Part
2, Sec. 2B2c
Sanctuary
Resources - Natural Resources
Benthic
Organisms
c.
Benthic Organisms
Benthic
invertebrates provide food for the vast array of fish species
found in the Stellwagen Bank, and larger Gulf of Maine area.
Invertebrate species such as shrimps, crabs, worms, mollusks
and echinoderms sustain many groundfish species. The health
and availability of these food supplies are integrally important
in assisting the assessment of variations in fish growth rates;
changes in fish egg production and survival rates of newly-hatched
young; deviations in normal fish migration routes and times
of migrations; and survival of juvenile and adult fish stocks.
To
date, few studies have been conducted to determine the particular
composition of benthic communities on offshore banks and ridges
similar in makeup to Stellwagen Bank within the greater Gulf
of Maine/Massachusetts Bay region. Baseline surveys of macrobenthic
communities conducted at Jeffreys Ledge, north of Stellwagen
Bank, identified 149 faunal and floral species within horizontal
and vertical communities, and at various depths. At a monitoring
station near Jeffreys Ledge, two major, ecologically distinct
benthic communities have been identified: an algal-polychaete
community, and a sponge-tunicate community (NOAA/NEFC, 1982).
However, these communities exist on rock or other hard surfaces
such as those comprising Jeffreys Ledge; bottom sediments at
Stellwagen Bank are quite different.
Investigations
conducted by NOAA's Northeast Fisheries Center into the macrobenthic
communities of the Georges Bank system included sampling stations
within the Stellwagen Bank vicinity; and findings are applicable
to the overall New England region, as well as to the Middle
Atlantic Bight (Theroux and Grosslein, 1987). There are four
dominant taxonomic groups of macrobenthic invertebrates found
in the Georges Bank/Gulf of Maine region: annelids, crustaceans,
mollusks, and echinoderms. Dominance among these four groups,
however, differs significantly depending upon whether species
are ranked by biomass, or by numerical abundance (density).
In general, both the largest biomass and the greater diversity
tend to be supported by gravel and sandy sediments (Campbell,
1987). Coarse-sand bottom sediments have been shown to support
the highest mean biomass of macrobenthic organisms, often in
the range of 371 g/m2 (Theroux and Grosslein, 1987). Biomass
and diversity are also generally greatest around the rim of
the Gulf of Maine, in waters depths less than 100 meters (Campbell,
1987).
Premised
on the predominantly sand to pebbly-sand composition of Stellwagen
Bank's bottom sediments, it is reasonable to suppose that macrobenthic
biomass on Stellwagen Bank is quite high. Major taxonomic groups
occurring on Georges Bank have been ranked by both biomass,
and population density (Theroux and Grosslein, 1987: Table 1).
Table
1: Macrobenthic Taxonomic Groups at Georges Bank, by Biomass
and Density
Taxon / Total Biomass (%)
Echinoidea 41.3
Bivalvia 37.8
Annelida
5.0
Ascidiacea
3.5
Ceriantharia
3.1
Taxon / Total Density %
Amphipoda 45.1
Annelida 26.3
Echinoidea
4.7
Chaetognatha
2.8
Bivalvia
2.5
Sampling
data from both mud and sand reference stations in Cape Cod Bay
within and outside the Massachusetts Bay Disposal Site (MBDS),
situated immediately northwest of the Stellwagen Bank study
area, indicate an overwhelming dominance of annelid species
in both mud and sand sediments. Annelids comprised between 89.6%
and 95.4% of macrobenthic species at mud reference stations;
between 85.9% and 86.1% at sand reference stations (Hubbard,
Penko, and Fleming, 1988). Species found at these stations are
listed below.
Mud
Site
Paraonis
gracilis
Heteromastus
filiformis
Cossura
longocirrata
Spio pettiboneae
Oligochaete
spp.
