Reproduction at Snug Harbor


Asexual Reproduction

Techniques of asexual reproduction at Cobble Beach include fragmentation and binary fission. Sponges like Ophlitaspongia pennata and Halichondria sp. can regenerate another sponge from a broken-off fragment. Urticina crassicornis, a sea anemone, can produce a clone by binary fission. Both organisms also reproduce sexually by spawning.

The sponge Halichondria and the anemone Urticina

Brooding

Amphipholis squamata, a brittle star, carries its eggs around in the bursae on the bases of its arms, which develop directly into juvenile brittle stars. This species of brittle star was seen pnly near the waterline on the more sheltered beach of Mitchell Bay.

On Cobble Beach one can find at least two distinguishable species of Henricia--one is small with orange arm tips , the other is blood red and relatively large (see photos to right) --although the taxonomy for these species complexes has not been worked out.  The smaller species has direct development and broods its young on the oral side of its body.  The larger-bodied species has more typical free spawning and indirect development via a planktonic larva. 

Indirect development: Free-swimming larvae

Many species in various phyla found at Snug Harbor have planktonic larval stages. Crabs including Hemigrapsus nudus and Petrolisthes sp. mate, and the female broods eggs. The eggs hatch into free-swimming nauplius larvae, which will develop into crab zoea, and finally into megalopae, which is the post-larval stage.

The larvae of Terebratalia transversa (Ph. Brachiopoda) swim using cilia.  After the larva starts production of its shell, it settles and attaches with the pedicle, a fleshy stalk on the exterior end the extends from the hinge between the shell valves. Barnacles Balanus and Semibalanus have a long penis, in which they use to fertilize neighboring barnacles. They then release nauplius larvae, which later become cyprid larvae before settling on a substrate. Membranipora membranacea (Ph. Bryozoa) has a feeding cyphonautes larva.

The sea cucumber, Cucumaria miniata, produces an auricularia larva, while sea stars like Evasterias sp. produce a bipinnaria larva.  Both larval types are characterized by a gel-filled, bilaterally symmetric body, a complete digestive tract, and prominent ciliated bands used in swimming and particle capture.

brittle droeb

The sea urchin Strongylocentrotus droebachiensis and the brittle star Ophiopholis aculaeata both have a pluteus larval form. The sea urchin larva is called an echinopluteus, and the brittle star larva is an ophiopluteus. This form of development of Ophiopholis, more typical of brittlestars, is a major contrast to the direct development of the brooding Amphipholis.


Brooding in egg masses or capsules

All of the egg masses we found at Snug Harbor were in the lower intertidal, in the first 2 or 3 quadrats. They all belonged to gastropods. Lacuna vincta egg masses are small (about 3 mm in diameter), yellow and donut-shaped. These were found attached to different kinds of algae in the first zone, at the waterline.

To the left, Nucella lamellosa is pictured laying eggs on the side of a large rock in the second intertidal zone.

The small dorid nudibranch Rostanga pulchra derives its color from feeding on the bright orange sponge Ophlitaspongia pennata (see the nearly indistinguishable orange blob atop the sponge colony to the left).  To add insult to injury, the nudibranch then lays its coiled ribbon egg mass on top of the sponge, thereby gaining cryptic protection from this association.

 

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