Aline Tribollet

Temporal and spatial comparison of the relative abundance of macroalgae across the Mariana Archipelago between 2003 and 2005

A.D. Tribollet and P.S. Vroom. 2007. Temporal and spatial comparison of the relative abundance of macroalgae across the Mariana Archipelago between 2003 and 2005. Phycologia 46: 187–197. DOI: 10.2216/06-46.1 Past studies have argued that macroalgae serve as useful bioindicators that herald possible environmental changes to reef ecosystems because they are often opportunistic, having high growth rates and responding quickly to environmental changes, such as increased nutrient availability, grazing pressures, or storm activity. In this study, we test their usefulness as reef monitoring management indicators. We investigated the spatial and temporal variability of the relative abundance of macroalgae (RAM) at the genus level in the Mariana Archipelago between two surveys in 2003 and 2005. Islands vary drastically across the archipelago (carbonate vs volcanic, populated vs unpopulated, small vs large) and often experience considerable storm activity. We showed that the diversity of macroalgal genera was generally highest at the southern end of the archipelago, probably because of increased habitat heterogeneity around these geographically larger islands. At the northern end of the archipelago, only Pagan and Maug were large enough or contained enough environmental diversity to exhibit macroalgal diversity similar to that of the southern carbonate islands. Despite the ubiquitous nature of turf algae, crustose coralline red algae, and the green alga Halimeda (Bryopsidales) across the archipelago, multivariate analyses revealed RAM to differ among islands with northern, unpopulated, volcanic islands grouping together and differing from southern, populated, carbonate islands. Also, RAM showed significant variability at the local scale (among sites within an island) and over time. We hypothesize that this variability results principally from differing oceanographic conditions such as sea surface temperature, human impacts such as fishing and pollution, typhoons, and volcanic activity across the archipelago. These results provide a baseline for future monitoring studies in the Mariana Archipelago and suggest that rapid ecological assessments of macroalgae in the field at the genus level are a reliable indicator that can be used to monitor change over time.

Comparing Chemistry and Census-Based Estimates of Net Ecosystem Calcification on a Rim Reef in Bermuda

Coral reef net ecosystem calcification (NEC) has decreased for many Caribbean reefs over recent decades primarily due to a combination of declining coral cover and changing benthic community composition. Chemistry-based approaches to calculate NEC utilize the drawdown of seawater total alkalinity (TA) combined with residence time to calculate an instantaneous measurement of NEC. Census-based approaches combine annual growth rates with benthic cover and reef structural complexity to estimate NEC occurring over annual timescales. Here, NEC was calculated for Hog Reef in Bermuda using both chemistry and census-based NEC techniques to compare the mass-balance generated by the two methods and identify the dominant biocalcifiers at Hog Reef. Our findings indicate close agreement between the annual 2011 census-based NEC 2.35±1.01 kg CaCO3•m-2•y-1 and the chemistry-based NEC 2.23±1.02 kg CaCO3•m-2•y-1 at Hog Reef. An additional record of Hog Reef TA data calculated from an autonomous CO2 mooring measuring pCO2 and modeled pHtotal every 3-hours highlights the dynamic temporal variability in coral reef NEC. This ability for chemistry-based NEC techniques to capture higher frequency variability in coral reef NEC allows the mechanisms driving NEC variability to be explored and tested. Just four coral species, Diploria labyrinthiformis, Pseudodiploria strigosa, Millepora alcicornis, and Orbicella franksi, were identified by the census-based NEC as contributing to 94±19% of the total calcium carbonate production at Hog Reef suggesting these species should be highlighted for conservation to preserve current calcium carbonate production rates at Hog Reef. As coral cover continues to decline globally, the agreement between these NEC estimates suggest that either method, but ideally both methods, may serve as a useful tool for coral reef managers and conservation scientists to monitor the maintenance of coral reef structure and ecosystem services.

Gross and microscopic pathology of hard and soft corals in New Caledonia.

We surveyed the reefs of Grande Terre, New Caledonia, for coral diseases in 2010 and 2013. Lesions encountered in hard and soft corals were systematically described at the gross and microscopic level. We sampled paired and normal tissues from 101 and 65 colonies in 2010 and 2013, respectively, comprising 51 species of corals from 27 genera. Tissue loss was the most common gross lesion sampled (40%) followed by discoloration (28%), growth anomalies (13%), bleaching (10%), and flatworm infestation (1%). When grouped by gross lesions, the diversity of microscopic lesions as measured by Shannon-Wiener index was highest for tissue loss, followed by discoloration, bleaching, and growth anomaly. Our findings document an extension of the range of certain diseases such as Porites trematodiasis and endolithic hypermycosis (dark spots) to the Western Pacific as well as the presence of a putative cnidarian endosymbiont. We also expand the range of species infected by cell-associated microbial aggregates, and confirm the trend that these aggregates predominate in dominant genera of corals in the Indo-Pacific. This study highlights the importance of including histopathology as an integral component of baseline coral disease surveys, because a given gross lesion might be associated with multiple potential causative agents.

