Moll, Dorothee, Kotterba, Paul and Polte, Patrick (2015) Spawning bed selection of Atlantic herring in coastal waters of the Western Baltic Sea. [Talk] In: European Marine Biology Symposium 2015 (EMBS 50). , 21.-25.09.2015, Helgoland, Germany .

Abstract

Coastal areas are essential spawning and nursery habitats for many fish species, however they are also subject to multiple anthropogenic threats. Within these shallow waters, submerged aquatic vegetation (SAV) often plays a crucial role in structuring the habitat and providing suitable substrate for feeding, predator avoidance and spawning. Some commercially important fish species, such as Atlantic herring in the Western Baltic Sea, are strongly dependent on the availability of appropriate spawning beds formed by meadows of SAV in shallow brackish lagoons. The SAV composition within these estuarine systems usually follows a depth-dependent gradient with a pondweed community in water depths below 2 meters and a seagrass dominated zone between 2 and 4 meters. Hypothesizing a distinct habitat-related utilization of these different zones as spawning beds, SAV meadows at fixed transects of different water depths were sampled weekly during the spring herring spawning season (March to June) in three successive years. Herring spawn concentrations and egg mortalities were quantified along with the amount and composition of SAV. Additionally, hydrographical features (temperature, salinity, turbidity, sea state and oxygen saturation) were measured to analyze the impact of these parameters on spawning intensity and egg mortality. Our results showed a strong seasonal variation in spawning bed utilization but also strong inter-annual changes in SAV-composition (e.g. increasing amount of floating algal mats) and resulting spawning intensities and egg mortalities. Considering the persistent eutrophication-related general trend in decreasing SAV meadows, our results underline the demand for an integrated and sustainable management of shallow coastal spawning grounds.

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