Life on the Continental Shelf Shipley Marine Biology Chapter 13 Life on the Continental Shelf Shipley Marine Biology

Life on the Continental Shelf The continental shelf is the submerged edge of a continental plate. The shelf extends from the low tide line to an area known as the shelf break. The slope of the continental shelf is normally more gradual, whereas, the slope past the shelf break is normally very steep.

Life on the Continental Shelf The slope of the shelf, the depth of the water at the shelf break and the distance of the shelf break from shore varies greatly by location (remember active versus passive margins). Remember from chapter 12 that estuaries are much more well developed in areas of the world where the continental shelf has a gradual slope and is very wide. This is the case on the East Coast of the US, which is the reason for the well developed estuaries there.

Life on the Continental Shelf The depth of water at the shelf break varies greatly with an average depth of around 490 feet. The width of the continental shelf also varies greatly from 0.6 miles to 470 miles with an average of 48 miles.

Life on the Continental Shelf The continental shelf is biologically the richest part of the ocean (more species present). This is also an area of potential natural resources such as oil and natural gas. For this reason, countries wanted a way to protect these resources from exploitation by other countries. In the 1950’s, the United Nations agreed that each country shall have control over the marine resources out to 200 nautical miles off their coast – this includes the continental shelf and its resources.

Life on the Continental Shelf A major portion of the fisheries global catch is caught over the continental shelf. The shelf is an important area for larvae and juveniles of many species as well as adults. A wide variety of organisms can be found on/in the continental shelf. Some of the most common includes sponges, cnidarians, worms, molluscs, fish and echinoderms.

Life on the Continental Shelf Temperature: Temperature of the water over the continental shelf varies much more than the water in the deep sea (but less than in an estuary). The temperature fluctuates more because the water is shallower than in the deep sea and because waves and currents keep the water circulating. This means that warmer surface waters are mixing readily with the rest of the water column.

Life on the Continental Shelf Water turbulence created by waves and currents keep the water column well mixed. This affects not only the temperature of the water, but also affects the nutrients available in the water. Nutrients never have a chance to “rain down” on the bottom and be lost the way they do in the deep sea. This constant water motion means the nutrients are available to the benthic organisms as well as those in the neritic zone.

Life on the Continental Shelf Water may have less clarity due to the many nutrients in the water and due to suspended sediments. Nutrients come from many sources, including: Autotrophs Decaying marine organic matter Nutrients delivered from estuaries and terrestrial ecosystems via rivers

Life on the Continental Shelf Thousands of animals consume nutrients on the seabed. Several species of worms may share an area, burrowing into the sediment and cementing the grains together into tubes of all shapes and sizes. Other burrowing animals include clams, lobsters, mud shrimp and fish. The abundant life in the sediment attracts predators.

Types of Communities on the Continental Shelf Soft-bottomed benthic Seagrass beds Kelp forests Hard-bottomed benthic

Life on the Continental Shelf Soft-bottomed benthic- Dominant bottom type on the continental shelf Infauna, epifauna and meiofauna are present as well as neritic species above the benthos Sessile types are rare due to lack of “hard substrate” for attachment (remember, limiting resources????) There are more species present in this area than in the adjoining intertidal, but the distribution is often patchy

Life on the Continental Shelf Soft-bottomed benthic- Larvae are often attracted to areas where adults reside This is thought to be the result of chemical cues in the water If it’s good enough for the adults, its good enough for the youngsters!

Life on the Continental Shelf Soft-bottomed benthic- A few varieties of infauna and epifauna are seen at right You may notice that many are tube-builders to assist with the stability of the habitat

Life on the Continental Shelf A wide variety of organisms also live in the spaces between the particles of sediment- meiofauna Many of these species are found no where else As you can see at the right, these species have appendages and attachment structures to lock themselves to the grains of sediments

Life on the Continental Shelf Soft-bottomed benthic- Many species in this area are deposit feeders (directly getting nutrients from the soft bottomed material) Many other species are suspension feeders and filter nutrients directly from the water Both are pictured at right

Life on the Continental Shelf Soft-bottomed benthic- Bioturbators (organisms that disturb bottom sediments) constantly “churn” the bottom This churning helps to oxygenate benthic soils Bioturbators can include worms, mollucs, fish and even whales Skates and stringrays as well as sperm whales are well known for their activity as bioturbators

Life on the Continental Shelf Seagrass Beds They are best developed in sheltered, shallow waters with good water clarity There are over 50 known species Species have particular tolerance levels with regards to temperature, water clarity and nutrient availability that determines their distribution

Life on the Continental Shelf Seagrass Beds Due to these tolerances, species normally prefer either cool waters OR tropical/subtropical waters, but not both normally They are often found in combination with algal species The density of individual seagrass plants tend to be very thick (high biomass) – this can been seen at right

Life on the Continental Shelf Seagrass Beds Thalassia (turtle grass) is a common seagrass in tropical and subtropical areas It is named turtle grass because it is often directly consumed by green sea turtles In fact, patches of turtle grass have been shown to be “farmed” by individual turtles In this farming, green turtles bite the tops off the turtle grass When the tops grow back, they are much more tender and easier to digest, which makes the turtles happy!!!!

Life on the Continental Shelf Seagrass beds Zostera or eelgrass prefers cooler, temperate waters It is mainly found in the Pacific and the North Atlantic Like turtle grass, it can be directly consumed by herbivores Both species are often important to the food chain after decaying

Life on the Continental Shelf Hard-bottomed subtidal- Less common Often, it is the result of a submerged rocky shoreline Rock formations attract a wide variety of organisms including many sessile types that cannot survive in soft bottomed communities Oyster reefs, worm tubes and calcareous algae can all serve as hard-bottomed subtidal communities as well

Life on the Continental Shelf Hard-bottomed subtidal- One of the best features of the hard-bottomed community is the hiding places it provides for prey and predators alike Insert fig 13.20

Life on the Continental Shelf Kelp community- Kelps are brown algae that are restricted to cold waters in distribution In addition to requiring cold water, kelps are very nutrient-needy This is the result of the fast growth seen in these algae (up to 20 inches a day)

Life on the Continental Shelf Laminaria is a species of kelp common in the North Atlantic, North Pacific and the Asiatic coast of the Pacific This is one of the smaller species of kelp at maximum heights of only around 10 feet Like other species, its rapid growth provides an enormous amount of primary production in the areas where it is found It can be found growing with larger kelp species in the North Pacific primarily

Life on the Continental Shelf Macrocystis is a large species of kelp that can grow heights of over 100 feet It is found mainly in the Pacific on the coasts of North and South America This species forms thick forests that serve as a MAJOR ocean ecosystem in the areas where it is found

Life on the Continental Shelf Kelp community- Sea urchins are by far the largest direct consumer of kelp In turn, many species feed on the sea urchins including their “cousins” the starfish and sea otters

Life on the Continental Shelf The diagram at the right shows the anatomy of a kelp forest Thousands of organisms are dependent on the kelp forests for shelter (habitat) or for trophic needs