Inorganic Nutrient Enrichment Research Articles

Eucheumatoid seaweed farming in the southern Philippines

Eucheumatoid seaweed farming (ESF) is an important enterprise that provides livelihood opportunities for tropical coastal communities. In this work, we surveyed the current practices of ESF in Tawi-Tawi and Sulu, southern Philippines, where major commercial ESF activities in the country are currently practiced. Seaweed farmers (N = 143) were interviewed using a structured questionnaire containing relevant information on the current farming practices. Results revealed that ESF is one of the primary livelihood sources for coastal inhabitants in the southern Philippines. Most farmers were male, 21–50 years old, and practiced farming for 6–10 years. Farmers mostly owned a farm with an area of 25–400 m2, mainly filled with the rhodophyte elkhorn sea mosses, either Kappaphycus alvarezii or K. striatus. Vegetative cuttings, the major seedling source, were tied using plastic straw into a 6–10 m rope line with a distance interval of 10–20 cm. Inorganic nutrient enrichment is practiced to increase growth and lessen ice-ice disease occurrence. The modified fixed-off bottom (stakes with floaters) is the most predominant farming method. Farms were visited 2–3 times a week for maintenance. Farming is year-round, with peak seasons between August and November. Harvesting is typically done after 21–30 days. Seaweeds are usually dried using the hanging method, which takes 4–6 days. Dried Kappaphycus fronds command higher prices (90–140 PHP/kg) compared to Eucheuma denticulatum (10–50 PHP/kg). Few farmers received government support; therefore, farmers reported many problems affecting their production. This study provides an update on the current ESF practices in the southern Philippines, which have not been well-documented for almost two decades.

A functional perspective of nematode assemblages as proxy of quality in tropical estuarine tidal flats

Functional aspects of biological communities influence ecosystem processes and it is urgent to understand how human disturbances affect functional diversity and ecosystem functions and services. Our purpose was to address the use of different functional metrics of nematode assemblages to evaluate the ecological status of tropical estuaries subjected to different human activities, aiming to advance and improve the knowledge about the usefulness of functional attributes as indicators of environmental quality. Three approaches were compared: functional diversity indexes, single trait, and multi traits using the Biological Traits Analysis. The RLQ + fourth-corner combined method was used to identify relationships among functional traits, inorganic nutrients, and metals concentrations. Lower values of FDiv, FSpe, and FOri indicate a convergence of functions, characterizing impacted conditions. A dominant set of traits was related to disturbance, mainly inorganic nutrient enrichment. All the approaches allowed for the detection of disturbed conditions, however, multi traits was the most sensitive one.

Inorganic nutrient enrichment of seaweed Kappaphycus: Farmers’ practices and effects on growth and ice-ice disease occurrence

Inorganic nutrient enrichment (INE) is an emerging practice among seaweed farmers in Sibutu, Tawi-Tawi, southern Philippines, as a response to the slow seaweed growth and as a control measure for the ice-ice disease. A survey on the practice of INE of Kappaphycus and a field experiment simulating the practice were conducted. From the 100 farmers, 83% practiced INE, 14% did not practice, and 3% stopped the practice. From those who practiced, 87% were using 16−20−0 fertilizer and 13% were using 14−14−14 fertilizer. Seaweeds were dipped into 8.82 g L−1 fertilizer solution for 5–60 s, piled up on a drying platform, covered with canvas overnight, and planted the following day. Seaweeds were hauled up 7–10 days post-cultivation for re-application of INE. Harvesting and/or mass propagating was done at 20 days post-planting. Respondents reported that this method increased seaweed growth and decreased ice-ice disease occurrence. For the field experiment, 8.82 g L−1(HC), 0.01 g L−1(LC), and 0.00 g L−1(UF) of 16−20−0 fertilizer concentrations were tested in Kappaphycus striatus farmed using the modified fixed-off bottom method. At 49 days post-planting, the growth of K. striatus in HC (3.75 % day−1) was significantly higher than in LC (1.82 % day−1) and in UF (1.56 % day−1). Ice-ice disease occurrence of K. striatus was significantly lower in HC (42.37%) than in LC (78.07%) and UF (77.72%). Higher growth and lower ice-ice disease were evident with INE; however, effects in farm environment and on carrageenan quality were also reported. Further, the use of inorganic commercial fertilizer in seaweed farm is discouraged by the Philippine National Standard. Thorough studies that will address these knowledge gaps are needed for science-based policy on regulation and management of use of inorganic fertilizers in Kappaphycus cultivation.

