UNIQUENESS OF LARVAL RELEASING OF Littoraria Scabra L. (GASTROPODA: LITTORINIDAE), IN TOMBARIRI MANGROVE, NORTH SULAWESI,INDONESIA (Keunikan Pelepasan Larva Littoraria Scabra L. Gastropoda : Littorinidae, Di Mangrove Tombariri Sulawesi Utara, Indonesia)

This research was found novelty of reproduction strategy uniqueness of L. scabra that very rare in nature, reverse male function fertilized eggs are sucked for brooding in mantle of male up to hatching as veligers, and thus, the males are capable of releasing the larvae in full and new moon at spring tide during the research. The second finding in reproduction strategy uniqueness of L. scabra that mating individuals, both males and females, released their larvae during research period.


INTRODUCTION
Nocturnal larval release is common in marine invertebrate because it minimizes predation (Morgan and Christy, 1995) and reduces the effects such as temperature stress and photodamage (Forward, 1987). Irregularities of larval release before the high tide occurs when light/dark cues entrain stronger rhythms than tidal cues.
In mangrove habitats, invertebrates perceive the tidal amplitude cycle by water pressure or even the tidal force (Hovel and Morgan, 1997).
The synchronised release of larvae has been argued to minimise the risks of predation and unfavourable environmental factors (Forward, 1987;Morgan, 1995). An error in timing of larval release could have fatal results for progeny and significant implications for local population. Timing errors of larval release could occur if adults did not have an adaption of endogenous release rhytms, or if entrainment to a cycle, on rare occurrences, increased the risk of mortality (Ricardo, 2011).
Littorinids living high on the shore are only reached by new or full moon spring tides, and hence most release their eggs or larvae during these periods (Berry 1986). Both Littoraria ardouiniana and L. melanostoma live in the upper zone of the mangrove trees (Yipp 1985;Lee and Williams 2002b;Reid 1986), and their bilunar periodicities of egg or larval release, associated with spring tides, matches those of many other rocky shore and mangrove littorinids (Gallagher and Reid 1974;Alifierakis and Berry 1980;Berry 1986). In Malaysia, however, Littoraria melanostoma mainly spawns during full moon spring tides, as tidal heights during this phase of the moon are higher than during the new moon phase (Berry and Chew 1973). Releasing large numbers of veligers in a single event could, therefore, be an effective strategy to compensate for this limitation. This behaviour can, however, also be a strategy to reduce predation risk. Shell crushing scars are frequently observed on individuals of both species, which may indicate severe predation risk from crabs in Hong Kong, as recorded in Australia (Reid 1992). By releasing more larvae at each larval release event within a shorter reproductive season, females of L. ardouiniana may spend less time immersed in seawater, and hence reduce their exposure time to predators. Reid (1989) suggested that shortterm brooding of embryos to the planktotrophic veliger stage in ovoviviparous Littoraria species may increase larval survival, whilst energetic costs may even be reduced as compared to producing eggs, due to the absence of a capsule gland in ovoviviparous females.
Females of L. ardouiniana release their entire brood of larvae faster and over a much shorter duration in a single event, as compared to the longer, slower and repeated release of eggs in L. melanostoma. Such differences in eggand larva-releasing behaviour have also been observed between members of another sympatric pair of oviparous and ovoviviparous Littoraria species in Florida, L. irrorata and L. scabra angulifera (Gallagher and Reid 1974). It seems reasonable to assume that rapid release of larvae in ovoviviparous species may reduce exposure to marine predators; thus, predation may be a selective force driving the development of ovoviviparity in Littoraria species (Reid 1989;Reid et al. 2010).
In the mangrove habitat studied at Cockle Bay, Crabs were the major predators of the larger postlarval stages of Littoraria species (Reid, 1984). The most common crab on the Rhizophora trees was Metopograpsus latifrons, a small, agile grapsid with relatively weak and unspecialized chelae. To avoid predation, invertebrate are expected to release larvae at times that minimise the risk of predation (Morgan and Christy, 1995).
Larvae are assisted by receding tidal currents and disperse outward into the estuary or the coast (Hovel and Morgan, 1997).

Methods
Research map of Tombariri mangrove can be seen in (Appendice 1). Ten individuals of each males and females collected were mature. The collection was done 4 days before new moon and full moon to avoid missing larval release period from February to December 2014.
Male and female JurnalIlmiahPlatax Vol. 6:(2), Juli 2018 ISSN: 2302-3589 3 http://ejournal.unsrat.ac.id/index.php/platax spawners were separated in different plastic containers. Males and females released larvae in the plastic bottle, and they were counted using a dissecting microscope / binocular. Also, 10 mating pairs were collected. The males and females were put in different plastic containers. They released larvae as well, and the larvae were counted. Larval release rate is number of larvae released per second (Ng, 2013). Number of larvae released was counted using a hand tally counter. Ten individuals of each males and females releasing the larvae were randomly selected. The larvae were released by withdrawing their snout and tentacle inside mantle cavity. Difference in larval release between male and female was estimated using t-test. The same test was also used for difference in the larvae released by mating male and females.

