Climate change is affecting salmon migration. Coral die-offs off Australia in the summer of 2024 are linked to rising Pacific temperatures. The world’s largest and most devastating sponge die-off has been recorded off New Zealand. Global warming will reduce the survival rate of shark embryos during spawning by up to eight times. The University of California Institute of Marine Science, along with a large team from other institutions, has created early warning systems that predict where marine heat waves (MHWS) will occur.
Climate change is affecting salmon migration. Several species of salmon are currently endangered, the most famous being Atlantic salmon, pink salmon, chum salmon, coho salmon, omul and others. These fish are considered an important source of food for many animals and people. They also play a significant role in the ecosystems they inhabit, providing nutrients and influencing biodiversity.
There are many factors that contribute to the decline of salmon, but the main ones are habitat loss and climate change. Rising water temperatures are having a particularly strong impact on their spawning season. Salmon are anadromous fish, meaning they are born and mature in rivers and streams before migrating to the ocean to spend the rest of their lives. When it’s time to spawn, salmon swim back from the ocean to their birthplace. This is a dangerous journey, as the fish swim thousands of kilometers to their spawning grounds. The already difficult return to their “birthplace” is made impossible by the oxygen stress of warmer waters. In addition, some groups of salmon have begun migrating earlier than others. These factors could have negative consequences if salmon do not adapt to future changes in the ocean.
A team of North American researchers has collected the world’s largest data set on juvenile Pacific salmon migration over 20 years, covering 66 populations of 6 species. The analysis found that the timing of juvenile migration for some species has changed significantly over the past 70 years. Pink and chum salmon in particular have shown the most rapid change in migration timing, with migration times changing by 7 days per decade (almost a week earlier every 10 years). Some salmon groups began their journey earlier and others later, despite the same level of warming. When salmon migration times coincide with food availability, this can have a positive effect on the number of adults returning to their “maternity ward.” However, the researchers are concerned that salmon are not adapting to changes in the ocean (primarily rising temperatures), which could lead to even greater changes under future climate change.
Scientists say one of the key successes of this study is the combination of scientists and datasets. The work also shows the importance of long-term datasets, which help predict which species or populations may be most vulnerable in the future. The study is published in the journal Nature Ecology & Evolution, reports the information and service portal InScience.News.
The death of corals off the coast of Australia in the summer of 2024 is associated with rising water temperatures in the Pacific Ocean. Scientists studied samples of corals that have grown on the Great Barrier Reef since the early 17th century.
Australian oceanographers have concluded that the mass death of coral polyps on the Great Barrier Reef over the past eight years was linked to record-high water surface temperatures in the Pacific Ocean over the past four centuries, the University of Wollongong press service reported.
“The ocean temperatures we have recorded are the highest they have been in four centuries. The Great Barrier Reef is on the brink of collapse due to human-induced global warming, and the survival of its inhabitants, including the corals that have lived here for centuries, is now under great threat,” said Helen MacGregor, a professor at the University of Wollongong, as quoted by the university’s press service.
Scientists made the discovery while studying samples of corals that have grown on Australia’s Great Barrier Reef since the early 17th century. They used the fossilized shells of these ancient polyps to reconstruct how surface temperatures in the Pacific Ocean have changed, as well as other parameters.
This information was possible because the ratio of strontium and calcium atoms, as well as the proportion of “heavy” oxygen-18 in the protective shells of corals, depends strongly on how warm the water was in which these polyps grew. This allows us to use the shells of long-lived madrepore corals of the genus Porites to study how environmental conditions changed during the life of these polyps.
Thus, scientists analyzed the composition of annual layers in the shells of the oldest and largest corals from the Great Barrier Reef, which allowed them to track how temperatures in the Pacific Ocean have changed from 1620 to the present day. These measurements showed that the temperature in recent decades has been about 1.5 degrees higher than at the beginning of the 17th century, with the highest temperatures recorded in 2004, 2016, 2017, 2020, 2022 and 2024.
During these same seasons, as the researchers note, there were several episodes of mass death of corals of the Great Barrier Reef, which indicates a direct link between warming waters and these incidents. According to the researchers, water temperatures in the Pacific Ocean in 2024 are especially high: they are almost three degrees higher than in the coldest years in the mid-17th century. These temperature records have already affected the condition of the corals and led to the destruction of a large number of polyp colonies, the oceanographers concluded.
