012 and compared to samples collected in the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone from 1966 to 1975. Mobile macrofauna communities exhibited changes in community structure and declines in diversity and evenness within a 6-month time period (August 2011-February 2012). Equivalent declines in diversity and evenness were recorded in the same region (Sargasso Sea, 25°-29°N) in 1972-1973. Recent community structures were unlike any documented historically, whether compared to sites of the same latitude range within the Sargasso Sea, or the broader historical dataset of sites ranging across the Sargasso Sea, Gulf Stream, and south of the subtropical convergence zone. Recent samples also recorded low coverage by sessile epibionts, both calcifying forms and hydroids. The diversity and species composition of macrofauna communities associated with Sargassum might be inherently unstable. While several biological and oceanographic factors might have contributed to these observations, including a decline in pH, increase in summer temperatures, and changes in the abundance and distribution of Sargassum seaweed in the area, it is not currently possible to attribute direct causal links. [ABSTRACT FROM AUTHOR]

Phylogeographical study of the brown macroalga, Sargassum aquifolium using nuclear internal transcribed spacer 2, plastidal RuBisCo spacer, and mitochondrial cytochrome oxidase subunit-III revealed the populations in Southeast Asia to be homogeneous. On the other hand, genetic differences were detected between populations from Southeast Asia and western Pacific Islands/Guam, suggesting the presence of genetic break between these regions. This further suggests that populations of S. aquifolium may have survived east of Sunda Shelf during the Last Glacial Maximum and recent recolonization led to homogeneity of the populations in the Sunda Shelf region. Recolonization could be facilitated by year-round reproduction of the populations and dispersal of germlings on floating thalli by coastal currents. Restricted current flow across Maluku Sea and directional equatorial current flows could have isolated the Pacific Island and Guam populations from those of Southeast Asia. Our results support the presence of multiple refugia as the source of different lineages of S. aquifolium populations with a lack of secondary contact in the post-glacial dispersal between Southeast Asia and western Pacific as the mechanisms behind the phylogeographical patterns observed. [ABSTRACT FROM AUTHOR]

Geological phenomena (e.g. drastic sea level fluctuations during the Quaternary Ice Age in the Northern Hemisphere) have been demonstrated to intensively affect the biogeographic patterns and tempo-spatial compositions of genetic diversity of marine organisms. However, it is poorly understood whether contemporary factors such as oceanic surface currents have also shaped inter-regional population genetics of specific coastal marine flora, with or without limited dispersal capability. In this study, we determined mtDNA Cox1 gene sequences of the brown seaweed Sargassum fusiforme from nine populations along the Chinese coast and one population from the west coast of South Korea, in an effort to understand what factors are contributing to their current genetic structure and geographic distribution patterns. Genetic analyses indicated a deep genetic break between the Yellow-Bohai Sea (YBS) and the other two marginal seas, the East China Sea (ECS) and the South China Sea (SCS). In particular, the amount of genetic exchange from the SCS to each of the ECS and YBS was significantly higher than that from the opposite directions. Our analyses supports the hypothesis that biogeographic patterns of genetic variation in S. fusiforme are probably an interactive consequence of post-glacial colonization from two scattered refugia driven by the offshore Kuroshio Current and asymmetric gene flow among adjacent sea margins. [ABSTRACT FROM AUTHOR]

Although sediment deposition has detrimental effects on macroalgal settlement and recruitment, fucoid algae (mainly Sargassum duplicatum) thrive on rocky reefs always overlaid with fine sediments in sheltered sites of Kagoshima, Japan. The aim of the present study was to assess their ability to settle and recruit onto sediment-covered substrata. A transplant experiment using boulders with Sargassum juveniles attached showed that the 30-day survival rate was as high as 50% even for the juvenile stage (<10 mm) on boulders completely buried with sediment. In addition, an outdoor tank experiment testing the effects of different sediment thicknesses (0-4 mm) on already settled 4-day old S. duplicatum germlings indicated significant reductions in growth by the presence of sediment cover even at 0.5 mm but no significant increase in mortality up to 2 mm. Furthermore, an in situ experiment in which sterilized cobbles were placed at a sediment-covered site to allow sediment to settle over them before the embryo release showed a uniformly high recruitment of Sargassum over the cobbles. This suggests the presence of unknown mechanisms to allow the settlement of propagules on substrata thinly but completely covered by fine sediments. [ABSTRACT FROM AUTHOR]

