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Presented by Charles & Linda Raabe
Mactan Island, The Philippines
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The Visayan Island Group located in the Philippines
Click here for a Map of the Philippine Islands

Click on any box to enlarge and view that areas underwater scene
Note: Photos will change as they are obtained

Google Satellite View, Click HERE

                                       Zone 1                                             Zone 2                    Zone 3                               Zone 4
  Sandy grass beds                                Macro Algae          Sargassum Kelp                    Coral Reef
                                Depth 0 - 4 feet                                  Rock Rubble           Large Boulders                 Depth 5 - 25 feet
                                                                                        Depth 2 - 6 feet        Depth 4 - 8 feet

 Changes made to the above :  14 July 07 - An Additional Reef Tour of Hilutungan Island added.  23 July 07 - Area 3 photo change.
  23 March 2008 - Area 18 photo change  27 May 2008 - Areas 38,39,40 updated

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Google Satellite View, Click HERE

                                     0 - 5 feet deep             5 - 20 feet deep                                   15 - 30 feet deep                                    200+

  This area of the island is where the deep vertical wall gets much closer to shore and is where I do all of my scuba diving because of that. As you can see in the above photo, the grassbed areas are much smaller than Marigondon's area, this is due to the fact that the landscape slopes down from shore much quicker. There is also not much sargassum kelp to speak of due to the greater depths.

  Changes made to the above:  05 June 07 - Added new area, look for the photos to change though as I get better ones, those shown were all taken today and are not the best of the best.   18 July 07 - Added a 2mb Movie of the reef crest located near area 18 (link above). 26 July 07 - Updated Areas 16 and 19.  22 August 07 - Updated Areas 12 and 5.  08 Nov. 07 - Updated Area 2.  11 Dec. 07 - Updated Areas 9 & 3.  04 Feb.08 - Updated Areas 6 & 11.

 Basic ocean parameters (as found on this reef) and personal observations :

Test Results taken on 30 Aug. 2007 at 2pm, High Tide

Temp. = 84F  Salinity = 32  Calcium = 420  KH = 9  pH= 8.4  Phosphates = 0  Nitrates = 0

  Having taken weekly temperature, salinity and pH tests since 2004, as well as observing seasonal changes, storms, tidal movement and other factors that effect the reef on a daily and long term basis, I have a fairly good idea as to what the local habitats and the animals that live within them are adapted to.
  The following notes include some hard data as well as some observations. Since this presentation is geared towards the reef keeping hobbyist, I hope that it will be of use in our own aquarium methodology. After all, the animals we keep aspets come from just such environmental conditions.
  If I were to make one point (which I am), it would be that we, as hobbyists, need to get the word "stable" out of our vocabulary. This reef is far from being any where near the description of stable. It does however have its daily and seasonal ranges, yet never static.
  Every thing is in a constant state of change or motion, how ever drastic or slight those changes may be, be it sand and rocks disturbed by tidal and storm activity, a particularly heavy rainfall, a lengthy period of cloud cover, the growth and decline of both corals and algae, down to all of the daily feeding activity makes for a very dynamic and ever changing system. All done within set tolerances.

  Temperature : Actually quite variable, but only variable within a set range. Which for this reef can be a low of 80 to a high of 90. The factors that determine any given temperature involves :
  Seasonal Fluctuations, Which for the tropics involves only two. A wet cloudy, thus cooler season, and a dry cloudless, much warmer season. On a seasonal average, I would say that during the wet season, the daily average is 80 F. While during the dry season, the daily average is 84 F. With an overall yearly average right at 82 F. Water depth and proximity to deeper water currents also greatly effect the day to day temperature swings.
  In the shallow grass beds, during a lull in the tides and on a sunny day, the temperature can easily reach 90 F. On that same day, the deeper, coral reef can reach 84 F. Yet when a low tide flushes the much warmer water out into the deeper reefs, the temperature climbs quickly to 86 F. The reverse happens when a high tide brings in cooler water from the much deeper open ocean. Going from 84 F. to 80 F. in a matter of hours. Night time temperature drops usually deducts about 4 degrees from the daytime average.

