Positive interactions between foundation species and their associated species are expected to be influenced by the degree of environmental stress as well as trait variations of the species involved. ...However, there is scarce empirical evidence regarding how these two factors interact and shape the intensity of facilitation. To test how facilitation varies with stress, a colonization experiment using artificial algal units that varied in a functional trait (morphological complexity) was conducted at different intertidal height levels. The isolated effects of shore‐height and host‐complexity are as expected: the number of species and overall abundance of epifauna decreased with lower complexity host units and greater exposure to environmental stress. However, in contrast to the initially proposed model, based on the stress gradient hypothesis, the magnitude of positive interactions increased at lower tidal heights (those levels with, presumably, milder environmental conditions). An additional predation exclusion experiment ruled out the effects of predation pressure as a major factor driving the structure of mobile epifaunal assemblages in these intertidal habitats. Thus, further studies are needed to identify the factors that explain the patterns of facilitation intensity found in the present study.
Macroalgae are the major habitat-forming organisms in many coastal temperate and subtropical marine systems. Although climate change has been identified as a major threat to the persistence of ...macroalgal beds, the combined effects of ocean warming and ocean acidification on algal performance are poorly understood. Here we investigate the effects of increased temperature and acidification on the growth, calcification and nutritional content of 6 common subtropical macroalgae; Sargassum linearifolium, Ulva sp., Amphiroa anceps, Corallina officinalis, Delisea pulchra and Laurencia decussata. Algae were reared in a factorial cross of 3 temperatures (23°C ambient, 26°C and 28°C) and 3 pH levels (8.1 ambient, 7.8 and 7.6) for 2 wk. The highest (28°C) temperature decreased the growth of all 6 macroalgal species, irrespective of the pH levels. In contrast, the effect of decreased pH on growth was variable. The growth of Ulva sp. and C. officinalis increased, L. decussata decreased, while the remaining 3 species were unaffected. Interestingly, the differential responses of macroalgae to ocean acidification were unrelated to whether or not a species was a calcifying alga, or their carbon-uptake mechanism—2 processes that are predicted to be sensitive to decreased pH. The growth of the calcifying algae (C. officinalis and A. anceps) was not affected by reduced pH but calcification of these 2 algae was reduced when exposed to a combination of reduced pH and elevated temperature. The 3 species capable of uptake of bicarbonate, S. linearifolium, L. decussata and Ulva sp., displayed positive, negative and neutral changes in growth, respectively, in response to reduced pH. The C:N ratio for 5 of the 6 species was unaffected by either pH or temperature. The consistent and predictable negative effects of temperature on the growth and calcification of subtropical macroalgae suggests that this stressor poses a greater threat to the persistence of subtropical macroalgal populations than ocean acidification under ongoing and future climate change.
Understanding how habitat attributes (e.g., patch area and sizes, connectivity) control recruitment and how this is modified by processes operating at larger spatial scales is fundamental to ...understanding population sustainability and developing successful long‐term restoration strategies for marine foundation species—including for globally threatened reef‐forming oysters. In two experiments, we assessed the recruitment and energy reserves of oyster recruits onto remnant reefs of the oyster Saccostrea glomerata in estuaries spanning 550 km of coastline in southeastern Australia. In the first experiment, we determined whether recruitment of oysters to settlement plates in three estuaries was correlated with reef attributes within patches (distances to patch edges and surface elevation), whole‐patch attributes (shape and size of patches), and landscape attributes (connectivity). We also determined whether environmental factors (e.g., sedimentation and water temperature) explained the differences among recruitment plates. We also tested whether differences in energy reserves of recruits could explain the differences between two of the estuaries (one high‐ and one low‐sedimentation estuary). In the second experiment, across six estuaries (three with nominally high and three with nominally low sedimentation rates), we tested the hypothesis that, at the estuary scale, recruitment and survival were negatively correlated to sedimentation. Overall, total oyster recruitment varied mostly at the scale of estuaries rather than with reef attributes and was negatively correlated with sedimentation. Percentage recruit survival was, however, similar among estuaries, although energy reserves and condition of recruits were lower at a high‐ compared to a low‐sediment estuary. Within each estuary, total oyster recruitment increased with patch area and decreased with increasing tidal height. Our results showed that differences among estuaries have the largest influence on oyster recruitment and recruit health and this may be explained by environmental processes operating at the same scale. While survival was high across all estuaries, growth and reproduction of oysters on remnant reefs may be affected by sublethal effects on the health of recruits in high‐sediment estuaries. Thus, restoration programs should consider lethal and sublethal effects of whole‐estuary environmental processes when selecting sites and include environmental mitigation actions to maximize recruitment success.
Biotic interactions such as predation are difficult ecological processes to quantify in the wild. This is especially the case in the marine environment due to logistical difficulties in capturing ...animal behaviour. Common approaches use aquarium‐based experiments, live‐tethering, or assays with bait as proxies for quantifying predation pressure. However, these methods often fail to account for natural interactions between species in the wild and may raise ethical and animal welfare concerns.
