Climate drives the geography of marine consumption by changing predator communities.

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.

A reciprocal transplant approach to predation in fouling communities found in natural and artificial habitats.

Human influence along the coastline is a significant threat to biodiversity and includes the alteration or replacement of natural habitat with artificial structures. Infrastructure such as docks and marinas are common throughout the world and typically have negative impacts on coastal flora and fauna. Impacts include the reduction of native biodiversity, the increase of introduced species, and the alteration of biotic interactions (e.g., predation). Many studies examine human disturbance on biotic interactions within a single habitat (i.e., docks or marinas) but what lacks are paired comparisons using standardized methods of biotic interactions between artificial and nearby natural habitats. In the current study, benthic fouling communities were allowed to develop, with and without predator access, in artificial and seagrass habitats. Cages were used to reduce predation and removed to expose communities to fish predators. Prior to exposure, communities were either left at their original site or transplanted to the opposite habitat and changes in the percent cover of species found were compared. Initially, community composition differed between habitats and when predation was reduced (caged vs. open). When developed communities within cages were exposed to predators, predation was strong but only in artificial habitats and regardless of where communities originated. In contrast, little predation occurred at seagrass sites on previously caged communities developed within seagrass beds or that were transplanted from artificial habitat. Taken together, results indicate that the strength of biotic interactions can differ depending on habitat, leading to changes in community composition. With the continuous expansion of artificial structures world-wide, it is becoming increasingly important to understand not only their effects on biotic interactions and biodiversity but also how these effects extend and compare to adjacent natural habitats.

Impacts of habitat and predation on epifaunal communities from seagrass beds and artificial structures.

Within the coastal marine environment, the increased presence of artificial habitat can have negative impacts on the functioning of marine communities. Artificial structures provide a novel, hard surface for the colonization and growth of a variety of marine species and disproportionally favor introduced species. With the global rise in hardened shorelines, it is imperative to examine the ecological processes that occur within these habitats to those occurring in natural habitats. Here, we compared habitat differences in fouling community composition of different successional ages as well as the impact of predation on those communities. Specifically, we investigated how communities differed with respect to natural (seagrass beds) and artificial (docks) habitats and then exposed previously caged communities to predators to examine prey-specific effects within each habitat and on different aged communities. We found that habitat was a good predictor of community structure including both total species richness and introduced species richness higher in artificial habitats. We expected predators to increase available space allowing increased species co-existence, however, this was not the case. Predators in both habitats reduced richness despite having a strong impact on the percent cover of dominant groups. Predators also reduced introduced species richness, particularly in artificial habitats. Artificial structures are an important pathway of success for introduced species and results here show the importance of biotic resistance within these habitats, potentially limiting the spread of introduced species into natural habitat. Overall, species found within the different habitats could be predicted based on life history traits and predators did not increase the similarity of communities between habitats though still acted in a comparable way, reducing the dominant groups.

Spatial and temporal shifts in the diet of the barnacle Amphibalanus eburneus within a subtropical estuary.

The success of many sessile invertebrates in marine benthic communities is linked to their ability to efficiently remove suspended organic matter from the surrounding water column. To investigate the diet of the barnacle Amphibalanus eburneus, a dominant suspension feeder within the Indian River Lagoon (IRL) of central Florida, we compared the stable isotopes ratios (δ13C and δ15N) of barnacle tissue to those of particulate organic matter (POM). Collections were carried out quarterly for a year from 29 permanent sites and at sites impacted by an Aureoumbra lagunensis bloom. δ13C and δ15N values of Amphibalanus eburneus varied across sites, but δ15N was more stable over time. There was a range of δ15N values of Amphibalanus eburneus tissue from 6.0‰ to 10.5‰ across sites. Because land-based sources such as sewage are generally enriched in 15N, this suggests a continuum of anthropogenic influence across sites in the IRL. Over 70% of the variation in δ15N values of Amphibalanus eburneus across sites was driven by the δ15N values of POM, supporting a generalist feeding strategy on available sources of suspended organic matter. The dominance of this generalist consumer in the IRL may be linked to its ability to consume spatially and temporally variable food resources derived from natural and anthropogenic sources, as well as Aureoumbra lagunensis cells. Generalist consumers such as Amphibalanus eburneus serve an important ecological role in this ecosystem and act as a sentinel species and recorder of local, site-specific isotopic baselines.