  Salinity : Maintained at a yearly average of 1.023 dropping to 1.022 during periods of heavy rainfall. Since the Camotes Sea is formed by a series of large islands, heavy rainfall will wash in a great deal of fresh water and for a few days, will lower the overall salinity until the tides bring in open ocean water.

  pH : This parameter does not seem to have a great deal of fluctuation with a daily 2pm average of 8.4 while dropping off to about 8.3 at night. I expected to see a greater swing and can only assume that with the vast amount of ocean water, such changes occur much slower due to a much greater buffering capacity.

  Tidal Movement : The only real source of water movement since the surrounding large islands block any wind formed waves as well as any oceanic currents. That is not to say that this area is calm. Far from it.
  During some of the larger tidal differences (between highs and lows), there have been many a time when I have regretted going too far out over the reef and have had to fight my way back in against a tide. On average though, tidal movement allows me to just drift along slowly and enjoy the view. This does not mean however, that there is a "slow" flow. The sheer volume of water passing by in a linear fashion is more power than we can usually imagine. Of course the landscape plays a large role as well. Any obstacles such as coral heads or rock outcroppings will break up the linear flow and form upwellings and calm pockets behind any such obstacles.
  Such flow can be observed by watching how the larger algae and less rigid corals are moved or not moved about. This particular reef area is a bit unique in that it has a large shallow (sea grass) shelf that extends quite far out. A half mile in up the shoreline, and the drop off or wall comes almost right up to the shoreline. This reef's extended shallow area also provides for a different flow during the tidal changes simply because you have alot of water coming directly out from shore hitting the stronger and deeper flow broadside. Which adds quite a bit of turbulence in the areas where they meet.
  This area of higher turbulence also happens to be exactly where the corals are at their highest density. Whether this is by chance or by design, I am not too sure of. To view greater details of this areas tides, please click HERE.

  Water Clarity / Turbidity : Another highly variable parameter. From day to day, week to week, it is never the same. On some days, underwater visibility can be but a few feet, other days, it can be as good as fifty feet.
  Having dived on a great many reefs throughout the world, I would have to say that this one is much more turbid (silty?) than most other reefs. As for a reason to the greater turbidity, I would have to guess that it is again due to being a narrow sea containing a shoreline on both sides of the sea, (see above map) providing for much greater shore based run off as well.
  Acting much like a large river during tidal movements. The average "cloudiness" of the water may explain why most of the corals are found living or restricted to a shallower depth than those found in much clearer waters. When I say most, I speak of those species that are most dependent upon sunlight for their needs. There are of course a good many species that I do find living in what I would call "dark" water.
  When it comes to what we, as hobbyists are usually told as to the lighting requirements of corals, I have found / observed that corals are a great deal more adaptable than we give them credit for. I have seen a coral species growing in two feet of water, sitting out in the full sun all day long, and being subjected to high temperatures for short periods and can then go out to the deeper reefs, and find that same species sitting at 25 feet deep with a lot less light and a bit cooler temperatures.
  This is something we can keep in mind the next time we fret over trying to provide a certain species of corals a very narrow range of parameters as told to us by any number of sources. But do also keep in mind that there are limits to any range or parameter, those ranges just happen to be a bit greater than I and most others have been lead to believe.



  As you can see in the above graphic, a deep trench forms the channel of the Bohol strait. In the shallow (light blue) areas, the average depth runs about six feet. It only drops down to 25 to 30 feet deep within 200 feet of the sheer vertical channel wall. The farther I go up the coast, the closer the channel wall will be to shore.
  In those areas down the coast, where there is a great deal of shallow water, it appears that these areas are under assault by a very fast growing sargassum kelp, which is high lighted below in Zone 3. I do not see the coral zone having much time left before it is over run by this "weed". Only by me going up the coast and finding much deeper water closer to shore do I see the corals as getting any relief from this pervasive algae.
  Another observation that deals with water depth, is that as I go up the coast and find deeper water close to shore, those coral reefs found in those locations are near pristine. Only because the water is too deep for the local people to wade out and do the destruction they cause by walking on the corals, and by turning over any rock or boulder that two or three people are capable of flipping over. Once flipped over, they leave it as such, dooming any life on the rocks, including the corals of course.

