Intertidal mussel reefs change the composition and size distribution of diatoms in the biofilm

Migrating diatoms are microscopic ecosystem engineering organisms that have functional consequences on the seascape scale by significantly contributing to the microphytobenthos biofilm. The microphytobenthos biofilm is a thin photosynthesising layer that covers the sediment on intertidal flats. It fuels the food web, increases sediment stability, and enhances the deposition of particles, providing ecosystem services to coastal communities. Here we tested the effect of another ecosystem engineering habitat, intertidal blue mussel reefs, on the composition and properties of migrating diatom communities. Small-scale reefs constructed in the intertidal mimicked and reinforced the natural pattern in diatom community composition and function that we documented in the field. The field experiment adding small reefs to the intertidal ran from 30 April to 10 June 2015 and the field samples were collected around a natural blue mussel bed on the same tidal flat on 7 October 2015 (N 53.489 degrees, E 6.230 degrees). Both the constructed small-scale reefs and the natural reef changed the community composition of diatoms in the biofilm by promoting higher numbers of smaller-sized cells and species. Small diatoms have higher growth and gross photosynthesis rates, indicating that this explains the higher production and chlorophyll-a concentration of the biofilm measured on natural intertidal shellfish reefs. Our results showed that shellfish reefs have a large impact on biofilm functioning. However, biofilms are also fuel for the shellfish, indicating that the two very different ecosystem engineers may facilitate coexistence on tidal flats through a positive feedback loop

Environmental Drivers of Mesophotic Echinoderm Assemblages of the Southeastern Pacific Ocean

Mesophotic ecosystems (50–400 m depth) of the southeastern Pacific have rarely been studied because of the logistical challenges in sampling across this remote zone. This study assessed how oxygen concentrations and other environmental predictors explain variation in echinoderm assemblages at these mesophotic systems, where this group is among the predominant fauna. We compiled data on echinoderm taxa at 91 sampling stations, from historical and recent surveys (between 1950 and 2019), covering a longitudinal gradient of approximately 3,700 km along with the Nazca, Salas y Gómez, and Juan Fernández ridges. Uni- and multivariate model-based tools were applied to analyze the patterns of benthic fauna in relation to environmental factors. Our results indicate a significant positive relationship between echinoderm species richness and depth, oxygen, and salinity. Changes in echinoderm community composition were significantly explained by oxygen, longitude, and chlorophyll-a. We observed notable species turnovers at ∼101 and ∼86°W, where assemblages tend to be more variable across stations. This turnover possibly reflects the effects of physical barriers to dispersion (e.g., currents) and habitat changes. Echinoderm assemblages observed around Easter and Desventuradas Islands presented a high occurrence of potentially endemic taxa and distinct species assemblages. This study is the first to assess the structure of mesophotic echinoderm assemblages of the southeastern Pacific Ocean along a large spatial scale. The information reported here could help design appropriate management tools for the vast, recently created, marine protected areas in the southeastern Pacific

Mussel beds are biological power stations on intertidal flats

Intertidal flats are highly productive areas that support large numbers of invertebrates, fish, and birds. Benthic diatoms are essential for the function of tidal flats. They fuel the benthic food web by forming a thin photosynthesizing compartment in the top-layer of the sediment that stretches over the vast sediment flats during low tide. However, the abundance and function of the diatom film is not homogenously distributed. Recently, we have realized the importance of bivalve reefs for structuring intertidal ecosystems; by creating structures on the intertidal flats they provide habitat, reduce hydrodynamic stress and modify the surrounding sediment conditions, which promote the abundance of associated organisms. Accordingly, field studies show that high chlorophyll a concentration in the sediment co-vary with the presence of mussel beds. Here we present conclusive evidence by a manipulative experiment that mussels increase the local biomass of benthic microalgae; and relate this to increasing biomass of microalgae as well as productivity of the biofilm across a nearby mussel bed. Our results show that the ecosystem engineering properties of mussel beds transform them into hot spots for primary production on tidal flats, highlighting the importance of biological control of sedimentary systems. (C) 2017 Elsevier Ltd. All rights reserved.</p

