Showing papers by "Charles H. Peterson published in 2005"

Assessing the Environmental Impacts of Beach Nourishment

Abstract: With sea levels rising under global warming, dredge-and-fill programs are increasingly employed to protect coastal development from shoreline erosion. Such beach "nourishment" can bury shallow reefs and degrade other beach habitats, depressing nesting in sea turtles and reducing the densities of invertebrate prey for shorebirds, surf fishes, and crabs. Despite decades of agency-mandat ed monitoring at great expense, much uncertainty about the biological impacts of beach nourishment nonetheless exists. A review of 46 beach monitoring studies shows that (a) only 11 percent of the studies controlled for both natural spatial and temporal variation in their analyses, (b) 56 percent reached conclusions that were not adequately supported, and (c) 49 percent failed to meet publication standards for citation and synthesis of related work. Monitoring is typically conducted through project promoters, with no independent peer review, and the permitting agencies exhibit inadequate expertise to review biostatistical designs. Monitoring results are rarely used to scale mitigation to compensate for injured resources. Reform of agency practices is urgently needed as the risk of cumulative impacts grows.

Habitat degradation from intermittent hypoxia: impacts on demersal fishes

Abstract: As eutrophication of estuaries and coastal oceans increases worldwide, the resulting expansion of hypoxic zones represents an increasingly frequent form of habitat degradation. Although impacts of prolonged hypoxia on benthic invertebrate species are well-documented, there is little understanding of how those effects subsequently influence the motile upper trophic levels in estuarine ecosystems. Quantitative nekton surveys in the Neuse River Estuary and field experiments in June and August 1999 using Atlantic croaker Micropogonias undulatus demonstrated that inter- mittent hypoxia decreased habitat quality for juvenile, demersal fish through 3 pathways: (1) hypoxia restricted the fishes in estuaries to shallow, oxygenated areas, where in the early part of the summer about 1 ⁄3 fewer prey resources were available. (2) This contraction of suitable habitat crowded the fish into smaller areas and may have resulted in density-dependent reduction of growth rates. (3) Most importantly, mortality of sessile infauna in deeper areas exposed to intermittent hypoxia decreased prey densities about 8-fold between the June and August experiments. Through these mechanisms, intermittent hypoxia may result in ecological crunches or bottlenecks. Field data collected from May to October in 3 yr (1998 to 2000) with differing levels of hypoxia support the conclusion that intermit- tent hypoxia may decrease habitat quality and result in ≥50% declines in juvenile fish growth rate. Incorporation of these indirect effects of hypoxia on juvenile growth rates into a population model demonstrated the potential for significant (~4%) reductions in population growth rate. Thus, sub- lethal effects of hypoxia-driven habitat degradation may impact fisheries production not only through reduced size at age, but also through reduced abundance of demersal fish populations.

Effects of eutrophication on bottom habitat and prey resources of demersal fishes

Abstract: Estuarine benthic habitats serve as essential feeding grounds for demersal finfishes and shellfishes and provide a link between the water column and demersal fisheries in coastal foodwebs. We hypothesize that the cascading linkages of water-column conditions to benthic invertebrates and from benthic invertebrates (as prey) to demersal fishes are a primary mechanism by which water- quality degradation affects sustainable production of demersal fisheries in coastal ecosystems. To evaluate these linkages, we related changes in water quality to changes in bottom-habitat quality for fishes (defined by the availability of prey resources) and assessed how changes in habitat quality affect fish diet. We examined the first link (water-column conditions to benthos) by intensively sam- pling the benthic community in the Neuse River Estuary, North Carolina, during 2 summers (1997 and 1998) in which depletion of bottom-water oxygen occurred. Dramatic decreases in the abun- dance of benthic macroinvertebrates were evident after hypoxia/anoxia in both years. Abundances of the clam Macoma balthica, a key prey item for fishes and crabs and the biomass dominant in the benthos, decreased by over 90% in deep and mid-depth areas (>2 m) throughout the estuary after hypoxia/anoxia in 1997. Although summer decreases in benthic macroinvertebrates were also exhib- ited in 1998, a year of less frequent and less severe hypoxia, the magnitude of decline was less than that of 1997. To evaluate how these changes in prey abundance may affect demersal fishes, we ana- lyzed the diet of Atlantic croaker Micropagonias undulatus, the most abundant demersal fish in the system, prior to and after summer hypoxia of 1998. This analysis demonstrated a shift in croaker diet away from clams, an abundant item before hypoxia, to less nutritional items such as plant and detri- tal material afterwards. This dietary shift reflects the decreased abundance of clams as a result of hypoxia/anoxia. We conclude from our study of the Neuse River Estuary that hypoxia/anoxia events degrade essential fish habitat and that this degradation has the potential to reduce the capacity of the system to support production of demersal fisheries.

Selective predation by the zoarcid fish Thermarces cerberus at hydrothermal vents

Abstract: This study investigates predation by the vent zoarcid fish Thermarces cerberus through gastrointestinal analyses of 27 specimens collected with the submersible ALVIN at vents at 9°50′N on the East Pacific Rise. T. cerberus fed most frequently on gastropod mollusks (mainly Lepetodrilus elevatus) and amphipod crustaceans (mainly Ventiella sulfuris). Species found occasionally in high abundance included the swarming amphipod Halice hesmonectes and the snail Cyathermia naticoides. Other items also found in gastrointestinal tracts, but in very low numbers, included polychaete worms, crustaceans and unidentified tissue clumps. The comparison between the size distribution of L. elevatus limpets ingested by T. cerberus and those found attached to vestimentiferan tubes suggest that the fish may selectively prey on large limpets. If the selective removal of large Lepetodrilus spp. limpets by T. cerberus does occur, then it would have potential community-level consequences at hydrothermal vents, since these mobile gastropods appear to inhibit the settlement of sessile vent species, including tube-building worms. Our results suggest possible direct and indirect effects of T. cerberus on benthic community structure at hydrothermal vents on the East Pacific Rise.

Effects of harvesting methods on sustainability of a bay scallop fishery: dredging uproots seagrass and displaces recruits

Abstract: Fishing is widely recognized to have profound effects on estuarine and marine ecosystems (Hammer and Jansson, 1993; Dayton et al, 1995) Intense commercial and recreational harvest of valuable species can result in population collapses of target and nontarget species (Botsford et al, 1997; Pauly et al, 1998; Collie et al 2000; Jackson et al, 2001) Fishing gear, such as trawls and dredges, that are dragged over the seafloor inflict damage to the benthic habitat (Dayton et al, 1995; Engel and Kvitek, 1995; Jennings and Kaiser, 1998; Watling and Norse, 1998) As the growing human population, over-capitalization, and increasing government subsidies of fishing place increasing pressures on marine resources (Myers, 1997), a clear understanding of the mechanisms by which fishing affects coastal systems is required to craft sustainable fisheries management