Invasive Alert: Details of a preliminary investigation on Mytella strigata (Hanley, 1843)
Reliable information has been collected from few shrimp farms and adjacent natural ecosystems on the presence of Black mussel Mytella strigata (Hanley, 1843) (Bivalvia; Mytilidae) in Muthupanthiya coastal belt in Northwestern province.
Empty bivalve shells were found at the edge of the main supply canal at Anawilundawa.The shells were similar to the marine brown mussel Perna perna, but quite different. A search through internet resources and investigation of samples gave the probable identity of Mytella strigata.
Important Facts
The first record of this species from the Indian subcontinent was reported by Jayachandran et al (2019) from the brackish backwaters in Cochin, Kerala, South India. The species had previously been identified as an alien invasive species in Southeast Asia by Lim et al. (2018) who found it present in the Johore Strait, Singapore. The Kerala find was the fourth from the Indo-Pacific, having been found in the Philippines in 2016 & 2017, and reported again from southern Philippines in 2021 (Fabiosa et al, 2021) and the Gulf of Thailand (2019). The first record of the species from clam ponds in Taiwan was reported in 2021 (Huang et al, 2021).
This species is known to clog the pipes and also spread rapidly in their introduced areas. Since it is already recorded along the Indian coastline, the occurrence in Sri Lanka could either be a free ride of the species attached to marine traffic or might also be associated to aquaculture as currently their presence in large numbers are confined to shrimp pond bottoms.
Outcomes of further investigations
On January 9th 2024 a prawn culture pond that had been drained was inspected. The bottom was littered with clusters of cf. Mytella strigata basically attached to hard objects or to each other in clumps partially buried in the soft substrate of the pond floor. Three and a half months previously when the pond had been filled with water, it hadbeen free of bivalves, as per the information from farmer.
How to identify
M. strigata shells are transverse, compressed side to side. Dorsally arcuate, not angulated, posterior rounded, ventral concave with a very narrow byssal gap. Umbones terminal, anterior narrowly rounded, pointing down. Exterior colour dark blackish-brown, interior purplish, largely discoloured by encrustations. The common brown mussel Perna perna found in intertidal marine habitats is a lighter brown, has a straight ligament margin anteriorly with an angulated dorsum and a straight postero-dorsum. The ventral margin is more or less straight.