Teacher s Guide to The Biology of Seashores A Video Program 2001, BioMEDIA ASSOCIATES By David Denning

Transcription

1 Teacher s Guide to The Biology of Seashores A Video Program 2001, BioMEDIA ASSOCIATES By David Denning Introduction and Use: CONTENT: This video provides an introduction to the ecology, biodiversity and natural history of Pacific coast seashores, from Baja California to Alaska. It covers many common intertidal species and provides information about adaptations used by organisms to survive in the dynamic and biologicallyinteresting habitats of the shore. AUDIENCE: The video is designed for general biology courses, introductory courses in ecology and marine biology, and other courses where ecology, natural history, and zoology are taught. It has been used at levels from beginning middle school up to beginning college/university. Many species featured on this video have counterparts on temperate Atlantic shores. Biology instructors will find the program useful for an overview of animal diversity and for comparing Pacific coast shore ecology with Atlantic coasts or with other ecosystems. It is useful for teaching about animal behavior, life histories, and adaptations. BIODIVERSITY: The video is ideal for teaching aspects of biodiversity. More than 80 common seashore species are featured in the video. Footage in this presentation shows six phyla of photosynthetic algae, and 15 different phyla of invertebrates. Part 1: CONDITIONS ON THE SEASHORE Introduction An introduction with a stress on the importance of studying intertidal life. This segment shows the video s ecological emphasis as well as the excitement and pleasure associated with biological investigations along the seashore. High biodiversity is characteristic of most seashores although on some shores (sandy beaches, for example) the diversity may not be easily revealed to the casual observer. Rocky shores tend to have diverse floras of macro algae. Representatives of more than 1/2 of the approximately 30+ known animal phyla, can be found in the intertidal zone. Tides This module covers four main concepts: 1) causes of tidal bulges and their relationship to the relative positions of moon and sun; 2) the daily cycle of tides as the earth rotates under these bulges; 3) The variation in the tidal cycle during the month; and 4) the delay of tides resulting from the moon moving in its orbit. Many people are not aware that the lowest tides of the month are around the time of full moon and new moon. Study tide tables to confirm these concepts.

2 Teacher s Guide to The Biology of Seashores, 2001, BioMEDIA ASSOCIATES page 2 Part 1: CONDITIONS ON THE SEASHORE - (continued) Seashore conditions: Abiotic Factors Waveshock And Abrasion On exposed rocky shores and sandy beaches, the impacts of waves are dominant physical features affecting life. Sand grains carried by waves and currents can tend to scour rock surfaces like sandpaper. Temperature And Salinity Physical features affecting life in the intertidal include immersion in saltwater during a variable portion of the day; drying conditions due to sun, wind and exposure at low tide; flushing with fresh water from rain or from river water floating on top of seawater; high temperatures on hot summer days; and freezing temperatures in winter. These factors are moderated by frequent immersion in water, so that organisms lower in the intertidal are less affected by them. Flow measurements indicate that intertidal organisms experience forces equivalent to winds blowing across the land at over 1000 km/hr (600 mph). Physical conditions are most extreme at the highest levels of the intertidal. Ask students to design an organism that could survive on a wave-washed rock. Experiments involving carefully pouring fresh water and sea water together in small containers reveal much about the density effects of salinity. Seashore conditions: Biotic Factors Competition Competition for space is a pronounced characteristic of intertidal habitats. Interspecific and intraspecific competition involve attached and encrusting animals and algae. Competition for space limits species diversity where intertidal habitats are homogeneous, but rocky sea shores tend to have considerable variation in microhabitats. Competition in these microhabitats favors increased biodiversity. Dense aggregations of organisms also create microhabitats. Production Producers on the sea shore include three types of macro-algae: red algae, brown algae, and green algae. Various species may compete for space, especially in the low tide zone where the effects of drying and temperature are moderate. Diatoms coat the surfaces of rocks. Densities of barnacles, mussels, aggregating anemones, and other large invertebrates may reach hundreds or even thousands of individuals per m 2 Only a few species of algae survive in the higher areas of the intertidal zone. One of them, Porphyra, can withstand drying out to a crispy state. 1) Discuss the reasons why competition for space is so pronounced in the intertidal. 2) Severe competition for space is characteristic of many terrestrial environments such as moist forests, but this competition involves plants, not animals. Challenge students to find terrestrial habitats where animal competition for space is pronounced, and then discuss the similarities and differences with the intertidal. Investigate the use of algae as a human food.

