Nearshore Ecosystems Overview

Nearshore Benthic Systems in the Gulf of Alaska

WHEN EXAMINED CLOSELY, NEARSHORE HABITATS SUPPORT A DIVERSE ARRAY OF PLANT AND ANIMAL SPECIES. THIS PHOTO SHOWS A TYPICAL INTERTIDAL ASSEMBLAGE OF MARINE LIFE FOUND ON THE KATMAI COAST, KATMAI NATIONAL PARK. (PHOTO CREDIT: JAMES PFEIFFENBERGER, NPS OASLC).

Who We Are

Heather Coletti, NPS Southwest Alaska Inventory & Monitoring Network

Daniel Esler, USGS Alaska Science Center

Daniel Esler, USGS Alaska Science Center

Kim Kloecker, USGS Alaska Science Center

Kim Kloecker, USGS Alaska Science Center

Daniel Monson, USGS Alaska Science Center

Daniel Monson, USGS Alaska Science Center

Ben Weitzman, USGS Alaska Science Center

Ben Weitzman, USGS Alaska Science Center

Brenda Ballachey, USGS Alaska Science Center

Brenda Ballachey, USGS Alaska Science Center, Emeritus

James Bodkin, USGS Alaska Science Center

James Bodkin, USGS Alaska Science Center, Emeritus

Thomas Dean, Coastal Resources Associates, Inc.

Thomas Dean, Coastal Resources Associates, Inc.

 

 

 

New moon pulls back drape
on life ‘neath ocean’s surface
Reflects a tide pool

Why are we sampling?

As described in the overview of the Nearshore Ecosystems Component, the nearshore is broadly recognized as highly susceptible and sensitive to a variety of both natural and human disturbances on a wide range of time and space. Nearshore systems are especially good indicators of change because organisms in the nearshore are relatively sedentary and accessible. In contrast to other marine habitats, scientists understand some of the mechanisms that link species to their physical environment in the nearshore. We are undertaking further exploration to expand our understanding of linkages that will help us discern causes of change in the nearshore and allow us to provide recommend management actions that will reduce harmful human impacts.

Where are we sampling?

We are sampling three regions in the Gulf of Alaska: Western Prince William Sound (WPWS), Kenai Fjords National Park (KEFJ), and Katmai National Park and Preserve (KATM). We also coordinate closely with our Gulf Watch Alaska partners in Kachemak Bay – the Kachemak Bay Nearshore Ecology project led by Katrin Iken and Brenda Konar.

How are we sampling?

We assess intertidal and nearshore communities through measurements of  water temperature, contaminants, intertidal invertebrates, seaweeds, and sea grasses. We also monitor various aspects of the ecology of sea otters, black oystercatchers, and other marine mammals and seabirds in the nearshore, including skiff-based surveys along coastal (nearshore) transects. In addition, we assess nearshore ecosystem productivity, factors that influence the recruitment and survival of important benthic prey like mussels, and predator-prey dynamics. Our sampling is coordinated with the National Park Service Southwest Alaska Network (SWAN) Inventory and Monitoring (I&M) Program.

What are we finding?

The 2014 Gulf Watch Alaska Interim Synthesis Report and 2015 Annual reports documented the following ecological trends in recent years. More information about the latest findings for this project can also be found in the SWAN I&M Program’s resource briefs.

  • A slight Increase in nearshore temperatures in summer, 2014. We observed only slightly higher than normal temperatures in the nearshore during early summer 2014 (through July) when unusually warm surface water temperatures were being observed in offshore areas. The extent to which elevated water temperature reach the nearshore is not well understood, and is complicated by many factors that are specific to water conditions in nearshore systems, including freshwater inputs, glacial melt, tidal exchange, and nearshore currents, etc.

 

  • Unusual numbers of common murres in nearshore areas during summer, 2015, compared to surveys during 2006-2014.  We observed increases in numbers along the Katmai and Kenai Fjords National Park coastlines. The increase was particularly evident in Katmai National Park where there are no murre colonies and densities of murres are generally low. We believe this increase in numbers is most likely a change in distribution that resulted from the movement of birds into inshore areas to feed after their failure to breed on their colonies. Our documentation of these unusual murre distributions correspond to later observations of large die-offs of murres throughout the north Pacific in winter 2015-2016. We speculate that high water temperature may have made prey less available or less abundant, which led to changes in murre distribution, behavior, condition, and eventually, the large number of deaths observed. Our results contribute to observations across GWA components that demonstrate that 2015 was an anomalous year.

 

  • Variable trends in sea otter populations, reflecting different relationships between sea otter numbers and the habitat carrying capacity in each area. We found that sea otter numbers varied by location based on environmental factors and prey availability. In the Katmai area, sea otter numbers have increased substantially since the early 1990s. Densities there are currently high and appear to have stabilized recently. In contrast, sea otter densities in the Kenai Fjords study area have remained relatively low and constant during the same period. These population trends reflect food availability, and thus the habitat carrying capacity, of the two areas. As sea otter numbers increased in the Katmai area, we observed otters collecting smaller prey which reduced the amount of energy they could recover with each foraging effort. The population likely increased until it reached the point where food resources limited any further increase. In comparison, since the Kenai Fjords population remained at low, but constant, densities, this is an indication that the population was at carrying capacity in that area with low food availability. These population trends provide a context for understanding the trend in the western Prince William Sound population, where sea otters have recently recovered from injury associated with the Exxon Valdez oil spill. Food has recently become a limiting factor which indicates the population may be reaching carrying capacity.

    THE GRAPH ON THE LEFT SHOWS THE DENSITY OF SEA OTTERS (ESTIMATED SEA OTTER ABUNDANCE/AVAILABLE SUITABLE HABITAT) IN KATMAI NATIONAL PARK (KATM), KENAI FJORDS NATIONAL PARK (KEFJ), AND WESTERN PRINCE WILLIAM SOUND (WPWS) STUDY BLOCKS. THE GRAPH ON THE RIGHT SHOWS ENERGY RECOVERY RATES (KILOCALORIES/MINUTE) FOR SEA OTTERS FORAGING IN EACH OF THE STUDY BLOCKS.

     

  • High recruitment of mussels in 2007-2008, followed by general declines in mussel bed size and density. Some recovery occurred for mussel beds in the Katmai area during 2012-2015. The decline of Pacific blue mussels, a key item for a large variety of predators in nearshore areas throughout the GOA would result in lower energy available to predators. In some areas, we observed that fewer mussels were eaten by sea otters and black oystercatchers after the mussel beds declined.

MUSSEL SIZE WERE MEASURED AT MUSSEL BEDS AT THE MONITORING SITES.

  • Steady decrease in the biomass of clams since 2007. We have observed no major recruitment events except in the case of rock-borers (Hiatella arctica) in 2015. These decreases occurred among the most common clam species at our sites:  butter clams (Saxidomus gigantea), Pacific littleneck clams (Leukoma staminea), cockles (Clinocardium nuttallii), rock-borers (Hiatella arctica), soft-shell clams (Mya arenaria), blunt gapers (Mya truncate), and multiple species of the genus Macoma. We plan to conduct further studies to understand what contributes to the population dynamics of these bivalves, beginning with the compilation and evaluation of bivalve abundance and size data from around the Gulf of Alaska and Northeast Pacific to ascertain the extent of intertidal clam declines. In collaboration with others, our aim will be to develop better monitoring tools to understand potential drivers behind clam recruitment and growth.