Marine Ecosystems and Biodiversity

•The connection between environment, biodiversity and ecological niches

Learning Outcomes

• Describe shoaling and explain why shoaling may be a successful strategy for feeding, reproduction and predator avoidance, with reference to tuna and sardines

• Shoal - any group of fishes that remains together for social reasons

• School - a polarized, synchronized shoal (has coordinated, directed movements)– schooling is an extreme form of

shoaling – fish move into and out of schools all the

time

Shoaling and commercial fish

• Many commercially important fish shoal and this behavior makes them more vulnerable to fishing pressure and capture in large numbers

• In many commercial species the largest shoaling occurs during migrations, when smaller shoals join together.

• Some North Atlantic herring shoals have been measured to be 279 million to 4,580 million m3 with densities of .5-1.0 fish per/m3

• Migrating mullet shoals in the Caspian Sea have been documented 100 km long

Shoals and Predators

• One strategy is to attack at low light levels

• Another strategy is to swim along shoal and pick off fish that are sick, don’t stay in form, or make an error in responding

• More effective is the to attack in schools – schooling fish cannot avoid another school as effectively as they can a lone predator

How do Schools Work?

• Requires great deal of coordination among individuals in the school

• Vision is primary sensory cue for coordinating movement

• Use of optomotor reaction - individual movement is coordinated with movement of some other visually distinctive object - e.g. a spot or a stripe

Functions of Schooling Behavior

1. increased hydrodynamic efficiency

2. increased efficiency finding food3. increased reproductive success4. reduced risk of predation

– Dilution and confusion effect– More eyes to detect danger

Functions of Schooling Behavior

• Hydrodynamic efficiency

– individuals obtain reduction in drag

by following in “slip-stream” of

neighbors

– limited evidence in support of this

Functions of Schooling Behavior

• Reduced predation risk– creates patchy distribution of prey -

large areas with no prey– once school is found, individual risk of

being captured is reduced by dilution– confusion of prey by protean displays,

encirclement, other behaviors

Functions of Schooling Behavior

• Feeding– increases effective search space for

the individual (more eyes, separated by greater distance)

– coordinated movements to help break up schools of prey - analogous to pack behavior in wolves - by tunas, jacks

Functions of Schooling Behavior

• Reproduction– increases likelihood of finding a mate– facilitates coordination of

preparedness (behavioral and pheromonal cues)

– facilitates arriving at right spawning site at right time

Fish Behavior & Communication

• Shoaling • A social grouping of fish • Occurs throughout life in about 25% of fish species • Half of all fish shoal at some time

• Benefits of Shoaling • Gives a predator many moving targets – Confuses predators – Increases chances at the individual level

– Increases food finding ability • Keeps potential mates in close proximity

Fish Behavior & Communication

• Pods • Tightly grouped school • Move as a single unit (including making quick turns) • Makes the school appear like one large organism – Protection from predators

Liabilities of Grouping Behavior

• Increased likelihood of disease & parasite transmission • Becoming more conspicuous to some predators – Harvested more easily by man

Sortment

Fish sort by parasite load-This is due to the parasites leaving black spots on the

skin of the fish -When the fish have too many parasites on them they

become phenotypically different and end up standing out from the rest of the school ….ie: the cootie effect

Fish sort by size-Because of the “confusion effect”, they tend to swim

with similar size fish-large fish tend to swim along the outside edges of the

school but move to the center when a predator was near

-With small fish the opposite was true. They tended to stay near the center and then forced to the outside when a predator was near by

-If a fish is dissimilar in size from the rest of the group they tend to forage less when they are the large-odd fish

Holy Crap, there’s life there?

• Bill Nye interviews Bob Ballard

• Significance? – Discovery of new marine ecosystems

which were independent of the photosynthetic food chain

• Prior to 1977, biologists thought that without the energy of sunlight to support a food chain, organisms in the deep sea ate only what debris fell from surface waters. Scarce food meant that organisms were few and far between.

Chemosynthesis

Deep sea is food limited

• Insufficient light below 250 m depths in the ocean (the mixed layer).– Reduced biomass– Reduced diversity– Little biogenic CaCO3 precipitation-

nothing but ooze

• The abyss as desert-(results of HMS Challenger expedition)

Background geology

• Geologists knew that cold water sunk into cracks in the ocean floor and hypothesized that this water was heated beneath the ocean crust. During heating, the hot water would dissolve minerals from surrounding rocks. The heated, mineral-laden water, hypothesized geologists, would rise from the seafloor at a vent.

What is a hydrothermal vent?

• At a hydrothermal vent, sea water that has sunken into cracks in the ocean crust and been heated (sometimes to over 180 degrees Farenheit!) by the interior of the earth escapes through crust cracks back into the ocean.

• Superheated water beneath the oceanic crust often dissolves minerals from nearby rocks. As hot vent fluids meet cold ocean water, minerals precipitate out of vent fluids.

• Precipitating minerals often give vent fluids different colored “smoky” appearances.

