Icons in trouble

With the increase of tourism and development, habitats are being damaged across the globe. In Florida, loss of habitat and an increase in boat strikes threatens one of the state’s most iconic species: the manatee. How long can it survive human pressures?

Words and photographs by Liam MacLean

When you think of Florida, theme parks, space shuttles and resort-lined beaches may first spring to mind. However, far away from these scenes, the south-eastern part of the state is distinctly characterised by its diverse and complex ecosystems of extensive coastline, wetlands, forests, and unique geological features that are home to Florida’s manatees.

Large, grey, and looking much like a potato, the Florida manatee is one of two subspecies of the West Indian manatee. These docile and gentle creatures are aquatic mammals that are relatively solitary and often travel alone or in small herds. The subspecies spends the cold winter months in the refuge of Florida’s warm water environments in the state’s interior waterways. Every winter, thousands of manatees gather in the constant 22 degrees Celsius water of the Florida springs and south Florida river environments, while avoiding the dropping ocean temperatures.

They sleep at least 12 hours a day in these shallow waters and spend a majority of their waking hours using their prehensile lips and sensory whiskers to forage for vegetation on the bottom of the sea or on riverbeds. Here, they feed on large quantities of aquatic vegetation, such as seagrass; fully grown adults can consume over 45 kilogrammes a day. But with depleting food sources, manatees are being forced to venture into more precarious waters where they risk cold water exposure and collisions with boats. Manatees are currently designated under the Endangered Species Act as threatened, but in the last few years there has been growing support to reclassify them as endangered.

Habitat loss, food scarcity, cold stress, and boat strikes have recently become an all-too-common occurrence for Florida’s manatee population, resulting in a significant and alarming die-off of the population. 2021 showed particularly distressing numbers with the Florida Fish and Wildlife Conservation Commission (FWC) recording a total of 1,101 manatee mortalities over the year – a staggering 10% of their total population. When compared to the recorded 637 mortalities of the previous year and the five-year average of 741, these startling numbers beg for restorative reconciliation. The main cause of death among the necropsied carcasses in the first three and coldest months of the year was attributed to malnutrition, showcasing how the increasing reduction of seagrass and food sources along the eastern coast of Florida, paired with low temperatures, compromises the already malnutritioned manatees. Fortunately, the trend has begun to level off, with 800 mortalities in 2022 and around 330 recorded in 2023. Although the numbers have dropped back closer to the five-year average, data shows that manatee mortality rates have been on the rise for over a decade.

Out of all the issues facing manatees, food source loss, specifically the loss of seagrass beds, is one of the major ones. Loss of seagrass in coastal ecosystems and springs deprives the manatees of their main food source, becoming an even bigger issue in the winter and spring months as the surrounding ocean and river temperatures drop. In order for manatees to maintain a safe internal body temperature, they need to be in water that is at least 20 degrees Celsius. Dropping ocean water temperatures in the winter months force manatees to journey from the surrounding ocean into warm water refuges like the Florida springs and industrial warm water outflows. Manatees will then congregate in dense numbers in the few locations that are able to maintain an adequate temperature. For example, daily manatee counts in the 1,000 to 2,000 range have been observed at the Cape Canaveral Power Plant and the surrounding waters during the winter and early spring months.

With this amount of cold and hungry manatees gathering, it puts a large strain on the surrounding seagrass beds. Such refuges cannot sustain the amount of food that is required, and the manatees are faced with a choice to either brave the colder waters to forage for food or go without food in order to stay warm. When these cold snaps last for days or weeks, it can lead to a large number of deaths from starvation. To combat this, the Florida Fish and Wildlife Conservation Commission (FWC) introduced a feeding programme at Cape Canaveral, a major aggregation site, to provide a source of food for the manatees during cold periods in the hopes of getting them through the winter.

Feeding programmes, though successful, are only a short-term solution, however. The real solution, researchers believe, lies in reversing the damage to seagrass beds. But what has caused this deterioration of seagrass in the first place? It can largely be traced to pollution in the coastal and riverine ecosystems of the region. Excess nutrients and waste such as nitrates and phosphorus from sources like agricultural runoff, septic tanks, and stormwater have changed the natural nutrient cycles within aquatic systems. This fuels algae blooms which create eutrophic and murky waters known to block sunlight and stop seagrass beds from photosynthesising. Some locations have seen as much as 75% reduction in seagrass bed coverage, with similar losses spread throughout the region.

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Issue 34
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This feature appears in ISSUE 34: SCOTTISH SEAS of Oceanographic Magazine

Issue 34
Supported by WEBSITE_sponsorlogos_ONLYONE
Supported by WEBSITE_sponsorlogos_ONLYONE

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