     Zone 1  -  Shallow Sea Grass Beds -  One of the most productive communities on earth, These vast meadows are habitat for large populations of invertebrates and fishes, providing some of the richest nursery and feeding grounds. I view this area as being much like a terrestrial field of grass, in that there is a great deal of organics from the leaf litter decomposing.
  This decomposition and its resultant rich "mud" provides for a great many animals that act on the "soil" much like earth worms do in similarly rich soils. While many of the larger, more visible worm species consume the dropped sea grass leafs in the earliest stages of decomposition, there are also a great many, much smaller worms within the "soil" consuming and further breaking down the remnants of the leaf litter. For more information and photos, please click HERE.

      Zone 2  -  Macro Algae covered Rock Rubble -  This area is comprised of small calcium carbonate based rocks and rubble, the average rock size is roughly eight square inches, with much larger and smaller rocks to be found as well. Some sections will hold nothing but the average to larger sized rocks with a few inches of sand bed in between.
  The sand bed in this area is much more like what we see within our aquariums, not having any where near the organic load that the grass beds have. In other areas, it is comprised of small rock rubble, no more than walnut sized, creating a six inch layer on top of a shallow sand bed, below the sand bed lies the lava bed rock. The small rubble areas do not hold much algae, which I attribute to the smaller rocks being easier to roll about, not giving the algae a chance to gain a foothold.
  All of this makes for a great many hiding and living places for a multitude of smaller life forms. Which in turn attracts its share of predators. For more information and photographs, please click HERE.

   Zone 3
 -  Sargassum Kelp covered Boulders -  While this area provides its own unique habitat with its shadows and thick cover, I can not help but to have a bit of a disdain for it. Simply because I am partial to the corals and have watched this plant creep ever so slowly into the corals habitat and smother out all other life where ever it is to be found.
  With that said, I also realize that this area provides a needed function by removing the excess nutrients before they can reach deeper waters and thus the corals, as well as providing food and shelter for a good many species of animals and algae. Since 2004 I have watched this plant ever so slowly take over areas once held by corals. During 2006, It was becoming apparent to me, that in just a matter of a few years, all of the corals would be in danger or lost outright. Very depressing.
  I have tried to limit this algae by pulling the plant off of a few rocks that I knew were once the corals domain. Needless to say, this plants growth can fast out pace any of my weak attempts at trimming it. I had all but given up and resigned myself to watching my pet shallow water corals smothered to death. For more information and photographs, please click HERE.

    Zone 4  -  The Coral Reef -  My pride and joy! Laying face down over a healthy coral reef not only inspires me to try and emulate what I see within my own aquarium system, it also fills me with wonder at the just the sheer diversity of life that can be found living here.
  Yes, corals are the most prominent feature and are what comes to mind when the word "reef" is thought of, but there are just so many other life forms included within that single word, most all of those life forms can however, thank the corals for providing a place to live.
  The sheer numbers of coral species here is truly staggering, even after a number of years of visiting the reefs on a weekly basis, I have come to learn that each dive will reveal a few species that I have not pesonaly seen in the wild yet. I have tried on a few occasions to name off the corals as I swam along and quickly lost count, there are just too many species to keep track of without having pen and paper handy.
  This area gently slopes downwards to a flat shelf that goes on for another few hundred feet before it drops off as a vertical wall. Along the slope, it is mostly large boulders and outcroppings that are covered in corals. Even the space between such formations hold a good number of species. Between those corals and the rocks, there is a sand substrate, although it is very shallow, no more than ten inches deep. Below the sand is the lava based bedrock.
  On any given boulder, I have counted on average, at least twenty species of corals, with some macro algae and sponges mixed in. Scattered throughout the area, growing on slight rises of the bedrock (sand free) there are single massive coral colonies that are as large as a kitchen table. I can only guess at the great many years it took to grow that large. For more information and photographs, please click HERE.

