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Multi-trophic conservation and management strategies may be necessary if reciprocal linkages between primary producers and their consumers are strong. While herbivory on aquatic plants is well-studied, direct top-down control of seagrass populations has received comparatively little attention, particularly in temperate regions. Herein, we used qualitative and meta-analytic approaches to assess the scope and consequences of avian (primarily waterfowl) herbivory on temperate seagrasses of the genus . Meta-analyses revealed widespread evidence of spatio-temporal correlations between and waterfowl abundances as well as strong top-down effects of grazing on . We also documented the identity and diversity of avian species reported to consume and qualitatively assessed their potential to exert top-down control. Our results demonstrate that and their avian herbivores are ecologically linked and we suggest that bird herbivory may influence the spatial structure, composition, and functioning of the seagrass ecosystem. Therefore, the consequences of avian herbivory should be considered in the management of seagrass populations. Of particular concern are instances of seagrass overgrazing by waterfowl which result in long-term reductions in seagrass biomass or coverage, with subsequent impacts on local populations of waterfowl and other seagrass-affiliated species. While our results showed that bird density and type may affect the magnitude of the top-down effects of avian herbivory, empirical research on the strength, context-dependency, and indirect effects of waterfowl- interactions remains limited. For example, increased efforts that explicitly measure the effects of different functional groups of birds on seagrass abundance and/or document how climate change-driven shifts in waterfowl migratory patterns impact seagrass phenology and population structure will advance research programs for both ecologists and managers concerned with the joint conservation of both seagrasses and their avian herbivores.

Human activities degrade and fragment coastal marine habitats, reducing their structural complexity and making habitat edges a prevalent seascape feature. Though habitat edges frequently are implicated in reduced faunal survival and biodiversity, results of experiments on edge effects have been inconsistent, calling for a mechanistic approach to the study of edges that explicitly includes indirect and interactive effects of habitat alteration at multiple scales across biogeographic gradients. We used an experimental network spanning 17 eelgrass (Zostera marina) sites across the Atlantic and Pacific oceans and the Mediterranean Sea to determine (1) if eelgrass edges consistently increase faunal predation risk, (2) whether edge effects on predation risk are altered by habitat degradation (shoot thinning), and (3) whether variation in the strength of edge effects among sites can be explained by biogeographical variability in covarying eelgrass habitat features. Contrary to expectations, at most sites, predation risk for tethered crustaceans (crabs or shrimps) was lower along patch edges than in patch interiors, regardless of the extent of habitat degradation. However, the extent to which edges reduced predation risk, compared to the patch interior, was correlated with the extent to which edges supported higher eelgrass structural complexity and prey biomass compared to patch interiors. This suggests an indirect component to edge effects in which the impact of edge proximity on predation risk is mediated by the effect of edges on other key biotic factors. Our results suggest that studies on edge effects should consider structural characteristics of patch edges, which may vary geographically, and multiple ways that humans degrade habitats.

Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37° of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas in situ water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions.

Distribution of Earth’s biomes is structured by the match between climate and plant traits, which in turn shape associated communities and ecosystem processes and services. However, that climate–trait match can be disrupted by historical events, with lasting ecosystem impacts. As Earth’s environment changes faster than at any time in human history, critical questions are whether and how organismal traits and ecosystems can adjust to altered conditions. We quantified the relative importance of current environmental forcing versus evolutionary history in shaping the growth form (stature and biomass) and associated community of eelgrass (Zostera marina), a widespread foundation plant of marine ecosystems along Northern Hemisphere coastlines, which experienced major shifts in distribution and genetic composition during the Pleistocene. We found that eelgrass stature and biomass retain a legacy of the Pleistocene colonization of the Atlantic from the ancestral Pacific range and of more recent within-basin bottlenecks and genetic differentiation. This evolutionary legacy in turn influences the biomass of associated algae and invertebrates that fuel coastal food webs, with effects comparable to or stronger than effects of current environmental forcing. Such historical lags in phenotypic acclimatization may constrain ecosystem adjustments to rapid anthropogenic climate change, thus altering predictions about the future functioning of ecosystems.

Mesoscale features within the Gulf of Mexico (GOM) are known to influence zooplankton dynamics. Here we describe the composition of the zooplankton assemblage off shelf during summer in relation to environmental conditions, with emphasis on hyperiid amphipods and salps. Zooplankton samples were collected in summer of 2015 and 2016 in the central and southern GOM and in the Yucatan Channel in 2015. Two anticyclonic gyres were present in the north and less intense coupled cyclonic-anticyclonic gyres in the south. Zooplankton abundances differed temporally and spatially. Copepods were the dominant group (>55% of total abundance), while several less abundant taxa contributed to inter-annual and spatial differences. Amphipods and salps comprised <3% and their abundances were positively correlated. Fifty-six hyperiid and 10 salp species were identified. The dominant amphipod species were: Lestrigonus bengalensis (summer 2015), Anchylomera blossevillei and Primno spp. juveniles (summer 2016). Dominant salp species were Ihlea punctata, Iasis cylindrica and Thalia spp. Lower salp and amphipod species richness and abundance were associated with anticyclonic structures. Spatial and temporal differences were partly associated with symbiotic relationships between the groups. This study supports previous evidence of high spatial and temporal variability in zooplankton abundance in off-shelf waters of the GOM.