We designed a novel field‐based method to quantify predator–prey interactions for marine fishes. The “predation dome” is a clear acrylic aquarium that contains a live fish. The dome is filmed and, in contrast to other methods, it allows for natural olfactory and visual cues, and the prey fish is returned to the wild after the assay. Here, we provide a step‐by‐step guide on building and deploying the predation dome in the wild. To demonstrate its use, we quantified predation pressure using the domes in two tropical and two temperate locations.
Piscivores were attracted to the domes and displayed predatory behaviours such as circling or striking. Although the overall number of predatory attacks did not differ among locations, predation domes revealed higher predation pressure by piscivores at the tropical locations in comparison to temperate reefs.
Our results show that predation domes represent an ethical and complementary approach to measure predation that may better represent piscivory as compared to other behaviours. Predation domes can be also used to measure other biotic interactions such as territorial defence or courtship.
Resumen
Las interacciones bióticas como depredación son procesos ecológicos difíciles de cuantificar en la naturaleza. Esto sucede específicamente en el medio marino debido a dificultades logísticas para registrar el comportamiento animal. Los enfoques más comunes utilizan experimentos en acuarios, cebos vivos, o experimentos con carnadas para cuantificar la presión por depredación. Sin embargo, estos métodos usualmente no tienen en cuenta las interacciones entre especies en la naturaleza y pueden generar preocupaciones éticas y de bienestar animal.
Diseñamos un método de campo novedoso para cuantificar interacciones depredador‐presa para los peces marinos. El “domo de depredación” es un acuario de acrílico transparente que contiene un pez vivo. El domo se filma y, a diferencia de otros métodos, permite el despliegue de señales olfativas y visuales naturales, y el pez es devuelto a la naturaleza después del experimento. Proporcionamos una guía paso a paso sobre cómo construir y utilizar el domo de depredación en la naturaleza. Para demostrar su uso, cuantificamos la presión de depredación usando los domos en dos sitios tropicales y dos templados.
Los piscívoros fueron atraídos a los domos y mostraron comportamientos depredadores, como dar vueltas o golpear el domo. Aunque el número total de ataques de depredadores no fue diferente entre los sitios, los domos de depredación revelaron una mayor presión de depredación por parte de los piscívoros en los sitios tropicales en comparación con los arrecifes templados.
Nuestros resultados muestran que los domos de depredación representan un enfoque ético y complementario para medir depredación, ya que pueden representar mejor la piscivoría en comparación con otros comportamientos. Los domos de depredación también se pueden usar para medir otras interacciones bióticas, como el territorialismo o el cortejo.
Large herbivores such as sea urchins and fish consume a high proportion of benthic primary production and frequently control the biomass of marine macrophytes. By contrast, small mesograzers, ...including gastropods and peracarid crustaceans, are abundant on seaweeds but have low per capita feeding rates and their impacts on marine macrophytes are difficult to predict. To quantify how mesograzers can affect macrophytes, we examined feeding damage by the herbivorous amphipods
and
sp., which construct burrows in the stipes of subtidal individuals of the kelp
in northern-central Chile, southeast Pacific. Infested stipes showed a characteristic sequence of progressive tissue degeneration. The composition of the amphipod assemblages inside the burrows varied between the different stages of infestation of the burrows. Aggregations of grazers within burrows and microhabitat preference of the amphipods result in localized feeding, leading to stipe breakage and loss of substantial algal biomass. The estimated loss of biomass of single stipes varied between 1 and 77%. For the local kelp population, the amphipods caused an estimated loss of biomass of 24-44%. Consequently, small herbivores can cause considerable damage to large kelp species if their feeding activity is concentrated on structurally valuable algal tissue.
Seagrasses that are predominantly clonal often have low levels of genetic variation within populations and predicting their response to changing conditions requires an understanding of whether ...genetic variation confers increased resistance to environmental stressors. A higher level of genetic diversity is assumed to benefit threatened species due to the increased likelihood of those populations having genotypes that can persist under environmental change. To test this idea, we conducted an
shading experiment with six geographically distinct meadows of the threatened seagrass
that vary in genetic diversity. Different genotypes within meadows varied widely in their physiological and growth responses to reduced light during a simulated short-term turbidity event. The majority of meadows were resistant to the sudden reduction in light availability, but a small subset of meadows with low genotypic diversity were particularly vulnerable to the early effects of shading, showing substantially reduced growth rates after only 3 weeks. Using the photosynthetic performance (maximum quantum yield) of known genotypes, we simulated meadows of varying genetic diversity to show that higher diversity can increase meadow resilience to stress by ensuring a high probability of including a high-performing genotype. These results support the hypothesis that complementarity among genotypes enhances the adaptive capacity of a population, and have significant implications for the conservation of declining
meadows close to the species range edge on the east coast of Australia, where the genotypic diversity is low.
