Eddy retention and seafloor terrain facilitate cross‐shelf transport and delivery of fish larvae to suitable nursery habitats

Abstract

For marine fish with ontogenetic shifts in habitat requirements, survival is dependent upon oceanographic transport of pelagic larvae from spawning locations and the arrival of settlement-stage larvae to nursery habitats. Settlement success for fish with nurseries on the continental shelf, such as many flatfish, relies on routes of transport that facilitate the delivery of larvae from offshore to suitable inshore habitats. To address spatial and temporal coupling between spawning, transport, and settlement, we utilized an individual-based biophysical model for the years 2000-2011 in combination with a juvenile habitat suitability model for arrowtooth flounder (Atheresthes stomias), an abundant predatory flatfish in the oceans off Alaska. Settlement success was inversely related to the availability of nursery habitat, but oceanographic variability dictated interannual patterns in larval supply to nurseries. Paradoxically, the majority of larvae were advected offshore and arrived to nurseries on the continental shelf. Shoreward bathymetric steering through glacial troughs that resulted in directed transport to nurseries was minimal despite the high proportion of larvae that accessed trough features. Based on modeling results and empirical observations, mesoscale eddies and retention near suitable settlement habitats enhanced settlement and recruitment magnitude. In advective ecosystems such as the Gulf of Alaska, settlement success and cross-shelf transport are augmented by transient retentive features that influence recruitment by facilitating the delivery of larvae to nursery habitats on the continental shelf. Survival for marine fish with a planktonic larval stage and a demersal juvenile stage is restricted by the successful transition from pelagic to benthic habitats, which can create a bottleneck to recruitment. High mortality during this early life-stage transition can be the result of intrinsic costs associated with morphological changes such as muscle and fin development and sensory improvements (Doherty et al. 2004; Almany and Webster 2006),

Source–sink recruitment of red snapper: Connectivity between the Gulf of Mexico and Atlantic Ocean

“…HYCOM and Mercator appear to present more variability (higher eddy kinetic energy) around the major currents (e.g., Loop Current, Florida Current, Gulf Stream) than the SABGOM model (Figure 2), and lower variability can result in fewer stochastic events (e.g., eddies, shifts in current) that can contribute to mixing of populations (Cetina-Heredia et al, 2019;Goldstein et al, 2020). Indeed, the rate of export Huebert et al, 2010).…”

“…HYCOM and Mercator appear to present more variability (higher eddy kinetic energy) around the major currents (e.g., Loop Current, Florida Current, Gulf Stream) than the SABGOM model (Figure 2), and lower variability can result in fewer stochastic events (e.g., eddies, shifts in current) that can contribute to mixing of populations (Cetina‐Heredia et al, 2019; Goldstein et al, 2020). Indeed, the rate of export from the Gulf to the Atlantic is more variable for Mercator and HYCOM experiments, both between years and between vertical distributions of larvae, corroborating that lower variability in the currents in SABGOM might lead to the patterns observed.…”

Multiple life‐stage connectivity of Pacific halibut (Hippoglossus stenolepis) across the Bering Sea and Gulf of Alaska

“…For example, egg and larval distributions are influenced by the strength and direction of ocean currents that vary among temperature regimes (Stabeno et al., 2012) and seasons (Stabeno, et al., 2016; Stabeno et al., 2002, 2016). Shifts in oceanographic currents can profoundly influence the survival of eggs and larvae through favorable transport to hospitable habitats that support growth and survival (Atwood et al., 2010; Bailey & Picquelle, 2002; Goldstein et al., 2020; Napp et al., 2000; Petitgas et al., 2013). Movement by young juveniles, however, is not dictated by oceanographic currents to the same degree as larval dispersal, and there is evidence for counter‐current migrations of Pacific halibut (Skud, 1977; St. Pierre, 1989; Clark & Hare, 1998; Webster et al., 2013).…”

Plankton size spectra as an indicator of larval success in Pacific sardine (Sardinops sagax)

“…The relationship between larval sardine, the EAC jet, and associated eddy habitats could be responsible for the negative relationship between recruitment potential and SST we observed. Several studies have associated upwelling cold‐core eddies with increased survival, citing reduced starvation‐driven slow growth and predation risk (Kasai et al, 2002; Shulzitski et al, 2016), as well as increased retention as possible mechanisms (Everett et al, 2015; Goldstein et al, 2020; Matis et al, 2014; Shulzitski et al, 2016, 2017). In contrast, our size distribution modelling revealed reduced mortality with increased SLA, a characteristic of anti‐cyclonic downwelling eddies (Everett et al, 2012).…”