Hyperiid amphipods collected during 4 IMECOCAL (Spanish acronym for Mexican Investigations of the California Current) cruises in January, April, July, and October 2005 were analyzed for seasonal variation in abundance and diversity and to determine the influence of surface circulation. The number of species was high in all seasons (between 79 and 92), but abundances showed remarkable differences. The total number of amphipods was lowest in January and highest in October (geometric means were 82 and 606 ind. 1000 m–3respectively). Multivariate analysis based on similarity indices demonstrated a tight coupling between species composition and mesoscale structures. The largest cluster joined 67 stations, with 40% of similarity being explained by 4 species (Vibilia armata,Lestrigonus schizogeneios,Eupronoe minuta, andPrimno brevidens). The geographic position of these stations coincided with the main California Current (CC) flow from spring to autumn. Subgroups were defined by minor seasonal differences. In contrast, the CC flow during winter was reduced to a meander off north Baja California, and was surrounded by oligotrophic water as indicated by the presence of the hyperiidsAnchylomera blossevilleiandPhrosina semilunataplus 3 of the dominant species (V. armata,E. minuta, andP. brevidens). To the south of this front, other clusters with high oceanic influence were formed. In 2005, 3 eddies were detected in the area: one anticyclonic eddy in April and 2 cyclonic eddies in July. The anticyclonic eddy located in the southwest had its own faunal cluster that had high diversity but low population density. The main species in the anticyclonic eddy wasPlatyscelus ovoides. Only one of the cyclonic eddies had a unique faunal identity, being strongly dominated byVibilia armata; this was located in the north between the CC flow and the coast. The other eddy was large and situated in the middle of the area, with a faunal array analogous to that in the CC flow. Correlation between hyperiid and salp species abundances suggested that the increase in salps (Salpa fusiformis,Thalia orientalis,Cyclosalpa bakeri) in spring could be relevant, as many hyperiid species showed a strong increase at this time. However, the most correlated salp wasCyclosalpa danae, which occurred only in October. Chains ofC. danaeaggregates were firmly attached in the samples. This would promote the aggregation and survival of amphipod hosts, particularly small species such asLestrigonus schizogeniosandL. bengalensis.

Salps off Baja California (BC) showed substantial changes during El Niño of 1997–1998 and La Niña of 1998–1999. Salps were particularly abundant during the warm phase and showed a decreasing trend after the transition to cool conditions (October 1998). Salp swarms (>1 salp m–3) were present throughout the study period, with the exception of October 1999 and October 2000. They appeared more frequently S of Punta Baja (30°N). The most abundant species wasThalia orientalisfollowed bySalpa fusiformis.T. orientalisdecreased in abundance from winter 1998 to autumn 1999, whileS. fusiformisshowed a strong increase during the development and establishment of La Niña (autumn 1998 and winter 1999). Other species (T. rhomboides,T. cicar,Cyclosalpa strongylenteron,C. polae,S. cylindricaandRitteriella amboinensis) associated with warmer waters were present off the southernmost part of the BC peninsula. They were probably advected into the area from the SSW by an intensified coastal poleward jet that characterized the El Niño peak in the area. Estimates of carbon ingestion from daily rations ofThaliaspp. andS. fusiformisindicated that swarms required from <1 to >100% of the daily primary production and phytoplankton biomass. Fecal pellet production of swarms of these species was estimated at between <1 and 609 mg C m–2d–1. Considering that size and sinking rates of fecal pellets are related to salp body size, the swarms ofThaliaandS. fusiformismay have had a differential impact on the pelagic ecosystem in terms of recycling and vertical transport of biogenic material through the water column.

The global distribution of primary production and consumption by humans (fisheries) is well-documented, but we have no map linking the central ecological process of consumption within food webs to temperature and other ecological drivers. Using standardized assays that span 105° of latitude on four continents, we show that rates of bait consumption by generalist predators in shallow marine ecosystems are tightly linked to both temperature and the composition of consumer assemblages. Unexpectedly, rates of consumption peaked at midlatitudes (25 to 35°) in both Northern and Southern Hemispheres across both seagrass and unvegetated sediment habitats. This pattern contrasts with terrestrial systems, where biotic interactions reportedly weaken away from the equator, but it parallels an emerging pattern of a subtropical peak in marine biodiversity. The higher consumption at midlatitudes was closely related to the type of consumers present, which explained rates of consumption better than consumer density, biomass, species diversity, or habitat. Indeed, the apparent effect of temperature on consumption was mostly driven by temperature-associated turnover in consumer community composition. Our findings reinforce the key influence of climate warming on altered species composition and highlight its implications for the functioning of Earth’s ecosystems.

While considerable evidence exists of biogeographic patterns in the intensity of species interactions, the influence of these patterns on variation in community structure is less clear. Studying how the distributions of traits in communities vary along global gradients can inform how variation in interactions and other factors contribute to the process of community assembly. Using a model selection approach on measures of trait dispersion in crustaceans associated with eelgrass (Zostera marina) spanning 30° of latitude in two oceans, we found that dispersion strongly increased with increasing predation and decreasing latitude. Ocean and epiphyte load appeared as secondary predictors; Pacific communities were more overdispersed while Atlantic communities were more clustered, and increasing epiphytes were associated with increased clustering. By examining how species interactions and environmental filters influence community structure across biogeographic regions, we demonstrate how both latitudinal variation in species interactions and historical contingency shape these responses. Community trait distributions have implications for ecosystem stability and functioning, and integrating large-scale observations of environmental filters, species interactions and traits can help us predict how communities may respond to environmental change.