Midge-stabilized sediment drives the composition of benthic cladoceran communities in Lake Mývatn, Iceland

The importance of environmental disturbances as drivers of ecological communities depends not only on the magnitude of the disturbance, but also on the disturbance-specific sensitivity of the community. Organisms that alter the physical structure of their surroundings can affect the sensitivity of their habitat to environmental disturbance, and may alter the potential for disturbance to shape ecological communities. Such organisms therefore act as ecosystem engineers by indirectly modifying the resources available to other species. The benthos of shallow, eutrophic Lake Mývatn, Iceland, is frequently disturbed by wind events that lead to sediment resuspension. The impact of wind, however, depends on the abundance of midges (Chironomidae) whose larval tubes bind sediment and reduce wind-driven resuspension. Here, we investigate the long-term effect of fluctuations in midge abundance on the benthic cladoceran community using two lake sediment cores representing 30 and 140 years of deposition. In both cores, midge remains show a significant positive correlation with abundance of a large benthic surface-dwelling cladoceran, Eurycercus lamellatus, relative to the abundance of a small within-sediment-dwelling cladoceran, Alona rectangula. To experimentally investigate whether this shift could have been caused by midges acting as ecosystem engineers, we subjected cladoceran communities to sediment resuspension events within mesocosms. We found a significant decrease in abundance of the large epibenthic E. lamellatus relative to the abundance of small infaunal Alona spp. when subjected to disturbance. These findings show that physical alteration of benthic sediment and hence the sensitivity of the sediment to disturbance may explain the community shift in cladocerans observed with fluctuating midge abundance in Lake Mývatn.National Science Foundation Graduate Research Fellowship. Grant Number: DGE-1256259 LTREB. Grant Number: DEB-1052160Peer Reviewe

A Multi-platform Bathyphotometer for Fine-Scale, Coastal Bioluminescence Research

Although bioluminescence (BL) in the open ocean has been extensively studied, coastal BL remains poorly understood due, in large degree, to a lack of BL instrumentation appropriate to measure the fine-scale biological and physical complexity of the coastal regime. As a contribution toward understanding coastal BL, we developed the Multipurpose Bioluminescence Bathyphotometer (MBBP). This compact, self-contained bathyphotometer (BP) was designed to function in a variety of deployment modes, including conventional shipboard profilers, towed platforms, autonomous underwater vehicles (AUVs), and profiling moorings. In all configurations, the instrument preserves signal structure at centimeter to meter scale resolution, the scale at which higher-flow instruments might disturb thin layers and other fine-scale water column features. In the MBBP, seawater is conveyed with minimal premeasurement excitation into a light-baffled stimulation and measurement chamber at a continuously measured flow rate of 350 to 400 mL s–1. A photomultiplier tube (PMT) records light from bioluminescent organisms after they are mechanically stimulated at the chamber entrance by a high-velocity impeller. Calibration and test protocols were developed to determine BL stimulation efficiency and MBBP measurement characteristics. To illustrate the capabilities of the MBBP to resolve the fine-scale structure of the BL community, measurements from two coastal environments are presented

Appendix C. Two-dimensional representations of the mathematical model.

Two-dimensional representations of the mathematical model

Appendix A. Sensitivity analysis of mathematical model.

Sensitivity analysis of mathematical model

Appendix B. Temperature dependencies of the vital rates of Lepomis sunfish, Daphnia pulex, and Daphnia lumholtzi.