The production of defence metabolites is assumed to be costly in metabolic terms. If this holds true, low-light stress should reduce the ability of seaweeds to defend themselves chemically against herbivory and fouling. We investigated the effect of energy limitation on the defensive status of seaweeds by assessing their attractiveness to mesograzers and their activity against a bivalve macrofouler in comparison with non-stressed conspecifics. The macroalgae Codium decorticatum (Woodw.) M. Howe, Osmundaria obtusiloba (C. Agardh) R. E. Norris, Pterocladiella capillacea (S. G. Gmel.) Santel. and Hommer., Sargassum vulgare C. Agardh and Stypopodium zonale (Lamour.) Papenf. collected at the southeastern Brazilian coast were exposed to six levels of irradiation (between 1 and 180 μmol photons m−2 s−1) for 10–14 days. After this period, algae from all treatment levels were: (a) processed as artificial food and offered to an amphipod community dominated by Elasmopus brasiliensis Dana and (b) extracted to test for differences in settlement rates of the fouling mussel Perna perna L. on filter paper loaded with the crude extracts. Generally, photosynthesis rates and growth were reduced under low light conditions. Attractiveness to herbivores and macrofoulers, however, was insensitive to energy limitation. We discuss possible explanations for the observed absence of a relationship between light availability and algal defence including the change in nutritional value of the algal tissue, the allocation of resources towards defence instead of growth and the absence of costs for defence. [ABSTRACT FROM AUTHOR]

Seasonal variation in coral reef macroalgal size and condition is well documented, yet seasonal variability of herbivory on macroalgae by coral reef fishes is unknown. Herbivore feeding intensity was quantified monthly on an inner-shelf reef on the Great Barrier Reef, using Sargassum bioassays. Removal rates of transplants displayed high levels of variation with significantly higher rates of removal during the summer months. Differences in Sargassum plant size and condition suggest that the variability in herbivore feeding intensity is attributed primarily to the variation in the condition of the macroalgae, especially epiphyte loads. The dramatic changes in macroalgal removal reveal a considerable decrease in herbivore activity in the winter. This highlights the clear distinction between ‘summer’ and ‘winter’ months in terms of reef processes, emphasizing the high seasonal variation in macroalgal removal rates at different time of the year. [ABSTRACT FROM AUTHOR]

Herbivory is widely acknowledged as a key process determining the benthic community structure and resilience of coral reefs. Despite numerous studies that have examined herbivory across reef gradients in the Caribbean, few studies have directly quantified this process on Pacific reefs. Bioassays of two species of erect macroalgae ( Sargassum swartzii and S. cristaefolium) were used to quantify variation in grazing intensity across seven habitats of varying depth and wave exposure on a mid-shelf reef in the northern Great Barrier Reef. Removal rates of Sargassum varied significantly among habitats, with both species displaying broadly similar patterns. The shallow habitats on the exposed aspect of the reef (i.e. reef crest, flat and back reef) experienced the highest reductions in mass (81.4–91.6% day−1) for both S. swartzii and S. cristaefolium, while the deeper exposed habitats (reef slope and base) displayed the lowest reductions (3.8–13.4% day−1) over a 24 h period. In contrast, the grazing intensity varied between the two species in the three habitats on the leeward aspect of the reef. Reductions in mass remained relatively high for S. swartzii on the patch reef and sheltered reef base and flat (62.7–76.5% day−1) but were considerably lower for S. cristaefolium (37.9–63.5% day−1) across the same habitats. Surprisingly, the rates of removal of Sargassum displayed no relationship with the density or biomass of roving herbivorous fishes or those species known to consume erect macroalgae, either collectively or independently. These results suggest that the relationship between browsing rates and herbivorous fish biomass is complex and may be driven by species that are underestimated in visual surveys. Direct quantification of browsing intensity using assays revealed a different pattern to inferences based on herbivore densities and highlights the potential difficulties of evaluating ecosystem processes based on visual census data alone. [ABSTRACT FROM AUTHOR]

