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Temtories of 4 species of herbivorous damselfish from coral reefs of the central Great Barrier Reef and Motupore Island, Papua New Guinea were shown to be zones of high algal biomass and primary productivity relative to surrounding epilithic algal communities. Productivity was rneasured in the field from die1 patterns in oxygen flux, employing in situ data-logging respirometers. Algal communities inside territories were 1.6 to 3.4 times more productive per surface area than surrounding algal substrata. Algal communities of damselfish territories maintain a rate of productivity per unit biomass 1.5 to 3.4 times h g h e r than that of algae growing outside the territories. Differences in primary productivity for the 2 different types of algal community are due to the higher photosynthetic efficiency (0.37 to 0.94 pg O2 PE-') and potential maximum rate of photosynthesis (57 to 249 pg Oz cm-2 h-') of algae from territories compared with algae of non-territory areas (0.20 to 0.35 pg O2and 24 to 78 pg O2 cm-2 h-', respectively). Photosynthetic compensation and saturation irradiance were similar for the 2 algal communities and ranged from 52 to 100 and 337 to 735 PE m-' S-', respectively. These temtories are shown to be important to reef net productivity since they cover a high proportion of the reef flat zones examined (up to 77 O/O of substratum). Several hypotheses are proposed to account for the significantly higher rates of prlmary productivity inside coral reef damselfish territories compared wlth adjacent substrata.

ABSTRACT. We compare the relative contributions of phototrophy (translocation of photosynthates from zooxanthellae) and heterotrophy (filtered particles) towards the carbon requirements for tissue and shell growth, and metabolism in 4 species of giant clam from the Great Barrier Reef. The primary aims were to determine whether the differences in growth rates of various clam species could be due to nutrition, and to quantify the relative roles of phototrophy and heterotrophy in the nutrition of tridacnids. The species examined were distinguishable by both absolute C flux and relative proportions of components of the C budget. For example, Trjdacna gigas was photosynthetically the most efficient, gaining twice as much nutrition as 7. crocea, and an order of magnitude more than Hippopus hippopus. In the case of the smallest clams tested (0.1 g tissue wt), intake of C via filter feeding was also highest in T. gigas, being 10 times that of the other species. These interspecific differences declined with clam size. Tridacna gigas, T. crocea, and T squamosa were able to satisfy all their growth and metabolic requirements from the intake of photosynthate and particulate food, in some cases with considerable energy to spare. In contrast, small H. tuppopus gained 80% of total C needs from these sources. We confirm that phototrophy is the most significant source of energy to clams. In all but the smallest H. hlppopus, this source provides sufficient C for growth and metabolic requirements. Filterfeeding decreases in importance with increasing size of clam. Ingested C provides 61 to 113% of total needs in 40 to 80 mm T. gigas and 36 to 44 % in H. hippopus, but was less significant to the other species (10 to 20%). H. hippopus allocated the highest proportion of C expenditure to growth (30 to 90 %), up to half of which went into shell. T. gigas and T. squamosa both put 20 to 40% of C into growth, compared with only 10 to 20% in T. crocea. There was no simple nutritional basis to the differences in growth of the 4 species. T. gigas has the greatest excess of energy available for growth, and the highest growth rate in terms of shell length. However, the connection between available energy and growth rate was not consistent across species. Actual growth in units of C was similar in T gigas and H. hippopus, yet small individuals of the latter species appear limited by availability of C. Despite a relatively high calculated 'scope' for growth, 7. crocea exhibited the lowest growth rate possibly because its growth is limited by physical constraints of its burrowing habit.

Particle-size selection was studied in 3 species of suspension feeding bivalves, a n ascidian and a sponge, using a direct and an indirect technique. All 3 bivalve species retained particles > 4 p m with 100 % efficiency, while the retention of 0.6 pm cells dropped to approximately 20 %. In contrast, sponges showed the highest retention for the smallest particles and a declining efficiency for larger particles, suggesting an effective food resource partitioning on the basis of particle size between these 2 groups of animals. The ascidians, however, retalned all particles > 0.6 pm with approximately 100 % efficiency. The sponges, were able to meet thelr entire carbon requirements by utilization of particles < 1 vm in diameter. This size fraction could only meet 5 to 21 % of the bivalves', and l? % of ascidian carbon requirements, while free-living bacteria at a concentration of 0.5 X 106 ml-', provided 1 to 4 % of the bivalves' carbon requirements, 17 % of the sponges' and approximately 3 % of the ascidians' carbon requirements.

The major groups of m o t~l e cryptofauna lnhab~tlng dead coral substrata across several environmental zones of Davies Reef In the central Great Barner Reef, Austral~a, have been quantified In general terms of both numbers and b~o m a s s the main groups of e p~b e n t h~c cryptofauna were harpach c o~d copepods, g a m m a r~d amph~pods, syll~d polychaetes and gastropod n~olluscs Other crustaceans abundant In some locat~ons were so pods t a n a~d s and ostracods Copepods compr~sed 55 to 60 % of total number of cryptofauna over all reef locations and up to 28 % of b~o m a s s Polychaetes were usually the dominant biomass component of the fauna Abundance of total cryptofauna vaned w t h reef locat~on, being h~g h e s t on the fore-reef region In terms of both density and biomass Damself~sh terntones were shown to be a refuge for cryptofauna In all locat~ons of the reef Mean density of anlmals i n s~d e territories was 58 300 m-2 an average of 3 6 tlmes h~g h e r than on adjacent, well-grazed surfaces Cryptofaunal abundance was closely related to algal abundance and not complex~ty of the coral rock substratum It IS predicted that cryptofauna are s~g n~f~c a n t consumers of epilithic algae and associated matenal In locations such as damselfish terntones, on coral reefs

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