The Effects of Marenzelleria spp on the Benthic Macro Fauna Community Structure in the Isefjord

Jeppe Olsen, Tore Reyhe, Elisabeth Happel & Ozan Kayikci

Studenteropgave: Semesterprojekt


In environmental biology, the interspecies interactions are always interesting and much studied as these relations may change the destiny and life of individuals and gradually the community structure in the given area. In addition to some regular relationships, such as symbiosis, commensalism, prey - predator and etc. there is also the term “invasive species”. The effect of such invasive species, Marenzellaria spp. is investigated in this survey. Marenzelleria spp. belongs to the Phylum Annelida (true worms), Class Polychaeta (bristle worms) and Family Spionidae. The Genus Marenzelleria has three species within, which are M. viridis, M. neglecta and M. arctia. Past studies showed us that this species can be one of the main “invasive species” in the Danish waters originally coming from the Americas and the North Sea over the past twenty years by means of ships ballast water. The area chosen to study is the Isefjord, one of the important brackish water system in Denmark, where can be considered as a sieve between the Atlantic Ocean and Baltic Sea, a good transition point. The main focuses of this report is on any changes of other species living locally in the fjord according to the presence or absence of this above mentioned species, another polychaeta Hediste diversicolor (which is likely to be the main rival of Marenzelleria spp..), Neanthes succinea; gastropoda Hydrobia spp., bivalvia Macoma balthica, Mya arenaria; and crustacea Corophium volutator. These interspecies balances also change according to the numbers of animals present in the area. This two make our main hypothesis and backbone of the whole project. Samples were collected from different parts of Isefjord, animals were counted and named into their species with the help of key books and research papers, the physical and chemical environment measured, i.e. salinity, organic content. Statistical analyses were on the collected data using the software Primer, maps and plans added, indices, graphs, tables made explaining both positive and negative correlations. These all showed us in the end that the different species are affected in different ways with the presence and changing abundance of Marenzelleria spp. and to our knowledge, the relationship between Hydrobia spp. and Marenzelleria spp. has been presented for the first time in this project showing a significant negative correlation. The presence of Marenzellaria spp. did show to change the community structure, but no evidence was found to suggest that the changes cause less biodiversity. Further studies should be made to understand better this very specific environment and its inhabitants’ relationships, as future is yet unknown for the locals against Marenzelleria spp. Key words: Marenzelleria spp., invasive species, brackish water, Isefjord, community structure, estuarine macro fauna, biodiversity, competition.

UddannelserMiljøbiologi, (Bachelor/kandidatuddannelse) Bachelor el. kandidat
Udgivelsesdato18 dec. 2008
VejledereGary Thomas Banta


  • Isefjord,
  • competition.
  • invasive species,
  • biodiversity,
  • brackish water
  • community structure,
  • estuarine macro fauna,
  • Marenzelleria spp.,