Geology topics

Kyle R. Hogrefe

Publications and source records attributed to Kyle R. Hogrefe.

10 recordsLinked to original sources

USGS2022

Spatial extent of seagrasses (Zostera marina and Ruppia maritima) along the central Pacific coast of Baja California, Mexico, 1999–2000

The seagrasses eelgrass ( Zostera marina ) and widgeongrass ( Ruppia maritima ) are prominent features of coastal lagoons along the Pacific coast of Baja California, Mexico, supporting a rich diversity of marine life. Yet little is known about their spatial distribution in this region. This is a concern because of declining trends in the abundance and distribution of seagrass in parts of northern Baja California and southern California. We used 7-band satellite imagery, 4-band digital multispectral videography, and 3-band color aerial photography to map the distribution of eelgrass and widgeongrass in six embayments along the central Pacific coast of Baja California. The total spatial extent of seagrass was estimated to be 42,697 hectares, of which about 70 percent was eelgrass. This seagrass was primarily lower in the intertidal than widgeongrass in all embayments. Eelgrass and widgeongrass composed the greatest proportion (47 percent) of the spatial extent in the two largest embayments, Lagunas Ojo de Liebre and San Ignacio, and these two embayments accounted for 85 percent of all seagrass in the study area. The native cordgrass ( Spartina foliosa ) and pickleweed ( Salicornia spp .) were the predominate vegetation cover type of marshes in the three northern and three southern embayments, respectively. The three southern embayments contained mangrove ( Rhizophora spp.) and the three northern embayments did not, thus marking the northern edge of mangroves along the Pacific coast of North America. This study establishes an embayment-wide baseline for continuing investigations and monitoring future changes in the spatial abundance of seagrasses in central Baja California.

Baja California↗

USGS2022

Abundance and distribution of eelgrass (Zostera marina) and seaweeds at Izembek National Wildlife Refuge, Alaska, 2007–10

Eelgrass ( Zostera marina ) meadows are expansive along the lower Alaska Peninsula, supporting a rich diversity of marine life, yet little is known about their status and trends in the region. We tested techniques to inventory and monitor trends in the spatial extent and abundance of eelgrass in lagoons of the Izembek National Wildlife Refuge. We determined if Landsat imagery could be used to assess eelgrass spatial extent in shallow (less than 4 meter water depth) coastal waters of the refuge. We determined that this seagrass could be differentiated using Landsat imagery from other cover types (that is, channels and unvegetated tidal flats) with a high degree of accuracy (greater than 80 percent) in Izembek and Kinzarof Lagoons. Eelgrass meadows represented the largest cover type in Izembek (about 16,000 hectares) and Kinzarof (about 900 hectares) Lagoons, comprising between 45 and 50 percent of the spatial extent of these lagoons, respectively. When compared to estimates of spatial extent of eelgrass from previous studies, our results suggest little change in the spatial extent of eelgrass in Izembek Lagoon during the 28-year period 1978 through 2006. Preliminary mapping of eelgrass in other embayments indicated that this seagrass was also expansive in Big Lagoon (about 900 hectares; or 34 percent of the lagoon area) and Hook Bay (about 900 hectares; or 36 percent of the bay area) but not in Cold Bay (about 100 hectares; less than 5 percent of the bay area). We conducted an embayment-wide point sampling technique to assess aboveground biomass and distribution of eelgrass and seaweeds and presence of six macro-invertebrates during a 4-year period (2007–10). We determined that, when present, mean aboveground biomass of eelgrass was greater in Kinzarof Lagoon (182.5 plus or minus 12.1 grams dry weight per square meter) than in Izembek Lagoon (152.1 plus or minus 7.1 grams dry weight per square meter) in 2008–10, possibly reflecting the warmer sea temperatures and higher salinities found on the Gulf of Alaska side of the Alaska Peninsula. Seaweeds were more abundant in Kinzarof Lagoon than in Izembek Lagoon, surpassing aboveground biomass of eelgrass in both lagoons in 2008. Gastropods (4 percent of all points) and Caprella shrimp (25 percent) were the most common of the six macro-invertebrates surveyed in Izembek Lagoon, and Telmessus crab was the most common macro-invertebrate in Kinzarof Lagoon.

