None of the invasive species becomes important in the Weddell Sea food web based on the PageRank centrality. Nor do they significantly change the food web structure in the perspective of the centrality measurements used here. The results from the general network metrics showed similar patterns with lack of significant differences due to the addition of these invasive species. There were only small increases in the values where the invasive species were included compared with those without them, but not in any considerable way. This was however expected due to the size and complexity of the food web and since only twelve species were added. Neither in the distribution of the species traits could any notable differences be distinguish due to the presence of these invasive species. The invasive species were limited to certain areas within the trait distributions, but did not have any unique traits or combinations of traits compared with the native species.

Currently there exist very little information of the diet of the deep water lithodids living south of the polar front, and their feeding behaviour. Recent studies claim that invasion of these durophagous (bone crushing) lithodid crabs threatens the Antarctic shallow marine ecosystems, and their native fauna of weakly calcified benthic invertebrate communities. However, it remains uncertain if the invasion will increase the risk of predation on  sedentary invertebrates and through that also decrease the native fauna of these ecosystems. Many of the regions deep water lithodids are opportunistic necrophagous scavengers, which could remove the pressure of direct predation. The most studied and specious region of the Southern Ocean, South Georgia, have a rich endemic fauna despite the presences of a number of large durophagous predators of crab species with high abundances. This suggest that these crabs do not affect the number of species or habitat type in any harmful way, they instead form a part of a highly diverse community. A reason suggested why some of the crabs do not affect these communities, is because of their omnivorous behaviour, which is thought to distribute the predation pressure more and prevent elimination of any particular species. Their omnivorous behaviour, or their spread of prey species, are reflected in their large numbers of prey species in the Weddell Sea compared to the native species, which is one of the overall things that determine their positions in the food web structure. This could thereby explain the low values the invasive crab species got in the PageRank analysis, and thus their lack of importance regarding the food web robustness.

There are less studies on how invasive durophagous sharks impact these types of ecosystems. In general sharks are important species in many of the ecological communities they are included in. They shape those marine ecosystems the live in, due to their roles as predators and scavengers they are essential to the health of these systems. They are toplevel carnivores, keeping abundances of other species in check, preventing overuse of resources and starvation, as well as remove sick and weak individuals. These predators also feed on remains of dead animals, which help the ecosystems with recycling of energy and nutrient. This knowledge about sharks assume that they will make an impact on the food webs structure and the species in the Weddell Sea if they manage to invade. Affecting the abundances of their prey species and probably creating imbalances in this already complex ecosystem, which can propagate through the food chains. However, the results show that the invasive shark species do not impact the Weddell Sea food web in any considerable way. They end up with the lowest values in the PageRank centrality analysis, and are therefore not considered to be important in this food web regarding to it’s robustness. Sharks eat just about anything that is available, they are opportunists. Their opportunism on what to prey upon could work out in a similar way as the durophagous crabs around South Georgia, spreading the predation pressure and not affect abundances or habitat in any harmful way. Predation pressure and abundances were, however, factors which were not included in this study, and did not directly impact the PageRank centrality and were not the direct reason for the invasive species low PageRank values. But there is a insinuation that these elements have an indirect effect on the outcome of the centrality analyses. The invasive species opportunism towards what to prey upon can be reflected by the large number of species they consume in the Weddell Sea food web. Together with their small or none existing number of species who predate on them, places them in their current positions in the food web structure, and is probably a vital reason why these invasive species got such low values in the PageRank analysis.

PageRank centrality constantly serve as a high performer across real and hypothetical food webs among other centrality measures. Other centrality metrics are often not adapted to food webs and how they work, which results in poor performances to evaluate species importance compared to the PageRank centrality. The similar result from the betweenness centrality, which is a similar model to the PageRank centrality, and the result from the sensitivity analyses, strengthen the result that these invasive species do not become important in this food web. What the reason could be for their lack of importance in the food web structure can only be speculated in. Most of the invasive species are highly connected, with numbers of interactions above the mean and median number of interactions per species in the Weddell Sea food web. And all of them are predators, where almost all have a broad spectrum of species that they predate upon and a small or none existing number of predators. Their many prey species are probably the reason why they became so closely connected to many of the species in the food web, and the reason why they ended up in the top of the ranking order in the closeness centrality analysis. Despite their closeness, the invasive species are at the ends of their food chains within the food web, which suggest a lower flow of energy through them, and thereof probably their low scores in the betweenness and PageRank centrality analyses. Their opportunism regarding of what to predate upon, and thereby their connectedness and thus their position in the network, are probably the main reason why the invasive species got such low PageRank values and do not become important in this food web. The result might have turned out differently if the elements of predation pressure and abundances had been included in the study, together with the local impact of the invasive species.

Invasion of species do not always have to be negative and include extinction of species to a food web, it can actually increase species richness. Which in some way seems to be the case in the marine ecosystem surrounding South Georgia, where the presence of a number of invasive crab species do not affect the highly diverse community negatively, instead it thrives. It has been shown that invaders can provide species at higher trophic levels than them self with habitat and food sources, which has resulted in positive effects on the diversity at higher trophic levels. Invasive species can also increase complexity and food chain length, as well as connectance and proportion of intermediate species. Changes in food web structure because of invasion of species seem to rather depend on changes in abundances of trophic groups than extinction of species. This could be the very reason why the invasive species did not seem to make any significant impacts on the food web structure in this study, since abundances were not included in the data. And when impacts of invasive species lead to extinctions, it do not always act as the cause by its own. Their impact can be a part of simultaneous events, as environmental changes that co-occur, which drive species to extinction. Co-occurring environmental changes will probably also occur in the Weddell Sea together with impacts from these invasive species, thought to invade, which could make the extinction risk higher. That part of the Southern Ocean experiencing one of Earth’s fastest rates of regional climate change. It’s surface temperature have increased more than 1 K in the last 60 years and the temperature of the deep water has risen as well, also the season of sea ice have become shorter. These changes will have an impact on the complex food web of the Weddell Sea in addition to that of the invasive species. It is also possible that the changes such as increased temperature will change how species do connect to each other within the food web, but those factors were not accounted for in this data set.