Microboring organisms in living stylasterid corals (Cnidaria, Hydrozoa)

ABSTRACT Microboring or euendolithic microorganisms, which colonize and penetrate various carbonate substrates, are abundant in coral reef ecosystems and play a major role in reef carbonate dissolution. A few studies reported the presence of euendoliths in stylasterid coral skeletons but the biological identity, distribution and abundance of these microorganisms remain largely unknown. Observations of over 100 stylasterid colonies, collected in the Indo-Pacific area, revealed for the first time that the association between these corals and euendolith organisms appears to be quite common in shallow tropical waters. The most abundant euendolith was identified as a cryptic stage in the development of the rhodophyte Porphyra (Conchocelis stage). The euendoliths were observed in the skeletons of seven species of three genera (four Stylaster, two Distichopora and one Lepidotheca). The presence of euendoliths inside skeletons conferred a particular colour to the studied stylasterid corals. Distribution and abundance of microborings varied significantly among stylasterid species and among branches of a single colony and so did the colour of their skeletons. Colonization of skeletons and the associated colour distribution were almost uniform in some stylasterids, forming an upward gradually diminishing or sharply limited gradient. This study shows that patterns of euendolith colonization and growth in stylasterid skeletons may depend on the stage of the euendolith development as well as on their environmental requirements such as light exposure.

Spatio-temporal variability in macroalgal assemblages of American Samoa

Tribollet A.D., Schils T. and Vroom P.S. 2010. Spatio-temporal variability in macroalgal assemblages of American Samoa. Phycologia 49: 574–591. DOI: 10.2216/09-63.1 Spatial and temporal variability of relative abundance of macroalgae at the genus and functional group levels was examined at 14 m depth across the six islands of American Samoa between 2004 and 2006. Diversity of common macroalgae was high with 54 taxa (50 genera and four algal functional groups) identified from sampled quadrats. The highest taxon richness (33) was found at the largest island, Tutuila. Crustose coralline algae, mixed turf algal assemblages, and the chlorophyte Halimeda were ubiquitous across all islands. Other algal genera or functional groups were, however, representative of specific areas. For instance, the chlorophyte Microdictyon was only found at Rose Atoll and Swains Island (the only low open-ocean atoll systems examined). Similarly, the siphonous green alga Rhipilia only occurred at Swains Island, where it was very abundant. Multivariate analyses revealed that macroalgal assemblages differed significantly among sites around a single island and among islands. All islands were significantly different from each other with Swains Islands having the most important dissimilarity with other islands. We hypothesize that Swains Island differs from the other islands because of its geographic isolation. Statistical analyses also highlighted significant differences in the relative abundance of macroalgae between years. The interaction between spatial and temporal variability was also significant, indicating that temporal changes in algal assemblages are island dependant, and spatial differences among islands are a function of the year in which surveys were conducted. Changes in algal assemblages between the 2004 and 2006 surveys were apparent for all islands except Swains Island and Tutuila, probably because of intense cyclone activity in the region during 2005 (Cyclone Olaf). This study contributes to the overall understanding of coral reef diversity and function in American Samoa and forms a baseline for future algal monitoring surveys.

Primary Life Stage Boron Isotope and Trace Elements Incorporation in Aposymbiotic Acropora millepora Coral under Ocean Acidification and Warming

Early-life stages of reef-building corals are vital to coral existence and reef maintenance. It is therefore crucial to study juvenile coral response to future climate change pressures. Moreover, corals are known to be reliable recorders of environmental conditions in their skeletal materials. Aposymbiotic Acropora millepora larvae were cultured in different seawater temperature (27 and 29oC) and pCO2 (390 and 750 µatm) conditions to understand the impacts of ‘end of century’ ocean acidification (OA) and ocean warming (OW) conditions on skeletal morphology and geochemistry. The experimental conditions impacted primary polyp juvenile coral skeletal morphology and growth resulting in asymmetric translucent appearances with brittle skeleton features. The impact of OA resulted in microstructure differences with decreased precipitation or lengthening of fasciculi and disorganized aragonite crystals that led to more concentrations of centers of calcifications. The coral skeletal δ11B composition measured by laser ablation MC-ICP-MS was significantly affected by pCO2 (p = 0.0024) and water temperature (p = 1.46 x 10-5). Reconstructed pH of the primary polyp skeleton using the δ11B proxy suggests a difference in coral calcification site and seawater pH consistent with previously observed coral pH up-regulation. Similarly, trace element results measured by laser ablation ICP-MS indicate the impact of pCO2. Primary polyp juvenile Sr/Ca ratio indicates a bias in reconstructed sea surface temperature (SST) under higher pCO2 conditions. Coral microstructure content changes (center of calcification and fasciculi) due to OA possibly contributed to the variability in B/Ca ratios. Our results imply that increasing OA and OW may lead to coral acclimation issues and species-specific inaccuracies of the commonly used Sr/Ca-SST proxy.

Surface ocean pH variations since 1689 CE and recent ocean acidification in the tropical South Pacific

Increasing atmospheric CO2 from man-made climate change is reducing surface ocean pH. Due to limited instrumental measurements and historical pH records in the world’s oceans, seawater pH variability at the decadal and centennial scale remains largely unknown and requires documentation. Here we present evidence of striking secular trends of decreasing pH since the late nineteenth century with pronounced interannual to decadal–interdecadal pH variability in the South Pacific Ocean from 1689 to 2011 CE. High-amplitude oceanic pH changes, likely related to atmospheric CO2 uptake and seawater dissolved inorganic carbon fluctuations, reveal a coupled relationship to sea surface temperature variations and highlight the marked influence of El Niño/Southern Oscillation and Interdecadal Pacific Oscillation. We suggest changing surface winds strength and zonal advection processes as the main drivers responsible for regional pH variability up to 1881 CE, followed by the prominent role of anthropogenic CO2 in accelerating the process of ocean acidification.Ocean acidification due to the industrial era is a major marine environmental concern, yet little is known on the historical ocean pH changes prior to human influence. Here, Wu et al. show that tropical South Pacific seawater pH is linked to ENSO pacing and has recently been decreasing rapidly.