Gibraltar monitors invasion of the Dictyota dichotoma

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HM Government of Gibraltar
Forkweed the brown alga

The ‘seaweed’ that has been turning up in Gibraltar waters over the past two years is a brown alga, commonly known as Forkweed (Dictyota dichotoma), which has increased tremendously in its distribution throughout the Bay. 

The alga has been turning up on shores around the north of the Bay, including Western Beach and the Playa de Poniente in La Linea.  It has also appeared growing and expanding in areas such as off Camp Bay and Seven Sisters where it is possibly beginning to interfere with other marine life.

 As part of its continued marine surveillance programme, the Department of the Environment and Climate Change (DECC) has been monitoring the increasing presence of the brown alga throughout Gibraltar’s waters.  

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Although this species is native to the north-eastern Atlantic and Mediterranean, where it is widely-distributed and common, scientists from the DECC are now investigating the reasons why this species is proliferating in Gibraltar’s underwater environment and washing up in large quantities on its shorelines. 

Initial observations suggest that the growth of Forkweed could be attributed to changes in regional currents and nutrients, and the possibility of climate change being a contributing factor cannot be discarded, since this species is not generally regarded as invasive.

Increases in algal biomass and changes in the structure of local algal assemblages are usually considered symptoms of eutrophication resulting from industrial, domestic, or agricultural wastes, so scientists would perhaps do well to monitor ongoing nutrient levels in affected areas.

Forkweed is also known to grow epiphytically on invasive species such as Caulerpa racemosa var. cylindracea, a species which probably entered the Mediterranean via the Red Sea that blooms during summer, so this may also be worthy of investigation.

At any rate, the DECC will apparently continue to monitor the growth of this species in British Gibraltar Territorial Waters in order to try and understand the phenomenon better.

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