Marine Biology - Part 4 The Benthos Some Benthic Communities 1. Rocky intertidal community 2. Sandy/cobble beach community 3. Salt marsh & estuary community 4. Coral reef community 5. Deep sea floor community 6. Hydrothermal vent community 7. Low temperature seep community 8. Deep biosphere communities The Benthos More than 98% of the known marine species are benthic Most on continental shelf Distribution like that of phytoplankton productivity (why?) 1
How long would your remains remain on the sea floor? Only about 1 day! Amphipods eating fish carcasses, 9600 meters deep, Philippine Trench, 1975 Limiting Factors & Tolerances Here, 2 species of barnacle compete for space on rocks in the intertidal zone. Competition The larger one (Balanus) is better at taking over space than the smaller one, but the smaller one (Chthamalus) can survive out of water better than the larger one. The result is that the larger one dominates lower down, while the smaller one dominates higher up. 2
1. Rocky Intertidal Community The intertidal zone is the area between high and low tides. Pros: Abundant food & light --> Desirable, crowded, high biodiversity Cons: Tough place to live --> Adaptations, zonation Zonation is a distinct feature of this community. Different species arrange themselves into distinct horizontal bands, or zones, within the intertidal zone according to their ability to withstand desiccation (drying out when tide is low) and inundation (when tide is high). Fig. 14.9, p. 334 Adverse Condition Drying out during low tide Strong wave activity Predators occupy area during low tide Difficulty finding mates for attached species Rapid changes in T, S, ph, O2 Lack of space or attachment sites Adverse Conditions of Rocky Intertidal Zones & Organism Adaptations to Those Conditions Adaptations * Ability to seek shelter. * Ability to withdraw into shell. * Thick exterior or exoskeleton to prevent water loss. * Hard structures adapted to withstand wave energy. * Algae: Strong holdfasts to prevent being washed away. * Animals: Strong attachment threads, muscular foot, multiple legs, or hundreds of tube feet to allow firm attachment to bottom. * Firm attachment. Stinging cells. Camouflage. Inking response. * Ability to break off body parts and regenerate them later. * Release of large numbers of eggs/sperm into water column during reproduction. * Long organs to reach others for sexual reproduction. * Ability to withdraw into shells to minimize exposure to rapid changes in environment. * Ability to exist in varied conditions for extended periods. * Attach to other organism. * Overtake another organism!s space. Examples Sea slugs, snails, crabs, kelp Kelp, snails, sea stars, mussels, sea urchins Mussels, sea anemones, sea slugs, octopi, sea stars Abalones, sea urchins, barnacles Snails, limpets, mussels, barnacles Bryozoans, barnacles, limpets Fig. 14.8a, p. 332 Rocky Shore 3
Rocky Shore Shells Pacific Atlantic Soft bodies Sea Anemone Stinging cells Macrocystis (kelp) Periwinkle Rock louse Buckshot barnacles See Figs. 14.2a & 14.3, pp. 327 & 328 4
2. Sandy & Cobble Beach Communities Beaches (sediment-covered shores) are also physically demanding. Pros: Less competition between species Abundant plankton, detritus, and light --> Species that can thrive here are often abundant Cons: Higher energy (waves, longshore current) Steeper slope Loose sand & cobbles are highly unstable & abrasive --> Adaptations, zonation, low biodiversity See Fig. 14.5, p. 329 Epifauna - Live on the bottom (attached = sessile, freely moving = motile) Infauna - Live buried in the substrate (sand, mud, etc) Meiofauna - Live in the spaces between sand/sediment grains! (interstitial) Sediment-Covered Shore Epifauna and Infauna Modes of feeding along a sedimentcovered shore 5
Meiofauna See Fig. 14-CO, p. 324 Mollusks: Phylum Mollusca The bivalves or clams are mollusks with a pair of hinged shells (called valves) which open and close. Most bivalves are suspension feeders who pump water into their shells and extract both food particles and oxygen from the water. Some clams live attached to the sea floor, while others burrow into sediments on the sea floor, reaching up to the water above with a pair of tubes called siphons. Mollusks: Phylum Mollusca Gastropods or snails possess a single coil-shaped shell, although many species do not have a shell. This very large group of mollusks includes species that are grazers on algae, suspension feeders on food particles floating in the water, and predators of various kinds. The cephalopods are the most active and intelligent of the mollusks. They are predators who catch prey with muscular tentacles lined with powerful suction cups. 6