Larval Periodicity of mating Littoraria scabra
Summary of research can be seen in (

Larval Periodicity of non-mating Littoratia scabra
This study found that both males and females released their larvae the Larval periodicity occurred along the year for either females or males. Rare finding was male L. scabra released their larvae along the year with the highest mean periodicity in Tombariri mangrove   ( Figure 3 and 4).
Most tropical species Littoraria release planktotrophic veligers but a few species brood embryos (Reid, 1984(Reid, , 1986. According to (Sanpanich et al., 2008), Littoraria strigata spawned regularly on the spring tides with 89 % of eggs appearing between one and five days after the new and full moon. However, full moon spwnings (when spring tides are highest) yielded an average of seven times more eggs than the weaker new moon tides (Berry, 1986). Burgett et al. (1987) reported Littoraria angulifera spawned through at least 10 months of the year, peaking in the spring and autumn between June and December and being minimal in December and March. Berry and Chew (1973) repoted that egg capsules of

Littoraria melanostoma
Larval release is defined as the deliverance of eggs or larvae from an adult into the water column, usually from the saltmarsh-mangrove to deeper waters (Ricardo, 2011). Littorinids including L. scabra living on high shore only reached by new or full moon spring tides, mostly release their larvae (eggs) during these periods. Both Littoraria ardouiniana and Littoraria melanostoma live in the upper zone of the mangrove trees (Lee and Williams, 2002), and their bi-lunar periodicities of egg or larval release, associated with spring tides, match those of many other rocky shore and mangrove littorinids (Gallagher and Reid, 1974).
In Malaysia, however, L. melanostoma mainly spawns during full moon spring tides, as the tide height during this phase of the moon is higher than during the new moon phase (Berry and Chew, 1973).

Larval Release Rate
Mean larval rate released by male L. scabra was 172.5 ± 33.15 per sec., while females averagely released 195.4 larvae ± 27,8 per sec. Based on the ttest, mean rate of the larval release was significantly different between males and females. Total duration of larval release was 2.2 -5.0 min or 132 -300 sec. This study found very rare and unique phenomenon in the nature where mating males and females release their larvae along the year in full and new moon following the tidal cycle. They had mean larval release rate of 88.65 ± 11.25 per sec. (95 % confidence level), n = 20, for males, and 138 ± 14.18 per sec., n = 20, for females.
The t-test on mating individuals shows also significantly higher number of larvae released by females than males. Gallagher and Reid (1974) showed that the ovoviviparous Littoraria angulifera could release up to 246,000 veligers in 30 minutes, while the oviparous Littoraria irrorata of similar size released a maximum of 32,000 egg capsules in 2.5 hours. According to Ng (2013), in each event of larval release, total duration of Littoraria ardouiniana releasing larvae (2.4 -7 min) was also much shorter than Littoraria melanostoma releasing eggs (31.3 -94.1 min). Releasing large numbers of veligers in a single event could, therefore, be an effective strategy to compensate this limitation. This behaviour can, however, also be a strategy to reduce predation risk (Ng, 2013). It seems reasonable to assume that rapid release of larvae in ovoviviparous species may reduce the exposure to marine predators; thus, predation may be a selective force driving the development of ovoviviparity in Littoraria species (Reid et al., 2010).
Larval release occurs more in reproductive season along the year, in which male and female L. scabra probably spend less time submerging in the seawater, and therefore, reduce time exposed to the predators. The larval release of L. scabra occurs along http://ejournal.unsrat.ac.id/index.php/platax the year indicated with (1) Male and female L. scabra mature all the year; (2) the continuous presence of mature oocytes in the ovary and the gonadial oviduct; (3) no evidence of gonad decrease period (gonadial regression), as supported in the littorinid in spawning season (Borkowski, 1971;Muggeridgeridge, 1979); (4) Spawning peak occurrence due to effect of tide (Borowski, 1971; Lalita, pers.obs), water temperature (Muggeridgeridge, 1979; Lalita, pers.obs), and phytoplankton abundance (Underwood, 1979), and (5) prolonged spawning period of L. scabra as response to high predation for small and newly settled individuals (pers.obs). Releasing large numbers of veligers in a single event could, therefore, be an effective strategy to compensate for this limitation. This behaviour can, however, also be a strategy to reduce predation risk. By releasing each larval release event within all the year, males and females of L. scabra may spend less time immersed in seawater, and hence reduce their exposure time to predators. Risks of predation and lodgement from wave action are likely to different between species living at high and low levels between rocky shores and mangrove habitats (Raffaelli and Hawkins 1996;Little et al. 2009).