3 Teacher s Guide to The Biology of Seashores, 2001, BioMEDIA ASSOCIATES page 3 Part 1: CONDITIONS ON THE SEASHORE - (continued) Plankton And Detritus As Food Two sources of food suspended in the ocean provide the major source of nutrition for the seashore ecosystem. Plankton, the living organisms drifting in the ocean, includes phytosynthesizing plankton - phytoplankton, and animals - zooplankton. Zooplankton includes many animals that live their entire lives suspended in the ocean (holoplankton), and the larvae of most seashore (and nearby seafloor) organisms. Vast quantities of dead and decaying material become suspended in the ocean, forming the important food source, detritus. Organisms that feed on suspended material, suspension feeders, usually consume both plankton and detritus. Compare coastal plankton with fresh water plankton any similarities? The BioMEDIA video, The Biology Of Lakes, Ponds And Wetlands will be an excellent resource to aid this comparison. Part 2: ADAPTATIONS FOR INTERTIDAL LIFE Adaptations for Wave Shock Wave shock adaptations include low profile, flexibility, strong attachments with adhesives, suction devises, cemented holdfasts, anchoring threads, hiding under rocks, and carving out protective habitats such as pockets in the rock. 1) Look at adaptations of other organisms that must deal with strong currents such as invertebrates living in streams. 2) If available, test the strength of mussel byssus threads Weapons Nematocysts (stinging structures found in stinging cells) are defensive and food capture devices of cnidarians. They can be borrowed functionally by some nudibranchs that feed on cnidarians. Noxious or toxic chemicals are common defense features of intertidal animals, especially those that encrust. These defensive chemicals can also be borrowed by some predators such as nudibranchs. Isolating biochemical compounds from marine organisms and testing their pharmacological properties is a hot area of research. Many active compounds have been first isolated from nudibranchs and then later traced to their point of origin, the nudibranch s food. 1) Discuss the following about evolution Did nudibranchs begin eating cnidarians for nourishment, or for their weapons? 2) Plants also use chemical defenses. Research the chemical defenses of local plants. Discuss the evolution of chemical defenses.

4 Teacher s Guide to The Biology of Seashores, 2001, BioMEDIA ASSOCIATES page 4 Part 2: ADAPTATIONS FOR INTERTIDAL LIFE (continued) Defensive Structures Defensive structures work at many levels in intertidal organisms. Shells (including those borrowed from other animals), avicularia (the birds-beak structures found on many bryozoan colonies), and the spines and pedicellaria (pinching claws) of sea urchins are among the many types of defensive structures. Escape Responses Defensive escape responses allow some animals to move away from, or deter, a predator. Swimming, rapid crawling, and twisting are among the escape behaviors. Adaptations for Feeding: Filtering sea water Strainers and fine-mesh nets have evolved in many intertidal animal groups, allowing them to take advantage of suspended food. In many cases, the driving force for bringing water through the strainer is the action of cilia. Mucus is usually involved in trapping the food and transporting it to the mouth. Strainer adaptations utilizing fine hair-like structures have evolved (e.g. fine hairs on the legs of barnacles). Feeding on Detritus Detritus is an important food source in the intertidal zone. A variety of strategies have evolved to utilize this food source including sticky tentacles and other structures which hold detritus particles and transport them to the mouth. Feeding: Rasping and Grazing Grazers consume algae in the intertidal zone. A large group of algae consumers is the rasping grazers. The radula of snails and limpets is a file-like organ attached by strong mouth muscles. Surface diatoms, young algae, algal mats and hard coralline red algae are grazed. Sea urchin spines and pedicellaria make a great study in radiation. Some urchins emphasize spines such as the tropical Diadema (12cm-long spines), while others emphasize pedicellaria (tropical species of Toxopneustes are covered with 5mm wide pedicellaria. Spines are tiny or absent). The green urchin is an intermediate form. Much has been learned about how the brain controls behavior by studying nervous control of the swimming escape in the nudibranch, Tritonia diomeda, in response to the sunflower star. Fine mesh strainers are either dragged through the water, as in the case of barnacles, or are held in water currents, often generated by the organism. Plankton and detritus are an interchangeable source of food for many suspension-feeding organisms. The importance of detritus is often overlooked. Investigators believe that grazing by snails and chitons greatly accelerates erosion on rocky coasts. 1) Compare the defensive structures of land animals (such as the spines of porcupines) with those of intertidal animals. 2) Discuss how pedicellaria may have evolved. Many gastropod molluscs use a twist to throw off predators, competitors, and unwanted mates. Observe and investigate this behavior in pond snails. Almost any pond will contain a number of different suspension filter feeders. Investigate the diversity of filter feeding strategies and carry out a detailed study of one mechanism. Clean white plates can be carefully placed in any aquatic ecosystem where water flow is low to observe and possibly quantify the rate of detritus deposition. In small aquaria which have been allowed to grow scum diatoms for a while, investigate rasping in pond snails.