Bioengineering experiment on Schiermonnikoog 2015: natural composition of diatom assemblages and biovolume measured across a mussel bed

In 2015 the Marine Ecology lab. (Eriksson Lab. at the Groningen Institute for Evolutionary Life Sciences [GELIFES], University of Groningen, The Netherlands); tested the effect of different intertidal bioengineering bivalve habitats on the sediment community. We did this by adding different small scale (0.5 by 0.5 m) bivalve assemblages to the intertidal; the treatments included blue mussel reefs, cockle beds, dead shell assemblages, different types of fencing a to protect the bivalves from bird and crab predation; and fencing controls to test for fence effects. We measured effects on sediment conditions (OM, cohesion, erosion), diatom community composition and development (species composition based on cell counts and biovolume, chlorophyll a concentrations), and infauna abundance. The field experiment in the intertidal ran from 30 April to 10 June 2015 and complementary field samples were collected around a natural blue mussel bed on the same tidal flat on 7 October 2015 (N 53.489, E 6.230 degrees)

Bioengineering experiment on Schiermonnikoog 2015: experimental effects on diatom composition and biovolume

In 2015 the Marine Ecology lab. (Eriksson Lab. at the Groningen Institute for Evolutionary Life Sciences [GELIFES], University of Groningen, The Netherlands); tested the effect of different intertidal bioengineering bivalve habitats on the sediment community. We did this by adding different small scale (0.5 by 0.5 m) bivalve assemblages to the intertidal; the treatments included blue mussel reefs, cockle beds, dead shell assemblages, different types of fencing a to protect the bivalves from bird and crab predation; and fencing controls to test for fence effects. We measured effects on sediment conditions (OM, cohesion, erosion), diatom community composition and development (species composition based on cell counts and biovolume, chlorophyll a concentrations), and infauna abundance. The field experiment in the intertidal ran from 30 April to 10 June 2015 and complementary field samples were collected around a natural blue mussel bed on the same tidal flat on 7 October 2015 (N 53.489, E 6.230 degrees)

Burrow morphology of Uca uruguayensis and Uca leptodactylus (Decapoda: Ocypodidae) from a subtropical mangrove forest in the western Atlantic

The continuous excavation of burrows by fiddler crabs generates bioturbation in the sediment, which can be estimated from burrow morphology. The aim of the present study was to describe the burrow morphology of Uca uruguayensis and U. leptodactylus and its relationship with demography of resident individuals and to estimate the level of bioturbation in the sediment generated by each species. For all individuals from each of the 2 species, sex was determined and the carapace width (CW; mm) measured. Burrows were characterized according to burrow diameter (BD; mm), maximum burrow depth (MBD; mm) and burrow volume (BV; cm(3)). The density of each species in the study area was also evaluated. In both species, the males were larger and occupied burrows with higher BV compared to females. Differences between sexes in relation to the burrow characteristics might reflect sexual dimorphism within the group and are probably related to the fact that males use the burrows for mating. BD and BV showed significant positive relationships with the size of resident crabs. The amount of sediment removed per burrow was estimated from mean BV: 10.78 cm(3) of sediment/burrow for U. uruguayensis and 12.38 cm(3) of sediment/burrow for U. leptodactylus. Despite the density and depth differences between the 2 species, the similarity in burrow volume suggests that U. uruguayensis and U. leptodactylus present the same importance in terms of the bioturbation process. Burrow morphology is highly associated with characteristics of the occupant, although extrinsic factors should also be considered, and its description can provide estimates on the bioturbation generated by Uca species in mangrove forests.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Functional diversity of macrobenthic assemblages decreases in response to sewage discharges

