From 14 May to 11 June 2013, members of consortium 3 conducted research off the northeastern coast of Normanby Island, Papua New Guinea (09°49.455’S, 150°49.073’E) aboard the MV Chertan with captain Rob van der Loos and his crew. The purpose of the cruise was to determine how marine organisms are acclimated to long-term ocean acidification and the resulting effect on biogeochemical cycles by studying organisms living in naturally CO2-rich coral reefs.
The collaborative project was lead by scientists from many institutes, including the Max Planck Institute for Marine Microbiology, the Bremen Marine Ecology Center for Research and Education at the University of Bremen, the Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, the GEOMAR Helmholtz Center for Ocean Research, the Australian Institute of Marine Science, and the National Oceanography Center at the University of Southampton. Participants included Dirk de Beer, Katharina Fabricius, Artur Fink, Christiane Hassenrück, Laurie Hofmann, Karin Hohmann, Craig Humphrey, Anna Lichtschlag, Sam Noonan, Joy Smith, Julia Strahl, Sven Uthicke, Nikolas Vogel and Marlene Wall.
Research activities included a multitute of collaborative experimental, monitoring and observational work, the highlights of which are summarized below.
In situ experiment investigating the effects of long term ocean acidification and nutrient enrichment on the physiology of corals, calcifying macroalgae and foraminifera
Katharina Fabricius, Gertraud Schmidt, Laurie Hofmann, Sam Noonan, Julia Strahl, Sven Uthicke, Nikolas Vogel, Marlene Wall
Many calcifying organisms are sensitive to ocean acidification, but it is not clear how multiple stress factors may interact to affect their physiology and ecology. Therefore we investigated how corals and algae acclimated to normal or high CO2 conditions respond to nutrient enrichment. Corals and algae were collected from CO2-impacted and unimpacted reefs and transplanted into cages with and without nutrient enrichment for a period of three weeks. Photosynthesis, calcification, and nutrient uptake rates were measured on board in incubation chambers, and samples were taken for later tissue and skeleton analysis. Strontium staining was used as a proxy for coral growth rates, and skeletal samples were taken for boron isotope analysis. Foraminifera were stained with calcein to monitor growth rates.
Joy Smith and the MV Chertan Crew
One of the main objectives of sampling for zooplankton is to observe any population shifts that might occur between low and normal pH water near natural CO2 vents. Observing zooplankton in a naturally high CO2 environment gives insight into which species may acclimate and adapt to ocean acidification over several generations. As you can see from samples collected on the first night at one of our field locations, the zooplankton can be quite different in quantity and species composition (see photo). By sampling for zooplankton from May to June, we can also compare the zooplankton community to samples collected in January of the same year to assess any seasonal changes that may have occurred. In total, 329 zooplankton samples were collected through traditional net tows, both horizontal and vertical, at midday and during the night. Additional samples were also collected to look at the chemical composition of individual organisms as well as the isotopic signature of bulk zooplankton samples.
In situ sediment profiling
Dirk de Beer, Artur Fink, Karin Hohmann and Anna Lichtschlag
We investigated how the rates of the main benthic processes, primary production and mineralization, are influenced by the vents. The process rates were determined by Artur Fink on sediment sampled from various locations near vents and a reference site. Dirk de Beer made the environmental characterization of the sites, using loggers that measured pH, CO2, O2, redox potential, T and pressure close to the seafloor, and using a microprofiler that measures these parameters (plus H2S) inside the sediments (so the actual microenvironment of the bacteria). We used 6 loggers, positioned at several locations for at least 3 dial cycles. We will search for correlations between the different parameters and investigate if seepage is controlled by tides. A total of 26 sets of microprofiles were recorded at 15 locations. Profound differences were recorded. Near seeps the pH in sediments drops below 6 within the top few cm, and oxygen penetration is often less than 2 mm. The pH in sediments at the control site differs less than 0.5 units from seawater, and oxygen penetrates several cm. No sulfide was found in sediments, although fresh seepage water contained sulfide. Seeps seem to also have high iron contents. The sulfide in seep water is very quickly converted or precipitated by metals in the pore water upon contact with the oxygenated seawater. Abundance and concentration of iron and other metals advected with the fluids will be analysed in samples collected from pore water of the different sediments (see photo below) as well as in water column samples collected above strong seepage sites by Anna Lichtschlag. In addition, she did detailed studies on the carbonate system and the nutrients of the seeps and associated sediments.