Alaska↗

USGS2022

Distribution of eelgrass (Zostera marina) in coastal waters adjacent to Togiak National Wildlife Refuge, Alaska

Declines in the distribution and abundance of seagrasses worldwide have prompted a need for baseline distribution maps of eelgrass ( Zostera marina ) in Alaska. We used high-resolution digital-color aerial photography and multi-spectral satellite imagery to map the distribution and spatial extent of eelgrass at 21 sites in coastal waters adjacent to Togiak National Wildlife Refuge (TNWR) in northwestern Bristol Bay and southern Kuskokwim Bay. The total spatial extent of eelgrass meadows was estimated to be 6,489 hectare (ha) almost equally divided between Bristol Bay (3,001 ha) and Kuskokwim Bay (3,488 ha). The four largest eelgrass beds occurred in Chagvan Bay (1,933 ha), the north side of Hagemeister Island (1,168 ha), Goodnews Bay (874 ha), and Nanvak Bay (599 ha). This report provides key baseline data useful for establishing a monitoring plan to assess trends in eelgrass along the coast of TNWR.

Alaska↗

USGS2022

Eelgrass (Zostera marina) and Seaweed Abundance along the Coast of Togiak National Wildlife Refuge, Alaska, 2008–10

We conducted a point-sampling survey to determine eelgrass ( Zostera marina ) and seaweed abundance in coastal waters adjacent to Togiak National Wildlife Refuge, Alaska, in July 2008–10. Eelgrass was known to be abundant in protected embayments of the southeastern Bering Sea and near the Togiak National Wildlife Refuge, but prior to this study, no systematic ground surveys had been conducted in these areas. We determined mean aboveground biomass of eelgrass to be highly variable among years observed, ranging from 32–72 grams dry weight per square meter (g/m 2 ) during successive years in Nanvak Bay and among the studied embayments in 2010: 47±4 g/m 2 in Nanvak Bay, 69±7 g/m 2 in Chagvan Bay, and 74±15 g/m 2 in Goodnews Bay. Seaweed density, abundance, and frequency scores were also highly variable among years and among embayments and were lower for seaweeds than for eelgrass in Nanvak and Chagvan bays, but not in Goodnews Bay. For all bays, mussels ( Mytilus spp.) and gastropods were the most common macro-invertebrates detected during surveys, whereas sea stars, crabs, and sponges were not observed in the embayments.

Alaska↗

USGS2022

Eelgrass (Zostera marina) and seaweed abundance along the coast of Nunivak Island, Yukon Delta National Wildlife Refuge, Alaska, 2010

Eelgrass (<em>Zostera marina</em>) is a highly productive seagrass that plays an essential role in the health of the estuarine and coastal ecosystems; however, information about its abundance and distribution is insufficient in the Bering Sea along the Yukon Delta National Wildlife Refuge. We inventoried the spatial extent and abundance of eelgrass and seaweed in Duchikthluk and Shoal bays on Nunivak Island in July 2010. Using Landsat Thematic Mapper imagery, we estimated the spatial extent of eelgrass to be 1,232 hectares in Duchikthluk Bay and 40 hectares in Shoal Bay. The overall accuracy of the assessments was high (86–87 percent) based on ground truthing using field reference points. We used point-sampling methodology to assess eelgrass abundance relative to the presence of associated seaweeds and selected macro-invertebrates within each of bays. Eelgrass was found at water depths ranging from 0.1 to 2.9 meters across both bays, but the greatest density (>75 percent cover) occurred primarily in moderate to deep water (0.7–1.4 meters) in Duchikthluk Bay and deeper water (>2 meters) in Shoal Bay. The mean aboveground biomass was 39.4±4.0 grams per meter squared in Duchikthluk Bay. The eelgrass biomass was greater (67.6±11.0 grams per meter squared) in Shoal Bay, but this estimate was based on a small sample size (n=3). Seaweeds, representing six species, occurred in low abundance across both bays and were primarily associated with eelgrass. Gastropods were the most common macro-invertebrate, occurring at 45 percent of field points in Duchikthluk Bay.

