Definition: In this task, you are given a text of many news articles seperated by special token "|||||". Your task is to summarize them.
Input: National Geographic/Getty Virgin Islands National Park in the U.S. Virgin Islands. Researchers have found that rising sea temperatures pose a threat to essential algae. 
  
 Rising sea temperatures can harm the tiny plant life that forms the base of the oceans' food chain as well as affect the diversity of marine life, two new studies have found. 
  
 Over the years, humans have affected the oceans by pollution and over-fishing and through habitat alteration caused by dredging and other activities. Less understood is the role of higher sea temperatures, which many scientists believe is linked to global climate change. Scientists estimate that the oceans have warmed a total of roughly half a degree Celsius on average over the past 100 years. 
  
 Oceans at Risk View Slideshow Nikon Small World Marine diatom cells (Pleurosigma), a group of phytoplankton More photos and interactive graphics 
  
 Researchers have long debated whether phytoplankton concentrations have increased or declined. The algae have flourished in many coastal areas because increased runoff from rivers brings nutrients that the algae gorge on. However, no one has properly assessed whether the global oceans are losing or gaining phytoplankton, which forms the base of the marine food chain, from crustaceans to fish and ultimately to humans. 
  
 Consistent satellite-based measurements exist only from 1997, so scientists at Dalhousie University in Nova Scotia, Canada instead used data obtained with a simple oceanography device known as a Secchi. Used by scientists since the late 1800s, a Secchi is a disk lowered into the water to provide an estimate of water clarity and thus serves as a proxy measure of phytoplankton abundance. 
  
 By collating and analyzing about half a million Secchi observations, plus other direct measurements of algae, the Dalhousie team estimated that phytoplankton levels declined by about 1% of the global average each year from 1899 onward. The data are more reliable for recent decades, translating into a 40% decline in algae since 1950. 
  
 The team investigated several factors that could have caused the decline, including wind intensity, cyclical climate changes and sea-surface temperature. "We found that temperature had the best power to explain the changes," said Boris Worm, a marine biologist at Dalhousie and co-author of the study. 
  
 Marine algae live in the upper layers of the ocean but rely on nutrients that circulate up from lower layers. Rising temperatures mean the different water layers mix less with each other, so fewer nutrients reach the algae. However, Dr. Worm notes that algal abundance can be affected by other factors, such as shifts in predator-prey populations. 
  
 Mike Behrenfeld, an expert on phytoplankton who has read the Nature paper, said it was similar to a 1992 study which also used Secchi data to show a long-term decline in marine algae in the north Pacific. "But this paper covers the globe," said Dr. Behrenfeld of Oregon State University. "And the scientists also took the next step of relating the [algal decline] to sea temperatures." 
  
 Another team of scientists, including Dr. Worm, mapped the diversity of marine life on a broad scale. One surprise finding was that while coastal marine species showed greater diversity at the equator, the diversity of oceanic species peaked in the mid-latitudes. That's unlike terrestrial diversity, which largely peaks at the tropics. 
  
 Related Article Scientists Affirm Warming Trend 
  
 The researchers also analyzed possible links between the global distribution of 11,000 marine species—big and small—to such environmental factors as temperature, oxygen levels and habitat availability. For all species types, only one factor showed a consistent correlation to diversity: sea temperature. 
  
 It's not clear what this means globally, however. When the water warms, some species may move elsewhere, reducing the diversity of their original habitat. Creatures that can't move may come under environmental stress or die off, also altering the ecosystem. 
  
 "While a changing climate is likely to lead to a change in patterns of diversity, we don't have the data yet to know what this response might look like," said Derek P. Tittensor, marine ecologist at Dalhousie and co-author of the second Nature paper, which analyzed marine diversity. 
  
 Meanwhile, other scientists are trying to assess how sea creatures respond to declining oxygen levels, caused by pollution or natural factors. Most of the 400 oxygen-depleted "dead zones" identified by scientists so far are near areas of human impact. Together, they cover an area of 96,500 square miles. 
  
 When oxygen levels drop, animals in the area fight for what's left, and many don't survive. A team of scientists from the University of Vienna lowered a plexiglass box to the Adriatic sea floor and used a time-lapse camera to document how various creatures inside responded as oxygen levels dropped. 
  
 A future catalog of such behaviors could help scientists identify areas in the ocean where oxygen depletion is under way. Some of the results will be published in Marine Ecology Progress Series, a scientific journal. 
  
 Write to Gautam Naik at gautam.naik@wsj.com ||||| Marine diatom cells, which are an important group of phytoplankton in the oceans. (Karl Bruun / Nostoca Algae Laboratory/Nikon Small World) 
  
 The world's phytoplankton appear to have been disappearing at a rate of about 1% a year for the last century, researchers announced Wednesday, a disturbing long-term trend for the microscopic algae that form the basis of the marine food chain and produce much of the world's oxygen. 
  
 In reporting their findings in the journal Nature, the Canadian team said that, since 1950, phytoplankton biomass has shrunk about 40%. Scientists had known the population was shrinking, but the long-term nature of that reduction came as a surprise. 
  
 "A global decline of this magnitude? It's quite shocking," said Dalhousie University marine scientist Daniel Boyce, lead author on the study. 
  
 The study combines historical records of ocean clarity with modern satellite data, the latter of which have been available only since the 1970s. Together, the modern and historical information provide an accurate long-term view of the state of phytoplankton, something scientists haven't had before now. 
  
 The historical data were based on measurements of ocean clarity called Secchi depth determinations. Developed by an Italian priest around 1865, the measurements were obtained by lowering what looked like a white dinner plate into the ocean until observers lost sight of it. Water murkiness increases or decreases depending on the amount of phytoplankton or, more specifically, the plant's green chlorophyll. The fewer phytoplankton, the clearer the ocean. 
  
 Thus, the scientists were able to convert historical data into specific measures of phytoplankton populations, using it with the modern information to create a virtually seamless timeline of the algae over the last century. 
  
 "They're creating a climate record out of something that really wasn't designed to do this, using sophisticated techniques," said David Siegel, a UC Santa Barbara marine scientist who co-wrote a commentary on the paper. "It fills in a piece of our history, so we're able to tell the story of what has been happening in the last 100 years." 
  
 The scientists noted that the global decline, which was observed in eight of 10 ocean basins, corresponded with a rise in ocean temperatures. 
  
 The scientists suspect that warming near the surface of the ocean makes each ocean layer more distinct, preventing the bottom layer, which is rich in nutrients, from mixing effectively with the upper layers and thus fertilizing the phytoplankton. 
  
 Boyce said he hoped the research would encourage more study of the phytoplankton decline. Looking into the past could help scientists determine how to reverse the drop, he added. 
  
 "This is the tip of the iceberg, in some respects," Boyce said. "Phytoplankton are key to the whole ecosystem. In terms of climate changes, the effect on fisheries, we don't know exactly what these effects will be." 
  
 amina.khan@latimes.com |||||
Output:
Rising sea temperatures are killing phytoplankton, the microscopic organisms that feed the lower rungs of the food chain in the world's oceans and create much of our oxygen, scientists say. Researchers at Dalhousie University in Nova Scotia used a combination of old records and newer satellite images to determine a 40% drop in algae since 1950 and a drop of about 1% annually over the last century. "A global decline of this magnitude? It's quite shocking," said a lead author of the study in Nature. "This is the tip of the iceberg, in some respects," added the researcher. "Phytoplankton are key to the whole ecosystem. In terms of climate changes, the effect on fisheries, we don't know exactly what these effects will be." The Wall Street Journal and the Los Angeles Times have more details.