Nitocra taylori, Gomez, Samuel, Carrasco, Nicola K. & Morales-Serna, Francisco Neptali, 2012

Gomez, Samuel, Carrasco, Nicola K. & Morales-Serna, Francisco Neptali, 2012, A new species of Nitocra Boeck, 1865 (Harpacticoida, Ameiridae, Ameirinae) from South Africa, with notes on its ecology and remarks on the status of Nitocra sewelli husmanni Kunz, 1976, ZooKeys 244, pp. 33-58 : 36-48

Nitocra taylori sp. n. Figures 29

Type material.

One female holotype (EMUCOP-080311-03) and one male allotype (EMUCOP-080311-06) preserved in alcohol, one female (EMUCOP-080311-04) and one male (EMUCOP-080311-05) dissected paratypes, and 15 adult females, 11 adult males, one CIII, three CIV and three CV paratypes preserved in alcohol (EMUCOP-080311-07) were deposited in the Copepoda collection of the Instituto de Ciencias del Mar y Limnología, Mazatlan Marine Biological Station; 26 additional paratypes (SAM-A45750) were deposited in the collection of the Iziko South African Museum; collected from Listers Point, St Lucia Estuary, South Africa; 8 March 2011; leg. N. K. Carrasco.

Type locality.

Listers Point, False Bay, St Lucia Estuary, South Africa (27 º 58'09.4"S, 32 º 22'48.11"E).

Etymology.

The species is named after Dr Ricky H. Taylor, former Regional Ecologist at Ezemvelo KZN Wildlife, St Lucia Estuary, for his invaluable help provided to research and his lifetime efforts towards the conservation of the St Lucia Estuary. The specific epithet is a noun in the genitive singular.

Female.Habitus (Figure 2A) tapering posteriorly; total body length measured from tip of rostrum to posterior margin of caudal rami ranging from 460 to 685 µm (mean, 537 µm; n= 11; holotype, 525 µm). Rostrum (Figure 2A, B) defined at base, elongate, small, barely reaching distal margin of first antennulary segment, with pair of sensilla subapically. Dorsal surface of cephalic shield and free prosomites without spinular ornamentation, with plain caudal frill (Figure 2A). P5-bearing somite with medially interrupted row of minute spinules close to posterior margin dorsolaterally, with deeply serrate caudal frill (Figure 2A, C). Subcuticular rib of genital double-somite with dorsolateral row of small spinules indicating former division between second and third urosomites (Figure 2A, C), but completely fused ventrally (Figs 3B, 10F); third urosomite with comparatively stronger spinules close to posterior margin dorsally and laterally, with median row of minute spinules ventrally, with deeply serrate caudal frill. Fourth and fifth urosomites as previous somite dorsally and ventrally, except for less and lack of sensilla in fourth and fifth urosomites, respectively. Anal somite somewhat shorter than previous somite, with strong spinules dorsally and laterally close to joint with caudal rami (Figs 2A, C, 3A), with comparatively smaller spinules ventrally (Figs 3B, C, 10F); rounded anal operculum with three strong spinules close to posterior margin, and flanked by pair of sensilla (Figs 2C, 3A). Caudal rami nearly as long as wide from dorsal view, but slightly longer than wide ventrally (Figs 2C, 3A, B, C, 10B), with seven setae as follows: seta I small, nearly as long as caudal ramus; seta II dorsal to seta I, about twice as long as the latter; seta III about twice as long as seta II, arising close to outer distal corner; setae IV and V well developed, the latter longest; seta VI arising from inner distal corner, slightly shorter than seta III; seta VII biarticulated, rather short, arising close to base of seta VI at inner distal corner.

Antennule (Figure 5A) eight-segmented, surface of segments smooth except for spinular row on first segment. Armature formula as follows: 1-(1), 2-(9), 3-(8), 4-(3 + [1+ae]), 5-(2), 6-(3); 7-(4); 8-(5+acrothek). Fourth segment with one outer spinule. Acrothek consisting of two setae and one aesthetasc fused at their base.

