Judul: Contribution of Mangrove Ecosystems to Primary Productivity of Coastal Waters in the Beejay Bakau Resort, Probolinggo
Abstrak: Probolinggo City is a coastal area with a mangrove area of about 90 hectares, located close to the Coastal Fishery Port (PPP) Mangunharjo Village, Probolinggo City. The mangrove ecosystem in this area was previously a waste disposal area with degraded mangrove conditions, then managed and rehabilitated into a tourist attraction under the name Beejay Bakau Resort (BJBR). Rehabilitation of the mangrove ecosystem can maintain the balance of the ecosystem by maintaining the supply of nutrients around it. The recovered mangrove ecosystem will produce more litter, which becomes a source of nutrients for the ecosystem. The nutrient content and abundance of plankton is one indicator for water productivity. This research was conducted in December 2020 in the BJBR mangrove ecosystem, Probolinggo. Determination of research stations using the purposive sampling method. Data collection of mangrove vegetation and environmental characteristics was carried out using the quadratic transect method. Water samples were taken at high and low tide and then analyzed for nutrients and plankton. Variations in environmental characteristics between research stations and the abundance of plankton between stations and environmental conditions were analyzed using Principal Component Analysis (PCA). Furthermore, multiple linear regression analysis was performed to determine the relationship between chlorophyll-a and dissolved nutrients. The results showed that the mangrove ecosystem of BJBR, Probolinggo has three mangrove species, namely Avicennia marina, Rhizophora stylosa, and Rhizophora mucronata. Mangrove density in this ecosystem varies, with dense density for the tree category, moderate for the sapling category, and medium-rare for the seedling category. The concentration of available P ranged from 37.00-69.32 mg/kg, the concentration of C-organic ranged from 1.30-2.61% and the concentration of N-total ranged from 2.57-4.80%. The estimation results using multiple linear regression showed that nitrate and orthophosphate significantly affected the chlorophyll-a concentration of 68.6% (F= 37.22, P=0.007). Phytoplankton found in the waters of the BJBR ecosystem consisted of three classes of phytoplankton, namely Bacillariophyceae, Cyanophyceae, and Dinophyceae, with the highest abundance were the class Bacillariophyceae. The zooplankton found consisted of the Protozoa, Crustaceae, Urochordata, Pelecypoda, Gastropods, Nematodes, Polychaeta, and Coelenterata groups, with the highest abundance in the Crustaceae class. The results of this study are expected to be used for management policies of BJBR's mangrove ecosystem based on fishery resources.
Keyword: BeeJay Bakau Resort, mangrove, klorofil-a, Probolinggo, produktivitas primer, plankton

Judul: Variasi Karakter Morfometrik Gastropoda Berdasarkan Karakteristik Habitat Mangrove di Kawasan Bee Jay Bakau Resort, Probolinggo
Abstrak: Beejay Bakau Resort (BJBR) in Probolinggo is a mangrove ecotourism rehabilitation area that has been planted for a long period. There are seven different varieties of mangroves in the BJBR area. The mangrove environment in BJBR is in good shape, and the local population used to catch shellfish in large quantities, but there is a section of the mangrove that has been harmed and even killed as a result of human activity (anthropogenic). The presence of related biota or gastropods is strongly influenced by the density of mangroves as the ecosystem's principal constituent. Gastropods play a crucial function in the mangrove ecosystem's food chain cycle. Environmental factors, food, and predators all influence the abundance and distribution of gastropods. The abundance of mangrove litter occurs because the density of mangroves is also great, allowing the snail to feed on the litter. This study took place in the BJBR area in December 2020. Purposive sampling approach was used to determine sampling based on the existence of mangrove vegetation zoning. The quadratic transect method was used to collect gastropod and mangrove vegetation data, while environmental parameters were measured in situ. Principal Component Analysis was used to investigate the association between morphometric characters and snail species (PCA). Correspondent Analysis was used to examine the link between research stations and morphometric features (CA). The findings revealed that there are seven families of gastropods in the BJBR area (Ellobiidae, Littorinidae, Potamididae, Nassaridae, Cerithiidae, and Muricidae) and 23 species of gastropods. The study station's average gastropod diversity and uniformity are in the middle range, while dominance is in the low range. Because numerous medium and big gastropods were found in the area, gastropods have a relationship between fluctuations in environmental variables and high mangrove density. A sedimentary substrate with clay proportion is present at all research stations. The findings of this study may be relevant in developing BJBR management policy based on mangrove ecotourism.
Keyword: abundance, Bee Jay Bakau Resort, gastropods, mangrove

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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