Macroalgal Tissue Research Articles

Measuring tissue water potential in marine macroalgae via an updated Chardakov method.

Regulation of tissue water potential is a key mechanism in macroalgal osmotic responses to changing external osmotic conditions, which are common in tidally influenced estuarine and intertidal systems. Nevertheless, significant knowledge gaps exist in our understanding of osmotic responses in macroalgae because few methods measure osmotic potential within macroalgal tissues. Leaf psychrometers have furthered understanding of osmotic potentials in terrestrial plant water relations, yet these have not been developed to measure the range of highly negative potential values found in marine macroalgae. To address these gaps, we present an effective, updated version of the Chardakov method to measure tissue water potential in macroalgae. Here, we present a case study examining macroalgal response in tissue water potential by two morphologically and evolutionarily distinct species, Ulva lactuca (Chlorophyta) and Hypnea musciformis (Rhodophyta) to four paired salinity and nutrient treatments at two temperatures. These treatments simulate a gradient from full coastal ocean conditions to brackish submarine groundwater discharge, an ecosystem type found on basaltic shorelines. Both algae demonstrated plasticity in osmotic response to submarine groundwater discharge with significant positive correlations between tissue water potential and proportion of submarine groundwater discharge in the treatment. These results are the first to describe macroalgal response in tissue water potential, a first step to understanding algal physiological ecology in such complex coastal environments. This revised Chardakov method is a valuable tool to better understand species-specific osmotic responses to ecologically relevant conditions, and can augment the study of other tidal systems and ontogenetic stages.

Re-introduction of a bioactive bacterial endophyte back to its seaweed (Ulva sp.) host, influences the host’s microbiome

Ulva is a commercially important marine macroalga. It hosts both epiphytes and endophytes. The latter are assumed to protect Ulva through secondary metabolites. Previously, we demonstrated bioactive endophytes from macroalgae with great potential to control diseases of aquaculture. In this study, we introduced a bioactive bacterial endophyte back into its original host (Ulva sp.) and demonstrated its survival over time in fresh and freeze-dried Ulva sp. We visualized the endophyte’s location and survival in the seaweed using a Green Fluorescent Protein (GFP) reporter gene. The isolate colonized the intercellular space and survived for at least 5 months in fresh, and 12 months in freeze-dried algae, while maintaining its bioactivity against the aquaculture pathogen Streptococcus iniae. We studied the influence of the endophyte on the bacterial community in the Ulva sp. We found that once introduced, the endophyte significantly changed algal microbiota diversity and abundance. Two of Ulva’s associated bacterial species were quantified over time, suggesting different trends in absolute abundance of these bacteria between treatments. To the best of our knowledge, this is the first report of the successful introduction of an endophytic microorganism into macroalgal tissue. These findings may be useful in applied research for the potential management of aquaculture diseases.

Detection and impact of sewage pollution on South Kohala's coral reefs, Hawai‘i

Sewage pollution from on-site sewage disposal systems and injection wells is impacting coral reefs worldwide. Our study documented the presence and impact of sewage on South Kohala's coral reefs, on Hawai‘i Island, through benthic water quality and macroalgal sampling (fecal indicator bacteria, nutrients, δ15N macroalgal tissue), NO3− stable isotope mixing models, water motion measurements, and coral reef surveys. Sewage pollution was moderate on the offshore reef from benthic seeps, and water motion mixed and diluted it across the benthos. These conditions likely contribute to the dominance of turf algae cover, and the severity and prevalence of growth anomalies and algal overgrowth on corals. Use of multiple indicators and studying water motion was necessary to assess sewage pollution and identify environmental drivers associated with impaired coral health conditions. Methods used in this study can be utilized by natural resource managers to identify and reduce anthropogenic stressors to coral reefs.

