Our work on the coast at Belle Mare and Palmar was split in a similar way to before – trips in the lagoon to look at the coral reef and seagrass beds, and walking the coast to look at defences and other issues. A major new issue here was the washing up of huge amounts of algal material onto the shoreline day after day. The Department of the Environment for whom we were working had done some preliminary investigations. The Beach Authority were trying to tackle the result. In a few days, a layer of algae would coat most of the beaches from one end of the lagoon to the other, and the rate would increase if the weather had been turbulent. Having decaying alga on your beaches is severely detrimental to your tourist image (you would not put it in your brochures!) so the hotels employed people to rake it off the beaches every day. That was not so bad where a resort had , say 100m of beach, but the larger resorts and the public beaches had kilometres to clear. In some places the work was on an industrial scale, with diggers coming down on the beach to scoop up the strandline, and trucks towing away the smelly , dirty loads. One day, when exploring the back of the district to look for possible reasons for why the algae was blooming in the lagoon, we discovered where they were dumping the problem – along a disused forest track there was several hundred metres worth of rotting algae over 3 metres high in places. It was posited with Environment that they could be looking at this as a valuable source of fertiliser is the salt could be washed out.
Before commencing the detailed survey we looked around the area to try and find the reason why the lagoon was starting to choke with algae. Pollution seemed the obvious culprit – enriching the lagoon with either agricultural inputs or human waste, but there were no natural run off channels along this part of the coast. Instead the coast was a sandy berm higher than the immediate hinterland. Behind the sand, in an intensely agricultural zone predominated by onion growing, were several freshwater lakes. We took a close look at them but could not see any concentrated sources where fertiliser could be running off – so unless it was the combined effort of all the onion growers or the large catchment from the island’s interior covered in sugar cane fields, we could not fathom it out. If it were just the drip drip effect of so much agriculture – why was the algae prevalent in the lagoon here but not elsewhere in the island where similar intensity of agriculture was in the catchments that fed into them.
We did work out how any pollutants could potentially be transferred from these lakes into the sea, though. A common feature of both sandy coastlines and ones where permeable rocks exist is that freshwater can leak through and appear at or below the shoreline. While we were walking the coast, we noticed damp patches in the sand, even pools in some places, and in a couple of instances could see water bubbling up in a spring. A quick finger in the water and taste test determined that the water was sweet and we duly noted these locations in case we found some pattern of these against the distribution of the algae in the lagoon itself. Only after a few taste tests like this did we suddenly think – what if this is a sewage leakage of some sort? Well, we spat out the sample as soon as we had our verdicts, and I never did get diarrhoea during this period, so it must have been “safe” – at least in a field working manner if not covering health and safety rules.
The other potential source was human effluent, but the resort hotels were meticulous about their sewage treatment – why would they not be – there was no point dumping waste in the lagoon you wanted your guests to swim, dive and sail in. Occasional transgressions may occur when some failure in the system caused a leak, but it would never be on the scale to cause such algal blooms.
The other potential source could be offshore. I know many beaches in the Caribbean can suffer from huge builds up of seaweed, thought to have been carried in on wind and wave from the Sargasso Sea, but I knew of no equivalent in the nearby Indian Ocean.