Reviews and syntheses: Spatial and temporal patterns in seagrass metabolic fluxes

Seagrass meadow metabolism has been measured for decades to gain insight into ecosystem energy, biomass production, food web dynamics, and, more recently, to inform its potential in ameliorating ocean acidification (OA). This extensive body of literature can be used to infer trends and drivers of seagrass meadow metabolism. Here, we synthesize the results from 56 studies reporting in situ rates of seagrass gross primary productivity, respiration, and/or net community productivity to highlight spatial and temporal variability in oxygen (O2) fluxes. We illustrate that daytime net community production (NCP) is positive overall and similar across seasons and geographies. Full-day NCP rates, which illustrate the potential cumulative effect of seagrass beds on seawater biogeochemistry integrated over day and night, were also positive overall but were higher in summer months in both tropical and temperate ecosystems. Although our analyses suggest seagrass meadows are generally autotrophic, the effects on seawater oxygen are relatively small in magnitude. We also find positive correlations between gross primary production and temperature, although this effect may vary between temperate and tropical geographies and may change under future climate scenarios if seagrasses approach thermal tolerance thresholds. In addition, we illustrate that periods when full-day NCP is highest could be associated with lower nighttime O2 and increased diurnal variability in seawater O2. These results can serve as first-order estimates of when and where OA amelioration by seagrasses may be likely. However, improved understanding of variations in NCPdic:NCPO2 ratios and increased work directly measuring metabolically driven alterations in seawater pH will further inform the potential for seagrass meadows to serve in this context

Evaluating Temporal Consistency in Marine Biodiversity Hotspots

With the ongoing crisis of biodiversity loss and limited resources for conservation, the concept of biodiversity hotspots has been useful in determining conservation priority areas. However, there has been limited research into how temporal variability in biodiversity may influence conservation area prioritization. To address this information gap, we present an approach to evaluate the temporal consistency of biodiversity hotspots in large marine ecosystems. Using a large scale, public monitoring dataset collected over an eight year period off the US Pacific Coast, we developed a methodological approach for avoiding biases associated with hotspot delineation. We aggregated benthic fish species data from research trawls and calculated mean hotspot thresholds for fish species richness and Shannon’s diversity indices over the eight year dataset. We used a spatial frequency distribution method to assign hotspot designations to the grid cells annually. We found no areas containing consistently high biodiversity through the entire study period based on the mean thresholds, and no grid cell was designated as a hotspot for greater than 50% of the time-series. To test if our approach was sensitive to sampling effort and the geographic extent of the survey, we followed a similar routine for the northern region of the survey area. Our finding of low consistency in benthic fish biodiversity hotspots over time was upheld, regardless of biodiversity metric used, whether thresholds were calculated per year or across all years, or the spatial extent for which we calculated thresholds and identified hotspots. Our results suggest that static measures of benthic fish biodiversity off the US West Coast are insufficient for identification of hotspots and that long-term data are required to appropriately identify patterns of high temporal variability in biodiversity for these highly mobile taxa. Given that ecological communities are responding to a changing climate and other environmental perturbations, our work highlights the need for scientists and conservation managers to consider both spatial and temporal dynamics when designating biodiversity hotspots

Patterns and Variation in Benthic Biodiversity in a Large Marine Ecosystem

While there is a persistent inverse relationship between latitude and species diversity across many taxa and ecosystems, deviations from this norm offer an opportunity to understand the conditions that contribute to large-scale diversity patterns. Marine systems, in particular, provide such an opportunity, as marine diversity does not always follow a strict latitudinal gradient, perhaps because several hypothesized drivers of the latitudinal diversity gradient are uncorrelated in marine systems. We used a large scale public monitoring dataset collected over an eight year period to examine benthic marine faunal biodiversity patterns for the continental shelf (55–183 m depth) and slope habitats (184–1280 m depth) off the US West Coast (47°20′N—32°40′N). We specifically asked whether marine biodiversity followed a strict latitudinal gradient, and if these latitudinal patterns varied across depth, in different benthic substrates, and over ecological time scales. Further, we subdivided our study area into three smaller regions to test whether coast-wide patterns of biodiversity held at regional scales, where local oceanographic processes tend to influence community structure and function. Overall, we found complex patterns of biodiversity on both the coast-wide and regional scales that differed by taxonomic group. Importantly, marine biodiversity was not always highest at low latitudes. We found that latitude, depth, substrate, and year were all important descriptors of fish and invertebrate diversity. Invertebrate richness and taxonomic diversity were highest at high latitudes and in deeper waters. Fish richness also increased with latitude, but exhibited a hump-shaped relationship with depth, increasing with depth up to the continental shelf break, ~200 m depth, and then decreasing in deeper waters. We found relationships between fish taxonomic and functional diversity and latitude, depth, substrate, and time at the regional scale, but not at the coast-wide scale, suggesting that coast-wide patterns can obscure important correlates at smaller scales. Our study provides insight into complex diversity patterns of the deep water soft substrate benthic ecosystems off the US West Coast

Invasive Pacific Lionfish Alters Native Community Interactions on Atlantic Coral Reefs

