Impact of Asian Seaweed on Fisheries in the Strait of Gibraltar

The Asian seaweed known as Rugulopteryx okamurae has had a significant impact on artisanal fisheries in the Strait of Gibraltar.

What kind of species is Asian kelp?

The Asian seaweed Rugulopteryx okamurae is an invasive seaweed, native to the Pacific, which has spread along the coasts of the Strait of Gibraltar and other areas of the Mediterranean. It is an invasive algal species that belongs to the group of brown macroalgae, specifically to the Dictyotaceae family.

This Asian seagrass is characterised by its rapid growth and its ability to form dense mats on the seabed, which can have a negative impact on native marine ecosystems by displacing native species and altering marine habitats. However, its proliferation can be a significant challenge for the management of marine resources and the conservation of biodiversity in areas where it is present.

The Asian seaweed Rugulopteryx okamurae is impacting negatively on artisanal fisheries in the Strait of Gibraltar. This algae invades the seabed and forms dense mats that trap fishing nets, damaging and destroying the traditional fishing gear used by local fishermen in Tarifa harbour.

In addition to its impact on fisheries, this Asian alga threatens marine biodiversity by displacing native species and modifying coastal ecosystems, as described by Maria Alatamirano Jeschke, Professor of Botany at the University of Malaga, in the following video.

Another point to note is that in addition to the fishing in the area, the Asian seaweed affects the aesthetic and bathing conditions of our beaches at certain times of the year, with the direct effect it can have on the city’s tourist activity.

To address this problem, research is ongoing and control strategies have been proposed to mitigate the spread of this invasive algae in the Strait of Gibraltar. However, the complexity of the problem and the need for coordination between different parties make it difficult to eradicate.

Asian seaweed has reached the waters of the Strait of Gibraltar and other areas of the Mediterranean as a result of the spread caused by several factors. Asian seaweed has reached the waters of the Strait of Gibraltar and other areas of the Mediterranean as a result of the spread caused by several factors. Here are some of the possible routes by which the Asian seaweed has reached these particular waters:

• Shipping and fishing nets: Asian kelp spores can attach themselves to fishing vessels and equipment. When these vessels navigate between different marine areas, they can inadvertently transport the algal spores from one place to another, facilitating their spread.
• Climate change and ocean currents: Climate conditions and ocean currents may play an important role in the spread of this algae. Changes in water surface temperatures and ocean currents may have contributed to their expansion in the same way that they contribute to the sedentarism of other species such as bluefin tuna.
• Lack of control and regulation: The lack of effective control and regulation measures to prevent the spread of invasive species such as Asian kelp has been a key factor in their proliferation in the Strait of Gibraltar and other areas of the Mediterranean.
• Resistance to adverse conditions: Rugulopteryx okamurae is known to be resistant to a variety of adverse environmental conditions, allowing it to survive and thrive in different marine habitats and even survive on other species such as crabs or other algal species.

The Asian seaweed Rugulopteryx okamurae causes a negative impact on several native species in the Strait of Gibraltar. Some of the species affected are listed below:

1. Posidonia oceanica: a marine plant endemic to the Mediterranean that plays a crucial role in the ecology of the region. Excessive growth of Asian kelp can cover and damage Posidonia meadows, affecting biodiversity and the health of coastal marine ecosystems.
2. Fish species: The invasive alga Rugulopteryx okamurae may also alter the breeding and feeding habitats of various fish species native to the Strait of Gibraltar. This may negatively affect fish stocks and fisheries in the Strait region.
3. Other marine species: In addition to Posidonia and fish, Asian kelp may harm other native marine species by modifying coastal ecosystems and the composition of the biological community in the Strait of Gibraltar. This can have cascading consequences throughout the marine food chain.

Overall, the impact of Asian kelp on native species in the Strait of Gibraltar is a serious problem affecting both biodiversity and economic activities, such as small-scale fishing.

The spread of the Asian seaweed Rugulopteryx okamurae in the Strait of Gibraltar has had a significant impact on a number of fish species caught in the region. Although no specific list of affected species is provided in the search results, it can be assumed that common fish species in the Strait of Gibraltar could be affected by the growth of this invasive algae.