Alaska↗

USGS2022

Eelgrass (Zostera marina) and seaweed assessment Alaska Peninsula-Becharof National Wildlife Refuges, 2010

We conducted the first assessment of eelgrass and seaweed distribution and abundance along the coast of the Alaska Peninsula-Becharof National Wildlife Refuges in Chignik Lagoon and Mud Bay. Areal extent of eelgrass, as determined from remote-sensing techniques, was estimated to be 2,414 hectares in Chignik Lagoon and 188 hectares in Mud Bay, and eelgrass was the dominant marine macrophyte in each of the embayments. During an embayment-wide point survey of Chignik Lagoon, eelgrass and seaweeds were observed on 76 and 62 percent of survey points, respectively. Average percent cover was greater for eelgrass (82 percent) than for seaweeds (37 percent) when each was present at a survey point. In contrast, eelgrass and seaweeds were distributed nearly equally in Mud Bay, occurring on 64 and 70 percent of the points, respectively, and when present, cover of eelgrass and seaweeds were 70 and 60 percent, respectively. Brown and red seaweeds, such as Polysiphonia pacifica, Saccharina latissima, Neorhodomela oregona, and Eudesme borealis, were the most common seaweeds in Chignik Lagoon, while green seaweeds, particularly Kornmannia leptoderma and Cladophora sericea, were dominant in Mud Bay. Standing crop of eelgrass was 44 percent greater in Chignik Lagoon (98.0±6.4 grams dry weight per square meter) than in Mud Bay (68.3±6.7 grams dry weight per square meter) in 2010. Five types of macro-invertebrates were assessed during the point survey. At least one of these macro-invertebrates was observed on 45 percent of points in Chignik Lagoon and 64 percent of points in Mud Bay. Gastropods were the most common of the macro-invertebrates, occurring on 40–57 percent of points in each of the embayments. This assessment of eelgrass and seaweeds can serve as a baseline for determining future changes in the distribution and abundance of these marine macrophytes in Chignik Lagoon and Mud Bay.

Alaska↗

USGS2022

Inventory of eelgrass (Zostera marina) and seaweeds at the end of the Alaska Peninsula, August–September 2012:

Coastal communities in Alaska are undergoing rapid environmental change from increasing temperatures and baseline data are needed to monitor potential impacts. We conducted the first surveys of the abundance and distribution of eelgrass ( Zostera marina ) and seaweeds in the western part of Izembek National Wildlife Refuge at the end of the Alaska Peninsula. Six embayments and two offshore islands were surveyed in August–September of 2012. Biotic (percent cover of eelgrass/seaweeds, presence/absences of five sessile invertebrates), and abiotic (water temperature, salinity, and depth) data were recorded at 257 survey points (range =9–74 points per site) across all sites. Twenty-two genera/species of seaweeds were identified at the six embayments. New seaweed species for the offshore islands of Sanak and Caton were added to an existing seaweed collection accessioned at the University of British Columbia Herbarium. We also collected samples of eelgrass to be accessioned at U.S. Geological Survey, Alaska Science Center-Molecular Ecology Laboratory, for future genetic analyses. Fifty-three species of birds and 13 species of mammals were observed and recorded during the survey period.

Alaska↗

USGS2018

Volcanic ash deposition, eelgrass beds, and inshore habitat loss from the 1920s to the 1990s at Chignik, Alaska