Nutrient (C, N and P) enrichment induces significant changes in the soil metabolite profile and microbial carbon partitioning

The cycling of soil organic matter (SOM) and carbon (C) within the soil is governed by the presence of key macronutrients, particularly nitrogen (N) and phosphorus (P). The relative ratio of these nutrients has a direct effect on the potential rates of microbial growth and nutrient processing in soil and thus is fundamental to ecosystem functioning. However, the effect of changing soil nutrient stoichiometry on the small organic molecule (i.e., metabolite) composition and cycling by the microbial community remains poorly understood. Here, we aimed to disentangle the effect of stoichiometrically balanced nutrient addition on the soil metabolomic profile and apparent microbial carbon use efficiency (CUE) by adding a labile C source (glucose) in combination with N and/or P. After incorporation of the added glucose into the microbial biomass (48 h), metabolite profiling was undertaken by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). 494 metabolites were identified across all treatments mainly consisting of lipids (n = 199), amino acids (n = 118) and carbohydrates (n = 43), >97% of which showed significant changes in concentration between at least one treatment. Overall, glucose-C addition generally increased the synthesis of other carbohydrates in soil, while addition of C and N together increased peptide synthesis, indicative of protein formation and turnover. The combination of C and P significantly increased the number of fatty acids synthesised. There was no significant change in the PLFA-derived microbial community structure or microbial biomass following C, N and P addition. Further, N addition led to an increase in glucose-C partitioning into anabolic processes (i.e., increased CUE), suggesting the microbial community was N, but not P limited. Based on the metabolomic profiles observed here, we conclude that inorganic nutrient enrichment causes substantial shifts in both primary and secondary metabolism within the microbial community, leading to changes in resource flow and thus soil functioning, however, the microbial community illustrated significant metabolic flexibility.

Effects of inorganic nutrient enrichment on the carrageenan yield, growth, and ice-ice disease occurrence of red alga Kappaphycus striatus

One of the problems in Kappaphycus farming is the slow growth in some farms due to nutrient insufficiency caused by overstocking. In the southern Philippines, most seaweed farmers practice inorganic nutrient enrichment of Kappaphycus to boost growth and decrease ice-ice disease occurrence using ammonium phosphate at an average concentration of 8.82 g L-1. In this study, experiments with Kappaphycus striatus enriched with inorganic nutrients were carried out at Pasiagan, Bongao, Tawi-Tawi, southern Philippines, using different inorganic nutrients (T1=8.82 g L-1 of urea, T2=8.82 g L-1 of phosphorus, and T3=control) within 45 days. Seaweeds were enriched in these three inorganic solutions for 30 seconds, placed into a large mat, covered with canvas, and left overnight. After 15 days, findings showed that the specific growth rates of T1 (6.99% day-1) and T3 (6.72% day-1) groups were significantly higher than the T2 (5.84% day-1) group (p<0.05). Inorganic nutrient enrichment did not significantly influence the occurrence of ice-ice disease. Moreover, inorganic nutrient enrichment did not affect the carrageenan yield after 45 days. K. striatus nutrient-enriched with urea could increase growth at day 15, but no effect on the occurrence of ice-ice disease and carrageenan yield. Hence, inorganic nutrient enrichment using urea provides a positive effect to farmed K. striatus by enhancing its growth without affecting its health and carrageenan yield.

