Plastic bottle washed ashore photo Andrew Pearson Plastic bottle washed ashore photo Andrew Pearson

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Published: Potential Impacts of Plastic on Marine Protected Species and Habitats

What are the potential impacts of marine plastic on the MPA network of England and Wales? Our report for Defra explores the issue.

Plastic pollution in the marine environment is widespread. In a standard benthic survey across English inshore waters, Natural England found microplastic particles inside and outside of Marine Protected Areas (MPAs) including twenty-two MPA study sites, and in 61.2% of the samples collected.

While the presence of plastic litter in the marine environment is well known, there is an evidence gap regarding its impact on protected species and habitats in England and Wales, as identified by Natural England, The Joint Nature Conservation Committee and Natural Resources Wales.

ABPmer was commissioned by Defra’s Marine Biodiversity Impact Evidence Group to review and report on available information to better understand plastic pollution impacts on English and Welsh inshore and offshore protected species and habitats.

Controlling factors influencing potential impact from marine plastics

A number of key controlling factors influence the potential for impact from marine plastics on habitats and species. Concentrations of plastic in the environment is of upmost importance when considering potential for impact; however, this is difficult to determine as reported concentrations can exhibit large spatial variability, and there is a lack of comprehensive data on environmental concentrations of different sizes and types of plastic.  

Many of the studies reviewed examined the effects of unrealistically high concentrations of plastic relative to observed existing environmental concentrations, so care is needed when inferring the current risk to MPA features.

Variations in plastic size, shape and type and functional groups and feeding strategies of species also give rise to differential impacts, though these are not always consistent across species groups.

Potential for impact from marine plastics

The potential impact from marine plastics on habitat features, sub-features, species and bird features was assessed and categorised as ‘High’, ‘Medium’, ‘Low’, ‘No effect’ or ‘Undetermined’.

The following impact pathways of marine plastics were considered for each MPA feature:

  • Ingestion
  • Toxicity
  • Entanglement
  • Smothering, abrasion or dislodgement
  • Substrate change
  • Habitat provision

Smaller organisms are only capable of ingesting smaller plastic particles (microplastics and nanoplastics). While small organisms have been shown to exhibit biological effects following ingestion, lethal effects are rarely observed, and where they are, the plastic concentrations tested in laboratory conditions tended to far exceed environmental relevance.

Larger marine species are more vulnerable to larger plastic debris that they may ingest or become entangled with, and significant effects on species at an individual level have been observed in the environment. For example, there is evidence of seals and bottlenose dolphins suffering severe injuries following entanglement in plastic debris and in some cases has ultimately led to death. However, no evidence suggests that this physical impact is having population level effects on MPA features.

Similarly, whilst studies suggest some potential effects on habitat functioning (e.g. through smothering or substrate change), the decline of habitats due to plastic pollution alone is not evidenced.

It should be noted that gradual declines in habitats are difficult to attribute to a particular single pressure, and it is possible that plastic poses an additional cumulative anthropogenic pressure.

Therefore, based on the evidence reviewed, the highest impact determined for any habitat or species feature was ‘Medium’. This meant that generally either:

  • Significant effects on species at an individual level have been observed;
  • Sub-lethal effects on species were found at environmentally relevant concentrations following exposure to plastic; or
  • There is some evidence of altered habitat functioning due to marine plastic.

Evidence gaps

It is important to note that the issue of marine plastics is a relatively new topic in scientific research, and the impact and effects of plastics in the environment are currently relatively poorly understood.

This is exemplified by our gap analysis, where most habitats and species had either no, or limited evidence on the impact of marine plastics. Equally, there is generally low to medium confidence in the assessment of the potential for impact.

Further, the assessment of the potential for impact is exclusively based on the evidence available for the species or habitat. It does not account for effects, impact pathways or plastic types, shapes or sizes not documented in the available evidence.

Plastic in the marine environment will continue to increase (possibly quite rapidly) and only degrade slowly into smaller plastic particles, increasing exposure to marine organisms in the long term.

Long-term risks or sub-lethal impacts of exposure to plastics are particularly uncertain at the current time, and the persistent nature of plastic means exposure would be continuous throughout all life stages and would not decrease in the environment.

Wider evidence gaps also exist relating (but not limited) to plastic type (e.g. nanoplastic), impact pathways (e.g. toxicity effects), receptors (e.g. species at larval and juvenile life stages, and sub-lethal effects to birds and marine mammals) and scalability to the population level.


Based on the available evidence, a list of protected features can be inferred as being of relatively higher risk from plastics, therefore are of higher priority for conservation effort related to plastic pollution.

However, available evidence is sparse in some areas. New studies on impacts of plastic are emerging all the time, evidence which should be considered as it becomes available.

Download the full report at the Defra website.

Image: Andrew Pearson

ABPmer routinely advises marine sectors on regulatory and policy matters and has a long history supporting government and its agencies in developing the evidence base against which policy decisions are made.