I. Benthos- an important subsystem of an estuary

A. Benthos interacts with water column – "benthic effect"

• benthic – pelagic coupling
• stores organic matter, detritus
• consumes and releases nutrients
• important food sources for fish, inverts, wildlife
• benthic "effect" – benthos may regulate the physical, chemical, and biological environment throughout the estuary

• easy to sample
• doesn’t move much
• patterns can be mapped
• processes can be experimented with
• indicator of stress/pollution

A. Epibenthic – lives on surface of benthos

• gastropods, amphipods, sea stars, crabs, oysters, tunicates
• barnacles, sponges, some polychaetes

• polychaete worms
• clams
• sea cucumbers
• shrimp (some species)

• epibenthic on rocks, boat bottoms – hard bottom or fouling community
• epibenthic or infaunal is shifting sediment – soft
• estuaries are mostly soft (mud, sand)
• some hard bottom/fouling – oysters

• macrofaunal greater than 500 m m (sieve size)
• meiofaunal -- m m but >44 m m
• microfauna -- <44 m m

1. Suspension feeder – filters food from water column

• clams, oysters, bivalves
• some polychaetes – epibenthic and infaunal
• barnacles
• bryozoans
• sponges
• tunicates

2. Deposit feeder – feeds on organic matter that has settled onto or into the bottom

• non-selective – ingests sediments with organic matter gastropods, many species of polychaetes
• selective – ingests enriched sediments – diatom films
• nematodes
• fiddler crabs
• sand dollars
 
3. Predators (raptorial feeders)
• polychaetes (some)
• decapods (blue crabs, penaeid shrimps)
• sea stars
• gastropods (oyster drill)
• nematodes
• turbellaria

4. Parasites/commensals

• copepods on crabs
• pea crab in oyster

A. Species Diversity

• estuaries have low diversity relative to other ecosystems (deep sea, coral reefs)
• although species diversity is low, numbers and biomass high relative to other ecosystems (production is high)
• estuarine minimum in species diversity occurs at 5 o/oo salinity (Fig. 9.2), because freshwater species decrease as salinity gets higher; and marine species decrease as salinity <<35 o/oo
• some doubt that the data support this idea (Abele & Walters 1979)

• estuary is a stressful environment in which very few species have evolved physiological and behavioral adaptations to be able to live there (Table 9.2)
• most species occur in marine sublittoral (40) and freshwater (54), in between diversity is lower
• estuary has few species, but high density and biomass (4 species; 100,000/m²)
• species diversity decreases with increasing latitude (Fig. 9.8) – tropical diversity high, Arctic low

• Hard bottoms – 2-D environment
• costly to shipping – creates drag on boats
• may require 40% more fuel if not cleaned every six months
• space is limited in almost every hard bottom community – competition
• meroplanktonic larvae always about, looking for a place to settle
• most forms are suspension feeders or predators – adults eat larvae
• adult/larval interactions – larvae settle preferentially near adults (chemical cues)
• suspension feeding habit can lead to high clearance rates in water
• oyster can filter 2/3 L/hr – removing organic matter, meroplankton, phytoplankton
• water is clear in high suspension feeder zones
• food can become limiting
• suspension feeders bioaccumulate toxins – leads to closed shellfish beds in polluted waters
• Soft bottoms 3-D environment; mudflats, sandy bottom areas
• macrofauna
• sample with bottom grab (Smith-McIntyre, Ponar)
• sample with cores
• sieves used (500 micron)
• polychaete worms dominate numerically and biomass, but also: snails, bivalves, sea cukes, sea stars, amphipods, isopods, anthropods
• Dutch Wadden Sea (Fig. 9.4) – Arenicola, Mya, Corastoderma, Nereis, Heteromastus, Macoma. 27g ash free dry mass/m² – average
• deposit feeding and suspension feeding common
• Trophic amensalim concept (Rhodes & Young 1970)
• deposit feeders – create turbid water by reworking sediments – muddy organic seds.
• suspension feeders – live in sandy bottoms, but because they filter, water rel. clear
• These two groups in competition for space and resources (interference and food competition)
• suspension feeders eat larvae of dep. feeders
• deposit feeders bioturbate sediments – clog filtering mechanisms – causes death
• Meiofauna
• small size – they were ignored for a long time due to this
• usually no larval meroplanktonic phase; small numbers of large offspring
• temporary meiofauna – small initially, but grow into macrofauna (polychaete larvae just settled)
• permanent meiofauna – never get larger than 200m m or so; to name a few groups:
• rotifers
• gastrotrichs
• kinorhyncha
• nematoda
• archiannelida
• tardigrada
• copepoda (harpacticoida)
• ostracoda
• oligochaeta