Finally, in collaboration with Laurie Hofmann and Julia Strahl, we performed physiological measurements on various algae and corals that have different sensitivities to pH. The effects of pH on gross- and net photosynthesis, and importance of carbonic anhydrase for primary production was investigated. Generally, net and gross photosynthesis was enhanced by low pH. However, in species that avoid seeps this enhancement by low pH was small or absent. This may indicate that the DIC uptake mechanism is important for the pH sensitivity of algae and corals, and can explain their distribution around seeps.
Long term monitoring, community mapping and seagrass growth
Katharina Fabricius, Sam Noonan
Katharina Fabricius focused on the question of pCO2 thresholds for reef accretion, the limits for the toughest groups of corals, and the limits for the more sensitive branching species of corals, sponges and soft corals. We systematically mapped coral and seagrass communities and two of the seeps and their control sites, continued to deploy pH loggers, and expanded on our now large existing data base on georeferenced samples of alkalinity, DIC and pH values. Across the institutions, we ended up with an impressive array of data loggers (see photo). We retrieval two pH loggers and a wave and current meter that had been deployed from January to May, which provided useful data on the long-term variability in pH exposure, and their main drivers (wave mixing, depth etc). We now have good data on temporal and spatial variation of pCO2 exposure as well as other variables (temperature, salinity etc.) from all three seeps, which will be useful for the interpretation of the results from other studies such as the complementary maps of reef communities.
Investigation of biofilm communities associated with marine sediment and marine macrophytes
Christiane Hassenrück, Laurie Hofmann
Parallel to the measurements of benthic processes and biogeochemical parameters by Dirk de Beer, Artur Fink and Anna Lichtschlag, Christiane sampled the microbial community of the sediment at 17 seep sites with varying degrees of CO2 influence and 4 control sites without the influence of CO2 seeps. She will use molecular tools based on DNA and RNA such as automated ribosomal intergenic spacer analysis (ARISA), next generation sequencing and functional gene analysis to determine the effect of long-term exposure to reduced pH levels on the composition of the microbial community in the sediment. Furthermore, in collaboration with Laurie Hofmann, she is investigating the biofilms on the macroalgae Halimeda spp. and the seagrass Enhalus sp. and their responses in terms of microbial community composition to low pH conditions. Her goal is it to integrate her data with the data collected by the other scientists on the cruise to the CO2 seeps in Papua New Guinea to get a picture as comprehensive as possible of the impact long-term exposure to reduced pH conditions will have on microbial communities.
Investigation of long-term CO2 effects on marine invertebrates
Sven Uthicke, Craig Humphrey, Katharina Fabricius, Sam Noonan
Scouring pads that were deployed during a previous cruise were collected and all contents preserved in ethanol to determine how invertebrate recruitment is influenced along the CO2 gradient. Tom complement microbial community and metagenomic studies in three sponge species, their density and abundance along a CO2 gradient were measured and samples were taken to determine the effect of long-term CO2 exposure on spicule composition and structure. Sea urchins were collected, stained on board with tetracycline, and released back into the reef. These organisms will be recaptured in one year to determine growth rates of urchins living under different CO2 conditions.
Overall the cruise was very successful, despite some windy and rainy weather. The participants are thankful to the hardworking and helpful crew of the MV Chertan, without whom the cruise would not have been possible. Thanks to fruitful collaborative efforts, they are expecting an exciting outcome and look forward to reporting more thorough results from the cruise in the future. They are already brainstorming for a potential second cruise in 2014.