ST. PETERSBURG — The number of manatee deaths in Florida this year has already exceeded the total for all of 2017. Blame Red Tide, which is suspected of killing more than 100 of them.So far, 554 manatees have died in 2018, with four months left to go. Last year’s total was 538.As of Aug. 18, the most recent date for the running total, the Red Tide bloom had been verified as the cause of death for 29 manatees, and was suspected of killing another 74. That makes a total of 103 that appear to have fallen prey to the lingering toxic algae. Most of the suspected or confirmed Red Tide victims were found dead in Charlotte, Lee and Collier counties, but one recently turned up floating in Terra Ceia Bay in Manatee County.RELATED: Red Tide: A primer. "We find that the primary route is through ingestion of seagrass that has the toxins on it," Dr. Martine de Wit of the state’s marine mammal pathology laboratory in St. Petersburg said Monday.Other factors are at play as well, De Wit said. A big cold snap early in the year proved deadly for manatees, and the number of manatees killed by speeding boats is above the five-year average, she said. The number killed by boats so far in 2018 is 81.Other variables, she said, include population size and location. For each of the past four years, biologists have counted more than 6,000 manatees swimming in Florida’s waterways.RELATED: The manatee population. "Numbers like these also have to be taken into context with the possibly increasing size of the manatee population and local abundance variations from year to year," she explained. "If more manatees hang out in more urban areas, one can assume that more carcasses will be found as opposed to years where they may get unnoticed."Save the Manatee Club president Pat Rose said this is part of a pattern that his group predicted last year when the U.S. Fish and Wildlife Service decided manatees should not be listed as endangered any more."The Fish and Wildlife Service said all this was under control, and it’s being shown that it’s not under control," Rose said.He predicted that it would be "really hard" for manatees to recover from what Red Tide has been doing to them this year."Florida’s manatees have no defense against this ecological disaster," said Jeff Ruch, executive director of the environmental group Public Employees for Environmental Responsibility, which blames Gov. Rick Scott for weakening the state’s water quality requirements and monitoring. Scott blames Sen. Bill Nelson, his Democratic rival in the Senate race, for not doing something before now to stop the recurring algae bloom.Ever since Jacques Cousteau featured them in a 1972 television documentary called Forgotten Mermaids, manatees have been a popular symbol of Florida’s natural bounty, not to mention the centerpiece of several tourist attractions and a mascot for many schools.As big as a couch and shaped like a yam with flippers, the manatee is a placid vegetarian with no natural enemies except humans. In 2016, boaters killed 106 of them, the first year in which the number topped 100, and last year they hit another 106.Low tolerance for cold water and a susceptibility to Red Tide toxins have also proven fatal to the state’s official marine mammal. The highest manatee mortality number for a single year is 830, a record set in 2013 amid a cold snap and a wave of Red Tide poisonings, as well as a mysterious ailment in manatees found in the Indian River Lagoon.Red Tide algae blooms and speeding boaters were major causes for last year’s total of 538 deaths.RELATED: Manatee deaths top 500 in 2017. Nobody knows what causes the scattered patches of microscopic Red Tide algae that float in the Gulf of Mexico all year to suddenly multiply by the millions and turn the water the color of rust. The blooms start 10 to 40 miles offshore, and then winds and currents move them toward shore. There they can be fueled by fertilizer in stormwater runoff and waste from leaking sewage lines and septic tanks.The one going on now has been hanging around offshore since November, killing not just manatees but also hundreds of sea turtles and thousands of fish.Last year, the U.S. Fish and Wildlife Service decided to drop manatees from the endangered list and reclassify them as merely threatened, despite the advice of manatee biologists."While it is not out of the woods, we believe the manatee is no longer on the brink of extinction," Larry Williams, head of the agency’s Vero Beach office, said at the time.Nearly 87,000 comments and petition signatures opposing the change were submitted during the 90-day public comment process. Only 72 people said they were in favor of lowering the protection level for manatees.Contact Craig Pittman at [email protected] Follow @craigtimes.