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Aquaculture is expected to expand significantly in the coming decades to meet growing demand. A key variable for understanding the potential benefit of and impact from this growth is efficiency; yet a comprehensive assessment of on‐farm area use and yield is limited. Much like land‐based agriculture, range and variation in yields across space, species, and practice provide insights into area use and production efficiencies. Current estimates of aquaculture yields (production per area per time) aggregate on‐farm and off‐farm land use into one 'land use' category; in contrast, we disaggregate this category to provide on‐farm yield estimates and account for water area use. We use a quantitative review of scientific literature to synthesize and compare on‐farm area use and yield patterns across countries, taxa, aquatic systems, data source, and production mode (n = 378). Because recirculating aquaculture systems (RAS) have been touted as a particularly efficient production mode, we also found estimates for RAS from industry (n = 4). Median, mean and range in yields among countries and taxa vary by orders of magnitude, with algal production greatly exceeding that of crustaceans, fishes and molluscs. Yields in marine systems were on average roughly 5× greater than yields in freshwater systems. RAS had particularly high yields but sparse data and estimates from private corporations were approximately 3.7× higher than literature estimates, on average. This comprehensive assessment of global aquaculture yields offers critical insight into the production efficiencies of different aquaculture forms and the large amount of variability, which could help guide aquaculture policy and practice. [ABSTRACT FROM AUTHOR]

Abstract Background Cnidocytes, the eponymous cell type of the Cnidaria, facilitate both sensory and secretory functions and are among the most complex animal cell types known. In addition to their structural complexity, cnidocytes display complex sensory attributes, integrating both chemical and mechanical cues from the environment into their discharge behavior. Despite more than a century of work aimed at understanding the sensory biology of cnidocytes, the specific sensory receptor genes that regulate their function remain unknown. Results Here we report that light also regulates cnidocyte function. We show that non-cnidocyte neurons located in battery complexes of the freshwater polyp Hydra magnipapillata specifically express opsin, cyclic nucleotide gated (CNG) ion channel and arrestin, which are all known components of bilaterian phototransduction cascades. We infer from behavioral trials that different light intensities elicit significant effects on cnidocyte discharge propensity. Harpoon-like stenotele cnidocytes show a pronounced diminution of discharge behavior under bright light conditions as compared to dim light. Further, we show that suppression of firing by bright light is ablated by cis-diltiazem, a specific inhibitor of CNG ion channels. Conclusions Our results implicate an ancient opsin-mediated phototransduction pathway and a previously unknown layer of sensory complexity in the control of cnidocyte discharge. These findings also suggest a molecular mechanism for the regulation of other cnidarian behaviors that involve both photosensitivity and cnidocyte function, including diurnal feeding repertoires and/or substrate-based locomotion. More broadly, our findings highlight one novel, non-visual function for opsin-mediated phototransduction in a cnidarian, the origins of which might have preceded the evolution of cnidarian eyes.

Coral reefs are shifting from coral to algal‐dominated ecosystems worldwide. Recently, Turbinaria ornata, a marine alga native to coral reefs of the South Pacific, has spread in both range and habitat usage. Given dense stands of T. ornata can function as an alternative stable state on coral reefs, it is imperative to understand the factors that underlie its success. We tested the hypothesis that T. ornata demonstrates ontogenetic variation in allocation to anti‐herbivore defense, specifically that blade toughness varied nonlinearly with thallus size. We quantified the relationship between T. ornata blade toughness and thallus size for individual thalli within algal stands (N = 345) on seven fringing reefs along the north shore of Moorea, French Polynesia. We found that blade toughness was greatest at intermediate sizes that typically form canopies, with overall reduced toughness in both smaller individuals that refuge within the understory and older reproductive individuals that ultimately detach and form floating rafts. We posit this variation in blade toughness reduces herbivory on the thalli that are most exposed to herbivores and may facilitate reproduction in dispersing stages, both of which may aid the proliferation of T. ornata. [ABSTRACT FROM AUTHOR]