Nitrogen stable isotopes (δ15N) and tissue nitrogen in shallow‐water and mesophotic macroalgae differ between the Main Hawaiian Islands and the Northwestern Hawaiian Islands

AbstractThe Hawaiian Archipelago stretches 2500 km from the Main to the Northwestern Hawaiian Islands, represents a complex gradient of oceanographic and anthropogenic drivers, and has a high abundance and diversity of native and invasive macroalgae. These photosynthetic organisms occur in intertidal to mesophotic (30–150+ m) depths and absorb nitrogen with limited fractionation associated with their physiology and source. Our goal was to examine nitrogen dynamics from shallow to mesophotic reefs using compositional patterns of two well‐characterized macroalgal tissue parameters: stable isotope ratio of nitrogen and tissue nitrogen content. We collected 813 macroalgal samples from 13 islands/atolls between 0 and 117 m depths. Within the Main Hawaiian Islands, macroalgal tissue stable N isotope ratios were higher in mesophotic depths; N content was higher in shallow depths. However, within the Northwestern Hawaiian Islands, no differences in stable N isotope ratios and N content were found between shallow and mesophotic depths. Regionally, stable N isotope ratios varied along a gradient of anthropogenic and oceanographic processes (in Main and Northwestern Hawaiian Islands, respectively), while N content reflected elevated nitrogen in the Main compared with the Northwestern Hawaiian Islands. Additionally, the invasive macroalga Avrainvillea lacerata had significantly higher N content than co‐occurring native bryopsidalean macroalgae at similar depths, and may be reshaping nutrient dynamics from shallow to mesophotic depths in the Main Hawaiian Islands. Nitrogen dynamics at mesophotic depths may be influenced by nearshore anthropogenically derived nitrogen via submarine groundwater discharge and/or inputs from deeper water within the Main Hawaiian Islands.

Spatial distribution and sources of nutrients at two coastal developments in South Kohala, Hawai'i

Nutrient sources to coastal waters with coral reefs are not well-characterized. This study documented spatial distributions of nutrients within coastal waters along two developments with coral reefs, and identified nutrient sources through nutrient mixing plots, δ15N measurements in macroalgal tissue, and NO3− stable isotope mixing models. Nutrients decreased from fresh groundwaters to offshore waters, with some surface waters higher in concentrations than benthic ones. Conservative and non-conservative mixing between fresh and ocean waters occurred, the latter suggestive of local nutrient sources and biological removal. δ15N in macroalgal tissue and NO3− concurred that fresh groundwater, ocean water, and fertilizers were dominant nutrient sources. Benthic salinity and NO3− + NO2− concentrations illustrated that submarine groundwater discharge delivered nutrients to reefs in pulses ranging from minutes to days. Information generated from this study is imperative for developing management actions to improve water quality and make coral reefs more resilient to stressors.

Macroalgae reveal nitrogen enrichment and elevated N:P ratios on the Belize Barrier Reef

Macroalgal blooms are increasing on the Belize Barrier Reef (BBR) as scleractinian coral cover declines. Although some have attributed this to reduced grazing, the role of land-based nutrient pollution has not been assessed. Nutrient enrichment was quantified through macroalgal tissue analysis from Belize City to the offshore fore reef and at several central BBR lagoon sites. These recent data were compared to baseline data from the 1980s. Significant nearshore-to-offshore gradients of %N, %P and δ13C in macroalgae all indicated land-based sources of these nutrients. Macroalgal δ15N values were generally enriched in nearshore waters where values matched those reported for human sewage. Notably, the N:P ratios of recent macroalgae measurements were elevated at all sites, more than two-fold higher than values from the 1980s (~30: 1 to 70:1). These results support the hypothesis that nitrogen enrichment from land-based sources has increased phosphorus limitation driving macroalgal blooms and coral stress on the BBR.

Age affects the strain-rate dependence of mechanical properties of kelp tissues.