• Precipitating minerals can fall out of vent fluids to form “chimneys”(like the one on the left) and other formations on the sea floor.

Geologists test a hypothesis

• In order to test their hypothesis, geologists decided send remote-controlled equipment to look for vents where oceanic plates pulled away from each other at the Galapagos Rift.

• Since the temperature of the deep sea varies very little from 35.6 degrees Farenheit, geologists searched for small changes in temperature.

Geologists find a vent!• After temperature-sensitive equipment returned

small temperature changes at one site along the Rift, cameras were sent to the same site and returned with pictures of heaps of clam shells.

• Repeated submarine dives to the same site revealed temperatures as high as 46.4 degrees and a variety of unusual organisms.

What are these thriving animals?What are these thriving animals?

• Jones (1980) proposes a new phylum: Vestimentifera• Cavanaugh et al. (1981) prokaryotic cells in

tubeworm sections-symbionts?

• Compared to the surrounding sea floor, upon which organic matter rains from above, hydrothermal vents boast a community of organisms that is 10,000 to 100,000 times denser.

The reason for this: the presence of sulfur-oxidizing bacteria as a food source either directly or through a kind of cooperative "agreement" between the bacteria and a particular vent organism.

The Base of the Food Web: Sulfur-Oxidizing Bacteria

Tube worms and giant white clams• Tube worms and giant

white clams are unique because they do not have a digestive tract. They have no way of “eating” food. Both organisms harbor symbiotic bacteria. The worms and clams transfer hydrogen sulfide and oxygen to a special area of their body filled with bacteria. Through chemosynthesis, the bacteria make carbohydrates to fuel themselves as well as their larger hosts.

These bacteria are able to oxidize (remove electrons) compounds such as hydrogen sulfide and store energy in the form of ATP (adenosine triphosphate), which is the universal "energy" molecule in all organisms, including humans.

These bacteria use this energy to transform carbon dioxide into simple sugars and other molecules, just like plants.

Nowhere is the importance of symbiosis better demonstrated than in the giant tube worm, Riftia pachyptila. When these worms were collected and examined in greater detail, some important parts were missing.

These worms have no mouth, no gut, and no anus. They are completely devoid of any digestive system whatsoever.

The tubeworm provides all the chemicals necessary for the bacteria to make food, including sulfur, oxygen, and carbon dioxide, and the bacteria manufacture sugars or some other form of energy-rich molecules that provide nutrition to the tubeworm.

The unusual vent life forms were different from any others recorded by scientists to date. A new age in deep sea biology and ecology had begun!

Spaghetti worms

How does a vent food web begin?

• In areas of the earth that receive sunlight or are near areas that receive sunlight, photosynthesizing plants are the basis of the food chain. Using the energy of the sun, plants turn water and carbon dioxide into carbohydrates. Carbohydrates are energy for plants and for the organisms who eat plants.

• Bacteria are the green plants of hydrothermal vents. Through a process known as “chemosynthesis”, bacteria use the energy in

hydrogen sulfide dissolved in vent fluids to join water and carbon dioxide into carbohydrates. Vent communities food chains are based on these bacteria!

Who else is in the food web besides bacteria?

• Most deep sea animals can not tolerate the chemicals or hot temperatures near vents. Vent animals are unique because they can withstand and even thrive upon conditions that kill most life. Some vent animals are related to more familiar organisms, but some, like the fluffy ball that vaguely resembles a dandelion, are not..

• Grazing vent animals include snails, crabs, and limpets. These animals graze on bacteria. Suspension feeders such as mussels, barnacles, and feather-duster worms remove food from the water. One kind of predator is the anemone. Anemones capture prey with their tentacles. White crabs and brittle stars are examples of scavengers that eat whatever live or dead animals and bacteria they can find

Feather-duster wormsMussels

• Vents are often far apart. They often exist for just a few decades or years. New vents are populated very quickly.

• Vent bacteria live in deep ocean water and in pores of deep ocean rocks all of the time in low numbers. When a vent pops up, bacteria populations flourish.

• Hot water streaming out of vents often plumes for 200 meters above the sea floor because it is less dense than surrounding cold water. Plumes probably carry larva into nearby currents. However, this still may not account for the great distances between vents. Scientists continue to test other hypotheses that consider “stepping stones”, or intermediate sites, where vent animals may grow without a vent and release larvae.

How are vents populated?

Where are the vents and how many are there?

• Nobody knows how many vents exist or where they all are. Hydrothermal vents are constantly being formed and destroyed, and many parts of the deep sea floor have yet to be seen by human eyes. Some of the known sites are marked on the map below. Most occur on or near boundaries between tectonic plates.

(f) Explain the meaning of the term succession and describe examples, including the tube worms

Tevnia and Riftia.

• Succession: to the gradual process of change that occurs in community structure over a period of time.

• This can be illustrated by the change which occurs in abandoned grassland. After a period of time, shrubby perennial plants become established and these are eventually replaced by tree seedlings, giving rise to woodland. As the plant communities change, there are corresponding changes in the animal communities associated with them.

