Nearshore seascape connectivity enhances seagrass meadow nursery function

Abstract

Diverse habitats composing coastal seascapes occur in close proximity, connected by the flux of materials and fauna across habitat boundaries. Understanding how seascape connectivity alters important ecosystem functions for fish, however, is not well established. For a seagrass‐dominant seascape, we predicted that configuration and composition of adjacent habitats would alter habitat access for fauna and trophic subsidies, enhancing nursery function for juvenile fish. In an extensive Zostera marina seagrass meadow, we established sites adjacent to (1) highly complex and productive kelp forests (Nereocystis luetkeana), (2) unvegetated sand habitats, and (3) in the seagrass meadow interior. Using SCUBA, we conducted underwater observations of young‐of the‐year (YOY) rockfish (Sebastes spp.) recruitment across sites. Using generalized linear mixed effects models, we assessed the role of seascape adjacency relative to seagrass provisions (habitat complexity and prey) on YOY recruitment. YOY rockfish collections were used to trace sources of allochthonous vs. autochthonous primary production in the seagrass food web, via a δ13C and δ15N isotopic mixing model, and prey consumption using stomach contents. Overall, seagrass nursery function was strongly influenced by adjacent habitats and associated subsidies. Allochthonous N. luetkeana was the greatest source of energy assimilated by YOY rockfish within seagrass sites. In seagrass sites adjacent to N. luetkeana kelp forests, YOYs consumed higher quality prey, which corresponded with better body condition relative to sites adjacent to sand. Moreover, kelp forest adjacency enhanced YOY rockfish recruitment within the seagrass meadow, suggesting that habitat complexity is a key seascape feature influencing the nursery function of nearshore habitats. In general, to promote seascape connectivity, the conservation and restoration of nursery habitats should prioritize the inclusion of habitat mosaics of high structural complexity and productivity. We illustrate and emphasize the importance of using a seascape‐level approach that considers linkages among habitats for the management of important nearshore ecosystem functions.

Kelp Forest Zooplankton, Forage Fishes, and Juvenile Salmonids of the Northeast Pacific Nearshore

“…Olson et al. () documented that kelp bed connectivity enhanced seagrass nursery function for rockfishes, and this is consistent with our hypothesis of a possible similar “adjacent” kelp forest function as a reservoir for forage fish prey. Similar prey–phytal relationships have been found for other species of fish in kelp beds (Koenigs et al.…”

“…Furthermore, kelp habitats may provide an important reservoir of phytal-associated zooplankton prey resources for fish that feed on these organisms, which may contribute to the higher presence of salmon, Surf Smelt, and Pacific Herring in as well as adjacent to open-water habitats. Olson et al (2019) documented that kelp bed connectivity enhanced seagrass nursery function for rockfishes, and this is consistent with our hypothesis of a possible similar "adjacent" kelp forest function as a reservoir for forage fish prey. Similar prey-phytal relationships have been found for other species of fish in kelp beds (Koenigs et al 2015).…”

“…Kelps and seagrasses provide a source of zooplankton prey, such as gammarid amphipods and harpacticoid copepods, for resident fish like young‐of‐the‐year rockfishes (Olson et al. ). Simenstad et al.…”

“…Boldt et al (2019) concluded that prey resources may dictate forage fish abundance. Kelps and seagrasses provide a source of zooplankton prey, such as gammarid amphipods and harpacticoid copepods, for resident fish like young-of-theyear rockfishes (Olson et al 2019). Simenstad et al (1988) noted that eelgrass meadows provide a source of harpacticoid copepods for Surf Smelt.…”

Spatial and temporal persistence of nearshore kelp beds on the west coast of British Columbia, Canada using satellite remote sensing

“…Because both nutrient availability and stratification are linked to temperature and mixing, this sub-region, particularly Sansum Narrows may experience better kelp growth conditions than the region as a whole. This is significant as the persistence of kelp populations here may be an important source of spores to adjacent areas and facilitate connectivity between habitats (Reed et al 2004;Coleman et al 2011;Olson et al 2019).…”