High prevalence of plastic ingestion by Eriocheir sinensis and Carcinus maenas (Crustacea: Decapoda: Brachyura) in the Thames Estuary

2020-02-12T14:24:49Z (GMT) by Dave Morritt Alex McGoran
These data were collected with the aim of investigating plastic ingestion by C. maenas and E. sinensis collected from the Thames Estuary. The hypotheses were 1) plastic ingestion would not differ between the species as both occupy a similar niche and are both generalist feeders 2) plastic would be more prevalent in the gastric mill, based on previous studies (e.g., Welden and Cowie, 2016).

A beam trawl with a standard mesh size of 80 mm and additional 16 mm fine mesh insert was deployed from the fishing vessel Boy Daniel SD4 at Erith, Thames Estuary. Samples were collected every three months. Between two and five benthic trawls were conducted per sampling session at a depth of between 9.2 m and –13 m. Brachyuran crabs were collected, identified and stored on ice overnight until they could be frozen the following morning at −20 °C. A total of 135 crabs were collected over a year, comprising C. maenas and E. sinensis. Trawls were undertaken on 4th December 2018, 6th March 2019, 14th June 2019 and 2nd October 2019.​

The carapace was removed and the gastric mill (GM), gastrointestinal tract (GIT) and gills were extracted and stored separately in 15 ml falcon tubes. These tubes were refrozen prior to digestion. A 10% potassium hydroxide (KOH) solution was used to remove organic material from the sample. The solution was heated to 60 °C and left to digest overnight. Filters were examined under a Leica MZ 6 microscope using mounted pins and forceps under 16–64 times magnification. All recovered items were photographed and stored in individual glass specimen tubes. Items were described by colour and shape and were measured (length and width) using ImageJ. Tangles of fibres were weighed on a Sartorius MC5 balance (to nearest 0.001g) and an estimate of the number of items in the tangle calculated. ​

Analysis of plastic pieces was undertaken using a PerkinElmer Spectrum One FTIR spectrometer, with an AutoIMAGE FTIR Microscope System PerkinElmer attachment. A representative subsample of ca. 10% (105 items overall) of each colour and shape combination (i.e., clear fibres, clear films and clear fragments) was analysed as per the recommendation of Lusher et al. (2017).