Oceans cover roughly 70 percent of the earth and contain about 97 percent of the planet’s water. They play an incredibly important role in determining climate and weather, and support an amazing level of life. Yet most of the oceans are unexplored and much of the ecosystem interactions within the oceans are not well understood. A recent study published in Biological Conservation and headed by researchers from the University of Auckland and IFREMER (the French Research Institute for the Exploration of the Sea) utilizes no-take marine reserves to determine the effect over-fishing has on the ecosystem through effects on the food web and its subsequent recovery.
Little research has been conducted on how fishing, especially the over-fishing of certain populations, affects the oceanic ecosystems in which these populations live. One of the obstacles is that there is little to no data from before the depletion of the target populations which can be compared to current circumstances. This is changing due to the introduction of no-take marine reserves- areas of the ocean in which no fishing, removal of material, or dumping of substances is permitted. These areas encourage the restoration of biodiversity in depleted areas and not only offer a glimpse into how over-fished areas may recover and what we can do to help, but also can serve as a standard of what the area may have been like before the fishing began.
Kevin Leleu, from the University of Auckland, and colleagues showed that an increase in higher trophic level predators led to a decrease in urchins. Previously, over-fishing along the New Zealand coastline the researchers were studying had contributed to a dramatic decrease in the number of urchin predators, allowing a marked increase in the urchin population. These urchin populations in turn grazed the ocean bottom to bare rock, completely eliminating the kelp forests and other areas sensitive to grazing by urchins. The increase in urchin predators in the no-take reserves has led to a decrease in the urchin population, resulting in an increase in the return of kelp forests. These forests, which are capable of housing great biodiversity, play a major role in determining interactions within the ecosystem, and their return is necessary for the recovery of the area. The reemerging kelp and algal species that returned to the reserve showed density and biomass from several to many times greater than that of the urchin grazed regions. The return of the kelp forests and the other algal species is important for the restoration of the area by providing three dimensional habitats for the individuals which inhabit them.
The current state of fishing vastly overexploits the fish populations and can lead to crashing populations which may not be able to recover. This will not only affect the people who depend on fish for their livelihood and for food, but will also have profound effects on the ecosystems due to trophic cascades. The mapping carried out by Leleu and his colleagues clearly shows that no-take reserves allow for the restoration of biodiversity and the recovery of the ecosystem. By comparing no-take reserves to the surrounding area, we are able to determine what impact, both direct and indirect, humans have made on the ecosystems. With the no-take reserves as an example, we also will be able to see what is necessary to restore and protect the oceans which play such a crucial role in lives of everyone on the planet.
Leleu K, Remy-Zephir B, Grace R, Costello MJ. 2012. Mapping habitats in a marine reserve showed how a 30-year trophic cascade altered ecosystem structure. Biological Conservation 155: 193-201.
From the National Oceanic and Atmospheric Administration