Abstract
Multi-tiered oyster aquaculture cages may provide habitat for fish assemblages similar to natural structured seafloor. Methods were developed to assess fish assemblages associated with aquaculture gear and boulder habitat using underwater video census combined with environmental DNA (eDNA) metabarcoding. Action cameras were mounted on 3 aquaculture cages at a commercial eastern oysterCrassostrea virginicafarm (‘cage’) and among 3 boulders on a natural rock reef (‘boulder’) from June to August 2017 in Long Island Sound, USA. Interval and continuous video recording strategies were tested. During interval recording, cameras collected 8 min video segments hourly from 07:00 to 19:00 h on cages only. Continuous video was also collected for 2-3 h on oyster cages and boulders. Data loggers recorded light intensity and current speed. Seawater was collected for eDNA metabarcoding on the reef and farm. MaxN measurements of fish abundance were calculated in video, and 7 fish species were observed. Black sea bassCentropristis striata, cunnerTautogolabrus adspersus, scupStenotomus chrysops, and tautogTautoga onitiswere the most abundant species observed in both oyster cage and boulder videos. In continuous video, black sea bass, scup, and tautog were observed more frequently and at higher abundance on the cage farm, while cunner were observed more frequently and at higher abundance on boulders within the rock reef. eDNA metabarcoding detected 42 fish species at the farm and reef. Six species were detected using both methods. Applied in tandem, video recording and eDNA provided a comprehensive approach for describing fish assemblages in difficult to sample structured oyster aquaculture and boulder habitats.
Highlights
Oyster aquaculture cages contribute structure to marine environments and may provide valuable habitat for ecologically and economically important species of fish
A total of 7 fish species were observed at the cage farm over the course of the deployments: black sea bass, banded rudderfish Seriola zonata, butterfish Peprilus triacanthus, cunner, scup, tautog, and yellow jack Carangoides bartholomaei
Abundance of the 4 most common fish species associated with oyster aquaculture cages varied over time (11 July, 3 and 23 August; Fig. 3)
Summary
Oyster aquaculture cages contribute structure to marine environments and may provide valuable habitat for ecologically and economically important species of fish. Traditional sampling methods (e.g. lift or drop net, fish traps, quadrats, suction dredge) are difficult to employ in structured habitats, but previous studies suggest that oyster cages create habitat that is functionally similar to natural structured seafloor (e.g. DeAlteris et al 2004, Tallman & Forrester 2007, Erbland & Ozbay 2008, Marenghi et al 2010, MercaldoAllen et al 2020) These studies support a strong association between the presence of structure-oriented fish species and oyster cages, but lack direct visual observation of fish interactions with cages, and provide limited insight into composition of fish assemblages and fish abundance and behavior in and around aquaculture gear
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