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Chapter 15 Summer 2025 — Transcript

by Jeffrey Ashley · 2,640 words · 425 segments · language en · Watch on YouTube

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0:00Hello, I'm Dr. Jeff Ashley and welcome
0:02to chapter 15. As opposed to chapter 14
0:05which dealt with animals of the pelagic
0:07environment, this chapter deals with the
0:09animals of the benthic environment.
0:11Let's get started. As we know from
0:13previous lectures, more than 98% of
0:16approximately the 230,000 known marine
0:19species live in or on the ocean floor.
0:23Benthic organisms live mainly on the
0:25continental shelves. However, they do
0:28appear in the open ocean as well.
0:31Benthic biomass is the mass of living
0:33organisms on the sea floor and it
0:36actually matches the distribution of
0:38chlorophyll in surface waters. This is
0:40because in order to support a vibrant
0:43and healthy benthic biomass, you need
0:46carbon raining down on that sea floor.
0:49Here we have a global map showing you
0:51areas where benthic organisms are
0:54abundant and not so abundant. And we can
0:57see fringing around the continents are
1:00benthic communities that are high in
1:02biomass. So dark purple shading
1:05indicates areas of high benthic biomass.
1:07The lighter shade here, that light blue,
1:10indicates areas of lower biomass. And
1:12you can just see by the coloration that
1:15it's really the continental margins
1:16here, those areas around the continents
1:19that allow for a higher abundance of
1:22benthic communities. We'll see why.
1:25Let's start off with communities on
1:26rocky shores. We've seen this term
1:29before, epifa. Epifa are attached to a
1:32substrate such as marine algae or they
1:36can move over the seafloor like crabs
1:38and snails. The opposite to epifa is
1:41infauna and those are organisms living
1:44on or within the sediment. Here we have
1:46a two-page table which is really
1:49extensive, but it goes through the
1:51organism's adaptations to rocky shores.
1:54Rocky shores have very adverse
1:57conditions. Rocky shorelines are
1:59inundated with high tide following by
2:01low tide. And this is a daily episode.
2:06Organisms have to adapt to this so they
2:09don't dry out during low tide. I won't
2:11list all the adaptations here, but I'll
2:13just hit some of the highlights that
2:15some organisms have to have the ability
2:17to seek shelter or withdraw into shells.
2:19Rocky shorelines are also inundated by
2:22strong wave activity. So, organisms need
2:25to adapt for that. In algae, we have
2:28strong hold fast to prevent them from
2:30being washed away. They are held to a
2:32substrate. Also, in rocky shorelines,
2:35predators occupy areas during low tide
2:37and high tide. An adaptation such as
2:40camouflage may help here. Rocky
2:42shorelines may have a difficulty in
2:45finding mates for attached
2:47species. So, organisms might adapt by
2:50releasing large numbers of eggs or
2:52sperm. Broadcast reproduction as we said
2:54and being exposed to elements here.
2:56There are rapid changes in temperature,
2:58salinity, pH, and oxygen content.
3:01Organisms have to have the ability to
3:03withdraw into shells to minimize
3:05exposure to these rapid changes in
3:08environmental
3:09conditions. And lastly, the lack of
3:12space or attachment sites. Organisms can
3:15take over other organisms space or they
3:18can attach to other organisms. Although
3:20this table is extensive and very
3:22detailed, I do want to leave you with
3:24the idea that the rocky shoreline has
3:27very adverse conditions, much like on
3:31land. This goes counter to what we said
3:33before that the ocean, the marine
3:35environment is actually not so varied.
3:39But here at the rocky shoreline, you see
3:41a whole bunch of varied conditions
3:43possible and adaptations leads to this
3:46wide variety of organisms that you see.
3:49So on the rocky shores there's a thing
3:51or a zone called intertidal zonation.
3:54This is called the spray zone. It's
3:56above the spring tide zone. Remember
3:58that's the highest high tide
4:00possible. There's a high tide zone which
4:03is relatively dry, a middle tide zone
4:06covered by all high tides exposed by all
4:09low tides and a low tide zone which is
4:12usually wet. So you can see the zonation
4:15and that zonation leads to different
4:17conditions. Those different conditions
4:19lead to various organisms that have
4:22adapted to those adverse conditions or
4:25maybe not so
4:26adverse. So within the spray zone or
4:29called the supra tidal zone, we have
4:31organisms that must avoid drying out.
