 Fish display an amazing array of colors. Some are blacker than charcoal, others have rainbow-colored stripes, and still others have a mottled appearance to help them blend into the background. And the variety extends to fish eyes. They can feature colorful specks, dark stripes, and irises from red to green. Some even shine in the dark.The eyes of most fish are pretty dull -- a black pupil surrounded by a white iris. But there are times when a different color scheme can be helpful. It might confuse predators, for example. They wouldn’t know which direction a potential prey was heading, so the prey might have an extra instant to escape. Or the color might help a fish blend into the bottom, making it easier to catch a meal.Some fish have stripes along the head or body that continue across the eye. That includes some blennies -- a red stripe from head to tail extends through both the iris and the pupil.Other fish have spots of color in their eyes. The striped mullet, for example, has a bright yellow splotch in its iris, while specks of blue-green decorate the pupils of the balloonfish.And still other fish have colorful irises. They’re usually in shades of yellow, orange, or red. The eyes of the striped burrfish, though, are bright green. So are the eyes of the greeneye. Its eyes look green even when the little fish is thousands of feet deep. That’s because the eyes produce their own light -- helping the greeneye keep a sharp eye on the ocean depths.

Science and the Sea podcast

Colorful Eyes

 The recent saga of life on Ascension Island is a series of miscalculations. When the island was first settled, in 1815, it was a haven for millions of birds. But colonists also brought rats, which overran the island. So the settlers brought in cats to eat the rats -- which they did. But the rats and cats also ate the birds and their eggs. That decimated the birds, driving at least one species to extinction. But the cats were eliminated a decade ago, so the birds are coming back.Ascension is the tip of a two-mile-high volcano. The small desert island is in the Atlantic Ocean, just south of the equator. It’s a thousand miles from Africa, and 1400 miles from South America. It’s home to about 800 people. It’s also home to hundreds of thousands of birds, including seabirds. They nest on cliffs at the rim of the island, or on tiny Boatswain Bird Island, just offshore. Many of the birds spend most of their time at sea, and visit the islands only to breed.One of the most common seabirds is the sooty tern. It’s also known as the “wide-awake” bird because it keeps people awake -- it never shuts up. The local airport is named Wideawake Field because of it.Another resident is the Ascension frigatebird. It’s large but lightweight, so it can soar for months without ever touching down. It’s not especially pleasant, though -- it sometimes feeds by forcing other birds to throw up. Still, it’s a part of the continuing saga of life on this remote Atlantic island.

Birds Galore

 You might not think that the way an iceberg melts would matter much -- but it does. As an iceberg melts, the change in ocean temperature and salinity can alter currents and have other effects. So scientists need to know how and how quickly icebergs melt to make sure their ideas of how the oceans work are accurate.Researchers in Australia recently contributed to that effort with experiments and mathematical models. Their work showed that icebergs don’t all melt the same way.They tested blocks of ice of different sizes and shapes in the laboratory. They then compared the results to their models, and found that real icebergs should melt in the same way as the ones in the lab.Among other findings, the researchers discovered that small icebergs should melt at a faster rate than big ones. In addition, a skinny iceberg with a lot of ice below the ocean surface should melt faster than a wide berg with less of its total mass below the surface. And turbulence below and around an iceberg as it plows through the water can make it melt up to 50 percent faster.All of this is important because more icebergs are breaking off glaciers and moving into the oceans. As they melt, they’re contributing a huge amount of freshwater to the oceans. But the time it takes for an iceberg to melt can range from months to years to decades. So having a better handle on how icebergs melt can help scientists make more accurate forecasts of how the oceans could change in the years ahead.

Melting Bergs

 The longfin damselfish is a feisty little farmer. It’s only a few inches long, but it will attack just about anything that enters its territory -- including people. Yet some damselfish in the Caribbean actually protect a tiny shrimp on their farms. That’s because the shrimps’ waste helps fertilize the farm -- which may make the damselfish stronger.The “farms” are patches of algae that the longfin damselfish protect. Scientists had noted that some of the farms contain dense blobs of mysid shrimp. The tiny crustaceans would seem to be a good food source for the damselfish. Instead, though, the fish leave the shrimp alone.To find out what was going on, marine biologists studied one such farm, off the coast of Belize. They found that the damselfish had “domesticated” the shrimp -- just as people have domesticated dogs. The shrimp provide a service, while the damselfish keep the shrimp safe. It’s the first example of such a relationship seen in the ocean.Scientists found that organisms that eat the shrimp tended to leave them alone if they were on the damselfish farms -- or if damselfish were around. They also found that damselfish on farms with mysid shrimp were healthier than those on farms without them. The nutrients provided by the shrimp may make the farms more diverse -- they produce more brown algae, which helps grow the turf algae that damselfish eat.Regardless of the cause, though, it seems clear that this fish-and-shrimp combo has a good thing going.