Biological invasions have been identified as one of the prominent drivers of global environmental change. In particular, invasive predators typically have substantial negative effects on populations of native prey, even driving species to extinction in extreme cases. However, beyond direct predatory effects, little is understood regarding the specific mechanisms by which invasive predators influence native communities and ecosystems. Therefore, the objective of this dissertation was to investigate whether and how an invasive predator, the Pacific red lionfish (Pterois volitans), alters native community interactions on Atlantic coral reefs. The lionfish invasion is unprecedented for a marine fish in the extent of rapid geographical spread, successful establishment across numerous habitats, and strong predatory effects on native species. By conducting behavioral observations and manipulative experiments in both the laboratory and field settings, I tested for a variety of direct and indirect mechanisms by which invasive lionfish potentially influence native fish communities and coral-reef ecosystems. I first conducted a model-bottle experiment in The Bahamas and Cayman Islands (Chapter 2) to test for aggression of a native territorial damselfish, Stegastes planifrons, toward invasive lionfish. Such territoriality could provide a possible source of biotic resistance that may provide behavioral refugia for native coral-reef fish recruits from lionfish predation. However, the behavior of this damselfish in response to invasive lionfish in a clear plastic bottle did not differ from the minimal response exhibited toward the empty bottle control. Therefore, the territories of this damselfish are unlikely to provide such biotic resistance to the invasion. To investigate whether invasive lionfish alter competition between native prey fishes, I then performed a manipulative field experiment in The Bahamas whereby I simultaneously tested for the effects of both competition and lionfish predation on two congeneric coral-reef fishes, the fairy and blackcap basslets (Gramma loreto and G. melacara, respectively). In the absence of invasive lionfish, competition within local populations of basslets under reef ledges had symmetrical effects on the juveniles of both species (Chapter 3). Interference between species drove juvenile basslets further back under ledges where feeding and growth rates of individuals were reduced. Within reefs with the invasive predator present (Chapter 4), lionfish reduced the density of juvenile fairy basslet, thereby reducing the effects of competition on juvenile blackcap basslet, and tipping the balance of competition between juveniles of these species from symmetrical to asymmetrical effects. Differential predation of invasive lionfish may be explained by a preference for fairy basslet, as demonstrated by a laboratory experiment (Chapter 5). Lastly, I examined possible mechanisms underlying a potential invasive lionfish-herbivorous fishes-macroalgae trophic cascade on large reefs in The Bahamas (Chapter 6). During a two-year field experiment, lionfish caused a decline in the density of small herbivorous fishes on reefs, and behavioral observations revealed that the presence of lionfish reduced grazing by both small and large fishes, which resulted in 66-80% less algae removed from reef substrata. Therefore, invasive lionfish have both consumptive and non-consumptive effects on the important ecosystem function of native herbivorous fishes: reducing the abundance of benthic algae that could otherwise displace corals. In sum, this dissertation indicates that throughout native coral reefs, invasive lionfish (1) are not attacked by native territorial damselfish that could otherwise provide local refugia for native recruit fishes; (2) alter the outcome of interspecific competition between native basslets via differential predation that tips the balance of competition from symmetrical to asymmetrical; and (3) have both consumptive and non-consumptive effects on native herbivorous fishes, which reduces grazing and indirectly benefits benthic macroalgae to the possible detriment of corals. This research broadens our mechanistic understanding of predation in the context of invasive species, which further informs predictions relevant for management and conservation initiatives

Record of lionfish collected near Little Cayman Island during 2011 (Lionfish Invasion project)

Dataset: lionfish collections Cayman 2011This dataset includes dates, locations, and biological information (e.g. length) of lionfish (Pterois volitans) that were collected off of Little Cayman Island, Cayman Islands during the summer of 2011. This dataset includes only lionfish that were collected (handled). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3987NSF Division of Ocean Sciences (NSF OCE) OCE-085116

Observations of damselfish (Stegastes planifrons) behavior in the presence of lionfish and other native fishes at Lee Stocking Island, Bahamas and Little Cayman Island in 2011 (Lionfish Invasion project)

Dataset: damselfish response to lionfishA field study was conducted to determine whether territorial aggression from three-spot damselfish (Stegastes planifrons) could limit local populations of invasive lionfish. The investigators observed damselfish behavior in the presence of lionfish relative to when other native fishes were present. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3992NSF Division of Ocean Sciences (NSF OCE) OCE-085116

Results of experiment comparing herbivorous fish grazing at reefs with manipulated lionfish densities at Lee Stocking Island, Bahamas in 2011 (Lionfish Invasion project)

Dataset: lionfish effects on grazingResults of experiment comparing herbivorous fish grazing at reefs with manipulated lionfish densities at Lee Stocking Island, Bahamas in 2011. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/4014NSF Division of Ocean Sciences (NSF OCE) OCE-085116

Record of lionfish sighted near Little Cayman Island in 2011 (Lionfish Invasion project)

Dataset: lionfish sightings Cayman 2011This dataset includes dates, locations, and biological information (e.g. length) of all lionfish (Pterois volitans) that were observed during field studies at coral reefs near Little Cayman Island, Cayman Islands during the summer of 2011. This dataset includes both lionfish that were sighted (but not handled) and those that were collected. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3988NSF Division of Ocean Sciences (NSF OCE) OCE-085116

Record of lionfish sighted and/or collected near Little Cayman Island, 2010 (Lionfish Invasion project)

Dataset: lionfish sightings Cayman 2010This dataset includes dates, locations, and biological information (e.g. length) of all lionfish (Pterois volitans) that were observed and/or collected during field studies at coral reefs near Little Cayman Island, Cayman Islands during the summer of 2010. This dataset includes both lionfish that were sighted (but not handled) and those that were collected. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3989NSF Division of Ocean Sciences (NSF OCE) OCE-085116

Record of lionfish collected near Eleuthera, Bahamas during reef surveys in 2012 (Lionfish Invasion project)

Dataset: lionfish collections EleutheraThis dataset includes dates, locations, and biological information (e.g. length) of lionfish (Pterois volitans) that were handled (collected) near Eleuthera, Bahamas during the summer of 2012. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/3968NSF Division of Ocean Sciences (NSF OCE) OCE-085116