Oxygen loss from seagrass roots coincides with colonisation of sulphide-oxidising cable bacteria and reduces sulphide stress.

Seagrasses thrive in anoxic sediments where sulphide can accumulate to phytotoxic levels. So how do seagrasses persist in this environment? Here, we propose that radial oxygen loss (ROL) from actively growing root tips protects seagrasses from sulphide intrusion not only by abiotically oxidising sulphides in the rhizosphere of young roots, but also by influencing the abundance and spatial distribution of sulphate-reducing and sulphide-oxidising bacteria. We used a novel multifaceted approach combining imaging techniques (confocal fluorescence in situ hybridisation, oxygen planar optodes, and sulphide diffusive gradients in thin films) with microbial community profiling to build a complete picture of the microenvironment of growing roots of the seagrasses Halophila ovalis and Zostera muelleri. ROL was restricted to young root tips, indicating that seagrasses will have limited ability to influence sulphide oxidation in bulk sediments. On the microscale, however, ROL corresponded with decreased abundance of potential sulphate-reducing bacteria and decreased sulphide concentrations in the rhizosphere surrounding young roots. Furthermore, roots leaking oxygen had a higher abundance of sulphide-oxidising cable bacteria; which is the first direct observation of these bacteria on seagrass roots. Thus, ROL may enhance both abiotic and bacterial sulphide oxidation and restrict bacterial sulphide production around vulnerable roots, thereby helping seagrasses to colonise sulphide-rich anoxic sediments.

Food supply confers calcifiers resistance to ocean acidification.

Invasion of ocean surface waters by anthropogenic CO2 emitted to the atmosphere is expected to reduce surface seawater pH to 7.8 by the end of this century compromising marine calcifiers. A broad range of biological and mineralogical mechanisms allow marine calcifiers to cope with ocean acidification, however these mechanisms are energetically demanding which affect other biological processes (trade-offs) with important implications for the resilience of the organisms against stressful conditions. Hence, food availability may play a critical role in determining the resistance of calcifiers to OA. Here we show, based on a meta-analysis of existing experimental results assessing the role of food supply in the response of organisms to OA, that food supply consistently confers calcifiers resistance to ocean acidification.

Sensitivity and Acclimation of Three Canopy-Forming Seaweeds to UVB Radiation and Warming.

Canopy-forming seaweeds, as primary producers and foundation species, provide key ecological services. Their responses to multiple stressors associated with climate change could therefore have important knock-on effects on the functioning of coastal ecosystems. We examined interactive effects of UVB radiation and warming on juveniles of three habitat-forming subtidal seaweeds from Western Australia-Ecklonia radiata, Scytothalia dorycarpa and Sargassum sp. Fronds were incubated for 14 days at 16-30°C with or without UVB radiation and growth, health status, photosynthetic performance, and light absorbance measured. Furthermore, we used empirical models from the metabolic theory of ecology to evaluate the sensitivity of these important seaweeds to ocean warming. Results indicated that responses to UVB and warming were species specific, with Sargassum showing highest tolerance to a broad range of temperatures. Scytothalia was most sensitive to elevated temperature based on the reduced maximum quantum yields of PSII; however, Ecklonia was most sensitive, according to the comparison of activation energy calculated from Arrhenius' model. UVB radiation caused reduction in the growth, physiological responses and thallus health in all three species. Our findings indicate that Scytothalia was capable of acclimating in response to UVB and increasing its light absorption efficiency in the UV bands, probably by up-regulating synthesis of photoprotective compounds. The other two species did not acclimate over the two weeks of exposure to UVB. Overall, UVB and warming would severely inhibit the growth and photosynthesis of these canopy-forming seaweeds and decrease their coverage. Differences in the sensitivity and acclimation of major seaweed species to temperature and UVB may alter the balance between species in future seaweed communities under climate change.

Ecophysiological responses of three Mediterranean invasive seaweeds (Acrothamnion preissii, Lophocladia lallemandii and Caulerpa cylindracea) to experimental warming.

The Mediterranean Sea is a hotspot for invasive species and projected Mediterranean warming might affect their future spreading. We experimentally examined ecophysiological responses to the temperature range 23-31 °C in three invasive seaweeds commonly found in the Mediterranean: Acrothamnion preissii, Caulerpa cylindracea and Lophocladia lallemandii. The warming range tested encompassed current and projected (for the end of 21st Century) maximum temperatures for the Mediterranean Sea. Optimal ecophysiological temperatures for A. preissii, C. cylindracea and L. lallemandii were 25 °C, 27 °C and 29 °C, respectively. Warming below the optimal temperatures enhanced RGR of all studied invasive seaweeds. Although sensitive, seaweed photosynthetic yield was less temperature-dependent than growth. Our results demonstrate that temperature is a key environmental parameter in regulating the ecophysiological performance of these invasive seaweeds and that Mediterranean warming conditions may affect their invasion trajectory.

Seagrass ecosystem response to long-term high CO2 in a Mediterranean volcanic vent.

We examined the long-term effect of naturally acidified water on a Cymodocea nodosa meadow growing at a shallow volcanic CO2 vent in Vulcano Island (Italy). Seagrass and adjacent unvegetated habitats growing at a low pH station (pH = 7.65 ± 0.02) were compared with corresponding habitats at a control station (pH = 8.01 ± 0.01). Density and biomass showed a clear decreasing trend at the low pH station and the below- to above-ground biomass ratio was more than 10 times lower compared to the control. C content and δ(13)C of leaves and epiphytes were significantly lower at the low pH station. Photosynthetic activity of C. nodosa was stimulated by low pH as seen by the significant increase in Chla content of leaves, maximum electron transport rate and compensation irradiance. Seagrass community metabolism was intense at the low pH station, with significantly higher net community production, respiration and gross primary production than the control community, whereas metabolism of the unvegetated community did not differ between stations. Productivity was promoted by the low pH, but this was not translated into biomass, probably due to nutrient limitation, grazing or poor environmental conditions. The results indicate that seagrass response in naturally acidified conditions is dependable upon species and geochemical characteristics of the site and highlight the need for a better understanding of complex interactions in these environments.