Functional groups are widely used to reduce complexity and generalize across ecological communities. These models assume that shared traits among species correspond to some ecological role, process or function, and that these traits can be leveraged to generate meaningful and distinct functional groups so that intergroup trait variation exceeds intragroup variation.We sought to validate the assumptions of the widely used functional group model (FGM) for marine macroalgae, which groups species based on morphological complexity, by testing the predictions of the FGM for several traits assumed to correspond with morphological complexity. The FGM predicts increased resistance to disturbance and herbivory as morphological complexity (tensile strength and thallus toughness, respectively) increases. The FGM also predicts a trade‐off between complexity and growth rate. To test predictions, we measured (a) thallus toughness (force to penetrate), (b) tensile strength (force to break) and (c) relative growth for both tropical and temperate macroalgae from different functional groups.Thallus toughness followed model predictions at the functional group level, though there was significant variability among species. However, the model did not predict tensile strength at any level for either tropical or temperate macroalgae. Furthermore, relative growth did not follow predictions; rather it was highly variable among species and functional groups.Synthesis. The assumptions of the FGM that differences in morphological complexity can be used to generate distinct functional groups and that intergroup trait variation outweighs intragroup variation were violated, providing strong evidence that individual species responses need to be considered. Furthermore, violations of assumptions indicate that functional groups should not be used to predict community responses to ecological drivers and/or species contributions to ecosystem function. Our study challenges the usefulness of functional form groups for marine macroalgae and emphasizes the need for a different conceptual framework. [ABSTRACT FROM AUTHOR]

Multiple stressors acting simultaneously on ecological communities are the new normal state. Stressor number and strength will increase with rising anthropogenic activity, making it critical to understand both stressor effects and interactions. Stressor temporal regimes vary in intensity, frequency, and duration, ranging from press to pulse. While stressors with different temporal regimes likely have divergent effects, this remains mostly unexplored, though there is some evidence communities are more resistant to pulse than press stressors. Coral reefs are among the most impacted marine communities, and degradation from coral to algal dominance has been attributed to increases in both local and global stressors. Overfishing, nutrient pollution, and increased sedimentation are all local stressors that have been implicated in shift dynamics. Nutrients and sediments are anthropogenically derived stressors to reefs that can have press and pulse temporal regimes. We conducted a 6‐month fully crossed factorial field experiment on algal turf communities in Moorea, French Polynesia, manipulating access by herbivores, enrichment regime, and sedimentation regime and tracked changes in benthic community composition. We found complex interactions among stressors and stressor regimes drove a series of transitions from healthy, short algal turf communities to degraded, long algal turfs, and ultimately to macroalgal‐dominated communities. While herbivory controlled final community composition after 6 months, 2‐ and 3‐way interactions among nutrient and sediment temporal stressor regimes over time drove transition dynamics, and matching of stressor temporal regimes accelerated shifts. Some stressors cryptically eroded the resilience of the community, which was only evident when the strong ecological processes that masked these effects were disrupted. Our research highlights the need to consider temporal stressor regime as well as stressor interactions, particularly in light of predicted increases in both local and global stressors and alterations to stressor temporal regimes. Our understanding of the impacts of local stressor temporal regimes is in its infancy. Here, we provide a novel demonstration that the effects of stressor temporal regime varied and multiple stressors interacted to exhibit complex, emergent interaction effects, demonstrating the need to explicitly contrast stressor temporal regimes under multiple conditions to understand how communities will respond to future challenges. [ABSTRACT FROM AUTHOR]