The genetic structure and phylogeography of the brown seaweed Sargassum horneri/filicinum complex in Japan were studied based on the mitochondrial cox3 haplotype. The cox3 haplotypes found were divided into three clades in a statistical parsimony network, among which there were large numbers of steps. Contrary to the reported large amount of drifting S. horneri along the Japanese coast, the three clades were dividedly distributed on the Japanese coast: the northern Pacific, the central Pacific, and western Japan. The western Japan S. horneri had haplotypes that were phylogenetically closer to those of S. filicinum than to the northern and central Pacific S. horneri populations. The S. filicinum populations were included within the western Japan clade and grouped together with the S. horneri samples from western Japan. Taken together with the unstable morphological diagnosis, this result suggests that S. filicinum should be reduced into a synonymy of S. horneri. The TMRCA analysis suggested that the divergence time of each clade may go back to the last interglacial period and a skyline plot suggested that the last glacial maximum had only a small effect on the population size of S. horneri. The geographic subdivision of the three groups, in spite of a large amount of drifting mats, suggests a limited contribution of drifting mats to gene flow on a large geographic scale. On a small geographic scale, a small number of haplotypes were shared between S. horneri-type and S. filicinum-type populations. This result suggests that populations of these two types are partially, though not completely, isolated from each other, possibly by selfing in S. filicinum-type populations or by a difference in peak reproduction. [ABSTRACT FROM AUTHOR]

The connectivity of fragmented landscapes is a function of the physical distance between suitable habitats and the characteristics of the habitat through which the animal is moving, i.e. the matrix. Experimental manipulations done to explain how spatial arrangement and composition of habitats affects biota remain scarce, particularly in marine systems. Holdfasts of the common kelp, Ecklonia radiata, are discrete units of habitat for small invertebrates (e.g. amphipods, isopods, molluscs, annelids) that can be isolated from other holdfasts by habitat, which may be less suitable (e.g. other species of algae or relatively bare space). We compared assemblages, which colonised defaunated holdfasts in experimentally created small-scale landscapes where patches of habitat (holdfasts) were distant versus close together and which had Sargassum spp. versus relatively bare space in the matrix. We also compared colonisation across matrices of crushed fucoid algae to assess whether the structural or chemical nature of algae in the matrix had the most influence on the colonisation. Assemblages in defaunted holdfasts differed between those that were close to and those that were distant from undisturbed holdfasts, where the matrix was devoid of vegetation. Where Sargassum spp. was present in the matrix, however, this difference disappeared and was possibly due to the chemical, rather than structural, characteristics of the fucoid matrix. The extent to which matrix habitat is a barrier to movement of invertebrates among holdfasts thus depends on not only how extensive it is but what type of habitat it contains. As within terrestrial systems, the nature of the matrix is also likely to be a fundamental component of the connectivity within marine systems. [ABSTRACT FROM AUTHOR]

Understanding which factors affect the feeding preferences of herbivores is essential for predicting the effects of herbivores on plant assemblages and the evolution of plant–herbivore interactions. Most studies of marine herbivory have focussed on the plant traits that determine preferences (especially secondary metabolites), while few studies have considered how preferences may vary among individual herbivores due to genetic or environmental sources of variation. Such intraspecific variation is essential for evolutionary change in preference behaviour and may alter the outcome of plant–herbivore interactions. In an abundant marine herbivore, we determined the relative importance of among-individual and environmental effects on preferences for three host algae of varying quality. Repeated preference assays were conducted with the amphipod Peramphithoe parmerong and three of its brown algal hosts: Sargassum linearifolium, S. vestitum and Padina crassa. We found no evidence that preference varied among individuals, thus constraining the ability of natural selection to promote increased specialisation on high-quality S. linearifolium. Most of the variation in preference occurred within individuals, with amphipod preferences strongly influenced by past diet. The increased tendency for amphipods to select alternate hosts to that on which they had been recently feeding indicates that amphipods are actively seeking mixed diets. Such a feeding strategy provides an explanation for the persistence of this herbivore on hosts in the field that support poor growth and survival if consumed alone. The effects of past diet indicate that herbivore preferences are a function of herbivore history in addition to plant traits and are likely to vary with the availability of algae in space and time. [ABSTRACT FROM AUTHOR]

