{"id":19717,"date":"2024-01-17T12:42:57","date_gmt":"2024-01-17T17:42:57","guid":{"rendered":"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/?page_id=19039"},"modified":"2024-07-08T15:13:22","modified_gmt":"2024-07-08T19:13:22","slug":"degrees-of-change","status":"publish","type":"post","link":"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/degrees-of-change\/","title":{"rendered":"Degrees of Change: Why Water Temperatures Matter"},"content":{"rendered":"\n\n\n\n\n

Estuaries are transition zones where land meets water, ocean meets rivers, and saltwater meets fresh. They are also \u201cthe nurseries of the sea,\u201d supporting juvenile fishes, crabs, and shrimps as they transition into adulthood by providing marshes, seagrasses, and oyster reefs \u2014 habitats that allow these species to find food and remain safe from predators when young.<\/p>\n\n\n\n

In fact, these habitats shelter many species vital to local ecosystems, recreational enjoyment, and commerce. According to information from the Albemarle-Pamlico National Estuary Partnership (APNEP)<\/a><\/span>, estuarine waters are a habitat for 75% of America\u2019s commercial fish catch and 80 to 90% of its recreational catch.<\/p>\n\n\n\n

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APNEP Watershed Map. Credit: Tim Ellis\/APNEP.<\/figcaption><\/figure>\n\n\n\n

Climate change and shifting water temperatures are among the most pressing considerations for ecosystem resiliency, and estuaries are no exception. Because of this, the lack of analysis of long-term data for North Carolina\u2019s estuarine temperatures surprised researchers who are spearheading a seminal Sea Grant project.<\/p>\n\n\n\n

\u201cThere\u2019s just this gigantic hole, which is concerning,\u201d says Joel Fodrie, an estuarine ecologist from the University of North Carolina at Chapel Hill\u2019s Institute of Marine Sciences (IMS). \u201cBecause temperature is a fundamental property of these systems.\u201d<\/p>\n\n\n\n

Janet Nye, a quantitative fisheries ecologist at IMS, had previously researched estuarine temperatures in New York. \u201cWhen I arrived here,\u201d she says, \u201cI asked, \u2018What\u2019s the temperature pattern across North Carolina\u2019s diverse estuarine systems?\u2019 And people were like, \u2018We\u2019re not really sure.\u2019\u201d<\/p>\n\n\n\n

Although various institutions and state monitoring programs have<\/em> collected these data, no one has compiled them to determine historical trends. Attempting to manage coastal resources and efforts for conservation without knowing these trends is \u201clike trying to fly a plane blind,\u201d says Fodrie.<\/p>\n\n\n\n

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Attempting to manage coastal resources and efforts for conservation without knowing water temperature trends is \u201clike trying to fly a plane blind,\u201d says Joel Fodrie (here). Credit: IMS.<\/figcaption><\/figure>\n\n\n\n

Fodrie and Nye\u2019s research will illuminate how multiple factors influence water temperatures \u2014 and the implications are complex. Temperatures that are detrimental to some species could welcome others, and as species dynamics shift, long-term effects are uncertain.<\/p>\n\n\n\n

Predicting temperature changes is a challenge. It may seem intuitive that estuaries would heat up faster, given their smaller volumes in comparison with open ocean waters, but this isn\u2019t always the case.<\/p>\n\n\n\n

\u201cEstuaries are relatively shallow,\u201d says Camryn Blawas, a graduate student in the Department of Earth, Marine, and Environmental Sciences at UNC-CH. \u201cBut they have a lot of interaction with the atmosphere and the air, as well as oceanic and riverine influence.\u201d<\/p>\n\n\n\n

Additionally, increased dredging, new inlet formation from hurricanes, and rising seas can drive water temperature change.<\/p>\n\n\n\n

\u201cAll of those things are increasing how much ocean water makes it into the estuary every tidal cycle,\u201d says Fodrie.<\/p>\n\n\n\n

Furthermore, different locations might not experience these factors equally, meaning that temperature change may vary.<\/p>\n\n\n\n

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The Labrador Current and the southern Gulf Stream meet off the coast of North Carolina, further complicating the potential effects of new temperature patterns. Credit: IMS.<\/figcaption><\/figure>\n\n\n\n

Degrees of Difference <\/strong><\/h2>\n\n\n\n

\u201cWe\u2019re seeing this signal of increasing temperature in certain places up and down the coast,\u201d says Blawas. \u201cWe\u2019re not seeing uniform warming, but on average, we\u2019re seeing a small amount of temperature increase per year.\u201d<\/p>\n\n\n\n

