Marine Intertidal Invertebrates
Resource Brief - March 2009
Importance/Issues
Intertidal marine invertebrates were selected as a SWAN vital sign because they provide a critical prey resource for various types of sea birds (e.g. some shorebirds and most sea ducks), marine mammals (sea otters, Enhydra lutris), marine fishes and larger invertebrates (e.g. octopus sp.), and may provide important sources of nutrients and energy to some terrestrial carnivores (e.g. black and brown bears (Ursus americanus and Ursus arctos), that may seasonally forage in marine habitats. Two habitat types are widely recognized in supporting important, although taxonomically quite different, intertidal invertebrate communities. The rocky intertidal community typically supports diverse and abundant kelps (Fucus gardeneri and Laminaria sp.) and other algae with invertebrate fauna dominated by mussels (Mytilus trossulus), barnacles (Balanus and Semibalanus sp.) limpets (Tectura sp. and Lottia) and snails (sp. Nucella sp.). Predatory sea stars (Pyncopodia helianthoides, sp. and Evasterias sp.) are also conspicuous and common species in the rocky intertidal.
The soft-sediment intertidal habitats are characterized by unconsolidated sediments ranging in grain size from fine clays to cobble boulders. Common marine macro-invertebrates (>5 mm), include a variety of clams (Protothaca staminea, Saxidomus giganteus, Mya truncata, Macoma sp.). Large benthic inverbrates that feed the higher trophic levels are ecologically diverse in terms of habitat and trophic requirements; have a wide range of physiological tolerances and feeding modes, and are relatively sedentary with relatively short generations times. Some of the bivalve mollusks can live for several decades and integrate environmental conditions that can be interpreted as variation in annual growth increments, which can be determined thought measurement of distances between growth rings. We will use analysis of growth rates in mussels and the little neck clam (Protothaca) to evaluate potential indices of primary production in nearshore habitats in the Gulf of Alaska. Measurements of species diversity, densities, size class distributions, and contaminant levels in intertidal invertebrates will provide useful inference relative to causes of change that will be detected in higher level consumers that occupy nearshore food webs.
Sampling Design and Objectives
The purpose of this protocol is to monitor long-term trends in invertebrate species richness and measures of abundance (densities, percent cover) at randomly selected 50 m transects in sheltered rocky and mixed sand-gravel habitats. Objectives also include: 1) document how the size distribution of limpets (Tectura persona) and mussels (Mytilus trossulus) is changing annually; 2) estimate long-term trends in abundance of littleneck clam (Protothaca staminea) and document how the size distributions and growth rates are changing annually; and 3) monitor status and trends in the concentration of metals, organochlorides, PCBs, and mercury in mussel tissue.
Progress and Current Efforts
In 2006, five permanent transects were established and sampled along the Katmai coast in Kukak, Kaflia, Kinak, Amalik Bays. Permanent stainless steel tags with the site numbers inscribed were bolted into place at 0.5 and 1.5 m MLLW tidal elevations at each site to mark the beginning of 50-m long transects. A Hobo temperature data logger was placed next to the 0.5 m transect marker at each site. Large motile invertebrates (primarily sea stars) were counted along a 4-m wide band extending upslope from MLLW and stretching the 100-m length of the sampling site. The percent cover of algae and sessile invertebrates, and the abundance of smaller invertebrates (littorine snails and limpets) were determined in 12 quadrats placed along each of the two transects. Approximately 240 mussels and 120 limpets were collected at each site. All limpets and a subset of 120 mussels were measured to determine size distribution. Two samples of approximately 60 large (greater than 35 mm) mussels were collected from each site and frozen for analysis of organics and metals. In 2007 at Katmai NP the five rocky sites established in 2006 were resampled and Hobo data loggers were replaced. In 2007, five permanent transects in soft sediment habitats associated with each of the sheltered rocky sites identified above were established and sampled. At each site 12, 0.5m X 0.5 m quadrats were excavated to a depth of approximately 25 cm. Sediments were sieved through a 10mm screen and all clams were removed, sorted by species, and measured to the nearest mm.
In 2007, five permanent transects in rocky sheltered habitats were established and five permanent transects were established and sampled in soft sediment habitats at Kenai Fjords National Park. Establishment and sampling of sites in both rocky and soft-sediment habitats at Kenai Fjords was similar to sites at Katmai National Park & Preserve in 2006 and 2007.
Brown bears foraging on clams in Amalik Bay, biologists conducting quadrate counts of invertebrates, and mussels being collected for contaminants analysis.
