Zebra mussel (Dreissena polymorpha) population in the newly formed Cardiff Bay

Zebra mussels are among the worlds most prolific invasive species, but few case studies assess occurrence and effects in artificial water bodies. Cardiff Bay was invaded soon after formation in 2001. Over four years, planktonic veliger surveys, Side Scan Sonar, under-water video, colonisation samplers and mesocosm experiments were used to investigate all life stages. Veligers were produced in 1-3 spawning events from May to September, with frequency and timing apparently varying facultatively under contrasting conditions between years. Peak densities reached 8-14 ind., with local variations reflecting flow, and numbers declined during high discharge. Veliger settlement as juveniles also declined at sits or times with the greatest flow, and settled densities in a dry year (2007) were 120 times greater than in a wet year (2008). Local substrate availability also affected settlement pattern. While no aggregation of zebra mussels occurred in the Bay's soft sediments, hard substrates and vertical surfaces at 0.5-7 m depth have been colonised extensively at densities of 250-6 600 . Local density estimates alongside crude assessments of habitat available suggest that Cardiff Bay could be occupied by a population of in excess of 10-31 million adults (excluding the Bay's aeration system), consistent with the large veliger density recorded in the water column. Most mussels are 1 year old, but year-class structure (4 cohorts) show that the Bay must have been occupied at least as early as 2003. These data are consistent with a rapidly established, large and extensive population of zebra mussels in Cardiff Bay now maintained by prolific larval production and settlement. In addition to the large risks of contamination of boats and onward dispersal, zebra mussels could have large ecological and environmental effects on Cardiff Bay.EThOS - Electronic Theses Online ServiceGBUnited Kingdo