Germling success in Bladderwrack (Fucus vesiculosus) depending on substrate type & slope

Abstract

Recruitment of new individuals is essential for a population to survive and flourish and bladderwrack (Fucus vesiculosus) is on the decline in some parts of the Baltic Sea. The causes being multitude and complex, culminating to the loss of light penetration being the main culprit. As society moves forward, artificial submerged structures may serve as new footholds for a waning population as well as an increase in complexity of local benthic marine communities. This would promote a higher biodiversity which is coupled with more ecosystem services such as carbon sinks, photosynthesis and nursing as well as feeding grounds for commercially important species utilizing the habitats. Such structures are however usually composed mainly of vertical surfaces which may not be optimal for Fucus vesiculosus germlings to attach to. Today no studies have been dedicated to understanding the germling success depending on the slope of the substratum. In this study germling growth success on concrete and granite substrates at three different slopes, 0°, 45° & 90° were evaluated. These were placed in two harbour areas and two natural areas, which were then seeded with F. vesiculosus in Öresund between Denmark and Sweden. Results show that the germlings may settle on all slopes and substrates but has its success depending on local conditions. Large variations are found at the sites suggesting the possibility for the utilization of vertical surfaces at the right environmental conditions. At steeper slopes the densities of zygotes were lower, even if they were present. Concrete is the most common material for manufacturing foundations and tend to be at steep slopes as well as a smooth substrate when put into operations. Such features are challenging for the establishment of large perennial macroalgae, yet it is shown in this study that it can be achieved. This opens for future measures like rougher or protruding surfaces when constructing or replacing artificial submerged structures. This study shows a potential for colonisation of even vertical substrates allowing for new areas to establish F. vesiculosus communities and their ecological benefits to be reaped by both society and the marine life alike

Popular Abstract

Can manmade structures help Bladderwrack regain lost ground?

Recent research point towards the ability to use steep and smooth surfaces, like that of bridge pillars, for growing the important seaweed, bladderwrack.

Bladderwrack is a species of the wrack family that is common in the Baltic Sea and is important as a home for other species such as the Atlantic Cod, which has been the centre of some debate in the fishing industry. Unfortunately, bladderwrack itself has suffered great losses during the past century and is at risk for a local extinction in the coming 10-15 years if the current pace is kept. This is due to historical issues, mainly high inputs of nutrients - so called eutrophication – into the water. Which in turn has led to large amounts of algal blooms of plankton that utilize sunlight in the free water mass, the largest can be seen from space! This effectively shades and reduces the amount of sunlight that may penetrate through the water. As these plankton later die, their bodies sink and since they are so many, they create a chocking layer on the bottom that further shades the plants. Furthermore, they consume oxygen during decomposure, killing much of the life found there. Bladderwrack has previously been found at depths down to about 12m during the 1940’s. The current maximum depth is about 8m but then it has to be very clean waters. Since light cannot go as deep as it has, much space that used to have the seaweed are now unavailable as it is simply too dark. The situation is worsened by the fact that bladderwrack also needs rocks or similar hard material to attach themselves to, adding more difficulty to the pile.

Urbanization is ever expanding, more and more construction occurs in the oceans with bridges, wave-breakers, harbours and wind-parks to name a few. These structures are potentially suitable new shallow areas for the wrack to live on. However, the most common material is concrete which is often smooth and built at vertical angles. These properties are challenging when you are a baby bladderwrack attempting to find solid ground. The plants release sperm and eggs into the water at the full moon in either May or June. The fertilized eggs sink until they touch a hard surface such as a rock. A very steep rock is difficult to sink onto so the odds of establishment are low. The recent research does however point to this being possible with some help and timing. An experiment has been done in the Sound between Sweden and Denmark. The experiment was successful when attempting to both naturally and artificially sow new bladderwracks onto concrete as well as granite. The results point to concrete being just as good as its natural cousin granite. Three different angles were used, 0°, 45° and 90° and they all came out successful. Although there were fewer and fewer baby-wracks as the angles steepened there was still new growth coming in. This is hopeful news as it shows that when building, replacing or repairing, humans can help by seeding the new structures if this is timed with the full moons in springtime. Normally the eggs would not be able to spread very far before sinking, todays estimate is about 10m. Therefore, with a little help we can give them a head start in new areas and new wrack-forests can grow for both humanity and the ocean life to benefit from.

• author: Albertson, Louise
• supervisor: Per Carlsson
• organization: Degree Projects in Biology
• course: BIOM02 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9113061
• date added to LUP: 2023-03-30 16:41:52
• date last changed: 2023-03-30 16:41:52