Bottom trawling, as its name implies, consists of a large conical net with a wide mouth and a small, closed end. In this type of fishing, the result is the capture of a large number of fish. In one hand, trawling fills supermarket shelves, yet it also empties the seabed. Plus, the decreasing of marine fauna and flora caused by this type of fishing, has already reached one of the most remote places on the planet, the Barents Sea (Arctic Ocean).
Barents Sea is an extremely rich habitat, with high primary productivity, making this place an important habitat for numerous species, such as marine sponges. Here, it is possible to find a large community of marine sponges, such as Geodia Barretti. These are considered fundamental to the habitat and serve as natural indicators of Vulnerable Marine Ecosystems. However, the increasing rate of trawling is also increasing the damage to the sea floor, which is often irreversible.
Figure 1. Geodia Barretti, a species of sponge that can be found in the Barents Sea.
This study aimed to analyze the effects of trawling on the abundance of Geodia spp. and diversity of associated fauna species. Therefore, were used images collected by an ROV (Remotely Operated Vehicle), of two locations with completely different levels of drag (location with low and heavy impact), which were compared. Through the analysis between the two locations, it is possible to verify the consequences that long-term trawling creates. In the place where trawling is not so frequent, it was possible to find a relatively diverse and abundant sponge community, in contrast to the place where trawling is more frequent.
Figure 2: Impact of trawling on communities where (a) not frequent and (b) is frequent.
Several studies have shown that the continuity of trawls in the same location leads to functional changes in benthic communities. Sponges have a high filtration rate, which allows them to remove a large amount of particles from the environment, including viruses and other pathogens. However, if the intensity of trawling continues to increase, and consequently to a decrease in the abundance of sponges in the Barents Sea, this habitat will experience an increase in the amount of particulate carbon deposited on the seafloor. With the increase in carbon, this location becomes more favourable for species that feed on dead organic matter. Which in turn leads to a change in the functional diversity of the system.
The authors concluded that bottom fishing significantly reduces sponge communities, reduces sponge abundance and size, and creates a change in species and functional diversity, and subsequently in ecosystem function and services.
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Source: Colaço, A., Rapp, H. T., Campanyà-Llovet, N., & Pham, C. K. (2022). Bottom trawling in sponge grounds of the Barents Sea (Arctic Ocean): A functional diversity approach. Deep Sea Research Part I: Oceanographic Research Papers, 183, 103742.
Author: Eva Lopes
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