Feeding ecology of organisms associated with floating Sargassum in the northwestern Gulf of Mexico was assessed using fatty acids. Nineteen groups were collected from the Sargassum community including four autotrophs, eight invertebrates, five juvenile fishes, and two adult fishes. Spatial and temporal variability in polyunsaturated fatty acid (PUFA) signatures of selected taxa ( Sargassum fluitans [autotroph], Leander tenuicornis [primary heterotroph], Balistes capriscus [secondary heterotroph]) was examined to quantify natural variation within these dietary tracers. Although PUFA signatures varied seasonally for all three taxa, no differences were detected between samples collected in year 2000 and 2001 or from different sample locations in the northwest Gulf. PUFA signatures made up 16.3–62.3% of the total fatty acid composition of main autotrophs present in the pelagic environment [particulate organic matter (POM), epiphytic algae, S. fluitans, S. natans], and PUFA profiles of selected primary producers were distinct. Specifically, levels of 20:5 n−3, 22:5 n−3, and 22:6 n−3 were significantly higher in POM than Sargassum spp. or epiphytic algae ( Cladophora sp.). Dominant PUFA in the tissue of invertebrate and vertebrate consumers were 18:2 n−6, 20:4 n−6, 20:5 n−3, 22:5 n−3, 22:6 n−3 and multivariate analyses indicated that PUFA signatures of all consumers were highly similar to POM. As a result, heterotrophs utilizing the Sargassum complex may rely heavily on phytoplankton production rather than production by Sargassum or associated epiphytic algae. [ABSTRACT FROM AUTHOR]

Invasions by non-indigenous species have the potential to alter the biodiversity of recipient systems. The magnitude of this effect often depends on the nature of the invaded communities and the ecology of the invader. We investigated the impacts of the Japanese seaweed Sargassum muticum (Phaeophyceae, Fucales) on biodiversity in a rocky and sedimentary environment on two islands in the North Sea. In each case, we compared the epibiota of non-indigenous S. muticum with epibiota communities on taxonomically related and structurally similar native seaweed hosts. Total and average species richness on S. muticum were similar on the rocky shore (60 species and 22±6 species, respectively) and the sandy shore (64 species and 20±3 species, respectively). However, community structure and species composition differed significantly between the environments. On the rocky shore, another native fucoid seaweed, Halidrys siliquosa, supported an epibiota community very similar to that of the invader. On the sandy shore, the only other abundant native habitat-providing algal species was Fucus vesiculosus. This species supported a different and less diverse assemblage of associated taxa. We conclude that S. muticum enhances epibiota diversity in the sedimentary environment, probably by increasing the substratum availability and habitat heterogeneity. In contrast, it has negligible impacts on epibiota diversity in the rocky shore environment, where it does not represent a fundamentally new habitat component. We conclude that even within the same region, the consequences of non-indigenous species on biodiversity cannot be generalised but depend on the composition and structural complexity of the species in the recipient community. [ABSTRACT FROM AUTHOR]

