Pelagic Zone Summary

1. Pelagic Zone Summary • Pelagic zone is a three dimensional environment with no structure to provide shelter or landmarks for orientation • Epipelagic organisms often possess great speed and navigational abilities, counter-shading camouflage and structures that improve buoyancy and aid swimming • They also grow rapidly and often migrate long distances • Mesopelagic species often vertically migrate daily, and migrators are usually better muscled, can withstand large temperature changes and possess adaptation that aid buoyancy.

2. Pelagic Zone Summary • Oxygen minimum layer selects for reduced oxygen consumption with depth, reduced athleticism and high oxygen binding ability in mesopelagic fishes • Mesopelagic fishes often have large mouths, counter-shading camouflage, large eyes and use bioluminescence to find mates, attract prey, and escape predators • Deep-sea pelagic fish are often small with reduced eyes, large mouths and are often hermaphroditic or have parasitic males • Deep-sea benthic fish are often muscular, with reduced eyes, big mouths and poor swimming ability. They are relatively large and long-lived (K-selected).

3. Coral Reef Summary • Zooxanthellae are dinoflagellate mutualists that live in the gastrodermis of hermathypic (reef building) corals • Hard corals use zooxanthellae during the day and filter feed at night, while soft corals are obligate filter feeders. • Hermatypic corals with small polyps rely heavily on zooxanthellae for nutrition, while corals with large polyps rely more on filter feeding • Corals reproduce asexually and sexually by mass spawning that produces planula larvae

4. Coral Reef Summary • Hermatypic corals require sunlight, clear water and warm temperatures (min of 20 degrees C) • Pacific coral diversity is much greater than in the Atlantic • Three types of reefs are: fringing, barrier and atolls • Reefs have separate zones, including the fore reef (often with a spur and groove zone), the reef crest (sometimes with an algal ridge) and the back reef

5. Coral Reef Summary • Branching corals occur in shallow, wave swept areas and massive, foliaceous and plating corals in deep water • Competition for space can be intense and slower growing corals are often more aggressive competitors for space than faster growing corals. • Corals use mesenterial filaments, sweeper tentacles and immunological defenses against other corals • Algae can often outcompete corals for space, if grazers are not present to control algae

6. Coral Reef Summary • Predation on corals can be intense, and much skeletal material can be abraded by grazers • Connectivity between coral reefs and adjacent seagrass meadows and mangrove forests is often high, with many animals using all these habitats • Cold water (ahermatypic) corals occur globally and support abundant fish and invertebrate life

7. Coral Reef Summary • Biological interactions are intense on reefs. and there are many examples of mutualisms • Many animals possess antipredatory adaptations • Many organisms abrade the coral skeleton to produce tons of coral sand every year. The net balance between coral reef growth and erosion is often small • Among human threats, herbivore removal, nutrient enrichment and disease are some of the most important

8. Mangrove Forests

9. Mangrove Forests • Found in coastal areas all over the tropics • Primarily in brackish water • salty and fresh mix • Cover approximately 22 million hectares in tropical and subtropical coasts, and replace salt marshes in the tropics

10. Ecosystem Functions & Threats • Serve as a buffer between sea and land • Lessen impact of intense storms • Reduce erosion and increase sedimentation • Serve as important coastal pioneer species • Act as basis for a complex, biologically diverse, and productive ecosystem • Increasingly threatened • Human development is most intense along coasts

11. Mangroves • Not a natural taxonomic group • Convergence among several groups • Possibly 16 convergent events • Based on physiological attributes • 54 species total world-wide • 16 Families • Principally: Avicenniaceae & Rhizophoraceae • These two families include 25 spp. • 20 Genera

12. Mangrove Location • Found: tropical areas only • Within the 20ºC isocline • More southerly on East side of continents • Due to southward moving warm Equatorial currents there James A. Danoff-Burg, Columbia University, jd363@columbia.edu

13. U.S. Mangrove Biogeography • Mangroves around Gulf of Mexico • Near northern limit of distribution • Occur with salt marshes • Florida has just 3 species, while Indo-Pacific has 30-40 species

14. Black Mangroves on the Chandeleur Islands

15. Terminology • Mangal • Community of organisms in the mangrove habitat; also mangrove forest or swamp • Mangrove • Trees that flourish in the mangal • Pneumatophore • Vertical root structures for air exchange • Lenticels - tiny pores for air exchange • Aerenchyma – tissue for air storage and transport

16. Characteristics of Mangal • Inundation with tides • Increasing salinity towards ocean • Sandy clay soil • Nutrient poor • Nitrogen & Phosphorus are limiting • Can limit mangrove growth. Best growth near river mouths (Why?) • Organic nutrients deposited via siltation • Fresh water streams & down-shore currents • Most all are of terrestrial origin • In sum: Mangal is a harsh place to live

