Evidence for regional‐scale controls on eelgrass (Zostera marina) and mesograzer community structure in upwelling‐influenced estuaries

Abstract

Community structure and function in ecosystems are dependent on top-down and bottom-up factors, which vary across local, regional, and temporal scales. In estuaries of the U.S. Pacific Northwest coast, eelgrass (Zostera marina) ecosystems are exposed to latitudinally varying oceanographic inputs in the form of ocean upwelling. Previous research suggests that ocean upwelling is critical to eelgrass and ulvoid macroalgae abundance, but the degree to which secondary producers are controlled by processes at regional vs. local scales is unknown. Here, we consider the relationships among primary producers (eelgrass, ulvoid macroalgae, and epiphytic microalgae), epifaunal mesograzers, and mesopredator fish within and across three Oregon, U.S.A., estuaries during a springsummer season to examine the role of multiple scales in structuring these communities. Our objectives were to determine the relative importance of local and regional scales in organizing eelgrass communities and the potential of regional oceanography and trophic interactions in regulating patterns of primary producers in this system. We found that regional and seasonal patterns strongly influenced eelgrass community structure, providing support for the hypothesis that regional bottom-up forcing predominantly controls these assemblages. Additionally, local effects were important to the patterns of primary producers, mesograzers, and mesopredator fish at specific sites, suggesting limited top-down control. Regarding management and conservation, the implications of our results are that in these highly productive systems, the potential for consumers to moderate the effects of eutrophication may be limited.

Regional processes are stronger determinants of rocky intertidal community dynamics than local biotic interactions

“…Instead, our results are consistent with the observational data of Menge et al (2015), which implicates regional environmental factors and ecological subsidies, mostly driven by ocean conditions, as important drivers of community structure. Other recent studies support the contribution of regional variability in organizing community structure in rocky intertidal (Moulton and Hacker 2011, Menge and Menge 2013, Vinueza et al 2014) and estuarine (Hessing-Lewis and Hacker 2013, Duffy et al 2015, Hayduk et al 2019) systems, and illustrate why it is important to take a meta-ecosystem approach when characterizing the factors important to local community structure.…”

“…, Hayduk et al. ) systems, and illustrate why it is important to take a meta‐ecosystem approach when characterizing the factors important to local community structure.…”

A Feeding‐Ecology‐Based Approach to Evaluating Nursery Potential of Estuaries for Black Rockfish

“…Interestingly, the isopod Pentidotea resecata was found to make up a large percentage of epifauna on eelgrass in Yaquina Bay (Hayduk et al. ), yet only one P. resecata was found in the diet of juvenile Black Rockfish. Although juvenile rockfish are thought to be opportunistic feeders (Reilly et al.…”

Latitudinal variation in plant defence against herbivory in a marine foundation species does not follow a linear pattern: The importance of resource availability

“…Along this latitudinal range, mean coastal sea surface temperature (SST) decreases from south to north (Figure 1) while the mean nutrient (i.e., NO 3 ) concentration exhibits a maximum off the coast of California where coastal upwelling is most intense (Figure 1b and Supporting Information Figure S2). This upwelling strongly influences the nutrient availability and community structure of coastal reefs (Menge & Menge, 2013) and estuaries in the US west coast (Hayduk et al, 2019;Hessing-Lewis & Hacker, 2013).…”

“…Although, to our knowledge, there are no comprehensive studies on the levels of herbivory along the sites of this study, numerous herbivores that feed on seagrass such as isopods, amphipods and waterfowl are present in the study sites (personal observation, G.H., K.B., S.K., F.T., Duffy et al, 2013;Hayduk et al, 2019;Kollars et al, 2017;Reynolds et al, 2012). While the studies that have explored patterns in herbivory pressure in seagrasses do not find a consistent latitudinal tendency (Vergés et al, 2018), temperate seagrasses are expected to suffer increasingly higher herbivory damage due to the poleward expansion of tropical herbivores (Hyndes et al, 2016;Vergés et al, 2014).…”