Marine Nearshore

Introduction

The nearshore can be defined as that section of the marine ecosystem that extends from the high tide line, offshore to depths of about 20 m. It can be divided into the backshore (zone that extends landward from the higher high water line, or “spray zone” influenced by storm tides), intertidal zone (between high-high water and lower-low water), and the nearshore subtidal (from lower-low water to depths of 20 m). The intertidal shorelines are geomorphologically diverse and vary from sheltered marshlands and beaches to steep rocky outcroppings subjected to high waves. The subtidal zone is a mix of cobble/ gravel, rocky outcroppings, and sand/silt. The subtidal substrate composition is only loosely correlated with that observed in adjacent intertidal zones.

The nearshore is considered an important component of the Southwest Alaska Network of National Parks (SWAN) and the Gulf of Alaska marine ecosystem because it provides:

• A variety of unique habitats for resident organisms (e.g. sea otters, harbor seals, shorebirds, seabirds, nearshore fishes, kelps, seagrasses, clams, mussels, and sea stars).
• Nursery grounds for marine animals from other habitats (e.g. crabs, salmon, herring, and seabirds).
• Feeding grounds for important consumers, including, killer whales, harbor seals, sea otters, sea lions, sea ducks, shorebirds, brown bears, and many fish and shellfish.
• A source of animals important to commercial and subsistence harvests (e.g. marine mammals, fishes, crabs, mussels, clams, chitons, and octopus).
• An important site of recreational activities including fishing, boating, camping, and nature viewing.
• A source of primary production for export to adjacent habitats (primarily by kelps, other seaweeds, and eelgrass).
• An important triple interface between air, land and sea that provides linkages for transfer of water, nutrients, and species between watersheds and offshore habitats.

The nearshore is broadly recognized as highly susceptible and sensitive to a variety of both natural and human disturbances on a variety of temporal and spatial scales. For example, observed changes in nearshore systems have been attributed to such diverse causes as global climate change, earthquakes, oil spills, human disturbance and removals, and influences of invasive species. Nearshore systems are especially good indicators of change because organisms in the nearshore are relatively sedentary, accessible, and manipulable. Also, in contrast to other marine habitats, there is a comparatively thorough understanding of mechanistic links between species and their physical environment that facilitates understanding causes for change. Also, the nearshore is the one habitat within which it is most likely that we will be able to detect relatively localized sources of change, tease apart human induced from naturally induced changes and, provide suggestions for management actions to reduce human induced impacts. Because many of the organisms in the nearshore are sessile or have relatively limited home ranges, they can be geographically linked to sources of change with a reasonable degree of accuracy.

The Southwest Alaska Network of National Parks identified the following “Vital Signs” as important for monitoring of nearshore marine habitats. In response, a protocol narrative was developed that describes the design of a monitoring program that incorporates and integrates specific sampling protocols (SOP’s) to improve our understanding of the processes contributing to change in the nearshore. The overarching question to be addressed by the SWAN nearshore vital signs program is: “How will nearshore resources within the Parks change over time?” A secondary question is “What are the potential causes for observed changes?” The objective of the SWAN nearshore program is to assess changes by annually monitoring vital signs at various locations within the SWAN parks and to describe changes and assess potential causes by comparing values for different vital sign metrics (e.g. number of sea otters) over time and by examining how the relative extent of change over time varies among locations.

Vital Signs Summary

Harbor Seal

Harbor seals (Phoca vitulina) are a common and important marine mammal in the Gulf of Alaska, commonly hauling out to rest on sand bars and intertidal reefs during periods of low tide. They occupy an upper trophic level position in a marine food web based on forage fish. Their populations have undergone dramatic declines in abundance in recent decades, similar in magnitude and geographic extent to the threatened western stock of Steller sea lion (Eumatopias jubatus).

Kelp and Seagrasses

Kelp and seagrasses are "living habitats" that serve as a nutrient filter, provide understory and habitat for planktivorous fish, clams, urchins, and a physical substrate for other invertebrates and algae. Kelps are the major primary producers in the marine nearshore and because they are located in shallow water they could be significantly impacted by human activities. These include spills of oil or other contaminants, dredging and disturbance from anchoring of vessels, and increased turbidity caused by runoff of sediments or nutrients.

Marine Invertebrates

Marine Intertidal Invertebrates and algae provide critical food resources for shorebirds, ducks, fish, bears, sea otters, and other marine invertebrate predators, as well as spawning and nursery habitats for forage fish and juvenile crustaceans. Benthic invertebrates and algae are ecologically diverse in terms of habitat and trophic requirements; have a wide range of physiological tolerances; are relatively sedentary, and have varied life-histories. As a result, they are good biological indicators of both short-term (e.g. annual) and long-term (e.g. decadal scale) changes in environmental conditions.

Marine Birds

Marine Birds are predators near the top of marine nearshore food webs. Marine birds are long-lived, conspicuous, abundant, widespread members of the marine ecosystem and are sensitive to change. Because of these characteristics marine birds are good indicators of change in the marine ecosystem, many studies have documented that their behavior, diets, productivity, and survival changed when conditions change. Public concern exists for the welfare of seabirds because they are affected by human activities like oil pollution and commercial fishing.

Black Oystercatcher

Black Oystercatchers are well suited for inclusion into a long term monitoring program of nearshore habitats because they are long-lived; reside and rely on intertidal habitats; consume a diet dominated by mussels, limpets, and chitons; and provision chicks near nest sites for extended periods. Additionally, as a conspicuous species sensitive to disturbance, the Black Oystercatcher would likely serve as a sentinel species in detecting change in nearshore community resulting from human or other disturbances.

Sea Otter

Sea Otters (Western Alaska Stock) were federally listed on September 2005 as threatened. Sea otters are keystone species that can dramatically affect the structure and complexity of their nearshore ecological community. They cause well described top-down cascading effects on community structure by altering abundance of prey (e.g. sea urchins) which can in turn alter abundance of lower trophic levels (e.g. kelps). Sea otters generally have smaller home ranges than other marine mammals; eat large amounts of food; are susceptible to contaminants such as those related to oil spills; and have broad appeal to the public.

Marine Water Chemistry

Marine Water Chemistry and Water Quality, including temperature and salinity, are critical to intertidal fauna and flora and are likely to be important determinants of both long-term and short-term fluctuations in the intertidal biotic community. Basic water chemistry parameters provide a record of environmental conditions at the time of sampling and are used in assessing the condition of biological assemblages. Water quality (especially levels of contaminants such as heavy metals and organic pollutants) are also critical in structuring nearshore marine ecosystems and can cause both acute and chronic changes in nearshore populations and communities.