Lake Worth Lagoon Fixed Transect Seagrass Monitoring Preliminary Results

Transcription

1 Lake Worth Lagoon Fixed Transect Seagrass Monitoring 2017 Preliminary Results

2 LWL Fixed Transect Program Longest dataset for Halophila johnsonii in Florida. 9 transects surveyed annually since 2001 Transects selected by proximity to LWL Partnership Grant projects or habitat improvement projects Main objective is to document annual changes in seagrass abundance and distribution at the permanent transects as an indicator of lagoon-wide seagrass health.

3 North Segment Transects Transect 1- adjacent to John D. MacArthur Beach State Park Transect 3- removed from monitoring plan in 2017 due to construction impacts from the Rybovich Marina expansion project

4 Central Segment Transects Transect 8- just south of Whitehall Museum in Palm Beach Transect 4- north of Southern Blvd between Fisherman s and Bingham Islands Transect 9- northwest of Hunter s Island in Palm Beach Transect 6- south central part of lagoon just south of Bryant Park

5 South Segment Transects Transect 2- ~ 300 ft south of the Ocean Avenue Bridge in Lantana Transect 5- due east of Half Moon Bay Condominiums in Lantana Transect 10- ~ 3,000 ft south of South Lake Worth Inlet and east of the Boynton Beach Canal (C-16) in Ocean Ridge

6 2015 North Segment Transect Additions Transect 11- due east of Little Munyon Island in Munyon Cove Transect 12- ~2,000 ft north of Transect 3 at Osprey Park; replaced Transect 3 Aerial Date: July 25-26, 2013

7 Total frequency of occurrence of seagrasses at the individual transect levelall 3 stations combined, Transect May 2000 Aug 2001 June 2002 June 2003 June 2004 July 2005 Transect Transect Transect Transect Transect Transect Transect Transect Transect Historical Total (incl. T3) Historical Total (excl. T3) Red- annual record lows during the monitoring period; blue-annual record highs Total frequency of occurrence of seagrasses at the station level, Station May 2000 Aug 2001 June 2002 June 2003 June 2004 July 2005 I II III Total

8 Summary showed fluctuations in seagrass cover with no obvious pattern of increase or decrease until the 2004 hurricanes. Major declines in cover and density in 2005 and 2006 throughout most of LWL. Recovery in 2007 with record high levels of seagrass cover and density, followed by slight decreases in 2008 and surveys documented the expansion of beds into deeper water.

9 Total frequency of occurrence of seagrasses at the individual transect levelall 3 stations combined, Transect Sep 2006 June 2007 July 2008 May 2009 June 2010 June 2011 July 2012 July 2013 July/Aug 2014 Red- annual record lows during the monitoring period; blue-annual record highs Aug 2015 July/Aug 2016 Transect Transect Transect Transect Transect Transect Transect Transect Transect Transect Transect Historical Total (incl. T3) Historical Total (excl. T3) Total (excl. T3, incl.t11&t12) July/Aug Total frequency of occurrence of seagrasses at the station level, Station Sep 2006 June 2007 July 2008 May 2009 June 2010 June 2011 July 2012 July 2013 July/Aug 2014 Aug 2015 July/Aug 2016 I II III Total *2017 total does not include Transect 3 July/Aug 2017*

10 Substantial reduction in seagrass cover in Dense Lyngbya and filamentous mat algal overgrowth followed pulses of high rainfall in March and April Overall seagrass frequency of occurrence in 2011 was the third highest during the entire monitoring period, just short of Similar to the 2007 survey, which followed a very dry wet season, the 2011 survey was preceded by a very dry dry season. Reductions in seagrass cover/extent were recorded in July 2012; overall average cover/frequency of occurrence was most similar to 2010.

11 Following the massive freshwater releases associated with Tropical Storm Isaac in 2012, the July 2013 survey recorded the lowest overall seagrass frequency of occurrence of the monitoring program. Overall seagrass frequency of occurrence at the permanent transects slightly increased from 2013 to 2014, seagrass cover was the second lowest recorded to date survey results show slight overall improvement driven by increases at 3 transects

12 Overall seagrass frequency of occurrence decreased from 2015 to 2016 due to elevated canal flow rates in response to a wet dry season and normal wet season. Seagrass continued to decline in Declines were expected due to the elimination of Transect 3 from the monitoring plan. However, removal of Transect 3 from historical data showed a similar trend of decline. During the 2017 survey, seagrass was only recorded at 2 of the 9 historic transects, Transects 1 and 10.

13 Transects 11 and Transects 11 and 12 supported the greatest seagrass cover and diversity during the surveys. Transect 11 is the only permanent transect to document Thalassia testudinum. Overall seagrass frequency of occurrence decreased slightly at both transects between 2015 to 2016 then increased in 2017

14 Seagrass bed edge extent at the 9 transects, Survey T1 T3 T8 T4 T9 T6 T2 T5 T * 44* 73 *Indicates single occurrence of H. decipiens at each location; no other seagrass was observed along or within the vicinity of the transect

15 North Segment Transects 1, 3, 11, and 12 0 = No seagrasses; 0.1 = Solitary shoots with small cover; 0.5 = Few shoots with small cover; 1 = Numerous shoots, less than 5% cover; 2 = Any number of shoots, 5% to 25% cover; 3 = Any number of shoots, 25% to 50% cover; 4 = Any number of shoots, 50% to 75% cover; and 5 = Any number of shoots, greater than 75% cover.

