Transcript Slide 1
Benthic Community Types: They are categorized by their depth zone, primary producers, and/or bottom type (e.g.: rocky intertidal, mud flat, sandy beach, kelp forest, seagrass meadow, coral reef, mangrove forest, salt marsh, deep-sea floor, and hydrothermal vent). Summary of some highly productive benthic communities: Community Latitude Bottom Depth zone Mangrove tropics soft intertidal Salt Marsh temperate soft intertidal Rocky Intertidal both hard intertidal Seagrass both soft sublittoral Coral Reef tropical hard sublittoral Kelp Forest temperate hard sublittoral Primary Production & Benthic Communities: • Phytoplankton • Symbionts of animals • Benthic microalgae (unicellular) • Vascular plants • Non-vascular plants; macroalgae (multicellular) Primary Producers & Benthic Communities: The contribution of phytoplankton productivity to benthic communities is variable. Can be very important to shallow sessile filter feeders like clams and oysters. However, after extensive decomposition during sinking deep, its contribution is exceptionally low in the deep-sea. Deep water sea cucumber (family Holothuroidea) Primary Producers of Benthic Communities: In hydrothermal vent communities of the mid-ocean ridge system there are animals in symbiosis with another type of primary producer - autotrophic bacteria that are chemosynthetic. The animal actually feeds off the bacteria inside them. Primary Producers of Benthic Communities: In shallow benthic habitats animals are also found in symbiosis with autotrophs, but these symbionts are photosynthetic algae, called zooxanthellae. Hard (hermatypic) corals are prime examples of this. The coral polyp gets food from both the symbionts and the capture of zooplankton via their tentacles. Nematocysts (“Stinging Cells”) * All Cnidarians (coral, sea-jellies, anemones, hydrozoans) have them. * Strong toxins that paralyze prey from zooplankton to small fish. Why not Nemo? Primary Producers of Benthic Communities: In most shallow sunlit benthic communities may receive a large amount of primary production from free-living benthic unicellular algae (e.g. diatoms). Benthic grazers like snails feed on the film of benthic algae on this mud/sand surface. Primary Producers & Benthic Communities: There are also multicellular plants in intertidal (littoral) and sublittoral benthic communities. Mangrove trees and shrubs are unique to the tropics. Salt marshes are mostly in estuaries at temperate latitudes. These marshes and their estuaries are some of the most productive and species rich marine ecosystems. Unlike these intertidal vascular plants, seagrass is found in the sunlit sublittoral waters of both tropical and temperate latitudes. These vascular plants are not grasses, but flowers. Mangrove forest of intertidal tropics. Vascular marine plants (trees and shrubs) specially adapted to tolerate low oxygen sediments which result from tidal inundation. Also adapted to salt water. High productivity of these trees is supplied to marine organisms in the form of detritus. Mangrove slow wave energy, facilitating the accumulation (accretion) of sediments. Serve as an excellent habitat for rearing juvenile fish and crustaceans. Health of coral reefs is linked to health of mangrove forests by trapping excess sediments and nutrients from rivers and providing cover for many reef fish. Salt-Marsh in an Estuary Intertidal Zone of Temperate Latitudes Vascular plants (grasses and herbs) adapted to salty and low oxygen sediments. Like mangrove of tropics, they are extremely productive and supply energy to the estuary ecosystem in the form of detritus. Salt marshes also trap sediments and nutrients. Serve as an excellent habitat for larvae and rearing juvenile fish and crustaceans. Also provide critical habitat for migratory waterfowl. Like mangroves, they are endangered by development and pollution. Seagrasses are typically found in shallow calm sublittoral depth. They are vascular flowering plants, unrelated to grasses on land. Macroalgae (“Seaweeds”) • Non-vascular plants; no vein-like tissues. • Extremely productive; yet a minor amount of global biomass when compared to all phytoplankton. • Classified by their accessory pigments: – Green Algae = Chlorophyta – Brown Algae = Phaeophyta – Red Algae = Rhodophyta Chlorophyta (green algae) Found shallow and intertidal. Some are calcareous. Ulva spp. and others are indicators of nutrient rich environments Phaeophyta (brown algea) Kelp forest are often on rocky coasts with nutrient upwelling and high wave energy; some species can reach 40 m long! Macrocystis sp. Kelp Forests: Like terrestrial forests in that there are layers, or strata. Recall the role of sea otters as keystone predators. Rocky Intertidal Note the macroalgae covers rocks and a kelp forest is just offshore. These are very resilient communities well adapted to conditions of high wave energy and tidal exposure (desiccation). Abundant and accessible supply of phytoplankton and detritus, as well as nutrients and sunlight, support a species rich community. Rhodophytes (red algea) Found deep. Some species are encrusting, helping to cement reefs together. Coral reefs Structured on limestone produced by calcareous algae and hard (hermatypic) corals; the community is rich in animals and plants. In a pristine state, these are very stable ecosystems having high species diversity and characterized by extreme competition for food, territory, and reproductive opportunities. Hard corals are very susceptible to damage due to low tolerance range for light, temperature, nutrient, and salinity conditions. Where you see mangrove in the intertidal there is seagrass and coral reef in the sublittoral. Where you see Kelp forest in the sublittoral, the wave energy is too high and substrate too rocky for seagrass; the intertidal is usually also rocky. Areas without kelp or mangrove may have salt marsh in the intertidal and seagrass in the sublittoral.