These small increases, generally 2\u00ba F to 4\u00ba F over a 20-year period, significantly affect the ecosystem. \u201cThat\u2019s actually a night-and-day difference for some processes and critters,\u201d says Fodrie. \u201cA one-degree change on average, or during a key part of the year \u2014 that\u2019s not trivial.\u201d<\/p>\n\n\n\n

In addition, the water originating from the Labrador Current and the southern Gulf Stream meet off the coast of North Carolina, further complicating the potential effects of new temperature patterns.<\/p>\n\n\n\n

\u201cWe have warm water that arises from the south, and cooler water that comes from the north. So we\u2019re in a transition zone,\u201d Fodrie explains. \u201cA lot of the critters that we see, to some extent, are near their temperature range limits.\u201d<\/p>\n\n\n\n

Fisheries are particularly vulnerable to these limits. \u201cIn cold-blooded organisms, the temperature of their bodies is the same as the temperature of the water around them,\u201d says Nye. \u201cThey\u2019re strongly impacted, perhaps more so than a mammal like you and me that can kind of control our body temperature.\u201d<\/p>\n\n\n\n

This inability to moderate body temperature means that fishes will follow the waters, moving along with the temperature changes.<\/p>\n\n\n\n

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\u201cIn cold-blooded organisms, the temperature of their bodies is the same as the temperature of the water around them,\u201d says Janet Nye (here). \u201cThey\u2019re strongly impacted, perhaps more so than a mammal like you and me that can kind of control our body temperature.\u201d Credit: IMS.<\/figcaption><\/figure>\n\n\n\n

Teasing out Temperature<\/h2>\n\n\n\n

Figuring out how shifting water temperatures drive change is deeply complex.<\/p>\n\n\n\n

\u201cIs it the range of temperature? Is it how variable temperature is? Is it the fall temperature? Is it the winter temperature?\u201d asks Fodrie. \u201cIt\u2019s difficult to nail down, but it may not be the summertime temperatures, when the water\u2019s hottest.\u201d<\/p>\n\n\n\n

Higher temperatures might be ideal or harmful, depending on the species and season. Warmer winters may mean that some species \u2014 those historically found farther south \u2014 stay longer on North Carolina\u2019s coast, and some might be more tolerant of a certain number of days outside their temperature threshold than others.<\/p>\n\n\n\n

That\u2019s why the team collected data on temperature changes throughout the year. Studying winter temperatures to understand warming waters might seem counterintuitive, but these temperatures influence the migration of species.<\/p>\n\n\n\n

Although rising summer temperatures might not significantly affect fishes accustomed to warmer waters, increasing winter temperatures could prevent some wintering species from visiting while also inviting some species northward up the coast.<\/p>\n\n\n\n

\u201cWinter temperatures are really the thing that has prevented organisms from moving northward before,\u201d says Nye. \u201cBut now winter isn\u2019t coming \u2014 or at least it\u2019s not as cold.\u201d<\/p>\n\n\n\n

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Spinner sharks (here) pass by the NC coast on a different schedule than they used to follow. Credit: FWC Fish and Wildlife Research Institute.<\/figcaption><\/figure>\n\n\n\n

Species on the Move<\/h2>\n\n\n\n

Stone crabs, croaker, white shrimp, and bonnethead sharks have been migrating farther north, following the warmer waters.<\/p>\n\n\n\n

Others, such as spinner and dusky sharks, now pass the coast at different times. Instead of May and August, they travel past in April and September. \u201cThere\u2019s this widening of that period when they\u2019re passing by,\u201d says Fodrie. \u201cThe temperatures are really what they\u2019re following.\u201d<\/p>\n\n\n\n

This means that warming waters may lead to the introduction of new species, an abundance of existing species, or fishes remaining in our waters longer. For example, fish such as the spotted sea trout, which are susceptible to colder temperatures<\/a><\/span>, could experience fewer instances of \u201cwinterkill\u201d \u2014 mass die-offs due to winter conditions.<\/p>\n\n\n\n

Although new species in North Carolina waters could even prove beneficial for the state\u2019s fishing economy, it is unclear how this would affect the food web long-term.<\/p>\n\n\n\n

In particular, warmer winter waters could lead to the loss of some species that are more tolerant of cooler waters<\/a>,<\/span> like summer flounder, smooth dogfish, striped bass, and Atlantic croaker. While anglers previously have found these species in North Carolina during the cooler months, these fishes have shifted farther north as temperatures have increased. In the future, North Carolina fishers will need to travel longer distances to catch these fish \u2014 or shift to other species.<\/p>\n\n\n\n