Young-of-the-year (YOY)Sebastes inermisuseZosteraandSargassumbeds as nursery grounds, although it is not known which habitat YOY prefer. In this study, YOYS.inermiswere accurately assigned toZosteraorSargassumbeds by two approaches: the width and length of the otolith nucleus and the composition of trace elements in otoliths. The otolith nucleus was initially opaque and then showed a marked shift to hyaline deposition once YOY settled in the nursery grounds. The first hyaline zone (FHZ) was deposited earlier inZosterabeds (from mid-May to early June) than inSargassumbeds (around mid-summer). Likewise, irrespective of settlement year, the FHZ was formed at both significantly younger ages and shorter back-calculated sizes (total length, TL) in theZosterabed (overall mean: 131±3 days; 2.5±1.7 mm TL) than in theSargassumbed (overall mean: 158±12 days; 61.3±1.00 mm TL). YOY collected in theZosterabed were born earlier (mainly in January) than YOY from theSargassumbed (mainly in February). In addition, a significant linear relationship was found between the age at formation of the FHZ and nucleus dimensions, suggesting that nucleus dimensions were a reliable macroscopic indicator of the time of formation of the FHZ and, consequently, also an indicator of the nursery where YOY grew. Linear discriminant function analysis (LDFA) based on the width and length of the otolith nucleus could distinguish juveniles fromZostera(88-96%) andSargassum(96-97%) beds with a high degree of accuracy. In the other approach, six detectable trace elements (Li, Mn, Ni, Cu, Zn, and Ba) in otoliths of YOY collected in the nursery grounds were measured by high-resolution, inductively coupled mass spectrometry. LDFA based on the trace elemental composition separated YOY from three nurseries with 100% of accuracy. Findings suggest that both the trace elemental composition and nucleus dimensions of otoliths can be used as natural tags of the nursery grounds ofS.inermis, offering a considerable potential for answering questions on habitat use and the contribution of nursery grounds to the adult stock. [ABSTRACT FROM AUTHOR]

Presents information on a study which assessed the levels of genetic diversity and genetic structure in the seaweed Sargassum polyceratium found around the island of Curacao. Description of the Sargassum polyceratium species; Materials and methods used; Diversity within and between stands; Habitat factors.

Bottom-up (e.g. resource quality) and top-down (e.g. predation) factors have strong effects on the fitness and distribution of small herbivores. Herein, we investigated how food quality and refuge offered by macroalgal hosts influence the distribution of a mesograzer. We used the herbivorous amphipod Cymadusa filosa and seasonally evaluated its association with the macroalgal hosts Sargassum filipendula, Padina gymnospora, and Dichotomaria marginata on a subtropical rocky shore from the Brazilian southeastern coast. Feeding experiments were conducted to test the food value of hosts, while predation experiments in the field and laboratory were performed to investigate the refuge value of the macroalgae. Cymadusa occurred on Padina in a density greater than that observed on Dichotomaria and Sargassum, while Dichotomaria harbored more amphipods than Sargassum. Adults of Cymadusa showed a higher consumption of Padina and Sargassum in both choice and no-choice feeding experiments and juveniles had greater growth and reproductive potential when feeding on such macroalgae. In the predation experiment in the field, Padina was a better refuge for Cymadusa than Sargassum. However, no difference in refuge value among hosts was observed in the laboratory assays. The distribution of Cymadusa was explained by a balance between food and refuge values of hosts, with higher abundances being observed in the high-quality food alga that provides refuge against predators (e.g. Padina), while fewer individuals occurred in other high-quality food that was less suitable as refuge (e.g. Sargassum). Therefore, predation may be more of a determinant for distribution of that mesograzer than resource quality. [ABSTRACT FROM AUTHOR]

Floating mats of Sargassum macroalgae provide a model system for studying multiple aspects of animal coloration. The endemic crab Portunus sayi has heterogeneous yellow and brown patterning, which matches its algal background. We show that by fluctuating the chromatophores underneath its transparent carapace, the crab can alter its coloration within hours in response to diel variability in the ambient light field and to changes in background reflectance. Held in a naturalistic illumination and temperature regime, P. sayi displayed a distinct diel cycle of coloration, being pale at night and darker during the day. Individuals under constant illumination showed a modified cycle, retaining their nocturnal shading but becoming significantly paler during day time. On monochromatic black, grey, and white surfaces, crabs showed an ability to change coloration in response to their backgrounds, as integrated reflectance (ΣR) of crabs generally followed background albedo. This study expands on earlier work which revealed that P. sayi utilizes a distinct camouflage strategy from other cryptic Sargassum crabs to achieve background color matching in the view of predators. Dynamic color change in this species may play roles including photoprotection and enhancing camouflage in a unique marine environment. [ABSTRACT FROM AUTHOR]