The resistance of macroalgae to hydrodynamic forces imposed by ambient water motion depends in part on the mechanical properties of their tissues. In wave-swept habitats, tissues are stretched (strained) at different rates as hydrodynamic forces change. Previous studies of mechanical properties of macroalgal tissues have used either a single strain rate or a small range of strain rates. Therefore, our knowledge of the mechanical properties of macroalgae is limited to a narrow fraction of the strain rates that can occur in nature. In addition, although mechanical properties of macroalgal tissues change with age, the effect of age on the strain-rate dependence of their mechanical behavior has not been documented. Using the kelp Egregia menziesii, we measured how high strain rate (simulating wave impingement) and low strain rate (simulating wave surge) affected mechanical properties of frond tissues of various ages. Stiffness of tissues of all ages increased with strain rate, whereas extensibility was unaffected. Strength and toughness increased with strain rate for young tissue but were unaffected by strain rate for old tissue. Young tissue is weaker than old tissue and, therefore, the most susceptible to breakage from hydrodynamic forces. The increased strength of young tissue at high strain rates can help the frond resist breaking when pulled rapidly during wave impingement, when hydrodynamic forces are largest. Because breakage of young tissue can remove a frond's meristem and negatively impact the survival of the whole kelp, strain-rate dependence of the young tissue's strength can enhance kelp's survival.

Nitrogen enrichment in macroalgae following mass coral mortality

Scleractinian corals are engineers on coral reefs that provide both structural complexity as habitat and sustenance for other reef-associated organisms via the release of organic and inorganic matter. However, coral reefs are facing multiple pressures from climate change and other stressors, which can result in mass coral bleaching and mortality events. Mass mortality of corals results in enhanced release of organic matter, which can cause significant alterations to reef biochemical and recycling processes. There is little known about how long these nutrients are retained within the system, for instance, within the tissues of other benthic organisms. We investigated changes in nitrogen isotopic signatures (δ15N) of macroalgal tissues (a) ~ 1 year after a bleaching event in the Seychelles and (b) ~ 3 months after the peak of a bleaching event in Mo’orea, French Polynesia. In the Seychelles, there was a strong association between absolute loss in both total coral cover and branching coral cover and absolute increase in macroalgal δ15N between 2014 and 2017 (adjusted r2 = 0.79, p = 0.004 and adjusted r2 = 0.86, p = 0.002, respectively). In Mo’orea, a short-term transplant experiment found a significant increase in δ15N in Sargassum mangarevense after specimens were deployed on a reef with high coral mortality for ~ 3 weeks (p < 0.05). We suggest that coral-derived nutrients can be retained within reef nutrient cycles, and that this can affect other reef-associated organisms over both short- and long-term periods, especially opportunistic species such as macroalgae. These species could therefore proliferate on reefs that have experienced mass mortality events, because they have been provided with both space and nutrient subsidies by the death and decay of corals.

Short-term fate of seagrass and macroalgal detritus in Arenicola marina bioturbated sediments

Seagrass meadows are globally important ecosystems for carbon (C) sequestration. However, bioturbation by benthic fauna can alter the distribution, degradation and overall preservation of C in the sediment. We performed a 4 wk laboratory experiment to investigate the short-term degradation and burial of 2 major C sources in bare sediments associated with seagrass ecosystems. Eelgrass Zostera marina and macroalgal (Fucus vesiculosus) detritus were amended in sediment with and without bioturbation by the common polychaete Arenicola marina. Bioturbation did not significantly affect the loss of eelgrass detritus (&gt;0.5 mm), but caused a rapid burial of this material as a discrete layer (55% recovery) at sediment depths ranging from 8 to 14 cm. A. marina effects on macroalgal detritus were more pronounced, resulting, in total, in an 80% loss of macroalgal detritus by microbial degradation and worm ingestion. We conclude that A. marina bioturbation effectively buries eelgrass detritus into deep anoxic sediments, but we cannot confirm that this leads to enhanced C preservation in coastal ecosystems. In contrast, A. marina bioturbation significantly increases the degradation of macroalgal tissue, and it is unlikely that this detritus is a major source for permanent C burial.