Furthermore, increasing temperatures could mean losing crucial vegetation for some of our fisheries.<\/p>\n\n\n\n

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Increasing temperatures could mean losing seagrass (here), vegetation that NC fisheries require. Credit: IMS.<\/figcaption><\/figure>\n\n\n\n

In Hot Water \u2014 Sweltering Seagrasses<\/h2>\n\n\n\n

\u201cWe are a very seagrass-rich state,\u201d says Fodrie. \u201cWe have more seagrass than all the other East Coast states combined, except Florida.\u201d<\/p>\n\n\n\n

Seagrasses support water quality, providing shelter for fish, helping minimize erosion, controlling the transportation of sediment, and mitigating the effects of climate change by capturing carbon. But temperature change threatens these benefits, because it can negatively impact salinity, sea-level rise, and oxygen levels in the water \u2014 which is problematic for the seagrasses and the species they support, such as red drum, blue crabs, oysters, flounder, shrimp, and grouper.<\/p>\n\n\n\n

\u201cSeagrasses can\u2019t move,\u201d says Nye, \u201cbut the fish are definitely moving.\u201d<\/p>\n\n\n\n

North Carolina represents the northern limit for shoal grass and the southern limit for eelgrass,<\/a><\/span> the latter of which is more sensitive to warmer temperatures. Eelgrass has upper-temperature limits of 77\u00ba F, and shoal grass 86\u00ba F. Although shoal grass might be more resilient, there are concerns that North Carolina will lose most eelgrass by 2050 due to temperature increases.<\/p>\n\n\n\n

The Economic Impacts of Changes in Water Temperature<\/h2>\n\n\n\n

Changes in estuary temperatures and the implications of those changes could be slow and take decades. These subtle changes can be particularly pernicious, threatening ecosystems that provide recreational and commercial benefits.<\/p>\n\n\n\n

But warming waters could also have potential economic advantages, at least in the short term. Some species, like stone crabs, croaker, and white shrimp, have become more plentiful off North Carolina\u2019s coast.<\/p>\n\n\n\n

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Changes in estuary temperatures and the implications of those changes could threaten ecosystems that provide recreational and commercial benefits. Credit: IMS.<\/figcaption><\/figure>\n\n\n\n

A few decades ago, the northern limit for stone crabs was Morehead City, but now their range extends to Hatteras. \u201cEvery year they creep perhaps another mile farther north,\u201d explains Fodrie, \u201cand the center of the croaker fishery has gone from near the southern border of the state to near the northern.\u201d<\/p>\n\n\n\n

White shrimp can now inhabit the Chesapeake and are more abundant for a longer portion of the year in North Carolina waters than in decades past. This means more shrimp for our state\u2019s commercial fishers, but the economic advantages could prove short-lived. Increases in the numbers of these species could affect the viability of other species we depend on.<\/p>\n\n\n\n

Fodrie and Nye\u2019s team hopes that collecting temperature data and assessing temperature patterns will bring answers to such questions.<\/p>\n\n\n\n

Charting New Waters<\/h2>\n\n\n\n

The researchers will share their findings at the conclusion of their project, citing interest from the organizations that have shared data, such as the North Carolina Division of Marine Fisheries, UNC Shark Survey, National Estuarine Research Reserves, and the National Oceanic and Atmospheric Administration.<\/p>\n\n\n\n

They also plan to release an interactive visualization tool on the North Carolina Sea Grant website, where visitors can track changes through the decades.<\/p>\n\n\n\n

\u201cThere was a lot of interest as I was asking for permission to use certain data sets,\u201d Blawas recalls. \u201cPeople were saying, \u2018Please let me know what you find out, because we\u2019ve had these data for so long,\u2019 and they want to know what trends we see in the temperature.\u201d<\/p>\n\n\n\n

Nye says their project is an effort to preserve what people love.<\/p>\n\n\n\n

\u201cThis project was really to wrangle the data, see what\u2019s happening with temperature, and see if we can give people a sense for how it may affect the species and organisms they care about. People love red drum and seagrasses. They feel a connection with that part of the marine environment.\u201d<\/p>\n\n\n\n

MORE<\/strong><\/p>\n\n\n\n

Coastwatch<\/em> on<\/span> climate change<\/a><\/span>, the blue economy<\/a><\/span>, fishing<\/a><\/span>, sharks<\/a><\/span>, and other species<\/a><\/span>.<\/span><\/p>\n\n\n\n

Marlo Chapman<\/strong> is a science communication intern with North Carolina Sea Grant and a graduate student at NC State University studying rhetoric and composition.<\/p>\n\n\n\n