Fish and Shrimp Combo

 The South Padre Island Convention Centre has hosted conferences, plays, concerts, and even basketball games. In February, though, it hosted an event like no other: a sea turtle rescue.A major winter storm chilled waters along the Texas coast. Sea turtles were stunned by water temperatures that plunged into the 40s and even 30s. Volunteers gathered about 13,000 turtles from the beaches and took them to rescue centers all along the coast, including the University of Texas Marine Science Institute. The facilities were overwhelmed, so they needed backup -- including the convention center, plus a naval air station in Corpus Christi.The storm drew national headlines for its effects on the human population -- lost power and water, dangerous roads, and high energy costs. But it took a toll on other life as well.Fish were killed all along the coast, especially the southern half. Official estimates said that almost four million fish were lost. Most of those were non-game fish, including a million hardhead catfish and more than a million silver perch. Major game-fish losses included spotted seatrout and red and black drum. Texas changed some regulations to help some of those species, but it could take years for them to recover.The sea turtles -- mostly green turtles -- fared a little better. Rescue organizations thawed them out and released them in warmer, deeper waters in the Gulf of Mexico. Even so, thousands of turtles died -- victims of a massive winter storm.

Deep Freeze

 For the humpback whales of Glacier Bay, Alaska, the early months of the COVID-19 outbreak may have been a blessing. Travel bans and cancelled cruises left the bay much quieter, especially during the summer tourist season. That meant the whales didn’t have to “talk” as loudly or simplify their messages as much as they do during normal summers.In fact, for several months the oceans got much quieter. As economies closed down, the number of cargo ships went down, too. Scientists monitored what was going on -- both at the shipping noise and at how marine creatures responded.Whales use sound to navigate, locate prey, and do much more. But noise created by people can overpower their calls. That could make it harder for whales and other creatures to get by.The COVID cutbacks offer a chance to see just how dramatic the impact is. Scientists recorded noise levels and animal behavior during the outbreak. When the outbreak is over, they’ll compare the observations to those made both before and after the COVID days. They’ve also taken blood samples from whales, and will take more when conditions return to normal, to compare the amount of stress hormones the creatures produce under different noise levels.Scientists have some early results. In Glacier Bay, human-generated noise was only half as intense in June of 2020 as in the previous year. And the whales spread out into regions of the bay they usually avoid -- waters calmed by a human pandemic.

Quieter Seas

 The smallest fish in the oceans grow fast and die young. And that may keep coral reefs going. The little guys are known as cryptobenthic fish -- crypto for “hidden,” and benthic for “ocean floor.” They’re no more than a couple of inches long, and most of them are much smaller. So that allows them to “hide” among the corals.But a study a couple of years ago showed that they don’t stay hidden from other organisms on the reef -- they may account for more than half of the food consumed by other fish. The study examined reefs in Australia, Belize, and the islands of French Polynesia, in the south-central Pacific Ocean. Researchers calculated the numbers of both adult fish and larvae -- fish that are newly hatched. They also considered mathematical models of fish populations on the reefs.The study found that the little guys grow quickly. And they don’t go far from the reefs where they’re born -- about two-thirds of the larvae within a few miles of a reef are cryptobenthics. That provides a huge food supply for larger fish. And the bigger fish take advantage. They eat up to 70 percent of the cryptobenthic fish on the reef every week. So there’s a huge turnover in the population -- 700 percent per year.So even though the fish are tiny, they add up. The study found that they account for almost 60 percent of the total amount of food consumed by other fish on the reef. That keeps the reef system busy and productive -- powered by the smallest fish in the oceans.

Reef Snacks

 Most islands don’t move around much. But for more than two decades, scientists and others operated from one that did. Known as T-3, the kidney-shaped island was seven miles long. It drifted close to the north pole. And eventually, it melted away. That’s because the island was made of ice -- it was a giant iceberg.T-3 was discovered after World War II, when the military was sending airplanes across the Arctic Ocean to keep an eye on the Soviet Union. In 1952, the Pentagon built a station on the island to record the weather.Over the next couple of decades, several more ice islands were used as floating outposts as well. But T-3 was the busiest. Bases there came and went. But the last one didn’t shut down until 1974.Scientists used T-3 and the other ice islands to study the Arctic. They collected organisms from the water. They used sonar and other techniques to map the bottom of the ocean. And they plotted the layers of water within the ocean. And scientists are still using those results. A study in 2019, for example, analyzed readings of the temperature of the ocean floor.The T-3 researchers also plotted ocean currents. T-3 drifted thousands of miles in the Beaufort Gyre, a current that loops around northern Alaska, Canada, and Greenland, and up to the north pole. In the early 1980s, though, T-3 was carried into the northern Atlantic, where it melted -- ending the travels of this mobile island.