Antenna (Figure 4A) with small coxa. Allobasis without abexopodal setae, and ornamented with one long spinule and a short row of minute spinules proximally. Free endopodal segment with inner spinules proximally and subdistally, with two lateral inner spines and one slender seta, and four single geniculate setae and one geniculate element fused basally to pinnate seta. Exopod one-segmented; with few spinules, and three setae (two pinnate spine like elements and one bipinnate seta).

Mandible (Figure 4B) robust; gnathobase with bi- and multicuspidate teeth, and one lateral seta. Mandibular palp two-segmented; first segment (basis) with some spinules and one seta; second segment (endopod) with one lateral and four apical setae.

Maxillule (Figure 4C). Arthrite of praecoxa with few spinules, with two surface setae, and three bare spines and two serrate/multicuspidate elements. Coxa with two elements. Basis seemingly with four setae; exopod vestigial represented by one seta; endopod two-segmented, first segment without any setae, second segment with two setae.

Maxilla (Figure 6A). Syncoxa with minute outer spinules; with one endite bearing three setae. Allobasis drawn into strong claw with one accompanying strong element. Endopod one-segmented, with two setae.

Maxilliped (Figure 6B) subchelate. Syncoxa with spinular rows and with one seta on inner distal corner. Basis unarmed, with longitudinal row of spinules, with some outer spinules distally. Endopod drawn into long and slender claw with one accompanying small seta.

P1 (Figure 4D, E). Intercoxal sclerite without spinular ornamentation; distal margin convex. Basis with inner and outer flagellate spine; with strong spinules at base of inner spine, between rami and at base of exopod. Exopod and endopod three-segmented; EXP1 without inner seta, EXP2 with plumose inner seta; EXP3 with one outer proximal bipinnate spine, two outer naked spines and two geniculate elements. Endopod three-segmented; slightly beyond EXP; first segment slightly shorter that second and third segments combined, reaching insertion level of inner seta of EXP2; first segment with inner seta ornamented medially with setules and with spinules along outer margin distally; second segment with plumose inner seta; third segment with one inner plumose seta apically, one median geniculate element, and one apical outer spine. Armature formula as below.

P 2 (Figure 5B). Intercoxal sclerite with transverse spinular row distally on both lobes. Praecoxa with spinules close to joint with coxa. The latter with long outer setules and minute spinules close to outer and inner distal corner, respectively. Basis with outer spine; with strong spinules between rami and at base of EXP. Exopod three-segmented; first segment without setae, second segment with plumose inner seta; third segment with three outer bipinnate spines, one outer apical seta ornamented with strong spinules and setules along outer and inner margin, respectively, one inner apical plumose seta and one inner plumose seta. Endopod three-segmented, reaching proximal fourth of EXP3; first and second segments with inner plumose and short seta; third segment with one strong inner seta ornamented with few setules medially and with spinules along outer margin distally, two apical plumose setae and one outer bipinnate spine. Armature formula as below.

P3 (Figure 6C). Intercoxal sclerite, praecoxa and coxa as in P2. Basis as in P2 except for outer seta-like element in P3. Exopod as in P2. Endopod as in P2 except for additional inner element in P3ENP3 ornamented with setules proximally and with spinules along outer margin distally; reaching proximal third of EXP3.

P4 (Figure 7A). Intercoxal sclerite without spinules. Praecoxa (not shown), coxa and basis as in P3. Exopod as in P3 except for comparatively stronger inner distal seta of P4EXP3 ornamented with outer and inner spinules, and for outer apical seta ornamented with inner setules and outer spinules. Endopod as in P3, except for bipinnate inner proximal seta on P4ENP3; slightly beyond EXP2.

P5 (Figure 7B). Both legs separated. Exopod and baseoendopod not fused. Exopod ovate; with inner and outer spinules; with six elements; relative length of the setae from inner to outer element as follows: 0.73, 1, 0.38, 0.69, 0.38, 0.25. Endopodal lobe with five setae/spines; relative length of the setae from inner to outer element as follows: 0.30, 0.31; 0.30, 1, 0.52; with inner and outer spinules.

Armature formula of female P1-P5 as follows:

P 6 (Figure 3D) represented by median plate in anterior half of second urosomite (first genital somite); each vestigial leg represented by one outer short and one inner long seta.

