A study originally intended to update the systematics and zoogeography of calanoid copepods in Philippine lakes has led to the discovery of an invasion by the Neotropical Arctodiaptomus dorsalis. It now occurs in 18 out of 27 lakes in the archipelago. Only four of the 12 previously recorded native and endemic calanoids have been encountered in the lakes, which may indicate that most have been displaced by A. dorsalis, although a general deterioration of water quality by fish culture may also have contributed to a suppression of the local fauna. Undescribed species may have been affected as well. A. dorsalis was first reported in the Philippines from Laguna de Bay in 1991, where it was said to have been introduced via ship drinking water reserves, but co-introduction with tilapia is more probable. Intensive aquaculture practices during the past 20 years have aided its dispersal to other areas and have provided environmental conditions that favor its survival. The rapid spread of A. dorsalis, paralleled by a loss of calanoid diversity in the Philippines, may repeat itself if this opportunistic species succeeds in spreading to mainland Asia
A massive invasion of the Neotropical calanoid copepod Arctodiaptomus dorsalis (Marsh, 1907) has been taking place in the Philippines since at least 1993. This copepod’s fecundity is known to depend on food concentration, increasing temperature appears to have detrimental effects on its hatching success and survivorship, but parameters that are truly predictive of the successful integration and propagation of this species in particular bodies of water have not yet been identified. We conducted a spatial analysis of morphometric features and reproductive capacity, the latter proxied by clutch size (CS), of different populations of A. dorsalis inhabiting 11 tropical lakes in the Philippines. Correlations between either morphometry or CS and selected water quality parameters were investigated based on collections and measurements made from December 2018 to April 2019. Means of morphometric measurements differed significantly (P < 0.001) among the populations of A. dorsalis in all lakes. Total length (TL) of adult males, TL of non-ovigerous adult females, and CS of ovigerous females all showed significant (P < 0.001) inverse correlations with lake depth, accounting for about 30% of the observed variability among lakes (r = –0.55, –0.55, and –0.58, respectively). Shallow lakes, which are more homogenous in terms of nutrient distribution throughout the water column, thus provide a more suitable habitat than deep lakes for A. dorsalis and provides a partial explanation of the widespread occurrence and abundance of the species in the shallower, more eutrophic lakes in the Philippines.
Arctodiaptomus dorsalis is an invasive calanoid copepod from America, and is now found in 23 out of 32 lakes and rivers in the Philippines. Live specimens of A. dorsalis were collected from Lake Taal and cultured in the laboratory. The specimens were reared under three different temperatures (25°C, 30°C, and 35°C) with the same food and light conditions, i.e. ~10 5 cells mL −1 of Chlamydomonas reinhardtii and 12L:12D at ~60 lx, respectively. Post-embryonic development times from hatching to adult decreased from 31.5 d to 18.3 d as the temperature increased, while those during naupliar stages were quite similar, i.e. 4.4, 2.8 and 2.3 d at 25, 30 and 35°C, respectively. The naupliar durations were substantially shorter than the copepodid stages. Clutch sizes were almost the same, 8.7-9.2 eggs clutch −1 , among all temperatures tested, while hatching success decreased from 85.9% at 25°C to 24.2% at 35°C. Overall survival rates from hatching to adult decreased as well from 67% at 25°C to 23% at 35°C. This is the first successful attempt to culture A. dorsalis collected from a freshwater lake in the Philippines.
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