Shrimp and other crustaceans inhabit ecosystems filled with microscopic plants and animals known as plankton. Phytoplankton is a specific group of plant life that drifts along ocean currents near the surface, providing an important food source for many marine animals.
The quick answer is that most species of shrimp do eat phytoplankton, but the extent to which they rely on phytoplankton depends on the shrimp’s specific diet and habitat.
In this article, we’ll dive deeper into shrimp’s feeding habits, discuss the relationship between shrimp and phytoplankton in detail, and explain which factors determine how much phytoplankton shrimp consume.
The Varied Diets of Shrimp
Herbivorous Shrimp Species
Many shrimp species are herbivores that feed on algae, phytoplankton and plant matter. Some examples of herbivorous shrimp include glass shrimp, ghost shrimp, bamboo shrimp, vampire shrimp and some species of filter feeding shrimp.
These shrimp use their fan-like appendages to filter phytoplankton and other microorganisms from the water column. Their diet consists primarily of diatoms, green algae, cyanobacteria and detritus. Herbivorous shrimp play an important role in aquatic ecosystems by grazing on algae and recycling nutrients.
Carnivorous and Omnivorous Shrimp
While some shrimp are herbivores, many species are carnivores or omnivores. Carnivorous shrimp are adept hunters that consume small fish, aquatic insects, worms, zooplankton and other crustaceans. Some examples include tiger shrimp, boxer shrimp, peppermint shrimp, coral banded shrimp and arrow shrimp.
These aggressive shrimp use their front claws to capture prey. Omnivorous shrimp like cherry shrimp, amano shrimp and some prawn species have a varied diet consisting of plant matter, algae, fish food and small invertebrates.
Their versatile eating habits allow them to thrive in captivity and varied natural environments.
Habitats and Feeding
The diet and feeding habits of shrimp depend largely on their habitat. Shrimp living in the nutrient rich waters of estuaries and salt marshes tend to be herbivores and detritivores, consuming phytoplankton and decaying plant matter.
Coral reef inhabitants like cleaner shrimp feed on parasites, fish mucus and other organic particles they pick off of fish. Shrimp in streams and rocky pools are opportunistic omnivores, feeding on anything edible they can find.
The diversity of shrimp species and their habitats leads to varied, specialized diets. However, phytoplankton and algae remain essential to many species.
The Role of Phytoplankton in Food Webs
Phytoplankton Basics
Phytoplankton are microscopic organisms that live in watery environments, including oceans, seas, lakes and rivers. They have a huge impact on marine and freshwater ecosystems. Phytoplankton are the foundation of the aquatic food web, serving as the first link in the food chain for many marine and freshwater species (1).
They play a vital role in sustaining life in water environments.
Phytoplankton are primary producers as they can produce their own food through photosynthesis. Like plants on land, phytoplankton convert sunlight into energy and absorb nutrients from the water to grow. There are thousands of different phytoplankton species with different shapes, sizes and colors.
Some examples are diatoms, dinoflagellates and cyanobacteria (blue-green algae) (2).
Zooplankton as a Crucial Link
Zooplankton are tiny aquatic animals that consume phytoplankton. Major groups include protozoa, rotifers and crustaceans. They serve as a vital intermediary between primary producers like phytoplankton and larger aquatic species (3).
For instance, brine shrimp eat phytoplankton and small zooplankton, and then become food for fish, birds and even whales.
Zooplankton play an integral role in marine and freshwater food chains by transferring energy from primary producers to higher trophic levels. As herbivores, they regulate phytoplankton populations and provide food that sustains the growth and reproductive success of larger aquatic organisms (4).
Simply put, without zooplankton to intermediate, many major fisheries would collapse.
Shrimp Consumption of Phytoplankton
Direct vs Indirect Consumption
Shrimp can consume phytoplankton both directly and indirectly. Direct consumption occurs when shrimp actively feed on phytoplankton in the water column. Indirect consumption happens when shrimp eat zooplankton or other organisms that have fed on phytoplankton.Small shrimp larvae mostly consume phytoplankton directly.