While the importance of top-down control by grazers in maintaining tropical reef community structure is well known, the effect of 'fishing down the food web', which simultaneously changes the abundance and size of herbivorous fishes, has received less attention. As many fishing practices target the biggest fish and regulations often set minimum size limits, understanding size-dependency of this controlling force is important. We evaluated the hypothesis that reduction in the abundance and size of fish, regardless of species identity, reduces the role of herbivory in controlling algal abundance on reefs and assessed variation in efficacy of this top-down control on different types of common macroalgae. We quantified herbivory rates within cages of differing opening sizes on assemblages of four common algal species ( Padina boryana, Dictyota bartayresiana, Halimeda opuntia and Galaxaura fasciculata) on two fringing reefs in Moorea, French Polynesia. Small acanthurids (<15 cm length) were the dominant herbivorous fish while other herbivorous fish were rare. For the two most palatable algae, the majority of herbivory occurred in open plots, with herbivory reduced by >50% in the largest opening cages (6 × 6 cm) where the maximum size fish entering was 12 cm in length (mean = 7.6, SE = 0.4). Fish entering medium (4.5 × 4.5 cm openings, maximum fish length = 8 cm, mean = 6.3, SE = 0.4) and small (3 × 3 cm openings, no fish observed entering) cages had herbivory rates approximately equal to the control treatment (1 × 1 cm openings). Consumption varied among algal species, with minimal consumption of physically and chemically defended algae and no pattern across treatments. Our results demonstrate a need for management plans to not only maintain the overall abundance of herbivorous fish but to protect the largest sizes for effective top-down control of algal communities. [ABSTRACT FROM AUTHOR]

Herbivory assays are a valuable tool used by field ecologists to understand many of the patterns and processes affecting herbivory, a widely recognized driving force in marine communities. However, methods vary substantially among studies in both design and operation, and the effect of these differences has yet to be evaluated. We assessed the effects of several key components of assay design on estimates of herbivory on a tropical reef, a system characterized by strong herbivory pressure by highly mobile grazers. Based on our results, we offer four recommendations. First, we found assays out-planted on sequential days in both predictable and random locations within a 60m2 site experienced temporal increases in herbivory by an increasingly diverse assemblage of fishes. Thus, we strongly advise against placing herbivory assays in the same site over a series of days. Second, we found while the amount of biomass consumed in assays was density-dependent, but the percent loss was not. Thus, it is our opinion that researchers should report percent consumption because this metric is robust to differences in biomass offered and will facilitate comparisons across studies. Third, we found associational effects, where proximity of species of differing palatabilities impacted estimates of herbivory rate on one or both species, but these impacts were not consistent across species or sites. Thus, we recommend the effect of association be directly tested for multi-species herbivory assays. Fourth, we found no effect of attachment method on estimates of herbivory rate and recommend researchers continue to use the attachment method in which they are most confident. We hope our experimental results prove useful in the future when designing, conducting, and interpreting herbivory assays. • Herbivory assays are a valuable tool used by field ecologists but methods vary. • We experimentally assessed these variations to understand the impact on estimates. • Based on our experimental results, we provide four pieces of advice for future assays. • We hope our results are useful for designing, conducting, and interpreting assays. [ABSTRACT FROM AUTHOR]

Enteromorpha intestinalis was subject to nitrogen (N) and phosphorus (P) enrichment supplied in four weekly pulses in a 10:1 molar ratio with six concentrations ranging from no addition to 1000 μM NO3+100 μM PO4. The alga reduced inorganic N to very low concentrations (<3.5 μM) across all nutrient additions while a larger proportion of the added P remained in the water at the end of the experiment (up to 20 μM in highest addition). Growth of E. intestinalis increased in proportion to enrichment across the lower four of the six treatments; range of growth was −6 to 60% change from initial wet wt. N concentration in the tissue decreased at the four lower loading rates due to dilution by growth, but increased greatly (from an initial of 2.7–5% dry wt.) in the highest loading rate partially due to lack of growth in this treatment. In contrast, the mass of N in the tissue increased linearly (slope=0.012, r2=0.779, P=0.0001) over all treatments, showing that uptake and storage were not always coupled to growth. Patterns of tissue P concentration and accumulation were similar to N. Significant amounts of dissolved organic N accumulated in the water, especially in the highest N pulses. Net retention of N in algal tissue ranged from 73 to 98% while retention of P ranged from 79 to 88%; the % lowest retention occurred when nutrient pulses were either very high or low. We hypothesize that this opportunistic, bloom-forming alga is adapted to pulses of nutrients, such that, when pulses are of very high concentration, E. intestinalis can delay growth in favor of saving energy to maximize nutrient uptake and storage. [Copyright &y& Elsevier]

