Brian A. Grantham

PROPAGULE DISPERSAL DISTANCE AND THE SIZE AND SPACING OF MARINE RESERVES

This study compiled available information on the dispersal distance of the propagules of benthic marine organisms and used this information in the development of criteria for the design of marine reserves. Many benthic marine organisms release propagules that spend time in the water column before settlement. During this period, ocean currents transport or disperse the propagules. When considering the size of a marine reserve and the spacing between reserves, one must consider the distance which propagules disperse. We could find estimates of dispersal distance for 32 taxa; for 25 of these, we were also able to find data on the time the propagules spent dispersing. Dispersal distance ranged from meters to thousands of kilometers, and time in the plankton ranged from minutes to months. A significant positive correlation was found between the log-transformed duration in the plankton and the log-transformed dispersal distance ( r 5 0.7776, r 2 5 0.60, df 5 1, 25, P 5 0.000); the more time propagules spend in the water column the further they tend to be dispersed. The frequency distribution of the log-transformed dispersal distance is bimodal (kurtosis 52 1.29, t 52 4.062, P , 0.001) with a gap between 1 and 20 km. Propagules that dispersed ,1 km spent less time in the plankton (,100 h), or if they remained in the plankton for a longer period, they tended to remain in the waters near the bottom. Propagules that dispersed .20 km spent more than 300 h in the plankton. The bimodal nature of the distribution suggests that evolutionary constraints may reduce the likelihood of evolving mid-range dispersal strategies (i.e., dispersal between 1 and 20 km) resulting in two evolutionarily stable dispersal strategies: dispersal , 1k m or.;20 km. We suggest that reserves be designed large enough to contain the short-distance dispersing propagules and be spaced far enough apart that long-distance dispersing propagules released from one reserve can settle in adjacent reserves. A reserve 4-6 km in diameter should be large enough to contain the larvae of short-distance dispersers, and reserves spaced 10- 20 km apart should be close enough to capture propagules released from adjacent reserves.

Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific.

Seasonal development of dissolved-oxygen deficits (hypoxia) represents an acute system-level perturbation to ecological dynamics and fishery sustainability in coastal ecosystems around the globe. Whereas anthropogenic nutrient loading has increased the frequency and severity of hypoxia in estuaries and semi-enclosed seas, the occurrence of hypoxia in open-coast upwelling systems reflects ocean conditions that control the delivery of oxygen-poor and nutrient-rich deep water onto continental shelves. Upwelling systems support a large proportion of the worlds fisheries, therefore understanding the links between changes in ocean climate, upwelling-driven hypoxia and ecological perturbations is critical. Here we report on the unprecedented development of severe inner-shelf (<70 m) hypoxia and resultant mass die-offs of fish and invertebrates within the California Current System. In 2002, cross-shelf transects revealed the development of abnormally low dissolved-oxygen levels as a response to anomalously strong flow of subarctic water into the California Current System. Our findings highlight the sensitivity of inner-shelf ecosystems to variation in ocean conditions, and the potential impacts of climate change on marine communities.

The Loch Eil project: Chlorophyll a and nutrients in the water column of Loch Eil

Monthly measurements of temperature, salinity, chlorophyll a, phosphate, nitrate, and ammonia were made at three stations in Loch Eil and one station in the Lynn of Lome, on the west coast of Scotland, during 1976 and early 1977. Dissolved inorganic phosphate ranged from < 0.03 to 0.91 μg-at.PO4-P/l, dissolved inorganic nitrate from < 0.05 to 8.4 μg-at.NO3-N/l, ammonia from < 0.1 to 2.8 μg-at.NH4-N/l, and chlorophyll a from 0.02 to 5.46 mg/m3. The main freshwater input to Loch Eil is at the seaward end of its mouth. This gives unusual hydrographie characteristics with an increased proportion of freshwater in the water column. Compared with Loch Creran, of similar dimensions and freshwater input, Loch Eil has a lower standing crop of phytoplankton, higher light attenuation from humic compounds, and a deeper surface mixed layer. There were no significant differences between stations in Loch Eil except for chlorophyll a at 15 m depth and below which decreased with distance from-the mouth. Many of the changes in the water column of Loch Eil appear linked to changes in rainfall which affect water column stability and loch circulation.

Surface nutrients, chlorophyll a and phaeopigment in some Scottish sea lochs

Abstract The distribution of several surface properties, both physical and chemical, of three Scottish sea lochs were studied during the spring phytoplankton bloom. Concentrations of nitrate, phosphate, and silicate have been determined and related to fluctuations in the freshwater input and uptake by the phytoplankton population. The ratios nitrate: phosphate and silicate: phosphate (on atom bases) in Loch Creran and Loch Linnhe were similar, but there were certain marked differences from those in Loch Etive. Nitrate, rather than phosphate, was a critical factor in the productivity of Loch Creran and Loch Linnhe. In Loch Etive the limitation of these nutrients was directly affected by the amount of fresh-water entering into the Loch. Patchiness of chlorophyll a and phaeopigments in Loch Creran and Loch Etive reflected those factors ( e.g. , freshwater/sea-water inflow, turbulence produced by the loch topography etc. ) which affect the surface circulation in the two lochs. The delay in the development of the phytoplankton bloom in Loch Linnhe may be attributed to a poor stability of the surface layers due to low run-off.