Multi‐scale spatial dynamics of the Chesapeake Bay nettle, Chrysaora chesapeakei

Abstract

Untangling organisms' multi-scale spatial distributions is challenging due to their interactions with environments at multiple spatial and temporal scales. We deployed an Adaptive Resolution Imaging Sonar (ARIS) in a Chesapeake Bay sub-estuary to investigate multi-scale spatial distributions of the bay nettle (Chrysaora chesapeakei) in May-September of 2016 and 2017. Nettles were found to be dispersed in aggregations of multiple individuals. The average density of bay nettles in 2017 was higher than in 2016. Small aggregations (<5 m) were persistent in both years but only contributed <10% of total observed nettles. Large patches (>30 m) contributed~40% of the total observed nettles. Large patches were more common in creek habitat where nettle density was higher. Nettle density was found to hit a peak value once in 2016, while there were two density peaks in 2017. Different aggregation patterns were observed during the second peak period in 2017 in which the number of large patches increased dramatically. Within the surveyed waterscape, the spatial patterns were consistent over time with higher abundance in the source creek than in the river channel, which underscores that C. chesapeakei requires hard substrate in shallow creeks for its benthic polyp stage. Using the ratio between nettles in the creek and near creek mouth as a proxy for dispersal rate, more nettles were transported out of the creek in 2017 than in 2016. The increase in patch size and high dispersion rate in peak periods in 2017 suggests that individuals were moving out of the creek habitat as density increased. Results highlight the complex spatial structure of bay nettles, which has major impacts on density estimates and subsequently affects our understanding of jellyfish population dynamics and long-term trends.

The Influence of a Deep‐Water Intrusion on the Distribution of Chrysaora melanaster in the Southeastern Bering Sea

“…Spatial distributions of scyphozoan jellyfish are often influenced by source‐sink processes because the benthic life stage is key in regulating their population dynamics (Lucas, 2000, 2001; Makabe et al., 2015). Source‐sink patterns have been observed in estuaries, where semienclosed systems provide hard substrate for benthic scyphozoan polyps (e.g., Breitburg & Burrell, 2014; Shahrestani & Bi, 2018) and retention of juvenile medusae (Costello et al., 2006; Shahrestani & Bi, 2018; Shahrestani et al., 2020). Source‐sink dynamics have also been described for medusae in the SEBS, using trawl data for the period 1982–2004 (Chen et al., 2014).…”

“…Finally, the distribution of large medusae is often patchy at multiple scales, which makes jellyfish difficult to sample effectively with conventional nets. ARIS can effectively resolve jellyfish distributions at a range of spatial scales (Shahrestani & Bi, 2018; Shahrestani et al., 2020). However, ARIS is not able to detect small medusae (<50 mm) and its image resolution declines with distance from the instrument.…”

“…See Shahrestani et al. (2020) for details. The ARIS 3000 was mounted on a towed‐body frame with a forward‐looking, fixed field of view (10 m, Figure 2).…”

“…All C. melanaster (Morandini & Marques, 2010) and other medusa species were identified and enumerated immediately onboard the vessels in order to validate the images acquired by the ARIS 3000 (Sound Metrics, Bellevue, WA), a dual frequency sonar imaging camera, which is capable of recording near video images. See Shahrestani et al (2020) for details. The ARIS 3000 was mounted on a towed-body frame with a forward-looking, fixed field of view (10 m, Figure 2).…”

“…The typical scyphozoan life cycle contains a free-swimming or pelagic medusa stage, in addition to a sessile (benthic) polyp stage (e.g., Arai, 2009;Shahrestani et al, 2017). Scyphozoan spatial distribution and abundance are often closely related to their life history and habitats (e.g., Doyle et al, 2007;Shahrestani et al, 2020). Previous studies examined jellyfish catch in fishery research trawls (Brodeur et al, 2002(Brodeur et al, , 2008 and identified medusa concentrations on the northern side of the Alaska Peninsula.…”