Extreme rainfall events pulse substantial nutrients and sediments from terrestrial to nearshore coastal communities: a case study from French Polynesia

Rainfall mobilizes and transports anthropogenic sources of sediments and nutrients from terrestrial to coastal marine ecosystems, and episodic but extreme rainfall may drive high fluxes to marine communities. Between January 13th and January 22nd, 2017, the South Pacific Island of Moorea, French Polynesia experienced an extreme rainfall event. ~57 cm of rain was delivered over a 10-day storm. We quantified pulsed sediments and nutrients transported to nearshore reefs. We determined the spatial and temporal extent of the sediment pulse with estimates of water transparency. We quantified pulsed nutrients at multiple spatial and temporal scales. To determine if terrestrial nutrients were incorporated into the benthic community, we collected macroalgae over 10 days following the storm and measured tissue nutrient concentrations and δN15. Pulsed sediments impacted water clarity for 6 days following the storm, with greatest impacts closest to the river mouth. Nitrite +nitrate concentrations were >100 times the average while phosphate was >25 times average. Macroalgal tissue nutrients were elevated, and δN15 implicates sewage as the source, demonstrating transported nutrients were transferred to producer communities. Future climate change predictions suggest extreme rainfall will become more common in this system, necessitating research on these pulses and their ramifications on marine communities.

Macroalgal Bioindicators of Recovery from Eutrophication in a Tidal Lagoon Following Wastewater Diversion and Earthquake Disturbance

Together, macroalgal tissue biochemical nitrogen indices (N-indices) and macroalgal abundance can be used as bioindicators of N-enrichment in estuaries. In this study, we examine the extent and rates of response of Ulva bioindicators during rapid N-enrichment perturbations in the eutrophic Avon-Heathcote Estuary (AHE) (Christchurch, New Zealand). With the diversion of the city’s wastewater discharge away from the estuary in March 2010, a ~ 90% reduction in the estuary’s N-concentration was expected. In turn, this was expected to reduce macroalgal biomass and improve the overall trophic condition of the estuary. We surveyed Ulva bioindicators over a five-year period spanning the diversion. There was a rapid (within one year) transition away from eutrophic condition reflected in N-indices (tissue-chlorophyll, -free amino acids, -N and -δ15N) following wastewater diversion, towards values corresponding with ‘cleaner’ water quality. This was accompanied by large reductions in Ulva percent cover, based on seasonal surveys conducted from 2001 to 2014. However, two large earthquakes in February and June 2011 caused a breakdown of the city’s wastewater infrastructure, resulting in overflows of untreated sewage into the estuary between February and November 2011. The re-enrichment of N and changes in N-sources (treated versus untreated sewage) were rapidly reflected in Ulva bioindicators, notably δ15N. Following repair of infrastructure, Ulva bioindicators again reverted towards a less eutrophic state. Overall, bioindicators were sensitive to changes in N-availability and N-source, and useful for identifying the position of algal populations on a eutrophic-to-oligotrophic gradient. These attributes demonstrated their utility as adjuncts to water quality monitoring and algal biomass surveys.

Responses of macroalgal assemblages dominated by three Mediterranean brown macroalgae with different life strategies to nutrient enrichment

ABSTRACT Increase of nutrient concentrations in coastal waters is a worldwide phenomenon with ecological consequences for natural assemblages. Little is known about species-specific nutrient dynamics among macroalgae in the Mediterranean Sea, which may be key to understanding competitive strategies driving the structure of macroalgal assemblages. We conducted an in situ nutrient enrichment experiment to evaluate whether increasing nutrient availability modified the relative abundance of the three dominant brown macroalgae Cystoseira brachycarpa, Halopteris scoparia and Padina pavonica and whether any such modifications were related to different nutrient dynamics of the three macroalgae under different chronic enrichment regimes. Tissue nitrogen, carbon and phosphorus were determined 6 and 18 months after the first exposure to nutrient enrichment. Under nutrient-enriched conditions, C. brachycarpa decreased in abundance over the experimental period, while P. pavonica and H. scoparia increased (albeit with different trends), the former mostly in the earlier phase and the latter in the subsequent phase. Nutrient content of the three macroalgae responded positively to enrichment in the first year, although it was exploited differently: C. brachycarpa only increased its internal reserves, while H. scoparia and P. pavonica also used available nutrients for growth. A completely different pattern was observed in the second year, as nutrient content of all macroalgae was affected very little, if at all, by nutrient enrichment. However, the different responses in terms of abundance observed during the second year indicated changing nutrient dynamics across species over the longer timescale of nutrient exposure. The results of the study confirmed the existence of species-specific response patterns of nutrient dynamics in the three macroalgae. They also suggest that nutrient dynamics are habitat-specific, since nutrient response was strongly conditioned by macroalgal tissue nutrient status, which reflects the nutrient history of the site.

