Coexistence of species is associated with differentiation of niches and partitioning of resources, which lessen niche overlap and the intensity of competition. Here, we used stable isotope analysis ...to evaluate and compare the trophic relationships and isotopic niche of two coexisting predators, the small octopus
Octopus tehuelchus
(d’Orbigny 1834) and the brooding sea star
Anasterias antarctica
(Lütken 1857), in the rocky intertidal community of northern Patagonia (Argentina). Our results show differences in the proportional contribution of sources between octopuses and sea stars. Octopuses consume mainly sessile filter-feeders, and sea stars show intra-specific diet differences, changing its preference with size and sex. Small and medium sea stars feed on sessile filter-feeders, such as small mussels, while large sea stars consume more frequently grazer gastropods and scavenger crustaceans. In the food web of the rocky north Patagonian ecosystem, differences in the isotopic niche space and the degree of dietary specialization between octopuses and sea stars indicate differential use of resources and trophic niche partitioning, possibly by limiting inter- and intra-specific competition.
Primary production hotspots in the marine environment occur where the combination of light, turbulence, temperature and nutrients makes the proliferation of phytoplankton possible. Satellite-derived ...surface chlorophyll-a distributions indicate that these conditions are frequently associated with sharp water mass transitions named “marine fronts”. Given the link between primary production, consumers and ecosystem functions, marine fronts could play a key role in the production of ecosystem services (ES). Using the shelf break front in the Argentine Sea as a study case, we show that the high primary production found in the front is the main ecological feature that supports the production of tangible (fisheries) and intangible (recreation, regulation of atmospheric gases) marine ES and the reason why the provision of ES in the Argentine Sea concentrates there. This information provides support to satellite chlorophyll as a good indicator of multiple marine ES. We suggest that marine fronts could be considered as marine ES hot spots.
Just as some species are used as model systems in organismal biology (e.g., physiology, genetics), many ecosystems are commonly used as model systems in ecology. Salt marshes, for instance, are great ...models to perform manipulative field experiments, and thus, were historically used to understand the drivers of community and ecosystem function. Decades of experimental work, indeed, made a strong contribution to community ecology as a discipline, but most of the emerged hypotheses and models were grounded in a few sites. When studies from new sites came onboard, looking to enlarge generalities, their results challenged the prevailing ideas. Here, we review more than 25 years of intense experimentation in South West Atlantic salt marshes, which helped not only to increase the knowledge about salt marsh functioning, but also to expand this knowledge beyond salt marshes helping to refine community and ecosystem function theory. We show that results coming from SW Atlantic marshes significantly contribute to understand 1) the separate and interactive effect of biotic and abiotic stress for species distribution and even for ecosystem stability, 2) the integrated role of species that can function as ecosystem engineers and as consumers, 3) the balance between stochastic and deterministic forces as drivers of community structure and 4) the regulation of cross-ecosystem fluxes. Nevertheless, we believe SW Atlantic salt marshes still have a lot more to offer, not only as conceptual models that help satisfy our intellectual curiosity, but also as key ecosystems that provide valuable benefits to our societies.
The carnivorous snail
Adelomelon ancilla
usually carries, attached to its shell, the anemone
Antholoba achates
, which also lives attached to hard substrates in the same area. Interaction between ...both species was studied by stable isotopes analyses (SIA), direct observations, and analysis of gut contents. Results did not show evidences of dietary overlap between anemones and snails.
A. ancilla
consumed mainly bivalves and secondarily gastropods. The diet of
A. achates
involved sea urchins and echiurids as main prey. The trophic niches of anemones and snails did not overlap; the species had similar δ
15
N values but differences in their δ
13
C values. Sessile and epibiotic anemones also showed differences in their δ
13
C means, revealing access to different resources. Whereas SIA provided information on trophic relationships and structure, observation of feeding events provided details of prey utilization patterns. Combining direct and indirect approaches helps to overtake method weaknesses and greatly improve dietary descriptions.
In this work, we evaluated the food web structure associated with a Patagonian scallop
Zygochlamys patagonica fishing bed using stable isotopes as an indirect technique. Scallops showed δ
13C isotope ...signatures between −17.9‰ and −18.8‰ in muscle and −20.9‰ and −22.6‰ in gonads, which may indicate additional fractionation during metabolic transfers among organs. The isotopic signatures also suggest that larger scallops feed on organisms higher in the food web. Coexisting species, such as sponges
, the ascidia
Paramolgula gregaria, the anemone
Actinostola crassicornis, colonial tunicates and Anthozoa, as well as the epibiont polychaete
Idanthyrsus armatus, showed much lighter values of C than scallops, which indicates that they are using different food sources. Isotopic signatures suggest that species whose diet includes scallops are the gastropods
Fusitriton magellanicus magellanicus, Odontocymbiola magellanica,
Adelomelon ancilla and the sun starfish
Labidiaster radiosus. The starfish
Calyptraster sp. appears to be a top predator in this area, most likely preying on the gastropods previously mentioned but not directly on scallops. Our results suggest that there are at least three consumer trophic levels. Therefore, any strategy toward managing predators in this system should take into account potential trophic cascade effects given that extracting starfishes could enhance gastropods with an undesirable negative effect on the target species, the Patagonian scallop.
