Hawaiian Sea Life reading - SOEST(from left): Phylum Echinodermata, Heterocentrotus mammillatus (pencil slate urchin) and Actinopyga mauritiana (speckled sea cucumber); Phylum Chordata

Fall 2008 OCN 201L

©2004 Department of Oceanography, University of Hawai‘i at Manoa

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Hawaiian Sea Life The coastlines surrounding the Hawaiian Islands contain several different marine communities including coral reef flats, sandy beaches, exposed tidepools, and wave-washed rocky shores. Each of these ecosystems hosts a unique combination of organisms, each of which has a niche, or functional role, in its habitat. The animals in these environments are classified into two major groups: invertebrates, or soft-bodied organisms lacking an internal skeleton, and vertebrates, organisms with an internal skeleton. Organisms that share similar features and evolutionary history are further classified into phylum. We will consider 7 of the animal phyla in next week’s lab: Porifera, Cnidaria, Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata (both an invertebrate and vertebrate phylum).

Overview of Hawaiian Marine Phyla Phylum Porifera includes sponges in either encrusting or vase-shaped masses that live on hard substrates. A sponge is a suspension feeder that strains plankton and small food particles from the water using the small pores covering its body. A large sponge may filter 1,500 liters of water each day. Sponges are simple organisms with no circulatory, respiratory, or nervous systems but do have individual digestive cells to process food particles. Sponges contain a network of spicules composed of either silica or calcium carbonate that help deter predators.

(from top left) Phylum Porifera, an encrusting sponge; Phylum Cnidara, Pocillopora meandrina coral; Phylum Cnidara, Zoanthus pacificus polyps; (from bottom left) Phylum Annelida, Eurythoe complanata (fire worm); Phylum Mollusca, Hexabranchus sanguineus, (spanish dancer slug); Phylum Arthropoda, Carpilus maculates crab.

Fall 2008 OCN 201L

©2004 Department of Oceanography, University of Hawai‘i at Manoa

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Organisms in phylum Cnidaria have stinging cells called nematocysts and exhibit radial symmetry, a body form that radiates from a central disc. Cnidarians have two body forms. Jellyfish and portuguese-man-of-wars are examples of the mobile medusa form, while sea anemones and corals are sedentary polyps. Some corals, sea anemones, and zoanthids contain endosymbiotic algae also known as zooxanthellae. The symbiotic relationship between the coral and zooxanthellae is mutualistic because the zooxanthellae photosynthesize to provide oxygen and carbohydrates for the coral, while the coral provides a house for the zooxanthellae as well as the carbon dioxide and nutrients necessary for photosynthesis. Phylum Annelida includes segmented worms of the class Polychaeta, the most abundant marine worms. Polychaetes are often brightly colored and can have bristly projections extending from segments or feather duster tops. Polychates are usually found in the sediment and can produce calcareous tubes that allow only their heads to emerge.

(from left): Phylum Echinodermata, Heterocentrotus mammillatus (pencil slate urchin) and Actinopyga mauritiana (speckled sea cucumber); Phylum Chordata, tunicate. Organisms in phylum Mollusca have a soft-body, internal or external shell, and foot. Common mollusks include snails, bivalves, squid, and octopus. External shells help protect their soft tissue that predators find especially tasty. Those without shells have other adaptations including sea slugs that secrete poison, octopus that change pigmentation for camoflague, or squid that secrete ink to fool their predator while they make a fast escape. Phylum Arthropoda includes an abundance of organisms including crabs, shrimp, lobsters, barnacles, and copepods. Arthropods are characterized by hard exoskeletons that fit so snugly that they must molt their exoskeleton during periods of growth. Arthropods have articulated joints that are able to bend at specific points and allow a full range of motion. Spiny-skinned organisms including sea stars, brittle stars, sea urchins, and sea cucumbers are classified into phylum Echinodermata. Echinoderms have radially symmetric bodies based on five sections, and reside on hard substrates, sandy bottoms, and sediments.