16 Central Segment Transects 4, 6, 8 and 9 0 = No seagrasses; 0.1 = Solitary shoots with small cover; 0.5 = Few shoots with small cover; 1 = Numerous shoots, less than 5% cover; 2 = Any number of shoots, 5% to 25% cover; 3 = Any number of shoots, 25% to 50% cover; 4 = Any number of shoots, 50% to 75% cover; and 5 = Any number of shoots, greater than 75% cover.

17 South Segment Transects 2, 5 and 10 0 = No seagrasses; 0.1 = Solitary shoots with small cover; 0.5 = Few shoots with small cover; 1 = Numerous shoots, less than 5% cover; 2 = Any number of shoots, 5% to 25% cover; 3 = Any number of shoots, 25% to 50% cover; 4 = Any number of shoots, 50% to 75% cover; and 5 = Any number of shoots, greater than 75% cover.

18 Lagoon-Wide Losses in Halophila johnsonii Cover A substantial reduction in H. johnsonii cover was detected throughout the lagoon since record high cover in June 2011 (643 cells). H. johnsonii was only recorded in the northern segment in 2013 (Transects 1 and 3) and 2015 (Transects 11, 12, and 3). In 2014, H. johnsonii was recorded in low abundance at Transects 3, 8, 4, and 2. H. johnsonii was absent from the 9 historic transects in 2016 and Transects 11 and 12 have supported H. johnsonii since 2015, with the highest cover recorded in 2017.

19 Segment/Site Total Seagrass (BB/Species) Within Quadrat Presence of Seagrass Along Line*/Within Radius 937* 0 0 N N 202* 0.5 Hj 0 Y Hj Y Hj** 673* 0 0 N N * 0.5 Hj 0.1 Hj N Y Hd, Hj Central 534* 0.1 Hw 0 N Y Hd, Hj 730* 0 0 N N Hd** 53* 0 0 N N 51 3 Hj, Hw 0 Y Hj, Hw N 317* 0 0 Y Hw N *indicates that the site was sampled using the line method in 2013 **indicates only a single occurrence of seagrass was observed

20 Segment/Site South Total Seagrass (BB/Species) Within Quadrat Presence of Seagrass Along Line*/Within Radius Hw 2 Hj Y Hw Y Hw, Hj 245b* 2 Hd 1 Hd N Y Hd 971* 1 Hd 0 N N Hj, Hw 0 Y Hj, Hw Y Hw 590* 0 0 N N 1004a* 0.1 Hj 0 N Y Hd 710* 0.5 Hw 0.5 Hw N Y Hw 660a* 2 Hd 0 N Y Hd 219* 0.5 Hd, Hj 0 N N *indicates that the site was sampled using the line method in

21 SFWMD Seagrass Monitoring C-17A- ~2,000 ft south of Transect 11; ~5,000 ft southeast of C-17 canal C-17B- ~3,700 ft south of Transect 1; ~5,700 ft north of C-17 canal C-51B- ~500 ft northeast of Transect 9; ~5,500 ft north of C-51 canal C-51C- ~400 ft northeast of Transect 6; ~13,000 ft south of C-51 canal

22 C-17A

23 C-17A Considerable declines were noted in seagrass frequency of occurrence at C-17A following the 2013 survey. Average seagrass cover at Transect 11 and Station C-17A decreased from 2015 to 2016, with slight recovery observed in Syringodium filiforme was recorded in low abundance in 2016 (4/25 cells), but was not recorded in 2015 or S. filiforme was not observed in the vicinity of Transect 11 in 2015, 2016, or 2017; and the species was lost from several ground-truthing sites in Munyon Cove between 2013 and Loss of T. testudinum was also noted in 2015; cover continued to decline at C-17A, Transect 11, and several ground-truthing sites between 2015 and 2017.

24 C-17B

25 C-17B Similar to Transect 1, C-17B supported low to moderate seagrass cover throughout the monitoring period. Declines were noted in 2013, with recovery through Seagrass cover reached record high at C- 17B in 2017; cover decreased at Transect 1 in 2017, however expansion of the bed into deeper water was observed. H. wrightii and H. johnsonii comprise the dominant cover, H. decipiens and T. testudinum were also recorded. Since 2012, Transect 1 supported H. decipiens only; T. testudunim has never been recorded at this transect

26 C-51B

27 C-51B 2009 through 2013 surveys at C- 51B show a similar seagrass community to Station I at Transect 9: mixed Halophila spp. and complete loss of seagrass in Low-density H. decipiens was recorded from 2014 to 2017; H. johnsonii was recorded in October Seagrass has not been recorded at Transect 9 since 2013.

28 C-51C

29 C-51C Seagrass at C-51C transitioned from low to moderate density to a zone of seagrass occurrence in Seagrass decreased from 2013 to 2014; H. johnsonii was present in only 3 cells in August 2014 and was absent in October Halophila johnsonii and S. filiforme were present in July 2015, and H. decipiens in August Seagrass was absent in Low density S. filiforme was recorded in June 2017 and H. johnsonii in August Seagrass has not been present at the permanent stations at Transect 6 since May 2009.

30 Slight increase in seagrass occurrence from 2014 to 2015 Increases in seagrass cover at the 2 northern transects and southernmost transect (1, 3 and 10) in closest proximity to inlets Seagrass continued to be absent at 2 central transects, 6 and 9, with continued muck deposits; slight recovery at Transects 8 and 4 since 2013 No improvement at Transects 5 and 2 in the southern segment

31 What drove the decrease from 2015 to 2017? Major losses in seagrass cover in the central and south segments. Seagrass was absent from Transects 8, 4, 9, and 6 in the central segment, and Transects 2 and 5 in the south segment. Elevated canal flow rates in 2016 and 2017 in response to high rainfall and storm events associated with the El Niño Southern Oscillation event.