Temperature dependencies of the vital rates of Lepomis sunfish, Daphnia pulex, and Daphnia lumholtzi

Bioluminescence to Reveal Structure and Interaction of Coastal Planktonic Communities

Ecosystem function will in large part be determined by functional groups present in biological communities. The simplest distinction with respect to functional groups of an ecosystem is the differentiation between primary and secondary producers. A challenge thus far has been to examine these groups simultaneously with sufficient temporal and spatial resolution for observations to be relevant to the scales of change in coastal oceans. This study takes advantage of general differences in the bioluminescence flash kinetics between planktonic dinoflagellates and zooplankton to measure relative abundances of the two groups within the same-time space volume. This novel approach for distinguishing these general classifications using a single sensor is validated using fluorescence data and exclusion experiments. The approach is then applied to data collected from an autonomous underwater vehicle surveying \u3e500 km in Monterey Bay and San Luis Obispo Bay, CA during the summers of 2002–2004. The approach also reveals that identifying trophic interaction between the two planktonic communities may also be possible

Spatial patterns reveal strong abiotic and biotic drivers of zooplankton community composition in Lake My´vatn, Iceland

Spatial patterns in the abundance of species are determined by local abiotic and biotic conditions, and by the movement of individuals among localities. For species distributed among discrete habitat ‘‘islands’’, such as zooplankton distributed among lakes, local conditions within lakes often dominate low movement rates among lakes to determine the composition of communities. Here, we ask whether the same abiotic and biotic environmental conditions can generate spatial patterns in the distribution of zooplankton within a lake where there are high horizontal movement rates. We conducted three spatial surveys of zooplankton communities in Lake My´vatn, Iceland, a moderately sized (37 km2) shallow lake with a high outflow rate. The pelagic zooplankton community showed strong spatial structure (spatial autocorrelation), with species composition varying with spatial variation in chlorophyll-a, the abundance of Anabaena (cyanobacteria), lake depth, light extinction coefficient, and temperature. These factors are known from other studies to be strong drivers of among-lake variation in freshwater zooplankton communities. However, in contrast with among-lake studies, fish (stickleback) abundance had no measureable effect on the abundance or species composition of the zooplankton community, although high local stickleback abundance was associated with low zooplankton:phytoplankton biomass ratios. Finally, a parallel study of the underlying benthic crustacean community showed much finer spatial variation (spatial autocorrelation to a range 0.6 km vs. 9 km for pelagic zooplankton), suggesting that the stationary character of the benthos allows finer grained spatial patterns. Given the high flow rate of water in My´vatn (.200 m/d), the generation of spatial patterns suggests very strong effects of variation in abiotic and biotic environmental conditions on the population dynamics of zooplankton in the lake

Spatial patterns reveal strong abiotic and biotic drivers of zooplankton community composition in Lake My'vatn, Iceland

Spatial patterns in the abundance of species are determined by local abiotic and biotic conditions, and by the movement of individuals among localities. For species distributed among discrete habitat "islands", such as zooplankton distributed among lakes, local conditions within lakes often dominate low movement rates among lakes to determine the composition of communities. Here, we ask whether the same abiotic and biotic environmental conditions can generate spatial patterns in the distribution of zooplankton within a lake where there are high horizontal movement rates. We conducted three spatial surveys of zooplankton communities in Lake Mývatn, Iceland, a moderately sized (37 km2) shallow lake with a high outflow rate. The pelagic zooplankton community showed strong spatial structure (spatial autocorrelation), with species composition varying with spatial variation in chlorophyll-a, the abundance of Anabaena (cyanobacteria), lake depth, light extinction coefficient, and temperature. These factors are known from other studies to be strong drivers of among-lake variation in freshwater zooplankton communities. However, in contrast with among-lake studies, fish (stickleback) abundance had no measureable effect on the abundance or species composition of the zooplankton community, although high local stickleback abundance was associated with low zooplankton:phytoplankton biomass ratios. Finally, a parallel study of the underlying benthic crustacean community showed much finer spatial variation (spatial autocorrelation to a range ≤0.6 km vs. 9 km for pelagic zooplankton), suggesting that the stationary character of the benthos allows finer grained spatial patterns. Given the high flow rate of water in Mývatn (>200 m/d), the generation of spatial patterns suggests very strong effects of variation in abiotic and biotic environmental conditions on the population dynamics of zooplankton in the lake