Arthropods: Phylum Arthropoda Marine arthropods include lobsters, crabs, shrimps, krill, copepods, and barnacles. All arthropods have an exoskeleton, articulation, and striated muscle. The exoskeleton is a protective covering made of the material chitin (a substance similar to your fingernails). The exoskeleton is flexible and hinged at various body joints. It provides protection and support while also allowing movement and flexibility. Articulation refers to the ability to bend appendages at specific points. Multiple bending points give arthropods a range of movement and flexibility, even within the restrictions of an exoskeleton. Arthropods: Phylum Arthropoda To grow larger, an arthropod must periodically molt its exoskeleton. During molting the animal grows in size rapidly, before the new exoskeleton solidifies on its body. This periodic growth is shown on this graph. Striated muscle is a form of muscle that is strong and lightweight, allowing for rapid movement and considerable power compared to many other invertebrates. Echinoderms: Phylum Echinodermata = spiny skin The echinoderms include the sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers. All echinoderms have a body that is radially symmetric and based on five sections. In other words, echinoderms have a body design that can be divided into 5 identical pieces that radiate out from a central point. A sea star (used to be called starfish ) is the most clear example, but all echinoderms have this type of body plan. Another feature that characterizes all echinoderms is the water vascular system (WVS) -- a set of water-filled tubes, valves, and projections used in feeding and movement. Echinoderms: Phylum Echinodermata The diagram shows the WVS of a sea star. The WVS is a hydraulic system. Water moving through tubes controls the movement of tube feet, dozens of small projections with suction cups on the ends. The tube feet are used to grab onto objects during feeding, and are also used in movement. 7
Estuary = Partially enclosed coastal body of water in which salty ocean water is significantly diluted by freshwater from land runoff. (River mouths, bays, inlets, gulfs, and sounds.) Salt marsh = Relatively flat area of the shore where fine sediment is deposited and salt-tolerant grasses grow. Also mud flats. Pros: Lower energy, gentler slopes Finer sediments, more stable Rich in nutrients, abundant sunlight --> Very high primary production, abundant food supply = Rich habitats Supports many organisms Easy to burrow or attach Cons: 3. Salt Marsh & Estuary Community Fluctuating salinity (often brackish) and temperature Very vulnerable to pollution & urban development (rivers, urban/agricultural, etc) Estuaries are often called marine nurseries because they form habitats for many juvenile organisms. Many fish are born and grow up in estuaries, and later migrate to the open ocean. Mangroves (AAAS) Figs. 14.3 & 14.6, pp. 328 & 330 Puget Sound - The Fertile Fjord http://www.wsg.washington.edu/pubs/fjord/fjord.html 4. Coral Reef Community Coral reefs are created by coral animals. Corals (phylum Cnidaria) are colonial cnidarians that secrete skeletal structures of calcium carbonate (CaCO 3 ). These form great mounds that rise up from the sea floor, creating habitat for vast numbers of species. Coral reefs have the greatest biodiversity of any marine community. More than one million species inhabit the coral reef ecosystem. % of modified shoreline [WA DNR, 1998] 8
Coral Reef Polyps precipitate CaCO 3 Mutual symbiotic relationship Zooxanthellae algae in coral Water: Shallow, normal salinity, warm, clear (not turbid) Sunlight Zoned on basis of water depth Light penetration Wave activity Different types of corals Fig. 14.11, p. 336 Fig. 14-12, p. 337 (The plural of genus is genera) Fig. 14-14, p. 339 9
Coral Reef Coral Reef Important Largest structure built by living organisms Great diversity of species Shelter, food, breeding ground Economic tourism Coral bleaching indicates warming of oceans Castro Marine Biology Chapter 14 (.pdf) Endangered Increased sewage and agricultural fertilizers Increase nutrient levels Increase phytoplankton Decrease corals Bioerosion Over-harvesting and damage by humans Crown-of-thorn sea star (Acanthaster planci) Climate change 10
Diseased Corals Coral Bleaching Crown-of-thorn sea star (Acanthaster planci) Fig. 14.15, p. 340 11
5. Deep Sea Floor Community One might expect that the tremendous cold and high pressure of the deep sea floor would mean little life, but this is not the case. Many species are found here that are adapted to eating a dependable food source -- detritus, the dead material that constantly sifts down to the sea bed from up above! This sea cucumber is one of many deep sea species that mines dead organic particles from the sea floor for food. Deep sea organisms have slow metabolism, so do not require much food. Many may feed as little as once a year, and some may live 100 years or more. Physical constraints Dark Cold High pressure High oxygen Currents move slowly Diversity much greater than expected! Deep Sea Floor Fig. 14.17a, p. 341 6. Hydrothermal Vent Community At the centers of mid-ocean ridges, where magma comes up close to the sea floor, water may circulate through cracks in the