Marine Ecology: Intertidal Ecology

When do spring tides occur?

Twice each lunar month (14 days apart).

One of the most striking features of the rocky intertidal area is the pattern of zonation seen in the distribution of organisms. Which of the following factors explains zonation?

A complex interaction of physical and biological factors

Which of the following is the best definition of an estuary?

A partially enclosed coastal area where freshwater and seawater meet and mix.

Fjords are often characterized by having stagnant water in their deepest area. Why might this be the case?

A volume of cold, higher salinity water becomes trapped at a depth greater than that of the sill at the mouth of the fjord.

The rocky intertidal areas of the Pacific and Atlantic coasts of North America differ dramatically in terms of species diversity. Which of the following may explain these differences?

All of the preceeding statements are correct.

One experimental approach to understanding the intertidal community has been to use cages to control access to portions of the community. Which of the following represents an effective experimental design using cages?

An open cage to test for the physical presence of the cage and a carefully selected control area. Each treatment should be replicated.

Which of the following is a common life cycle among fish species found in estuaries?

Feeding on zooplankton, detritus, and macroinvertebrates when young, then moving offshore as adult predators of other fish.

Studies of succession in intertidal algal assemblages indicate that succession in this community is a combination of which successional models?

Inhibition and facilitation.

Beaches appear to be relatively devoid of living organisms because:

Most beach residents are small and burrow in the sand.

Mussels (e. g., Mytilus) seem capable of dominating many intertidal areas. What often limits mussel dominance?

Predation

Which of the following may affect New England intertidal communities during winter?

Scouring by ice

The main limiting resource in the rocky intertidal zone is

Space

"Salt wedge" estuaries often have hypoxic (low oxygen) or anoxic (no oxygen) at greater depths. This is because:

Stratification of the water column prevents mixing and the oxygen is depleted by biological activity.

Find a World Wide Web site that offers predictions for local tidal cycles (e. g., http://co-ops.nos.noaa.gov/tp4days.html or http://www.saltwatertides.com). Choose a location and note the times of the high and low tides over several days. You will notice that high and low tides do not occur at the same time each day, but appear to be approximately 50 minutes later each day. What does this indicate to you about the nature of the tidal cycle?

That the fundamental tidal period is not merely a function of the 24-hour period of the earth's rotation.

Both the times of high and low tide and the amplitude (difference between high and low tide) may vary between locations that are comparatively close. This is due to:

The effect of the local topography on the movement of water.

One factor in the generation of tides is the gravitational influence of the sun and the moon. Which of the following describes their relative influence?

The effect of the moon is about twice that of the sun.

Estuarine invertebrates often migrate to the lower portions of estuaries to release their eggs because:

The osmoregulatory abilities of larvae are limited.

Generally, estuarine organisms have a smaller body size and often have a lower reproductive rate and fecundity than marine species. What is at least one likely reason?

The physiological stresses of living in an estuary have an effect.

Salt marsh plants have evolved a specialized gas transport tissue because:

Their roots are typically in hypoxic or anoxic sediments.

Although the salinity of the water column of an estuary may fluctuate significantly, the salinity of the interstitial water of the sediments may show less variability. This is because:

There is a slow exchange of water between the water column and the sediments.

Estuarine invertebrate species typically face fluctuating salinities. Although, there are exceptions, what generalization can be made about their physiological responses?

They may osmoregulate at lower salinities and respond as osmoconformers in more saline water.

Some salt marsh plants have a specialized gas transport tissue called

aerenchyma

Estuaries are characterized by having soft, muddy substrates. Which of the following is the source of these sediments?

all of the above

Estuaries are sometimes referred to as "nutrient traps". This is because:

all of the above

A significant source of primary productivity in the shallower areas of estuaries are

benthic diatoms

The majority of the organic material that enters the estuarine food web does so in the form of

detritus

Sand and muddy shores are actually different points of a continuum that reflects the influence of

exposure to wave activity.

Recent studies on salt marshes have shown that different species may have positive effects on one another, but they are not necessarily dependent on each other. The termed applied to such cases is

facultative mutualism.

The time for a given amount of freshwater to be discharged from an estuary is called the

flushing time

Some intertidal species (e. g., mussels and some algae) can escape predation by

growing to a size greater than the predators can handle.

The conclusion of studies of the "Pisaster-Mytilus" community of the Pacific coast is that community structure is affected by

interactions among competition, disturbance, predation, and recruitment.

Two physical factors that are important in understanding the zonation patterns of salt marshes are

salinity and oxygen availability in the soil.

Recent studies of intertidal community ecology have resulted in a concept referred to as "supply side ecology". This refers to the importance of

larval recruitment

Another name for the intertidal zone is the

littoral zone.

While there are many similarities, one major difference between European and North American Atlantic estuaries is

rooted vegetation is more important in North American estuaries.

The fact that estuaries have many energy pathways that have a detrital base implies that a disproportionate number of estuarine species are

omnivores

The physical characteristics of a beach are determined by

particle size, wave action, and slope.

Sand flats are extremely variable and patchy in the distribution of species. This suggests that the sand flat community is affected by

predation and disturbance.

Some intertidal algae deter attacks by herbivores by

producing chemical compounds that are detrimental to the herbivores.

The shallow, enclosed nature of estuaries results in a phenomenon that is unusual in other portions of the marine environment, which is

that zooplankton and suspension feeders may compete for food.