Coral-dominated reefs typically have abundant refuges and limited resources for herbivores; conversely, algal-dominated reefs have abundant resources but often have limited refuges. This difference results in a trade-off between risk and reward for herbivorous fishes. However, disturbances that kill coral but retain topographic complexity can decouple this tradeoff, challenging this paradigm. Many fringing reefs in Moorea, French Polynesia are algal-dominated with heterogeneous structural complexity likely driven by disturbances associated with crown-of-thorns predation and typhoons, which occurred between 2006 and 2010. Short turfs are a good recruitment surface for coral larvae, and thus has a greater potential to recover to coral dominance than long turfs. To explore how variation in complexity impacts the behavior of herbivorous fishes, we compared abundance, residence time, and time budgets of Acanthurus nigrofuscus , a common herbivore species, in paired high versus low complexity areas. We chose areas in close proximity to maximize the likelihood fish could choose between complexity types. We also measured turf height in high versus low complexity plots. Fish were ~3× more abundant, spent roughly double the time in, and budgeted more than 4× as much time to hiding in high complexity reef areas. Although, on average, individual herbivores spent the same proportion of time foraging in both areas, their greater abundance and longer residence time suggests their local herbivory rates could be 7.5 times higher in high complexity areas. We also found turfs in high complexity plots were roughly 75% the height of turfs in low complexity plots. This provides some evidence for stronger overall herbivory pressure in high complexity areas, albeit differences in absolute turf height were modest (~0.5 mm). Combined, these results suggest reefs that retain structural complexity following disturbance may be more likely to recover due to the higher localized herbivory rates resulting from uncoupling of the tradeoff between structural complexity and resource limitation. • Disturbances are shifting tropical reefs from coral to algal dominance worldwide. • Some disturbances retain reef structural complexity, potentially affecting herbivores. • We compare fish behavior and herbivory in high vs. low complexity patches of reef. • High complexity patches had shorter turf and more fish that spent more time hiding. • Co-occurrence of structural complexity and food resources may enhance reef recovery. [ABSTRACT FROM AUTHOR]

• Halophila decipiens can grow as shallow asintertidally; however, we only found it > 6.4 m deep in Moorea, French Polynesia. • Transplanting seagrass into a shallow reef site showed that H. decipiens grew when herbivores were excluded. • We found H. decipiens can grow in shallow habitats on Moorea, but that herbivory pressure may limit its proximity to reefs. Seagrasses are important foundational species that frequently display distinct depth distributions, although the drivers of these patterns can be spatially and temporally variable. While the pantropical seagrass Halophila decipiens is known from waters as shallow as 1 m deep, in Moorea, French Polynesia we only found it > 6.4 m deep. To explore factors affecting depth distribution, we transplanted H. decipiens into 3 habitats: the existing seagrass bed (control), just outside the seagrass bed, and shallower habitat adjacent to a fringing coral reef. Results showed that growth was not significantly different between the control and just outside of the seagrass bed; however, number of shoots and rhizome length were significantly reduced adjacent to the reef. Transplanting seagrass into the shallow reef site with and without herbivore exclusion cages showed that H. decipiens grew in herbivore exclusion treatments, but lost both shoots and rhizomes in the control. These results indicate that H. decipiens can grow in shallow habitats adjacent to reefs on Moorea, but that herbivory pressure, presumably from the reef, limits its depth distribution. [ABSTRACT FROM AUTHOR]