7. Pests, introduced species, diseases and algal blooms
Outbreaks of diseases, non-natural algal blooms and infestations by pests have been assessed as symptoms of an unhealthy marine ecosystem. The results of research estimates indicate that a very high percentage of the pollution currently discharged into the coastal area is done by the local inhabitants. Untreated waste on beaches and in the nearshore zone is directly related to the health status of the local population. Epidemics such as typhoid fever, cholera and similar outbreaks are the results of poor sanitation or the symptoms of consuming raw or partially cooked oysters, clams and mussels harvested from coastal waters into which raw or inadequately treated sewage had been discharged (Meith-Avcin and Helmer, 1978).
High concentrations of harmful nutrients and microorganisms are usually contained in untreated and inadequately treated waste. Aquatic ‘over nourishment’ from nutrients may lead to eutrophication of coastal receiving water bodies like estuaries and bays bringing various negative consequences such as plankton blooms, oxygen depletion and fish kills. Such adverse circumstances are sometimes observed in the streams, rivers, and estuaries but they go unrecorded.
The Sierra Leone marine environment is overall in good condition with regards to pests, introduced species, algal blooms and outbreaks of diseases that can disturb the ecological balance of the aquatic realm. However, the problem of coastal and marine invasive species is likely to worsen over the coming decade due to increases in shipping activities throughout the region. Ship traffic is projected to continue growing into the coming decade with economic growth and therefore the outlook for transfer of alien organisms through ship‘s ballast water could be expected to grow. The Queen Elizabeth II quay is the primary international gateway for all foreign vessels entering into the country. There have not been documented any pest species from this quay or any of the wharfs to have caused any significant ecological impact in the local areas. There have been reports of malaria and such outbreaks, especially in coastal areas of high urbanisation and population densities, and these have been attributable to poor sanitation where mosquitoes have been able to proliferate in stagnant water settlements. The high risk areas for such incidents to happen are in Sector II (Sierra Leone River estuary) and Sector IV (Yawri Bay) in and around the port and other smaller shallow bays and estuaries.
There is limited knowledge on adverse marine impact or outbreaks affecting populations of birds and marine mammals. Incidents of poisoning of marine species affecting the trophic hierarchy of the marine food chain have also not been reported recently.
There are visible evidences of fouling organisms such as barnacles on ships’ hulls but these are local mollusc species which are not known to be harmful to man or other marine species. In fact they are edible for local residents! The intense level of shipping activity that is associated with the increasing traffic at the main port in Sector III has probably made a big contribution to this minor problem. However, no data are available on the ecological impacts of such fouling and, for now, these effects are assumed to be neutral in terms of ecological function.
There are occasional incidents of natural algal blooms and the proliferation of jelly fishes (Physalia sp.) occurring in some coastal areas directly connected to the ocean, like the Peninsula, but only low levels. Blooms of Sargassum spp. have been occurring in coastal waters since 2011. Worst areas affected include the coastal water column and beaches along the entire coastline.
In other bay areas of coastal and related development occurred outbreaks of cholera due to poor catchment management in these areas because of sediment and nutrient input (such as in floods), local groundwater contamination, urban run-off and sewage. No data exists on the relationship between these causes and effects.
In the 1980s there had been reports of one pest species, the grey triggerfish from the family Balistidae (Balistes spp.) Its proliferation on the Sierra Leone shelf had been a source of great worry because its presence was associated with the decline in the population of some other more highly valued species. Its occurrence however had been attributable to hydrographic cycles when colder waters from the northern Canary currents affected distribution patterns in the lower latitudes until the Gulf of Guinea.
The Queen Elizabeth II Quay is an international port and therefore exposed to the many hazards including the introduction of invasive species from ships’ ballast waters. These questions have not been scientifically investigated and as such no comparison or conclusion can be drawn about such issues.
There were evidences of the proliferation of the crown-of-thorns starfish at No. 2 River estuary acting as a ‘fouling’ organism on cultured oysters. That observation was only in the 1980s and such population increases have not been observed during the past two decades. The proliferation of populations of the sea urchin is sometimes still reported by local fishermen at fishing grounds especially in the southern parts below the Freetown peninsula, but these occurrences are sporadic and do not cause alarm. There have been no reports of fish kills over the past 5-10 years. Little information is available on this subject and no assessment was produced.