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The British Isles are a group of islands in the North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner and Outer Hebrides, the Northern Isles, and over six thousand smaller islands. They have a total area of 315,159 km2 (121,684 sq mi) and a combined population of almost 72 million, and include two sovereign states, the Republic of Ireland, and the United Kingdom of Great Britain and Northern Ireland. The Channel Islands, off the north coast of France, are normally taken to be part of the British Isles, even though they do not form part of the archipelago.

The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Southern Europe and Anatolia, on the south by North Africa, and on the east by the Levant. The Mediterranean has played a central role in the history of Western civilization. Geological evidence indicates that around 5.9 million years ago the Mediterranean was cut off from the Atlantic and was partly or completely desiccated over a period of some 600,000 years during the Messinian salinity crisis before being refilled by the Zanclean flood about 5.3 million years ago.

Spain, or the Kingdom of Spain, is a country primarily located in southwestern Europe with parts of territory in the Atlantic Ocean and across the Mediterranean Sea. The largest part of Spain is situated on the Iberian Peninsula; its territory also includes the Canary Islands in the Atlantic Ocean, the Balearic Islands in the Mediterranean Sea, and the autonomous cities of Ceuta and Melilla in Africa. The country's mainland is bordered to the south by Gibraltar; to the south and east by the Mediterranean Sea; to the north by France, Andorra and the Bay of Biscay; and to the west by Portugal and the Atlantic Ocean. With an area of 505,990 km2 (195,360 sq mi), Spain is the second-largest country in the European Union (EU) and, with a population exceeding 47.4 million, the fourth-most populous EU member state. Spain's capital and largest city is Madrid; other major urban areas include Barcelona, Valencia, Seville, Zaragoza, Málaga, Murcia, Palma de Mallorca, Las Palmas de Gran Canaria, and Bilbao.

Italy, officially the Italian Republic or the Republic of Italy, is a country in Southern and Western Europe. Located in the middle of the Mediterranean Sea, it consists of a peninsula delimited by the Alps and surrounded by several islands; its territory largely coincides with the homonymous geographical region. Italy shares land borders with France, Switzerland, Austria, Slovenia and the enclaved microstates of Vatican City and San Marino. It has a territorial exclave in Switzerland, Campione. Italy covers an area of 301,230 km2 (116,310 sq mi), with a population of about 60 million. It is the third-most populous member state of the European Union, the sixth-most populous country in Europe, and the tenth-largest country in the continent by land area. Italy's capital and largest city is Rome.

France, officially the French Republic, is a country located primarily in Western Europe. It also includes overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans, giving it one of the largest discontiguous exclusive economic zones in the world. Its metropolitan area extends from the Rhine to the Atlantic Ocean and from the Mediterranean Sea to the English Channel and the North Sea; overseas territories include French Guiana in South America, Saint Pierre and Miquelon in the North Atlantic, the French West Indies, and many islands in Oceania and the Indian Ocean. Its eighteen integral regions span a combined area of 643,801 km2 (248,573 sq mi) and had a total population of over 68 million as of January 2023. France is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre; other major urban areas include Marseille, Lyon, Toulouse, Lille, Bordeaux, and Nice.

The Maghreb, also known as the Arab Maghreb and Northwest Africa, is the western part of the Arab world. The region comprises western and central North Africa, including Algeria, Libya, Mauritania, Morocco, and Tunisia. The Maghreb also includes the disputed territory of Western Sahara and the Spanish cities Ceuta and Melilla. As of 2018, the region had a population of over 100 million people.

The dinoflagellates are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. Their populations vary with sea surface temperature, salinity, and depth. Many dinoflagellates are photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey.

Hurricane Katrina was a devastating Category 5 Atlantic hurricane that resulted in 1,392 fatalities and caused damage estimated between $97.4 billion to $145.5 billion in late August 2005, particularly in the city of New Orleans and its surrounding areas. At the time, it was the costliest tropical cyclone on record, tied now with Hurricane Harvey of 2017. Katrina was the twelfth tropical cyclone, the fifth hurricane, and the third major hurricane of the 2005 Atlantic hurricane season. It was also the fourth-most intense Atlantic hurricane on record to make landfall in the contiguous United States.

Paralytic shellfish poisoning (PSP) is one of the four recognized syndromes of shellfish poisoning, which share some common features and are primarily associated with bivalve mollusks. These shellfish are filter feeders and accumulate neurotoxins, chiefly saxitoxin, produced by microscopic algae, such as dinoflagellates, diatoms, and cyanobacteria. Dinoflagellates of the genus Alexandrium are the most numerous and widespread saxitoxin producers and are responsible for PSP blooms in subarctic, temperate, and tropical locations. The majority of toxic blooms have been caused by the morphospecies Alexandrium catenella, Alexandrium tamarense, Gonyaulax catenella and Alexandrium fundyense, which together comprise the A. tamarense species complex. In Asia, PSP is mostly associated with the occurrence of the species Pyrodinium bahamense.