Between the tides Marine ecosystems 1 Intertidal Delimited by the highest high tide and the lowest low tides marks The best studied and best-understood by humans Relatively easy to sample compared to other ecosystems Inexpensive Repeatability Unique features and challenges Regularly exposed to the air Organisms must cope with this exposure Permanent action of waves Adaptations to withstand wave action are needed Types of intertidal communities Vertical zonation 1) Hard bottom coasts: rocky shores 2) Soft bottom coast: sandy beaches bottom type matters! Specific pattern of banding: different organisms at different levels is based on the amount of time each part is covered by water Specific organisms dominate each layer US Pacific coast US Atlantic coast Upper: Almost never submerged, mostly affected by wave splash Middle: Covered by water on a regular basis Lower: Submerged most of the time 1
Rocky shores Steep coasts without large amounts of sediments Geologically young coasts Many are present in active margins of the oceans What is the main problem for organisms that live attached to the rocks? Desiccation: Water loss. Animals tend to dry when they are out of water Strategies? 1- Run and hide if you can! Tide pools, places that keep moisture mussels periwinkles 2- Form dense clumps to retain moisture 3- Live permanently in moist areas seaweeds chitons Up to 75% 4- Lose water at low tide and recover it at high tides Up to 90% 5- Clam-up strategy Organisms have a sort of protective covering that can close to hold the water operculum in snails Or they clamp tightly to the rocks in order to reduce water loss How do rains affect the intertidal community? Freshwater is fatal for most marine organisms Rainstorms during low tides may cause sometimes the mass mortality of intertidal organisms What type of feeding strategy is more common? Deposit feeders? Filter feeders? Grazers? Predators? Almost no sediments in Rocky shores, particles can never deposit because of the wave shock Most sessile animals are filter feeders Algae are always present! Grazers are always present too! Always! Can you think of an environment where predators are absent? 2
Coping with the wave shock The ability of organisms to withstand wave shock Determines the diversity of organisms present at a given place Strategies Seaweeds: Anchor to the substrate with holdfasts Are flexible and can go with the flow A compact shape always reduces drag Have specific structures Grow in dense groups Mussels Have byssal threads secreted by a specific gland that allow them to firmly attach to the rocks Limpets and chitons Use their muscular foot like a powerful suction cups Tide pool fish Lack swim bladders so they sink and stay at the bottom Gobies and cling fishes Also have a sort of suction cup Formed by modified pelvic fins Sea anemones Reduce drag By having short body lengths in non sheltered areas 3
Competition: the battle for space Light: always present Oxygen: not a problem either! Nutrients: Plenty of them Constant recirculation of food and organic matter due to wave action Strategies What is the main problem here then, apart of the wave s action and the exposure to the air? To keep the place where you live! All the sessile organisms need to compete for the space (1) Efficient dispersal mechanisms (inter/intra) Allow to be the first to colonize an empty spot Most intertidal organisms disperse via larvae or spores (2) Fast growing and reproduction (inter/intra) Allow to rapidly occupy a new place (3) Have other better adaptations (intra) Determine that some species appear only in specific spots where the dominant species are not present Upper intertidal Saltwater comes only from wave s splash or spray Life is limited by physical factors: air exposure & seawater absence Producers are encrusting organisms Lichens, cyanobacteria, filamentous green and red algae Consumers are mainly grazers Adapted to live almost with NO water Periwinkles and limpets (gastropod mollusks), Sea lice or roaches (isopod crustaceans) Carnivorous predators are occasional Crabs (decapods crustaceans) Snails (gastropod mollusks) Periwinkles 4
Middle intertidal Main problem are the space, wave action, and air exposure Life is limited by a combination of physical and biological factors Predation & competition Physical factors desiccation Biological factors Predation & competition Producers are either encrusting or attached organisms Rockweeds, brown seaweeds, are particularly dominant Fucus, Pelvetia Sea anemone barnacles mussels Consumers are both grazers and carnivorous Barnacles (cirripedian crustaceans) Mussels (bivalve mollusks) Sea anemones (anthozoan cnidarians) Crabs (decapods crustaceans) Snails (gastropod mollusks) Middle intertidal Tide pool fish Sea star (asteroidea echinoderms) Spiny lobsters (decapods crustaceans) upper lower Barnacles 1 Barnacles 2 Mussels Rockweeds 5
Carnivorous predators Regulate the number of sessile organisms & the diversity of the middle intertidal Without predation Only the best competitors survive at each place Diversity is severely reduced Excessive number of predators Reduce diversity as well Lower intertidal Main problem is space Life is limited by biological factors Predation & competition macrocystis Producers are mainly attached organisms Brown, green, and red seaweeds are dominant Sea grasses may be also present Many with floating adaptations to keep blades close to the light Competition for space between seaweeds is more important here egregia Consumers are both grazers and carnivorous Sea anemones (cnidarians) Crabs (crustaceans) Snails (mollusks) Tide pool fish Sea star (echinoderms) Sea urchins (echinoderms) Worms (annelids) 6
Soft bottom shores Wider coasts with large amounts of sediments Always present in passive margins of the oceans Disadvantages Most animals burrow in the sediment To avoid being eaten Or being washed away Advantages Silt and clay sediments remain wet even at low tide No risk of desiccation Kind and size of sediments is one of the most important physical factors 1) Places for attachment 2) Chances for sea grasses and some algae 3) Dissolved O 2 more More unstable Sediments are always shifting Water clarity (more suspended sediments) less Food web in soft bottom shores Producers are mainly phytoplankton Few places with seagrasses (large producers) Consumers depend on organic matter: detritus: organic debris created by disintegration of animals or plants Abundance of deposit and filter feeders The amount present depend on the grain size of the sediments The finer and better sorted The more organic matter Muddy bottoms More organic matter to decay But less oxygen available Are anoxic below the upper layer 7
Vertical zonation in soft bottom shores May not be obvious but also exists Especially in sandy beaches Upper intertidal Crabs (detritus feeders) Birds and others (predators) Some crustaceans Middle intertidal Worms Mollusks Lower intertidal Crustaceans Echinoderms Mollusks 8