Influence of different concentrations of ammonium phosphate on nitrogen assimilation of red seaweed Kappaphycus striatus

Eucheumatoid farming is among the most popular source of livelihood for coastal dwellers, especially in the southern Philippines. Kappaphycus and Eucheuma are the two major cultured eucheumatoid species. However, seaweed farmers have been experiencing low seaweed production for the past years. The slow growth of Kappaphycus spp. in the farm is linked to extensive farming, causing nutrient depletion in the seawater. Hence, seaweed farmers in the province of Tawi-Tawi, southern Philippines, enrich their seaweeds, Kappaphycus striatus, with a wide range of inorganic nutrient solution concentrations with an average of nearly 9 g L⁻¹. To provide standard concentration (g L⁻¹) of inorganic nutrient solution for soaking before farming the seaweed, this study investigated nitrogen assimilation using the Kjeldahl method. Treatments were the concentrations of commonly used inorganic fertilizer [ammonium phosphate, (NH4)3PO4] dissolved in filtered seawater namely; T1 = 0 g L⁻¹ as control, T2 = 3 g L⁻¹, T3 = 6 g L⁻¹, and T4 = 9 g L⁻¹. Results showed that the total nitrogen (%) of T4 (0.68±0.01) and T3 (0.59±0.07) were significantly higher (p<0.05) than T2 (0.48±0.02) and T1 (0.46±0.02). This suggests that using inorganic nutrients as enrichment to K. striatus at a concentration of 6 or 9 g L⁻¹ is effective for obtaining high nitrogen assimilation. Therefore, considering the cost-effective inorganic nutrient enrichment practice, this study recommends using 6 g L⁻¹ of inorganic nutrient concentration to help seaweed farmers boost production by improving the growth performance of K. striatus, especially when planted in nutrient-depleted farms.

Nutrient pollution enhances productivity and framework dissolution in algae- but not in coral-dominated reef communities

Ecosystem services provided by coral reefs may be susceptible to the combined effects of benthic species shifts and anthropogenic nutrient pollution, but related field studies are scarce. We thus investigated in situ how dissolved inorganic nutrient enrichment, maintained for two months, affected community-wide biogeochemical functions of intact coral- and degraded algae-dominated reef patches in the central Red Sea. Results from benthic chamber incubations revealed 87% increased gross productivity and a shift from net calcification to dissolution in algae-dominated communities after nutrient enrichment, but the same processes were unaffected by nutrients in neighboring coral communities. Both community types changed from net dissolved organic nitrogen sinks to sources, but the increase in net release was 56% higher in algae-dominated communities. Nutrient pollution may, thus, amplify the effects of community shifts on key ecosystem services of coral reefs, possibly leading to a loss of structurally complex habitats with carbonate dissolution and altered nutrient recycling.

Dissolved inorganic nutrient enrichment does not affect sponge growth or condition