4:34Many animals here have shells. There are
4:37few species have actual marine algae. In
4:40the high tide zones, we have animals
4:43have shells to avoid drying out. We have
4:46marine algae, rockweeds with thick cell
4:49walls because of the tidal action and
4:51wave action and rockweeds colonized
4:54there. First in the middle tide zone
4:57more types of marine algae have seen are
4:59seen. We have softbodied animals without
5:02shells. Barnacles and muscles are
5:04present. And we have carnivorous snails
5:07and starfish. Here in the middle tide
5:09zone, you'll see such things as sea
5:10anemies. They have stinging
5:12pneumaticists on their tentacles to
5:14poison prey. This image shows a low
5:18tide, but you can see the high tide mark
5:20right up here. And we see in that area
5:23between high tide mark and low tide, we
5:26have a bed of muscles here. So muscles
5:28are adapted to being exposed to the air
5:31for a certain portion of the day. In the
5:34middle tide zone, you might see such
5:35things as hermit crabs. They have
5:38armored claws and an upper body, soft
5:40abdomen, and they inhabit abandoned
5:43shells. We also have sea urchins here.
5:46These are five tooththedmouthed
5:47organisms. They have a hard spherical
5:50shell and hard spines for protection.
5:53Don't ever step on one. Take it from me.
5:56In the low tide zone, we have abundant
5:58algae and surf grass as this image
6:00depicts. And many animals like to hide
6:03or seek shelter here in the seaweed and
6:05seaggrass. low tide zone. We have
6:07various shore crabs. These are
6:09scavengers which keep the shore clean.
6:12They hide in rock and rocks and cracks
6:15during the day and feed on algae at
6:18night. It's really cool. If you go
6:20crabbing at night here, you can see the
6:23large abundance of these types of
6:25organisms in different species of crabs.
6:27Their hard exoskeleton prevents rapid
6:30dehydration. So communities along the
6:32sediment covered shores depend upon the
6:35sediment size and that's related to wave
6:37and current strength as we saw in past
6:39chapters. We could have beaches which
6:42are primarily coarse boulders or large
6:45sediment particles or we can have finer
6:48grain sand beaches. We could have salt
6:51ma marshes or we could have very mucky
6:54mud flats. So epifa was on top or
6:58attached to infauna is burrowing
7:00animals. Nearly all large organisms
7:03along sandy beaches are
7:06infal. There's no stable or fixed
7:08surface. They rely upon burring to
7:11provide them with a stable environment.
7:14There's less risk of temperature
7:16extremes and drying out through a
7:18burrowing process. So here we see the
7:19intertital zonation again. And based on
7:23the region, we're going to have
7:24different species of benthic organisms.
7:27Sandy beach organisms have specific
7:30adaptations. For example, by valve
7:33molllesks have soft bodies and hard
7:35shells like clams and muscles. Analid
7:38worms have U-shaped burrows and can pass
7:42sand directly through their digestive
7:43tract. Common, especially on the east
7:45coast of the United States, if you just
7:47dig down in that sand, you can find
7:49these guys. I call them sand fleas.
7:51They're sand crabs in common name.
7:53They're crustaceians. Their segmented
7:55bodies, hard exoskeleton, and paired
7:58jointed limbs. They bury themselves in
8:00the sand. Ainoderms have spiny skin,
8:04five tapered legs, for example, a
8:06starfish or a heart urchin. They bury
8:08themselves into the sand and can undergo
8:11a water exchange by sending up a
8:13respiratory channel. Moa, they're small.
8:16They feed on bacteria. These include
8:19such things as polyets, molllesks,
8:21arthropods, and nematodes. They live
8:24within the sediment from the intertidal
8:26zone to the deep ocean trenches. What
8:28about communities along the sediment
8:30covered shores that have mud. These are
8:32called mud flats. You'll find eel grass
8:34and turtle grass common there. You also
8:37see by valves and other mlllesks. Here,
8:40the fiddler crab likes to call its home.
8:43Males have one small and one large claw.
8:46Offshore we have oceanf flooror
8:48communities such as the subtitle zone.