rock and become very hot. Hydrothermal vents are sites where this superheated water containing dissolved minerals and gases escapes through fissures, or vents. This escaping hot water forms chimneys called smokers. Chemosynthetic bacteria (Archaea) use the hydrogen sulfide (H 2 S) that comes out of these smokers as an energy source to grow and reproduce. These bacteria are the primary producers in this community, forming a food source for a host of other species. This entire community exists independent of sunlight! Fig. 14.18a, p. 343 Animals unusually large for deep ocean Some in symbiosis with Archaea Species diversity low Larvae transported by deep-ocean currents Vent areas probably short lived Hydrothermal Vents Shrimp at N. Atlantic vent 12
7. Low-Temperature Seep Communities Are these the conditions under which life began in oceans billions of years ago? Hypersaline seep Hydrocarbon seep Subduction seep Lower temperature water Archaea use chemosynthesis H 2 S and CH 4 Subduction seep Hydrocarbon seep Hypersaline seep (46.2 ) 8. Deep Biosphere Communities Microbes Pore waters Below seafloor surface More biomass than expected Stay tuned! 13
Review of Some Important Concepts Marine organisms are found in communities: groups of interacting producers, consumers, and decomposers that share a common living space. Each species within the community has a particular habitat: a specific location ( address ) it occupies within the community. Each species within the community also has a particular niche: a specific role ( job ) it performs within the community. Every species requires a balance of particular physical and biological factors to exist and thrive. Organisms within a community compete with one another for space, food and other resources. But in many instances they also depend upon one another in specific ways. Symbiosis describes the situation where the lives of two species are extremely closely intertwined; so closely in some cases that one organism may be totally dependent upon the other. Marine Communities Examples of marine communities, each with its own particular physical and biological characteristics:! Open ocean community (pelagic)! Rocky intertidal community! Beach community (sandy/cobble)! Salt marsh & estuary community! Coral reef community! Deep sea floor community! Hydrothermal vent community! Low temperature seep community! Deep biosphere communities Biodiversity refers to the variety of species in a community:! High biodiversity = Many different species live there! Low biodiversity = Only a few species occur there Physical and Biological Factors Recall the concept of limiting factors. A proper balance of physical and biological factors is important for the success of each organism in the community. Distribution of Organisms in a Community Different organisms have different tolerances for specific physical or biological factors. Steno- is a prefix meaning narrow. Eury- means wide. Stenohaline means an organism can only live within a narrow range of water salinity Eurythermal means an organism can live in a wide range of water temperature Individuals within a community will have a certain population density: the number of individuals per unit area (or volume). These individuals may be distributed in several ways. Random - The position of one individual has no relation to the position of another. Clumped - Individuals occur in tight groups, or clumps. Uniform - Individuals are distributed in a manner that maximizes the space between each one. Fig. 14.1, p. 326 14
Growth Rate & Carrying Capacity With unlimited resources, a population will grow in size over time as shown by the J-shaped curve. But because resources in the environment are nearly always limited, there is environmental resistance to population growth. This resistance increases with increasing population size, resulting in the S-shaped curve. A balance is achieved when the final population size evens out around a specific value. This is called the carrying capacity -- the size of population that the community can support under a stable set of environmental conditions. Change in Marine Communities Marine communities change through time. Changes can occur slowly due to climate cycles or seafloor spreading, or quickly due to factors such as a volcanic eruption that disrupts the sea bed. A climax community is a stable, long-established community. If a climax community is disrupted, it may be restored through the process of succession. During succession, the composition of a community changes in a regular way, as early temporary inhabitants are gradually replaced by long-term inhabitants. Eventually, if no major disturbances happen, the community will again become a stable climax community. 5-Minute Write Summarize the main points of today s lecture. List 3 to 5 questions you have, based on today s s lecture. What did you find most interesting about today s s lecture? How was the lecture relevant to you? Fig. 14-8b, p. 333 15