Assessing effects of non-native crayfish on mosquito survival

Introductions of non-native predators often reduce biodiversity and affect natural predator–prey relationships and may increase the abundance of potential disease vectors (e.g., mosquitoes) indirectly through competition or predation cascades. The Santa Monica Mountains (California, U.S.A.), situated in a global biodiversity hotspot, is an area of conservation concern due to climate change, urbanization, and the introduction of non-native species. We examined the effect of non-native crayfish (Procambarus clarkii) on an existing native predator, dragonfly nymphs (Aeshna sp.), and their mosquito larvae (Anopheles sp.) prey. We used laboratory experiments to compare the predation efficiency of both predators, separately and together, and field data on counts of dragonfly nymphs and mosquito larvae sampled from 13 local streams. We predicted a lower predation efficiency of crayfish compared with native dragonfly nymphs and a reduced predation efficiency of dragonfly nymphs in the presence of crayfish. Dragonfly nymphs were an order of magnitude more efficient predators than crayfish, and dragonfly nymph predation efficiency was reduced in the presence of crayfish. Field count data showed that populations of dragonfly nymphs and mosquito larvae were strongly correlated with crayfish presence in streams, such that sites with crayfish tended to have fewer dragonfly nymphs and more mosquito larvae. Under natural conditions, it is likely that crayfish reduce the abundance of dragonfly nymphs and their predation efficiency and thereby, directly and indirectly, lead to higher mosquito populations and a loss of ecosystem services related to disease vector control.     

MEETING THE CHALLENGE OF POLICY-RELEVANT SCIENCE: LESSONS FROM A WATER RESOURCE PROJECT1

ABSTRACT: Water resource scientists face complex tasks in evaluating aspects of water projects, but relatively few assessment procedures have been applied and accepted as standard applications. Decision-makers often rely on environmental assessments to evaluate the value and operation of projects. There is often confusion about scientists' role in policy decisions. The scientist can affect policy-making as an expert withess, an advocate or a surrogate. By understanding the policy process, scientists can make their work more “policy relevant.” Using the Terror Lake hydro project in Alaska as a guide, three lessons are discussed: (1) not all problems are able to be solved with technology; (2) policy-relevant technology is rarely imposed on a problem; and (3) the scientist need not just react to the policy process, but can have an impact on how that process unfolds.     

Alfalfa rapidly remediates excess inorganic nitrogen at a fertilizer spill site

By 19%, standard remediation techniques had significantly reduced the concentration of nitrate nitrogen (NO3- -N) in local ground water at the site of a 1989 anhydrous ammonia spill, but NO3- -N concentrations in portions of the site still exceeded the public drinking water standard. Our objective was to determine whether local soil and ground water quality could be improved with alfalfa (Medicago sativa L.). A 3-yr study was conducted in replicated plots (24 by 30 m) located hydrologically upgradient of the ground water under the spill site. Three alfalfa entries ['Agate', Ineffective Agate (a non-N2-fixing elite germplasm similar to Agate), and MWNC-4 (an experimental germplasm)] were seeded in the spring of 1996. Corn (Zea mays L.) or wheat (Triticum aestivum L.) was seeded adjacent to the alfalfa each year. Crops were irrigated with N-containing ground water to meet water demand. During the 3-yr period, about 540 kg of inorganic N was removed from the aquifer through irrigation of 4.9 million L water. Cumulative N removal from the site over 3 yr was 972 kg N ha(-1) in Ineffective Agate alfalfa hay, compared with 287 kg N ha(-1) for the annual cereal grain. Soil solution NO3- concentrations were reduced to low and stable levels by alfalfa, but were more variable under the annual crops. Ground water quality improved, as evidenced by irrigation water N concentration. We do not know how much N was removed by the N2-fixing alfalfas, but it appears that either fixing or non-N2-fixing alfalfa will effectively remove inorganic N from N-affected sites.     

Reproduction and genetic variation in the deposit-feeding sea star Ctenodiscus crispatus

The gonad index in the deposit-feeding asteroid Ctenodiscus crispatus (Retzius) in the Gulf of Maine (USA) is seasonally less variable than in any other sea star, ranging from 2.99 to 4.98% of dry body weight in females and from 2.28 to 3.42% in males, and varies in concert with, rather than reciprocal to, the pyloric caecum index. Biochemical composition and, hence, caloric content, of the gonads also show little seasonal change, suggesting that reproduction is aseasonal and continuous in this population. Oocyte development is asynchronous, all females having a full size range of oocytes (from less than 30 m to greater than 400 m diameter) throughout the year. Seasonally determined size-frequency distributions of juveniles, oocyte cytology and size-frequency distributions, responsiveness of adult females to 1-methyladenine, and oxygen uptake rates indicate that variations in reproductive intensity are superimposed on continuous reproduction, and seem related to changes in phytoplankton production rather than to temperature. The rich neutral lipid content (ca. 50% of total lipid) and large egg size (>400 m) in the ovaries suggest that development is direct. The population is extremely variable genetically, polymorphism among 13 enzyme-coding genes being 77% and average heterozygosity being 0.174. The reproductive pattern and genetic variation in the eurybathic C. crispatus are similar to those in deep-sea echinoderms. This may be related to the constancy of the population's detrital food source, to small-scale heterogeneity of its physical environment, and to low individual vagility.