Ice Islands

 One of the most endangered groups of whales in the world hangs out in the northeastern corner of the Gulf of Mexico. It’s down to fewer than a hundred members. And although it’s protected as an endangered species, challenges in the Gulf could make it hard for the whale to recover.The Gulf of Mexico Bryde’s whale stretches about 40 feet long and weighs about 30 tons. It’s most often seen off the Florida Panhandle, near a small gash in the ocean floor known as DeSoto Canyon. It’s usually seen alone or in pairs, and generally stays at depths of a couple of hundred to more than a thousand feet. It uses a comb-like structure known as baleen to filter tiny organisms from the water, probably near the bottom.It’s related to other Bryde’s whales, which are found in fairly large numbers around the world. They’re named for Johan Bryde, a Norwegian who established the first whaling station in South Africa.The Gulf Bryde’s whale was declared an endangered species in 2019. Biologists estimate the group lost about 17 percent of its members as a result of the Deepwater Horizon oil spill, which fouled half of its range.Future spills are among the many challenges facing the whales. So are habitat destruction, water pollution, and collisions with boats. And propellers, sonar, and other human-generated noise can scramble a whale’s internal navigation, causing strandings and other problems. So the whale faces a difficult future in its little corner of the Gulf of Mexico.

Bryde’s Whales

 One of the adages of modern science is that if a butterfly in China flaps its wings, it might lead to a hurricane weeks later in the Atlantic Ocean. There’s no way to prove or disprove that idea. But there does seem to be some evidence of a connection going the other direction: Warmer water in the northwestern Atlantic may be one factor in creating heatwaves over China, Korea, and Japan.Eastern Asia has undergone several deadly heatwaves in recent years. A month-long hot spell in 2018 broke a century-old record in Korea, with temperatures reaching 105 degrees.Several factors combine to create the hot weather, including high pressure over the Himalayas and the Pacific Ocean, and warmer waters in the northern Pacific. But researchers have identified a link with the North Atlantic as well.Earlier studies had already found some connections. Long-term changes in surface water temperatures in the North Atlantic and the northwestern Pacific seem to be linked, for example. And changes in the North Atlantic can influence Asian typhoons.The recent research looked at 40 years of Asian climate records. Scientists compared those numbers to sea-surface temperatures in the northwestern Atlantic. They found a link. They report that warmer water in that part of the Atlantic can create a “wave” in the atmosphere. It connects with global circulation patterns. As it reaches eastern Asia, the wave helps make conditions hotter and dryer -- contributing to deadly heatwaves.

Making Connections

 As its name implies, the icefish is cold-blooded. But it’s also clear-blooded. It’s the only known vertebrate in the world that doesn’t have red blood cells -- or the protein that gives those cells their color.The first icefish was discovered in the 1920s in the Southern Ocean, which surrounds Antarctica. It was called the white crocodile icefish. It has a see-through body -- you can even see its brain -- plus big eyes and a long snout with a lot of teeth, like a crocodile.Since then, biologists have identified at least 16 species of icefish. The fish grow to a foot or two in length. They mainly eat other fish -- some up to half their own size.The icefish’s most interesting feature, though, is its transparent blood. It has no hemoglobin -- the red protein that transports oxygen through the bodies of humans and other vertebrates. Without it, the fish’s gills are much less efficient at absorbing oxygen from the water.The icefish can survive without hemoglobin because it’s not very active -- it sits on the bottom and waits for prey to swim by -- and because of its environment. Temperatures in the Southern Ocean hover near freezing, so the water contains more oxygen than warm water.The icefish also has a much bigger heart and bigger blood vessels than other fish of about the same size, so it can circulate the blood faster. And its blood contains proteins that act as an antifreeze. All of those adaptations keep the icefish alive and well in some of the coldest waters on Earth.