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 634:77-88 (2020) - DOI: https://doi.org/10.3354/meps13184 Dissolved inorganic nutrient enrichment does not affect sponge growth or condition Blake D. Ramsby1,2,3,*, Joshua Heishman3,4, Mia O. Hoogenboom1, Steve Whalan5, Nicole S. Webster2,3,6 1College of Science and Engineering and ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, Queensland 4811, Australia 2Australian Institute of Marine Science, Townsville, Queensland 4810, Australia 3AIMS@JCU, Australian Institute of Marine Science and James Cook University, Townsville, Queensland 4811, Australia 4Department of Biological Sciences, College of Science, Purdue University, West Lafayette, Indiana 47907, USA 5Marine Ecology Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, New South Wales 2480, Australia 6Australian Centre for Ecogenomics, The University of Queensland, St Lucia, Queensland 4072, Australia *Corresponding author: blake.ramsby@my.jcu.edu.au ABSTRACT: Changing land use and an increasing human population have led to increased terrestrial runoff, which delivers nutrients, pesticides, and heavy metals into aquatic ecosystems. Elevated nutrient levels can adversely affect nearshore corals by reducing the amount of light reaching the benthos, exacerbating coral disease and bleaching, as well as stimulating algal growth, but the effects on other reef taxa are poorly understood. We investigated the effects of dissolved inorganic nutrient enrichment and changes in irradiance on the growth and condition of 5 common Great Barrier Reef sponges: 4 sponges with photosynthetic symbionts and 1 lacking photosynthetic symbionts. Concentrations of up to 7 µM total dissolved inorganic nitrogen (DIN) did not significantly affect the growth, condition, or chl a content of any sponge species after 10 wk exposure. However, 2 species lost >20% volume across all nutrient treatments, suggesting that aquarium conditions may have been suboptimal for these species. Irradiance (80 vs. 160 µmol quanta m-2 s-1) did not affect 4 of the 5 sponge species; however, higher irradiance resulted in higher organic content and chl a levels in the bioeroding sponge Cliona orientalis, the only studied species that associates with the photosynthetic dinoflagellate Symbiodinium, suggesting that sponge-Symbiodinium associations may be more sensitive to irradiance levels than sponge-Cyanobacteria associations. While elevated nutrient levels are exacerbating the decline of reef-building corals, exposure to the average DIN levels within flood plumes that reach inshore reefs appears to have negligible effects on reef sponges. KEY WORDS: Nitrogen · Phosphorus · Light · Pollution Full text in pdf format Supplementary material PreviousNextCite this article as: Ramsby BD, Heishman J, Hoogenboom MO, Whalan S, Webster NS (2020) Dissolved inorganic nutrient enrichment does not affect sponge growth or condition. Mar Ecol Prog Ser 634:77-88. https://doi.org/10.3354/meps13184 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 634. Online publication date: January 23, 2020 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2020 Inter-Research.

Organic matter compounds as a tool for trophic state characterization in a hypersaline environment: Araruama Lagoon, Brazil

Araruama Lagoon, located in Rio de Janeiro (SE, Brazil), is considered the largest hypersaline lagoon in the world. Over the last decades, this environment has been influenced by urban growth around its margins, which has consequently led to the discharge of untreated sewage, particularly during the summer season (December–March). Excessive nutrient discharges may lead to the rapid enrichment of organic and inorganic nutrients and consequently, eutrophication. Within this context, organic matter quality and amount evaluations become an essential tool to assess the trophic state of coastal environments. Therefore, the present study aims to characterize the trophic state and define the depositional dynamics based on biopolymer content (carbohydrates, lipids and proteins), total organic carbon, total sulfur and sediment granulometry at the Araruama Lagoon region affected by urban activities (Itajuru Channel and adjacencies). The integration of physio-chemical water and sediment data allowed for the identification of four regions presenting different trophic condition, namely the Itajuru Channel - sandy with high hydrodynamics and undergoing marine influence; a region influenced by salt-production activity; the innermost region, presenting high protein concentrations originating from microbiological activity and the most eutrophic area, located in a marina activity region, marked by high anthropogenic organic matter levels.

A glimpse into the littoral nutrient dynamics of a lake system connected to the sea

In South Africa more than 80% of estuaries are small, dynamic and predominantly linear systems. Nutrient characteristics in these systems are mostly influenced by external catchment processes, except during extended periods of closure. However, a small percentage of the country’s estuaries (&lt; 3%) comprise larger estuarine lakes mostly evolved from drowned river valleys. The physical properties of these systems suggest relatively low flushing rates, and the potentially stronger influence of in-situ processes on nutrient characteristics. This study investigates dissolved inorganic nutrient dynamics in the littoral zones of these estuarine lake systems, and potential influencing factors, using the Wilderness Lake System as a case study. Comparison of inter-annual and seasonal trends in dissolved inorganic nutrients (NOx-N, NH4-N and PO4-P) in river inflow and in the three lakes confirmed that external catchment fluxes are most likely not the sole, or even the dominant drivers of average long-term or seasonal dissolved inorganic nutrient patterns in the lake littoral zones. Relatively low NOx:NH4 ratios (mostly less than 1) in the lakes (especially in Eilandvlei and Langvlei) indicated a stronger influence of in-situ processes, such as bacteriological remineralisation, similar to observations in other lake type systems with low flushing rates. Low NO3:NH4 ratios are known to stimulate cyanobacteria, having the metabolic ability to potentially produce microcystins. Therefore, incremental dissolved inorganic nutrient and organic matter enrichment may cause these systems to tip into eutrophic, possibly toxic, aquatic states that will be difficult, if not impossible, to reverse given their weak flushing mechanisms. The findings from this study highlight the importance of appropriate water resource management, both in the catchments and within the floodplains of estuarine lake systems.

