Intra- & Interspecific Interactions Between the Non-Indigenous Round Goby, Neogobius melanostomus, and the Native Benthic Community of Öresund

Abstract

Numerous broad insights have emerged in the last decades concerning the invasive non-indigenous round goby (Neogobius melanostomus) and its expanding presence in the Baltic Sea. The waters surrounding the Danish isles are the final frontiers separating the Baltic Sea from the North Sea, and although they offer highly favourable habitats, the biotic resistance in Öresund by native competitors might interfere with the further spread of opportunistic goby colonizers. This study has investigated interactions between goby conspecifics and interspecific interactions of two native benthic species in situ, the shore crab (Carcinus maenas) and the European flounder (Platichthys flesus), with the invasive round goby, with regards to their common prey, the blue mussel (Mytilus edulis). Experiments were conducted in aquaria with artificial eelgrass and open sand habitats, with ten mussels placed in the centre of the aquaria. Trials consisted of single introduced gobies invading systems with conspecifics, shore crabs or European flounders, alone as well as together, for half an hour (controls were set as single introduced gobies). Introduced gobies stayed longer in the open habitat in the presence of a conspecific, compared to the other treatments, which suggests that round gobies are more prone to seek refuge when either or both natives are present. The number of mussels eaten by the introduced goby was higher in both treatments containing crab and flounder alone, indicating that gobies’ competitive behaviour of nearby resources may not be limited by single interspecific interactions. Competitive similarities between an established and invading goby will most likely cause a rise in the gobies dispersal in Öresund, since neither will limit one another. However, the native benthic composition in Öresund might be capable of temporarily limit the round gobies northward dispersal by forcing invading individuals towards refuge. Future studies should therefore investigate how other species in these waters may further limit the round gobies dispersal in the Öresund region.

Popular Abstract

Uninvited guests in troubled waters

The continuous movements of species beyond their geographical ranges are amongst one of the main threats towards biodiversity in many ecosystems around the world, since many of these have been unintentionally transported by the acts of humans. The invasive round goby (Neogobius melanostomus), a fish that originates from the Ponto-Caspian regions of Eurasia, began to appear in the Baltic Sea by the end of the 20th century via the ballast water from transoceanic shipping vessels. This has led to increased interactions, mostly as competition, with the native species that dwells in the bottom of the Baltic Sea. As a result, many species have suffered great losses in both numbers and spawning areas. Some gobies have already reached the Öresund strait, but it’s still unclear whether the native species in these waters will be able to hold back the gobies from expanding any further in the Öresund strait.

Two species, the European flounder (Platichthys flesus) and the shore crab (Carcinus maenas), were both caught in Öresund and used as native competitors for the invasive round goby. The idea was to let round gobies invade systems with either of the species alone or in a combination of both, for half an hour. I also looked at the same interactions between only goby individuals. The aquariums were each divided by two habitats, eelgrass on one side and sand on the other. Blue mussels (Mytilus edulis) were placed in the middle of each aquaria to act as a common food source. Four interactions by the invading goby were investigated: the starting time for when they ate their first mussel, the total amount of time they spent feeding, the total number of mussels eaten per individual and lastly the total amount of time spent in each of the two habitats.

Invading gobies spent the majority of time hiding in the eelgrass in the presence of either the flounder and crab alone, as well as both combined, indicating that both species might be able to force invading individuals to seek shelter. Further on, the presence of another goby increased the amount of time the invading individuals stayed outside the eelgrass, this might suggest that gobies may choose to stay separated if another goby is nearby. However, invading gobies still ate the largest amount of mussels in the presence of either a flounder or crab alone, which could mean that they rather seek and compete for nearby resources than to stay hidden. Interestingly, the shore crab seemed to be more threatening than the timid European flounder, mainly by pinching their claws towards the round goby whenever it swam closer to the mussels. I conclude that the native species of Öresund might very well be able to force invading gobies towards refuge, but the sad truth is that it will most likely only be a matter of time until the round gobies will negatively affect this ecosystem through its competitive strength for resources.

Many studies on the round gobies have emerged for the past decades, but only a handful has focused on the ecosystem of Öresund and its native inhabitants. This study may therefore give valuable information for future investigations about the invasive round goby in the waters around the Danish isles.






Master’s Degree Project in Biology/Aquatic Ecology/Marine Ecology 30 Credits 2018/30/09
Department of Biology, Lund University

Advisor: Anders Nilsson & Anders Persson
Department of Biology, Aquatic Ecology, Lund University

• author: Ottvall, Len-Oliver
• supervisor: Anders Nilsson
• organization: Degree Projects in Biology
• course: BIOM02 20172
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8963771
• date added to LUP: 2018-12-03 14:03:43
• date last changed: 2018-12-04 12:05:52