Lethal effect of filamentous algal blooms on Atlantic herring (Clupea harengus) eggs in the Baltic Sea

Abstract

1. During this study, the effects of epiphytic filamentous algae on the survival of demersal spawned fish eggs were investigated in one of the most important spawning grounds of herring in the western Baltic Sea, which is subject to intense and ongoing eutrophication.2. In coastal marine ecosystems all over the world, eutrophication is a primary water quality issue, often resulting in mass developments of bloom-forming algae.Macro-algal blooms have immense ecological effects, as they alter the structure and the function of an ecosystem. Numerous fish species are affected, as they depend on those coastal areas for spawning and as juvenile habitats.3. A comparison of the survival of herring eggs on two natural spawning beds revealed an immense impact of a filamentous algal bloom. The mortality rate reached nearly 100% in the area with massive occurrence of filamentous brown algae.4. Hypothesizing that the presence of filamentous algae facilitates herring egg mortality, field and laboratory experiments were conducted and revealed particular effects of distinct algal species. The survival rate of artificially spawned eggs on algal substrates and control substrates was compared. Whereas filamentous forms of the green alga Ulva intestinalis induced no immediate effect, significantly higher egg mortality was documented in experiments with the filamentous brown alga Pylaiella littoralis. Considering the ecological and economical importance of herring and othercoastal spawners on the one hand and the persisting and increasing effects of eutrophication and climate change on the other hand, the results of our study clearly underpin the necessity to increase global efforts to reduce nutrient loads in coastal waters.

Reduced Reproductive Success of Western Baltic Herring (Clupea harengus) as a Response to Warming Winters

“…As a result, herring eggs are extremely exposed to storm-induced wave action, and increasing storm frequencies greatly affect egg mortality (Moll et al, 2018). Furthermore, some filamentous, epiphytic brown algae, such as Pilayella littoralis, can cause drastic egg mortality on herring-spawning beds (Aneer, 1987;von Nordheim et al, 2020). The sum of the direct and indirect stressors outlined above, together with additional top-down effects, especially by egg predation (Kotterba et al, 2014(Kotterba et al, , 2017, demonstrates the diverse suite of environmental factors affecting herring reproductive success in coastal systems.…”

Caught in the middle: bottom-up and top-down processes impacting recruitment in a small pelagic fish

“…This spatial compression goes hand in hand with a reduced availability of the macrophyte species that herring could use as spawning substrates. In eutrophicated waters, certain algae, such as the epiphytic brown algae Pylaiella littoralis, can have mass occurrences in herring spawning areas, which can lead to massive egg mortalities up to 100% in Greifswald Bay (von Nordheim et al 2020) and other Central Baltic spawning grounds (Aneer and Nellbring 1982). These negative effects on herring eggs are likely related to the release of algal biotoxic exudates (Aneer 1987), as has also been suggested for the red algae Furcellaria spp.…”

Impact of temperature on Downs herring (Clupea harengus) embryonic stages: First insights from an experimental approach

“…In nature, oxygen solubility decreases with rising temperature, posing a potential risk to organisms unable to seek more suitable areas, such as embryos present in benthic substrates. Moreover, temperature rise can also be associated in the wild with other stress sources such as increased occurrence of fungal spores or algal blooms [108,109]. Therefore, further work needs to evaluate the combined impact of temperature and co-occurring stressors to reflect more accurately potential future consequences in the natural environment.…”