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. Takegaki, A. Nakazono J. Exp. Mar. Biol. Ecol. 253 2000 149 –163
Fig. 2. Cross-section of a spawning burrow after spawning. The male is tending the eggs and the female is constructing and maintaining the mound.
their fanning frequency and duration in response to DO concentrations in the burrow Takegaki and Nakazono, 1999c. Because the DO concentrations in the egg-tending
burrow are lower than those out of the burrow Takegaki and Nakazono, 1999c, the supply of external oxygenated sea water into the burrow should reduce the parental
burden of males.
In this study, we first tried to confirm the water-exchange function of the V .
longipinnis mound in the field, and its effect on DO concentration in the burrow. Second, to examine the ecological roles of the mound, mound and or female removal
experiments were conducted.
2. Materials and methods
2.1. Study sites Field studies were carried out on the coral reefs at Kunri Beach, Sesoko Island
26 8399N, 1278529E in 1994 and 1995, and at Nagahama Beach 268429N, 1278579E,
northern coast of Motobu Peninsula, Okinawa, Japan in 1996 and 1997. At both study sites, V
. longipinnis were distributed in the near-shore moat at depths of 1–3 m; the substratum consisted mainly of sand and dead-coral fragments, with scattered coral
colonies and rocks.
T . Takegaki, A. Nakazono J. Exp. Mar. Biol. Ecol. 253 2000 149 –163
153
2.2. Ink-injecting experiment To confirm the effect of the mound on water-exchange in the field, ink was injected
into burrows at Nagahama Beach in 1996. Before spawning, a tube Teflon pipe: about 30–40 cm long, 3.0 mm in outside diameter, 2.0 mm in inside diameter was inserted
into the potential spawning burrows through one of the several openings of each burrow.
3
Blue-black ink 5 ml; mean density 6S.D. 5 1.0257460.00404 g mm , n 5 10 was
injected using a syringe through the tube between 2 h before and after high tide flow velocity is about 10–15 cm s. The site from which ink subsequently appeared was
recorded. To exclude and examine the influence of male fanning activity on water- exchange see Section 3, the experiments were performed both on vacant burrows 1
day after egg care; n
5 25 and egg-tending burrows n 5 19. Eight of 25 trials on the vacant burrows were conducted after removal of the mound to clarify the effect of the
mound on the water-exchange. The mound materials were carefully removed by hand so as not to reveal the burrow opening.
2.3. Measurements of DO in the burrow To investigate the effect of water-exchange function of the mound on DO in the
burrow, we compared DO concentration in a burrow before and after removal of the mound. The burrow used in these experiments was situated about 50 m from shore and
in water 2.5 m deep at Nagahama Beach. We conducted two experiments here: 1 just after egg-hatch vacant burrow and 2 during the egg-tending period with a male and
eggs inside to examine the effect of male fanning behavior on water-exchange in the burrow.
2.3.1. Experiment 1: vacant burrow A pair male, 157 mm in SL; female, 152 mm spawned on 31 April, 1996 and the
male finished egg-care on 3 May. The pair was removed on 3 May so they could not affect the burrow and mound. We measured DO 12 times at 37–54-min intervals on 4
May 09:15–17:32 h with a mound 37 cm in major axis, 35 cm in minor axis, 13 cm high and 10 times at 35–57-min intervals on 7 May 09:43–17:06 h without the
mound. The mound was removed by hand on 6 May without any of materials falling into the burrow. We also measured DO out of the burrow and flow velocity on the sea floor to
control for these factors. DO in the burrow was measured by sampling sea water about 110 ml in the burrow with a syringe through the same Teflon tube used for ink injection
above. Before sampling the water, we exhausted the bubble from the syringe completely, and then withdrew about 5 ml water from the burrow to flush out the
syringe. The sampling tube allowed the water to be sampled from the burrow without further disturbance. In preliminary experiments, more than 3000 ml of polyester resin
were used to make casts of four spawning burrows; therefore, removal of 110 ml during sampling approximately once per hour should have little influence on the DO in the
burrow. In an aquarium experiment, DO in the water sampled by syringe was not different from that sampled by siphon the differences were less than 3.7, Wilcoxon
signed ranks test, P
5 0.39, n 5 11. Sea water outside the burrow was collected on the
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. Takegaki, A. Nakazono J. Exp. Mar. Biol. Ecol. 253 2000 149 –163
sea floor adjacent to the burrow by syringe. We fixed samples chemically on each sampling occasion, and analyzed the DO by the Winkler method in the laboratory. Flow
velocity was calculated from the distance ink flowed per unit time on the sea floor. This velocity was measured 3–5 times for every measurement of DO.