CO₂ and inorganic nutrient enrichment affect the performance of a calcifying green alga and its noncalcifying epiphyte.

Ocean acidification studies in the past decade have greatly improved our knowledge of how calcifying organisms respond to increased surface ocean CO2 levels. It has become evident that, for many organisms, nutrient availability is an important factor that influences their physiological responses and competitive interactions with other species. Therefore, we tested how simulated ocean acidification and eutrophication (nitrate and phosphate enrichment) interact to affect the physiology and ecology of a calcifying chlorophyte macroalga (Halimeda opuntia (L.) J.V. Lamouroux) and its common noncalcifying epiphyte (Dictyota sp.) in a 4-week fully crossed multifactorial experiment. Inorganic nutrient enrichment (+NP) had a strong influence on all responses measured with the exception of net calcification. Elevated CO2 alone significantly decreased electron transport rates of the photosynthetic apparatus and resulted in phosphorus limitation in both species, but had no effect on oxygen production or respiration. The combination of CO2 and +NP significantly increased electron transport rates in both species. While +NP alone stimulated H. opuntia growth rates, Dictyota growth was significantly stimulated by nutrient enrichment only at elevated CO2, which led to the highest biomass ratios of Dictyota to Halimeda. Our results suggest that inorganic nutrient enrichment alone stimulates several aspects of H. opuntia physiology, but nutrient enrichment at a CO2 concentration predicted for the end of the century benefits Dictyota sp. and hinders its calcifying basibiont H. opuntia.

An experimental study on the effects of nutrient enrichment on organic carbon persistence in the western Pacific oligotrophic gyre

Abstract. Carbon sequestration in the ocean is of great concern with respect to the mitigation of global warming. How to hold the fixed organic carbon in the presence of tremendous numbers of heterotrophic microorganisms in marine environments is the central issue. We previously hypothesized that excessive nutrients would ultimately decrease the storage of organic carbon in marine environments. To test this, a series of in situ nutrient enrichment incubation experiments were conducted at a site (17.59° N, 127.00° E) within the western Pacific oligotrophic gyre. Five treatments were employed: glucose (Glu), algal exudation organic material (EOM), nitrate (N) and phosphate (P), N and P in combination with glucose and a control with no added nutrients. The results showed that the dissolved organic carbon consumption rates and bacterial community specific growth rates were enhanced by inorganic nutrient enrichment treatments during the initial 48 h incubation. At the end of 14 days of incubation, about one-third (average 3.3 μmol C kg−1) more organic carbon was respired in the glucose-enriched incubation with the addition of inorganic nutrients compared to that without. In contrast, when nutrients were limiting, glucose could not be efficiently used by the bacteria and thus it remained in the environment. These results suggest that repletion of inorganic nutrients could facilitate microbial consumption of organic carbon and thus has a significant impact on carbon cycling in the environment.

On the Response of pH to Inorganic Nutrient Enrichment in Well-Mixed Coastal Marine Waters