Assessment of Terrigenous Nutrient Loading to Coastal Ecosystems along a Human Land-Use Gradient, Tutuila, American Samoa

Anthropogenic nutrient loading is well recognized as a stressor to coastal ecosystem health. However, resource managers are often focused on addressing point source or surface water discharge, whereas the impact of submarine groundwater discharge (SGD) as a nutrient vector is often unappreciated. This study examines connections between land use and nutrient loading through comparison of four watersheds and embayments spanning a gradient of human use impact on Tutuila, a high tropical oceanic island in American Samoa. In each study location, coastal radon-222 measurements, dissolved nutrient concentrations, and nitrogen isotope values (δ15N) in water and in situ macroalgal tissue were used to explore SGD and baseflow derived nutrient impacts, and to determine probable nutrient sources. In addition to sampling in situ macroalgae, pre-treated macroalgal specimens were deployed throughout each embayment to uptake ambient nutrients and provide a standardized assessment of differences between locations. Results show SGD-derived nutrient flux was more significant than baseflow nutrient flux in all watersheds, and δ15N values in water and algae suggested wastewater or manure are likely sources of elevated nutrient levels. While nutrient loading correlated well with expected anthropogenic impact, other factors such as differences in hydrogeology, distribution of development, and wastewater infrastructure also likely play a role in the visibility of impacts in each watershed.

Mechanical properties of the wave-swept kelp Egregia menziesii change with season, growth rate and herbivore wounds.

The resistance of macroalgae to damage by hydrodynamic forces depends on the mechanical properties of their tissues. Although factors such as water-flow environment, algal growth rate and damage by herbivores have been shown to influence various material properties of macroalgal tissues, the interplay of these factors as they change seasonally and affect algal mechanical performance has not been worked out. We used the perennial kelp Egregia menziesii to study how the material properties of the rachis supporting a frond changed seasonally over a 2year period, and how those changes correlated with seasonal patterns of the environment, growth rate and herbivore load. Rachis tissue became stiffer, stronger and less extensible with age (distance from the meristem). Thus, slowly growing rachises were stiffer, stronger and tougher than rapidly growing ones. Growth rates were highest in spring and summer when upwelling and long periods of daylight occurred. Therefore, rachis tissue was most resistant to damage in the winter, when waves were large as a result of seasonal storms. Herbivory was greatest during summer, when rachis growth rates were high. Unlike other macroalgae, E. menziesii did not respond to herbivore damage by increasing rachis tissue strength, but rather by growing in width so that the cross-sectional area of the wounded rachis was increased. The relative timing of environmental factors that affect growth rates (e.g. upwelling supply of nutrients, daylight duration) and of those that can damage macroalgae (e.g. winter storms, summer herbivore outbreaks) can influence the material properties and thus the mechanical performance of macroalgae.

Determining the Sources of Macroalgae During Beach Stranding Events from Species Composition, Stable Isotope Analysis, and Laboratory Experiments

