Reproduction at Eagle Cove

Reproduction by invertebrates at Eagle Cove runs the gamut from free spawning of gametes followed by a planktonic larval stage, to asexual clonal fission in anemones, to parthenogenesis, to specialized epitokous stages in nereid polychaetes, to brooding that is typical of crustaceans.  Here are a few highlights of reproduction... the Sandy Beach the Rocky Promontory the Cobble Beach
Who am I and how do I reproduce?
Who spawned all these sperm?
Who brooded all these young?

Sandy Beach Reproduction

At the sandy beach, a surprising array of taxa with small body forms--including copepods, nematodes, gastrotrichs, polychaetes, cnidarians, and cladocerans--live "interstitially" between sand grains. How do these species reproduce in an environment that seems inhospitable for reproduction?  Here are just a few examples...


These small, worm-shaped animals go through cycles of parthenogenesis, a form of asexual reproduction where an unfertilized egg develops into a new individual.  This same individual can also reproduce sexually when conditions change and food is less plentiful.  In this way, gastrotrichs may be able to take advantage of good conditions by rapidly reproducing through parthenogenesis and yet ensure high levels of genetic diversity among offspring when conditions deteriorate.

gastrotrich collected from sand

an interstitial copepod brooding embryos

a mysid shrimp

Various Crustaceans

Most crustaceans found in the sand have special pouches in which they can brood young. Interstitial cladocerans ("water fleas") typically reproduce by parthenogenesis (like gastrotrichs) and brooding. The young are then released just before the mother molts. Also like the gastrotrichs, cladocerans can combine asexual amplification with sexual reproduction.

Copepods, another type of crustacean that is abundant in the sandy beach, are strictly sexual reproducers. They also keep their embryos in specialized brood sacs.

One can find other brooding crustaceans, such as mysids ("opossum" shrimps) and cumaceans, at the sandy beach by sieving the uppermost layer of sand with a fine net.  Mysid shrimps and cumaceans, as well as closely related isopods and amphipods, have a brood chamber on their thorax (called a marsupium) where their eggs develop.   After a few days or even up to months of development, the young hatch out of as fully formed larvae.

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Rocky Promontory Reproduction

Different types of reproduction are often associated with particular microhabitats.  Here we describe invertebrate reproduction in three distinct areas (the high intertidal; the mid-intertidal/tidepools & crevices; and the low intertidal- Phyllospadix zone) that are interesting, important to understanding the community, and just plain cool!



Conspicuous members of the rocky promontory, especially at higher tidal heights, are the sexually-reproducing barnacles. Although barnacles remain fixed in place throughout their lives, they manage to fertilize internally by copulation with close neighbors. Individuals (all hermaphrodites) extend a relatively long penis and deposit spermatophores into the mantle cavities of close neighbors, where fertilization takes place.  After fertilization, eggs are brooded and later released as nauplii larvae that can spend weeks or months in the plankton. The nauplii larvae metamorphose into cyprid larvae, which search for a good settlement site. Upon settlement, the cyprid will attach itself permanently to the rocky substrate and spend its life kicking its legs into the water to feed .

high barnacle density in a quadrat


Molluscs of the mid-intertidal have diverse modes of reproduction. Chitons (such as Katharina tunicata) are typically free-spawners, releasing large numbers of gametes (sperm and eggs) into the water column. Sexes are separate, so that reproduction is most effective when individuals spawn in close proximity.
katharina sperm
Katharina tunicata
and its sperm
egg capsules
Nucella egg mass between Semibalanus barnacles

Some gastropods, including snails in the genus Nucella, lay benthic egg capsules. These snails' larvae develop completely inside the egg capsules and then hatch out as fully-formed but tiny Nucella juveniles.

Other organisms found in this habitat have not one, but two modes of reproduction.  The sea anemone Anthopleura elegantissima can reproduce repeatedly by asexual fissioning, where an individual will dive itself in two. The same anemone can also reproduce sexually by free-spawning, which results in pelagic, feeding planula larvae that disperse much farther than a fissioned clone. Sea anemones like A. elegantissima often form large mats of individuals, called clones, in mid-intertidal pools and crevices that stay wet at low tide.  

Anthopluera elegantissima
clone in a crevice

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During the very lowest tides, one can find at the base of the rocky promontory clumps of the eelgrass Phyllospadix. Detritus and sediment accumulates in the roots of Phyllospadix, creating a unique habitat that harbors a variety of polychaetes worms (we counted 10 different polychaetes families in our quadrats), grazing snails, and juvenile crabs. Below are two examples of reproductive modes for invertebrates in our sample.

Benthic polychaete worms of the family Nereidae undergo a life-history transformation of the adult body into a stage called an epitoke.  Epitokes are sexually mature worms that become highly specialized for swimming and releasing gametes into the water column.  Spawning times are usually highly synchronized within species to improve chances for successful fertilization.
Worms of the family Lumbrinaridae are also abundant in the eelgrass. Unlike the nereids, these worms do not form a specialized stage and instead deposit benthic eggs, which are brooded and may produce crawl-away juveniles that resemble adult worms.

Head of a nereid epitoke.  Notice the paddle-like parapodia modified for swimming.
Mmmm...Donuts - a bowl full of L. vincta egg masses

Two very similar grazing snails, Lacuna vincta and Lacuna variegata, are very conspicuous and abundant on Phyllospadix .  One way to tell the two species apart is to look at the egg masses that they deposit.  L. vincta's egg masses are donut shaped (with a hole in the middle), while L. variegata's, although circular in shape, have a less distinctive hole.

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Cobble Beach Reproduction

Most of the invertebrates found in the cobble beach habitat are strictly sexual-reproducers, and the majority of these are crustacean brooders.  (Exceptions to this pattern include some free-spawning limpets, such as Lottia scutum ).

Idotea wosnesenskii female with hatched juveniles

Isopods and amphipods are both abundant under the loose cobble, and each have marsupium for brooding young.  In the photo to the left, the young isopods being brooded, and perhaps released prematurely upon handling, are visible near the mother.
Shore crabs (Hemigrapsus sp.), porcelain crabs (Petrolisthes sp.), and hermit crabs (Pagarus sp.) also brood their eggs, but they release free-swimming larval stages called zoea. In the plankton, the zoea increase their size by feeding and molting.  As they become ready to settle, they molt into a post-larval stage called a megalopa.  As you can see from the picture, megalopa look similar to a little crab with a prominent abdomen, which is reduced and tucked under the cephalothorax in adults. 

megalopa larva of Hemigrapsus sp.


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