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One major pollutant in the coastal environment is agricultural run-off. Whether inland, or coastal, the waste products of farming complexes, make their way through the water system and into the marine environment, where their effects make themselves evident.


Rainfall can cause any chemicals or fertilisers applied to crops or livestock to be washed off into river systems and be carried downstream to the sea. In recent years the use of toxic biocides, like DDT (the world’s first and best known pesticide), have been reduced, but fertiliser is still causing major issues. Nitrates and phosphates in the fertilisers are major causes of nutrient enrichment, also known as eutrophication. This increase in nutrients can directly cause algal blooms (Figure 1), which can pose dangers to marine life and humans alike. In recent years, these blooms have become increasingly more frequent (Sellner et al. 2003).


Figure 1: Algal blooms visible at Lough Hyne

What makes the blooms so detrimental to the marine environment, is the resulting oxygen depletion. The nutrients in the water cause the rapid growth of algae, which continue to proliferate until all nutrient supply has been exhausted, the algae then dies off and sinks to the seabed where bacteria help break it down. It is this breakdown that reduces the level of oxygen in the water, creating anoxic “dead zones” where it is impossible for most marine organisms to continue their survival. They are of particular danger to sessile*, benthic organisms*, such as anemones and corals, which do not have the ability to move to an area with higher oxygen levels. Also known as red tides, these blooms occur almost annually around the Irish coast, even in areas free from industrial influence like Lough Hyne Marine Reserve (Jessopp et al. 2007). Many of these red tides also contain harmful toxins that can become airborne, causing health complications in humans and animals alike (Watkins et al. 2008). These toxins can also bio-accumulate in filter feeding organisms, like mussels, which is what causes neurotoxic shellfish poisoning, a disease caused by the consumption of contaminated shellfish. In 1997, up to two dozen people contracted diahrretic shellfish poisoning from consuming only 10-12 individual mussels (Twiner et al. 2008). Depending on toxicity levels, species and site, the incidence of these infections can range from 0.2% to 14% (Hinder et al. 2011). This poses particular danger to the shellfish industries based out of Bantry Bay area in West Cork whose industry shifted to processed mussel populations in the early 90’s in part due to the impact of these naturally occurring tides (Bantry Bay charter).

Seán & Orla-Peach


* Sessile Organisms: Organisms that are fixed in one place; immobile.

** Benthic Organisms: Organisms that occur in the lowest level of a body of water


Hinder, S. L., Hays, G. C., Brooks, C. J., Davies, A. P., Edwards, M., Walne, A. W., & Gravenor, M. B. (2011) Toxic marine microalgae and shellfish poisoning in the British isles: history, review of epidemiology, and future implications. Environmental Health : A Global Access Science Source, 10(1), 54.

Jessop, M., McAllen, R., O’Halloran, J., & Kelly, T. (2013) Nutrient and Ecosystem Dynamics in Ireland’ s Only Marine Nature Reserve ( NEIDIN ).

Mostofa, K. M. G., Liu, C. Q., Vione, D., Gao, K., & Ogawa, H. (2013) Sources, factors, mechanisms and possible solutions to pollutants in marine ecosystems. Environmental Pollution, 182, 461–478.

Sellner, K. G., Doucette, G. J., & Kirkpatrick, G. J. (2003) Harmful algal blooms: Causes, impacts and detection. Journal of Industrial Microbiology and Biotechnology, 30(7), 383–406.

Twiner, M. J., Rehmann, N., Hess, P., & Doucette, G. J. (2008) Azaspiracid shellfish poisoning: A review on the chemistry, ecology, and toxicology with an emphasis on human health impacts. Marine Drugs, 6(2), 39–72.

Watkins, S. M. (2008). Neurotoxic Shellfish Poisoning. Marine Drugs, 6(3), 430–455

Title image – Runoff of Soil and Fertilizer