Seagrasses

Seagrasses

Jonathan Lowrie

Walk into a local fish store, and take a peek at the tanks.  You would see a variety of freshwater fish, plants, saltwater fish, corals, and inverts, supplies, etc.  But no saltwater plants.  You might find a bag of Caulerpa, most likely some excess from a local hobbyist who traded it in for a new fish. The freshwater hobby abounds with diversity in the plant arena.  In fact, veteran freshwater hobbyist consider a well-planted biome to be the saltless reef equivalent.  This seems to be true, as my planted freshwater tank is full of a diverse array of invertebrate life, as well as fish.  But for those of us with saltwater aquariums as well, don’t despair.  Plants too live in the ocean.

Seagrasses are the sole marine representatives of the angiospermae family of plants.  All seagrasses belong to order Helobnidae, and are in either family Potomogetonaceae, or family Hydrocharitaceae.  Currently, there are 58 species of seagrasses recognized.  The great land down-under, Australia, is home to over half, 30, of the species.  These species belong to only 12 genera.  Grasses that could tolerate the high salt environment and the rigors of ocean life have been around for many millions of years.  Fossil records indicate that early seagrasses were abundant in the Cretaceous period, and even before around the ancient Tethys Sea.  Geological history and archaeological history show that the habitat once occupied by seagrasses has been declining the past 50 million years. Rather than being early ancestors of terrestrial plants, seagrasses were thought be a migration back to the sea by terrestrial plants. 

Seagrasses spend the majority of their existence submerged, although they may be exposed to air with tidal changes.  Their flowers, when produced, are pollinated underwater.  They remain anchored to the substrate via a network of underground root/rhizomes.  Because they are photosynthetic, they tend to be found in shallow water, like coastal areas, salt marshes, estuaries, and in the tropics, associated with mangrove forests.

Seagrasses are unique plants, adapted to live entirely beneath the water.  However, they share many characteristics with their terrestrial cousins the grasses and flowering plants, or angiosperms.  As true vascular plants, they utilize the rhizome to obtain nutrients in the sediment, and use the blades and sunlight for photosynthesis.  Most of these grasses are located in soft, silty sediments, but some species like Phyllospadix do attach to rocks. This adaptation back to the saline environment involves some complex physiological adaptations and anatomical features to allow for a submerged lifestyle. 

As fully aquatic plants, they blades of the grasses must be buoyant to catch the suns light.  They have single layer of tissue (cholorphyllous) called the epidermis, below which is a thick colorless layer with large air canals running the length of the blade.  In the sea, food sources via light may be limited, because of silty conditions, so these plants utilize the rhizome, the large submerged root as a source of nutrient.  Like many plants- potatoes for example, seagrasses store starches in their rhizome. The roots also contain root hairs, which allow for absorption of nutrients from the substrate.  When they flower, the do so underwater.  And the pollination also occurs underwater.  With sexual reproduction, many seeds are produced and are spread via water currents.  Seagrasses may also reproduce asexually, using the rhizome to extend new blades out along the seafloor. 

As aquarists why should we even care about seagrass?  Simply because they form some of the most biologically productive habitats in the world.  They perform a vital function in the physical and biological relationships between plants and animals.  Seagrass meadows provide a nutrient source for fish, waterfowl and other wildlife.  The epiphytic communities living upon the blades of seagrasses provide a rich nutrient source for many other species, as well as a nursery ground for thousands of species. These nursery meadows provide protection from predators for juvenile fish, shrimp, crab and other animals.  They also serve as a major contributor of organic material for nutrient recycling in estuarine waters.  And dense crops of grasses help prevent soil erosion and stabilize sediment loss via their dense root system.

Widespread and dramatic changes to the terrestrial ecosystem often bring corresponding changes to the human populations which have to depend on this natural resource as a means of food and fuel.  In the past decades, increases in human populations and the closer pairing of man and the infringement on the ecosystem have impacted the balance of the ecosystem.  These changes are most noticed not in the loss of a few acres of seagrass, but in the change to the commercial fisheries community.  Because of the destruction of habitat, and the fact that many seagrasses now live only in protected areas, they have been tough to acquire for the hobby.

