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The marine algae Ulva spp. are commonly used as model biofouling organisms. As biofouling studies are primarily conducted using field-collected specimens, factors including species identity, seasonal availability, and physiological status can hinder the replicability of the results. To address these limitations, a protocol was developed for the on-demand laboratory culture and release of Ulva zoospores. The biofouling potential of laboratory-cultured and field-collected Ulva blades was compared using a waterjet. No significant differences were found between field and laboratory-cultured samples in either spore adhesion (before waterjet) or the proportion of spores retained after waterjet exposure. However, there was significant variability within each session type in pre- and post-waterjet exposures, indicating that spore adhesion and retention levels vary significantly among trial runs. In addition, all our laboratory cultures were Ulva Clade C (LPP complex). In contrast, our field samples contained a mix of Ulva Clade C, U. compressa clade I, and U. flexuosa Clade D. This protocol for on-demand production of Ulva spores can improve biofouling research approaches, enables comparison of results across laboratories and regions, and accelerate the development of anti-biofouling strategies. [ABSTRACT FROM AUTHOR]

Sustainable aquaculture includes the aquaculture of non-fed crops that provide ecosystem services including nutrient extraction and water quality improvement. While shellfish are the most farmed sustainable aquaculture crops in the USA, shellfish farmers in the northeastern US have an interest in diversifying their crops and incorporating seaweeds into their farms. In this study, we worked with oyster farmers to investigate the potential for farming sugar kelp, Saccharina latissima, across different environmental regimes in coastal Rhode Island USA. Kelp seed spools were outplanted at two time points in the fall/winter of 2017 and 2018 at four sites and cultivated until harvest the following spring. Kelp performance (length, width, yield), tissue content, and nutrient extraction were determined for each line in each year; oyster growth was also measured monthly for one year at each site. We found that kelp could successfully grow in both shallow coastal lagoons and estuarine sites, although the timing of planting and placement of sites was important. Lines that were planted earlier (as soon as water temperatures<15°C) grew longer and yielded more biomass at harvest; overall, kelp blade yield ranged from 0.36 ± 0.01 to 11.26 ± 2.18 kg/m long line. We report little variation in the tissue quality (C:N) of kelp among sites, but differences in biomass production led to differences in nutrient extraction, which ranged from 0.28 ± 0.04 to 16.35 ± 4.26 g nitrogen/m long line and 8.93 ± 0.35 to 286.30 ± 74.66 g carbon/m long line. We found extensive variability in kelp growth within and between lines and between years, suggesting that crop consistency is a challenge for kelp farmers in the region. Our results suggest that, as there is a lower barrier in terms of permitting (versus starting a new aquaculture farm), it may be a worthwhile investment to add sugar kelp to existing oyster farms, provided they have suitable conditions. At current market rates of US$0.88-$3.30 per kg, farmers in southern New England have the potential to earn US$2,229 per 60 m longline. While seaweed aquaculture is growing, considerable barriers still exist that prevent wide-scale kelp aquaculture adoption by existing aquafarmers. [ABSTRACT FROM AUTHOR]

The use of camera and video technologies for conducting underwater surveys has rapidly expanded over the past several decades. However, the utility of these systems can be significantly hampered by numerous logistical factors, including limited underwater visibility, rough bottom topography, and ease of use for the operator. Video studies can be difficult to compare when methods and terminologies differ. Here, we describe the development of a cost‐effective diver‐propelled underwater ski‐based video system for rapidly acquiring videos in challenging shallow, high‐energy rocky benthic habitats for quantifying fish, macroalgae, and invertebrates in a coastal temperate system. The ski held the camera at a (relatively) fixed distance from the seafloor, we used parallel lasers to quantify our observations, and we used the standardized language of the Coastal and Marine Ecological Classification Standard to acquire consistent quantitative data to serve as an ecological baseline, also including archived images. Our results indicate that the ski proved to be an effective tool for capturing insightful data that would otherwise be very difficult and time‐consuming to collect. Our baseline and repeatable methods can be used by other investigators at this or other locations for monitoring, re‐evaluation, or comparisons to other sites. [ABSTRACT FROM AUTHOR]

Marine macroalgae (seaweeds) are important primary global producers, with a wide distribution in oceans around the world from polar to tropical regions. Most of these species are exposed to variable environmental conditions, such as abiotic (e.g., light irradiance, temperature variations, nutrient availability, salinity levels) and biotic factors (e.g., grazing and pathogen exposure). As a result, macroalgae developed numerous important strategies to increase their adaptability, including synthesizing secondary metabolites, which have promising biotechnological applications, such as UV-absorbing Mycosporine-Like Amino Acid (MAAs). MAAs are small, water-soluble, UV-absorbing compounds that are commonly found in many marine organisms and are characterized by promising antioxidative, anti-inflammatory and photoprotective properties. However, the widespread use of MAAs by humans is often restricted by their limited bioavailability, limited success in heterologous expression systems, and low quantities recovered from the natural environment. In contrast, bloom-forming macroalgal species from all three major macroalgal clades (Chlorophyta, Phaeophyceae, and Rhodophyta) occasionally form algal blooms, resulting in a rapid increase in algal abundance and high biomass production. This review focuses on the bloom-forming species capable of producing pharmacologically important compounds, including MAAs, and the application of proteomics in facilitating macroalgal use in overcoming current environmental and biotechnological challenges. [ABSTRACT FROM AUTHOR]