Male. Habitus (not shown) as in female, except for distinct second and third urosomites; total body length measured from tip of rostrum to posterior margin of caudal rami ranging from 385 to 520 µm (mean, 437 µm; n= 7; allotype, 490 µm). Ventral spinular ornamentation of third-sixth urosomites coarser and stronger than in female (Figs 8, 10D). Caudal rami (Figs 8, 10D) as in female.

Sexual dimorphism expressed in the antennule, P1Basis, P3ENP, P5 and P6.

Antennule (Figure 9A) haplocer, nine-segmented; armature formula difficult to define, but most probably as follows: 1-(1), 2-(11), 3-(8), 4-(1), 5-(14+[1+ae]), 6-(1), 7-(2); 8-(1); 9-(9+acrothek); fifth, sixth and seventh (Figure 9B) and eight (Figure 9C) segments with modified setae and blunt spines/processes. Acrothek consisting of two setae and one aesthetasc basally fused.

Antenna (Figure 10E), mandible, maxillule, maxilla and maxilliped (not shown) as in female.

P1-P4 as in female, except for sexually dimorphic male P1 Basis (Figs 9D, 10A) and P3ENP (Figure 9E). The former with modified inner spine. The latter three-segmented; first and second segment as in female; third segment with outer longitudinal row of small spinules and armed with five setae/spines.

P5 (Figs 9F, 10C). Both legs fused medially. Exopod and baseoendopod separated. The former ovate, with six setae, relative length of elements from inner to outer margin as follows: 0.47, 0.35, 1.0, 0.44, 0.17, 0.39. Baseoendopodal lobe poorly developed, with three elements; relative length of elements from inner to outer margin as follows: 1.0, 0.79, 0.67.

P 6 (Figs 9G, 10C) represented by two setae situated rather laterally, outer seta smaller than inner element.

Ecology.

Habitat characteristics. During closed-mouth conditions, the St Lucia Estuary was characterised by a reversed salinity gradient, with salinities ranging from near freshwater conditions at the Mouth and Narrows, to up to 200 psu at times in the northern regions of the lake (Table 1). Salinity levels were also more variable in the lakes than in the Mouth and Narrows region. Throughout the study period, salinity levels at the Mouth ranged from 3.2 to 37.6 psu, while at Listers Point they ranged from 18.3 to 216 psu. During closed-mouth conditions, water depth was also generally highest at the Mouth and Esengeni and shallower (~0.2 m) in the lakes (Table 1). High wind action, coupled with the fine sandy substratum in the lakes, also resulted in higher turbidity levels experienced here relative to the Mouth and Narrows. Listers Point and Charters Creek generally experienced the highest turbidities, while levels at the Mouth were usually at least one order of magnitude lower (Table 1). During open-mouth conditions, there was little disparity between sites in terms of the physico - chemical parameters measured. Salinity was generally within the range of sea water (~35 psu) across the estuarine lake and water levels in the lakes rose to approach the levels recorded at the Mouth and Narrows (Table 1).

Nitocra taylori sp. n. abundance and distribution.

Occurrence of Nitocra taylori sp. n. through the study years has been irregular and the distribution has been limited to Catalina Bay and Charters Creek in South Lake and Listers Point in False Bay (Figs 1, 11). Nitocra taylori sp. n. was first recorded at Charters Creek in February 2006 in low densities (10.4 ind.m-3), while maximum densities (2.2 x 105 ind.m-3) were recorded at Listers Point in March 2011. These high densities followed heavy dilution of hypersaline waters after high rainfall in early 2011. Densities remained high in this region up until May 2011, after which salinities rose again above 53.7 psu and Nitocra taylori sp. n. virtually disappeared. Correlation analysis found significant positive correlations between the abundance of Nitocra taylori sp. n. and salinity (R = 0.621, p <0.05, df = 12) and turbidity (R = 0.681, p <0.05, df = 12). Nitocra taylori sp. n. individuals were able to withstand a wide range of fluctuations. They were found at salinity levels ranging from 9.81 to 53.7 psu, turbidities ranging from 2 to 102 NTU and temperatures from 20.9 to 34.8 ºC (Figure 12). In many instances specimens preserved in phloxine-stained formaldehyde did not take up the stain, but were rather completely transparent, resembling discarded exoskeletons. While these individuals were perfectly intact, it is unlikely that they were alive at the time of collection.