Succession

(f) Explain the meaning of the term succession and describe examples, including the tube worms

Tevnia and Riftia.• Succession also occurs around hydrothermal vents in the

deep oceans.

• 1st organisms to grow around a vent are bacteria small crustaceans, mollusks, crabs and fish a complex community consisting of many different species is established.

• One of the first animal species to inhabit the area around a hydrothermal vent is the tube worm Tevnia. This species is replaced by the larger and faster growing tube worm Riftia. Tube worms form symbiotic relationships with chemosynthetic bacteria, which provide organic substances directly to the tissues of the tube worms.

• GOOGLE SCHOLAR Assignment

Tubeworm Succession

• Succession also occurs around hydrothermal vents in the deep oceans. The first organisms to grow around a vent are bacteria, which are followed by small crustaceans, mollusks, crabs and fish. Eventually, a complex community consisting of many different species is established. One of the first animal species to inhabit the area around a hydrothermal vent is the tube worm Tevnia. This species is replaced by the larger and faster growing tube worm Riftia. Tube worms form symbiotic relationships with chemosynthetic bacteria, which provide organic substances directly to the tissues of the tube worms.

Succession in Hydrothermal Vents

• New vent forms at diverging plates• Chemosynthetic bacteria • Amphipods, copepods• Grazers/filter feeders: limpets, clams, mussels • Scavengers: vent crabs, worms, fish• Predators: vent crabs, octopi• Symbiotic with primary producers (bacteria):

vestimentiferan worms, giant clams– 1. Tevnia jerichonana– 2. Riftia pachyptilia

Longevity of vent itself estimated at years to decades

Deep Sea biota

• 75% of sea floor is below 3000 m depth• Imported nutrients from photic zone• Seasonal pulses of organic matter• Seafloor communities low biomass but

surprisingly high biodiversity• Most benthic organisms in the deep sea

(polychaetes, arthropods, molluscs, echinoderms) survive on detritus in sediment

• Low biomass but high diversity of fish species (why?): scavengers and predators

Factors Driving Methane Vent (Cold Seep) Systems

• High pressure• Low temperature • Depth• Lack of sunlight• Lack of photosynthesis• Scarcity of food resources • Enormous volume of water further reduces

encounter probability

Counteracted by:• Chemosynthetic bacteria (primary producers)• Cold, mineral-rich water• Location – advantages and disadvantages

Learning Outcomes

• Understand why extreme and unstable environments tend to have relatively low biodiversity, giving examples including coral reefs (stable and not extreme), sand on a reef slope (unstable), and hydrothermal vents (extreme)

Tolerance and Need

• A proper balance of physical and biological factors is important for the success of each organism and the community.

• Different organisms have different tolerances for specific factors and may be broadly or narrowly tolerant of different conditions.

• Steno- is a prefix meaning “narrow”. It can be used to describe organisms that have narrow tolerances for specific factors, e.g. stenohaline.

• Eury- is a prefix meaning “wide”. It can be used to describe organisms that have wide tolerances for specific factors, e.g. eurythermal.

Diversity: richness, evenness & dominance

• Two communities with same 10 species;

• If we selected groups at random from a & b, how long would we have to sample before we got all 10?

• What is the dominant species in a, b?

• What happens to a & b if each is affect by an elephant disease?

(g) Understand why extreme and unstable environments tend to have relatively low biodiversity, giving examples including coral reefs (stable and not extreme), sand on a reef slope (unstable) and hydrothermal vents (extreme).

• In general, environments that are unstable or extreme tend to have a low biodiversity. – Sand, for example, easily dries out and is easily eroded by wind

and water currents. Some organisms are able to survive by burrowing into sand.

– The water surrounding hydrothermal vents is under very high pressure and at a high temperature; relatively few organisms are adapted to survive in these conditions.

– Coral reefs provide a stable and favorable environment for many different organisms and have a correspondingly high biodiversity.

(h) Give examples of organisms that occupy specialized and generalized niches, including coral-eating butterfly fish and tuna.

• Organisms with a specialized niche have a narrow range of food requirements or live in a specific habitat,

• those with a generalized niche can exploit a wider range of food sources and live in a wider range of habitats. – Most species of butterfly fish feed on corals

and sea anemones. Many species are also territorial and live closely associated with a specific area of coral.

– Tuna feed on a range of different species of fish, as well as squid and crustacean. Tuna are also highly migratory fish, Bluefin Tuna, for example, are widely distributed in the Atlantic Ocean.

i) Explain why habitats with high biodiversity tend to contain narrow ecological niches.

• Narrow niches tend to reduce the extent of overlap and therefore reduce interspecific competition. Coral reefs have a high biodiversity and include many species with narrow niches, including fish exploiting a variety of different food sources such as corals, seaweeds, and small animals living in the coral.

i) Explain why habitats with high biodiversity tend to contain narrow ecological niches.

• High biodiversity means that many different species live within one ecosystem.

• Each species of organism has its own niche within the ecosystem; if niches overlap, one species will die out as a result of interspecific competition.