Global unbalance in seaweed production, research effort and biotechnology markets.

Exploitation of the world's oceans is rapidly growing as evidenced by a booming patent market of marine products including seaweed, a resource that is easily accessible without sophisticated bioprospecting technology and that has a high level of domestication globally. The investment in research effort on seaweed aquaculture has recently been identified to be the main force for the development of a biotechnology market of seaweed-derived products and is a more important driver than the capacity of seaweed production. Here, we examined seaweed patent registrations between 1980 and 2009 to assess the growth rate of seaweed biotechnology, its geographic distribution and the types of applications patented. We compare this growth with scientific investment in seaweed aquaculture and with the market of seaweed production. We found that both the seaweed patenting market and the rate of scientific publications are rapidly growing (11% and 16.8% per year respectively) since 1990. The patent market is highly geographically skewed (95% of all registrations belonging to ten countries and the top two holding 65% of the total) compared to the distribution of scientific output among countries (60% of all scientific publications belonging to ten countries and the top two countries holding a 21%), but more homogeneously distributed than the production market (with a 99.8% belonging to the top ten countries, and a 71% to the top two). Food industry was the dominant application for both the patent registrations (37.7%) and the scientific publications (21%) followed in both cases by agriculture and aquaculture applications. This result is consistent with the seaweed taxa most represented. Kelp, which was the target taxa for 47% of the patent registrations, is a traditional ingredient in Asian food and Gracilaria and Ulva, which were the focus of 15% and 13% of the scientific publications respectively, that are also used in more sophisticated applications such as cosmetics, chemical industry or bioremediation. Our analyses indicate a recent interest of non-seaweed producing countries to play a part in the seaweed patenting market focusing on more sophisticated products, while developing countries still have a limited share in this booming market. We suggest that this trend could be reverted by promoting partnerships for R and D to connect on-going efforts in aquaculture production with the emerging opportunities for new biotech applications of seaweed products.

Benthic community composition and faunal stable isotopic signatures differ across small spatial scales in a temperate estuary.

Anthropogenically induced changes to estuaries, including shifts from seagrass to macroalgae-dominated habitats, have led to concerns about the ability of estuaries to support fish and invertebrates. To assess differences in habitat quality of seagrass and macroalgae, we examined faunal community structure and consumer carbon assimilation in adjacent areas of seagrass, macroalgae, and bare sediments in Sage Lot Pond, Waquoit Bay, MA. Vegetation was an important factor controlling abundances, and both seagrass and macroalgae provided suitable habitat for a range of benthic fauna. Differences in consumption and assimilation of carbon of seagrass and macroalgal origin were demonstrated by shifts in δ(13)C values of consumers between the seagrass meadow and adjacent macroalgal mats. Overall, consumers generally reflected incorporation of carbon from the dominant producers in the habitat where they were collected although macroalgae was an important carbon source for organisms in this study. These results revealed differences in carbon flow from producers to consumers across very small spatial scales (<10 m) within an estuary.

Differences in urbanization and degree of marine influence are reflected in delta13C and delta15N of producers and consumers in seagrass habitats of Puerto Rico.

Couplings between land use and marine food webs in tropical systems are poorly understood. We compared land-sea coupling in seven sites around Puerto Rico, differing in the degree of precipitation and urbanization, by measuring delta(13)C and delta(15)N in producers and consumers. delta(15)N values were influenced by human activity: the food web from sites near urbanized centers was on average 1 per thousand heavier in delta(15)N compared to undeveloped sites. This is most likely due to wastewater inputs from septic systems relatively near the shoreline. Changes in delta(13)C were best explained by differences in the degree of marine influence. Where terrestrial inputs from a major river dominated, delta(13)C values were lighter, whereas sites further from land and in locations exposed to oceanic currents had heavier delta(13)C values, characteristic of a marine source of dissolved organic carbon. We found no significant effect of precipitation on connectivity in spite of a twofold difference in annual average rainfall between the north and south coast. The results suggest there is some connectivity between land and sea in Puerto Rico, despite high rates of evaporation relative to precipitation.

Effect of field exposure to 38-year-old residual petroleum hydrocarbons on growth, condition index, and filtration rate of the ribbed mussel, Geukensia demissa.

In September 1969, the Florida barge spilled 700,000 L of No. 2 fuel oil into the salt marsh sediments of Wild Harbor, MA. Today a substantial amount, approximately 100 kg, of moderately degraded petroleum remains within the sediment and along eroding creek banks. The ribbed mussels, Geukensia demissa, which inhabit the salt marsh creek bank, are exposed to the spilled oil. Examination of short-term exposure was done with transplantation of G. demissa from a control site, Great Sippewissett marsh, into Wild Harbor. We also examined the effects of long-term exposure with transplantation of mussels from Wild Harbor into Great Sippewissett. Both the short- and long-term exposure transplants exhibited slower growth rates, shorter mean shell lengths, lower condition indices, and decreased filtration rates. The results add new knowledge about long-term consequences of spilled oil, a dimension that should be included when assessing oil-impacted areas and developing management plans designed to restore, rehabilitate, or replace impacted areas.