We analyzed the effects of sewage discharge on a subtropical estuary by comparing the functional diversity of intertidal macroinvertebrate assemblages in contaminated with non-contaminated reference areas. Functional structure was assessed using biological traits analysis (BTA) and four multivariate indices (FRic, FEve, FDis and Rao's Q) of functional diversity. Our results showed clear and temporally consistent changes in macrobenthic functional structure in contaminated areas. However, these results depended on whether abundance- or biomass-based measurements were used, with abundance-based analyses distinguishing most clearly between sewage contamination conditions. Differences between contaminated and non-contaminated conditions were also displayed by BTA for all the functional trait categories. FDis (functional divergence) and Rao's Q (functional dispersion) were higher in the non contaminated condition and increased with higher benthic environmental health, as measured by the AMBI index. These patterns of higher functional divergence and dispersion were driven by the numerical dominance of opportunistic annelids in the contaminated condition. We suggest that abundance-based BTA, and the FDis and/or Rao's Q indices are reliable approaches to detect changes in functional structure with respect to sewage pollution. They have a great potential for environmental assessment and monitoring of subtropical estuarine ecosystems. (C) 2016 Elsevier Ltd. All rights reserved

Burrows with Chimneys of the Fiddler Crab Uca thayeri: Construction, Occurrence, and Function

Joao B. L. Gusmao-Junior, Glauco B. O. Machado, and Tania M. Costa (2012) Burrows with chimneys of the fiddler crab Uca thayeri: construction, occurrence, and function. Zoological Studies 51(5): 598-605. Building of soil structures is observed in a variety of semi-terrestrial crustaceans. In fiddler crabs (Genus Uca), this behavior occurs in several species, some of which build structures that are largely ornamental and others construct barriers that are apparently for defense. Although there is a relative abundance of studies on this type of behavior in Uca, the relationship between the social context and the occurrence of these structures remains poorly studied. Thus, this study attempted to analyze in detail the construction, occurrence, and function of mud chimneys built by the fiddler crab Uca thayeri; these sedimentary structures are possibly associated with burrow defense. Field investigations and laboratory experiments were conducted. Both sexes were often found in burrows with chimneys; however, laboratory experiments showed that only females actively built and maintained chimneys, with some difference in the morphology of these structures between sexes. The social context had little influence on the construction of chimneys, which showed that the stimulus for constructing chimneys could be endogenous. Our results suggest that burrows with chimney of U. thayeri may have functions other than defense, and may act in regulating the internal conditions of the burrow, as observed in other crustaceans with such building behavior. http://zoolstud.sinica.edu.tw/Journals/51.5/598.pdfFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Resting Dynamics and Diel Activity of the Green Turtle (Chelonia mydas) in Rapa Nui, Chile

Understanding animals' daily activity patterns such as foraging and resting is key to the effective conservation of individuals, populations, and species. Expanding habitat usage by humans today is likely one of the major factors influencing animal habitat use and behavior. Rapa Nui, a remote Chilean island located at the easternmost corner of the Polynesian Triangle, hosts a population of green turtles, Chelonia mydas, that have been monitored by citizen scientists since 2010. Through the collaborative work of divers from the local community and professional scientists, we describe C. mydas daily underwater resting and foraging patterns in Rapa Nui. We identified 15 individuals by monitoring 19 specific resting locations within the Rapa Nui coral reef. A high level of spatial fidelity for specific resting sites was observed in 12 turtles that used the same location for as long as 5 yrs. Moreover, we observed a clear temporal pattern in the daily use of resting habitats, with 79% of resting activity occurring during low tide. In contrast, the daily peak in feeding activity was associated with high tides. Abiotic characteristics (depth and cardinal orientation) of resting sites did not show significant relationships. The information from this study will inform management of the Rapa Nui Multiple Uses Coastal Marine Protected Area to increase the protection of marine turtles residing at this isolated Pacific Island.Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) 21170169 21160168 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 317039