ResourcesIdentification of Important Habitats in Coastal New HampshireChapter 8. Blue MusselThe blue mussel, Mytilus edulis, is a largely intertidal shellfish
common to coastal waters of the middle and north Atlantic. It is commercially
harvested and cultivated in the Gulf of Maine, and forms reefs which serve
as structure for fishes and invertebrates. Mussels are an important prey
of fishes and birds, particularly waterfowl. The following tables are
components of a model to map blue mussel habitat. Information was compiled
from summaries by Newell 1989, and by examination of conditions
associated with known mussel beds in Great Bay. Known mussel beds were
digitized from maps in Nelson et al. (1981, 1982) and from sites drawn
on base maps for us by Richard Langan (Jackson Estuarine Research Laboratory).
We also located and mapped beds by field survey, using GPS to determine
spatial coordinates. The model operates on four parameters: substrate, salinity, temperature,
and depth. The model indexes the relative suitability of each environmental
parameter on a 0 to 10 basis, with 10 being optimal and 0 being unsuitable.
These suitability index values are combined by computing their geometric
mean for each grid-cell in the study area. Thus, optimal habitat for any
life stagewould occur where the index values were the maximum for each
of the four inputs; no value is attributed to areas where any condition
is completely unsuitable. Suitability is calculated for each season, to
accommodate annual changes in salinity and temperature. Habitats were mapped for conditions needed by juveniles and adults, for
reproduction, and for larval stages. The latter included planktonic stages
and settlement of larvae onto a substrate. Because juvenile and adult
mussels are sessile and cannot avoid adverse temperatures or salinities,
their habitat suitability values were computed as the geometric mean of
values for all four seasons. An area that was completely unsuitable for
any season would, therefore, register as unsuitable on the habitat map.
The reproductive/larval habitats were mapped as the maximum or most favorable
score of either spring or summer, in consideration of the flexibility
in the timing of reproduction. The substrate limitations on juvenile and
adult habitat restrict the value of habitats which might otherwise be
useful to larvae. Therefore, overall habitat was mapped as the geometric
mean of the combined juvenile/adult habitat and the combined reproductive
adult habitat. This gives maximum scores to areas which are suitable for
both stages, moderate value to areas which are at least useful to both
stages, and no value to areas which are unsuitable for either stage (Figures
of; Spawning Habitat, Adult/Juvenile
Habitat, Combined Life Stages). SUBSTRATE PREFERENCES Substrate Suitability Index: 0 to 10 scale; 0 = unsuitable,
10 = optimal condition ADULT AND JUVENILE
REPRODUCTION, LARVAE
SALINITY PREFERENCES Salinity (ppt) Suitability Index: 0 to 10 scale; 0 = unsuitable, 10 = optimal condition Salinities between 5 and 15 ppt are tolerated by adults and juveniles
for relatively short periods; in the study area mussels only survive the
year within areas having 'typical' salinities above 15 ppt for all 4 seasons.
ADULT AND JUVENILE,
REPRODUCTION AND LARVAE
TEMPERATURE PREFERENCES Temperature (C) Suitability Index: 0 to 10 scale; 0
= unsuitable, 10 = optimal condition ADULT AND JUVENILE
REPRODUCTION, LARVAE
DEPTH PREFERENCES Depth (feet, mlw*) Suitability Index: 0 to 10 scale;
0 = unsuitable, 10 = optimal condition ADULT AND JUVENILE
REPRODUCTION, LARVAE
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