Marine Science Lecture: afternoon Nectin Adaptations, Pelagic Zones, and Cephalopod Biology
Lab and Field Schedule
Current Lab Focus: The class is working on Labs 1, 2, and 3 simultaneously. Specifically, the afternoon session is dedicated to making observations on zooplankton and phytoplankton (Labs 2 and 3 in the notebook).
Field Trip Planning: * Option discussed: Salt Marsh trip versus staying for a lecture. * Decision: The class opted for a Salt Marsh field trip to find a specific sea anemone (Nematostella vectensis). * Time: Tomorrow from to . * Objective: Hunting for "Stella" (Nematostella).
Lab 1 Requirements: Making observations on the nectonic community of Mobile Bay, including mapping CTD (Conductivity, Temperature, Depth) data provided by Josh Goff.
Definitions of Marine Life and Zones
Nectin Definition: Animals that are capable of counteracting currents and swimming purposefully to different locations.
Broad Classifications: * Pelagic: Organisms living in the water column. * Benthic: Organisms living on the bottom. * Nectin: Pelagic swimmers purposefully moving in any direction. * Plankton: Drifting organisms. * Neuston: Organisms living at the surface film of the water. * Nectobenthos: A classification for organisms that are clearly benthic but can move and swim against currents (e.g., flounder).
Water Column Divisions: * Benthic Zone: The bottom of the ocean, regardless of depth (continental shelf, abyssal plane, or trench). * Pelagic Zone: The entire water column. * Neritic Zone: Pelagic water situated above the continental shelf. * Oceanic Zone: Water off the edge of the continental shelf (open ocean).
Vertical Stratification: * Epipelagic Zone: The sunlight zone, encompassing the entire shelf and the first to of depth. This is the primary focus of the class. * Mesopelagic: The zone below the epipelagic. * Bathypelagic: The deep ocean zone below the mesopelagic. * Abyssopelagic: The deepest parts of the ocean.
Adaptations to Life in the Epipelagic Zone
Environmental Constraints: * Lack of substrate, bottom, or refugia (hiding places). * Difficulty in evading predation and being a predator.
Physical Adaptations: * Speed: Strong selection for being fast. Leads to "torpedo" or streamlined body shapes. * Musculature: Powerful muscles for chasing prey or escaping. * Maneuverability vs. Straight-line Speed: A "cat and mouse" evolutionary game. Larger things often have straight-line speed but less maneuverability.
Coloration Patterns: * Countershading: Darker on the dorsal (top) side and lighter on the ventral (bottom) side. This makes the organism harder to see from both above (blending with the dark depths) and below (blending with the sunlight). * Transparency: Common in the gelatinous planktonic community as a form of camouflage.
Buoyancy Mechanisms: * Swim Bladders: Found in many bony fish. * Fatty Livers: Used by cartilaginous fish (like sharks) lacking swim bladders to maintain lift.
Phylum Mollusca: Class Cephalopoda
Etymology: "Cephalopod" translates literally to "head-foot."
Anatomical Features: * Body Structure: Large head covered in a mantle with feet modified into arms. * Appendages: * Octopuses: Have eight arms and zero tentacles. * Squid: Have eight arms and two longer arms called tentacles (catch tentacles). * Suckers: Used to catch/hold prey and, in the case of octopuses, to wedge themselves into burrows. * Shell: Usually reduced and located within the mantle.
Physiological Adaptations: * Jet Propulsion: Swimming by sucking water into the mantle and shooting it out through the siphon. * Circulatory System: They possess three hearts. * Chromatophores: Colored cells in the skin that contract and expand to change color instantly. Their skin acts as a sensory organ to detect background colors. * Feeding: They possess a beak, which is a modified radula resembling a parrot's beak. * Intelligence: They have large brains and complex vision. Cephalopod eyes are a classic example of convergent evolution, possessing visual capabilities similar to human compound eyes.
Vertebrate Taxonomy and "Fish" Classifications
Taxonomic Reality: "Fish" is not a valid scientific taxonomic category because the group is paraphyletic.
Major Evolutionary Divisions: * Class Agnatha: Jawless fish. Primarily parasites or detritivores (e.g., lampreys and hagfish). Hagfish are known for producing massive amounts of mucus or "slime bombs." * Class Chondrichthyes: Cartilaginous fish, including sharks and rays. They have skeletons made of cartilage and specialized sense organs. * Class Osteichthyes: Bony fish. * Ray-finned fish: Most common modern fishes. * Lobe-finned fish: The group from which terrestrial vertebrates (amphibians, reptiles, birds, mammals) evolved.
Ichthyological Characteristics and Sensory Adaptations
Sensory Organs: * Lateral Lines: Used by all fish to detect disruptions, vibrations, and directionality in the water. * Ampullae of Lorenzini: Found in sharks and rays; these allow the detection of electrical field currents. * Vision: Well-developed eyesight is crucial in the epipelagic sunlight zone ().
Tail Morphology and Speed: * Forked/Caudal Tails: A strong, forked tail (like a tuna) indicates a powerful swimmer built for straight-line speed but often lacking flexibility/maneuverability. * Red Blood Cells: Tuna have high concentrations of red blood cells for endurance, resulting in darker meat.
Lab Procedures: Phytoplankton and Zooplankton Observation
Microscopy Strategy: * Dissecting Scopes: Use these first for larger zooplankton to see movement and behavior. * Compound Microscopes: Use these for smaller phytoplankton on slides.
Identification Targets: * Copepods: Characterized by two long antennae and mandibles. Notes should describe their swimming behavior. * Larval Stages: * Nauplius (Nauplii): General crustacean larval stage. * Zoea: A specific molting stage for crabs. * Mystery Species: Students must identify mystery species from local trays, including various fish and a specific ray.
Case Study: Nematostella vectensis (The Starlet Sea Anemone)
Habitat: The only species of sea anemone in the world that lives in salt marsh habitats.
Morphology: It is a burrowing species. Instead of a well-developed pedal disc, it has a physa for burrowing into soft sediments.
Scientific Importance: * It was the first anemone to have its genome sequenced. * It is a model organism for developmental biology and neurobiology.
Taxonomic and Geologic History: * Native to the East Coast of the United States. * Invasive in England, though it is technically listed as threatened there due to misidentification. * Suwannee Seaway: About to million years ago, an open seaway connected the Northern Gulf of Mexico to the Atlantic. This created a continuous salt marsh habitat until the seaway closed.
Biological Traits: * It does not photosynthesize. * It has separate sexes but can also propagate clonally by splitting in half. * Very small (a few millimeters across) and clear-bodied.
Field Trip Logistics: The Salt Marsh Trip
Sampling Method: Scooping mud into Ziploc containers and covering it with water. The anemones will eventually burrow out of the sediment and show their tentacles on top.
Clothing Requirements: * Long Pants: Necessary to protect legs from Juncus (sharp marsh grass). * Tight Shoes: Shoes must be tied very tightly; otherwise, the thick marsh "muck" will suction them off. Wear shoes that can be ruined.
Odor: The salt marsh environment often has a strong sulfur smell.
Questions & Discussion
Question (Student): "Is that what they stuck to you?"
Response (Instructor): Part of the adaptation involves suckers on both the tentacles and the arms. These are used for catching prey, holding on, and wedging into burrows.
Question (Student): "When they expand is when they change color?"
Response (Instructor): Yes, chromatophores expand to change color and contract quickly.
Question (Student): "Do we need gloves today?"
Response (Instructor): No, gloves are not needed for the plankton microscopy lab today.