John Stimson

The temporal pattern and rate of release of zooxanthellae from the reef coral Pocillopora damicornis (Linnaeus) under nitrogen-enrichment and control conditions *

Abstract The rate of loss of zooxanthellae from intact Pocillopora damicornis (Linnaeus) was determined for colonies growing in laboratory tanks supplied with either ambient seawater or seawater enriched with dissolved inorganic N. Algal release peaked during midday in both treatments. Corals in N-enriched water released 40% more algae · U −1 surface area · day −1 than did control corals. However, algal densities in the N-enriched corals were three times higher than in controls, so specific release rate was lower for N-enriched corals. Lipid content of the N-enriched corals was also lower than in the controls. These results suggest that N enrichment results in: greater algal standing stock and a reduced rate of transfer of photosynthate to the host. N enrichment more than doubled algal densities in this coral indicating that zooxanthellae in situ may be nutrient limited and that algal densities are, to some extent, a function of nutrient levels in the external environment and not entirely regulated by the host.

The Role of the Territory in the Ecology of the Intertidal Limpet Lottia Gigantea (Gray)

The marine mollusk Lottia gigantea, a large grazing limpet of the upper intertidal zone, grazes algal film from a territory which it defends against intrusions by conspecifics and other grazers as well as the gradual encroachment of sessile organisms. The areas of the territories are correlated with the length of the resident Lottia, but for a given size of Lottia the areas vary greatly at different study sites. The thickness of the algal film charcteristic of the territory fluctuates, being greatest in spring. Experimental removal of abundant algal film from some territories in spring was followed by enlargement of these territories relative to controls. Growth rates of Lottia are positively correlated with the thickness of the algal film in their territories. The smaller limpets (1—2 cm in length) of the genus Acmaea are able to crop the algal film more closely than Lottia and will remove almost all the algal film from a territory if the territory—resident is removed. Experiments to determine whether te...

Mode and timing of reproduction in some common hermatypic corals of Hawaii and Enewetak

Common Hawaiian and Enewetak corals were examined to determine the method and mining of reproduction. Of the 7 Hawaiian species examined for the release of planulae, only 2 have planulated in captivity, Pocillopora damicornis and Cyphastrea ocellina. Both planulate year-round and both are characteristic of reef flats. Four of the 5 species which did not planulate were found to contain eggs, but not planulate, when polyps were examined microscopically. These 5 species do not usually occur on reef flats. Seven of the 12 Enewetak species examined in June, July, August and January planulated; 4 of these were pocilloporids, all of which are common in shallow water. Only 3 of the 8 species of Acropora planulated, and these 3 occur solely in shallow water. A greater proportion of the Pocillopora spp. colonies than Acropora spp. colonies planulated and they released more planulae per head. In previous studies and in this one, coral species which have released planulae are characteristic of shallow-water environments such as reef flats. Most of the 10 species reported on here which failed to planulate in captivity are not commonly found on reef flats. The failure to detect planulation in so many species, particularly those of deeper water, suggests that common hermatypic corals may not all reproduce in the same way, and that mode of reproduction may be related to habitat.

The annual cycle of density of zooxanthellae in the tissues of field and laboratory-held Pocillopora damicornis (Linnaeus)

Abstract Three data sets collected over a number of years indicate that the density of zooxanthellae in the tissues of the hermatypic coral Pocillopora damicornis (Linnaeus) living in shallow water is approximately twice as high in winter as in summer. One of the data sets was obtained by sampling reef flat colonies. A second data set was obtained by sampling colonies maintained in outdoor laboratory tanks continuously supplied with sea water (laboratory controls) and a third set was maintained in similar tanks which were continuously supplied with ammonium enriched sea water. The set of nutrient-enriched corals showed higher algal densities than the control corals. Comparison of the annual pattern in these three sets with environmental variables suggests the pattern may be in response to seasonal differences in insolation, either visible or UV.

Nitrogen efflux from the sediments of a subtropical bay and the potential contribution to macroalgal nutrient requirements

The concentration of dissolved inorganic nitrogen (DIN) in the porewaters of shallow-water tropical marine sediments can be as high as 50-100 µM, at sediment depths of shallow as 20 cm. These concentrations are at least two-orders of magnitude greater than the DIN concentration in the overlying water. High porewater concentrations, and the resulting concentration gradient, result in substantial efflux of DIN from the sediments to the water column. This sediment-derived DIN may be an important nutrient source for benthic algae. In Kaneohe Bay, Hawaii, a mean ammonium efflux rate of 490 µmolm(-2)day(-1) and a mean nitrate+nitrite efflux rate of 123 µmolm(-2)day(-1) were measured on reef slopes in the habitat occupied by benthic algae. It has been demonstrated that this nutrient source is essential for the growth of at least one abundant alga, Dictyosphaeria cavernosa, and possibly others. The DIN concentrations in Kaneohe Bay sediment porewaters, and the rates of DIN efflux from those sediments, are greater than porewater concentrations and efflux rates reported for other, more pristine tropical sites. The rate of sedimentation of particulate nitrogen is similar to rates reported from other tropical lagoons, and about twice as high as the efflux rate of total dissolved nitrogen. Given the present low nutrient concentrations in the water column of the Bay, these results support the view that nutrient efflux from the benthos is in part responsible for the persistence of D. cavernosa on these reefs. It is possible that efflux of DIN from sediments may be responsible for sustained benthic algal productivity in similar habitats on other tropical reefs.

