Effects of the Burrowing Brittlestar, Microphiopholis gracillima (Echinodermata: Ophiuroidea), on the Flux of Lithium, an Inert Tracer, Across the Sediment-Water Interface

Burrowing and ventilation activities of infaunal organisms have been shown to affect geochemical processes in sediments and at the sediment-water interface. Although burrowing brittlestars are dominant in many benthic environments, their role in these processes is poorly known. We tested the effect of the amphiurid brittlestar, Microphiopholis gracillima, on the flux of lithium ion from the sediment to the overlying water by using sediment cores with false bottoms for continuous flow of a Li+1-seawater solution. Brittlestars at densities of 300 and 600 individuals m-2 caused a twofold increase in the rate that Li was transported through the sediment. Density of brittlestars appeared to have no effect on the flux of Li+1 from the sediment, indicating a possible threshold beyond which density increases do not influence fluxes of solute from the sediment

Vectors with autonomy: what distinguishes animal-mediated nutrient transport from abiotic vectors?

Animal movements are important drivers of nutrient redistribution that can affect primary productivity and biodiversity across various spatial scales. Recent work indicates that incorporating these movements into ecosystem models can enhance our ability to predict the spatio-temporal distribution of nutrients. However, the role of animal behaviour in animal-mediated nutrient transport (i.e. active subsidies) remains under-explored. Here we review the current literature on active subsidies to show how the behaviour of active subsidy agents makes them both ecologically important and qualitatively distinct from abiotic processes (i.e. passive subsidies). We first propose that animal movement patterns can create similar ecological effects (i.e. press and pulse disturbances) in recipient ecosystems, which can be equal in magnitude to or greater than those of passive subsidies. We then highlight three key behavioural features distinguishing active subsidies. First, organisms can transport nutrients counter-directionally to abiotic forces and potential energy gradients (e.g. upstream). Second, unlike passive subsidies, organisms respond to the patterns of nutrients that they generate. Third, animal agents interact with each other. The latter two features can form positive- or negative-feedback loops, creating patterns in space or time that can reinforce nutrient hotspots in places of mass aggregations and/or create lasting impacts within ecosystems. Because human-driven changes can affect both the space-use of active subsidy species and their composition at both population (i.e. individual variation) and community levels (i.e. species interactions), predicting patterns in nutrient flows under future modified environmental conditions depends on understanding the behavioural mechanisms that underlie active subsidies and variation among agents' contributions. We conclude by advocating for the integration of animal behaviour, animal movement data, and individual variation into future conservation efforts in order to provide more accurate and realistic assessments of changing ecosystem function

Culturing Echinoderm Larvae Through Metamorphosis

Echinoderms are favored study organisms not only in cell and developmental biology, but also physiology, larval biology, benthic ecology, population biology and paleontology, among other fields. However, many echinoderm embryology labs are not well-equipped to continue to rear the post-embryonic stages that result. This is unfortunate, as such labs are thus unable to address many intriguing biological phenomena, related to their own cell and developmental biology studies, that emerge during larval and juvenile stages. To facilitate broader studies of post-embryonic echinoderms, we provide here our collective experience rearing these organisms, with suggestions to try and pitfalls to avoid. Furthermore, we present information on rearing larvae from small laboratory to large aquaculture scales. Finally, we review taxon-specific approaches to larval rearing through metamorphosis in each of the four most commonly-studied echinoderm classes—asteroids, echinoids, holothuroids and ophiuroids.https://scholarworks.wm.edu/asbookchapters/1091/thumbnail.jp

Utilization of algal and bacterial extracellular polymeric secretions (EPS) by the deposit-feeding brittlestar \u3cem\u3eAmphipholis gracillima\u3c/em\u3e (Echinodermata)

Like many deposit-feeding organisms, the burrowing brittlestar Amphipholis gracillima feeds on particulate organic matter in surface sediments. Microbial exopolymeric secretions (EPS) are carbohydrate-enriched polymers produced by microalgae and bacteria that bind aggregates and form dense biofilms near the sediment-water interface. EPS are assimilable by some benthic infauna and may be utilized as a significant carbon source. EPS are absorbed by some deposit-feeders, including a holothurian, and may be supplemental sources of nutrition. The burrowing brittlestar A. gracillima is a deposit-feeder that was used in a mass balance approach to model the incorporation of radiolabeled EPS by bottom feeders. Brittlestars were fed 14C-labeled, laboratory cultured EPS from the marine bacterium Pseudoalteromonas atlantica and a benthic diatom (Nitzschia sp.) via sediment-bound and aqueous exposures. Comparison of absorption efficiencies (AE) showed that both polymer types are highly absorbed by A. gracillima (AE = 83 to 99%). Absorption of sediment-bound bacterial and algal EPS was similar (92.2 and 90.1%), but bacterial EPS absorption was significantly (p\u3c0.05) higher in sediment-bound (92.2%) than aqueous (83.3%) exposures. Algal EPS absorption was significantly higher in aqueous (99.9%) exposures. These findings suggest that EPS may represent a significant energy source for this deposit-feeding ophiuroid and other organisms with similar feeding habits. Additionally, A. gracillima appears to be especially adept at utilizing EPS resources from benthic diatom communities