​​​​Key Message

​​This indicator is a HELCOM supplementary indicator and is applicable in assessment units shared by Finland and Sweden.

The rate of embryo malformations indicates reproductive toxicity due to the presence of hazardous substances in the bottom sediments. The threshold value has not been achieved on all stations within each basin indicating that toxic effects of contaminants may be present. The variability of the malformation rate is much greater within a basin than between the Bothnian Sea and the Baltic proper.

The indicator evaluation results are based on the monitoring data on malformations in Monoporeia affinis carried out by Sweden, with complementary data for other amphipods in the Gulf of Finland provided by Russia.

ReproductiveDisorders Key message figure 1.png

Key message figure 1: Status assessment results are based on the evaluation of the indicator Reproductive disorders: malformed embryos of amphipods. The assessment is carried out using scale 2 HELCOM assessment units (defined in the HELCOM Monitoring and Assessment Strategy Annex 4), since no difference between the coastal and the offshore stations was found in the existing data.


The confidence of the indicator in the assessed areas is moderate to high since more than 20 years data for setting the threshold values has been used and the assessment data are collected from multiple stations surveyed on annual basis within each assessment unit.

The indicator is applicable in the waters of Finland and Sweden.

Preliminary evaluation has been conducted in the Bornholm basin (Hano Bight) and Southern Gulf of Finland (Russia); these results however require further analysis.

Relevance of the supplementary indicator

Amphipod embryos are sensitive to sediment toxicity during the embryogenesis, and a high rate of malformations develop if the sediment where the female forages are loaded with toxic chemicals (Key message figure 2). Many chemical pollutants induce various embryo aberrations (Key message figure. 2), which makes them useful as ecologically relevant indicators for chronic biological effects of environmental contaminants. For example, in amphipods, PAHs and PCBs increase frequency of malformed and membrane-damaged embryos (Löf et al. 2015), whereas frequency of embryos with arrested development increases due to elevated concentrations of some PAHs and metals.

Various amphipods and some fish species can be used for the indicator-based assessment. The amphipod Monoporeia affinis is a keystone species in the Baltic Sea. Its decreasing population due to impaired reproduction is a serious threat to the integrity of the ecosystem. Monoporeia affinis is an important food source for fish and other invertebrates; it also performs important bioturbation functions related to sediment oxygenation. Other amphipod species, such as Gmelinoides fasciatus, Pontogammarus robustoides and Gammarus tigrinus, that were used for the indicator development in the eastern Gulf of Finland are key members in the benthic communities in the coastal areas of the Baltic Sea (Gulf of Riga, Gulf of Finland, Curonian and Vistula Lagoons) and are an important prey of local fish and birds.​

ReproductiveDisorders Key message figure 2.png

Key message figure 2. Normal embryos of Monoporeia affinis of different developmental stages (to the left) and malformed embryos (to the right).


In the Baltic Sea, occurrence of malformed embryos in amphipods has been used as a bioindicator for reproductive toxicity caused by pollutants in benthic invertebrates for the last 20 years. The elevated frequencies of malformed embryos are regarded as a significant biological response for assessing the population-relevant effects induced by the combined exposure to the environmental contaminants in the sea sediments. The indicator provides information on the reproductive success and thereby population- persistence and stability.​

Policy relevance of the core indicator

BSAP segment and objective​​s

MSFD descriptor and criteria

Primary link

  • Healthy wildlife​

D8 Contaminants

D8C2 The health of species and the composition of habitats (such as their species composition and relative abundance at locations of chronic pollution) are not adversely affected due to contaminants including cumulative and synergetic effects.​​

Secondary link

  • Viable populations of species

  • Concentrations of hazardous substances are close to natural levels​


Other relevant legislation: WFD Biological quality (fish, benthic invertebrate, aquatic flora)


Cite this indicato​r

HELCOM (2017). Reproductive disorders: malformed embryos of amphipods. HELCOM supplementary indicator report. Online. [Date Viewed], [Web link].

ISSN 2343-2543

Download full indicator report​

HOLAS II component - Core indicator report – web-based version July 2017 (pdf)