Ocean Acidification and its affect on Corals and Phytoplankton
In addition to bleaching, we are experiencing an acidification effect that is derived from the increased CO2 concentration in the atmosphere over the past 150 years. It is important to understand how this phenomenon is affecting the inhabitants of the marine realm. In our current research (Fine and Tchernov 2007), we have discovered that corals can withstand low pH values (7.2-7.4 versus modern value 8.2). The corals lose their aragonite skeleton which disassociated while their polyp biomass increased fivefold. Moreover, the coral lost its colonial structure and separated into a multitude of single polyps. These polyps maintained their reproductive ability.
This find has vast implications on our understanding of coral evolution in light of the fact that marine pH has shifted dramatically during the earth's history. There are two major 'reef gaps'- a period in the geological record which is absent of coral fossils. One occurred during the Permian-Triassic mass extinction event (251 million years ago) and another occurred during the Triassic-Jurassic boundary extinction event (206 million years ago). The lack of fossilized coral in the geological record during those periods can now be better understood. Interestingly, molecular clocking has produced a phylogenetic tree that dates the origin of scleractinian corals at 280 million years ago, yet there is no such marker in the geological record. Again, our findings provide an explanation for this incongruency.
I am currently expanding this research to a multitude of species and testing both their physiological and biochemical reactions to acidification in an attempt to elucidate the mechanisms behind those very dramatic responses.
In addition, we have found that the colony separation into individual polyps is executed through apoptotic pathways. This finding is linked to the apoptotic response that we have discovered is heat-stress related and causes, in many cases, the annihilation of the whole colony. Therefore, these studies are providing a broader view of the evolution of corals in light of their changing environment over their history.
I am also pursuing questions related to how acidification impacts phytoplankton in the water column as a means to create a dependable tool for paleoreconstruction of past climates. A major determinant of global climate is the atmospheric CO2 concentration. A possible tool for making such assessments is through the use of various forms of organic phytoplankton remains in the sediments. These methods have been developed and tested during the last decade and found to be lacking in several aspects, mainly these methods did not consider significant physiological characteristics of phytoplankton such as active carbon transport. I have developed a model that may be capable of extracting paleo atmospheric CO2 concentration values from the stable carbon isotope composition of phytoplankton, considering the typical physiological parameters for each species. The model is based on both in situ and in vivo measurements. This work is summarized in two separate manuscripts (Tchernov and Lifshultz in revision, and Tchernov et al. submitted) that show the impact of temporal and spatial changes in the water on the stable carbon isotopes composition of phytoplankton.
c. Deep Coral Physiology
Most of the world's reefs lie below a depth of 50 meters, and normally continue to 150 meters, particularly in the Indo-Pacific realm. This means that most of the reef has never been thoroughly investigated due to technological limitations. Recently, due to advancements in SCUBA technology (namely, more accessible and affordable TRIMIX and rebreather systems) it has become possible to study the coral reefs at these depths in Eilat. Because this is an entirely new research area, there is a substantial amount of work underway analyzing and understanding the basic physiology of the organisms living in those deep reefs.
Our findings include the description of a totally new photosynthetic pathway and organization. Deep corals and also macroalgae seem to have an extremely low photosynthetic rate and an almost complete absence of PS1 functional response. In the case of corals, this makes this symbiosis questionable in terms of the benefit of the hosts. We believe that the host is actually contributing carbohydrates to the algal symbionts. If this is true, it redefines the nature of the symbiosis between corals and their algal symbionts.
Surprisingly, the photosynthetic organisms that dwell at those depths have not lost their ability to produce high rates of photosynthesis at high light intensities, and do not show the characteristic non-photochemical quenching evident from corals and macro algae living in shallower depths.
We are currently in the final stages of fortifying and retesting these results using different techniques prior to publishing. Because of the novelty of this research, in the process of analysis we have developed new techniques and machinery that enable us to acquire data. For example, we have now a membrane inlet mass spectrometer that is linked to both a fast repetition rate fluorometer and a pulse-amplitude modulated fluorometer, especially modified for this purpose. I believe that this is a promising new research direction that will be the foundation for a wide range of studies in the future.