Blue carbon ecosystems (BCEs) are important nature‐based solutions for climate change‐mitigation. However, current debates question the reliability and contribution of BCEs under future climatic‐scenarios. The answer to this question depends on ecosystem processes driving carbon‐sequestration and ‐storage, such as primary production and decomposition, and their future rates. We performed a global meta‐analysis on litter decomposition rate constants (k) in BCEs and predicted changes in carbon release from 309 studies. The relationships between k and climatic factors were examined by extracting remote‐sensing data on air temperature, sea‐surface temperature, and precipitation aligning to the decomposition time of each experiment. We constructed global numerical models of litter decomposition to forecast k and carbon release under different scenarios. The current k averages at 27 ± 3 × 10−2 day−1 for macroalgae were higher than for seagrasses (1.7 ± 0.2 × 10−2 day−1), mangroves (1.6 ± 0.1 × 10−2 day−1) and tidal marshes (5.9 ± 0.5 × 10−3 day−1). Macrophyte k increased with both air temperature and precipitation in intertidal BCEs and with sea surface temperature for subtidal seagrasses. Above a temperature threshold for vascular plant litter at ~25°C and ~20°C for macroalgae, k drastically increased with increasing temperature. However, the direct effect of high temperatures on k are obscured by other factors in field experiments compared with laboratory experiments. We defined "fundamental" and "realized" temperature response to explain this effect. Based on relationships for realized temperature response, we predict that proportions of decomposed litter will increase by 0.9%–5% and 4.7%–28.8% by 2100 under low‐ (2°C) and high‐warming conditions (4°C) compared to 2020, respectively. Net litter carbon sinks in BCEs will increase due to higher increase in litter C production than in decomposition by 2100 compared to 2020 under RCP 8.5. We highlight that BCEs will play an increasingly important role in future climate change‐mitigation. Our findings can be leveraged for blue carbon accounting under future climate change scenarios. [ABSTRACT FROM AUTHOR]

Coastal wetlands are known for exceptional productivity, but they also receive intense land-based nitrogen (N) loading. In Narragansett Bay, RI (USA), coastal ecosystems have received anthropogenic N inputs from wastewater for more than two centuries. Greenhouse gas fluxes were studied throughout a growing season (2016) in three coastal wetlands with contrasting histories of nitrogen loading. The wetland with the highest historic N load (Mary’s Creek, Warwick, RI) had significantly greater nitrous oxide (N2O) and methane (CH4) emissions than the other two sites. However, the two marshes with historic N loads (Mary’s Creek and Mary Donovan, Little Compton, RI) also had greater rates of CO2 uptake than the reference site (Nag Marsh, Prudence Island, RI). Their CO2 uptake rates far outpaced their other greenhouse gas emissions. Mary’s Creek had the greatest above- and below-ground plant biomass, vertical accretion rates, and carbon content of soils. Spartina alterniflora height was greatest at Mary’s Creek and Mary Donovan marsh. The following growing season (2017), greenhouse gases were compared across four plant-defined ecological zones in Mary’s Creek. Higher rates of CO2 uptake and CH4 emissions were found in the S. alterniflora-vegetated creekbank compared to high marsh zones or bare mudflats. Potential denitrifying enzyme activity did not significantly differ across the four zones nor between Mary’s Creek and Nag Marsh, suggesting a consistently high capacity to completely reduce N loads. These results support efforts to protect and restore these coastal ecosystems for their carbon sequestration function even despite prevalence of anthropogenic N loading. [ABSTRACT FROM AUTHOR]

Ocean acidification and eutrophication have direct, positive effects on the growth of many marine macroalgae, potentially resulting in macroalgal blooms and shifts in ecosystem structure and function. Enhanced growth of macroalgae, however, may be controlled by the presence of grazers. While grazing under ocean acidification and eutrophication conditions has variable responses, there is evidence of these factors indirectly increasing consumption. We tested whether a common marine herbivorous snail, Littorina littorea, would increase consumption rates of macroalgae (Ulva and Fucus) under ocean acidification (increased pCO2) and/or eutrophication conditions, via feeding trials on live and reconstituted algal thalli. We found that increased pCO2 resulted in reduced grazing rates on live thalli, with snails feeding almost exclusively on Ulva. However, eutrophication did not impact consumption rates of live tissues. In addition, similarity in consumption of reconstituted Ulva and Fucus tissues across all treatments indicated that physical characteristics of algal tissues, rather than tissue chemistry, may drive dietary shifts in a changing climate. In this system, decreased consumption, coupled with increased growth of macroalgae, may ultimately enhance algal growth and spread. [ABSTRACT FROM AUTHOR]

Global climate change has led to increased sea surface temperatures and altered precipitation patterns worldwide. Concurrently, macroalgal blooms in coastal systems have been increasing in frequency and severity globally and are successful due to their fast growth rates and broad environmental tolerances. Here, we examine the responses of the bloom-forming green algae Ulva compressa and U. lacinulata to individual and interactive effects of increased temperature and rain (divided into salinity and nitrogen effects). We assessed these impacts on the growth, photosynthetic efficiency, and tissue carbon and nitrogen content of both species. We found that temperatures ranging from 15–27 °C had no significant effect on the growth rate of either U. compressa or U. lacinulata, although both species tended to have lower growth rates after exposure to 27 °C for 3 weeks. High nitrogen, defined as a pulse of 60 µM NO3 and 20 µM NH4, enhanced the growth rate of U. compressa but not U. lacinulata and did not impact the photosynthetic efficiency of either species, although the C:N ratio revealed significant N limitation in both species. Lastly, we found the effects of temperature and rain (via added nitrogen) were not additive. Our results suggest that direct deposition of nitrogen via rain will enhance the growth of U. compressa, while increased temperatures likely will not. Together, our findings indicate that the prevalence of macroalgal blooms in coastal systems will likely increase under global climate change. [ABSTRACT FROM AUTHOR]

Sea level rise within New England is accelerating at a rate faster than the global average, leaving salt marshes particularly susceptible to degradation. Hydrological alteration is a type of climate change adaptation technique that can be used to combat the effects of sea level rise within salt marshes. Runnels (shallow channels) are a type of climate adaptation strategy used to enhance drainage in drowning marshes. In this study, we investigated the impacts of runnel installations, 3–5 years post‐implementation, on soil properties, vegetation composition, and greenhouse gas fluxes. We studied two runnel treatments (Low Elevation Runnel and High Elevation Runnel) and found that in the Low Elevation Runnel areas Spartina alterniflora stem density significantly increased in the three growing seasons after runnels were installed, and the high marsh plant, Spartina patens, persisted in the High Elevation Runnel areas. There was a significant difference in carbon dioxide uptake rates among treatments, with the unmanipulated (Reference) areas having the highest uptake rates and an increase in CO2 uptake over time seen in the Low Elevation Runnel treatment. These findings highlight the potential use of a climate change adaptation strategy to combat sea level rise impacts and provide insights for future adaptation efforts. [ABSTRACT FROM AUTHOR]