Chaetozone
setosa
Mediomastus
ambiseta
Myriochele
oculata
Trochochaeta
multisetosa
Prionospio
steenstrupi
Thyasira
flexuosa
Aricidea
quadrilobata
Sternaspos
scutata
Maldane
sarsi
Sand
Site
Exogone
verugera
Prionospio steenstrupi
Anobothrus gracilis
Nicomache spp.
Paraonis gracilis
Ampharetid spp.
Myriochele oculata
Chone infundibuliformis
Astarte undata
Phloe minuta
Praxillura longissima
Exogone hebes
Mediomastus ambiseta
Spio pettiboneae
Cossura
longocirrata
Streblosoma
spiralis
Similarly,
sampling conducted by NOAA's Northeast Monitoring Program at
two stations in the Gulf of Maine between 1978 and 1985 indicated
dominance by polychaetes at Station 35, situated near the Massachusetts
Bay Disposal Site location (NOAA/NMFS, 1990). Seasonality of
polychaetes was indicated, and biomass levels were ranked between
100 and 250 g/m2. Polychaetes were dominated by Spio
filicornis. This and other polychaete species (sabellids
and nereids) provide important prey for flounders. The echinoderms
Ctenodiscus crispatus and Molpadia oolitica
were also found in abundance.
The
second sampling site (Station 28), located in the extreme western
portion of Georges Bank, was overwhelmingly dominated by echinoderms,
primarily two species: Brisaster fragilis (urchin),
and Ophiura sp. (brittlestar). Ophuroids in particular
are important prey for cod and plaice.
Typical
inhabitants of the Stellwagen Bank (areas primarily of sand
or pebbly-sand composition) include organisms adapted to loose
and occasionally shifting substrate, such as:
Echinarachnius
parma, common sand dollar
Crangon septemspinosis, sand shrimp
Lunatia heros, (carnivorous gastropod mollusk)
Nassarius trivitattus,(carnivorous gastropod mollusk)
Spisula solidissima, surf clam
Astarte castanea, chestnut astarte
Leptocuma, (cumacean crustacean)
Chiridotea, (isopod crustacean)
Pagurus acadianus, Acadian hermit crab
Ophelia, (polychaete worm)
Goniadella, (polychaete worm)
Clymenella, (polychaete worm)
Heterostigma, (tunicate)
Molgula, (tunicate)
Haustorid and phoxocephalid amphipods, (beach fleas)
In
the few areas of Stellwagen Bank where sediment composition
is partially gravel, the following invertebrate fauna may be
found:
Polymastia,
(sponge)
Clionia, (sponge)
Myxilla, (sponge)
Balanus crenatus, (barnacle)
B. hameri, (barnacle)
Tubularia, (hydroid)
Eudendrium, (hydroid)
Sertularia, (hydroid)
Bougainvillia, (hydroid)
Brachiopoda terebratulina, (lampshells)
Gersemia, (soft corals)
Boltenia, (tunicate)
Ascidia amaroucium, (tunicate)
Modiolus, (bivalve mollusk)
Placopecten, (bivalve mollusk)
Anomia, (bivalve mollusk)
Musculus, (bivalve mollusk)
Serpula, (polychaete worm)
Chone, (polychaete worm)
Spiorbis, (polychaete worm)
Solaster, (starfish)
Crossaster, (starfish)
Neptunea, (gastropod)
Hyas, (toad crab)
Doris, (nudibranch)
Dendronotus, (nudibranch)
Ophiopholis, (brittlestar)
Ophiacantha, (brittlestar)
(Species
list from Wigley, 1968)
Western
Stellwagen Basin infauna are dominated by several polychaetes:
shrimp; brittle starfish (Ophiura sarsi and O.
rubusta; and pink anemome (Bolocera tuediae).
A sizeable shrimp population is also located in Jeffreys Basin,
between Cape Ann and Jeffreys Ledge; and another shrimp species,
Dichelopandalus leptocerus, is widely-spread and
abundant in the overall northeast region.
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