The Florida Keys are well-known as an idyllic tourist destination, but not all of the area’s inhabitants have benefited from the increase in notoriety. Over the past half-century, human activity along the coast has devastated the habitats of much of the local wildlife and led to the onset of large-scale conservation crises that show no sign of abating anytime soon.
A recent study conducted by a team of researchers from Texas A&M University, the University of Florida and the U.S. Fish and Wildlife Service and published in the journal Global Change Biology assessed the impact of human development and sea-level rise (SLR) on the population viability of the Lower Keys marsh rabbit (LKMR), an endemic species that is currently classified as federally endangered.
The study found that from 1959 to 2006, LKMR habitat decreased by 64%, with 48% of the decline attributed directly to SLR. There was also a strong negative correlation between the amount of development and how much new habitat was formed, with islands that had greater than 8% of their land area developed generally incapable of generating new LKMR habitat.
Only 8% of the observed habitat loss was due to conversion to impervious surfaces such as walls, roads and buildings. This suggests that development exerts its effects on habitat loss indirectly, primarily by blocking the inland migration of habitat that occurs following sea level change. Taken together, SLR and development thus represent a growing conservation concern that promises to remain relevant as sea levels continue to rise.
Population growth and its associated increases in development have been studied for more than 50 years, but human-induced SLR only began receiving serious attention from the scientific community during the 1990’s when the yearly rate of sea level rise nearly doubled from 1.7 mm/yr to 3.3 mm/yr. Increasing sea levels have been associated with loss of wetland habitats and changes in plant communities that increase the extinction risk of already threatened wildlife.
In the past, habitats have been observed to shift in response to events such as SLR or erosion. The associated fauna migrate with the habitat as well. In areas such as the Keys, however, development provides an impermeable barrier to this inland habitat migration. The ecosystem thus finds itself trapped between the ocean and these hardened surfaces with nowhere to go. As a result, this ‘coastal squeeze’ effect results in a net loss of habitat for all resident species.
Between 1970 and 2000, some of the islands in the Florida Keys experienced an almost 10-fold increase in population. The LKMR’s numbers have declined steadily during this time, decreasing by nearly 50% since the 1980’s alone. The rabbits are currently confined to low-lying freshwater wetlands and transitional vegetative communities on 13 islands in the Lower Keys. It has been speculated that the rabbit’s reliance on these fragile coastal areas puts them at serious risk of exposure to the deleterious effects of SLR.
In order to test their theory that SLR has been the main driver in the decline of the LKMR, the research team performed a comprehensive analysis of aerial photographs of the Keys dating from 1959 to 2006. Using these images, they were able to quantify LKMR habitat change over time and attribute these variations to either changes in sea level, human development or other factors.
As stated earlier, nearly half of the observed decline in LKMR habitat was a direct result of SLR. This was the first recorded instance in which human development was not the primary driver of habitat degradation, most likely because the extremely low-lying locales of the LKMR are largely unsuitable for building and thus are more vulnerable to the effects of rising sea levels.
Development clearly has a negative impact on LKMR sustainability as well, but it mainly functions indirectly to exacerbate the conditions initially brought about by SLR. Though it is not the primary threat to the persistence of the LKMR, mitigating the effects of development represents the most plausible potential solution to this problem. Sea level change functions on a global level and takes decades to impact, but decreasing the effects of coastal squeeze by facilitating inland habitat migration could be handled on a local basis, would be-relatively- inexpensive and extend positive benefits to other threatened low-lying coastal species as well.
Rising seas are far from a new problem in coastal conservation, but their true impact has largely remained a mystery until now and is projected to get worse in the coming years. Coupled with human development, SLR threatens the existence of coastal species such as the Lower Keys marsh rabbit. Quick, strong intervention is needed to reverse these effects before it is too late.
Schmidt JA, McCleery R, Seavey JR, Cameron Devitt SE, Schmidt PM. 2012. Impacts of a half century of sea-level rise and development on an endangered mammal. Global Change Biology. 18(12):3536–42.
Link to article: http://onlinelibrary.wiley.com/doi/10.1111/gcb.12024/pdf