We quantified the shallowing of the seafloor in five of six bays examined in the Chignik region of the Alaska Peninsula, confirming National Ocean Service observations that 1990s hydrographic surveys were shallower than previous surveys from the 1920s. Castle Bay, Chignik Lagoon, Hook Bay, Kujulik Bay and Mud Bay lost volume as calculated from Mean Lower Low Water (Chart Datum) to the deepest depths and four of these sites lost volume from Mean High Water to the deepest depths. Calculations relative to each datum were made because tidal datum records exhibited an increase in tidal range in this region from the 1920s to the 1990s. Our analysis showed that Mud Bay is quickly disappearing while Chignik Lagoon is being reduced to narrow channels. Anchorage Bay was the only site that increased in depth over time, perhaps due to erosion. Volcanoes dominate the landscape of the Chignik area. They have blanketed the region in deep ash deposits before the time frame of this study, and some have had smaller ash-producing eruptions during the time frame of this study. Remobilization of land-deposited ash and redeposition in marine areas - in some locations facilitated by extensive eelgrass ( Zostera marina ) beds (covering 54% of Chignik Lagoon and 68% of Mud Bay in 2010) - is the most likely cause of shallowing in the marine environment. Loss of shallow water marine habitat may alter future abundance and distribution of several fish, invertebrate and avian species.

Alaska↗

USGS2017

Growth of black brant and lesser snow goose goslings in northern Alaska

Gosling body mass can affect first year survival, recruitment, adult body size, and future fecundity of geese, and can serve as an indicator of forage availability and quality on brood-rearing areas. From 2012–2014 we measured body mass of 76 black brant ( Branta bernicla nigricans ) and 268 lesser snow goose ( Chen caerulescens caerulescens ) goslings of known age on the Colville River Delta (CRD) of northern Alaska to determine if there was evidence of density-dependent declines in gosling growth following recent population increases of those species and sympatric greater white-fronted geese ( Anser albifrons frontalis ). We contrasted contemporary body mass of brant goslings and forage biomass in brood-rearing habitats that were shared by all species, with measures obtained on, and near the CRD in the 1990s, prior to the establishment of snow goose nesting colonies in the area. Body mass of brant goslings recaptured between 25 and 32 days of age had not changed over the past 2 decades, despite an influx of snow geese, and increases in populations of brant and white-fronted geese. At 30 days of age, body mass of brant goslings on the CRD was 100–400 g heavier than for brant goslings of the same age on the Yukon-Kuskokwim Delta (YKD), Alaska. Contemporary biomass of grazed Carex subspathacea on CRD brood-rearing areas was comparable to the 1990s and was 2–4 times greater than for the same plant community on the YKD. Historical data on growth of snow goose goslings were not available for the CRD. However, average body mass of 34-day-old snow goose goslings was > 230 g heavier than for conspecifics of the same age in the Hudson Bay region. We conclude that the establishment of nesting snow geese on the CRD has not negatively affected brant gosling growth, and that recent population increases of all species have likely not been constrained by forage availability on brood-rearing areas. Barring demographic changes elsewhere in their annual cycles, we predict that goose populations will continue to increase in northern Alaska. However, snow geese are increasing more rapidly than brant in the region. Because the black brant population has periodically been below conservation objectives, the effects of the increasing number of snow geese on forage biomass and growth of brant goslings in northern Alaska should be monitored.

Alaska↗

USGS2014

Establishing a baseline for regional scale monitoring of eelgrass ( Zostera marina ) habitat on the lower Alaska Peninsula

Seagrass meadows, one of the world’s most widespread and productive ecosystems, provide a wide range of services with real economic value. Worldwide declines in the distribution and abundance of seagrasses and increased threats to coastal ecosystems from climate change have prompted a need to acquire baseline data for monitoring and protecting these important habitats. We assessed the distribution and abundance of eelgrass ( Zostera marina ) along nearly 1200 km of shoreline on the lower Alaska Peninsula, a region of expansive eelgrass meadows whose status and trends are poorly understood. We demonstrate the effectiveness of a multi-scale approach by using Landsat satellite imagery to map the total areal extent of eelgrass while integrating field survey data to improve map accuracy and describe the physical and biological condition of the meadows. Innovative use of proven methods and processing tools was used to address challenges inherent to remote sensing in high latitude, coastal environments. Eelgrass was estimated to cover ~31,000 ha, 91% of submerged aquatic vegetation on the lower Alaska Peninsula, nearly doubling the known spatial extent of eelgrass in the region. Mapping accuracy was 80%–90% for eelgrass distribution at locations containing adequate field survey data for error analysis.

Alaska↗