Scientists believe that corals are among the most vulnerable creatures to global warming. Researchers estimate that about 20% of coral reefs and other polyp colonies, including Australia’s Great Barrier Reef, could disappear completely this century. Their existence is threatened by the accumulation of carbon dioxide in the water, rising ocean surface temperatures, new infections, and other factors.
Tens of millions of sea sponges have died due to heat waves. The world’s largest and most devastating die-off of sea sponges has been recorded off the coast of New Zealand, with tens of millions of the invertebrates killed, the New Zealand Herald reports.
During the 2022 heatwave in Fiordland (southwest of the country), more than 90% of Cymbastela lamellata sponges bleached. They are one of the most common species in the region and play a crucial role in the ecosystem because they provide habitat and recycle nutrients that support marine life. Scientists say the die-off was not just the largest in the world, but the largest on record.
The 2022 sponge bleaching event affected 50 million individuals and halved the population, according to researchers. It was blamed on a severe marine heatwave that lasted 259 days and raised water temperatures by 4.4ºC above average. Drought and unusually low rainfall that coincided with the heatwave may have allowed more light to penetrate Fiordland’s normally dark waters, causing the sponges to bleach and die.
Global warming will reduce the survival rate of shark embryos during spawning by almost eight times. Scientists have come to this conclusion as part of their observations of the growth of a large number of European catshark embryos.
European biologists have concluded that further increases in global temperatures will reduce the probability of successful shark spawning from 82% to 11% if average global temperatures increase by about four degrees Celsius by the end of the century, the press service of the Society for Experimental Biology (SEB) reported.
“Shark embryos are particularly vulnerable to changing environmental conditions. Their survival rate is a critical factor in determining the fate of these slow-living fish populations. We were therefore very surprised to find that only 11% of the embryos would survive under the worst-case climate scenario,” said Noémie Coulon, a researcher at the Laboratory of Aquatic Life and Ecosystems, as quoted by the SEB press service.
Scientists came to this conclusion while observing the growth of a large number of embryos of European catsharks, whose representatives are widely found in the Atlantic off the coast of Europe and Africa, as well as in the Mediterranean Sea. Like many other sharks, these sea predators lay so-called “mermaid’s purses” – eggs enclosed in hard horny capsules. The embryos of these fish spend from 5 to 11 months inside such structures, which makes them especially sensitive to changes in environmental conditions.
Guided by such considerations, European biologists have observed how water temperature, its acid-base balance and other environmental conditions affect the probability of embryo survival, its growth rate and the first months of life of young sharks after they emerge from the “mermaid’s purse”. The researchers used this information to predict how further changes in the Earth’s climate will affect the growth of young sharks.
Their calculations showed that with a decrease in greenhouse gas emissions, as well as a moderate increase in global temperatures (2.7 degrees Celsius by 2100), the probability of successful shark spawning will be 81-83%, which is close to current values. If average global temperatures increase by 4.4 degrees Celsius, then only 11% of shark fry will survive until they are ready to leave the “mermaid’s purse.”
The researchers say the drop in spawning success is due to the fact that high temperatures and changes in seawater acidity prevent the embryos from absorbing yolk, slowing their growth and preventing the formation of internal gills. Understanding this, biologists hope, will help develop measures to protect shark populations from sharp declines as a result of global warming.
At the University of California, the Institute of Marine Science, together with a large team from other institutions, we have created early warning systems that predict the location of marine heat waves (MHWS). The system was built by analyzing four large waves observed in the North Pacific Ocean (2014, 2015, 2019, 2020) and their impact on the spatial distribution of 14 top marine predators, covering several major groups: seabirds, mammals, turtles, tuna, and sharks.
The impact of MHWS on most of these species has not been studied before. Marine life often shifts its range due to heat, and the new system can predict their migration routes. This will protect animals from accidental or deliberate destruction. For example, in 2016, a heat wave along the California coast brought humpback whales there. They fed on anchovies, which had multiplied in the warm conditions. Then crab fishing season opened in the same waters; this caused many whales to become entangled in crab pot lines.
During the course of their research, the team discovered that it was not only water temperature that influenced the animals’ behavior; oxygen content in the surface layer, wind conditions, and the circulation of water currents themselves were also important factors in migratory behavior. With these parameters in place, the forecasts turned out to be much more accurate.
The scientists comment that the responses of marine species to heat waves vary greatly, but are generally predictable: the models have proven themselves thanks to extensive validation in space, time and taking into account new factors. As a result, in their opinion, the forecasts can be further adapted to the needs of the fisheries industry. An early warning system will notify about approaching heat waves and transmit this data to interested organizations, which is especially important for saving endangered animal species.
