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The Mystery of the Polar Boom: Why does Phaeocystis form giant breeding waves in the Arctic and Antarctic?
Phaeocystis, a type of algae belonging to the class Prymnesiophyte, it is difficult to imagine that they would form such a huge breeding tide in the Arctic and Antarctic waters. This type of phytoplankton with a special structure can survive in a wide range of temperature and salinity environments and is undoubtedly an important part of the polar marine ecosystem. One of the special features of this algae is its polymorphic life cycle, which can exist as free-living cells or form large aggregates. As aggregates form, hundreds of cells become entrapped in a polysaccharide gel matrix, causing their numbers to surge during reproductive waves.
Explosive reproduction of Phaeocystis mainly occurs in polar seas, especially in P. pouchetii in the Arctic and P. antarctica in the Antarctic.
In the cold waters of the Arctic and Antarctic, Phaeocystis reproduces more frequently than elsewhere. This breeding wave usually lasts for about three months, covering most of the southern hemisphere's summer. These thriving ecosystems of Phaeocystis are closely associated with commercially important crustaceans, molluscs, fish and marine mammals. However, the performance of Phaeocystis is not only positive. When its breeding tide ends, smelly foam will form on the beach, which may also have a negative impact on human activities, such as fish farming and coastal tourism.
Phaeocystis not only plays an important role in the ocean carbon cycle, but also produces large amounts of dimethyl sulfide (DMS), a substance that plays a key role in the sulfur cycle.
Globally, free-living forms of Phaeocystis are found in a variety of marine habitats, including coastal oceans, open oceans, polar seas and sea ice. Seven species of this genus are now known, namely P. antarctica, P. jahnii, P. globosa, P. pouchetii, P. scrobiculata, P. cordata and P. rex. These species, especially P. globosa, P. pouchetii and P. antarctica, are closely associated with the formation of breeding tides in eutrophic areas, which can be modified by natural or anthropogenic factors.
Unlike P. globosa, which often breeds in warmer waters, P. pouchetii and P. antarctica are more adapted to the cold waters of the Arctic and Antarctic. It is worth noting that P. pouchetii can actually tolerate higher water temperatures and has even been observed in temperate waters. In addition, genome comparison showed that in Phaeocystis species, the sequence of the RUBISCO spacer region is highly conserved in closely related species, which may affect their physiological properties.
Phaeocystis can exist both as free-living forms and aggregates, and can exhibit a variety of morphological characteristics. All species can appear as scaly flagellates, with only P. scrobiculata and P. cordata being observed. Three species exist as aggregates, P. globosa, P. pouchetii and P. antarctica, and can also exist as flagellated plants without scales and filamentous structures. In Phaeocystis aggregates, the outer layer of the aggregate may provide protection from small zooplankton and viruses, which plays a key role in their survival.
The reproductive cycle of Phaeocystis includes diploid and haploid stages, among which sexual reproduction is the main one, which is of great significance for the formation and destruction of aggregates.
In addition to its ecological importance, Phaeocystis is also considered a major producer of three species of dimethylsulfide propionic acid (DMSP), the precursor of dimethyl sulfide (DMS). Each year, biologically released DMS contributes approximately 1.5×10^13 grams of sulfur to the atmosphere, which has a significant impact on the global sulfur cycle and may affect cloud formation and even have a potential impact on climate regulation.
In addition, Phaeocystis is also an endosymbiont of acanthoenterans. Acanthoenterans collected from different sea areas host different species of Phaeocystis as main symbionts; P. antarctica is the main symbiont of acanthoenterans in the Southern Ocean. The mutual benefit of this symbiotic relationship is still under discussion, because within this ecological relationship Phaeocystis may undergo dramatic cellular remodeling, including a sudden increase in the number of chloroplasts and an enlargement of the central vacuole. However, this change may prevent the symbiotic cells from dividing in the future, thus affecting the survival of Phaeocystis.
Phaeocystis thrives not only on its own biology, but also on its complex role in polar ecosystems. Do these phenomena have further implications in the context of climate change?
