{"id":6127,"date":"2018-04-18T21:05:41","date_gmt":"2018-04-19T01:05:41","guid":{"rendered":"https:\/\/mote.org\/?p=6127"},"modified":"2024-04-13T21:27:04","modified_gmt":"2024-04-14T01:27:04","slug":"intense-red-tide-can-threaten-stone-crabs-and-more-research-is-needed","status":"publish","type":"post","link":"https:\/\/mote.org\/news\/intense-red-tide-can-threaten-stone-crabs-and-more-research-is-needed\/","title":{"rendered":"Intense red tide can threaten stone crabs, and more research is needed"},"content":{"rendered":"

Florida red tide algae toxins can stress and even kill sublegal stone crabs \u2014 young adults whose claws are growing toward legal harvest size \u2014 according to preliminary research results published recently in the scientific journal Marine Environmental Research<\/em>, indicating a strong need for continued studies.<\/p>\n

Mote Marine Laboratory scientists led the project in collaboration with the Florida Fish and Wildlife Conservation Commission\u2019s Fish and Wildlife Research Institute (FWRI). The study was inspired in part by questions from stone crab fishermen.<\/p>\n

\u201cI was at the state\u2019s Commercial Stone Crab Advisory Panel meeting, and some of the fishermen from the Gulf Coast were asking why their traps were relatively empty during six months of red tide,\u201d said Mote Postdoctoral Research Fellow Dr. Phil Gravinese, first author of the study. \u201cAlso, some reported catching crabs that looked lethargic. The scientists present at the meeting didn\u2019t have a clear answer about whether red tide was affecting the crabs, so we designed an initial study to learn more.\u201d<\/p>\n

The stone crab fishery, centered along west Florida, was valued at $31.3 million in the 2016\u201317 season, but since 2000 the average annual commercial harvest has declined by about 25 percent. Mote scientists are investigating multiple potential challenges that might contribute to this decline.<\/p>\n

Scientists know that elevated concentrations, or blooms, of the Florida red tide alga Karenia brevis<\/em> produce toxins that can kill fish and sicken or kill sea turtles and marine mammals. However, red tide impacts remain more mysterious in crabs and other crustaceans. According to FWRI, at least some crustaceans may die during red tide, but it\u2019s unclear whether the killer is red tide toxicity, decreased oxygen related to algal bloom dynamics, or both.<\/p>\n

So far, research suggests that red tide exposure can alter some crustaceans\u2019 feeding behavior and movement.<\/p>\n

Through separate published research<\/a> not focused on red tide, FWRI scientists found that certain stone crab reflexes \u2014 for instance, retracting certain body parts when they are touched \u2014 offer clues to their stress levels and survival odds. These reflexes are in some ways similar to the human knee-jerk reflex checked by doctors. Through this research, FWRI successfully applied a tool called the \u201creflex action mortality predictor\u201d (RAMP) to investigate how often stone crabs survive trapping and handling by fishermen. RAMP gives crabs a number score for reflex impairment, which is used to estimate the crabs\u2019 chance of survival.<\/p>\n

If stone crabs encounter red tide for more than a week, do their reflexes show signs of stress and does their chance of survival decrease?<\/p>\n

Mote scientists and FWRI partners undertook the first study to answer this question. In late 2017, project partners brought 36 stone crabs from New Pass, Sarasota, to Mote\u2019s City Island research campus. They kept 12 crabs in tanks with filtered seawater, 12 in tanks with high levels of toxic K. brevis<\/em>, and 12 in tanks with a low-toxin strain of K. brevis<\/em>. All K. brevis <\/em>was grown in a controlled setting: Mote\u2019s phytoplankton culture laboratory.<\/p>\n

\u201cFor this study, we used concentrations of Karenia brevis<\/em> similar to what would be found along the west coast of Florida during a moderately high bloom,\u201d said Dr. Vince Lovko, Phytoplankton Ecology Program Manager at Mote and a co-author on the study. \u201cIt\u2019s quite possible for stone crabs in this area to encounter concentrations of red tide ranging from \u2018low,\u2019 meaning elevated above the sparse \u2018background\u2019 concentration normally present in the Gulf of Mexico, to levels many times above what was used in this study.\u201d<\/p>\n

All crabs in the study were sublegal \u2014 young adults with claws too small for harvest.<\/p>\n

\u201cSublegal crabs represent the next year\u2019s harvest; what we learn from them is applicable to management of the fishery,\u201d Gravinese said.<\/p>\n

Over nine days, the researchers monitored their sublegal crabs for any decreases in feeding, indicating stress. They also tested the crabs\u2019 reflexes \u2014 retracting an eye stalk or leg, closing the mouth and other movements in response to touch or pressure. They scored any reflex impairment with the RAMP method and used a mathematical model analyzing those reflex scores and other variables (such as crab size) to predict a crab\u2019s survival odds daily.<\/p>\n

Over the full experiment, crabs exposed to toxic red tide had the worst reflex scores and appetite, indicating greatest stress. Crabs exposed to the toxic red tide also experienced the greatest mortality.<\/p>\n

Results, on average, for each treatment group:<\/p>\n