Caffeine is present in coastal environments worldwide and there is a need to assess its impact on marine organisms. Here, we exposed two species of ecologically important marine macroalgae (Chondrus crispus and Codium fragile subsp. fragile) to a suite of caffeine concentrations and measured their response. Caffeine concentrations of 10–100 ng L−1 had no significant effect on the growth rate or photosynthetic efficiency of either algae. Extremely high concentrations (100–200 mg L−1), which may occur acutely, produced sublethal effects for both species and mortality in C. fragile subsp. fragile. Our results highlight the need to understand how caffeine impacts marine species. [ABSTRACT FROM AUTHOR]

Introduced, or nonnative, marine species are a threat to local biodiversity, disrupt marine industries, and can have negative effects on coastal communities. Colpomenia peregrina (Sauvageau, 1927) is one of the most successful brown algal invaders in the world. Originating from the Northwest Pacific, Colpomenia peregrina was first collected in the Northwest Atlantic in Nova Scotia, Canada in the 1960s. Since then populations of C. peregrina have been discovered at 57 sites ranging from Grand Barachois Lagoon, Saint Pierre and Miquelon to South Wellfleet, MA, USA. The spread of Colpomenia peregrina can be attributed to its broad tolerance to environmental conditions, buoyant morphology that aids dispersal, and generalist epiphytic biology. Here we report the occurrence of Colpomenia peregrina at five sites in Rhode Island, USA for the first time, representing the crossing of a major biogeographic boundary by this species. The spread of C. peregrina will likely continue, warranting research on its impact on native communities and host algae. [ABSTRACT FROM AUTHOR]

Abstract: Forests make up a large portion of terrestrial plant biomass, and the long‐lived woody plants that dominate them possess an array of traits that deter consumption by forest pests. Although often extremely effective against native consumers, invasive species that avoid or overcome these defenses can wreak havoc on trees and surrounding ecosystems. This is especially true when multiple invasive species co‐occur, since interactions between invasive herbivores may yield non‐additive effects on the host. While the threat posed by invasive forest pests is well known, long‐term field experiments are necessary to explore these consumer‐host interactions at appropriate spatial and temporal scales. Moreover, it is important to measure multiple variables to get a “whole‐plant” picture of their combined impact. We report the results of a 4‐yr field experiment addressing the individual and combined impacts of two invasive herbivores, the hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa), on native eastern hemlock (Tsuga canadensis) in southern New England. In 2011, we planted 200 hemlock saplings into a temperate forest understory and experimentally manipulated the presence/absence of both herbivore species; in 2015, we harvested the 88 remaining saplings and assessed plant physiology, growth, and resource allocation. Adelgids strongly affected hemlock growth: infested saplings had lower above/belowground biomass ratios, more needle loss, and produced fewer new needles than control saplings. Hemlock scale did not alter plant biomass allocation or growth, and its co‐occurrence did not alter the impact of adelgid. While both adelgid and scale impacted the concentrations of primary metabolites, adelgid effects were more pronounced. Adelgid feeding simultaneously increased free amino acids local to feeding sites and a ~30% reduction in starch. The cumulative impact of adelgid‐induced needle loss, manipulation of nitrogen pools, and the loss of stored resources likely accelerates host decline through disruption of homeostatic source‐sink dynamics occurring at the whole‐plant level. Our research stresses the importance of considering long‐term impacts to predict how plants will cope with contemporary pressures experienced in disturbed forests. [ABSTRACT FROM AUTHOR]

Herbivore-induced changes in host quality mediate indirect interactions between herbivores. The nature of these indirect interactions can vary depending on the identity of herbivores involved, species-specific induction of defense-signaling pathways, and sequence of attack. However, our understanding of the role of these signaling pathways in the success of multiple exotic herbivores is less known. Eastern hemlock (Tsuga canadensis) is attacked by two invasive herbivores [elongate hemlock scale (EHS; Fiorinia externa) and hemlock woolly adelgid (HWA; Adelges tsugae)] throughout much of its range, but prior attack by EHS is known to deter HWA. The potential role of phytohormones in this interaction is poorly understood. We measured endogenous levels of phytohormones in eastern hemlock in response to attack by these invasive herbivores. We also used exogenous application of methyl jasmonate (MJ) and acibenzolar-S-methyl (ASM), a salicylic acid (SA) pathway elicitor, to test the hypothesis that defense-signaling phytohormones typically induced by herbivores could deter HWA. Resistance to adelgid attack was assessed using a behavioral assay. Adelgid feeding significantly elevated both abscisic acid (ABA) and SA in local tissues, while EHS feeding had no detectable effect on either phytohormone. HWA progrediens and sistens crawlers preferred to settle on ASM-treated foliage. In contrast, HWA crawlers actively avoided settlement on MJ-treated foliage. We suggest that induction of ABA- and SA-signaling pathways, in concert with defense-signaling interference, may aid HWA invasion success, and that defense-signaling interference, induced by exotic competitors, may mediate resistance of native hosts. [ABSTRACT FROM AUTHOR]

