Dataset of taxonomic identification from surface water in the coastal area of Peninsular Malaysia

This article describes the abundance of phytoplankton community structures in Port Dickson, Negeri Sembilan and Pulau Tinggi, Johor during the Southwest and Northeast Monsoons and includes data from 48 selected sampling sites collected between July and December 2023. The seawater samples from 1-meter depth were obtained by using a Niskin water sampler, concentrated in a 50 ml centrifuge tube and immediately preserved with Lugol's iodine solution. The data include phytoplankton density (cell L−1), the total density of phytoplankton in each station, and the total number of genera obtained in every station. Additional data are presented, including chlorophyll-a concentration, as a proxy for biomass and photosynthetic active radiation. This article presents data on 30 genera, including unidentified genera, as well as the percentage of the main community group.


Subject
Oceanography, Marine Biology Specific subject area Taxonomic identification of phytoplankton species at Port Dickson, Negeri Sembilan, and Pulau Tinggi, Johor Type of data Table Data collection An inverted microscope (Olympus x70) was utilised for phytoplankton counting and genus identification.The ambient photosynthetic active radiation (PAR) was measured using a PAR Smart Sensor (S-LIA-M003, Onset HOBOware).Chlorophyll-a concentration was determined by filtering 800 -1000 mL of the sample onto GF/F (Whatman), extracted with 90 % acetone for 12 h in the dark at 4 °C, centrifuged for 10 min, and then measured with a UV-visible spectrophotometer (UVD-30 0 0, Labomed Inc. USA).The chlorophyll-a concentration was calculated according to [ 1 ], substituting the equation from [ 2 ].Data

Value of the Data
• The samples were obtained from two locations: Port Dickson, Negeri Sembilan (west coast) and Pulau Tinggi, Johor (east coast).Data from Port Dickson were collected during the Southwest (SW) and Northeast (NE) monsoons.• Data can serve as a point of reference for the analysis of phytoplankton variability in the coastal area and continental shelf of Peninsular Malaysia.• Data can be used to explain the potential sources of surface-active substances and biogenic volatile organic compounds emissions from the surface ocean.• A comparative study of the phytoplankton population in Port Dickson and Pulau Tinggi can be conducted from these datasets.

Background
Phytoplankton are valuable indicators of shifting oceanographic conditions, climate change, and declining water quality because of their high turnover rates and sensitivity to environmental changes [ 4 ].We provide a dataset for the spatial variation of phytoplankton in Port Dickson (west coast) and Pulau Tinggi (east coast), Malaysia during the SW and NE monsoons.In Malaysia, there are still limited studies on the phytoplankton's taxonomic and biomass, particularly for both monsoon events.Previous studies show that phytoplankton production can produce a significant amount of surface-active substances (SASs) [ 5 , 6 ] and biogenic volatile organic compounds (BVOCs) emissions from the surface ocean [7][8][9].This research hypothesizes that phytoplankton biomass will be higher during the SW monsoon than the NE monsoon.The datasets are available under the FAIR principle of Findability, Accessibility, Interoperability, and Reusability.

Data Description
The data was collected at Port Dickson and Pulau Tinggi, Malaysia during the SW and NE monsoons ( Table 1 and Fig. 1 ).The datasets involve information on phytoplankton density  1 , meanwhile, Tables 2-4 provide information on phytoplankton density (cell L −1 ), total number of genera, and total density of phytoplankton.Tables 5 and 6 show the percentage abundances for the major groups of phytoplankton in both locations.

Table 2
Data on the density of phytoplankton species (cell L −1 ) and total no. of genus in Pulau Tinggi, Johor.Note: (-) no organisms found are described.

Sampling activity
All data provided in this article were collected from two locations which were Pulau Tinggi, Johor and Port Dickson, Negeri Sembilan from July 2023 until December 2023 ( Fig. 1 and Table 1 ).Sampling activity in Pulau Tinggi was conducted in August 2023 (station PT1 -PT10).Meanwhile, sampling activities at Port Dickson have been done during the Southwest (SW) monsoon (station S1 -S21) and Northwest (NW) monsoon (station S22-S38).The sampling activities have been done during low to moderate wind speeds (0.11 to 6.07 ms −1 ).For phytoplankton enumeration, the seawater samples from a 1-meter depth were collected using a Niskin bottle and then were concentrated and stored in a 50 ml centrifuge tube.Samples were immediately preserved with Lugol's iodine solution and stored in the dark until microscopic analysis.The ambient photosynthetic active radiation (PAR) was measured using a PAR Smart Sensor (S-LIA-M003, Onset HOBOware).

Species identification and phytoplankton cell counting
The identification of genus was based on morphological characteristics according to the reference of phytoplankton identification [ 10 ] and verified with Ocean Data Center ( http:// oceandatacenter.ucsc.edu/PhytoGallery/phytolist.html ) and AlgaeBase ( https://www.algaebase.org ) Microscopic determination and counting were done using an inverted microscope (Olym-

Table 3
Data on the density of phytoplankton species (cell L −1 ) and total no. of genus in during the Southwest monsoon Port Dickson, Negeri Sembilan.Note: (-) no organisms found are described.

Genus
Stations

Table 4
Data on the density of phytoplankton species (cell L −1 and total no. of genus) during the Northeast monsoon in Port Dickson, Negeri Sembilan.Note: (-) no organisms found are described.pus x70) at 10x magnification based on Utermöhl [ 11 ].The samples were determined as far as possible at the genus level.
Chlorophyll-a concentration was calculated according to [ 4 ], substituting the equation from [ 7 ].

Limitations
The data in this article have limitations while collecting the data.Taxonomic identification can be challenging for many phytoplankton taxa since many tiny phytoplankton species cannot be recognised using light microscopy, identification of these organisms is typically done at a coarser taxonomic level.

Fig. 1 .
Fig. 1.Map of the sampling locations at a) Port Dickson, Negeri Sembilan and b) Pulau Tinggi, Johor.

Table 1
Location of sampling stations, PAR values and Chl-a concentrations.
consisting of 30 genera from 48 stations, including unidentified genus.The information on chlorophyll-a concentration and PAR values were also presented in Table