A Philippine Reef Tour, Zone 1

Within the very organic laden substrate, there are a great many small life forms that are the foundation of the food web within sea grass beds. The majority of them are not visible without the aide of a microscope yet there are still a good many animals that are visible to the naked eye. All of which break down the organics on which the sea grass depends upon for its nutrients. All of this life attracts its share of predators, most notably, crabs, snails and fish, some are full time residents, others are transients from deeper water.

The thick layer of leaf litter also provides a hiding and hunting place for a number of juvenile fish and crab species. Most notably, puffer fish, lizard fish and an assortment of goby species. During periods of deeper water, schools of rabbit fish will come close to shore devouring the Ulva and filament algae that abound after a heavy rain fall has occurred. Schools of juvenile sea catfish are also a common sight as they root about in the sand/detritus for food. Small juvenile hermit crabs are also extremely abundant and appear to graze the leaf litter picking through it for algae matter and any number of small invertebrates.
Above the leaf litter, grazing on the algae that coats the sea grass leafs, there are a number of sea slug herbivores as well as a great many species of snails. The most commonly seen are members of the Astrea and Cowry families.

Used for algae control, but is not suited for a rocky habitat

Cowry snails are usualy seen with mantles covering their entire shell

With all the available detritus laying on and below the surface, there are a number of synaptid species (relatives of the sea cucumbers) and sea cucumber species that spend their entire existence crawling ever so slowly about mopping up the abundant organic particles.

A sand dwelling Synaptid species and a Surface dwelling Synaptid species

Various Sea Cucumber species which tend to be nocturnal, spending their day hiding either just below the sand, or under rock ledges.

The dominant species of sea grass' are Thalassia hemprichii and Syringodium isoetifolium, both found mixed in together so much so that if one lifts up a handful of sea grass, you can not avoid getting both species. In one small area, there is a very large species of sea grass, Enhalus acoroides, which I have measured its leafs at up to fifty inches long and one inch wide. Within small bare spots or on the edges of the grass beds, you will find Halophila ovalis (paddle weed) growing. Being the only species within such bare areas, suggests to me that Halophila acts as a pioneer species, capable of growing in sandy, less organically rich areas and in time, through its own growth and decay, prepares the "soil" for the other sea grasses.

During some of the low tides, the grass beds can be fully exposed for a period of about two hours or so, which the sea grass seem to endure quite well. It is only on the rare occasion that the low tide coincides with a clear sunny day at high noon does the sea grass seem to suffer as the top 2/3rds of its leaves become dried out and fall away, leaving the sea grass looking as if it was freshly mowed.
I believe sea grass beds provide a very nutrient rich feeding ground and a habitat for countless species of invertebrates and a great many fish species while acting to stabilize the sand / mud and prevent its loss due to tidal and wave action. The grass beds also act to collect and trap sediments washing into the ocean from shore. Should the grass beds be lost, I believe it would have a cascading effect all the way out to the deeper coral reef by having the sediments unlocked from the grass beds, which would quickly smother all other life and spell the end of nearby habitats.
Fish species include an assortment of damsels who have staked out their territories amongst the porous lava substrate and can retreat downwards into the substrate to follow the water during the lowest of tides . The larger coral colonies usually hold a number of three stripe damsels which when frightened, duck into the corals for protective cover. Only during the periods of high tides and tidal changes can you find other species of fish which come in from deeper water to search for food. Wrasses seem to make up the majority of these deep water interlopers with the occasional bursa trigger.

A Habitat within a Habitat

Scattered throughout the grass beds, there are low lying areas, usually two feet deeper than the surrounding grass beds forming "bowls" that average fifteen square feet. These bowls have had their sand removed / scoured away down to the lava base rock, on which grows a number of coral species. The most prevalent being a member or two of the Pavonas, A few Montiporas, Galaxea, Favia and Lobophyllia. Any corals that find themselves within these bowls are restricted to growing no taller than the low water mark and form low, encrusting formations. Those that do branch, form very short, thick branches.