Fall 2008 OCN 201L

©2004 Department of Oceanography, University of Hawai‘i at Manoa

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Phylum Chordata includes several invertebrates as well as all vertebrates. During development, some invertebrates including tunicates (sea squirts) display several features characteristic of vertebrates and are therefore included in this phylum. About 95% of chordates are true vertebrates that possess backbones. Vertebrate chordates present in Hawai‘i include fish, mammals (humpback whale, spinner dolphin, monk seal), reptiles (turtles), and seabirds. The Hawaiian monk seal is an endangered mammal that is found in northwest Hawai‘ian islands and occasionally Kauai and Oahu. The monk seal may travel for up to a month, and searches for undeveloped coastline for breeding. The monk seal, like other seals, can dive as deep as 600 ft for up to 20 minutes! They are able to slow their heart rate from a normal rate or 55-120 beats per minute (bpm) to 4-15 bpm while diving, a physiology known as bradycardia. Why might a slowed heart rate be beneficial to the monk seal?

A female monk seal and pup in the Northwest Hawaiian Islands. Phylum Summary Table: Phylum Characteristics Marine examples Porifera pores, spicules, suspension feeder sponge Cnidaria nematocysts, radial symmetry,

some with endosymbionts coral, jellyfish, sea anemones

Annelida segmented, buried in sediments or hard substrates

polychaetes

Mollusca soft-body, external or internal shell, bilaterally symmetrical, well developed nervous system

snails, bivalves, squid, octopus

Arthropoda hard exoskeleton (molts), articulated joints

crabs, shrimp, lobsters, barnacles, copepods

Echinodermata spiny skin, radial symmetry with 5 sections

sea stars, sea urchins, sea cucumbers

Chordata (invertebrates)

notochord, primitive nervous system sea squirts

Chordata (vertebrates) backbone fish, mammals (whale, dolphin, monk seal), birds, reptiles

Fall 2008 OCN 201L

©2004 Department of Oceanography, University of Hawai‘i at Manoa

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Coral Reef Ecology and Zonation

Diagram modified from Lerman (1986) Marine Biology: Environment, Diversity & Ecology Coral reef ecosystems are the most productive marine environment due to their large diversity of organisms. The physical environment and ecological interactions largely determine the abundance and distribution of organisms on a reef. The shallowest reef zone, the boulder zone, experiences high light, high wave energy and terrestrial run-off. This area is dominated by low coverage of cauliflower coral, and algae overgrowing dead coral skeletons and boulders. Boring sea urchins can often be found in the boulders. The reef bench zone extends from 2-6 m and usually experiences high wave action. A large diversity of organisms including lobe coral, cauliflower coral, rice coral, seaweeds, and shore fish are found here. The moderate light zone extends from 6-25 m and often contains large lobed and columnar finger corals, sea cucumbers and snails as well as butterflyfish and wrasses. In the deep slope zone below 25 m, light is very limited and the coral adapts to this condition with a large plate-like morphology to maximize light energy received while minimizing energy spent on a skeleton. Coral reef communities in Hawai‘i are unique due to their relative young age and geographic isolation. Reef development is generally proportional to age, and since the Hawai‘ian Islands are geologically young, they are less developed than Indo-Pacific reefs. Many Indo-Pacific locations exhibit 300-400 species of coral while Hawaii contains only 40 species. Corals are especially sensitive to changes in their environment and display ‘bleaching’ conditions under stress. In response to extreme changes in temperature, salinity, UV radiation, or toxins, or with onset of disease, corals can expel their zooxanthellae and/or the zooxanthellae decrease their photosynthetic pigments. The expulsion of zooxanthellae results in an overall decrease in coral color. Corals that bleach are not necessarily dead, and many can recover by either taking in a new population of zooxanthellae, or rebuilding their photosynthetic pigments. Hawai‘ian reefs are also subject to a number of anthropogenic, or human-induced, impacts including pollution, over-fishing, and damage by boat anchors.

Reef bench zone Moderate light zone

Deep slope zone

Boulder zone