On beach plants and lights.

In a natural environment, i.e. with little or no human development, the windward side of Caribbean islands tends to contain sandy beaches, which are backed by more or less of an extent of dunes. These beaches and dunes are inhabited and used by various species, including sea turtles. The vegetation on these beaches typically constitutes a sere where the vegetation changes along an environmental gradient. Closest to the water, there is the pioneer zone with grasses, succulents and creepers. Further inland, there is a coastal shrub with species such as bay cedar, or inkberry, which in turn is backed by the tropical hardwood hammock. This last zone, also referred to as maritime or coastal forest typically contains large trees such as seagrape, West Indian almond, canella, and manchineel, and is the most stable zone and can be regarded as the climax of the ecological succession.

An undisturbed beach. Green Island, Antigua. ©D.Tilley

In general vegetated areas – excluding the coconut palm – are undesirable on beaches and usually make way for human development. However, these ecosystems play vital roles in terms of biodiversity and in terms of coastal protection. The pioneer zone is frequently washed out by storm surges but the rest of the beach usually fears much better as the root systems hold down sand and the vegetation reduces wind erosion.

Vegetation also plays a vital role for hawksbill turtles. Unlike any other species of sea turtle, hawksbills tend to favour vegetated areas when selecting nest sites. This may seem counter intuitive, as low branches could impede the turtles, roots make it more difficult to dig and can potentially trap hatchlings. However, it seems to work and has done for some 60 million years. In terms of root related problems, empirical evidence seems to suggest that the beloved coconut palm is a much greater problem to turtles than any other plant species on the beach. 

Vegetation is important to hawksbill turtles as it helps maintain suitable incubation temperatures and thus keeps a more balanced sex ratio. Indeed, the incubation temperature determines the sex of the hatchlings with pivotal temperature, where there will be a 50-50 M/F sex ratio, at about 29.2°. Hawksbills dig relatively shallow nests, at about 50cm, but they are in keeping with their relatively small size and thus the shade cover provided by vegetation buffers the heat of the sun.

Nesting under cover of vegetation provides protection for the adult and stable incubation temperatures. ©D.Tilley/JBHP

Moreover, the vegetation on the beach helps block out light pollution. Turtles use various environmental cues to orientate, and light is used to find water. On a natural beach, the lightest point will always be the horizon over the water. Turtles have been using this as a cue for millions of years, and it has clearly worked for them. Problems arise with human development and lights; a very simple solution – but not always practical - is to switch the lights off, alternatively using different light fittings and specific low intensity light bulbs – often more expensive – can help. Of course there is another solution: leave the beach vegetation in place.
Tall trees not only help maintain the stability of the beach, but also cut out the glare in the sky which as is a serious problem for turtles - and star gazers – and a difficult one to resolve.

Light pollution. ©D.Tilley/JBHP

The shorter coastal shrub cuts out low level lighting – i.e. the house lights. The direct consequence of light pollution is disorientation of adult turtles and hatchlings which in most cases leads to the death of the animals. Adults fair a better chance, but some have close escapes.

Hatchlings in pool after being disorientated by light. ©D.Tilley/JBHP

Hatchlings crawling around a light fixture 75m away from the nest. ©D.Tilley/JBHP

It must be noted than human development doesn't have to be detrimental to nesting turtles; selective pruning and planting, can help mitigate the impact of coastal development. This of course combined with appropriate light fixtures.

Tiki hut and sun beds in front of coastal forest ©D.Tilley/JBHP

It is always a sad day when trees are felled and coastal scrub is removed.

Looking seaward, before large sections of vegetation were removed. ©D.Tilley/JBHP

Looking seaward, after large sections of vegetation were removed. ©D.Tilley/JBHP

More information on lights:

A short video about lights. 

An article on 365Antigua.com 

In the Spotlight: An Assessment of Beachfront Lighting at Four Hotels in Barbados, with Recommendations for Reducing Threats to Sea Turtles. 

Reducing Light Pollution in a Tourism-Based Economy, with Recommendations for a National Lighting Ordinance.

More WIDECAST publications.

Edit: November 6th. Some of the offending lights have now been switched off, which is a good thing. The street lights however are still on, and will remain on. The vegetation that once obscured them from the beach and thus from hatchlings is gone and will take years to recover, if it is allowed to do that. I have my doubts.