Coralliths : I see this odd coral formation from time to time within the grass bed's sand areas as well. Formed by small coral fragments that get turned over on a regular basis by the areas tidal movements. Usualy no more than golf ball sized, which may be a limiting factor for this formation as I am sure, that as they get larger, and thus heavier, the tides may not be able to turn them over, which for the side that ends up face down in the sand means the loss of living coral while the "lucky" side continues to grow.

Both sides of a Corallith, the brightness on the right is due to sunlight

These bowls also seem to act as a low tide refuge (tide pool?) for the black long spine urchins which graze the grass beds during deeper water feeding not on the sea grass itself, but on the algae that manages to grow on the odd larger rock scattered about. It is quite the sight, to see a "herd" of a hundred sea urchins marching across the shallows while having a great number of gold colored cardinal fish hovering in amongst their spines.
Overall, these bowls appear to be their own miniature habitats and I am surprised at the number of different animals that make these areas their homes. I can easily forget the time and spend an entire afternoon within a single bowl marveling at what will come into view if one only remains still long enough.

Long Spinded Urchins with commensal Cardinal Fish and a PipeFish hunting amongst the seagrass

Summary : No matter where in the world that grass beds are found, they play a critical role in the formation of, and health of coral reefs. In short, as goes the grass beds, so goes the reefs. A few key roles that grass beds play include:
(A) - Sediment stabilization, Without the sea grass trapping and holding sediment particles, it is unlikely the coral reefs could form in the first place, by keeping the water clear of drifting sediments, the sea grass allows the continuation of those reefs that have formed in near shore areas.
(B) - A habitat unto its own, the fine sediment and abundant nutrients creates a home for a great many microscopic plants and animals, which forms the foundation of the sea grass nutrient web. These in turn feed a great many other higher life forms, who become food for yet larger animals. A lot of detrivores could not find suitable habitat if not for these areas as well.
(C) - A nursery area, with the shallow and abundant cover, The juveniles of a great many species of both crustaceans and fish can be found living and hiding amongst the blades of the sea grass. Few, if any, larger predators venture into such shallow zones, thus giving the juveniles a chance to grow up and move out to other, deeper habitats.

Application within the Reef Keeping Hobby - If a separate, very large, shallow aquarium could be tied into your aquarium's system and set up with a deep very fine "live" sediment, heavily planted with sea grass. I feel this alone would create a much more natural environment for all of the pets that you keep. The production of micro life alone would add a lot of live food that the corals and fish would benefit from. The amount of nutrient processing that such an addition would provide would also greatly improve the day to day water quality of the entire system. In order for us, as hobbyists, to make the claim that we have a "reef" aquarium, I feel we need to include all of the habitats that encompass the word "reef", when possible.

The Human Factor - There is of course a downside to being able to observe a reef, and that is having to watch the effects that people have upon it. For a sea grass habitat, the biggest problem is of shore run off. Within a day of a heavy rainfall, the near shore area becomes choked in the free floating Ulva macro and filament algae. The bacterial count must also go "off the scale" as I have learned the hard way that swimming shortly after a heavy rain almost always leads to me coming down with a sore throat and a fever. Another effect is by just the physical damage that people do during their foraging for food. During the lowest of tides when the grass beds are exposed, there will be at least fifty people wandering the grass beds flipping over every rock in the entire area in search of what ever it is that they find edible. The problem in their doing so, is that there is a lot of life living on the "sunny " side of the rock. Once flipped over most of that life is doomed, unless by chance, it is again flipped over at the next low tide. Most of the larger herbivores have also been removed. All of the sea urchins except the black long spine species have been collected and eaten. I have seen piles mounded up in the shallows consisting of nothing but sea urchin skeletons. Any of the larger snail species, such as the Conch, are snapped up just as fast as they migrate into the area. It is my hope, that soon, I will be able to put together some educational material that I can pass out to the people who frequent this area, and hopefully teach them some less destructive methods, such as putting the rocks back the way they found them and to please not step on corals that are doing their best to eek out a living . I suppose the first step would be to inform the locals of what a coral is. You would be surprised at how many people here have no idea that the brown or green weird looking rock that they stand upon is actually a living animal.

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