Large accumulations of stranded macroalgae on the beaches of Sanibel Island from 2004 to 2007 were unusual and thought to be driven by high rainfall and river flows stemming from a high frequency of hurricanes. The southwest Florida shelf was thought to be isolated from far-field effects such as high river flows and urbanization but field- and laboratory-based studies suggest that nitrogen enrichment, fragmentation, and species composition of macroalgal communities on the shelf and in the estuary contribute to beach stranding events. Macroalgae were sampled using a belt transect method to determine species distribution and abundance. Macroalgae were abundant (1) in the lower estuary with abundant seagrass and (2) on limestone outcroppings in the Gulf of Mexico. An MDS analysis of the quadrat samples indicated two distinct macroalgal community types, a “Sound” assemblage around Pine Island Sound and a “Gulf” assemblage, associated with a live bottom and patch reef in the Gulf of Mexico. Peak abundances for the two community types differed with the Gulf having peak abundances from July to November, while peak abundances in the Sound occurred from January to July. Sound macroalgal tissue had significantly enriched δ15N compared to Gulf tissue when all species were combined and in five of six species collected at both locations suggesting that stable isotope analysis could be useful in combination with species composition in determining the source of macroalgae during stranding events. In addition, a laboratory study was conducted on four species that were sampled and frequently collected as a result of stranding events. Laboratory growth experiments demonstrated the potential for three of four common species (Solieria filiformis, Gracilaria tikvahiae, Agardhiella subulata) to fragment and grow significantly more under elevated nitrate conditions.

Trophic Transfer of Macroalgal Fatty Acids in Two Urchin Species: Digestion, Egestion, and Tissue Building

Sea urchins are ecosystem engineers of nearshore benthic communities because of their influence on the abundance and distribution of macroalgal species. Urchins are notoriously inefficient in assimilation of their macroalgal diets, so their fecal production can provide a nutritional subsidy to benthic consumers that cannot capture and handle large macroalgae. We studied the assimilation of macroalgal diets by urchins by analyzing the profiles of trophic biomarkers such as fatty acids (FAs). We tracked macroalgal diet assimilation in both Strongylocentrotus droebachiensis and S. purpuratus. Juvenile S. droebachiensis and adult S. purpuratus were maintained for 180 and 70 days, respectively, on one of three monoculture diets from three algal phyla: Nereocystis luetkeana, Pyropia sp., or Ulva sp. We then analyzed FA profiles of the macroalgal tissue fed to urchins as well as urchin gonad, gut, digesta, and egesta (feces) to directly evaluate trophic modification and compare nutritional quality of urchin food sources, urchin tissues, and fecal subsidies. In the S. purpuratus assay, there were significantly more total lipids in the digesta and egesta than in the algae consumed. The FA profiles of urchin tissues differed among urchin species, all diets, and tissue types. Despite these differences, we observed similar patterns in the relationships between the urchin and macroalgal tissues for both species. Egesta produced by urchins fed each of the three diets were depleted with respect to the concentration of important long chain polyunsaturated fatty acids (LCPUFAs), but did not differ significantly from the source alga consumed. Both urchin species were shown to synthesize and selectively retain both the precursor and resulting LCPUFAs involved in the synthesis of the LCPUFAs 20:4⍵6 and 20:5⍵3. S. droebachiensis and S. purpuratus exhibited consistent patterns in the respective depletion and retention of precursor FAs and resulting LCPUFAs of Pyropia and Ulva tissues, suggesting species level control of macroalgal digestion or differential tissue processing by gut microbiota. For both S. droebachiensis and S. purpuratus, macroalgal diet was a surprisingly strong driver of urchin tissue fatty acids; this indicates the potential of fatty acids for future quantitative trophic estimates of urchin assimilation of algal phyla in natural settings.

Gut content, fatty acid, and stable isotope analyses reveal dietary sources of macroalgal-associated amphipods along the western Antarctic Peninsula

Shallow water subtidal marine communities along the western Antarctic Peninsula are characterized by dense beds of macroalgae and strikingly dense assemblages of associated amphipods. However, direct grazing by amphipods on the dominant macroalgae is unlikely as most of these algae elaborate secondary metabolites known to be herbivore feeding deterrents. What resources, then, support this vast macroalgal-associated amphipod assemblage? We addressed this question by analyzing the gut contents, fatty acids, and stable isotopic ratios of 15 different amphipod species associated with the macrophyte community. The δ15N and δ13C stable isotope values revealed that most of the abundant species of amphipods are primary consumers whose ultimate carbon source is derived from some combination of brown macroalgae, epiphytic diatoms, and endo/epiphytic filamentous algae. Gut contents revealed that a large percentage of the amphipod diets are comprised of diatoms and macroalgal tissues, both filamentous and multiseriate. Fatty acid analysis corroborated our conclusions based on stable isotope and gut content data, demonstrating the importance of diatoms to assimilated material, but also highlighting the rich diversity of diets within the macroalgal-associated amphipod assemblage. Our findings suggest that amphipods routinely clean their host macrophytes of potentially harmful epiphytes, including both diatoms and emergent filaments from brown algal endophytes. Some prominent species of amphipods may also derive a small percentage of their carbon from palatable and, in one case, unpalatable, chemically defended red algae. These results, combined with previous studies showing that the amphipods gain refuge from predators by associating with unpalatable macroalgae, support the hypothesis that amphipods along the western Antarctic Peninsula are living in mutualism with their macrophyte hosts rather than consuming the host directly.

