Marine Phytoplankton 2024 PDF

BI2MBC1 MARINE BIOLOGY AND CONSERVATION MARINE PHYTOPLANKTON RENEE LEE ・ WEEK 4, SEMESTER 1  AIMS & LEARNING OUTCOMES  Describe what are marine phytoplankton  Discuss the importance of marine phytoplankton  Identify the different types of marine phytoplankton  Understand the proc...

BI2MBC1 MARINE BIOLOGY AND CONSERVATION MARINE PHYTOPLANKTON RENEE LEE ・ WEEK 4, SEMESTER 1  AIMS & LEARNING OUTCOMES  Describe what are marine phytoplankton  Discuss the importance of marine phytoplankton  Identify the different types of marine phytoplankton  Understand the process of photosynthesis  Describe how marine phytoplankton overcome carbon limitation  Discuss the future of marine phytoplankton SeaWiFS 10 year average (1997-2007) ocean chlorophyll concentration and land Normalized Difference Vegetation Index MARINE PHYTOPLANKTON Diverse, single celled photosynthetic organisms that drift with the currents in marine waters  Responsible for more than 45% of Earth’s annual net primary production  Found in the euphotic zone  Almost all phytoplankton are obligate photoautotrophs with the exception of some mixotrophs Falkowski et al. (2004) Science 305: 354-360; Archibald and Keeling (2002) Trends in Genetics 18: 577-584 WHY ARE THEY IMPORTANT? Falkowski (2012) Nature 483: S17-S20 ATMOSPHERIC OXYGEN GLOBAL CARBON CYCLE  WHY ARE THEY IMPORTANT? The Biological Carbon Pump  A process by which carbon dioxide in surface ocean water is transformed by ocean organisms into carbon compounds  These carbon compounds are transferred to deep ocean layers through dead organisms, fecal matter and calcified skeletons/shells  Responsible for the transfer of ~10 gigatonnes of carbon per year from the atmosphere ATMOSPHERIC OXYGEN GLOBAL CARBON CYCLE THE AQUATIC FOOD WEB  CYANOBACTERIA PRASINOPHYTES DIATOMS COCCOLITHOPHORES DINOFLAGELLATES  CYANOBACTERIA  Photosynthetic prokaryotes  Often referred to as blue-green algae  One of the oldest organisms on Earth  Responsible for the oxygenation of our planet  CYANOBACTERIA SYNECHOCCUS PROCHLOROCOCCUS Size varies from 0.8 to 1.5 µm Approximately 0.6 µm Ovoid to cylindrical cells, motile Most abundant photosynthetic organism on Earth Coccoid cells, non-motile CYANOBACTERIA Summed effort of 35 years of research cruises and time series provide a basis for quantifying the global abundance of Prochlorococcus and Synechococcus within their realized niche Prochlorococcus  Found in tropical oceans  Dominate oligotrophic regions Synechococcus  Found in temperate to tropical oceans  Abundant in nutrient-rich environments Flombaum et al. (2013) PNAS 110: 9824 - 9829  PRASINOPHYTES van Baren et al. (2016) BMC Genomics 17: 267  Class of unicellular green algae (division Chlorophyta)  Include marine planktonic species and some freshwater representatives  Most are 2 μm or less and have a single chloroplast and mitochondrion  They can be non motile or motile with one or more flagella  DIATOMS  Photosynthetic eukaryotes (superphylum Heterokonta) with a siliceous skeleton (frustule)  They can be planktonic or benthic  Appear as solitary cells or colonies (chains or filaments)  They are non-motile, or capable of only limited movement Armbrust (2009) Nature 459: 185-192  DIATOMS  Reproduce primarily by mitotic divisions interrupted infrequently by sexual events  Particularly abundant in nutrient-rich coastal ecosystems and at high latitudes  Two groups distinguished by the shape of the frustule – centric and pennate Thalassiosira Phaeodactylum weissflogii tricornutum Soppa et al. (2014) Remote Sensing 6:10089-10106; Malviya et al. (2016) PNAS 113: E1516-25 COCCOLITHOPHORES  Photosynthetic eukaryotes (phylum Haptophyta)  Surrounded with a microscopic plating (coccolith) made of limestone (calcite)  Found in highly productive eutrophic waters in temperate and subpolar regions to the permanently oligotrophic waters of the subtropical gyres  Not normally harmful to other marine life de Vargas et al. (2007) Evolution of Primary Producers in the Sea pp. 251-287 COCCOLITHOPHORES  Contain a functional or vestigial haptonema  Coccolithogenesis occur in a Golgi derived vesicle  Coccolithophores have a major impact on the global carbon cycle  Coccolithophores produce dimethyl sulfide (DMS) that is instrumental in the formation of clouds Billard & Inouye (2004) Coccolithophores pp.1-29 DINOFLAGELLATES  Roughly half of the species are photosynthetic, some mixotrophic or exclusively heterotrophic  Encased in a plate of armor (called amphiesma)  Possess two dissimilar flagella  Photosynthetic dinoflagellates have eyespots – light-sensitive organelles Steidinger & Tangen (1996) Identifying Marine Diatoms and Dinoflagellates pp. 387-584  DINOFLAGELLATES Symbiodinium Karenia brevis Nocticula scintilans