5 Teacher s Guide to The Biology of Seashores, 2001, BioMEDIA ASSOCIATES page 5 Part 2: ADAPTATIONS FOR INTERTIDAL LIFE (continued) Feeding: Predation and the Role of Chemicals Chemical reception is important for orientation of many intertidal predators. Structures with chemical reception capabilities include sea star tube feet, tentacles on the margins of many predators, and specialized organs such as the rhinophores of nudibranchs. Reproductive Strategies Asexual Reproduction Asexual reproduction by splitting in two or budding off new individuals is an important means of building populations and colonial structures of many intertidal organisms. Broadcast Spawning Broadcast spawning, used by a large number of intertidal organisms, leads to fertilization in the sea. Other fertilization strategies and behaviors serve to improve reproductive success of individuals. Proximity to females during egg laying, hermaphroditic mating, and the extendible penises of barnacles are among the strategies that have evolved to improve fertilization and reproduction. Touch is important, especially for sedentary predators such as anemones. Sight is used for finding food by predators such as birds and fish. Budding produces clones or clonal colonies. Clone members are often capable of recognizing whether other individuals are members of their own clone. In aggregating anemones, fierce competition occurs between clones. Spawning of eggs and sperm in sea stars is regulated by a hormone produced in the radial nerves. Production of the hormone is probably influenced by changes in temperature and light. Investigate terrestrial predators (scavengers?) that orient toward prey through chemical perception (such as ants). Compare with intertidal predation. Discuss the advantages and disadvantages of asexual reproduction. Why would an animal reproduce sexually? Investigate the fertilization strategies of pond animals. Sea Urchin Reproduction Echinoderm development demonstrates the complexity of the life cycles of sea shore organisms. Larvae develop from fertilized eggs (zygotes) through a series of cell divisions. Larval stages punctuate the development, as cells, tissues, and organs develop. In echinoderm larvae (as in many other marine larvae) fairly drastic metamorphosis may lead to dramatic rearrangements of the organism, especially as it changes from a free-swimming larva to adult form. It is fairly easy to induce spawning in the lab using sea urchins (spring/summer), sea stars (spring), or sand dollars (fall) in order to follow fertilization and development. Development can be observed into the early feeding stages, or longer if algal cultures can be obtained.

6 Teacher s Guide to The Biology of Seashores, 2001, BioMEDIA ASSOCIATES page 6 Part 2: ADAPTATIONS FOR INTERTIDAL LIFE (continued) The Planktonic Nursery Planktonic Larvae Most intertidal organisms start their lives as larvae that develop in the plankton. Larval release is timed to coincide with plankton blooms. Larva may develop for a time attached to or inside the parent. A comparison of larvae helps to elucidate evolutionary relationships. Alternating Life Cycles An alternation of generations between sexually and asexually reproducing phases is characteristic of most algae and many cnidarians. Plankton samples collected any time of the year, but especially in the spring and summer, will yield a rich assortment of planktonic larvae. Larval form can be so different from adult form that it is often difficult to match a larva to the group of adult animals to which it belongs. Obelia has long been a classic example of a life cycle with alternating generations. Other cnidarians exhibit fascinating variations on this life history. Using diagrams/photos of a number of larvae from different taxonomic groupings, build an evolutionary tree for the groups represented. Investigate to see if pond animals or plants exhibit alternation of generation of generations or similar life cycles. If any are found, what leads to these patterns. PART 3: SEASHORE HABITATS AND INHABITANTS Rocky Shores Intertidal Zonation Rocky seashore environments, especially open coast shores, may exhibit horizontal bands of animal and algae distribution, demonstrating that species survive only in a narrow vertical range of the intertidal habitat. An organism s upper limit is determined by exposure, while predation and competition determine its lower range. High Intertidal Zone The high tide zone includes the areas wet only by wave splash down to the region covered by the sea about percent of the time. Occupants of the high tide zone, (including limpets, acorn barnacles and shore crabs), are dependent on the tidal cycle to provide plankton or to encourage the growth of algae on the surface of rocks. In the lower parts of this zone, the rockweed Fucus supports communities of small animals. Intertidal zonation is present on all sea shores, but distinct banding patterns are viewed only on some shores. Protected rocky shores and muddy bays show fewer signs of zonation patterns than do open coast shores. Local variation in terrain and wave-wash dynamics have a big effect on zonation patterns. Often, other biological factors, such as predation from birds or fish, may also influence distribution patterns even at the upper limits of a species range. A transition between two habitats or ecosystems is called an ecotone. Investigate an ecotone such as a transition between forest and meadow, and compare the species dynamics there to those of the intertidal zone. Isopods make good subjects for looking at how animals might evolve from marine organisms to terrestrial life. Comparative studies of the several species of sowbugs, and if possible, the rock louse, Ligia, can help to elucidate this evolutionary process.