17. Mangrove Adaptations • Salt tolerance • Sequester salt in tissue (bark, stem, root) • Secrete salt through leaves • Exclusion by negative hydrostatic pressure • Frequent inundation • Aerenchyma tissue & aerial roots for dealing with soils low in oxygen; hypoxia or anoxia

18. Mangrove Consequences of Adaptations • Greater root mass • Relative to rest of plant & relative to non-mangrove species • For water exchange & air exchange • Lower growth rates • Consequence of salt & air exchange • Tradeoff between salt tolerance & frequent inundation • Can adapt for one or other, not both

19. U. S Mangrove Zonation Pattern

20. Red Mangroves(Rhizophora mangle) • Seaward zone dominated by Red mangrove - prop roots stabilize trees and are sediment traps and “ land builders”

23. Rhizophora mangle: RED MANGROVE

24. Red Mangrove Understory

25. Black Mangroves(Avicennia germinans) • possess pneumatophores - specialized root extensions that penetrate from the sediments to the atmosphere ( allow plant to respire in waterlogged, anoxic sediments) • Most cold tolerant • Inshore of red mangroves • specialized glands to excrete salt

26. Avicennia germinans: BLACK MANGROVE

27. Black Mangroves Pneumatophores

28. SALT ON AVICENNIA LEAF

29. White Mangroves(Laguncularia racemosa)

30. White Mangroves(Laguncularia racemosa) • The base of its leaves have two salt-excreting glands which allow it to get rid of excess salt. • All mangroves have trouble with cold weather and freezes, but the white mangrove is the least cold tolerant of the three common U.S. species

31. Salt glands on Laguncularia leaves

32. Conocarpus erectus: BUTTONWOOD

33. Costs of High Salt Tolerance • Roots take up water less freely • Mangroves grow much slower than other plants • Nutrients can be limiting, and mangroves near river mouths grow faster than those away from nutrient sources

34. Reproduction • Pollination by wind or insects and birds • Propagules • Seeds remain on tree for a period of time • Seedling dispersed by waves • Vivipary. (e.g., red mangrove Rhizophora)

35. Red mangrove seeds (propagules) germinate on the tree. When they drop from the tree they can float for up to a year. • Propagules are eventually carried by the currents until they reach shallow water where the root end touches bottom and sends out roots and begins to form a new tree.

36. Propagules red white black

37. Associated Organisms

38. Bacteria/fungi: initial litter breakdown Microalgae: limited production Macroalgae: hi diversity/biomass Zooplankton: hi abundance/diversity; holoplankton- copepods. meroplankton-70% of total zooplankton. Epifauna/epibionts: sponges, hydroids, etc.-mutualism w/ rootlets Infauna: sediments: great diversity Crustacea: especially important for juvenile shrimp Molluscs: bivalves and gastropods: detritus breakdownand fecal deposits Fauna and Flora

39. Fish: 260 spp. in Vietnam; up to 20 g/m2 biomass; serves as critical “nursery” habitat for seagrass /coral reef spp. Reptiles: crocs, gators, turtles, lizards, snakes Amphibians: 4 species of marine frogs Birds: migratory passerines: forage/rest: waders/water birds: nest/rest Mammals: primates live in Indo-Pacific mangrove forests Fauna and Flora (2)

40. Roles of Mangroves • Roots are 3-D substratum for invertebrates • Basis of detritus food web – leaf fall occurs year round, greater in rainy season • 39% flushed to downstream bays, lagoons and estuaries • 60% of leaf litter consumed by detrivores

41. Consumers that positively affect mangroves • When present, burrowing crabs (ex. fiddlers) lead to increased production rates and growth. Burrows aerate the sediments reducing the build up of H2S (inhibits plant health and root biomass) • Oysters on roots add nutrients by depositing fecal material on the sediments

42. Consumers that negatively affect mangroves • Burrowing isopod – decreases root growth rate and production rate (50%) • Barnacles – settle on surface and decrease root and production rates • Crab – seedling predation. Australian zonation pattern is more a function of the crab species that feed on the seedlings than on the physiological tolerance or competition

43. Community Structure Previously thought to be supported predominantly by detrital food chains

44. Litterfall from Rhizophora

45. Litter and Detritus Detritus feeders

46. Peat Production • Low wave energy, depositional environments • Primarily root material • May be several meters thick

47. Odum (1970) • Conducted study in the Florida Keys and Everglades. • Examined gut contents (>10,000 organisms; 120 species) • Concluded that detritus was the major energy source for mangrove community consumers

48. From Detritus to Detritus

49. And Not Only Leaves

50. Odum (1970) Revised • Since then studies have examined stable isotope ratios (C, N and S) as a way of tracing food source. This technique that allows the identity of the source of energy ingested during the lifetime of the organism • Algae have different ratios than vascular plants. It has been found that algal carbon is a much more important source of energy than Odum (1970) had concluded. Direct herbivory is also more common that Odum concluded