2.3.2. Experiment 2: egg-tending burrow The same pair spawned on 21 May in the same burrow. Measurements of DO were
taken 11 times at 42–55-min intervals on 22 May 09:40–17:40 h on a burrow with a mound 29
3 25 3 9 cm and 11 times at 40–53-min intervals on 23 May 10:24–18:14 h on a burrow without a mound. We removed the paired female on 21 May to prevent
her from reconstructing the mound, and removed the mound on 22 May. DO in and out of the burrow and the flow velocity on the sea floor were measured as in Experiment 1.
2.4. Female mound maintenance behavior after spawning To estimate the costs of female mound construction and maintenance, we compared
the rates of feeding and burrow mending behavior primary mound construction and maintenance behavior; see Takegaki and Nakazono, 1999b during the egg-tending
periods with other periods for the same female. Underwater observations were carried out by snorkeling at Kunri Beach during 25 May–25 August, 1994, and 6 June–4 July,
1995. The study area 300
3 100 m was situated in the near-shore moat at depths of 1.0–2.5 m. We captured seven paired females mean SL
6S.D. 5 143.0614.6 mm, range
5 130–161 mm, n 5 7 with a barrier net and hand net, measured their body size standard length, SL mm and determined sexes by the shape of the genital papillae see
Takegaki and Nakazono, 1999a. Gobies were marked by hypodermically injecting acrylic paint on each side of the body and sewing a plastic bead 1.5 mm long, 3.0 mm
in diameter with nylon fishing line into the dorsal musculature anterior to the dorsal fin. After marking, the fish were returned to their respective collection sites. We conducted
10-min observations 6.6 times on average for paired females during the egg-tending periods range, 1–13 times, n
5 7 and 14.3 times before and after egg-tending periods range, 4–44 times, n
5 7. To determine the effect of female mound construction and maintenance on the
structure of the mound, mound height was measured daily from the day of spawning until hatching. Mound height was measured by a stainless steel ruler with a level, from
the burrow opening to the summit of the mound. We compared any change in mounds maintained by females n
5 26 with those mounds where the female either disappeared or was removed on the day of spawning n
5 9. This investigation was conducted using SCUBA at Nagahama Beach from 14 May–20 July, 1997.
2.5. Mound and female removal experiments To investigate the relationship between the mound and male egg-tending behavior, we
removed both the mound and female just after spawning at Kunri Beach in 1995 and Nagahama Beach in 1996 n
5 18. Removals were made on the day of spawning. We observed males each day after removal to determine if they continued to tend eggs
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155
usually 2 or 3 days; Takegaki and Nakazono, 1999a. When the males emerged from the burrow before the day or time of hatching and ceased to enter the burrow, we checked
the eggs in the burrow by partly breaking the burrow entrance. In our aquarium observations, all four deserting males ate their eggs completely before desertions
Takegaki, unpublished data. Therefore, absence of eggs in those burrows was recorded as egg-desertion by the male. One day after the removals, DO in each spawning burrow
was measured see methods above between 1 h before and after low tide, when the DO in the burrow drops to the lowest level Takegaki and Nakazono, 1999c, see Section 3.
Moreover, we removed a paired female alone i.e., burrow left intact just after spawning to examine female influence on male egg care n
5 13.
3. Results
