© Angelos K. Hannides
Last modified: February 2010
My research is fairly broad and, on occasion, opportunistic, but runs a common thread: the function of organic matter as a conduit for marine ecosystem functioning, especially the marine sediment component, and its impact on global biogeochemical cycles. I am interested in the interplay of biotic and abiotic processes and how these affect sources and supply of organic matter to sediments, how organic matter impacts transport of matter between sediment and overlying water further, and how its processing determines sedimentary ecosystem function.
My research interests include benthic ecosystem function and early diagenesis in marine sediments, benthic-pelagic matter-and-energy coupling, permeable sediment biogeochemistry and biodiversity, animal-sediment interactions, large organic falls, and deep-sea biodiversity.
More information about my most important research activities can be found below, as well as in my extended cv (pdf file).
Since 2002, I have been participating in numerous field research projects concerning deep-sea ecosystems. These have included deep-sea basins (California Borderland Basins), oxygen minimum zones (Hindus margin), seamounts (Anaximenes Seamount), the deep abyssal plain (Arabian Sea, Northern Pacific) and the euphotic zones of sub-tropical (North Pacific sub-tropical gyre), temperate (North Pacific) and boreal (Bering Sea) systems. I have conducted sampling, observations, experiments, and specialized analysis with a gamut of tools of varying sophistication. During this work, I developed an appreciation for how regional- and global-scale human activity may affect these remote but sensitive ecosystems, spurned early on by a synthesis I published as a book chapter (pdf file) with Craig Smith, one of my mentors at the University of Hawai`i.
It is this appreciation that guides me in my future research efforts in this field:
In a project led by Cecelia Hannides, and in collaboration with Marina Argyrou of the Marine Environment Division of the Department of Fisheries and Marine Research of Cyprus, we have been conducting a study which aims to demonstrate how stable isotopes can inform us about the impact of human activities on ecosystem function. In this project, we use the nitrogen isotope signal of fish food added to fish cages in the open sea to discern the spatial and temporal impacts of this organic enrichment on the surrounding food web. The findings suggest that directly or indirectly many different trophic levels absorb the introduced matter and do so over a relatively long distance from the open sea cages. The impacts of this activity are accentuated here since our marine environment is ultra-oligotrophic, so our study is providing new insights on the effects of this anthropogenic enrichment process.
As a member of Craig Smith's laboratory at the University of Hawai`i at Manoa, I became acquainted with a special type of deep-sea habitat: large organic falls, which are represented most famously by dead whales, seagrasses, and wood. These falls provide a large amount of nutritious material to a very small surface area of otherwise poorly-supplied deep-sea floor. They are biodiversity hot-spots, they are processed by a large variety of specialized animals that disperse what they don’t consume to the surrounding sea floor, where microbes take over and process this material at such rates that they give rise to conditions that establish chemosynthetic communities, communities that use sulfide or methane instead of oxygen as the energy-yielding molecules.
In marine sediments surrounding natural and experimental whale, kelp and wood falls, I measured dissolved sulfide, organic carbon and total nitrogen. I explored their spatial and temporal distribution and relation to fall type, which elucidated the flow of large organic fall material through the surrounding ecosystem and how it may lead to the rise of chemosynthetic communities. My work has shown that sulfidic conditions rise much more readily the more palatable the material is, as when one compares whale versus wood, for example.
I have also modeled the processing of large organic falls in the deep sea, such as whales and wood by specialist communities (scavengers and borers respectively). I used field data-driven modeling to simulate the rise of conditions that favor the establishment of chemosynthetic communities. This modeling work has surprisingly revealed that these different animal communities process their falls at the same rate despite differences in the type, whether it’s whale blubber or wood. One would say that it’s a remarkable example of evolving to exploit available resources that nobody else does. I am continuing my modeling work in this field.
This work involves linking my existing model of fall fragmentation and supply with a comprehensive multi-component reaction-transport model. This work will hopefully help us elucidate the dynamics of the rise of biogenic chemosynthetic communities.
A large portion of my doctoral dissertation (under the supervision of Frank Sansone and Eric Gaidos at the University of Hawai`i at Manoa) was devoted to studying organic matter cycling and nutrient dynamics in permeable sediments:
This research demonstrated that the microbiota in sands not only have the ability to rapidly decompose organic particles and recycle them to nutrients, but also to retain a significant portion of those nutrients in the sands, instead of releasing them into the water column and fuel productivity there. The combination of field studies and lab incubations demonstrated previously unsuspected metabolic diversity, both genetic and functional, in sand microbes. Processes, such as benthic denitrification, which is incompatible with the surrounding oxic conditions, can take place in microniches within the sand column or on the sand grains themselves, suggesting that these microniches are significant not only for marine ecology, but also for the global cycling of bio-essential elements. Moreover, the above findings support the idea that the sea-floor-associated food web plays a significant role in coastal ecosystem production.
Future work in this area aims to focus on:
I realized the importance of the interaction between animals and sediments for organic matter cycling, while being a Master's student of Bob Aller at Stony Brook University (then State University of New York at Stony Brook). In 1983, Bob published a seminal paper, which demonstrated that the way inorganic solutes behave when encountering burrow linings is dictated by their charge. Work by two of his graduate students (Shannon Dunn and myself) investigated additional aspects of such biogenic materials' impact on diffusion, including the effects of size on organic solute diffusion and comparisons between pedal mucus of gastropods and burrow linings. We found that the charge and the size of the molecules trying to diffuse through these secretions determines how fast they do so. This is of great significance for two reasons: because the transport of dissolved matter in muddy sediments is dictated by diffusion, and because these animals essentially use mucus as a niche-forming tool, to control the physical and chemical conditions of their immediate environment (read more about this work in our relevant paper (pdf file). In addition, experiments with natural microbial assemblages revealed that mucus encourages the decomposition of unpalatable organic material that would otherwise be buried into the sediments. This process, known as co-metabolization, is underappreciated in microbial ecology, and that it may have important implications for soil and sediment remediation after organic pollution, such as oil spills.
© Angelos K. Hannides
Last modified: February 2010