7 Teacher s Guide to The Biology of Seashores, 2001, BioMEDIA ASSOCIATES page 7 PART 3: SEASHORE HABITATS AND INHABITANTS (continued) Mid Intertidal Zone The mid intertidal zone extends from the region covered about 40% of the time on down to the average low tide line, where submergence is about 90%. Bathed more than half of the time in sea water, organisms living here grow well, and there is often a high biomass of mussels, gooseneck barnacles, aggregating anemones, and algae. Low Intertidal Zone The low intertidal zone is the area exposed from about the average low tide on down to that exposed by the most extreme low tide. It is submerged in seawater more than 90% of the time. Sandy Beaches and the Meiofauna Few large invertebrates can tolerate the abrasive conditions of sandy beaches. Mole crabs have strategies to survive and feed in retreating waves. Most intertidal sand beach life is microscopic. A freshwater-shock isolation technique reveals an elaborate fauna of tiny interstitial animals called the meiofauna. At the top of the beach, drift piles support communities that include beach hoppers. Mudflats and Estuaries Muddy bays, estuaries, and eel grass beds are among the most productive habitats known. They are used as breeding or nursery grounds for many species of open water animals such as crabs and fish. Strategies for survival in the mud include using hemoglobin pigments to lock up the limited available oxygen. Feeding by filtering is an important strategy, especially by clams. Docks and Pilings Bathed constantly in sea water, docks are home for communities of filter/suspension feeding animals. Micro-communities are supported by some attached organisms such as the wiry colonies of Obelia. Pilings support communities of organisms, and areinfluenced by tidal conditions. At the lower margin of this zone live predators such as sea stars. The assemblage of organisms living here is more diverse and colorful than other intertidal zone, and includes true marine species as well as abundant algae. A variety of meiofauna isolation techniques have been used over the years, but this simple technique has revolutionized the study of marine meiofauna. Early specimens of the most recently described phylum, Loricifera, were largely collected using this technique. Worms and clams dominate the muddy substrate. The substratum of muddy bays varies considerably, from relatively sandy sediments to thick black ooze that is impossible to walk on. Substrate is critical in determining species distribution and success. Muddy bays support large communities of migrating and resident shorebirds. Docks are excellent places to observe larval settling and succession. A porcelain plate hung from a dock by a stout cord can be raised at intervals to reveal how animals and algae colonize surfaces. Live mussels can be obtained at seafood stores in many cities, even those away from the sea. (The species available is usually the quiet-water bay mussel, but it is generally similar to the outer coast California mussel). Investigate the mussel in the lab (dissections and feeding experiments using artificial seawater?) to develop a picture of the dynamics of the mid intertidal zone. The low tide zone is a window into the benthic marine life of shallow waters that can be seen without diving or snorkeling. Low tide field studies are extremely valuable for developing a biological perspective on animal life, and these can be supplemented with studies carried out in most public aquaria. Using the technique shown in the video, concentrations of marine sandy-beach meiofauna animals are easy to obtain. Investigations of diversity and population density are easily carried out in a laboratory equipped with good microscopes Muddy substrates of all aquatic ecosystems are interesting biologically. Investigate a local aquatic/mud habitat by placing thin layers of the mud in petri dishes examined with the dissecting scope. Floats and logs in lakes are sometimes good locations to investigate communities of suspension feeders. Freshwater sponges and bryozoan colonies are among the animals that may be observed.