Forest pests drive tree mortality through disruption of functional traits linked to nutrient acquisition, growth and reproduction. The impacts of attack by individual or multiple above-ground herbivores on root functional traits critical to tree health have received little attention. This is especially true for exotic herbivores, organisms often found in disturbed forests., We excavated whole-root systems from eastern hemlock ( Tsuga canadensis) individuals experimentally infested with hemlock woolly adelgid ( HWA: Adelges tsugae) and elongate hemlock scale ( EHS: Fiorina externa) individually, or in combination, for periods of 2 and 4 years. Below-ground root biomass, functional traits and storage nutrients were measured to assess impacts of herbivory. We also quantified ectomycorrhizal fungal ( EMF) colonisation of fine roots and used culture-independent methods to examine EMF diversity., Trees infested with HWA had a greater root mass fraction (root to total biomass ratio), although feeding had no observable effects on root functional traits (e.g. specific root length) or on resource allocation to roots. HWA feeding did significantly reduce EMF colonisation of hemlock fine roots, though surprisingly, EMF diversity and that of other fungal associates were unaffected. In contrast to HWA, EHS (alone or in conjunction with HWA) feeding had no observable effect on below-ground traits or EMF colonisation alone; however, its presence mediated HWA effects when trees were co-infested. Simultaneous infestation within the same year yielded significant reductions in EMF colonisation, whereas prior EHS attack weakened HWA effects., Our results collectively suggest that prior EHS attack dampens the impact of HWA on below-ground functional traits. This highlights how the timing and sequence of herbivore arrival can alter plant-mediated interactions between herbivores and their effects on above-below-ground linkages and associated tree health., A is available for this article. [ABSTRACT FROM AUTHOR]

The success of the invasive Asian shore crab, Hemigrapsus sanguineus, stems partly from its ability to exclude established crab species from preferred rocky and cobble intertidal habitat. Here, we assessed preference and competition for habitat types (cobble vs. sand) for H. sanguineus and two competitor species; the previous invasive green crab, Carcinus maenas, and the native rock crab, Cancer irroratus, in New England. In simple laboratory experiments, we paired similarly sized heterospecifics and conspecifics from each species, and also grouped combinations of C. maenas and H. sanguineus in a series of four-individual sets in order to dissect the outcome of intra- and inter-specific competition at different densities. Individually, all three species preferred cobble substrate. With paired conspecifics, H. sanguineus individuals would cohabitate in cobble, whereas C. maenas and C. irroratus individuals each excluded conspecifics from cobble. In heterospecific pairs, H. sanguineus excluded both C. maenas and C. irroratus from cobble. C. maenas and C. irroratus, were equally likely to exclude the other species, but rarely excluded H. sanguineus. In larger assemblages, H. sanguineus preferentially grouped under cobble, whereas C. maenas were more evenly distributed among habitat types. These observations demonstrate that conspecific tolerance and heterospecific competition can be effective, complementary mechanisms for overcoming invasion resistance. Such mechanisms help explain the well-studied success of H. sanguineus following its introduction into New England coastal habitats, and the resulting exclusion of preexisting crab species. [ABSTRACT FROM AUTHOR]

Intertidal crabs exhibit high occurrences of injury, including claw and leg loss. While it can be challenging to determine the specific cause of such injuries, the resulting distribution of injured individuals across habitat types is relatively easy to assess. We surveyed populations of crabs along Rhode Island, USA rocky intertidal shorelines to determine the distribution of injured vs uninjured individuals. We found that the invasive Asian shore crab Hemigrapsus sanguineus (De Haan, 1835) (Varunidae) dominated the surveys, with few other crab species found across our sites. There was little evidence for differences in the distribution of injuries across intertidal zones, with half of all crabs exhibiting loss of at least one limb. There were no differences in claw loss across the sampled populations, though mature crabs were 22% more likely than juveniles to be missing legs. Gravid females had the lowest frequency of injury of all crabs, being three times less likely to be injured than non-gravid females. Relative to other crabs, gravid females and juveniles were also less likely to be found in the high intertidal zone. Our results underscore the complexity of patterns of injury and resulting impact on demography, and help illuminate the role these patterns play in the ecology of intertidal animals. [ABSTRACT FROM AUTHOR]

Rapid adaptation to novel biotic interactions and abiotic factors in introduced ranges can be critical to invasion success of both exotic terrestrial and aquatic plants. Seaweeds are extremely successful biological invaders in marine environments. Along with herbivores, foulers − ubiquitous enemies in the marine environment − have the potential to determine the success or failure of invasive seaweeds. However, research on the topic of rapid adaptation of seaweeds to biotic challenges is still in its nascent stages and rapid adaptation of seaweeds to fouling is unexplored., We tested whether the impressive invasion success of the red macroalga Gracilaria vermiculophylla may be enhanced by the rapid adaptation of chemical control (defence) of new bacterial epibionts in the invaded range., The native and invasive G. vermiculophylla populations investigated were equally well defended against currently co-occurring bacterial epibionts isolated from their respective ranges. In contrast, the native populations were weakly defended against bacterial epibionts from the invaded range, whereas the invasive populations were weakly defended against bacterial epibionts from their native range. Apparently during the invasion process, invasive populations have adapted their control capacity to cope with the new epibionts but have lost the capacity to fend off old epibionts., Synthesis. These results provide the first evidence that a change in habitat and, thus, confrontation by new enemies, may trigger rapid defence adaptation of seaweeds, which could be necessary for invasiveness. Such adaptation dynamics as found in the current study could be also applicable to other types of host plant - enemy interaction e.g. plant root - microbe interactions, freshwater plant - fouler interactions in general and for cases of shifting plant - enemy interactions in course of climate change. [ABSTRACT FROM AUTHOR]

Many aspects of global change affect the variability of species population densities, in terms of both the magnitude and pattern of density fluctuations. However, we have limited empirical understanding of the consequences of altered temporal variability of populations, independent of changes in their mean densities, for the structure and stability of natural communities and the responses of ecosystems to additional stressors., We used a field experiment to test the effects of altered temporal variability of a single consumer species on community structure and stability. Specifically, we manipulated the temporal variability of populations of a key grazer species on temperate rocky shores ( Littorina littorea), independent of their mean densities, over 12 months and measured the responses of algal communities in terms of multiple measures of structure and stability. Further, we tested whether consumer variability determined the effects of an additional perturbation, elevated sedimentation, on algal communities., The effects of sedimentation on the structure and stability of algal communities were regulated by the temporal variability of consumer populations. In particular, elevated sedimentation led to a decrease in algal evenness, but only when consumer densities were held constant, and resulted in a decrease in the rate of local algal extinctions, but only when consumer temporal variability was increased., Independent of sedimentation, increased temporal variability of consumer populations led to a shift in algal assemblage structure and affected the stability of algal communities in terms of both compositional turnover and resistance to environmental perturbations. Further, these effects varied according to the temporal pattern of consumer density fluctuations., Synthesis. Our results demonstrate that changes in the temporal variability of a single species can modify multiple aspects of both the structure and stability of natural communities and alter their responses to perturbations. However, the effects of consumer variability cannot be predicted without knowledge of the temporal pattern of density fluctuations. These findings have profound implications for our understanding of the effects of multiple disturbances on ecosystems. [ABSTRACT FROM AUTHOR]

