Density of the blue-black urchin Echinotrix diadema (Linnaeus, 1758) in Tomini Bay, Indonesia

The blue-black urchin has been widely known and utilized as food in the world, including Indonesia because sea urchin gonad can be consumed. However, the utilization of sea urchins in Gorontalo has not been performed. On the other hand, natural resources information is needed as the database for natural resources management in Tomini Bay. The aim of this study is to document the blue-black urchin Echinotrix diadema. This study conducted at Blue Marlin Beach, South Leato, Gorontalo, from November 2019 to December 2020. Sea urchin density was calculated with a 1 m × 1 m transect quadrate that positioned at interval 5 m in distance along 15 m of the transect line at the coral reef ecosystem. In parallel with the measurement of the density, sea urchin test diameter was measured with a Vernier caliper (0.01 mm accuracy), and the water temperature was measured with a thermometer. The results show that the average of sea urchin density is 3 ind. m–2 in November and December and 1 ind.m–2 in January. That density has no significant difference among the month. Moreover, the average size of the sea urchin test diameter is 60 mm in November, 63 mm in December, and 66 mm in January. The seawater temperature is 34 °C in November, 37 °C in December, and 33 °C in January. That results show that sea urchin density in the blue marlin beach is very low.

Impact of Overfishing on Density and Test-Diameter Size of the Sea Urchin Tripneustes gratilla at Wakatobi Archipelago, South-Eastern Sulawesi, Indonesia

Sea urchin Tripneustes gratilla is one of an economically important fisheries resource product for localities at Wakatobi archipelago. High demands for sea urchin gonad have intensified high fishing activity. The hypothesis of this study is that sea urchins in Wakatobi have been overfished. To answer that hypothesis, the density and its test diameter size were measured at two different sites. Those two sites are Pulau Tomia (resident area) and Pulau Sawa (nonresident area and very distant from the localities). The results show that sea urchin density and its test diameter are significantly different. The densities (mean±SE) T. gratilla at Pulau Sawa and Pulau Tomia were 10±0.6 (ind.m-2) and 2.7±0.9 ind.m-2, respectively. Moreover, the test diameter at Pulau Sawa and Pulau Tomia were 69.7±2.1 mm and 58.5±1.7 mm (mean±SE), respectively. These results have shown that overfishing has occurred. Therefore, sea urchin with test diameter 66–75 mm, 76–85 mm, and 86–95 mm have disappeared at Pulau Tomia. The Conclusion reveals that fishing of sea urchin Tripneustes gratilla at Pulau Tomia has been overfished.

Impact of overfishing on density and test-diameter size of the sea urchin Tripneustes gratilla at Wakatobi Archipelago, south-eastern Sulawesi, Indonesia

Sea urchin Tripneustes gratilla is one of an economic important fisheries resources product for localities at Wakatobi archipelago. High demands for sea urchin gonad have intensified high fishing activity. We hypothesize that sea urchins at Wakatobi have overfished. To answer that hypothesizes; we measure the density and its test diameter size at two different sites. They are Pulau Tomia (inhabited area) and Pulau Sawa (uninhabited area and very distant from the localities). The results show that sea urchin density and its test diameter is significantly different. The densities (mean ± SE) Tripneustes gratilla at Pulau Sawa and Pulau Tomia are 10 ± 0.6 (ind./m2) and 2.7 ± 0.9 ind./m2, respectively. Moreover, the test diameter at Pulau Sawa and Pulau Tomia are 69.7 ± 2.1 mm (mean ± SE), and 58.5 ± 1.7 mm (mean ± SE), respectively. These results have indeed shown that overfishing has occurred. Therefore, sea urchin with test diameter 66–75 mm, 76–85 mm, and 86–95 mm have disappeared at Pulau Tomia. Our conclusion reveals that fishing of sea urchin Tripneustes gratilla at Pulau Tomia has overfished.

Habitat Preferences of Juvenile Abalone (Haliotis mariae Wood, 1828) Along the Dhofar Coast of Oman and Implications for Conservation

Surveys were conducted along the eastern Dhofar coast of Oman to investigate densities and habitat preferences of juvenile Haliotis mariae (< 3 cm SL). Average density was 0.62 m-2 (SD 0.56); average urchin density was 3.4 urchins m-2 (SD 3.9). Relationships between juvenile abalone densities and small boulders (<30 cm in diameter (Ø)) tested significant (p = 0.049), as did those between juvenile abalone and urchin densities (p = 0.031). Selectivity (w) and standardized (B) ratios quantifying the relative probability of selection by juvenile abalone for different categories of resource available were calculated. For the studied area B values tested significantly different for (p = 0.004) the different habitats, urchins, boulders <30 cm, 30> <50 cm, and >50 cm Ø, respectively. B values were highest for urchins (6 times that for small boulders), and for boulders <30 cm Ø (double that for boulders 30> <50 cm Ø). B values for boulder habitats decreased as boulder size increased. Urchin utilisation by juvenile abalone as shelter ranged between geographic areas from a minimum of 15.5% to a maximum of 47.6%. The proportion of total habitat that is preferred by more than 97% of juvenile abalone found, including urchins and boulders < 50 cm Ø, comprises 29% of surveyed substratum. While the role urchins play on wild juvenile H. mariae has not proved vital, it is definitely significant. Although juvenile densities are low and are not currently limited by the availability of suitable habitat, it is crucial to identify and conserve those microhabitats that support recruitment of H. mariae. The abundance of these areas should be among the criteria used in selecting protected conservation areas.

Demographic structure suggests migration of the sea urchin Paracentrotus lividus in a coastal lagoon

The demographic structure of a population of Paracentrotus lividus living in a coastal Mediterranean lagoon was studied in 1990. Analysis of this structure revealed that the population examined was made up of four distinct cohorts which represented individuals 2, 3, 4 and over 4 y of age. The variability in demographic structure as a function of biotope revealed that sea urchin migration occurred from the pebble area (recruitment area, high sea urchin density and overgrazing facies) towards areas made up of Cymodocea nodosa sea grass beds (growth areas, low density and abundant prefered food). These migrations seem to have been caused by food limitation in the former biotope coupled with a shift in diet in young individuals.