Boat anchors not OK: Loss of Dugong grass (Halophila ovalis) population structure in Havelock island of Andaman and Nicobar Islands, India

AbstractAnthropogenic disturbance due to deployment of boat anchors and loss of seagrass ecosystem is not well understood in India. So, we used Govind Nagar beach of Havelock Island of Andaman and Nicobar Islands (ANI)to assess the impacts of boat anchors from traditional fishing and recreational activities on the seagrass Halophila ovalis population structure. H. ovalis density, biomass, morphometrics, canopy height and percentage cover were estimated from two stations of Govind Nagar beach i.e., one highly impacted from boat anchors (Station1) and a sheltered station (Station 2). A clear evidence in reduction of shoot density of H. ovalis was observed at station 1, exception was similar apex densities between both stations. H. ovalis morphometrics, such as number of leaves per shoot, leaf length, width and horizontal rhizome length were observed with significant lower values at station 1 compared to the sheltered station 2. Reduction in seagrass morphometrics also resulted in the loss of seagrass canopy height and percentage cover. A clear evidence of loss of seagrass population structure under the influence of physical disturbances caused by boat anchors were observed. We report for the first time the impacts of boat anchors on seagrass ecosystems of India and our results pitch for wider studies across India. The impact of boat anchors is small-scale, but in long-term loss of seagrass ecosystem services will have dire consequences on fish habitat and carbon storage. Therefore, proper management and conservation measures should be taken to prevent the loss of important dugong grass habitats of ANI.HighlightsPhysical disturbances caused by boat anchors decreased the shoot density of H. ovalis by 1.2-fold.1 to 2-fold reduction in canopy height and the morphological features of individual plants were observed due to damage caused by boat anchorsHabitat disturbance reduced 1.6-fold percentage cover of H. ovalis at Havelock Island of Andaman and Nicobar Islands, India

Download Full-text

Loss of Dugong Grass [Halophila Ovalis (R. Brown)] Population Structure Due to Habitat Disturbance in an Island Ecosystem

10.20944/preprints202009.0415.v1 ◽

2020 ◽

Author(s):

Amrit Kumar Mishra ◽

Sumantha Narayana ◽

Deepak Apte

Keyword(s):

Plant Density ◽

Habitat Disturbance ◽

Leaf Length ◽

Canopy Height ◽

Coastal Development ◽

Small Scale ◽

Physical Damage ◽

Percentage Cover ◽

Halophila Ovalis ◽

The Impact

Seagrass ecosystems are lost due to habitat disturbance, coastal development and human pressure. We assessed the impact of boat anchors from traditional fishing and recreational activities on the seagrass Halophila ovalis from the Andaman and Nicobar Isalnds of India. The plant density, biomass, morphometrics, canopy height and percentage cover were estimated from two sites of Govind Nagar beach of Andaman and Nicobar Islands. The shoot density of H. ovalis was reduced by physical damage caused by boat anchors. The morphometrics of H. ovalis, such as number of leaves per ramet, leaf length, width and horizontal rhizome length were significantly reduced when impacted by boat anchors. Seagrass canopy height and percentage cover were reduced by 41% and 47% respectively. Though the impact of boat anchors reported here is on small-scale, it may impact feeding grounds of locally endangered dugongs. Therefore, proper management and preventive measures should be implemented to prevent the loss of dugong grass habitats from tourism, recreational and fishing activities.

Download Full-text

Population structure of a newly recorded (Halodule uninervis) and native seagrass (Halophila ovalis) species from an intertidal creek ecosystem

10.20944/preprints202103.0392.v1 ◽

2021 ◽

Author(s):

Amrit Kumar Mishra ◽

Mukunda Kesari Khadanga ◽

Shesdev Patro ◽

Deepak Apte

Keyword(s):

Population Structure ◽

Root Length ◽

Leaf Growth ◽

Shoot Density ◽

Seagrass Species ◽

Sediment Grain Size ◽

Halophila Ovalis ◽

Halodule Uninervis ◽

Plastochrone Interval ◽

Intertidal Creek

The present study documented the presence of seagrass Halodule uninervis for the first time along with previously documented Halophila ovalis at Haripur creek. The population structure of both these seagrass species is assessed. The physico-chemical parameters were similar for both seagrass species except for the sediment grain size fractions. The sand content of H. ovalis patches was 1.2-fold higher than H. uninervis beds, whereas the silt content of H. uninervis beds was 2-fold higher than H. ovalis patches. The pH levels were lower than the standard oceanic pH of 8.2. Macroalgae like Ceramium sp. and Gracilaria verrucosa were growing on the leaves of H. uninervis due to high nitrate and phosphate levels of the creek waters. Leaf reddening was only observed in the leaves of H. ovalis. Under similar environmental conditions, H. ovalis (5004 ± 114.51 ind. m-2) had a 2-fold lower shoot density than that of the H. uninervis (11598 ± 187.52 ind. m-2). Both above- and below-ground biomass of H. ovalis (96.34 ± 10.18 and 197.5 ± 18.30 g DW m-2) was 2-fold lower than that of H. uninervis (198 ±7.45 and 456 ± 9.59 g DW m-2). H. uninervis leaves were 9-fold longer than that of H. ovalis, whereas H. ovalis leaves were 5-fold wider than H. uninervis. The leaf plastochrone interval is 2.3 days for H. ovalis and 9.6 days for H. uninervis. Consequently, the leaf growth rate of H. ovalis is 2-fold lower than that of H. uninervis. H. ovalis had 2.6-fold longer internodes than H. uninervis. The root length of H. uninervis was longer than H. ovalis. Consequently, the shorter root length of H. ovalis led to higher branching frequency than H. uninervis. The total C and N content were higher in the leaves of H. ovalis than H. uninervis.

Download Full-text