Animals frequently face trade-offs between their requirements for maximizing growth and minimizing mortality risk. The partition of habitat use in foraging arenas and refuges as an answer to this ...trade-off has been evaluated in intertidal crabs but is poorly known in subtidal crabs. The subtidal crab Ovalipes trimaculatus lives and is captured by artisanal fishermen on sandy bottoms of the San Matías Gulf (Lat 41 °S; Argentina). Whereas these bottoms are poor in potential prey, the nearby rocky outcrops are much richer with relatively high abundance of potential prey for the species. Hence, we investigated if crabs in this area are using rocky bottoms as a foraging arena. Stomach content and stable isotopes analysis show that none of the evaluated prey (small teleosts, echinoderms, mollusks and crustaceans) contributed to more than 10% of O. trimaculatus diet, however prey from hard bottoms jointly contributed to 50–80% of the diet. Thus, O. trimaculatus is a generalist carnivore that, despite inhabiting mainly open sandy bottoms, uses rocky outcrops habitats as a foraging arena, probably due to their higher prey availability.
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•Ovalipes trimaculatus inhabits sandy bottoms, poor in potential preys.•Nearby rocky outcrops are richer, with relatively high abundance of potential preys.•Stomach contents and stable isotopes analysis showed it forages on rocky outcrops.•Neither prey contributed to more than 10% to the diet composition.
Summary
Legume plants develop two types of root postembryonic organs, lateral roots and symbiotic nodules, using shared regulatory components. The module composed by the microRNA390, the Trans‐Acting ...SIRNA3 (TAS3) RNA and the Auxin Response Factors (ARF)2, ARF3, and ARF4 (miR390/TAS3/ARFs) mediates the control of both lateral roots and symbiotic nodules in legumes.
Here, a transcriptomic approach identified a member of the Lateral Organ Boundaries Domain (LBD) family of transcription factors in Medicago truncatula, designated MtLBD17/29a, which is regulated by the miR390/TAS3/ARFs module. ChIP‐PCR experiments evidenced that MtARF2 binds to an Auxin Response Element present in the MtLBD17/29a promoter. MtLBD17/29a is expressed in root meristems, lateral root primordia, and noninfected cells of symbiotic nodules.
Knockdown of MtLBD17/29a reduced the length of primary and lateral roots and enhanced lateral root formation, whereas overexpression of MtLBD17/29a produced the opposite phenotype. Interestingly, both knockdown and overexpression of MtLBD17/29a reduced nodule number and infection events and impaired the induction of the symbiotic genes Nodulation Signaling Pathway (NSP) 1 and 2.
Our results demonstrate that MtLBD17/29a is regulated by the miR390/TAS3/ARFs module and a direct target of MtARF2, revealing a new lateral root regulatory hub recruited by legumes to act in the root nodule symbiotic program.
Macroalgae in Mar Chiquita coastal lagoon (37° 40′ S, 57° 23′ W, Argentina) settle on small-hard substrates on sediments and complex reef-like structures with tubes and crevices of the invader ...polychaete Ficopomatus enigmaticus (Fauvel, 1923) acting as ecosystem engineers with multiple community structuring effects. In this study, we compared the structural effects of macroalgae generating new habitat for other organisms in two systems with originally different structural complexity. Therefore, we hypothesized that macroalgae relative importance as an ecosystem engineer providing new habitat and refuge for other organisms would be higher in flat soft-sediments than on reefs. Through sampling and experimental studies, results showed that macrofaunal assemblages were different between areas with and without macroalgae in both reefs and sediment. Experimental results on macroalgae and macroalgae-mimics to separate structural effects in both reefs and sediment showed that macroalgae affect macrofauna on both systems but, structural mechanisms did not prevail in the reefs or sediment. The effect varied on species responses and physical gradients (i.e., depth) of each type of area. Therefore, our results did not support our hypothesis and suggest that macroalgae effects are the result of a summary of their multiple effects in interaction with species and habitat type.
•Ficopomatus enigmaticus reefs are highly structured habitat compared to sediment.•Macroalgae ecosystem engineer's effects should be more important in less structured habitats.•Macroalgae structuring factor are equally important on reefs and sediment.•F. enigmaticus does not affect macroalgae-structuring role due to occurrence of multiple structuring mechanisms.
Feeding ecology of juvenile green turtles (
Chelonia mydas
) was studied from 2008 to 2011 at Samborombón Bay (35°30′–36°30′S, Argentina), combining data on digestive tract examination and stable ...isotope analysis through a Bayesian mixing model. We found that animal matter, in particular gelatinous plankton, was consumed in large proportions compared to herbivorous food items such as terrestrial plants and macroalgae. This diet is facilitated by the high abundance of gelatinous plankton in the region, thus confirming the adaptive foraging behaviour of the juveniles according to prey abundance in the SW Atlantic. To our knowledge, this is the first study to employ this combination of techniques and to conclusively demonstrate that animal matter, in particular gelatinous plankton, is important in the diet of the neritic green sea turtles.
Over the history of ecology, well-established generalizations were refined or even changed after the appearance or consideration of new evidence. Here, we review results obtained in Southwestern ...Atlantic salt marshes (between southern Brazil −32° 1′ S- and the Argentinean Patagonia −53° 48′ S-). Most of these salt marshes are inhabited by the intertidal burrowing crab Neohelice granulata, a species that influences many ecological processes through bioturbation and herbivory. The experimental evaluation of these processes shows that in some cases, the results were not consistent with generalizations and models of salt marsh ecological functioning. However, this does not imply that the generalizations grounded mainly on the results from North American sites are not valid. In turn, we suggest that these apparently conflicting results emerged because two major processes, herbivory and bioturbation, have been overlooked until recently. Thus, their relative contribution has not been included in the models of salt marsh functioning. In conclusion, we believe that there is a need for performing parallel and simultaneous experiments comparing distant sites with varying environmental (i.e., abiotic and biotic) conditions to be able to uncover common processes and causes of contingencies. Particularly, Southwestern Atlantic salt marshes could lead the way in providing information to better incorporate herbivory and bioturbation into current models or paradigms about how salt marshes work.
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