Question

tracking ocean productivity
as we saw earlier, the color of the oceans and lakes on
earth varies according to water depth and the presence of
particulates such as algae in the water column. in the oceans
and lakes, phytoplankton, primary productivity
(photosynthesis by organisms in the water column) and
fluorescent data are also used to track algal blooms and even identify
the type of organisms responsible for the bloom based on the
color information.
almost all photosynthesis in the oceans (ppo) is carried out
by phytoplankton (algae but also photosynthetic bacteria).
light is the major limiting factor for photosynthesis, such as
the deep - sea zone, but this is only a very fraction of total primary
production of the oceans. while the oceans are among the
least productive ecosystems on earth (in terms of carbon
accumulated per unit volume per unit time), their sheer size
makes up for this so that marine primary production (mpp) is about
50 gigatonnes of carbon per year ( - 50 gt c/yr). ocean
photosynthesis, therefore plays a crucial role in the carbon
and oxygen cycles, removing atmospheric carbon dioxide and
replacing a large portion of the earths oxygen.
blooms do not accumulate in the ocean in the same way
as on land because of grazing by zooplankton like the phonic - forming algae, found in
aquatic. this export of organic carbon to the role of oceans
as a carbon sink, removing carbonates from the atmosphere.
at right: bloom of algae (mostly coccolithophores) near
alaskas pribilof islands (sept. 22 2011) the water is green
because of the algae. in spring, after winter ice
melts minerals and nutrients are abundant near the surface.
staying in the light
productivity in the ocean is a delicate balance between
light and nutrients. much phytoplankton biomass leaves
productive regions in surface waters and sinks. in nutrient - poor tropical and
subtropical water, grazing on small phytoplankton
by microzooplankton is very efficient. waste are
decomposed rapidly within the water column and there
is very little net export. in nutrient - rich regions, larger
phytoplankton dominate and grow rapidly so much more
accumulated biomass sinks out of the water column.
phytoplankton diversity varies globally too. diatoms are the
dominant producers in high - latitude, coastal, and upwelling - based on the
environments, whereas cyanobacteria (which are bacteria
not algae) are important in nutrient - poor waters.
some phytoplankton, mostly some dinoflagellates,
are mixotrophs with ingestion of prey. the
zooplankton are also important as symbionts with
corals. these symbionts keep the algae in the photic zone
algae are not uniformly distributed through the water
column, but are adapted to different intensities of
light. some species, notably cyanobacteria, have
various means of adjusting their absolute light of one color
and emit more of another color. these color changes make
more red light available for photosynthesis.
(a) explain how photosynthesis in aquatic environments is affected by light penetration.
(b) explain some of the ways in which aquatic producers overcome limitations to photosynthesis.

Explanation:

(a) Light penetration in aquatic environments is crucial for photosynthesis. Shallow - water areas receive more light, allowing photosynthetic organisms like phytoplankton to carry out photosynthesis effectively. Deeper waters have less light penetration, which limits the rate of photosynthesis as light is a key reactant. Some organisms may adapt to lower - light conditions by having pigments that can absorb different wavelengths of light available at those depths.
(b) Aquatic producers overcome photosynthesis limitations in several ways. In nutrient - poor regions, some phytoplankton like cyanobacteria can fix nitrogen, providing a necessary nutrient for growth. In areas with limited light, some algae have specialized pigments to capture the available light. Also, in regions with fluctuating light and nutrient availability, some species can rapidly grow and reproduce when conditions are favorable.

Answer:

(a) Light penetration affects photosynthesis in aquatic environments as it is a key factor for the process. Shallow waters have more light for photosynthesis, while deeper waters have less, limiting the process. Organisms may adapt with specialized pigments for low - light conditions.
(b) Aquatic producers overcome photosynthesis limitations by nitrogen - fixing (e.g., cyanobacteria), having specialized light - absorbing pigments, and rapid growth and reproduction when conditions are right.