Recent concerns about declining pH in the surface ocean in response to anthropogenic increases of carbon dioxide (CO2) in the atmosphere have raised the question of how this declining baseline of oceanic pH might interact with the much larger diel and seasonal variations of pH in coastal marine ecosystems. Nutrient enrichment, which can amplify both production and respiration, has the potential to reduce or exacerbate the impacts of ocean acidification in coastal waters. Here, we present results from a multi-year experiment in which replicate phytoplankton-based mesocosms with a 5-m deep well-mixed water column (salinity = 27–31) and intact benthic community were exposed to a gradient in daily inorganic nitrogen (N), phosphorous (P), and silica (Si) addition. We show that the response of water column pH to nutrient enrichment was the greatest during the autotrophic winter-spring period, and there was no significant decline in pH across treatments during the heterotrophic summer-fall period. We believe that the differences in response lie in the seasonal cycles of production and respiration, where spring production peaks are large and discrete, and respiration is more temperature-driven but occurs diffusely throughout the year. The observed basification associated with enhanced nutrient inputs may have consequences for phytoplankton community structure, some species of submersed aquatic vegetation, cycling of Si, and perhaps other ecological processes.

Distribution of living planktonic foraminifera in relation to oceanic processes on the southeastern continental Brazilian margin (23°S–25°S and 40°W–44°W)

The vertical distribution (0 to 100m) of planktonic foraminifera was investigated based on 40 tow samples that were collected in eight stations, during the austral summer of 2002, in a geographically restricted area (23°S–25°S and 40°W–44°W) on the southeastern Brazilian continental margin. Species' abundances are low (less than 10 specimens/m3), which is typical of an oligotrophic area. The foraminifera assemblage is mainly composed of warm water species (Globigerinoides ruber white and pink forms), with a predominance of spinose and symbiont-bearing species. Temperature and inorganic nutrient enrichment of the surface are the main factors that control foraminiferal abundance and diversity; nevertheless salinity can also influence the ecological descriptors. The role of the deep chlorophyll maximum (DCM) in the distribution of foraminifera is not always clear, but the increase in the abundance of G. ruber (white and pink) seems to be related to a deeper DCM, and high salinities (S>36.5). The ecological habitat of these species is affected by the depth of the mixed layer, with a predominance of the white form in deeper layers. Increases in the foraminiferal diversity are related to the dynamics of the Brazil Current system, which displaces the area of high productivity in the euphotic zone off the coast. The abundances of Globigerina bulloides, Globigerina falconensis, Globigerinella calida and Globigerinella siphonifera follow the nutrient enrichment of the surface water mass, corroborating the usefulness of these species as paleoproductivity proxies in the study area. These data confirm the use of diversity measurements and assemblages composition for reconstructing past water column structures in subtropical oceans.

In-Situ Effects of Simulated Overfishing and Eutrophication on Benthic Coral Reef Algae Growth, Succession, and Composition in the Central Red Sea

Overfishing and land-derived eutrophication are major local threats to coral reefs and may affect benthic communities, moving them from coral dominated reefs to algal dominated ones. The Central Red Sea is a highly under-investigated area, where healthy coral reefs are contending against intense coastal development. This in-situ study investigated both the independent and combined effects of manipulated inorganic nutrient enrichment (simulation of eutrophication) and herbivore exclosure (simulation of overfishing) on benthic algae development. Light-exposed and shaded terracotta tiles were positioned at an offshore patch reef close to Thuwal, Saudi Arabia and sampled over a period of 4 months. Findings revealed that nutrient enrichment alone affected neither algal dry mass nor algae-derived C or N production. In contrast, herbivore exclusion significantly increased algal dry mass up to 300-fold, and in conjunction with nutrient enrichment, this total increased to 500-fold. Though the increase in dry mass led to a 7 and 8-fold increase in organic C and N content, respectively, the algal C/N ratio (18±1) was significantly lowered in the combined treatment relative to controls (26±2). Furthermore, exclusion of herbivores significantly increased the relative abundance of filamentous algae on the light-exposed tiles and reduced crustose coralline algae and non-coralline red crusts on the shaded tiles. The combination of the herbivore exclusion and nutrient enrichment treatments pronounced these effects. The results of our study suggest that herbivore reduction, particularly when coupled with nutrient enrichment, favors non-calcifying, filamentous algae growth with high biomass production, which thoroughly outcompetes the encrusting (calcifying) algae that dominates in undisturbed conditions. These results suggest that the healthy reefs of the Central Red Sea may experience rapid shifts in benthic community composition with ensuing effects for biogeochemical cycles if anthropogenic impacts, particularly overfishing, are not controlled.

