The Proterozoic-Cambrian transition records the appearance of essentially all animal body plans (phyla), yet to date no single hypothesis adequately explains both the timing of the event and the evident increase in diversity and disparity. Ecological triggers focused on escalatory predator–prey “arms races” can explain the evolutionary pattern but not its timing, whereas environmental triggers, particularly ocean/atmosphere oxygenation, do the reverse. Using modern oxygen minimum zones as an analog for Proterozoic oceans, we explore the effect of low oxygen levels on the feeding ecology of polychaetes, the dominant macrofaunal animals in deep-sea sediments. Here we show that low oxygen is clearly linked to low proportions of carnivores in a community and low diversity of carnivorous taxa, whereas higher oxygen levels support more complex food webs. The recognition of a physiological control on carnivory therefore links environmental triggers and ecological drivers, providing an integrated explanation for both the pattern and timing of Cambrian animal radiation.

/pdf/oxygen-ecology-and-the-cambrian-radiation-of-animals-224cfa1nxc.pdf

Oxygen, ecology, and the Cambrian radiation of animals

Threats to coral reefs may be manifested through an increase in macroalgae. Across the globe, phase-shifts from coral to macroalgal dominance have been reported from the Caribbean, Indian and Pacific Oceans. While the Great Barrier Reef (GBR) is in relatively good condition, inshore reefs may exhibit over 50% macroalgal cover. However, our understanding of the processes preventing the macroalgal expansion remains uncertain. Using a remote video bioassay approach, this study quantified herbivory in three bays along the leeward margin of Orpheus Island. Despite significant with-in bay variation in herbivory there was no detectable statistical difference in the rates of herbivory among bays. Furthermore, of the 45 herbivore species recorded from the island, only three played a significant role in bioassay removal, Siganus canaliculatus, Siganus javus and Kyphosus vaigiensis, with only one species predominating in each bay. Reefs of the GBR may therefore be more vulnerable than previously thought, with the removal of macroalgae depending on just a few species, which exhibit considerable spatial variability in their feeding behaviour.

Local variation in herbivore feeding activity on an inshore reef of the Great Barrier Reef

In this study, we analyze the current state of knowledge on extant Eunicida systematics, morphology, feeding, life history, habitat, ecology, distribution patterns, local diversity and exploitation. Eunicida is an order of Errantia annelids characterized by the presence of ventral mandibles and dorsal maxillae in a ventral muscularized pharynx. The origin of Eunicida dates back to the late Cambrian, and the peaks of jaw morphology diversity and number of families are in the Ordovician. Species richness is heterogeneous among the seven recent families, with more than half of the valid species belonging to the Eunicidae + Onuphidae clade, one of the latest clades to diverge. Eunicidans inhabit soft and hard substrates from intertidal to deep waters in all oceans. The few freshwater species are restricted to Histriobdellidae, a family exclusively commensal/parasite of crustaceans. The reproductive biology, development and ecology of most families are poorly known and the information available suggests low dispersal ability. However, all families have records of widely distributed species. Scrutiny of these wide distributions has often revealed the presence of exotic species or more than one species. The exploration of the deep-sea and of new habitats has led to recent descriptions of new species. Furthermore, the revision of type specimens, the examination of new morphological features and the use of molecular data have revealed hidden biodiversity under unjustified synonyms, poor understanding of morphological features and incomplete descriptions. Molecular studies are still very few or nonexistent for the families Histriobdellidae, Hartmaniellidae, Lumbrineridae and Oenonidae. The integration of new methodologies for morphological and molecular study, along with information on biological and ecological traits appears to be the path to improve the knowledge on the diversity of Eunicida.

The Current State of Eunicida (Annelida) Systematics and Biodiversity

The oligochaete Limnodrilus hoffmeisteri Cleparede was exposed to sediment-amended pyrene (0-1,196 nmol/g dry wt) for 2, 5, and 10 d to investigate sediment particle-size preference, tissue pyrene bioaccumulation (using biota-sediment accumulation factor, BSAF), fecal pyrene concentrations (using fecal-sediment accumulation factor, FSAF), and pyrene biotransformation. In non-pyrene-amended sediment, L. hoffmeisteri preferentially ingested finer sediment particles ( 199 nmol/g dry weight resulted in a decreased preference for finer particles, presumably reducing pyrene exposure. Particle selectivity also changed with time such that after 10 d, worms showed an increased preference for finer particles. At high pyrene exposure, tissue pyrene concentrations rapidly attained equilibrium (maximum body residue 4.4 mumol/g wet wt, close to values cited for hydrocarbon critical body residues). Levels of biotransformation were low (mean 14%) and independent of time or pyrene concentration. Biota-sediment accumulation factor showed a negative relationship with sediment pyrene concentration; this trend may be due to reduced availability at high sediment pyrene concentrations or due to reductions in both ingestion rate and selectivity for fine, pyrene-rich particles. Fecal pyrene concentrations were depleted compared to sediment levels, suggesting removal of pyrene during gut passage by absorption. Fecal-sediment accumulation factor showed a negative relationship with increasing sediment pyrene levels.

Pyrene bioaccumulation, effects of pyrene exposure on particle‐size selection, and fecal pyrene content in the oligochaete Limnodrilus hoffmeisteri (Tubificidae, Oligochaeta)

Burrow-wall micromorphologies produced by nine different intertidal invertebrates were characterized by scanning electron microscopy. Minimally disturbed burrows and host sediment associated with Heteromastus filiformis, Saccoglossus bromophenolosus, Corophium volutator, Clymenella sp., Phoronopsis viridis, Cirriformia luxuriosa, Arenicola marina, Nereis virens, and Upogebia pugettensis were collected from various locales along the western coast of Washington and California. Scanning electron micrographs show several unique sedimentary characteristics present in the burrow lining of each invertebrate. Three traits—grain orientation and grain-size distribution, the nature of the mucus lining, and the presence of wall sculpture—appear significant in describing the microscale burrow lining. In several burrow types, the burrow structure was distinguishable from the matrix by changes in the modal grain size and sorting of the burrow-wall sediment. Variations in the type of packing—cubic versus rhomboh...

https://bioone.org/journals/palaios/volume-25/issue-1/palo.2009.p09-026r/VARIATION-IN-BURROW-WALL-MICROMORPHOLOGIES-OF-SELECT-INTERTIDAL-INVERTEBRATES-ALONG/10.2110/palo.2009.p09-026r.pdf

Variation in burrow-wall micromorphologies of select intertidal invertebrates along the pacific northwest coast, usa: behavioral and diagenetic implications

The burrowing and feeding behaviour of an intertidal population of Lumbrineris cf. latreilli Audouin & Milne-Edwards, 1834 in Westernport Bay, Victoria, Australia was studied in 1982. Gut contents showed they were depositfeeders, ingesting predominantly sediment. Individuals were discretely motile, constructing semi-permanent burrows from which they fed upon subsurface deposits. Individuals in this population of L. cf. latreilli were selectively ingesting smaller particles. This is consistent with the predictions of optimal foraging theory modified for deposit-feeders.

Selective deposit-feeding by Lumbrineris cf. latreilli (Polychaeta: Lumbrineridae), with a new method for assessing selectivity by deposit-feeding organisms

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Selective deposit-feeding by Lumbrineris cf. latreilli (Polychaeta: Lumbrineridae), with a new method for assessing selectivity by deposit-feeding organisms