Effects of Iron- and Organic-Rich Waters on the Baltic Blue Mussel

Abstract

Brownification is an increasing problem in the Northern Hemisphere. In the south of Sweden, the Kristianstads commune, its Vattensriket biosphere, and the local farmers and fishermen are particularly affected by the brownification of their main river, the Helge Å. The iron concentration and the concentration of dissolved organic matter have increased by 284% and 118%, respectively, in 40 years. Furthermore, the Hanö bay, in which the Helge Å discharges itself, is currently suffering from troubles whose source have yet to be identified. In order to determine the effects of the iron- and organic-rich water of the Helge Å on the marine fauna, and possibly detect a link with the Hanö bay’s recent troubles, four experiments using the local blue mussels have been performed. Taking advantage of the mussel’s filteringcapacities, abundance, widespread presence, and their ability to accumulate metals such as iron, these experiments observed their growth, filtering efficiency and iron content in relation to their exposure to the Helge river water. The results indicate that the river’s organic richness offer the mussels a short-term benefit, however it may be inducing a long-term penalty due to particle- or iron- related constant lowlevel stress. Additional observations indicate the potential influences of dredging of the local port, indicating further interesting paths of investigation.

Popular Abstract

In the east coast of Skania, in the Hanö Bay, problems have been reported regarding fish and eel health. Previous investigations have narrowed the problem’s source to two phenomena, one of which is brownification. Brownification is the process in which the colour of water becomes more brown due to the increase of dissolved organic matter and iron. Helge Å, the river that feeds into the Hanö bay, is known to have endured intense brownification: its iron content has almost tripled in 40 years.

In order to investigate whether the Helge Å’s brownification is a cause to the disruptions in the Hanö Bay, four experiments were devised using the Baltic’s strongly present blue mussel. The mussel is not only a strong candidate for evaluating the levels of iron in the water, but it also remains in one location regardless of troublesome water, which offers a strong advantage in studying its reaction to the Helge Å water. Additionally, because the blues mussels filter vast amounts of water through gills in order to feed, the effects observed on the mussel’s gills could be assumed to be similar on fish and eel gills. Finally, the large amounts of water passing through the mussels gills could accentuate and accelerate any negative effects conferred by the water, making mussels highly sensitive detectors of water anomalies.

In this project, two laboratory experiments questioned the mussels’ immediate reaction and short term growth when in contact with Helge Å water, and two field experiments questioned the mussel’s short term and long term growth in regard to their proximity to Helge ’s estuary in the Hanö Bay.

For the immediate reaction, individual mussels were placed in different flasks with the phytoplankton called Rhodomonas as food. The mussels’ feeding speed was evaluated by counting the amount of food remaining in the flasks through time.

For the laboratory short term observations, an experimental setup was made in order to feed six aquaria with Rhodomonas during 2 months. Three of the aquaria had Helge Å water flowing through, while the three other aquaria had clear water flowing through.

For the field short term observations, cages containing mussels were placed at different distances from the Helge Å estuary in Åhus. The cages were left in the Baltic during the months of October and November and were collected at the beginning of December.

Finally, for the long term observations, mussels were collected in the wild at different distances from the Helge Å estuary. The mussels’ length, weight, age and location were compared to their iron content in order to identify if a mussel’s distance to the Helge Å estuary had any bearing on the amount of iron they accumulated.

The results of the experiments have demonstrated that the mussels have a bit more difficulties feeding in the Helge Å water while still getting a certain short term nutritional benefit from it. However, their long term growth appears to diminish when in proximity to Helge Å’s estuary. This suggests that the organic-rich and iron-rich waters induce a certain low-level stress on the mussels while offering a rich food-source, pointing towards a potential important source of stress for other species that do not benefit from the nutritional aspect of the Helge Å water.

Supervisor: Emma Kritzberg and Per Carlsson
Master´s Degree Project - Aquatic Ecology 45 credits, 2015
Department of Biology, Lund University

• author: Fruh, Johan
• supervisor: Emma Kritzberg; Per Carlsson
• organization: Degree Projects in Biology
• course: BION35 20132
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8596254
• date added to LUP: 2016-02-03 12:25:59
• date last changed: 2016-02-03 12:25:59