Macroalgal blooms occur worldwide and have the potential to cause severe ecological and economic damage. Narragansett Bay, RI is a eutrophic system that experiences summer macroalgal blooms composed mostly of Ulva compressa and Ulva rigida, which have biphasic life cycles with separate haploid and diploid phases. In this study, we used flow cytometry to assess ploidy levels of U. compressa and U. rigida populations from five sites in Narragansett Bay, RI, USA, to assess the relative contribution of both phases to bloom formation. Both haploid gametophytes and diploid sporophytes were present for both species. Sites ranged from a relative overabundance of gametophytes to a relative overabundance of sporophytes, compared to the null model prediction of √2 gametophytes: 1 sporophyte. We found significant differences in cell area between ploidy levels for each species, with sporophyte cells significantly larger than gametophyte cells in U. compressa and U. rigida. We found no differences in relative growth rate between ploidy levels for each species. Our results indicate the presence of both phases of each of the two dominant bloom forming species throughout the bloom season, and represent one of the first studies of in situ Ulva life cycle dynamics. [ABSTRACT FROM AUTHOR]

Herbivore impacts on macrophyte growth vary with the identity of the herbivores and macrophytes, as well as under different abiotic conditions. This interaction is further complicated by anthropogenic alterations to the environment, such as eutrophication. In this study, we utilized in situ herbivore exclusion experiments and mesocosm feeding preference assays to examine the impacts of different herbivores on the growth of two morphologically similar, co-occurring macroalgal bloom Ulva species in a nutrient-rich environment. We found that herbivory had a measurable impact on Ulva biomass, though the rate of consumption rarely surpassed growth for either Ulva species. We determined that the primary herbivores within the blooms were amphipods and mud crabs, and that their effects varied among study sites and months. Our results also confirmed that, even with a diverse suite of consumers, Ulva blooms are capable of escaping herbivore control, particularly early in the growing season when growth rates peak and herbivore activity is limited. Furthermore, our experiments revealed species-specific feeding preferences among herbivores, as well as differences in growth rates and chemistry between the two Ulva species, which likely influence bloom dynamics. [ABSTRACT FROM AUTHOR]

Concern over the relative importance of different sample preparation and storage techniques frequently used in stable isotope analysis of particulate nitrogen (δ15N) and carbon (δ13C) prompted an experiment to determine how important such factors were to measured values in marine organisms. We stored the marine macroalgae Ulva and Gracilaria in four different ways and analyzed replicates every three months over the course of a year to assess treatment effects on stability. Treatments consisted of algae dried at 65°C, ground to a powder, and stored in a desiccator until analysis; algae left in a drying oven or in a freezer and processed (dried and ground) just prior to analysis, as well as some dried, ground samples kept out in the lab and reanalyzed quarterly for 12 months. Concurrently, to assess the ecological range in isotope values over the course of a year, samples were freshly collected from the same location and analyzed along with the other treatments at each time step. Neither storage technique nor time had an impact on either δ15N or δ13C values or the %N and %C of the algae tissues. There were clear and consistent differences between species and some large seasonal differences in the freshly collected samples. The interspecies differences and seasonal ranges of values underscore the stability associated with method and duration of sample storage. [ABSTRACT FROM AUTHOR]

Temperate coastal estuaries worldwide, such as Narragansett Bay, Rhode Island, are influenced by seasonal macroalgal blooms (e.g., Ulva) during warm months, whereas bloom-forming macroalgae are rarely encountered during winter. We assessed the ability of distromatic Ulva to overwinter through fragments, recruits, and/or microscopic propagules. We documented (a) small tissue fragments in sediment cores and the water column, (b) recruits and microscopic propagules on field-based settlement tiles, and (c) production of reproductive propagules, throughout the winter months. Laboratory culturing experiments indicated that both fragments and propagules are viable. Our data indicate that bloom-forming overwintering Ulva simultaneously use multiple reproductive strategies. [ABSTRACT FROM AUTHOR]

Macroalgal bloom-forming species occur in coastal systems worldwide. However, due to overlapping morphologies in some taxa, accurate taxonomic assessment and classification of these species can be quite challenging. We investigated the molecular and morphological characteristics of 153 specimens of bloom-forming Ulva located in and around Narragansett Bay, RI, USA. We analyzed sequences of the nuclear internal transcribed spacer 1 region ( ITS1) and the chloroplast-encoded rbcL; based on the ITS1 data, we grouped the specimens into nine operational taxonomic units ( OTUs). Eight of these OTUs have been previously reported to exist, while one is novel. Of the eight OTUs, all shared sequence identity with previously published sequences or differed by less than 1.5% sequence divergence for two molecular markers. Previously, 10 species names were reported for Ulva in Rhode Island (one blade and nine tube-forming species) based upon morphological classification alone. Of our nine OTUs, three contained blade-forming specimens ( U. lactuca, U. compressa, U. rigida), one OTU had a blade with a tubular stipe, and six contained unbranched and/or branched tubular morphologies (one of these six, U. compressa, had both a blade and a tube morphology). While the three blade-forming OTUs in Narragansett Bay can frequently be distinguished by careful observations of morphological characteristics, and spatial/temporal distribution, it is much more difficult to distinguish among the tube-forming specimens based upon morphology or distribution alone. Our data support the molecular species concept for Ulva, and indicate that molecular-based classifications of Ulva species are critical for proper species identification, and subsequent ecological assessment or mitigation of Ulva blooms. [ABSTRACT FROM AUTHOR]

