Arcata Marsh Wildlife Sanctuary
Saltwater Vegetation

Background

Producers in The Saltwater Marsh

Growth Patterns

Background:

The salt marsh is more tahn the barren, muddy tangle of weeds that it might first appear. It's a dynamic system constantly receiving and constantly giving--to wildlife and to people. Acting as a giant sponge, the salt marsh absorbs large volumes of water, thus minimizing the impacts of flooding and erosion and recharging groundwater. Moreover, salt marsh plants help purify water by absorbing toxins and in some cases metabolizing them into harmless substances. Perhaps most importantly, salt marshes are among the most productive food factories on earth.

The Producers of the Salt Marsh: Death yields Life

The entire estuary ecosystem depends on the primary producers in the water and in the salt marsh. The primary source of food for the estuary originates in the thick salt marsh vegetation. Only a small amount is consumed directly; most is eaten after it dies. Upon its death, it is partially decomposed by bacteria and fungi into minute particles called detritus, the bacteria potentially doubling the protein content of the dead plant. Washed into thr estuary at hight tide, the detritus creates a nutritious "sea soup" which forms the base of the estuarine food chain.

 

Other producers inhabit the estuary as well. Each drop of water contains a variety of phytoplankton, eaten directly by zooplankton and filter feeders. Larger algae and eel grass, a seed plant, grow in the water and provide food as they decay. Diatoms coating the mud surface photosynthesize when the tide goes out.

 

This productivity could not occur without an abundant nutrient source. Estuaries tend to collect nutrients, making them available for the plants there. Nutrient-laden waters from the stream and from the ocean meet and wash over the salt marsh at high tide and deposit nutrients in the grasses. Many nutrients are held in the system by cycling through animals. For example, the ribbed mussel siphons a gallon of water per hour, in the process collecting detritus, some of which it ejects as pseudofeces. Lastly, as saltwater and freshwater meet at incoming tide, vertical mixing may occr, causing nutrients to be held in the system. Adaptations for a harsh environment: Who would guess, judging by its productivity, that the salt marsh is a harsh place to grow? In this environment, writes Elna Bakker, "plants and animals must make their peace with ta world that is rained on, tide flooded, sun warmed, drained off, and mud stuck." Salt marsh plants, called halophytes, all possess adaptive features for a salty, wet existence.

 

Salinity is probably the toughest condition faced by salt marsh halophytes. The salty conditions actually mimic the desert condition of insufficient water supply. Consider osmosis. Since water generally moves toward a more concentrated solution, the water of plant cells tends to be drawn out into the salty substrate. Halophytes have mechanisms for reversing the osmotic effect. They concentrate salt ions in their roots, so that the salt concentration is greater there than in the surrounding soil, and water flows into the roots.

 

Halophytes also remove excess salt by various strategies. Cordgrass (Spartina) and saltgrass (Distichlis) both have glands through which salt is excreted. Films of salt crystals are visible on their stems and leaves. Pickleweed (Salicornia) rids itself of excess salt by means of joints which allow a part of the plants to be broken off. The plant sends salt to its tips and, in the fall, these compartments dry up and break off.

 

Salt marsh plants must also be tolerant of continual submergence and the resulting low oxygen level. Many salt marsh plants are equipped with hollow passages through which air can pass, connecting stomata on the leaf surfaces with roots and providing essential oxygen to root cells. In addition, a chemical reaction between the roots and the surrounding soil produces iron oxide and ferrous sulfate, important nutrients which are particularly essential to cordgrass. The light brown color around the roots reveals this oxidation process.

Patterns of growth in the salt marsh:

Every salt marsh plant has a limited range of salinity tolerance. Cordgrass and pickleweed are by far the best adapted plants for regular tidal inundation; many other halophytes do well just above the regular high tide level.

 

Humboldt Bay's species of cordgrass (Spartina densiflora) and pickleweed (Salicornia virginica) appear to grow together on the lowest banks of the salt marsh, with pickleweed often starting slightly lower and extending slightly higher than cordgrass (see Eicher, 1987). In contrast, in many other parts of the state, where different species of cordgrass tends to grow at lower elevations than pickleweed.

 

Other species find niches higher on the banks of the salt marsh. Species most commonly found just above the area of regular tidal inundation include jaumea, arrowgrass, Point Reyes bird's beak (a rare species), and saltbush. Several other species, such as saltgrass, sea lavender, dodder, gumplant, and Humboldt Bay owl's clover (also rare), can grow in that zone as well but are best adapted to still higher ground.

 

This pattern of growth, in which salinity level restricts where halophytes grow, is called zonation. In this activity, students see the effects of zonation. In this activity, students see the effects of zonation by doing a transect study.

 
 

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