Wintertime enrichment of inorganic nutrients in the Ballenas Channel, Gulf of California

Three oceanographic cruises were carried out in the region of the Ballenas Channel (BC) during winter 2002, spring 2003, and summer 2004, in order to study the impact of vertical mixing of the water column (ф) on the surface concentration of dissolved inorganic nutrients (NO3, PO4, and Si(OH)4). Mean nutrient concentrations integrated over the upper 100 m of BC showed a clear seasonal variation, with higher values in winter (18.2 ± 1.1 ± µM NO3, 2.36 ± 0.08 µM PO4, and 35.4 ± 3.2 µM Si(OH)4), associated with a well-mixed water column (ф = 0.7–16 J m–3), and low values in summer (7.1 ± 1.0 µM NO3, 1.22 ± 0.06 µM PO4, and 16.0 ± 2.1 µM Si(OH)4), related to vertically stratified water column conditions (ф = 150–223 J m–3). In contrast, below 200 m the seasonal variability of the three nutrient concentrations was reduced. The hydrographic analysis indicated that the wintertime surface nutrient enrichment was due to an intensification of the water column mixing, which vertically transported Subtropical Subsurface Water (SSW, cold and nutrient-enriched) to the surface of BC. In contrast, nutrient impoverishment in summertime was due to biological consumption combined with the stratification of the water column, which reduced the vertical flow of SSW and, consequently, the supply of nutrients to the surface of this system. The N:P and Si:N ratios and an excess of PO4 &gt; 0.65 µM in surface waters indicated that NO3 was the potential limiting nutrient for primary production in this oceanographic province of the Gulf of California.

In-situ Effects of Eutrophication and Overfishing on Physiology and Bacterial Diversity of the Red Sea Coral Acropora hemprichii

Coral reefs of the Central Red Sea display a high degree of endemism, and are increasingly threatened by anthropogenic effects due to intense local coastal development measures. Overfishing and eutrophication are among the most significant local pressures on these reefs, but there is no information available about their potential effects on the associated microbial community. Therefore, we compared holobiont physiology and 16S-based bacterial communities of tissue and mucus of the hard coral Acropora hemprichii after 1 and 16 weeks of in-situ inorganic nutrient enrichment (via fertilizer diffusion) and/or herbivore exclusion (via caging) in an offshore reef of the Central Red Sea. Simulated eutrophication and/or overfishing treatments did not affect coral physiology with respect to coral respiration rates, chlorophyll a content, zooxanthellae abundance, or δ 15N isotopic signatures. The bacterial community of A. hemprichii was rich and uneven, and diversity increased over time in all treatments. While distinct bacterial species were identified as a consequence of eutrophication, overfishing, or both, two bacterial species that could be classified to the genus Endozoicomonas were consistently abundant and constituted two thirds of bacteria in the coral. Several nitrogen-fixing and denitrifying bacteria were found in the coral specimens that were exposed to experimentally increased nutrients. However, no particular bacterial species was consistently associated with the coral under a given treatment and the single effects of manipulated eutrophication and overfishing could not predict the combined effect. Our data underlines the importance of conducting field studies in a holobiont framework, taking both, physiological and molecular measures into account.

Inorganic nutrient availability affects organic matter fluxes and metabolic activity in the soft coral genus Xenia