Some of the fish species affected include:

1. Sardines: Sardines are a very common fish species in the Strait of Gibraltar and are an important food source for many other marine species.
2. Small Anchovy (boquerones): Anchovies are another common small fish species found in the Strait of Gibraltar and are important to the local fishing industry.
3. Hake: Hake is a larger type of fish that is also caught in the Strait and is valuable for commercial fishing.
4. Tuna Fish: Tuna is a species of great commercial importance and is found in the waters of the Strait of Gibraltar.
5. Sea bream and sea bass: These species are popular sport and commercial fisheries in the area and could be affected by changes in food availability due to the proliferation of Asian kelp.

It is relevant to note that the presence and abundance of these fish species can be influenced by a number of factors, including invasive algal blooms such as Rugulopteryx okamurae. The alteration of marine ecosystems due to the presence of this algae may affect food availability and migration patterns of fish species in the Strait of Gibraltar.

And how does it affect Voracious or Pinta Bream?

Click on the photo to see a video of fishing for the Pinta Bream or Voraz fish

The Voraz fish (Pez Voraz), also known scientifically as Pagellus bogaraveo , is a species of fish found in the Mediterranean Sea, including the area of the Strait of Gibraltar. Asian algal blooms can affect Voracious fish in a number of ways:

1. Habitat alteration: Asian kelp can alter the seabed and modify the habitats where ravenous fish are found. This may affect the availability of shelter and food for this species.
2. Competition for resources: The expansion of Rugulopteryx okamurae may lead to increased competition for food resources among marine species, including Pinta bream. If the growth of the algae displaces other marine life that is prey to the ravenous fish, it could affect its food availability.
3. Biodiversity decline: The presence of invasive algae can contribute to the reduction of biodiversity in the marine ecosystem. This affects the diet and overall health of Pez voraz by reducing the variety of prey available.
4. Impacto en la pesca: Dado que el pez Voraz es una especie de valor comercial en la pesca, cualquier alteración en su hábitat o disponibilidad podría tener un impacto económico en la pesca artesanal del Estrecho de Gibraltar.

The proliferation of the Asian alga Rugulopteryx okamurae in the Strait of Gibraltar may have an indirect impact on the Voracious fish by modifying its habitat and food availability. However, it is important to note that the exact relationship between this invasive algae and fish populations, including Voracious fish, may be complex and require more detailed research to fully understand its impact.

How is Asian kelp being eliminated from the environment of the Strait of Gibraltar?

The complete removal of the Asian seaweed Rugulopteryx okamurae from the Gibraltar environment and other areas where it has spread is a considerable challenge due to its ability to grow and reproduce. Management of this invasive algae generally focuses on control and reduction of its spread rather than total eradication. Here are some strategies and methods that have been used to control this invasive algae:

1. Manual removal: In some areas, divers and volunteers have carried out manual seaweed removal operations, cutting and removing the seaweed from the seabed. This is a laborious and time consuming task but can be effective in small, localised areas.
2. Physical barriers: Physical barriers, such as nets and tarpaulins, have been tested to contain the spread of algae. These barriers can help prevent the algae from spreading to additional areas.
3. Herbicides and biocontrol: In some cases, specific herbicides and biocontrol organisms have been used to reduce the density of the algae. However, these methods can have environmental impacts and should be used with caution.
4. Research and monitoring: Continued research and monitoring of the spread of the algae is essential to better understand its behaviour and to find effective ways to control it. As described by Prof. Altamirano, the localisation of the temporary production of Asian algae and its preventive sighting when taking measures can severely mitigate the harmful effect of this weed on other species.
5. Legislation and regulation: The implementation of regulations and enabling legislation to prevent the spread of Asian kelp and limit its impact is essential. This may include restrictions on the transport of vessels and equipment that may carry algal spores.

It is essential to emphasise that the management of Asian seaweed is an ongoing challenge and requires long-term efforts. Cooperation among scientists, local authorities, fishermen and the wider community is essential to address this problem effectively. In addition, control strategies may vary depending on the location and extent of the infestation.

Our fishing environment in the province of Cadiz is aware of the seriousness of the issue of Asian algae and the influence it is having on our coastline, which is why we are joining forces in terms of the transmission of knowledge and the concentration of efforts aimed at alleviating this problem. A good example of this common interest is the organisation of seminars such as the one held on 28 September 2023 in the Casa del Mar in our sister town of Conil de la Frontera.

In summary, the spread of Asian kelp in the Strait of Gibraltar is the result of a combination of factors, including unintentional human transport via boats and fishing gear, favourable environmental conditions and the lack of effective control measures. Its ability to colonise new sites has made it a challenging invasive species to manage in the region..