: The recent invasion of the red alga Heterosiphonia japonica in the western North Atlantic Ocean has provided a unique opportunity to study invasion dynamics across a biogeographical barrier. Native to the western North Pacific Ocean, initial collections in 2007 and 2009 restricted the western North Atlantic range of this invader to Rhode Island, USA. However, through subtidal community surveys, we document the presence of Heterosiphonia in coastal waters from Maine to New York, USA, a distance of more than 700 km. This geographical distribution spans a well-known biogeographical barrier at Cape Cod, Massachusetts. Despite significant differences in subtidal community structure north and south of Cape Cod, Heterosiphonia was found at all but two sites surveyed in both biogeographic provinces, suggesting that this invader is capable of rapid expansion over broad geographic ranges. Across all sites surveyed, Heterosiphonia comprised 14% of the subtidal benthic community. However, average abundances of nearly 80% were found at some locations. As a drifting macrophyte, Heterosiphonia was found as intertidal wrack in abundances of up to 65% of the biomass washed up along beaches surveyed. Our surveys suggest that the high abundance of Heterosiphonia has already led to marked changes in subtidal community structure; we found significantly lower species richness in recipient communities with higher Heterosiphona abundances. Based on temperature and salinity tolerances of the European populations, we believe Heterosiphonia has the potential to invade and alter subtidal communities from Florida to Newfoundland in the western North Atlantic. [ABSTRACT FROM AUTHOR]

Despite excessive growth of macroalgae in estuarine systems, little research has been done to examine the impacts of increased algal biomass that drifts into nearby salt marshes and accumulates on intertidal flats. The accumulation of macroalgal mats and subsequent decomposition-related releases of limiting nutrients may potentially alter marsh communities and impact multiple trophic levels. We conducted a 2-year in situ study, as well as laboratory mesocosm experiments, to determine the fate of these nutrients and any bottom-up impacts from the blooms on the dominant salt marsh plant ( Spartina alterniflora) and herbivores. Mesocosm results showed that macroalgal decomposition had a positive impact on sediment nitrogen concentrations, as well as S. alterniflora growth rates. In contrast, our in situ results suggested that S. alterniflora growth was hindered by the presence of macroalgal mats. From our results, we suggest that macroalgal accumulation and subsequent release of nitrogen during decomposition may be beneficial in nitrogen limited areas. However, as marshes are becoming increasingly eutrophic, releasing lower marsh plants from nitrogen limitation, this accumulation of macroalgal biomass may hinder S. alterniflora growth through smothering and breakage of culms. As macroalgal blooms are predicted to intensify with rising temperatures and increased eutrophication, the ecological impacts associated with these changes need to be continuously monitored in order to preserve these fragile ecosystems. [ABSTRACT FROM AUTHOR]

The invasive Asiatic red alga Gracilaria vermiculophylla has recently spread rapidly around the globe. In the Northwest Atlantic, it was first collected in Virginia during 1998; in New England, it was first recorded from Narragansett Bay, Rhode Island in 2007. Until now, the specific dates of its introduction and current distribution in New England have been poorly understood. We employed a combination of field collections, evaluations of historical herbarium specimens, and molecular investigations (including mt-CO1 gene sequencing) to document its present distribution and approximate dates of introduction within New England. We found G. vermiculophylla at 18 of 24 Northwest Atlantic sites growing with native Gracilaria populations. Presently, it is recorded from Stamford, CT to Greenland, NH, with no populations known from five Maine sites where the native G. tikvahiae grows. Molecular screening of historical specimens revealed that G. vermiculophylla was collected from five sites in Massachusetts during 2000, whereas it was first documented in New Hampshire from the middle of the Great Bay Estuarine System (i.e., Dover Point) during 2003. In Rhode Island, initial specimens were documented during 2007, and those in Connecticut were first confirmed during 2010. As G. vermiculophylla has gone primarily undetected in New England since at least 2000, this highlights the difficulty of documenting the arrival and spread of an invasive species that closely resembles a native congener. Hence, DNA sequencing is critical in clarifying the introduction and expansion of such non-native seaweeds. [ABSTRACT FROM AUTHOR]

Herbivores can facilitate macrophyte growth through stimulation of overcompensation pathways, removal of neighbouring or fouling competitors or increasing nutrient availability via nitrogenous waste inputs., We examined the facilitative relationship between the mud snail Ilyanassa obsoleta and two morphologically similar bloom-forming Ulva species, Ulva compressa and Ulva rigida. Through mesocosm experiments, we determined the occurrence and underlying mechanisms responsible for facilitating Ulva growth. In situ snail enclosure experiments determined the occurrence of this facilitative pathway under natural conditions., We found that both U. compressa and U. rigida are facilitated by I. obsoleta, but despite their morphological similarity, the primary facilitative mechanism differed for each species. Ulva compressa experienced increased growth via snail nitrogenous waste inputs, while U. rigida was facilitated by the removal of fouling microalgae. These results suggest that physiological differences exist between these two species, potentially sustaining their coexistence within blooms., Ground tissue assays showed I. obsoleta preference for microalgal foulers in whole-tissue assays was driven by Ulva blade morphology rather than chemical or nutritive properties. This indicates that the underlying mechanism for I. obsoleta's facilitation via grazing is an inability of the snail's radula to effectively puncture Ulva blades, confining their grazing activities to fouling organisms on the blade surface., In contrast to our mesocosm results, in situ experiments failed to find a positive impact of mud snail presence on Ulva blade growth. However, Ulva blades within these experiments were located at a highly eutrophic site and isolated from potential competitors. Consequently, this may have created an environment where I. obsoleta facilitation was not required for maximum Ulva growth., Synthesis. We demonstrated two mechanisms by which top-down forces can facilitate macroalgal growth: herbivore nitrogenous waste inputs and removal of microalgal fouling organisms. This facilitation may occur within the large mats of macroalgae that form during bloom events, exacerbating bloom conditions. [ABSTRACT FROM AUTHOR]