The release of organic matter (OM) by scleractinian corals represents a key physiological process that importantly contributes to coral reef ecosystem functioning, and is affected by inorganic nutrient availability. Although OM fluxes have been studied for several dominant reef taxa, no information is available for soft corals, one of the major benthic groups in tropical reef environments. Thus, this study investigates OM fluxes along with other key physiological parameters (i.e. photosynthesis, respiration and chlorophyll a tissue content) in the common soft coral genus Xenia after a 4-week exposure period to elevated ammonium (N; 20.0 μmol l(-1)), phosphate (P; 2.0 μmol l(-1)) and combined inorganic nutrient enrichment treatment (N+P). Corals maintained without nutrient enrichment served as non-treated controls and revealed constant uptake rates for particulate organic carbon (POC) (-0.315±0.161 mg POC m(-2) coral surface area h(-1)), particulate nitrogen (PN) (-0.053±0.018 mg PN m(-2) h(-1)) and dissolved organic carbon (DOC) (-4.8±2.1 mg DOC m(-2) h(-1)). Although DOC uptake significantly increased in the N treatment, POC flux was not affected. The P treatment significantly enhanced PN release as well as photosynthesis and respiration rates, suggesting that autotrophic carbon acquisition of zooxanthellae endosymbionts influences OM fluxes by the coral host. Our physiological findings confirm the significant effect of inorganic nutrient availability on OM fluxes and key metabolic processes for the soft coral Xenia, and provide the first clues on OM cycles initiated by soft corals in reef environments exposed to ambient and elevated inorganic nutrient concentrations.

Rapid Shifts in the Structure and Composition of a Protistan Assemblage During Bottle Incubations Affect Estimates of Total Protistan Species Richness

Changes in the structure and composition of a protistan community were characterized through the analysis of small-subunit ribosomal RNA gene (18S) sequences for a 3-day bottle incubation using a single sample collected in the western North Atlantic. Cloning and sequencing was used to investigate changes in perceived species richness and diversity as a consequence of environmental perturbation. The treatments included a control (unamended seawater), inorganic nutrient enrichment, and enrichment with a complex organic mixture. Five clone libraries were constructed and analyzed at the time of collection (t-0 h) and after 24 (t-24 h) and 72 (t-72 h) h for the control, and at t-72 h for the inorganic and organic enrichments, resulting in an analysis of 1,626 partial 18S rDNA sequences that clustered into 238 operational taxonomic units (OTUs). Analysis of the clone libraries revealed that protistan assemblages were highly dynamic and changed substantially at both the OTU level and higher taxonomic classifications during time frames consistent with many oceanographic methods used for measuring biological rates. Changes were most dramatic in enrichments, which yielded community compositions that were strongly dominated by one or a few taxa. Changes in community structure during incubation dramatically influenced estimates of species richness, which were substantially lower with longer incubation and especially with amendment, even though all incubated samples originated from the same aliquot of seawater. Containment and enrichment of the seawater sample led to the detection of otherwise undetected protistan taxa, suggesting that characterization of protistan diversity in a sample only at the time of collection could lead to an underrepresentation of unique taxa. Additionally, the rapid increase in the relative abundance of some members of the "rare biosphere" in our results implies an ecological importance of at least some of the taxa comprising the "rare biosphere."

Leucine‐to‐carbon empirical conversion factor experiments: does bacterial community structure have an influence?

The suitability of applying empirical conversion factors (eCFs) to determine bacterial biomass production remains unclear because seawater cultures are usually overtaken by phylotypes that are not abundant in situ. While eCFs vary across environments, it has not been tested whether differences in eCFs are driven by changes in bacterial community composition or by in situ environmental conditions. We carried out seawater cultures throughout a year to analyse the correlation between eCFs and bacterial community structure, analysed by catalysed reporter deposition fluorescence in situ hybridization. Gammaproteobacteria usually dominated seawater cultures, but their abundance exhibited a wide range (25-73% of cell counts) and significantly increased with inorganic nutrient enrichment. Flavobacteria were less abundant but increased up to 40% of cells counts in winter seawater cultures, when in situ chlorophyll a was high. The correlations between eCFs and the abundance of the main broad phylogenetic groups (Gamma-, Alphaproteobacteria and Flavobacteria) were significant, albeit weak, while more specific groups (Alteromonadaceae and Rhodobacteraceae) were not significantly correlated. Our results show that the frequent development of the fast-growing group Alteromonadaceae in seawater cultures does not strongly drive the observed variations in eCFs. Rather, the results imply that environmental conditions and the growth of specific phylotypes interact to determine eCFs.