It is also changing in ways almost no one can see.<\/p>\n
Over the past two decades, the bay has grown warmer, saltier and more acidic, according to a new University of Miami study<\/a> that analyzed 20 years of monthly water quality readings. The shifts are real but gradual\u2014too slow for even the divers, anglers and scientists who spend their lives on the water to see directly. \u201cSince I have been here, the bay has been salty,\u201d said Ana Zangroniz, a Florida Sea Grant agent who has worked on the bay since 2017, describing change so incremental it goes unnoticed.\u00a0<\/p>\n What the eye misses, the data captures: a bay sliding steadily from an estuary to something closer to the open ocean, a transition the study\u2019s authors say sea-level rise has made effectively irreversible.\u00a0<\/p>\n The bay\u2019s fish are already registering the shift. Joseph Serafy, a NOAA research fishery biologist who has tracked Biscayne Bay fish communities for two decades, has watched the catch change as the water grows saltier. Snook, seatrout and mullet\u2014species that thrive where fresh and salt water mix\u2014have declined, he said, while fish that tolerate a wide range of salinity, like gray snapper and grunts, hold on. It is the signature of a bay tilting away from its estuarine past: As the brackish conditions vanish, so do the creatures built for them.<\/p>\n Meanwhile, median water temperatures rose half a degree Celsius bay-wide over the two decades the scientists analyzed, and nearly twice that (0.8 degrees Celsius) in the North Bay, the most urbanized and poorly flushed stretch of water.\u00a0<\/p>\n But the slow climb in averages is not what worries Serafy most. It masks a more dangerous trend of sharper, more frequent extremes. Cold snaps, heat waves, stretches of hypersalinity and sudden crashes in oxygen do the real damage, and a warmer, saltier baseline makes each spike more punishing, according to Serafy.<\/p>\n The summer of 2023 showed what that looks like. A marine heat wave drove water temperatures off South Florida to levels never before recorded, including a reading of 101 degrees Fahrenheit in shallow Manatee Bay that may have been the hottest seawater ever measured. The region\u2019s coral reef was bleached from end to end. Warm water holds less oxygen; so does salty water. When both climb at once and seagrass dies back, fish can suffocate, the mechanism behind die-offs that Manatee Bay had seen before.<\/p>\n The pattern traces back, in part, to how South Florida moved its water. A century of canals replaced the sheet flow\u2014the slow, shallow film of freshwater that once spread across the Everglades miles wide instead of rushing through canals\u2014that once seeped into the Biscayne Bay along a broad brackish shoreline with abrupt, pulsed releases that swing salinity up and down. Restoring that gentler, more consistent flow is among the central goals of the multi-billion-dollar Everglades restoration effort.<\/p>\n For the hammerhead sharks, the danger runs through their food. Juvenile great hammerheads depend almost entirely on the bay for their first two years, feeding on a narrow diet of small stingrays and other bottom dwellers, animals that themselves eat the crabs, mollusks and shelled creatures that are most vulnerable to acidifying water.\u00a0<\/p>\n This story is funded by readers like you.<\/p>\n Our nonprofit newsroom provides award-winning climate coverage free of charge and advertising. We rely on donations from readers like you to keep going. Please donate now to support our work.<\/p>\n Donate Now<\/a> <\/p>\n \u201cAcidification has the potential to affect both sharks themselves physiologically and prey species that are important to them,\u201d said Catherine Macdonald, director of the Shark Research and Conservation Program at the University of Miami, whose team documented the nursery. When the base of a food pyramid shrinks, she explained, everything above it must shrink too: \u201cThe shark population has to shrink in response, definitionally, because the energy is not in the system to support them.\u201d<\/p>\n Macdonald\u2019s larger fear is starker. The bay\u2019s hammerheads return to the same waters to give birth; if those waters become unsuitable, an entire genetic lineage could vanish with them. \u201cI really deeply hope that we don\u2019t end up [with] the first nursery that is reported to disappear because of climate change,\u201d she said.<\/p>\n![\"\"](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/06\/BiscayneBayMiamiFL700px.png\"\/)
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