In order to effectively study, manage, conserve, and sustain shallow-subtidal ecosystems, a spatial inventory of the basic resources and habitats is essential. Because of the complexities of shallow-subtidal substrates, benthic communities, geology, geomorphology, and water column attributes, few standard protocols are fully articulated and tested that describe the mapping and inventory processes and accompanying interpretations. In this paper, we describe a systematic approach to map Rhode Island's shallow-subtidal coastal lagoon ecosystems, by using, integrating, and reconciling multiple data sets to identify the geology, soils, biological communities, and environments that, collectively, define each shallow-subtidal habitat. We constructed maps for these lagoons via a deliberate, step by step approach. Acoustics and geostatistical modeling were used to create a bathymetric map. These data were analyzed to identify submerged landforms and geologic boundaries. Geologic interpretations were verified with video and grab samples. Soils were sampled, characterized, and mapped within the context of the landscape and geologic boundaries. Biological components and distributions were investigated using acoustics, grab samples, video, and sediment profile images. Data sets were cross-referenced and ground-truthed to test for inconsistencies. Maps and geospatial data, with Federal (eographic Data Committee (FGDC I-compliant metadata, were finalized after reconciling data set inconsistencies and made available on the Internet. These data allow for classification in the revised Coastal and Marine Ecological Classification Standard (CMECS). With these maps, we explored potential relationships among and between physical and biological parameters. In some cases, we discovered a clear match between habitat measures; in others, however, relationships were more difficult to distinguish and require further investigation. [ABSTRACT FROM AUTHOR]

Marine assemblages are influenced by the rate and timing of species settlement and recruitment. Both abiotic factors and biotic interactions can impact recruitment rates of marine species in a variety of systems. However, the impacts of species which recruit at the same time upon each other are less well understood. We investigated the relationship between the recruitment of Lacuna vincta, a small (<6 mm shell diameter) marine snail, and two species of algal epiphytes, the native Ceramium virgatum and the invasive Neosiphonia harveyi, in the shallow subtidal zone of Narragansett Bay, Rhode Island. All three species exhibit peak recruitment densities during two months in the summer. We found that the presence of algal epiphytes facilitates the recruitment rate of L. vincta, regardless of the epiphyte species composition. We also found a positive relationship between the number of L. vincta present and epiphyte recruitment, which is disproportionately driven by higher recruitment of N. harveyi than C. virgatum. Understanding recruitment dynamics and interactions is vital to effectively mitigate the effects of and adaptations to changes due to the establishment of non-native species. [ABSTRACT FROM AUTHOR]

Narragansett Bay has been heavily influenced by human activities for more than 200 years. In recent decades, it has been one of the more intensively fertilized estuaries in the USA, with most of the anthropogenic nutrient load originating from sewage treatment plants (STP). This will soon change as tertiary treatment upgrades reduce nitrogen (N) loads by about one third or more during the summer. Before these reductions take place, we sought to characterize the sewage N signature in primary (macroalgae) and secondary (the hard clam, Mercenaria mercenaria) producers in the bay using stable isotopes of N (δ15N) and carbon (δ13C) The δ13N signatures of the macroalgae show a clear gradient of approximately 4‰ from north to south, i.e., high to low point source loading. There is also evidence of a west to east gradient of heavy to light values of δ15N in the bay consistent with circulation patterns and residual flows. The Providence River Estuary, just north of Narragansett Bay proper, receives 85% of STP inputs to Narragansett Bay, and lower δ15N values in macroalgae there reflected preferential uptake of 14N in this heavily fertilized area. Differences in pH from N stimulated photosynthesis and related shifts in predominance of dissolved C species may control the observed δ13C signatures. Unlike the macroalgae, the clams were remarkably uniform in both δ15N (13.2±0.54‰ SD) and δ13C (-16.76±0.61‰ SD) throughout the bay, and the δ15N values were 2-5‰ heavier than in clams collected outside the bay. We suggest that this remarkable uniformity reflects a food source of anthropogenically heavy phytoplankton formed in the upper bay and supported by sewage derived N. We estimate that approximately half of the N in the clams throughout Narragansett Bay may be from anthropogenic sources. [ABSTRACT FROM AUTHOR]

Sargassum fusiforme (Harvey) Setchell has been shown to be a highly effective inhibitor of HIV-1 infection. To identify its mechanism of action, we performed bioactivity-guided fractionation on Sargassum fusiforme mixture. Here, we report isolation of a bioactive fraction SP4-2 (S. fusiforme), which at 8 µg/ml inhibited HIV-1 infection by 86.9%, with IC50 value of 3.7 µg. That represents 230- fold enhancement of antiretroviral potency as compared to the whole extract. Inhibition was mediated against both CXCR4 (X4) and CCR5 (R5) tropic HIV-1. Specifically, 10 µg/ml SP4-2 blocked HIV-1 fusion and entry by 53%. This effect was reversed by interaction of SP4-2 with sCD4, suggesting that S. fusiforme inhibits HIV-1 infection by blocking CD4 receptor, which also explained observed inhibition of both X4 and R5-tropic HIV-1. SP4-2 also inhibited HIV-1 replication after virus entry, by directly inhibiting HIV-1 reverse transcriptase (RT) in a dose dependent manner by up to 79%. We conclude that the SP4-2 fraction contains at least two distinct and biologically active molecules, one that inhibits HIV-1 fusion by interacting with CD4 receptor, and another that directly inhibits HIV-1 RT. We propose that S. fusiforme is a lead candidate for anti-HIV-1 drug development. [ABSTRACT FROM AUTHOR]

There is a growing awareness of the role that indirect interactions play in influencing food webs and ecosystem structure. In this study, the hypothesis that crustose algal epibionts provide gastropods associational resistance from predation was investigated through field surveys and laboratory feeding assays. In rocky low intertidal/shallow subtidal systems in the northeast Pacific, several species of crustose algae (the red alga Peyssonnelia meridionalis and crustose corallines) can colonize the shells of living Tegula brunnea snails. The growth patterns of these epibiontic crustose algae allow them to cover their host’s surface completely, which may, in turn, protect their hosts from predation. A multi-site field survey of T. brunnea revealed that >60% of snails were at least 75% covered with one or more species of crustose algae, with 35% fully covered, indicating that this is common in the field. Laboratory feeding assays revealed that sea stars, a primary predator of T. brunnea, distinguished among snails with different shell coverings; Pisaster consumed nearly three times as many bare (i.e. no crustose algae) snails as those covered with Peyssonnelia, while Pycnopodia consumed four times as many bare snails as those covered with crustose corallines. These results suggest that epibiont crustose algae can benefit their hosts via associational resistance; this finding may have implications for the role of associational resistance in trophic interactions. [ABSTRACT FROM AUTHOR]