8:50It's a rocky bottom. Here we see kelp
8:54forests. Kelp attaches to rocky bottoms
8:56with a strong
8:58holdfast. Stips and blades support
9:01pneumatices. Kelp forests. These are
9:03beds of giant brown bladder kelp or bull
9:07kelp. They're fast growing. They're
9:09highly productive e ecosystems and they
9:11provide a wonderful shelter for a wide
9:13variety of organisms. Here we see kelp
9:16forest distribution mainly AC across the
9:19western portions of continents such as
9:22North America, South America, the tip of
9:25South Africa and the western and the
9:29southern part of Australia. What about
9:31rocky bottom shallow offshore ocean
9:33floor communities? Here you'll see
9:35lobsters. These are large spiny aeni
9:37that they have. They live in water
9:39deeper than 20 meters. They are
9:41scavengers. They also feed on live
9:44animals. Here you also see oysters. They
9:47are non-movable or cesile by valve
9:49molllesks. They have thick shells. They
9:52are food for sea stars, fish, crabs, and
9:54snails that bore through the shell.
9:56Oyster beds are actually dead, empty
9:59shells with living generations on top.
10:02They are very common in Delaware and the
10:04Chesapeake Bay. Here's an interesting
10:06organism, the oyster drill snail. The
10:09oyster drill snail alternates between
10:11rasping the oyster shell with its regula
10:14and secretreting a calcium dissolving
10:16acid through a special organ. This
10:19allows the snail's mouth parts to be
10:21inserted in the hole, releasing the
10:22enzymes that digest the oyster. Let's
10:25switch to coral reefs. And I'm thankful
10:27that you watched that documentary called
10:29Chasing Coral. You know something about
10:30these already. Reefs are shallow water
10:33communities restricted to the tropics.
10:35Here you'll see polyps, individual
10:37corals. So between the Tropic of Cancer
10:39and the Tropic of Capricorn you find the
10:41tropics and here you'll find coral reef
10:44distribution. Due to the gys in both
10:47north and south hemispheres we see water
10:50warm water being sloshed over here to
10:53the western boundaries of the Pacific
10:55Ocean and also the Indian Ocean. So here
10:59you see a predominance of coral reefs.
11:01What are the conditions for coral reef
11:03development? Well, warm sea water, you
11:06have to sun, you have to have sunlight
11:07because
11:08zoanth, you have to have sunlight as
11:11well because zo zanthle, a symbiotic
11:15photosynthic microscopic algae uh grows
11:18in coral tissue, clear seawater, and a
11:21lack of
11:21turbidity, normal ocean salinity, and
11:25you need hard substrate. Coral reefs are
11:27made up of algae, mllusks, forinifera,
11:30as well as corals. Here we have
11:34hermatypic coral, a mutualistic
11:36relationship between algae. Algae
11:39provide food and the corals provide the
11:41nutrients. We see other reef animals
11:43with symbiotic relationships as well.
11:46You might see mixotroofes. They derive
11:48part of the nutrition from algae. These
11:51include coral, forams, sponges, and
11:53mllisks. Coral reef development. Coral
11:56reefs actually develop on formal coral
11:58reefs. So typical reefs can be many
12:00kilometers thick. The top experiences
12:03sunlight that the corals need. The
12:05bottom was once actually in the surface
12:07waters. With all that weight piling up
12:10of new material it submerge. The largest
12:13structures are created by living
12:15organisms. The Great Barrier Reef is the
12:18largest coral reef structure and it's
12:20estimated that it's around 2,000 km
12:23long. The second largest coral reef is
12:25off the coast of Bise in the Caribbean.
12:28Here you have a great diversity of
12:30species. These are the tropical
12:32rainforest of the marine environment.
12:35They're important touristic loces. They
12:38provide a great means for fisheries,
12:40although they can be exploited. And
12:42reefs protect shorelines from storms. So
12:46we know from our documentary Chasing
12:47Corals that coral bleaching is a major
12:50threat to the health of coral reefs.
12:52This is a loss of color in corals. The
12:55symbiotic zoanthille die. They leave and
12:58become toxic. The bleached coral lacks a
13:01nourishment for algae. Coral bleaching
13:04is definitely linked to climate change
13:06and ocean warming. Some other causes
13:09might be high surface water
13:11temperatures, elevated UV levels, a
13:14decrease in sunlight blocking
13:16atmospheric
13:17particles, pollution, salinity changes,
13:20and also disease. 30% healthy today,
13:24down by 41% healthy in 2000. One-third
13:27of corals are at a risk of extinction.
