We surveyed the benthic community structure and population density of the longspined sea urchin Diadema antillarum on the shallow fore-reefs of the Gandoca-Manzanillo Wildlife Refuge, Caribbean Costa Rica, in September and October 2004. In zones with high densities of D. antillarum (> 0.6 ind. m -2 ), the cover of non-calcareous macroalgae, known coral competitors, was low and that of live coral was high, whereas the opposite occurred in zones with low densities of D. antillarum (< 0.1 ind. m -2 ). D. antillarum density was not related to the coverage of calcareous macroalgae, which are not viewed as coral competitors. Mean density of D. antillarum was 0.2 ind. m -2 and the total area covered by live coral was 14%. D. antillarum density and area covered by live coral were 2 and 7 times larger, respectively, than those reported 4 yr earlier for the study site. Within the same period, the proportion contributed by non-calcareous macroalgae to total algal cover declined from 79 to 48%. Results indicate that various families of scleractinian corals in the Caribbean coast of Costa Rica have increased in abundance, that non-calcareous macroalgae have declined, and that recovering D. antillarum densities are correlated with these observations. KEY WORDS: Diadema antillarum · Scleractinian coral · Costa Rica · Coral reef recovery · MacroalgaeResale or republication not permitted without written consent of the publisher

One contribution of 17 to a theme issue 'Biodiversity and ecosystem functioning in dynamic landscapes'. The link between biodiversity and ecosystem functioning (BEF) over long temporal scales is poorly understood. Here, we investigate biological monitoring and palaeoecological records on decadal, centennial and millennial time scales from a BEF framework by using deep sea, soft-sediment environments as a test bed. Results generally show positive BEF relationships, in agreement with BEF studies based on present-day spatial analyses and short-term manipulative experiments. However, the deep-sea BEF relationship is much noisier across longer time scales compared with modern observational studies. We also demonstrate with palaeoecological time-series data that a larger species pool does not enhance ecosystem stability through time, whereas higher abundance as an indicator of higher ecosystem functioning may enhance ecosystem stability. These results suggest that BEF relationships are potentially time scale-dependent. Environmental impacts on biodiversity and ecosystem functioning may be much stronger than biodiversity impacts on ecosystem functioning at long, decadal-millennial, time scales. Longer time scale perspectives, including palaeoecological and ecosystem monitoring data, are critical for predicting future BEF relationships on a rapidly changing planet.

Abstract. Microfossil assemblages provide valuable records to investigate variability in continental margin biogeochemical cycles, including dynamics of the oxygen minimum zone (OMZ). Analyses of modern assemblages across environmental gradients are necessary to understand relationships between assemblage characteristics and environmental factors. Five cores were analyzed from the San Diego margin (32∘42′00′′ N, 117∘30′00′′ W; 300–1175 m water depth) for core top benthic foraminiferal assemblages to understand relationships between community assemblages and spatial hydrographic gradients as well as for down-core benthic foraminiferal assemblages to identify changes in the OMZ through time. Comparisons of benthic foraminiferal assemblages from two size fractions (63–150 and >150 µm) exhibit similar trends across the spatial and environmental gradient or in some cases exhibit more pronounced spatial trends in the >150 µm fraction. A range of species diversity exists within the modern OMZ (1.910–2.586 H, Shannon index), suggesting that diversity is not driven by oxygenation alone. We identify two hypoxic-associated species (B. spissa and U. peregrina), one oxic-associated species (G. subglobosa) and one OMZ edge-associated species (B. argentea). Down-core analysis of indicator species reveals variability in the upper margin of the OMZ (528 m water depth) while the core of the OMZ (800 m) and below the OMZ (1175 m) remained stable in the last 1.5 kyr. We document expansion of the upper margin of the OMZ beginning 400 BP on the San Diego margin that is synchronous with other regional records of oxygenation.

Paleoecological reconstructions of past climate are often based on a single taxonomic group with a consistent presence. Less is known about the relationship between multi-taxon community-wide change and climate variability. Here we reconstruct paleoecological change in a Late Quaternary (16.1-3.4 ka) sediment core from the California margin (418 meters below sea level) of Santa Barbara Basin (SBB), USA, using Mollusca (Animalia) and Foraminifera (Rhizaria) microfossils. Building upon previous investigations, we use multivariate ordination and cluster analyses to interpret community-scale changes in these distinctly different taxonomic groups across discrete climate episodes. The strongest differences between seafloor biological communities occurred between glacial (prior to Termination IA, 14.7 ka) and interglacial climate episodes. Holocene communities were well partitioned, indicating that sub-millennial oceanographic variability was recorded by these microfossils. We document strong evidence of chemosynthetic trophic webs and sulfidic environments (from gastropod Alia permodesta and bivalve Lucinoma aequizonata), which characterized restricted intervals previously interpreted as well oxygenated (such as the Pre-Bølling Warming). Mollusc records indicate first-order trophic energetic shifts between detrital and chemosynthetically-fixed carbon. Molluscs associated with widely different physiological preferences occur here within single, decadal intervals of sediment, and as such mollusc assemblages may reflect significant inter-decadal oceanographic variability. Foraminifera assemblages provide exceptional records of the sequential, chronological progression of the deglacial climatic and oceanographic events, whereas mollusc assemblages reflect non-chronological similarities in reoccurring communities.Foraminifera taxa that drive community similarity here are also independently recognized

Here we present a record of size-normalized shell weight for four species of benthic foraminifera through a period of rapid environmental change during the most recent deglaciation (Santa Barbara Basin, CA). A strong Oxygen Minimum Zone (OMZ), the product of high surface productivity and poor ventilation, characterizes the eastern Pacific; this subsurface zone is mechanistically coupled with high concentrations of dissolved inorganic carbon. The OMZ migrated vertically during warming of the last deglaciation, leading to rapid shifts in the oxygenation and inorganic carbon system of the benthos. The size-normalized weight (SNW) of benthic foraminifers Uvigerina peregrina, Bolivina interjuncta, and Bolivina tumida reflect only the broad trends of the vertical migration of the OMZ, and inorganic carbon system, overshadowed by clear species-specific trends. The relative importance of OMZ migrations versus other environmental variables and optimal growth conditions differs across species of benthic foraminifera. In U. peregrina, SNW primarily peaks with foraminiferal density and increased abundance of that species, while B. interjuncta and B. tumida increase in SNW with a shrinking of the OMZ (and carbon maximum) in the late Holocene. Bolivina argentea shows no long-term trends in SNW potentially due to its ability to migrate through the sediment. Our results suggest that, while inorganic carbon and dissolved oxygen may play a role in determining shell weight across species of benthic foraminifera, neither parameter alone is responsible for changes in benthic foraminiferal shell weight in the fossil record.