The tiny larvae drift through the water column, filtering out phytoplankton cells. As shrimp grow larger, they tend to rely more on indirect consumption by preying on zooplankton and benthic organisms.
However, adult shrimp will still directly consume phytoplankton when available.
Factors Affecting Direct Consumption
Several factors influence the rate of direct phytoplankton consumption by shrimp:
- Abundance of phytoplankton – More abundant phytoplankton results in higher direct consumption rates.
- Size and developmental stage of shrimp – Smaller larvae consume phytoplankton at higher rates than larger juveniles and adults.
- Filtration mechanisms – Shrimp species with more efficient filtering appendages and mechanisms will ingest phytoplankton at faster rates.
- Presence of alternative prey – When other food like zooplankton is abundant, direct phytoplankton consumption decreases.
- Water temperature and salinity – Suboptimal temperatures and salinities can reduce feeding and filtration rates.
Measuring and Tracking Phytoplankton in Shrimp Diets
Several methods can be used to quantify the proportion of phytoplankton in shrimp diets:
- Gut content analysis – Microscopically examining stomach contents to identify and count phytoplankton cells.
- Stable isotope analysis – Tracking ratios of isotopes like carbon-13 and nitrogen-15 to estimate phytoplankton contribution.
- Fatty acid profiling – Determining signature fatty acids produced by phytoplankton.
- DNA metabarcoding – Using genetic techniques to identify phytoplankton DNA sequences in gut contents.
These methods help researchers understand the relative importance of direct versus indirect phytoplankton consumption at different shrimp life stages. Tracking phytoplankton in shrimp diets also provides useful information for aquaculture feed management.
The Phytoplankton-Shrimp Relationship Over Time
Phytoplankton Blooms
Phytoplankton are microscopic marine algae that form the base of the aquatic food web. These tiny plants drift along ocean currents and undergo massive blooms when conditions are right. Dramatic phytoplankton blooms occur annually in coastal regions worldwide and play a crucial role in supporting shrimp populations over time.
According to an authoritative report by NOAA, the timing, location and extent of phytoplankton blooms depends on factors like sunlight, temperature, nutrients and salinity (NOAA). When blooms occur, they can span hundreds of miles and be detected from space by satellites!
During prolific phytoplankton blooms, the algae multiply rapidly, turning coastal waters green, red or brown. These huge biomasses of phytoplankton form the foundation of the marine food chain. As phytoplankton are consumed by zooplankton, fish larvae and shrimp, energy passes up the food chain.
In this way, periodic phytoplankton blooms help sustain global fisheries over time by boosting shrimp growth and survival. Scientists can even use characteristics of the blooms, like timing and extent, to predict shrimp harvests in the coming months.
Impacts on Shrimp Populations
When massive phytoplankton blooms occur in coastal habitats, they have a positive, cascading effect on local shrimp populations. As these critical primary producers flourish, they enable increased zooplankton numbers. More zooplankton means more food for shrimp larvae and juveniles to eat.
With readily available nutrition, young shrimp experience faster growth rates and improved chances of survival. For example, research shows penaeid shrimp growth is directly related to seasonal phytoplankton production (Nunes and Parsons, 2000).
So in years with substantial blooms, shrimp numbers also boom, benefitting commercial fisheries.
However, human activities are impacting phytoplankton bloom patterns in some areas. Polluted runoff and warming coastal waters appear to be shifting the timing and location of blooms. According to one 20-year analysis, rising sea surface temperatures near Florida corresponded with declines in a key annual phytoplankton bloom (Hu and Murch, 2016).
These types of disruptions to primary production can ripple up the food chain, potentially leading to future fluctuations in regional shrimp populations.
Conclusion
Shrimp depend on phytoplankton both directly and indirectly to fulfill key nutritional needs. While not all shrimp species graze extensively on phytoplankton, these microscopic plants form the foundation of aquatic food webs that support shrimp growth and survival.
Understanding the close ties between phytoplankton, zooplankton, and shrimp can provide insights into shrimp population changes and inform efforts to promote sustainable shrimp fisheries.
