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BULLETIN OF MARINE SCIENCE. 65(1): 227-234.1999 CORAL REEF PAPER

COMMUNITY STRUCTURE OF THE LIVING FOSSIL CORALLINESPONGE POPULATIONS AT THE GROTIO, SAIPAN,NORTHERN MARIANA ISLANDS

Norman J Quinn and Barbara L. KojisABSTRACTAn extensive hermatypic sponge community at a popular dive site called The Grotto is

described from Saipan, Commonwealth of the Northern Mariana Islands. The community is dominated by the coraBine sponge Acanthochaetetes wellsi with a maximum density of 672 individuals m- 2 The coralline sponge As/rosclera willeyana, and the lithistidsponge Leioderll/atiu", sp. are also present but at lower densities. A. 'A.'ellsi and A. willeyanawere most dense at depths >9-16 m. These sponges prefr the low illumination found inspecialized cryptic habitats in warm tropical waters, but are not necessarily found oncoral reefs. Two previously unreported hermatypic sponge communities on Saipan andon the neighboring island ofTinian are briefly mentioned. There was no evidence thatpresent dive practices are damaging these cryptic communities. However, owing 10 theslow growth of these sponges, recovery from damage to the community may take a century or more.

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~ 2 BULLETIN Of MARINE SCJFJ\CE, VOL 05.:'-10 1. 1999

Unai Fanuchubuan

t

Figure la. Location orthe Grotto on Saipan. Commonwealth of the Northem Mariana Islands.

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229UINN AND KOllS: CORALLINE SPONGE COMMUNITY

Table 1. Population statistics of Acallthochaeleles wellsi at the Grotto, Saipan.Depth Density n Mean C. V. (%) of Maximum %(m) (m-') individuals diameter diameter diameter cover(em) (em)39 220 275 2.4 21 5.0 14>9-16 672 840 3.9 67 8.5 65>16-23 284 355 5.1 49 10.5 58Lamanibot and about 150 m from shore (Fig. I B). The entrances are at 10, 16 and 22 m. The TinianGrotto is smaller than the Saipan Grotto and covers an area of approximately 2000 ml . Owing to thelogistic difficulty in accessing the Tinian site and the surge within the Grotto, no quantitative measurements were made. Work performed in the presence of strong surges would have resulted indamage to the community.

CORALLINE SPONGE COMMUNITY SURvEY.-The population density ofcoralline sponges in the mainSaipan Grotto were quantitatively surveyed in July/August/September 1995 using scuba equipment. Density and diversity of the coralline and lithistid sponges on the walls were quantified from15 0.25 m2 quadrats. Quadrats were located along a vertical transect extending from 3 to 23 m onthe wall in the middle of the Grotto between the two eastern underwater entrances. A metal rcbarwas driven into the wall at 10m to help relocate the transect. The quadrats were assigned to threedepth ranges (five quadrats in each of three depth ranges) (Table J). The numbers of individuals foreach species from each depth range were standardized to number of individuals m-2 and expressed

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230 llLlLLETIN Of I\fARI\iE . ~ C T E \ i C c \'OL 65. -"'0.1,1999

T,lbJe 2. Population statistics of ASfrOsdf!J"o \lj/leyLma at the Grotto, Saipan.Depth Density n Mean C.V (%) of Maximum %( Ill) (m-') individuals diameter diameter diameter cover(em) (em)3-9 20 25 2.8 11 4.0 1>9-16 136 170 3.2 18 5.5 11>16-23 92 115 3.5 16 4.5 9

identification \vas beyond the reasonable resolution of this technique. Light Je'vels were approximated at various dcpths using the intcmal1ight meter in a Nikonos RS llnden'iuter C

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Q l ' r ' ~ ' \ I AND ROJIS CORALU)\'L SPOl\GE COM\1UNlTY 23]

8070w

60u:2: 50uE 40'0ill 30.0E 20 10

02 3 5 6 7 8 9 10

Diameter (em)D !lc;"nlhoc;haeleles wellsl Astrosclera wllieyana

Figlln:: 3. Size frequellcy distribulion histogram ofAcal1t!Jocli

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..,., .., BIJLLETli\ OF I,,1Af{INF. ~ ( l E J \ C F . VOL. 65. NO.1. 1999

GrOlto "Up to 18 cm". However, the largest specimen (A. 1-Fellsi) that we observed in 15dives at the Grotto was only 10.5 cm maximum diameter. Considering that Goreau collected specimens, it is possible that he coUected the largest individnals of these 510\'1'gro\\'lug organIsms.Although sclerllctiui

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233UINN AND KOJIS Cl1RAlLl\E SPO"

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Vacelel.1. 1985. Coralline sponges and the evolution of Porifera. Pages 1-13 in S. C. Morris, 1. D.George, R. Gibson and H. M. Platt, eds. The origins and rei