Infaunal Benthic Invertebrate Community

Nereis succinea Macoma mitchelli Macoma balthica Cyathura sp.


Infauna: Aquatic animals that live in the substrate of a body of water, especially in a soft sea bottom.

Benthic: (of, relating to, or occurring at the bottom of a body of water)

A program to sample the benthic infauna of the Rhode River was instituted in 1979. Macroinvertebrates such as crustaceans, worms and mollusks comprise the Rhode River's soft bottom community. They live in or on the bottom of the river in mud, sand, clay, marsh detritus, leaf litter combinations of these sediment types. Infaunal species are responsible for significant interactions within the benthic environment, which, in turn, impact the biodiversity and functional processes within the entire estuarine ecosystem. Long term data on these species gives us 1) information on the species composition and fluctuating abundance of these organisms over time and in differing habitats, and a 2) better understanding of the processes that regulate their community and population dynamics. Such dynamics include trophic levels, predator-prey interactions, recruitment, habitat use, as well as effects of salinity, temperature and dissolved oxygen on their populations. Integrating benthic infaunal data with our other long term sampling programs provides insight into processes structuring ecosystem interactions in the Rhode River.

Fifty benthic species including mollusks, worms and small crustaceans have been identified in the Rhode River's soft bottom sediment of sand and mud. Variation of species composition and abundance is tracked with seasonal sampling on a long term basis.

As part of a complex food web, infaunal communities are composed of both predators and prey. Trophic level of these species may change during its lifecycle as the organism grows and its size, feeding mechanism, and nutritional requirements change during ontogeny. Infauna comprise crucial food resources for blue crabs and many species of epibenthic fishes, such as spot, croaker, and flat fishes.

Processes such as bioturbation, or sediment disturbance, is caused by infaunal burrowing and feeding, especially by deposit feeder species such as worms or certain species of clams. Bioturbation can, among other things, affect oxygen levels in sediments, cause redistribution and decomposition of organic matter, and alter the amount of suspended particles in the water. This, in turn, may negatively or positively affect water quality, refuge patterns and feeding behavior of animals.

 

sifting mud core samplescuba diving for mud corespole coring

Methods

  • Five sites in the Rhode River
    • Two sand sites-depth 2-3m
    • Three mud sites-depth 1-4m
    dissecting microscope identification of species
  • Seven cores/site
  • Samples taken seasonally-winter, spring, summer and fall (four to eight times/year)
  • Cores taken with 0.08-m2 pipe core either attached to the end of a pole at mud stations or operated by a SCUBA diver at sand stations. The core penetrates to a depth of 35 cm in all sediments.
  • All cores sieved on 0.5 mm mesh screen, fixed in 10% formalin and stained with Rose Bengal.
  • Organisms are sorted, counted and identified to species under dissecting microscope;
  • Mollusks are measured. All data are recorded and entered into database for analysis.

map of benthic core sites


The above graph shows mean abundance of species/month over a sixteen-year period. Note recruitment of species in spring months and decline in summer when predatory fish and crabs are in high abundance and actively foraging for prey.