Icefish

 No place is safe. Trash and pollution make their way into just about every nook and cranny on Earth -- including the deep oceans. A few years ago, for example, explorers found a plastic bag in the Mariana Trench, the lowest spot on the entire planet. And in 2020, scientists reported that organisms in two ocean trenches contained high levels of mercury -- most of which was produced by human activities.Mercury is pumped into the atmosphere by coal-fired power plants, silver mines, and other facilities. It can waft high into the air, where it can travel thousands of miles before settling to the land or oceans. It’s ingested by microscopic organisms. They convert it to an especially nasty form, known as methyl-mercury, which can cause birth defects and other health problems.In the oceans, larger organisms eat the microscopic ones. So the mercury works its way through the food chain. When the larger organisms die, their remains drop to the bottom.Researchers sampled life from depths of more than six miles in two trenches in the Pacific Ocean -- the Mariana and the Kermadec. And they found that levels of mercury in the sampled animals were similar to those found in fish from closer to the surface, where there should be more mercury. They also found that the mercury came mainly from human activities. That suggests that dead fish carry mercury from near the surface all the way to the bottom. So even the deepest parts of the oceans can’t escape this nasty element.

Deep Threat

 The giant squid is one of the biggest animals in the oceans. A typical adult is 35 or 40 feet long, and some are even bigger. Yet it’s almost never seen. Much of what we know about the creature comes from dead ones that washed up on shore. Only a few have been photographed alive and well in the oceans.In 2018, though, a research team easily detected the giant squid’s presence in the Sea of Japan -- through molecules of its DNA in the water. The technique could help scientists keep tabs on the squid population throughout the world.In fact, eDNA -- “e” for “environmental” -- could help keep tabs on just about all marine life. Every organism sheds bits of DNA -- through its wastes or dead skin cells, for example. Marine scientists could scoop up a bucket of water from anywhere, then test it against a library of genetic “barcodes” for the DNA of just about any creature they could think of -- like a cashier checking out an order of groceries.E-DNA could be used to monitor the populations of fisheries, track endangered species, determine the impacts of oil spills and other environmental problems, and much more. A recent test in the waters off New Jersey found there was a good match between the species caught in nets and those identified through their DNA in the water. And as technology matures, the match is expected to get even better. That will allow scientists to keep their “eyes” on animals throughout the world’s oceans -- even the elusive giant squid.

Keeping Tabs

 Melting glaciers are a big problem. As their water pours into the oceans, it raises the global sea level -- a problem that will get worse in the years ahead. But they could trigger more immediate problems for people who live near them: tsunamis.As our planet warms up, glaciers are getting thinner. And they’re backing away from the coastline, exposing land that might have been covered up for millennia. Such land might be unstable, so it could create a massive landslide. As the rocks and dirt slam into the ocean, they could generate a tsunami that would ripple along the coastline and beyond.Researchers studied that possibility in Prince William Sound in southeastern Alaska. It’s best known as the site of the Exxon Valdez oil spill, in 1989. Today, it’s ringed by several small towns. In non-COVID times, it’s a popular spot for cruise ships and other visitors.A glacier on an inlet known as Barry Arm Fjord has been trickling away for decades. Researchers used satellites to track its retreat, and computer models to simulate what might happen in the years ahead.They found that the exposed slope at the edge of the glacier has slipped by about 400 feet in the last few years. And an earthquake or other big event could cause it to plunge into the sound in seconds -- generating a tsunami. It could overwhelm the settlements on the sound. And it could churn up oil at the bottom of the sound left over from the Exxon Valdez -- just one more possible problem from melting glaciers.

Glacial Tsunami

 Anyone whose quiet afternoon at the beach has been disturbed by loud boats will feel sympathy for the male oyster toadfish. Boats can overwhelm its call to females. And it can get the fish all mixed up as well, causing it to change its call or even clam up for hours.The oyster toadfish isn’t the most sympathetic looking creature in the sea. It’s about a foot long, with a big head, a body covered in mucus and warts, a powerful bite, and spines on its back that are venomous. It lives in shallow bays and estuaries, mainly around oyster reefs. It’s found along the East Coast, mainly from Cape Cod to Florida.When it’s time to mate, the male toadfish builds a nest on the sea bed. When the nest is ready, the fish emits a loud call. It’s called a boatwhistle, although it sounds more like a foghorn.The female swims over the nest of her selected mate and lays her eggs. The male watches over them until they hatch, then keeps an eye on the youngsters for a few weeks more.A recent study, though, found that boats and other human-created sounds may disrupt that cycle. Researchers listened in to the calls of oyster toadfish in a saltwater pond on the coast of Massachusetts. They found that when boats were zipping through the pond, their engines overpowered the toadfish calls. The fish then changed their calls, or stayed quiet. The changes lasted for hours. So loud boats could keep toadfish apart -- perhaps cutting the populations of these ugly little fish.

Noisy Toadfish

The goal of Science and the Sea is to convey an understanding of the sea and its myriad life forms to everyone, so that they, too, can fully appreciate this amazing resource.

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