  Regardless of the habitat, they all face threats from quite a few fronts, all caused by mankind of course. The most problamatic and most likely, the least thought of, is that what we do on the land has a great effect on the nearby reefs.
  As the island populations grow, and with such a poor economy, deforestation for both fire wood and the planting of crops allows for a great amount of silt to enter the ocean, thus choking entire regions of reef. Add to this, the unregulated and untreated waste waters being dumped directly into the oceans greatly increases the available nutrients, allowing algae to dominate all substrates once held by corals. I see this becoming ever invasive as each year passes.
  As if the above was not enough, There are still quite a number of peaple that rely upon what they can hunt and gather from the near shore reefs for their daily food needs. While primitive methods are usualy employed, they are still very effective in doing long term sustained damage as the people turn over any and all boulders looking for anything that may be living or hiding under such substrates, most always, there are corals and a host of other invertebrate species that once called the top of such substrates, home, only to see sunlight again when the next person flips the rock, most often, far too late for any corals on the rocks any chance to survive.
  In addition, any and all reef fish, sea urchins, sea cucumbers and anything else that one can create a recipe for is much sought after. I have seen small children, spend entire days snorkeling in the shallows with very small home made spear guns shooting at reef fish no larger than a few inches long. Being simple pointed spears, quite a few of the fish, when hit, are able to swim off and die slowly, which I find from time to time and become saddened at such waste. On occassion, I even see fish still swimming about with huge chunks of their flesh missing from poorly aimed spear guns. Of course these fish are also doomed to a slow death as well.
  Being that humans are all about making life easier through the use of more efficient methods, the locals have also discovered quite some years ago that by simply mixing some plant fertilizor and some diesel fuel, they can make very deadly soda bottle bombs, that are then tossed onto the reef to allow the resulting blast to stun and kill all nearby fish.
  Makes for easy pickings and one can go home early. Of course, the blast also destroys great swaths of living reef that the much sought after fish need to live and reproduce. Something I do not think such so called fishermen think about or much care about obviously.
  On the bright side, and I am so glad to be able to say that there is actually a bright side, there are now a good many local island communities that designate entire island regions as sanctuarys and enforce the restrictions themselves that the government is unable to do. With increasing tourism, and charging just a dollar or two for dive boats to have the privelage to bring divers into the sanctuary, such communities are able to earn tens of thousands of dollars each year, giving the fishermen an alternate source of income other than blowing up the reefs.

A sound I used to hear far too often while diving, that is, untill local enforcement stopped it.

 MoalBoal -
Located on the southern end of the island of Cebu, this area, famous as a Diving destination held many beautiful sights. A two hour drive from our home, it was well worth the trip and would recommend it to anyone considering a diving/snorkeling vacation.

 Hilutungan - Located offshore of Mactan island as one of many very small islands that surround nearby Olango island. A designated reef sanctuary where the reef fish have no fear of mankind and will readily take food offerings right out of your hand. The reef wall is pristine and was a joy to know that such a reef is still in exsistence. This was my first dive here in the Philippines that I was acting as the Divemaster for a group of tourists as well.

  There are other habitats of course, such as the sheer vertical wall that begins at about 40 feet deep, the numerous caves along the wall, as well as the deep substrate at the bottom of this sea which is about 250 feet deep. Areas that I do not have access to, either due to the lack of cave diving equipment or by it being too deep.

A few scenes from just up the coast

      Linda, also known as the safety advisor                        Chuck, also known as the chief cause of concern

  Acknowledgments: I would be remiss if I did not give thanks to my wonderful wife Linda, who shares my child like fascination with the ocean. A special thanks also goes out to Eric Borneman, Dr. Ron Shimek, Leslie Harris and a host of others who have shared their wealth of knowledge and their friendship.

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