13:30The threats include man-made effects
13:33such as we just saw and also natural
13:36events like
13:37hurricanes, floods, and tsunamis.
13:40However, most scientists agree that
13:42humans are the greatest threat to coral
13:44reefs. There's a high propensity for
13:46over fishing of reef species, either for
13:48aquaria or fruit. Runoff with sediment
13:51and pollution damages reefs. Plastic
13:54trash entangles reefs and stresses
13:56corals. It provides lack of light
13:59through light deprivation, buildup of
14:01toxins and also
14:03suffocation. Also with atmospheric
14:06carbon dioxide levels increasing that
14:08dissolves in seawater and increases
14:10acidity which leads to the demise of
14:13coral reef structures. Now let's shift
14:16our emphasis to deep ocean flooror
14:17communities. They're harder to explore
14:19than the nearshow communities. So we
14:21know less about them. They're expensive
14:24to explore. They have limited oxygen and
14:27robotic technology is usually needed for
14:29the exploration. We mentioned these
14:31terms before. These are the abyssal
14:33plains, the bathl and the hallel zones.
14:36Light is absent below 1,000 m.
14:39Temperatures are usually very cold
14:40between
14:42-1.8° and
14:433°. However, these cold deep waters do
14:47have high oxygen, but they also have
14:49high pressure. There are such things
14:51called abyssal storms. And these affect
14:53bottom currents. They're created by warm
14:55and cold eddies from the surface
14:57currents and they can last weeks. In the
15:00deep dark ocean basins, there's no
15:03primary productivity because of lack of
15:05sunlight. Only 1 to 3% of the euphotic
15:09food is present that rains down upon it
15:11from the upper water column. Organisms
15:14here have special adaptations for
15:15detecting food, including
15:17bioluminescence. Species diversity is
15:20incredibly rich here and equivalent to
15:22rainforest and coral reef environments.
15:24So what are the food sources for these
15:26deep sea organisms that are living in
15:29the absence of light? Well, we can have
15:31migrations of zop plankton and other
15:33fish. We have downward transport of
15:35sediments that can contain nutrients. We
15:38have plankton that die and end up
15:40minimally reaching the abyssal plane or
15:42the deep ocean. We have fecal pellets.
15:45Remember the fecal pellet express? Those
15:47are conglomerations of organic matter
15:49and fecal matter that actually rain down
15:53at a fairly rapid rate to the deep sea.
15:57We have fish dumping. We have crustation
15:59molting which will deliver some um
16:03exoskeletons to the bottom of the sea.
16:06And we have dead large carcasses here
16:09like whales ending up being delivered to
16:12the abyssal plane. And as we talked
16:14about deep sea hydrothermal vents, they
16:17have support a wide range of organisms
16:19in their communities. We talked about
16:22the venting system or these chimneys,
16:24the black smokers and the white smokers.
16:26Again, these are investigated by deep
16:28sea diving submersibles like this one,
16:30Alvin. And a whole rich community exists
16:33there, fueled by
16:35chemosynthetic processes. Here you'll
16:37see the giant tubeworms, which we saw
16:39videos of, giant clams, giant muscles,
16:42crabs, microbial mats, and as I said,
16:45life is truly supported by the one
16:47thing, not photosynthesis, but
16:49chemosynthesis. Taking hydrogen sulfide
16:51and turning it into a chemical source of
16:54energy. So, I leave you with this. Much
16:56has been explored uh in the oceans. The
16:59deep oceans haven't been explored to the
17:01degree that we want to. But what's the
17:04next thing, the new frontier? Well, this
17:06is called the deep biosphere and exists
17:08within the seafloor or beneath the
17:10seafloor. We know that water can
17:12permeate down. We knew that from
17:14hydrothermal vents, but microbes live
17:16there also in these poor fluids. It
17:19might represent much of Earth's total
17:20biomass, but we have no idea right now.
17:23Further exploration is needed. So, that
17:26concludes the chapter on benthic
17:28animals. And I hope you enjoyed it.
17:31Please read the chapter and uh we'll see
17:34you soon.

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