Many species of marine algae have life cycles that involve multiple separate, free-living phases that frequently differ in ploidy levels. These complex life cycles have received increasing scientific attention over the past few decades, due to their usefulness for both ecological and evolutionary studies. I present a synthesis of our current knowledge of the ecological functioning and evolutionary implications of the isomorphic, biphasic life cycles commonly found in many species of marine algae. There are both costs and benefits to life cycles with 2 morphologically similar but separate, free-living phases that differ in ploidy levels (haploids and diploids). Evolutionary theory predicts that the existence of subtle yet important differences between the phases may be what allows these life cycles to be maintained. Different phases of the same species can vary in abundance, in demographic parameters such as mortality and fecundity, in their physiology, and in their resistance to herbivory. Stone taxonomic groups within the red algae have received significant attention toward these issues, while our knowledge of these properties for brown and green algae remains limited. [ABSTRACT FROM AUTHOR]

Selective grazing by herbivores can have large effects on the population dynamics and community structure of primary producers. However, the ecological impacts of within-species herbivore preference for tissues of different phases (e.g., ploidy levels) or reproductive status remain relatively poorly known, especially among algae and other species with free-living haploid (gametophyte) and diploid (sporophyte) phases. We tested for herbivore selectivity among tissue types of the isomorphic (identical haploid and diploid free-living stages) red alga Mazzaella flaccida. Laboratory feeding assays demonstrated that the snail Tegula funebralis exhibited more than a threefold preference for gametophyte reproductive tissue over other tissue types, due to morphological differences. In contrast, the urchin Strongylocentrotus purpuratus did not distinguish as clearly between gametophytes and sporophytes; but it did prefer sporophyte reproductive to nonreproductive tissue, due to differences in water-soluble chemicals. Field surveys of grazer damage on M. flaccida blades were consistent with these laboratory preferences, with more damage found on gametophytes than sporophytes and reproductive than nonreproductive tissues. Differential fecundity can contribute to a skew in relative frequencies of phases in the field, and our results suggest that differential grazing by snails may contribute to this pattern and thus play a role in algal population biology. [ABSTRACT FROM AUTHOR]

Anthropogenically induced global climate change has profound implications for marine ecosystems and the economic and social systems that depend upon them. The relationship between temperature and individual performance is reasonably well understood, and much climate-related research has focused on potential shifts in distribution and abundance driven directly by temperature. However, recent work has revealed that both abiotic changes and biological responses in the ocean will be substantially more complex. For example, changes in ocean chemistry may be more important than changes in temperature for the performance and survival of many organisms. Ocean circulation, which drives larval transport, will also change, with important consequences for population dynamics. Furthermore, climatic impacts on one or a few ‘leverage species’ may result in sweeping community-level changes. Finally, synergistic effects between climate and other anthropogenic variables, particularly fishing pressure, will likely exacerbate climate-induced changes. Efforts to manage and conserve living marine systems in the face of climate change will require improvements to the existing predictive framework. Key directions for future research include identifying key demographic transitions that influence population dynamics, predicting changes in the community-level impacts of ecologically dominant species, incorporating populations’ ability to evolve (adapt), and understanding the scales over which climate will change and living systems will respond. [ABSTRACT FROM AUTHOR]

Although human-mediated extinctions disproportionately affect higher trophic levels, the ecosystem consequences of declining diversity are best known for plants and herbivores. We combined field surveys and experimental manipulations to examine the consequences of changing predator diversity for trophic cascades in kelp forests. In field surveys we found that predator diversity was negatively correlated with herbivore abundance and positively correlated with kelp abundance. To assess whether this relationship was causal, we manipulated predator richness in kelp mesocosms, and found that decreasing predator richness increased herbivore grazing, leading to a decrease in the biomass of the giant kelp Macrocystis. The presence of different predators caused different herbivores to alter their behaviour by reducing grazing, such that total grazing was lowest at highest predator diversity. Our results suggest that declining predator diversity can have cascading effects on community structure by reducing the abundance of key habitat-providing species. [ABSTRACT FROM AUTHOR]

We develop and test models for the population dynamics of species that undergo regular alternations of generations between independent, free-living, haploid and diploid phases. The models are patterned after the dioecious, haploid-diploid lifecycle of many marine algae. If the two phases have equal demographic rates, all models (with or without density dependence) predict a stable distribution with a ratio of &radic2:1 (∼60% haploids and 40% diploids). We find that observable deviations from this distribution can occur when the demographic rates (mortality, fecundity) between phases vary widely. Field surveys of three macroalgal species with independent, free-living haploids and diploids, Mazzaella flaccida, M. laminarioides, and M. splendens, reveal a consistent pattern of haploid dominance that significantly exceeds this null model expectation (72%, 76%, and 66%, respectively). These species also exhibit significant variation in haploid frequency among sites. We estimated the per capita fecundity and mortality rates for each phase of both M. flaccida and M. laminarioides and used this information to address two basic questions: (1) Which parameter better explains the overall high relative haploid abundance for each species? and (2) Which parameter better explains the variation in relative haploid abundance among sites? Differences in haploid and diploid mortality rates did not explain the high relative abundance of haploids for either M. flaccida or M. laminarioides. However, differences in fecundity rates between phases were consistent with the high relative abundance of haploids for M. flaccida; diploids usually had significantly higher per capita fecundity rates than haploids. For M. laminarioides, there were no significant differences in fecundity rates between phases. For M. flaccida, among-site variation in relative abundance of haploids can be explained by differences in mortality rates. [ABSTRACT FROM AUTHOR]