Ceratium macroceros  Considered to be amongst the most primitive group of eukaryotes  Adapted to a variety of pelagic and benthic habitats from arctic to tropical seas  Particularly diverse with more than 2,000 extant species described  Some cause ‘red tides’ and harmful blooms whilst others are beneficial endosymbionts PHOTOSYNTHESIS THE TWO REACTIONS  THE CARBON REACTIONS Ribulose bisphosphate THE CALVIN-BENSON- carboxylase/oxygenase BASSHAM CYCLE RuBisCO CARBOXYLATION REGENERATION REDUCTION OUTPUT  THE PROBLEM – OCEAN CHEMISTRY Dissolved carbon dioxide in the ocean occurs mainly in three inorganic forms  Oceans have a natural buffering capacity  At pH8.1 (present day) bicarbonate is the dominant carbon species  CO2 (aq) is subsaturating (10-30 μM) – slow diffusion rate is insufficient to saturate Rubisco  THE PROBLEM - RUBISCO RUBISCO CENTRAL TO LIFE ON EARTH Large, slow and confused!  PHOTORESPIRATION Occurs when RuBisCO fixes oxygen instead of carbon dioxide  Kinetic properties of RuBisCO  Concentration of CO2 and O2  Temperature An energetically costly salvage pathway that converts 2 x 2-PG to 3-PGA, CO2 and NH3 75% carbon is returned to the Calvin cycle 15% lost in the form of CO2 Leegood (2007) Nature Biotechnology 25: 539-540 CARBON CONCENTRATING MECHANISMS Heureux et al. (2017) Journal of Experimental Botany 68: 3959-3969 CARBON CONCENTRATING MECHANISMS INORGANIC TRANSPORTERS  Build intracellular pools of bicarbonate (DIC)  Requires energy (ATP, NADPH or ion gradient) CARBONIC ANHYDRASE CO2 + H2O H2CO3 HCO3- + H+ Carbonic anhydrase MICROCOMPARTMENT  Packages the majority of Rubisco  Minimise CO2 leakage CARBON CONCENTRATING MECHANISMS CYANOBACTERIA  CO2 enters the cell by diffusion or CO2 uptake system whilst HCO3- is actively transported  HCO3- diffuses through the carboxysome and is converted by a carbonic anhydrase to CO2  Contains a polyhedral protein shell (carboxysome) that prevents CO2 leakage Badger et al. (2003) Journal of Experimental Botany 54: 609-622; Badger et al. (2006) Journal of Experimental Botany 57: 249-265 CARBON CONCENTRATING MECHANISMS EUKARYOTIC PHYTOPLANKTON Giordano et al. (2005) Annual Review of Plant Biology 56: 99-131; Reinfelder (2011) Annual Review of Marine Science 3: 291-315  CARBON CONCENTRATING MECHANISMS  Carbonic anhydrases (CA) play an important role. How CA might support inorganic carbon uptake depends on its cellular location External or extracellular CA generate CO2 at the cell surface Cytosolic CA convert CO2 to HCO3- Chloroplastic (or pyrenoid) CA provide direct supply of CO2 to Rubisco  CO2 diffuses through the cell, whilst HCO3- is transported by a variety of transporters  Subcellular microcompartments known as pyrenoids maintain a CO2 rich environment around Rubisco  C4 carbon fixation has also been proposed – however this still remains inconclusive Giordano et al. (2005) Annual Review of Plant Biology 56: 99-131; Reinfelder (2011) Annual Review of Marine Science 3: 291-315  A SUMMARY CYANOBACTERIA EUKARYOTIC PHYTOPLANKTON Yes Yes Inorganic transporters Outer and thylakoid membrane Plasma and chloroplast membrane * Thylakoid membrane? Yes Yes Carbonic anhydrase Carboxysome External, cytosol, chloroplast, pyrenoid Microcompartment Carboxysome Pyrenoid Other CCMs? No C4 mechanism? SOME KEY FACTS 90% of the heat trapped by carbon emissions is absorbed by the oceans The six hottest years in the oceans had occurred since 2015 2021 is the warmest year on record The Not even worldwide a blip lockdown in terms offrom totalCOVID-19 CO2 in thein 2020 cut carbon emissions atmosphere and had by about 7% no measurable effect on ocean heating! CLIMATE CHANGE – INCREASE IN TEMPERATURE  Sea surface temperature is approximately 1°C higher now than 140 years ago  Gradual warming has caused a decline in global phytoplankton in the past century  Increase in sea surface temperature disrupts the nutrient supply Boyce et al. (2010) Nature 466: 591-596 CLIMATE CHANGE – INCREASE IN TEMPERATURE Doney (2006) Nature 444: 695-696 CLIMATE CHANGE – OCEAN ACIDIFICATION  Serious implications on calcifying marine organisms  Seagrasses, fleshy algae and diatoms are less affected  Overall impact on the global carbon cycle Kroeker et al. (2013) Global Change Biology 19: 1884-1896 https://www.nature.com/scitable/knowledge/library/ocean-acidification-25822734  RECOMMENDED VIDEOS NASA Earth Observatory https://earthobservatory.nasa.gov/features/Phytoplankton BBC Earth – Plankton. The Most Vital Organisms on Earth https://youtu.be/UjnYJVKysfo Five Reasons to Thank Plankton https://youtu.be/23mrtGCkAH8 The Carbon Cycle http://earthobservatory.nasa.gov/Features/CarbonCycle/page1.php Please go to the BI2MBC1 Blackboard site to supplement this lecture with the recommended reading material!