Some of the best seagrasses for the home aquarium are now available through limited channels.  Turtle grass, Thalassia testudinum is a grass that colonizes the deeper waters of many regions.  It can tolerate higher salinities, and is quite tolerant of salinity flux.  Eelgrass, Zostera marina is another coastal grass. Its blades are considerably thinner, and it appears as a much more wiry grass. Syringodium filiforme is yet another species that can make it into the hobby.  As for lighting, these all like high intensity light.  I have kept them all successfully in shallow tanks under 2 48-inch gro lux or vitalights.  I have found they do best with natural sunlight, or compact fluorescent lighting.  They have a constant growth cycle, and look healthy.

The most crucial aspect to success with seagrasses in the home aquarium has to do with transplantation.  These grasses utilize their roots for nourishment, and stability. The rhizomes are also covered with fragile root hairs, and if these are severely damaged or torn, the acclimatization of the grass to the aquarium can be rough.  As with all plants that utilize roots, seagrasses have root tips with an apical meristem.  This region contains some undifferentiated cells and a high concentration of hormones.  If at all possible, make sure you plant grasses with the apical portion of the rhizome intact.  This will facilitate new shoots to grow in your tank.  I have found that the transport of these grasses should be semi- wet.  If the rhizomes were collected with the natural sediments, then these should be packed in wet newspaper and transported that way.  This will also ‘seed’ the tank with the associated fauna.

Besides creating habitat and providing décor for the lagoon system, seagrasses also play a role in nutrient conversion.  In nature, seagrasses are able to take light energy and store it as sugars starches, and fibers many grazers take advantage of this source of nutrients.  Since they also uptake nutrients from the sediment, they can provide a form of nutrient export and conversion.  In a closed system, they grasses will also provide a food source to the tank animals.  And they will also uptake nutrients from their root structures.  As for significant nutrient uptake in a closed system, you will have to look elsewhere.  Much like mangroves, seagrasses do uptake primary nitrogenous wastes from the sediment and water, but not in the quantities needed to perform sole denitrification in an aquarium.  Of all the algaes that could accomplish this task only the fast growing turf algaes have the growth needed to uptake the vast quantities of nutrients produced in a typical reef.

Seagrasses are gaining popularity with home aquarists, and a few facilities have begun to cultivate them for sale.  Not only is this beneficial for the natural grass beds, but it allows for a grass that is already adapted to typical lighting in an aquarium, and the mixture of sands and gravels commonly used in today’s aquariums.  Of course, not all systems are candidates for seagrasses.  If you have a reef crest tank, with many Acropidae species, then you would not find any seagrasses associated with this habitat.  But if you have a more lagoonal, or reef trough type of habitat, with corals that require slower currents, then seagrasses would make an excellent addition to your captive eco-system.

Something Fishy- Off to the (sea)horse races

Off to the (sea)horse races

It is always amazing to see someone's expression when they first 'meet' a seahorse in person.  One of the most common questions I get is ' is this real?'.  For which I reply 'absolutely!'.

Seahorses are actually fish, contrary to popular myth.  Their closest relative is the elongated pipefish, and both seahorses and pipefish belong to the sygnathiformes family of fish.  If you look closely at the mouth of both a seahorse and pipefish, you will see the similarities.

Seahorses come in many shapes, sizes and colors  Some like the Hippocampus rosterae, the Florida Dwarf seahorse are only 3/4 of an inch long as adults  Yet others like the Brazilian seahorse, Hippocampus reidi can be almost 16 inches.  Some are yellow, others red, they might be black, or even stripped.  None can match the myriad of shape and color the searagons of Australia posses.  These seahorses have adpated to life in the weedy seagrasses and alages and look much like a scrap of sargassum alage than any resemblence to a fish.  These beautiful and majectic creatures are considered a rarity and are not common, and should best be enjoyed in public aquairums or SCUBA diving.