Density dependent recruitment in the reef fish Chaetodon miliaris

SynopsisRecruitment of reef fish has generally been found to be unrelated to or positively related to adult densities. This paper reports an inverse relationship between the number of recruits of Chaetodon miliaris and the density of conspecific adults. C. miliaris are non-territorial, planktivorous butterflyfish. The study populations occurred on the flanks of patch reefs of about 30 m in diameter. At their peak densities populations consisted of 300–400 C. miliaris. Recruitment (the appearance in the stock of fish less than ∼ 3.5cm in total length) occurred primarily from April to June and corresponded to the new moon period in these months. Populations generally showed a steady decline in numbers during months of the year when recruitment was not occurring: the finite rate of decline was approximately 30% per month. Populations varied in the density of adults at the start of the spring-summer period of recruitment, and the magnitude of recruitment to a reef was inversely related to the density of these conspecific adults. Reduction of the densities of adult C. miliaris through trap fishing, resulted in increased recruitment to the fished stock. These results provide evidence that in some. species of reef fish, benthic processes may play an important role in determining the magnitude of recruitment to an adult stock, in contrast to the widely held view that recruitment is in large part a result of chance events in the plankton or that recruitment is directly related to adult densities.

Reproduction of Some Common Hawaiian Reef Corals

The study of coral ecology has primarily been one of distribution and zonation and little attention has been paid to the adaptations of particular species, aside from the obvious one of morphology. Now workers are beginning to study such questions as the relative ability of different species to capture zooplankton food (Porter, 1974; Johannes & Tepley, 1974) and how coral species rank in terms of predator-preferences (Goreau, et al, 1972). Such studies can be useful in interpreting coral community structure. In this work I have asked whether different coral species have different modes and temporal patterns of reproduction, and if they do, how these might represent adaptations to the environments of these species.

Archipelago-wide episodic recruitment of the file fish Pervagor spilosoma in the Hawaiian Islands as revealed in long-term records

The endemic filefish, Pervagor spilosoma, has long been known to recruit infrequently but in large numbers to shallow water habitats in Hawai‘i. When it does recruit, as it did in 1944, 1975 and 1982–1987, it becomes the most abundant or one of the most abundant species on Hawaiian reefs. At these times of high abundance, juvenile individuals also become abundant in the off-shore pelagic environment and in deeper benthic habitats. The results of two previously published studies and this one show that the last heavy recruitment occurred throughout the Hawaiian Island chain in the period from 1982–1988. The earliest strong recruitment in this interval occurred on the leeward, or northwest Hawaiian Islands in 1982, then on O‘ahu in 1983, then on the island of Hawaii, at the southeast end of the island chain in 1985. At the Kane‘ohe Bay, O‘ahu, sampling site, strong recruitment occurred in 1983–1987. Fish that had recruited in the summer of a year survived less than a year at these shallow (<15 m) sites or moved off the reefs. No other fish species among the 30 species censused in a 20 year period at Kane‘ohe Bay has shown the extremes of abundance displayed by this species, nor did any other species recruit so strongly in the 1983–1987 period. The latter event suggests that the pattern of recruitment in this species was not solely due to a particular pattern of ocean circulation, because if that were the case, other species would also show strong recruitment. The rarity of large recruitment events in this species, the high density of the recruits, the length of individuals at recruitment, the observation by others of juveniles and possibly young adults in the water column, and the sequential nature of the recruitment down the length of the island chain may in part be the result of metamorphosis in the pelagic environment and a pelagic juvenile stage in this species.

Experimental investigations into the basis of the uniform dispersion pattern of Pocillopora meandrina Dana var. nobilis Verrill, 1864

Experiments show that the close proximity of a large live colony of Pocillopora meandrina Dana var. nobilis Verrill, 1864 decreases the survival of small colonies compared to the survival of small colonies in the open. The close proximity of either large dead colonies or clusters of small colonies did not affect the survival rate of individual small colonies. The existence of this form of interaction between large and small colonies of the same species raises the question of whether the phenomenon occurs in more diverse and complex coral communities and whether it is contributing to the maintenance of high diversity in such situations by preventing the development of pure stands.