Consumer pressure in benthic communities is predicted to be higher at low than at high latitudes, but support for this pattern has been ambiguous, especially for herbivory. To understand large-scale ...variation in biotic interactions, we quantify consumption (predation and herbivory) along 2500 km of the Chilean coast (19°S–42°S). We deployed tethering assays at ten sites with three different baits: the crab
Petrolisthes laevigatus
as living prey for predators, dried squid as dead prey for predators/scavengers, and the kelp
Lessonia
spp. for herbivores. Underwater videos were used to characterize the consumer community and identify those species consuming baits. The species composition of consumers, frequency of occurrence, and maximum abundance (MaxN) of crustaceans and the blenniid fish
Scartichthys
spp. varied across sites. Consumption of
P. laevigatus
and kelp did not vary with latitude, while squid baits were consumed more quickly at mid and high latitudes. This is likely explained by the increased occurrence of predatory crabs, which was positively correlated with consumption of squidpops after 2 h. Crabs, rather than fish, were the principal consumers of squid baits (91% of all recorded predation events) at sites south of 30°S. Fish and crustaceans preyed in similar proportion on
P. laevigatus
, with most fish predation events at northern sites. The absence of any strong latitudinal patterns in consumption rate of tethered prey is likely due to redundancy among consumers across the latitudinal range, with crustaceans gaining in importance with increasing latitude, possibly replacing fish as key predators.
Aim: The aim was to quantify latitudinal patterns in seagrass–herbivore interactions in the context of a warming climate. Location: We carried out a global meta-analysis combined with a field ...experiment across 1,700 km and 12° of latitude in Western Australia. Time period: 1984–2014. Major taxa studied: Seagrasses. Methods: We first synthesized the global literature on herbivore exclusion experiments in seagrasses to test whether differences in herbivore impacts are related to latitude and sea surface temperature. We then quantified leaf production and consumption rates in the field at nine meadows of the seagrass Amphibolis antarctica across 1,700 km, from tropical to temperate latitudes. Seagrass biomass and nutritional traits (nitrogen, C:N, phenolics) were also measured. Results: Our meta-analysis showed that herbivores had a similar net impact on seagrasses across 37° of absolute latitude, and there was little variation in herbivore exclusion effects at different temperatures. In the field, rates of both production and consumption of seagrass were greatest in the tropics and decreased with latitude. Seagrass nutritional quality was lowest in the tropics, where fish removed c. 30% of primary production. Consumption of the more nutritious temperate seagrasses was lower overall but also highly variable and dominated by invertebrates. Main conclusions: In tropical latitudes, faster growth rates compensated for greater consumption of A. antarctica by herbivores. This resulted in similar net impacts of herbivores across latitudes, because higher latitude plants grew more slowly but also suffered less herbivory. This match between consumption and production rates might explain the global patterns derived from the literature, which show little latitudinal variation in the effects of consumers on seagrasses. As ocean temperatures continue to rise and overall herbivory levels are expected to increase in temperate regions, the survival of seagrass meadows in higher latitudes will depend on the ability of plants to increase growth at compensatory rates.
Coastal urbanization has led to large-scale transformation of estuaries, with artificial structures now commonplace. Boat moorings are known to reduce seagrass cover, but little is known about their ...effect on fish communities. We used underwater video to quantify abundance, diversity, composition and feeding behaviour of fish assemblages on two scales: with increasing distance from moorings on fine scales, and among locations where moorings were present or absent. Fish were less abundant in close proximity to boat moorings, and the species composition varied on fine scales, leading to lower predation pressure near moorings. There was no relationship at the location with seagrass. On larger scales, we detected no differences in abundance or community composition among locations where moorings were present or absent. These findings show a clear impact of moorings on fish and highlight the importance of fine-scale assessments over location-scale comparisons in the detection of the effects of artificial structures.
•Underwater video quantified the effects of boat moorings on fish communities.•Fine and large-scale contrasts assessed the abundance and feeding behaviour of fish.•Abundance and feeding rates of fish were lowest in close proximity to boat moorings.•These patterns were not observed at the location where seagrass is present.•A large-scale contrast was insufficient to detect impacts of boat moorings on fish.
Abstract
One way to improve the value of citizen science data for a specific aim is through promoting adaptive sampling, where the marginal value of a citizen science observation is dependent on ...existing data collected to address a specific question. Adaptive sampling could increase sampling at places or times—using a dynamic and updateable framework—where data are expected to be most informative for a given ecological question or conservation goal. We used an experimental approach to test whether the participants in a popular Australian citizen science project—FrogID—would follow an adaptive sampling protocol aiming to maximize understanding of frog diversity. After a year, our results demonstrated that these citizen science participants were willing to adopt an adaptive sampling protocol, improving the sampling of biodiversity consistent with a specific aim. Such adaptive sampling can increase the value of citizen science data for biodiversity research and open up new avenues for citizen science project design.
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