Some seahorses can be kept in captivity, although only experience aquairists with the time and experience should try.  You see, seahorses require regular feedings of specialized foods.  Mnay will be rather finicky and eat only live Artemia (brine shrimp), Mysis ( a type of small shrimp), or baby fry (from guppies or Mollies).  Most aquairsts will only doom themselves to endless frustartion, an their seahorse to detah by keeping them in aquairua.  If I have not yet convinced you, consider the fact that that many seahorse must be fed these foods live.  So you must have a culture of Artemia, and / or Mysis handy for multiple daily feedings.  Eventually with patience and a bit of luck, you can train the seahorses to take frozen prepared foods. But never anticipate this when you purchase a seahorse.  Besides finiscky water requirements, seahorses require specialized aquaria.  They are easily blown away by powerful currents,and can be sucked into many filters.  Because they are docile, and slow moving fish, they are easily bullied by fish such as Damsels, clownfish and tangs.  Even a sea anemone can prove deadly to un unsuspecting seahorse.  With other faster and hungry tankmates, its easy to see why many seahorses stave to death in healthy reef tanks.

If you feel you have the skill and time necessary to try these magnificent creatures, then look for a captive bred specimen.  Captive bred seahorses will be more tolerant of the foods avaiabl to you, and you know you did not take any from the environment.  Seahorses typically live for only 3 years, and don't repoduce until they are 1 year of age.  With all the 'dried; seahorses for sale, and the live one imported, they are declining in nature.  So as responsible hobbiyists we should select those that have been bred in casptive aquairums.  If you are doing it all properly- you should be rewared with regular broods of babies in your home tank.

One of the best specimens to keep in captivity is Hippocampus kuda.  It has many common names, such as lined seahorse, Pacific seahorse, and many others.  They reach an adult size of 10 inches from nose to tail.  In nature they will assume various color morphs ranging from black, brown, yellow to even red.  H. kuda comes from the Indo-Pacific ocean area and is found among the coral skeletons and seaweeds. They have an affinity for the algae Caulerpa.  As fish, they do have a backbone and are vertebrates, even though close observation may not suggest this.

Seahorses are not very active fish, so must be kept in an aquarium that has a light to moderate water flow.  We never want to make them cling to their coral branch for fear of being blasted across the tank!  Live rock is a must, as is a dee sand bed.  Seahorses will always enjoy the extra meal provided by copepods, and gammarus found in good live rock and healthy sand beds.  Another factor to consider is filtration.  Seahorses do not tolerate poor water quality, so they must be housed in a stable, well establsihed system, and are definitely NOT suitable for new tanks.  One of the problems with smaller seashorses is that they mistake small air bubbles for food. So any skimmers or pumps that produce air bubbles must be checked before that water returns to aquarium.

As mentioned, their diet can incorporate live adult Artemia, also known as brine shrimp.  I like to soak mine in Super Selco to further enrich it with fatty acids and vitamins.  I also feed rotifers, and Mysis shrip, both of which can be cultured.  For some of my larger specimens, I feed an occaisional live guppy, just born of course, since seahorses have such tiny mouths.  Eventually you may be fortunate to have your seahorse eat frozen foods. Some of mine will eat chopped krill, but other will only take live foods, so it's a not a guarantee.

The most bizzare aspect of an already unusual fish is the means of reproduction.  The male seahorses have the babies. Actually, they have a pouch, much like a kangaroo, and the female deposits eggs into this pouch, and the male fertilizes them.  After about 20 days, baby seahorses are born.  This phenomemen is shared only with the cousisn, the pipefish.  Because the babies are so tiny, you must feed newly hatch Artemia nauplii and rotifers.  With daily water changes, and clean cultures, you can have a high survival rate with your young seahorses.  Some of mine have had 60 babies at one time.  Because of their size, its best to raise them in  smaller and separate aquairum.

Mysterious, beatiful and gracefull, all words to describe these creatures.  But again, they ar best enjoyed from a distance at public aquariums.  With all the harvesting of wild seahorses, in some areas populations are crashing, and they are experience critically low numbers in the wild.  For such a magnificent animal, we would not wish to contribute to this downfall.  If you must try seahorses, makesure you are well prepared, and equipped, and use only captive bred seahorses.