Origin here, impact there—The need of integrated management for river basins and coastal areas

This study highlights the effect that estuarine polluted waters may have on adjacent coastal waters and the need of an integrated management of the coastal area. Pollution of land-to-sea water plumes varies spatially and temporally, being difficult, costly and time consuming to determine. However, the reduction in water quality of both estuarine and coastal environments and the consequent degradation of its biological communities is at issue. Chlorophyll-a analysis from water and stable nitrogen isotopic analysis (δ15N) from opportunistic macroalgae Ulva species were respectively used as proxies to detect phytoplankton proliferation and nitrogen related nutrient fluxes in the water. These analytical techniques were combined with the use of three-dimensional hydrodynamic models, and revealed to constitute reliable early warning instruments, able to identify coastal areas at risk, and supporting an integrated management of coastal and river basin areas. The approach detected synchronized δ15N signal variations along time between estuarine sites (Mondego estuary, Portugal) and nearby adjacent coastal shore sites (NE Atlantic coast). The higher values recorded by macroalgal tissues’ δ15N signals, which occurred simultaneously to higher chlorophyll-a values, were linked to the anthropogenic contamination of the water, probably related with the Mondego valley land use patterns throughout the year (reflecting the opening of sluices that drain agriculture fields). Modeling scenarios point to a Mondego’s influence that is able to reach its adjacent coastal shores in about 7km from its river mouth. The methodology used here is replicable elsewhere and allowed to track nutrients from the source, inside the estuary, until the final area of impact, where primary producers may use those for growth, and to define vulnerable areas on adjacent coastal zones.

Identifying nitrogen sources to thermal tide pools in Kapoho, Hawai'i, U.S.A, using a multi-stable isotope approach

Nitrogen (N) enrichment often results in coastal eutrophication, even in remote areas like Hawai‘i. Therefore, determining N sources to coastal waters is important for their management. This study identified N sources to tide pools in Kapoho, Hawai'i, and determined their relative importance using three stable isotopes (δ15N, δ18O, δ11B). Surface waters and macroalgal tissues were collected along 100-m onshore-offshore transects in areas of high groundwater input for three months at low tide. Water samples from possible N sources were also collected. Mixing model output, along with macroalgal δ15N values, indicated that agriculture soil (34%) was the largest anthropogenic N source followed by sewage (27%). These findings suggest that more effective fertilizer application techniques and upgrading sewage treatment systems can minimize N leaching into groundwater. Overall, our multi-stable isotope approach for identifying N sources was successful and may be useful in other coastal waters.

Screening of Endophytic Fungi from Chlorophyta and Phaeophyta for Antibacterial Activity

Chlorophyta and Phaeophyta macroalgae are important sources of secondary metabolites with pharmaceutically relevant antibacterial, antifungal and antiviral bioactivities. Oftentimes, these algae-derived compounds are, in fact, produced by endophytic fungi living inside the macroalgal tissue. Numerous studies have shown that endophytic fungi can produce a broad range of active metabolites such as terpenes, alkaloids, and quinones. The aim of the present study was to screen fungal strains isolated from a variety of Caulerpa spp., Halimeda spp., and Sargassum spp. for antibacterial activity against Staphylococcus aureus and Escherichia coli. Thirteen morphologically different isolates were tested. Two of them showed pronounced activity against S. aureus in agar diffusion assays.